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[Display omitted] • The paper reviews the reduction mechanism and process of hematite, limonite, siderite, manganese ore and vanadium-titanium magnetite under carbon-based reduction process. The research progress of process parameters of different iron ore carbon-based reduction processes is discussed. And the current engineering application status of carbon-based roasting reduction technology is discussed. • The paper reviews the reduction process and transformation mechanism of different mineral phases in the process of hydrogen-based reduction of hematite, limonite and vanadium-titanium magnetite. The optimum process parameters of different iron ores in hydrogen-based reduction process were analyzed, and the industrial application status of hydrogen reduction technology was discussed. • The differences between carbon-based reduction and hydrogen-based reduction processes are compared, and the advantages and disadvantages of hydrogen-based reduction process are proposed. The research direction of promoting the large-scale application of hydrogen-based reduction technology in the future is proposed. Iron ore is the raw material for smelting steel, and the steel smelting industry occupies an important position in the development of the national economy. In China, the reserves of iron ore are large, but the iron ore has the characteristics of low grade and sorting is difficult, which limits the application of domestic iron ore. In order to meet the demand for raw materials in China's steel industry, China has long imported iron ore from other countries. Therefore, China's strong dependence on imported iron ore and the low utilization rate of domestic iron ore need to be solved urgently. Studies have shown that magnetic roasting reduction technology is an effective method to reduce the iron ore phase in iron ore and improve the magnetic properties of iron ore. And magnetic roasting reduction technology can optimize the magnetic separation selectivity of iron ore. Through the magnetic separation of the iron ore after magnetization roasting, high-grade fine iron ore can be obtained. The magnetization roasting-magnetic separation process can effectively improve the enrichment and separation efficiency of domestic ores and improve the utilization rate of domestic ores. In this paper, the reduction effect of siderite, hematite and limonite as the main iron ore phase after carbon-based roasting reduction technology or hydrogen-based roasting reduction technology and the research status of the quality of concentrate iron ore after magnetic separation are reviewed, and the best reduction system of different ore reduction roasting process is put forward. The transformation law and reaction mechanism of each mineral phase in the process of carbon-based roasting reduction and hydrogen-based roasting reduction of ores with different iron ore phases are introduced. The future development direction of magnetic roasting reduction technology is analyzed, which has guiding significance for the selection of magnetic roasting reduction technology for other refractory iron ores and the development of subsequent mineral enrichment and separation technology. [ABSTRACT FROM AUTHOR]

The recovery of valuable minerals in froth flotation industry relies on finding inexpensive and environmentally friendly reagents that selectively adsorb upon surfaces and interfaces. Computer simulations, especially when extended, provide access to detailed mechanistic information on solvent configurations and may ascertain crucial dynamical events over the adsorption process. Further, in silico throughput screening can prevent both the high cost of experiments and the related risks to the environment. Yet, a better compromise between accuracy and computational cost must be met. Machine learning (ML) simulations may ease the latter and suggest solidophilic reagents able to improve the flotation efficiency, shedding new light on discerning descriptors able to accurately capture the nature of the molecule-surface interaction. In this work, our recent advancements in modeling of new accurate mineral-water interfaces based on active learning of ab initio molecular dynamics trajectories have been introduced. The case of some habitual oxides and minerals liberated in mining industry will be taken as examples. • How the mineral slab may influence the layering of surfactant water molecules. • Water kinetics at the hematite, ferrosilite and magnetite interfaces. • Competing adsorption phenomena between oleic acid and amylopectin on calcite surface. • In silico screening of flotation reagents employing machine learning methodologies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Selective flocculation of ultrafine hematite and quartz has been demonstrated. • High molecular weight anionic polyacrylamide selects hematite unlike cationic PAM. • In-situ probe measurements demonstrate hematite flocs of between 50–150 μm. • Adsorption varies with charge density, but median floc chord length does not vary. • Sodium hexametaphosphate reduces heterocoagulation and APAM adsorption on quartz. Recovering fine valuable material has been a significant challenge in minerals processing. This primarily stems from insufficient collision opportunities between fine particles and bubbles, specifically when utilising traditional recovery methods such as froth flotation. This research endeavours to address this challenge by exploring the use of various commercially available, high molecular weight polymers- specifically polyacrylamide (PAM)- to selectively aggregate hematite from quartz. Investigation of the conditions in which selective aggregation of hematite over quartz occurs, with the goal to achieve aggregate sizes of between 20 and 150 μm, were undertaken. Targeting this size range ensure that conditions are optimised for future use in conventional mechanical flotation cells as an efficient mineral recovery method. The study investigates the selectivity of charged PAM towards hematite and quartz at pH 10, using adsorption studies. Anionic PAM demonstrates a preference for hematite, with a range of charge density studies, highlighting stronger adsorption capacity with lower charge density polymers. Using BlazeMetrics probe technology for in-situ sizing and imaging, it was observed that conditioning 50–300 g APAM per t of hematite resulted in aggregates in the range of 30–230 μm after 5 min. Interestingly, the charge density of APAM does not markedly affect the size of the hematite aggregates, although altering the charge density of the polymer impacts the selectivity towards quartz. Additionally, cationic PAM results in the simultaneous aggregation of both hematite and quartz, not demonstrating selectivity. To mitigate heterocoagulation between minerals, a common dispersant, sodium hexametaphosphate (SHMP), was employed, which notably prevents quartz aggregation. Separation of aggregated hematite from quartz by sedimentation was only slightly effective with the majority of quartz settling with the hematite. Adding up to 1000 g of dispersant per t of hematite reduced the amount of quartz in the sediment bed by 23 %. The dispersant increased the magnitude of the negative zeta potential of the two minerals, particularly hematite, lowering heterocoagulation and improving effectiveness of hematite flocculation. [ABSTRACT FROM AUTHOR]

• Established CCM based on the adsorption mechanism of NaOL at hematite/quartz-water interfaces. • Calculated the binding constants of NaOL at hematite/quartz-water interfaces. • Predicted the adsorption behavior and surface potential of minerals for NaOL. • Provided valuable insights for the intelligent separation efficiency of minerals. The interaction of surfactants at minerals-water interfaces in flotation system plays an important role in minerals separation. Although the increasing number of reports have been published on the sodium oleate (NaOL) adsorption at the mineral–water interface, there has been little development in describing and predicting its adsorption behaviors from a quantitative molecular insight. In this study, based the adsorption experiments, the adsorption characteristics of NaOL on the hematite/quartz-water interfaces were quantitatively depicted using the surface complexation model (SCM). There was a monodentate binding form between the function group on NaOL and the hematite and quartz surface sites during SCM fitting. The binding constants (logK) of NaOL are 10.72 (≡Fe-OL) and 8.03 (≡Si-OL), respectively. Notably, there are more positive ≡FeOH 2 + site on the hematite surface, and it has strong adsorption capacity with anionic surfactant NaOL. Moreover, the minerals surface potentials, NaOL adsorption capacity and flotation recovery in mixed ore systems were successfully predicted by the model. This study provides a credible evaluation of the adsorption characteristics of NaOL under a broad scope of pH and concentration conditions. Meanwhile, quantitative analysis of surfactants adsorption at minerals-water interfaces is beneficial for the intelligence of mineral processing technology and efficient separation of minerals. [ABSTRACT FROM AUTHOR]

