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Liquid-liquid mixings in stirred tanks are commonly found in many industries. In this study, we performed computational fluid dynamics (CFD) modeling and simulation to investigate the liquid-liquid mixing behavior. Furthermore, the population balance model (PBM) was used to characterize the droplet size distribution. The PBM model parameters were calibrated using the experimental data of droplet sizes at different agitation speeds. Additionally, we employed the steady-state Sauter mean droplet size to validate the developed CFD-PBM coupled model at different dispersion phase holdups. Then, the validated CFD-PBM coupled model was employed to evaluate the role of impeller structural parameters on the liquid-liquid mixing efficiency based on a user-defined mixing index. It was found that the position of impellers significantly affects the mixing efficiency, and an increase in stirring speed and the number of impellers improved the mixing efficiency.

The alkaline leaching process of arsenic-containing solid waste discharged during nonferrous metal smelting affords typical high-salinity alkaline arsenic-containing wastewater (HSAW). In this study, for the first time, Me (Ca

Sodium silicate (SS) is often used as a depressant or a dispersant to improve the selectivity of froth flotation. The depressing ability of SS changes with its concentration and the solution pH. However, the depressing mechanism is unclear. In this paper, sum frequency generation spectroscopy was used to investigate the water structure at the mineral-water interface to provide a molecular understanding of SS adsorption and its role in flotation. Our study shows that a significant amount of silicate species adsorbs at the fluorite-water and silica-water interfaces in a wide range of pH, independently of the surface potential. The adsorption layer of silicate species on the fluorite surface can be removed at low pH (acidic condition), but its removal becomes difficult at high pH