• Reducing the steel industry's carbon footprint by producing high-quality raw materials. • Significant silica reduction in iron ore magnetic separation concentrates. • Transforming low-grade iron ores into valuable resources through flotation. • Enhancing iron ore concentrate quality using reverse cationic flotation. • Assessing reagents and flotation parameters for direct reduction-grade iron ore concentrate. The steel industry holds a pivotal position in modern society, widely acknowledged as the most significant basic industry globally. Nonetheless, its substantial energy consumption and carbon emissions present significant challenges, contributing notably to global warming and climate change. Consequently, the sector has been fervently pursuing greener steelmaking processes. Among the various options, hydrogen direct reduction technology stands out as the most promising. Thus, the quest for new sources of high-quality iron ore concentrates has intensified in recent years, aimed at supplying the necessary raw material for direct reduction processes. In this context, the Mont Reed iron deposit, located in Quebec, Canada, emerges as a promising asset. The deposit comprises both magnetite and hematite-rich ores, presenting an average iron grade of 30 % along with complex gangue minerals. The present study evaluates the implementation of a flotation process to enhance the quality of the concentrate generated through low-intensity magnetic separation in the Mont Reed flowsheet, targeting direct reduction (DR) levels. The research involved the assessment of various industrial reagents to concentrate the magnetite present in the ore, as well as the execution of a design of experiments conducted using the most effective combination of reagents and different parameters. Ether amine, ether diamine, amidoamine, and phosphoric ester were evaluated as collectors, while starch, dextrin, CMC, and humic acid were assessed as depressants. Bench-scale flotation experiments presented promising results, demonstrating the feasibility of reducing the silica grade of the concentrate by 75 % (from 6.90 % SiO 2 to 1.68 % SiO 2), while producing a high-grade product containing 70.04 % Fe. The addition of a desliming stage was mandatory to achieve these results, and a Design of Experiment (DoE) campaign determined optimal flotation conditions: 150 g t−1 of collector, 400 g t−1 of depressant, pH 10, and 30 wt.% solids in pulp, achieving the target concentrate quality with a yield of 23.9 % and an Fe recovery of 52.0 %. These findings enhance the value of the Mont Reed deposit, positioning it as a potential source of DR pellet feed for the global iron ore market. The study also offers insights for similar operations, highlighting flotation as a viable solution when magnetic separation alone cannot achieve the necessary silica levels for DR products. [ABSTRACT FROM AUTHOR]

• The dissolution behavior of industrial hematite in H 2 SO 4 solution was studied for the first time. • The shrinking core model with inert reactant layer was employed to describe the dissolution process of industrial hematite. • This research is helpful to the development of low-temperature and short-duration hematite process. Here, the effect of H 2 SO 4 concentration, temperature, liquid to solid ratio and particle size on the dissolution behavior of industrial hematite in H 2 SO 4 solution. Among them, temperature and H 2 SO 4 concentration have significant effects on the dissolution efficiency of Fe from industrial hematite. Below 363.15 K, the dissolution efficiency of Fe increases with the increase of temperature, but the opposite is true above 363.15 K. Increase H 2 SO 4 concentration to promote the dissolution of industrial hematite. Liquid-solid ratio and particle size had little effect on the Fe concentration after dissolving at 180 min, but it has a significant influence on the Fe dissolution efficiency. The Fe dissolution efficiency of hematite with large particle size is significantly higher than that with small. Shrinking core model with inert reactant layer was employed to describe the dissolving kinetics of industrial hematite in H 2 SO 4 solution. In the temperature range of 303.15 − 343.15 K, the interfacial chemical reaction control is the rate-limiting step. Apparent activation energy (E a) is 48.1 kJ·mol−1. Based on this, four methods were recommended to prevent the re-dissolution of hematite in industrial practice: (1) increasing the reaction temperature, (2) extending the residence time of hematite in high temperature autoclave, (3) reducing the acidity of the slurry in autoclave though add neutralizer, (4) separating immediately hematite from slurry discharged from the autoclave. This work is of great practical value in terms of iron removal and recycle from the ZnSO 4 solution though the hematite process with efficient, clean and low temperature at 423.15 K. [ABSTRACT FROM AUTHOR]

[Display omitted] • New insights into the oxidization roasting of magnesian flux pellets were clarified. • Metallurgical property of magnesia flux pellets was discussed successfully. • Oxidization behavior and consolidation mechanism were systematically discussed. • Evolution mechanism of magnetite and maghemite was clarified. A systematic study of the preparation and metallurgical properties of magnesia flux pellets was used to elucidate the mechanism for oxidation and consolidation occurring during oxidative roasting. The compressive strength of the finished pellets was 3545 N/P. With sufficient basicity and MgO contents, magnetite (Fe) x [Fe] 2 O 4 and maghemite γ-Fe 2 O 3 with spinel-type crystal structures combined with MgO/CaO to form nonstoichiometric Mg x Fe 1-x Fe 2 O 4 (0 < x < 1) and Ca y Fe 1-y Fe 2 O 4 (0 < y < 1). With higher basicity and MgO contents, the participation of CaO/MgO was the driving force for gradient conversion from olivine Fe 2 SiO 4 to olivine Mg x Ca 2-x SiO 4. The CaO/MgO combined with magnetite (Fe) x [Fe] 2 O 4 and maghemite γ-Fe 2 O 3 to form stable (Ca, Mg) x Fe 1-x Fe 2 O 4 , CaFe 2 O 4 and CaFe 3 O 5 , thereby inhibiting recrystallization of the pellets and resulting in poorer metallurgical properties of the magnesia flux pellets. [ABSTRACT FROM AUTHOR]

• Experiments were conducted using the Reflux Classifier to upgrade itabirite iron ore. • The underpinning partition surface of the Reflux Classifier was established. • The work shows how to predict the grade-recovery curve for any feed. This work assessed the potential of a single stage Reflux Classifier to upgrade itabirite iron ore to high grade at satisfactory recovery. Part I reported on the detailed findings of the experimental program and the physical transport of the particles through the system. A key purpose of the present paper was to deduce the underlying partition surface from relatively basic feed information on the Fe assays obtained as a function of the particle size. Conversion of the feed data into a simple binary description based on the density of hematite and density of silicates was used. This approach then provided a basis for applying the partition surface to a given feed to predict the separation performance. Data from the experiments were compared to values predicted from the partition surface. A least squares objective function was used to implicitly deduce the parameters governing the partition surface, notably the key exponent n and the Écarté Probable, Ep. Across 12 of the experiments, the exponent, n, governing the partition surface was found to be 0.26 ± 0.02. This result was in very good agreement with the value of 0.28 determined previously. The second key parameter, the Ep , was also determined for each of the experiments. The lowest Ep , found to be 365 kg/m3 for a low slimes viscosity, was also in good agreement with the result reported previously for a deslimed feed. This work provides confidence in the application of the partition surface to predict similar dense mineral separations, and stronger insights into the mechanisms responsible for the separation. [ABSTRACT FROM AUTHOR]

• Evaluation of Crago process to beneficiate iron ores. • Tailings recovery strategies in iron ore industry. • Direct anionic flotation of hematite applied to iron ores. • Comparison between reverse cationic flotation and anionic direct flotation for iron ores. Mont-Wright mine is an important asset of ArcelorMittal located in the province of Quebec, Canada. This asset annually produces 25 million tons of iron ore concentrate with an assay of 66 % Fe, achieved through a beneficiation circuit comprised entirely of spiral concentrators. Nevertheless, 45 million tons of tailings are discarded to the tailings dam and, due to the intrinsic inefficiency of the spiral concentrators used there, the iron content increases in the size fraction below 106 µm, which presents a good potential to be recovered. Thus, the Crago flotation process was evaluated to recover the iron contained in the finest fraction of the Mont-Wright tailings. Since it was patented in 1942, the Crago process with fatty-acid rougher flotation followed by deoiling and amine cleaner flotation has become the standard for phosphate flotation in USA operations. When applied to Mont-Wright tailings, the Crago process was able to produce a concentrate assaying 65.63 % Fe and 2.14 % SiO 2 , from a sample with 20.96 % Fe. When compared to a usual reverse flotation circuit, Crago based flowsheet was more selective and presented better results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various SNMRs for starch gelatinization were examined as an innovative and fundamental investigation. • SNMR = 5:1 promoted the lowest flotation recovery with the highest induction time and the lowest contact angle. • At SNMR = 5:1, Amylopectin (AP) molecules are the largest in solution. • At SNMR > 5:1, the gelatinization is incomplete, as debris is identified. • At SNMR < 5:1, AP molecules are smaller and less abundant in solution. Starch is a traditional depressant for hematite beneficiation by cationic reverse flotation separation from silicates. Alkali or thermal gelatinization must be used to prepare starch and promote its dissolution in water. In industry, gelatinization is typically carried out using sodium hydroxide at room temperature at different starch/NaOH mass ratios (SNMR). Surprisingly, no investigation has systematically studied the optimum SNMR for boosting hematite depression. This work examined the influence of starch gelatinization under various SNMR (3:1, 5:1, 7:1, and 9:1) on hematite depression (at pH = 10.5, 22 °C) by exploring flotation response (R), contact angle (θ), induction time (τ), hydrodynamic diameter (d H) of starch macromolecules, total energy of interaction starch/hematite (GTOT), based on its two components: the attractive Lifshitz-van der Waals energy (GLW) and attractive/repulsive electrostatic energy (GEL). Flotation test results indicated that SNMR = 5:1 promoted the lowest hematite recovery (14.8 %), coupled with the highest induction time (τ = 55 ms) and the lowest contact angle (θ = 11°). The hydrodynamic diameter (d H) of macromolecules in solutions prepared under different SNMR was determined by Dynamic Light Scattering, showing three peaks: amylopectin (350 < d H < 420 nm), amylose (50 < d H < 100 nm) and debris from gelatinization (d H ∼ 5000 nm). Since the latter only occurred in solutions prepared under SNMR of 7:1 and 9:1, deficient hematite depression might be caused by incomplete gelatinization. As amylopectin is the starch component that is responsible for its depressant ability, larger amylopectin macromolecules (d H = 411 nm) found in solutions prepared at SNMR = 5:1 contrast with smaller macromolecules (d H = 353 nm) produced at SNMR = 3:1. Considering starch macromolecules as a sphere, and hematite's surface as a plane; GLW, GEL, and GTOT were calculated in function of the sphere/plane separation distance (2 nm < H < 20 nm). GLW was determined based on the assessment of the Hamaker constant of the starch/water/hematite system (2.9 × 10−20J < A 132 < 3.3 × 10−20J), whereas GEL was determined based on the zeta potential of starch (−2mV < ζ 1 < −4mV) and hematite (ζ 2 = −29 mV). GTOT for starch gelatinized at SNMR = 5:1 (−502.9 × 10−21 J) is greater than GTOT for starch prepared at SNMR = 3:1 (−468.8 × 10−21 J) and SNMR = 7:1 (−469.0 × 10−21 J), at a confidence level of 95 %. These results corroborate the more intensive hematite depression by starch prepared at SNMR = 5:1 compared to the other values explored by this study. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyacrylamide adsorption on iron oxide is selective over silica as a function of pH. • The adsorption of polyacrylamide on magnetite and hematite was compared. • Anionic polyacrylamide adsorbed more strongly to iron oxide at low pH. • Anionic polyacrylamide adsorption exceeded that of neutral polyacrylamide at low pH. Acrylamide-based polymers such as polyacrylamide (PAM) and their derivatives are widely used as additives to enhance solid-liquid separation in the mineral processing industry. Thus, an investigation of polyacrylamide behaviour at oxide-aqueous solution interfaces is of vital importance. In this work, the adsorption of different molecular weight polyacrylamides onto iron oxides and silica was quantified at different pH values. Mineral oxides were characterised by zeta potential, particle size distribution, scanning electron microscopy images and X-ray diffraction. The Sauter mean D [3,2] diameter of the hematite, magnetite and silica were measured to be 0.8, 1.9, and 2.0 µm respectively. An anionic polyacrylamide (PAM A, MW 520 kg/mol) exhibited strong variation in adsorbed amount with pH, while the adsorption of two neutral polyacrylamides (PAM N, MW 40 & 5500 kg/mol) had a weak dependence on pH. All three polyacrylamides had similar adsorption capacity on the iron oxides particles, thus minimal influence of molecular weight was observed. The adsorption isotherms were fit to the Langmuir model to facilitate interpretation of the adsorption mechanism. The highest adsorption plateau density of 11.4 mg/m2 on magnetite and 7.4 mg/m2 on hematite for PAM A was found to be at lower pH. At the same pH, high molecular weight PAM N shows the highest adsorption plateau density of 7.8 mg/m2 and at unadjusted pH, low molecular weight PAM N adsorbs to 5.2 mg/m2 on magnetite. All PAM samples selectively adsorb on the iron oxide particles compared to silica particles. These quantified adsorbed amounts are concordant with the current use of high molecular weight PAM as an effective flocculant. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tannic acid and PEO polymer mix flocculated quartz and reduced its entrainment. • The degree of quartz entrainment reduction was dependent on floc size distribution. • Too large or too small flocs were not conducive to selective flotation separation. • Tannic acid reduced the surface activity and foaming property of PEO in flotation. • Tannic acid is critical in assisting PEO-quartz flocculation and lowering PEO surface activity. In the present study flocculation flotation (floc-flotation) of ultrafine hematite and quartz was investigated in a laboratory-scale flotation column. A direct flotation scheme was used to float hematite using in-house synthesized n-octyl hydroxamic acid (OHA) as a collector. A polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) was used to flocculate quartz to reduce its entrainment. The effects of agitation intensity and foam stability on floc size distribution, entrainment reduction, and flotation kinetics/recovery were investigated. It was shown that the dual polymers TAN-PEO were effective in reducing quartz entrainment, and that the degree of entrainment reduction was affected by the intensity of agitation. A correlation was established between the mean floc size and a reduction in quartz entrainment. TAN-PEO dual polymer system also enhanced the flotation kinetics and recovery of hematite by OHA, originating from a synergistic effect between PEO and OHA. Therefore, higher separation efficiency was achieved from synthetic ultrafine hematite and quartz mixtures when TAN-PEO was added after OHA. The underlying mechanisms were studied by floc size distribution, surface tension, and foam height and decay time measurement. This work helps understand the relationship between hydrodynamic condition, flocs size, and mechanical entrainment when polymeric flocculation is used for entrainment reduction in fine and ultrafine minerals flotation. [ABSTRACT FROM AUTHOR]

This study investigates the microwave carbothermal reduction of low grade banded hematite jasper iron ore ∼37% Fe. Due to complex association of the iron phase and impurities, the conventional beneficiation was found futile. The susceptibility of iron phases to microwave exposure assists in the liberation of iron values from impurities. The thermodynamic calculations revealed the selective reduction of iron ore phases in the Fe-O-C-Si-Al system. The preliminary experiments revealed that during a few minutes of microwave exposure, a temperature of ∼400 °C and ∼1100 °C was achieved for feed and charcoal mixture respectively. Besides iron enrichment in the concentrate, the ferrite balls were also observed in statistical design experiments. It was found that a small fraction of microwave irradiated BHJ ore-charcoal mixture was rapidly melted to produce ferrite balls. The presence of a sufficient amount of bonded silica content in the BHJ ore leads to an easy formation of the fayalite phase. The iron grade falls at prolonged exposure due to the interaction of iron phases with the quartzite as revealed by the XRD analysis. The optimal condition 720 W power, 9% charcoal and 8 min based on statistical design yielded a magnetic concentrate having ∼61.6%Fe, ∼73.4% recovery at a yield of 44% and has a potential to be used for pellet making industry. Similarly, the experimental condition 900 W power, 12% charcoal and 8 min yielded a magnetic concentrate with ∼49.1%Fe, ∼89.3% recovery at a yield of 59.7% along with ferrite balls with a saturation magnetization of ∼153 emu/g. [ABSTRACT FROM AUTHOR]

• Addition of starches decreased the R f and R c of quartz or hematite particles. • At each experimental condition tested, R f was much higher than R c. • The decreases in R f and R c coincided with the increase in the aggregate size. • The R f and R c of Fe in the flotation of quartz-hematite mixture were measured. This paper reports the measured froth zone (R f) and collection zone (R c) recoveries in the flotation of pure quartz, pure hematite, and a quartz-hematite mixture with one of three corn starches with different mass ratios of amylose to amylopectin: waxy starch (0:100), normal starch (27:73), and Gelose 50 (50:50). The flotation tests were carried out at continuous mode using a three-product column at different pHs and starch concentrations with sodium oleate as collector and calcium chloride as activator. It was found that both R f and R c were significantly affected by pH and starch type and concentration. In the flotation of pure quartz or hematite, addition of each of the corn starches tested would decrease the R f and R c , with the effects following the order of waxy starch > normal starch > Gelose 50. The decreases in R f and R c coincided with the increase in the aggregate size caused by addition of these starches. Possible correlations between R f , solid flux at the pulp-froth interface and R c were examined. In the flotation of the quartz-hematite mixture, the changes in R f and R c of Fe caused by varying starch type and dosage were consistent with those in the flotation of pure hematite. [ABSTRACT FROM AUTHOR]

• Maximum concentration difference between RCOO− and oleate dimer was at neutral solution. • Strong chemical bond formed as RCOO− directly acted upon the Fe of siderite. • RCOOH RCOO− laid on hematite through weak chemical bond and hydrogen bond. • Van der Waals and hydrophobic forces were the main forces to connect oleate chains. To separate siderite from carbonate-bearing iron ore efficiently, specific adsorption configurations and effective species were investigated to compare the adsorption differences of sodium oleate (NaOL) on siderite and hematite surfaces. The species were analysed in neutral conditions, under which the direct flotation of siderite from hematite and quartz was carried out. Changes in the zeta potential, Fourier-transform infrared spectroscopy spectra and X-ray photoelectron spectroscopy spectra caused by the adsorption of oleate species were compared to confirm the adsorbed species on siderite and hematite. Molecular dynamics simulations were carried out to further verify the specific adsorption configurations. Chemisorption of oleate species was detected on both siderite and hematite. The differences in the relative concentration changes of the elements indicate that NaOL worked on siderite and hematite via adsorption of various groups or species. The main functional species were RCOO− for siderite and RCOOH RCOO− for hematite. A strong chemical bond formed as RCOO− directly acted upon the Fe of siderite. The carbon chains bent and interweaved to form the hydrophobic layer on siderite. The two chains of RCOOH RCOO− laid upon hematite via weak chemical bonds and hydrogen bonds. Van der Waals and hydrophobic forces were the main interforces of the two chains. [ABSTRACT FROM AUTHOR]

• The main reactions during calcination of laterites are identified. • A combination of model-free and model-fitting methods were used for kinetic analysis. • Individual kinetic parameters for the main reactions are calculated. • Avrami-Erofeev model is selected as the kinetic model for the main reactions. Calcination and partial reduction at temperatures below 1000 °C is a primary step in pyrometallurgical extraction of nickel from laterites. Identifying the main reactions that occur during this process and investigating their kinetics provide valuable information on the rates of the reactions and their degree of completion. The main reactions were identified using thermal gravimetric analysis-differential scanning calorimetry (TGA-DSC), X-ray diffraction, and scanning electron microscope energy dispersive spectroscopy (SEM-EDS) tests. Transformation of goethite to hematite, dissociation of lizardite to forsterite and silica, and decomposition of silicate were identified as the main reactions. The kinetic parameters for the three main reactions were obtained using both model-free and model-fitting methods. Comparing the activation energy obtained by the two kinetic approaches, Avrami-Erofeev model was selected as the kinetic model for the aforementioned reactions. [ABSTRACT FROM AUTHOR]

Highlights • The billion litters of acid mine drainage (AMD) are produced every day. • AMD have high content of iron and acidity that cause great environmental damage. • Selective precipitation of Iron produce iron oxide with high purity without Al, Zn and Mn contaminates. • Iron sludge without contaminants can be converted to yellow pigment (goethite) through alkaline precipitation. Abstract Acid mine drainage (AMD) in the coal mining industry is recognized as one of the major sources of environmental damage. The active treatment of AMD involves adding alkaline reagents to wastewater so as to raise pH and to precipitate dissolved metals in the form of oxides/hydroxides. Studies have shown that yellow pigment (goethite) can be produced from the iron present in AMD. However, the presence of other metals can prevent the formation of pigment. Therefore, this paper seeks to evaluate several processes for purifying iron sludge so as to obtain raw material that can be recovered from AMD and thereby obtain a good quality of yellow pigment. The experiments were carried out by causing precipitation with strong and weak bases and removing other metals from the sludge by washing and filtering the sludge or by centrifugation. The results show that the color, type and morphology of the compounds changed, depending on the number of contaminants, and that these factors are strongly dependent on the type of reagent and less dependent on the separation process and the repetition of washes. [ABSTRACT FROM AUTHOR]

Highlights • The surfactant α-Bromolauric acid (α-BLA) was used for the first time to separate fluorapatite (FAp) from hematite. • The α-BLA obtained good low-temperature flotation result compared to lauric acid. • Chemical bonding was the main adsorption mechanism of α-BLA on apatite. Abstract Flotation collector α-Bromolauric acid (α-BLA) was used to separate fluorapatite (FAp) from hematite. Flotation performance was presented by pure mineral and mixed binary minerals flotation experiments. The adsorption mechanism of α-BLA on FAp surface was investigated by zeta-potential, FT-IR spectra, and XPS measurements. Flotation results showed that the α-BLA reduced the phosphorous grade of the concentrate to 0.25% and achieved the iron recovery of 91.67% at 19 °C. The mechanism research revealed that the anion of α-BLA interacted with calcium ion of the FAp surface by chemisorption making the FAp mineral float up despite the existence of cornstarch. [ABSTRACT FROM AUTHOR]

• The grain-boundary cracks that expose the hematite can be observed in the products of high voltage pulse discharge (HVPD). • During the roasting process, cracks, and pores in the HVPD products continue to develop. • The HVPD products has a higher degree of reduction than mechanical crushing after magnetizing roasting. High voltage pulse discharge (HVPD) is a new type of crushing technology with good application. Existing studies have focused on the crushing characteristics, with less reports on follow-up work. This study magnetization roasts hematite ore after mechanical crushing and HVPD, analyzing the difference in the roasting effect between the two crushing methods by establishing a new system of HVPD-magnetization roasting. For a roasting temperature of 500 °C, roasting time of 30 min and number of pulses of 100 times, the grade and recovery of magnetic separation concentrate obtained from HVPD products after secondary separation were 64.69% and 82.05% respectively, which were 0.28 and 1.96 percentage higher than those of mechanical crushing. X-ray diffraction (XRD), vibrating sample magnetometry (VSM), Brunauer-Emmett-Teller (BET), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) were used to analyze the process and showed that the specific surface area, pore volume and average pore size of the HVPD products were improved. Grain boundary fracture and burn marks were present in the HVPD products. [ABSTRACT FROM AUTHOR]

• The low temperature hematite process with adding neutralizer was proposed for the first time. • The operating temperature of the hematite process was dramatically decreased to 423.15 K, even 393.15 K. • The operating duration of the hematite process was significantly reduced to <100 min, and the iron removal efficiency can reach 99%. • The iron ions in the zinc leaching solution were recycled as resources, and the environmental problem of iron removal residue storage was solved. Here, a clean, low-temperature hematite process using a neutralizer was proposed to remove iron ions from a zinc leaching solution and reutilize iron removal residue. The results showed that the solution acidity played a crucial role in this process. For a ZnSO 4 solution with an Fe2+ concentration of 12–14 g/L and an initial pH > 3.0, the iron ion concentration decreased to 20 mg/L within 95 min when using the low-temperature hematite process with pure ZnO (10–13 g/L) added as a neutralizer in the temperature range of 408.15–423.15 K. The iron removal efficiency reached 99%. Increasing the initial pH of the initial solution significantly improved the iron removal efficiency, and it was necessary to control the pH above 3.0. After ferrous ion mineralization, the residual iron concentration in the solution was inversely proportional to the final pH. The precipitated hematite products contained an Fe content of >55%, with a Zn loss of <1% and S contamination level of <3%. These hematite products can be sold as raw materials for ironmaking to solve the environmental issues associated with the storage of iron removal residue. The results showed that zinc oxide dust could not be used as a neutralizer because it resulted in the loss of valuable metals such as Pb, Ag, and In. Compared with the hematite process (453.15–473.15 K, reaction time of 3.0 h) used by the Iijima Refinery of Akita Zinc Co. in Japan, the ferrous ion mineralization in this study was shortened to <100 min. This significantly increased the treatment capacity of the low-temperature hematite process for zinc leaching solutions. The low-temperature hematite process could be performed at 393.15 K, 408.15 K, and 423.15 K, which can realize energy savings and consumption reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel low-foam viscous cationic collector DTDAB was synthesized. • DTDAB exhibited superior collector ability and selectivity than DTAB. • Insertion of hydroxyl could reduce interface tension and foam coalescence of collector. • Better selectivity was achieved by regulating the size of the polar group. Traditional cationic collectors generally exist some disadvantages, such as high foam viscosity and difficulty in defoaming, which worsening the flotation separation effect. Herein, a novel cationic collector-dodecyl trihydroxyethyl ammonium bromide (DTDAB) with low-foam viscous was synthesized to optimize the reverse flotation system of hematite ore, which was achieved by introducing three hydroxyethyl groups into the nitrogen atoms of dodecyl trimethyl ammonium bromide (DTAB). The analysis of foam collapse performance indicated that the introduction of hydroxyl groups into hydrophilic head groups of DTAB reduced the interface surface tension and bubble coalescence, which were consistent with the design expectations. Meanwhile, flotation behaviors were systematically studied, and the results showed that the concentrates with 63.89 % total iron (TFe) grade and 89.27 % total iron recovery was obtained at pH 6.81, when the concentration of DTDAB and starch was 20 mg/L and 5 mg/L, respectively. Besides, the possible flotation mechanism was further studied by means of contact angle, Atomic force microscope (AFM), Fourier transforming infrared spectra (FT-IR), X ray photoelectron spectroscopy (XPS), and Density functional theory (DFT) calculation. The results comfirmed that the adsorption between DTDAB and quartz was caused by electrostatic force and hydrogen bonding affinity. In conclusion, it can be confirmed that the novel cationic collector DTDAB with low-foam viscous has the potential for the hematite reverse flotation desilication. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new fast way to determine the Bond work index method is proposed to ball mills. • It is possible to determine the work index using a 3 kg sample and 5 min time. • Use only one grind and the population balance model to predict the work index. • The values estimated for SSE are less than 0.4. The Frederick C. Bond has several grinding indices (ball, rod, abrasion), one of which has been a significant guide for ball mills. The Bond ball mill work index is an expression of the material's resistance to ground and a measure of the grinding efficiency. The test is a standardized methodology that ends when a circulating load of 250% is obtained. In this paper, a new method based on the Population Balance Model (PBM) is proposed and validated to estimate the results of the Bond ball mill work index test (Wi B). The model presented in this study combines the first cycle of the Work Index test (at 250% circulating load) with the PBM. Impure limestone, fluorite, chalcopyrite, and hematite ores were used to run both tests with a good confidence level (SSE less than 0.4 in all samples tested). As stated, based on the methodology the operational parameters for grinding (charge level, ball size distribution, and critical speed) were kept constant. The methodology developed showed great simplicity and potential applicability to a wide range of minerals by carrying out only one grinding test and numerical iteration to obtain a 250% circulating load. [ABSTRACT FROM AUTHOR]

• A novel collector (DHDAB) introducing hydroxyethyl was designed and synthesized. • DHDAB was first used in flotation separation of quartz and hematite. • DHDAB existed excellent selectivity for quartz against hematite. • Strong hydrogen bonding and large steric hindrance made DHDAB good selectivity. The quaternary ammonium salt collectors display great application prospects in minerals flotation, and introducing the second polar group has been an effective method to enhance the performance of flotation reagents. In this study, the hydroxyl group was introduced into quaternary ammonium salt to design and synthesize a novel containing hydroxyl group quaternary ammonium salt collector dodecyl hydroxyethyl dimethyl ammonium bromide (DHDAB) for the flotation desilication of hematite, which was characterized by Fourier transform infrared spectroscopy (FT-IR), mass spectrometry, and nuclear magnetic resonance (NMR). Based on the reverse flotation desilication system of hematite, the differences in flotation performance of DHDAB and dodecyl trimethyl ammonium bromide (DTAB) were compared, and the flotation separation behaviors of DHDAB to quartz and hematite were also studied by micro-flotation tests. Both DHDAB and DTAB showed great pH adaptability, and DHDAB had better flotation selectivity than DTAB through flotation studies. The selective flotation separation mechanism of DHDAB to quartz and hematite was also analyzed by zeta potential tests, FT-IR analyses, contact angle tests, X-ray photoelectron spectroscopy (XPS) tests and density functional theory (DFT) analyses, meanwhile, the influence mechanism of the hydroxyl group on the performance of collectors was also studied. The contact angle test results showed that the surface hydrophobicity of quartz and hematite treated by DHDAB was more different. These results also indicated that DHDAB was selectively adsorbed on the mineral surface mainly through electrostatic attraction and hydrogen bonding. Introducing the hydroxyl group into DHDAB could produce stronger hydrogen bonding, increase the interaction site with the quartz surface, and increase the steric hindrance to enhance the selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Iron ore tailings (IOT) were processed by a hydrometallurgical route. • Leaching resulted in a ferric liquor and a solid fraction rich in silica. • A simplified route for synthesis of silica-free iron oxide was stablished. • Micro- and nanoparticles of silica-free hematite with 64% iron content were synthesized. • Iron oxide has compatible characteristics for high-quality pellets production and for commercialization as pigment. • The process supports the environmental sustainability of the iron mining and steel production. The processing of iron ore generates large volumes of tailings. Acid leaching enables the solubilization of iron in an aqueous solution, allowing the production of ferric liquor and a silica-rich residue. The purpose of this investigation was to use the leachate resulting from this process to synthesise high-quality iron oxide. The conducted methodology involved acid leaching, selective iron precipitation as a function of pH, and the thermal conversion of the precipitated iron oxy-hydroxides into iron oxide particles. The iron oxide consisted of micro/nano Fe 2 O 3 particles which were free of silica, with iron contents of 64% and particle sizes of less than 28 μm. The process presented an overall iron recovery around 84%. The resulting material could be used as a commercial pigment or be incorporated into steel-making iron pellets. The hydrometallurgical conversion of iron ore wastes into valuable products may contribute to the future of mining and to green steel production. [ABSTRACT FROM AUTHOR]

Oolitic iron ores are a distinctive subset of iron ore deposits, and are characterised by their spherical grains composed of concentric layers containing hematite and goethite along with impurity elements such as silicon and phosphorus. Depending on their petrology, oolitic iron ores may require very simple or extremely complex flowsheets for their processing. This review focussed on beneficiation by conventional mineral processing techniques and also more energy intensive processes involving heating (roasting) or leaching. The aim of roasting is to transform minerals like hematite and goethite to magnetite or metallic iron, making them amenable to concentration by magnetic separation. The overall aim of this review was to highlight possible techniques for economically processing oolitic iron ores for the subsequent production of iron and steel. An attempt has been made in assembling this review to strike a balance between more historical documentation and a plethora of recent information readily obtainable by searching electronic data bases. [ABSTRACT FROM AUTHOR]

In mineral recovery, the flotation of fine and ultrafine particles is poor, and the process is dependent on the bubble size and the hydrophobicity of the particles. This low recovery is mainly related to the low bubble/particle collision efficiency. However, this problem can be overcome by reducing the size of the bubbles. The electroflotation process is an attractive alternative for the concentration (recovery) of fine particles using hydrogen and oxygen bubbles smaller than 100 μm. In this context, the present work presents a study on the electroflotation of fine hematite particles in a modified Partridge–Smith cell using Rhodococcus opacus as a bioreagent and hydrogen or oxygen bubbles. The influence of the current density and system pH on bubble size of the hydrogen and oxygen was also evaluated with the aid of a bubble sizer equipment. The Sauter mean bubble diameter ( d 32 ) was found to range from 40 to 60 μm for the hydrogen bubbles and 50 to 70 μm for the oxygen bubbles. The hematite electroflotation tests were conducted in a modified Partridge–Smith electroflotation binary cell with 0.38 L usable volume. The process variables studied were the concentration of R. opacus , particle size, pH, and current density. The optimum pH value found for hematite flotation was around 6, and the higher hematite recovery values were about 80% and 65% with hydrogen and with oxygen bubbles, respectively. [ABSTRACT FROM AUTHOR]

Comparative mineral liberation and separation tests of hematite ores were conducted for three comminution flowsheet options to produce relatively fine products at the 70% and 90% passing 74 µm: Option A uses a high pressure grinding roll (HPGR) with screening and subsequent ball milling, Option B uses an HPGR with an air classification, and Option C uses a jaw crusher with screening and subsequent ball milling. Cracks growing inwards are relatively flat along the direction of applied force during conventional crushing. However, cracks surround the weak interface during HPGR crushing, generating a large number of “mosaic-type” locked-particles. Mineral liberation was only affected after the final grinding mode, not by the crushing method before grinding. “Mosaic-type” locked-particles produced via the particle-bed breakage have no better way to liberate in downstream ball-mill grinding. Fine mineral grains are then detached from the ore under the high compressive stress, which leads to a significant and clean liberation of the mineral phases in HPGR coarse grinding. Overall, HPGR grinding is more beneficial to the quartz liberation, while ball mill grinding is more beneficial to oxidised iron minerals at a coarse grinding fineness; these advantages disappeared after the further fine grinding. The coarse-sized liberated quartz, although well-liberated, raised rejection of coarse gangue in magnetic separation during HPGR grinding. Finally, recovery of the HPGR grinding process increased by 4.4–5.2 percentage points higher than that of the ball milling process. [ABSTRACT FROM AUTHOR]

Bauxite and bauxite residue, a by-product of alumina production, were studied using a combination of microanalytical techniques — electron microprobe wavelength dispersive spectrometry, laser ablation inductively coupled plasma mass spectrometry and μ-Raman spectroscopy. The aim of the work was to reveal the modes of occurrence of scandium (Sc). The motivation behind this effort was to provide mineralogical insight for the support of ongoing development of Sc extraction technologies from bauxite residue. In the analyzed bauxites and residue, Sc is mainly hosted in hematite, where Sc 3+ probably substitutes Fe 3+ . The average concentration of Sc in the hematite matrix of bauxite is about 200 mg/kg, while in the bulk sample it ranges from 42 to 53 mg/kg Sc. In bauxite residue, the average concentration of Sc in hematite matrix is about 170 mg/kg, and in the bulk sample it is 98 mg/kg. In bauxite residue, goethite was also identified to host Sc with a concentration of about two times more than in hematite — 330 mg/kg. In bauxite residue, hematite, goethite and zircon host respectively 55 ± 20%, 25 ± 20% and 10 ± 5% of the total Sc. The effect of the Bayer process to the modes of occurrences of Sc is minor. The secondary bauxite residue minerals formed during bauxite processing do not capture any or capture very low amounts of Sc. New evidences of Sc leaching behavior from bauxite residue show that Sc is first released from goethite, then from hematite and the unrecovered proportion of Sc is likely associated with zircon. [ABSTRACT FROM AUTHOR]

Phase transformation of weakly magnetic iron minerals into a strongly magnetic magnetite is a promising technique for iron ore beneficiation with the further magnetic separation. Thermal decomposition of siderite leads to both magnetite and carbon monoxide formation. Carbon monoxide, as a reductant, sequentially triggers the transformation of hematite into magnetite. Therefore, this method of magnetite formation does not require any additional reducing agent. In the present paper, the source materials were hematite and siderite ores, which were mixed in different mass ratios. Phase transformation of ores’ mixture was performed at various temperatures and for various time intervals. It was shown within the experiments that siderite and hematite transformed to magnetite. The starting temperature of magnetite formation was about 400 °C. X-ray diffraction analysis confirmed the formation of the spinel structure that corresponds to magnetite. The saturation magnetization of transformed samples increased immensely up to 70 Am 2 /kg for the sample in 1:1 ratio of hematite to siderite. Optimal conditions for the conversion included heating the mixture at 600 °C for 12 min. Under these conditions, siderite and hematite completely transformed to magnetite, since solely magnetite was detected in transformed samples. Simultaneous roasting of hematite and siderite ores is a simple and an economically efficient technique for magnetic powder preparation. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) well logging is a well-established technique for in-situ fluid measurement. It is however not routinely used in the mining industry to quantify water content in high magnetic susceptibility iron ore rock cuttings because the ore’s magnetic properties adversely affect the measurement. In this study the relationship between NMR signal intensity and magnetic susceptibility is studied using a low magnetic field (2 MHz) benchtop NMR instrument. Magnetic susceptibility is commonly measured during well logging protocols and therefore could be used to correct and hence render quantitative NMR measurements of moisture content in iron ore. In this study NMR signal from water-saturated synthetic samples (magnetite/maghemite/hematite mixed with borosilicate glass beads) is measured as a function of iron content and magnetic susceptibility to obtain such a correlation. This correlation is then applied to iron ore rock cuttings. Comparison with gravimetric measurements show that a standard error of estimate of water content across all samples tested of 6.4 wt% using no correction, is reduced to 1.5 wt% using the corrections, corresponding to a relative error reduction from 47% to 11%. Additional comparison with whole rock cores shows that a higher magnetic susceptibility threshold for using the corrections is required for whole rock cores than for the rock cuttings, this difference requires further study. These results encourage the broad use of these types of correlations for NMR measurements of iron rich cuttings and application of NMR well logging to iron ore deposits. [ABSTRACT FROM AUTHOR]

India has around 28.52 billion tons of hematite and magnetite ore reserves, over 20% of which is in the form of fines. Also during the mining, crushing and washing of ore, huge quantities of fines are generated, majority of which end up into tailing ponds owing to their high alumina contents (∼10–15%). Selective dispersion flocculation is a promising route for beneficiation of such fine ores as opposed to conventional gravity and magnetic separation techniques; however, one requires selective reagents for effective beneficiation. We are engaged in the design and development of selective reagents for beneficiation of iron ores based on a molecular modelling approach. In the present study we have employed density functional theory (DFT) to calculate the interaction energy of hematite (0 0 0 1), goethite (1 0 0), gibbsite (0 0 1) and kaolinite (0 0 1) surfaces with carboxymethyl cellulose (CMC). The magnitudes of the computed interaction energies follow the trend: Hematite > Goethite ∼ Gibbsite ∼ Kaolinite Al–OH terminated > Kaolinite Si–O terminated. Electronic structure analysis revealed that the O-atoms in the hydroxyl and carboxyl groups of CMC form coordinate covalent bonds with surface Fe-atoms of hematite while forming only weak hydrogen bonds with goethite, gibbsite and kaolinite surfaces thus explaining the trends in the interaction energies. These DFT findings were validated by experimental flocculation results which show that a final concentrate of 64.4% Fe, 4.2% Al 2 O 3 , and 1.9% Silica with a yield of 56% can be obtained from a feed containing 56.5% Fe, 7.0% Alumina, and 4.9% Silica. Mineral wise estimation of chemical assay shows that CMC can be selective in flocculating hematite mineral particles over goethite, gibbsite and kaolinite. Our work thus highlights the important role of molecular modeling techniques such as DFT in screening and design of selective reagents for beneficiation of alumina-rich iron ore slimes. [ABSTRACT FROM AUTHOR]

The effects of non-polar oil on hydrophobic flocculation and micro-flotation of fine hematite (−20 µm) were studied when sodium oleate, octyl hydroxamic acid, or oleoyl hydroxamic acid was used as a collector. The micro-flotation test was carried out under neutral pH, and kerosene was used as the non-polar oil. Focused Beam Reflectance Measurement (FBRM) particle size analysis coupled with optical microscopy was performed to monitor the real-time evolution of hematite particles during flocculation. In addition, contact angles and zeta potentials of hematite were determined and used as parameters in the extended-DLVO theory interaction force estimation. The micro-flotation tests showed a beneficial effect of kerosene at high collector dosages regardless of the type of collectors used. The FBRM and optical image analysis indicated that the sizes of hematite aggregates induced by sodium oleate or oleoyl hydroxamic acid was much larger than by octyl hydroxamic acid; and the addition of kerosene further enhanced the aggregate size differences. The extended-DLVO theory calculation was carried out to explain the differences in the aggregation behaviors. The results indicated that the hydrophobic interaction energies between hydrophobic hematite particles induced by sodium oleate or oleoyl hydroxamic acid were stronger than by octyl hydroxamic acid. When kerosene was added, the aggregates grew to a much larger size due to the strong hydrophobic interaction between hematite particles and kerosene droplets. [ABSTRACT FROM AUTHOR]

The direct measurement of adsorbed oleate onto hematite removes the uncertainty of depletion of oleate onto non-hematite surfaces. Direct measurement of oleate onto hematite at pH 4 and as a function of pH at constant oleate addition was made using Differential Scanning Calorimetry. Oleate adsorption measurements were conducted on conditioned, concentrate and tailing samples, corrected for their surface areas. Adsorption measurements were complemented by flotation tests. At pH 4, oleate adsorption on conditioned samples reached a complete monolayer by vertical orientation at the critical micelle concentration (CMC) of the oleate. The onset of multilayer adsorption by vertical orientation on the concentrate samples was determined at the CMC, and monolayer coverage on the non-floated material was always less than one monolayer under two-point and vertical oleate orientation. Flotation recovery of hematite at pH 4 remained high under equilibrium oleate concentrations above the critical hemi-micelle concentration of oleate. Oleate adsorption on hematite as a function of pH showed maxima at pH 4 and 9, suggesting co-adsorption of molecular and ionic oleate species at pH 4. Hematite flotation with 10 −4 molar oleate addition was high for pH values above 4. [ABSTRACT FROM AUTHOR]

The interactions between fine and coarse hematite particles were investigated, and their effects on the flotation of the hematite using sodium oleate as a collector were studied through micro-flotation tests, supplemented by optical microscopic analysis, extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theoretical analysis, and focused beam reflectance measurement (FBRM) particle/aggregate size analysis. The micro-flotation results show that the recovery of hematite from fine-coarse hematite mixtures did not decrease monotonously with increasing the fine hematite mass ratio. The highest recovery was obtained when the fine and coarse hematite were approximately equal in mass ratio, indicating that the interactions between fine and coarse hematite particles could promote the overall flotation recovery. The results of optical microscopy analysis, EDLVO calculation, and FBRM measurements showed that the interaction energies and aggregation tendencies between fine and coarse hematite particles were stronger than that among the fine hematite particles, and the aggregation would weaken when the coarse and fine fractions were mixed in extreme mass ratios, which explained the observed effects of different mixing ratios of fine and coarse hematite particles on their flotation. [ABSTRACT FROM AUTHOR]

Slime coating is a significant phenomenon in froth flotation. The adverse effects of slime coating, by which a value mineral is covered by slimes and prevented from direct contact with collectors and/or air bubbles, have been recognized for decades. It happens ubiquitously in the flotation of various minerals, including sulfide minerals (sphalerite, galena, chalcopyrite, pentlandite, etc.), oxide minerals (hematite, wolframite, scheelite, etc.), salt minerals (fluorite, potash, etc.), coal and bitumen. In this paper, an attempt was made to present a comprehensive review of slime coatings in froth flotation including particle adhesion mechanisms, slime coating measurement techniques, influencing factors, control methods and mitigation measures. It was shown that the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and the extended DLVO theory, are the mainstream mechanisms underpinning slime coatings. According to their sources, the slimes can originate from gangue minerals and value-gangue composite particles, or from colloidal compounds formed during ore dressing due to grinding, mineral surface oxidation and chemical precipitation. The origin and property of the slimes, the types and concentrations of electrolytes, and solution pH are the main factors influencing slime coatings. Current techniques employed to study slime coatings are mainly focused on the interactions between two particles in a static and ideal environment, which cannot account for slime coatings under commercial froth flotation conditions. Physical mitigation methods such as ultrasonic treatment and high intensity conditioning are often more effective than chemical mitigation methods that usually entail the use of dispersants. Gaps in the existing literature are discussed and potential research directions are suggested. [ABSTRACT FROM AUTHOR]

[Display omitted] • Depressant plays an important role in the reverse flotation separation of iron ores. • Biodegradable reagents can be effectively used as depressants in reverse hematite flotation. • Polysaccharides and polyphenolics are promising green depressants for hematite. • H-bonding is the most common adsorption mechanism between iron and green depressants. Due to environmental issues and the restrictions imposed on mineral flotation separation, the use of biodegradable and environmentally friendly reagents has gained widespread international attention. So far, several investigations have been conducted regarding the eco-friendly flotation separation of iron oxide ores for moving toward sustainable development and cleaner production. Yet, no critical review is specified on the green and eco-friendly depression reagents through their reverse flotation beneficiation. Therefore, this study will comprehensively discuss the previously conducted works in this area and provides suggestions for future assessments and developments. This robust study explored various adsorption aspects of natural-based depressants (polysaccharide-, polyphenolic-, and lignosulfonate-based) on iron oxide minerals (mainly hematite) to create a possible universal trend for each biodegradable depressant derivative. The laboratory and industrial experiments indicated that these depressants (except lignosulfonate-based) could selectively depress hematite at alkaline pHs and enhance its reverse flotation separation from their gangue phases (especially silicates as the main gangue phases). Although these eco-friendly depressants showed promising metallurgical results, several gaps still need to be addressed, notably in surface analyses and their adsorption mechanisms. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of eco-friendly ozone oxidation on the properties and depressive performance of starch was studied. • Ozone-oxidized starch rendered the hematite surface more hydrophilic than native starch. • Ozone treatment triggered starch depolymerization along with a desirable increase in starch solubility and acidity. • An enhanced affinity of starch for hematite was observed after ozone treatment. In this study, ozone as an eco-friendly oxidant was employed to improve the depressive performance of starch in the reverse flotation of fine hematite. Micro-flotation results showed that ozone-oxidized starch (OS) better depressed hematite flotation as compared to the native starch (NS). Particle surface wettability and size distribution analysis suggested that OS rendered the hematite surface more hydrophilic in the presence of an amine collector while maintaining a comparable flocculation performance to that of NS. Solubility, rheology, carbonyl and carboxyl content measurements, together with atomic force microscopy (AFM) imaging were performed to examine the variations in the structure and properties of starch upon ozonation and their correlation with the depressive performance of starch. It was found that ozone treatment not only increased starch acidity and solubility, but also concurrently depolymerized starch with the yield of low molecular weight derivatives. These favorable changes appeared to be responsible for the superior performance of OS. Furthermore, the stronger interaction of OS with hematite was verified by X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

The behaviour of cationic amine collectors used in the reverse cationic flotation of quartz from iron oxide minerals appears to change from one mineral system to the other, deviating from theoretical predictions based on the reagent chemistry. The performance of five amine collectors in the flotation of a South African iron ore and a Brazilian iron ore, each with different textural characteristics was investigated using reverse flotation techniques from Brazil. Furthermore, the overall collection efficacy of the five collectors in iron ore reverse flotation was analysed. Batch flotation tests and a mineralogical characterisation of the ore using QEMSCAN was conducted. Mineral liberation heavily influenced the flotation behaviour of the two ores. A well liberated Brazilian iron ore was amenable to reverse cationic flotation, whereas, the texturally complex South African iron ore did not respond well to reverse cationic flotation. Alkyl ether amines proved to be superior to quaternary amine compounds in the flotation of quartz from hematite. [ABSTRACT FROM AUTHOR]

Over the years there have been a number of instances describing a minimum in the flotation recovery of hematite in the alkaline pH region when oleate is used as the collector. These cases usually coincide with the use of a commercial oleate sample containing other fatty acids and/or salts as the collector. It is the purpose of this paper to provide experimental data involving the effects of pH on the flotation of a natural hematite sample using two collectors containing oleate and compare these data to changes in surface tension and bubble characteristics of aqueous oleate systems also as a function of pH. The main aim of this paper is to highlight and address this difference in hematite flotation behaviour with oleate solution characteristics and develop a better understanding of these interactions. It is proposed that this flotation minimum is associated with a reduction in both contact angle and bubble-particle flotation rate constant under these conditions, even though the surfactant solution chemistries would suggest that flotation should still be strong in this region. [ABSTRACT FROM AUTHOR]

Comminution modeling aims to predict the size and liberation distribution of mineral particles and the required comminution energy. The current state-of-the-art comminution models provide a calculation of neither particle size distribution, grinding energy and throughput dependency with neither a broad understanding of how the mineral grade varies by size nor the liberation distribution of the product. The underlying breakage mechanisms affect the liberation of mineral grains and are dependent on modal mineralogy and mineral texture (micro structure). It has also been a challenge to model comminution systems to predict the optimal energy and size for better mineral liberation because of the variability of the mineral particle properties i.e. grains arrangement and composition. A detailed mineralogical study was carried out in order to broaden the understanding of the nature and distribution of comminuted particles in a ball mill product. Focusing on iron ore samples the study showed how the particle breakage rate decreases when the particles reach the grain size of the main mineral component. Below that size, comminution does not increase mineral liberation and therefore in most of the cases passing over that boundary is only a waste of energy. The study involving iron ores from Malmberget and Kiruna, Northern Sweden, showed that certain shortcuts can be applied to empirically model the mineral liberation distribution of the particles in a ball mill based on the mineral grade-by-size pattern from a geometallurgical program. In Malmberget and Kiruna the mineral grade-by-size pattern is depending on the mineral distribution and grain size of gangue as well as magnetite or hematite minerals. A significant difference between mineral breakage of the same grade and gangue minerals can be observed due to texture differences. [ABSTRACT FROM AUTHOR]

Polysaccharides are some of the most widely employed flotation reagents in the mineral processing industry. Among several, starch is of particular importance for reverse flotation of iron ores. It is known to behave as an efficient depressant for hematite and, therefore, its interaction is of great relevance. In this paper, we investigate the surface chemistry of starch adsorbed onto hematite by means of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Our results indicate that starch undergoes an important oxidation process under industrial gelatinization conditions, which favors the binding of starch molecules. Meanwhile, the oxide surface is subjected to full hydroxylation, leading to strong polysaccharide-metal hydroxide interaction. Previously proposed starch interaction mechanisms are discussed, and the importance of acid-base interactions is underscored. [ABSTRACT FROM AUTHOR]

The use of natural products is essential in the processing of iron oxide ores by flotation. It is the purpose of this review to trace the historic development of the use of some natural products in the processing of iron oxide ores. The reagents used for floating either iron oxides or activated silica are usually derived from vegetable origin, frequently from wood products containing primarily unsaturated carboxylic acids. In the reverse flotation of iron ores, the iron oxides are often depressed using polysaccharides, with various starches being extensively used. Hematite depression is usually conducted at high values of pH, and cationic surfactants are generally used to float off the silica. It is through the previous research and development of natural products that global commercial processing of iron oxide ores by flotation is economically viable, and the only method for treating fine grained iron ores. There are also some reports of the use of bacteria to modify the surfaces of the hematite leading either to its flotation or depression, but this has not been adopted at industrial scale as yet. [ABSTRACT FROM AUTHOR]

The use of microorganisms and/or their metabolic products is becoming an attractive alternative in mineral processing. In that sense, this research deals with the use of the hydrophobic gram positive Rhodococcus erythropolis bacteria as a possible substitute of synthetic reagents used in hematite flotation. Bacterial growth experiments, using culture media of tryptic soy broth (TSB) and yeast and malt extract with glucose (YMG) separately, showed a greater bacterial density for the first one. In addition, it was observed that the isoelectric point (IEP) of hematite was shifted after biomass interaction, suggesting that the bacterial cells were adhered onto the mineral surface. Moreover, bacterial adhesion was higher at acidic pH, which also suggests an electrostatic attraction between the mineral surface and the biomass at this pH range. Microflotation tests were carried out in a modified Hallimond tube achieving a maximum hematite floatability of 83.86% at pH 6. Finally, the kinetics of the process followed a second order model. [ABSTRACT FROM AUTHOR]

The current study presents a novel processing approach for the separation of the iron oxide from Red Mud (RM), based on the gentle reduction by hydrogen in static conditions followed by wet magnetic separation. The conversion degree of hematite, initially contained in RM, to magnetite was investigated in relation to reduction time, temperature, and the H 2 supply. The maximum achieved conversion reached 87% at 480 °C. The phase transformations during the thermal reduction were investigated via X-ray diffractometry, Mössbauer spectroscopy, electron microscopy, and magnetic measurements. After reduction at the optimal conditions, the reduced RM sample was subjected to magnetic separation and a magnetic fraction with over 54 wt% magnetite concentration was obtained. Such magnetic fractions could be used as a feed in the pig iron industry, while the non-magnetic fraction could be further treated in order to recover the rare earths or to be used as a raw material for building materials. [ABSTRACT FROM AUTHOR]

Understanding the complex interplay of physics and chemistry inside a flotation cell is the ultimate goal of most flotation research. Key to the development of a model of flotation is the ability to validate it from measurements of a real flotation system. This work uses positron emission particle tracking (PEPT) to track directly activated mineral particles, hydrophobic and hydrophilic, in a lab-scale flotation cell. In contrast to other particle activation methods the direct activation technique allows mineral particles with their original surface characteristics to be used in PEPT experiments. In this work the flotation separation investigated was the separation of hematite from quartz from a synthetic ore using a combination of an oleic acid collector and sodium silicate depressant. This work represents the first time in which particles of typical flotation size (−106 + 90 μm diameter) with real bulk mineral properties and surface chemistry have been tracked in a flotation cell. The results illustrate small particles flow behaviour in the cell for a hydrophilic particle. The trajectory and velocities of the tracer particle are shown as it is transported inside the flotation cell. [ABSTRACT FROM AUTHOR]

• Quartz particles significantly enhanced the froth stability. • The finer the particle size, the more stable the froth. • Mechanism of quartz obviously improving froth stability was proposed. • Pulp viscosity, contact angle, ToF-SIMS and MD simulation were conducted. • The model of three-phase froth was established. The effect of hematite and quartz with different particle sizes on the three-phase froth stability using dodecylamine (DDA) as a collector was investigated, and the mechanism of how quartz improves froth stability was explored. Microflotation experiment, three-phase froth stability experiment, froth morphology photography, pulp viscosity measurement, contact angle measurement, zeta potential measurement, time-of-flight secondary ion mass spectrometry analysis, and molecular dynamics simulation were conducted in this investigation. Results showed that flotation performance and froth stability were obviously different for minerals with different particle sizes. The froth half-life was remarkably higher in the presence of quartz particles compared with hematite particles, forming stickier froth, especially for quartz particle sizes below −18 μm. Fine quartz was found to be a key factor in improving the froth stability in hematite flotation using DDA as a collector. The high pulp viscosity, damping coefficient, and maximum capillary pressure resulting from quartz with low density, small size, and high concentration hindered liquid drainage and reduced the desorption probability of particles from the bubble surface, thereby preventing the coalescence of two adjacent bubbles. DDA was found to be more readily adsorbed on the quartz surface, leading to a higher adsorption capacity, better hydrophobicity, and increased distribution of counter ions at the interface. This condition reinforced the mutual repulsion force between liquid film surfaces and prevented further thinning of the liquid film, ultimately strengthening froth stability. [ABSTRACT FROM AUTHOR]

The presence of iron in pregnant leach solutions presents significant processing challenges. The removal of iron impurities from leach solutions by means of iron phosphate precipitation may be a feasible alternative to more conventional iron oxide/iron hydroxide precipitation processes. This study compares the performance of the iron phosphate precipitation process with that of the hematite process at different operating temperatures (40 °C–90 °C), pH conditions (pH 1–pH 3) and seeding measures for the removal of iron from a chloride leach solution. The extent of iron removal, co-precipitation of nickel and copper, and solid-liquid separation were used as performance criteria for the comparison. Seeded iron phosphate precipitation at pH 1 and 40 °C resulted in 98.8% iron removal with 0.5% nickel and 2.8% copper losses. 99.8% iron removal was achieved with the iron phosphate precipitation process at pH 1 and 80 °C, but the nickel and copper losses increased to 8.7% and 20.8%, respectively, with the increase in temperature. Seeded hematite precipitation at pH 1 and 80 °C yielded 99.6% iron removal with 3.5% nickel and 1.7% copper losses. For the hematite process, nickel and copper losses decreased with an increase in temperature. Increasing the pH yielded higher nickel and copper losses for both processes. All seeded precipitation experiments produced easily filterable precipitates. Unseeded iron phosphate precipitates produced at 40 °C and pH 1 were filterable, but increased nickel and copper losses were observed. Unseeded hematite precipitation resulted in high nickel and copper losses, with the precipitates practically impossible to filter. Iron phosphate precipitates exhibited more favourable settling characteristics than the precipitate produced with the hematite process. [ABSTRACT FROM AUTHOR]

Iron can be precipitated out of leaching solutions by using high pressure processes. The focus of this study is on the various iron phases forming during the pressure oxidation of sulfates. Artificial solutions were produced from sulfuric acid, copper and iron sulfates in an attempt to recreate the matrix composition and conditions used for copper sulfides autoclaving. The influence of the following factors was investigated: initial free acidity, initial copper concentration and initial iron concentration. There were three solid species formed in the autoclave: hematite, Basic Iron Sulfate (BIS) and hydronium jarosite. Free acid is the main factor influencing the composition of the residue. The increase of BIS content in the residue is not gradual and occurs over a change of a few grams per liter of sulfuric acid. Increasing copper sulfate concentration in the solution hinders the formation of BIS. This effect seems to be related to the buffering action of copper sulfate, decreasing the overall acid concentration and thus extending the stability range of hematite. Increasing iron concentration on the precipitate chemistry seems to promote BIS formation. At high iron level, the most noticeable effect is the inhibition of jarosite. The results were reported within a Cu-Fe-S ternary system and modeled. The modeling confirmed the experimental observations. [ABSTRACT FROM AUTHOR]

An iron ore mineral processing plant in Brazil treating Itabirite ore was assessed by sampling a circuit consisting of Wemco 144 mechanical cells, as part of the AMIRA P9P collaborative research project. This paper presents and discusses the results of entrainability, water recovery and quartz and hematite grades associated to hydrodynamic parameters. The results indicated strong correlation between water recovery and hematite losses which was intensified by the operating conditions of the circuit. A potential alternative to reduce the hematite losses through entrainment and to increase quartz removal was to modify the traditional circuit design to treat rougher and cleaner/recleaner tails in different stages. In addition, the scavenger residence time must be matched to the quartz floatability. Changes to design and operation of these circuits are needed to sustain concentrate recovery and grade as iron ores become finer. [ABSTRACT FROM AUTHOR]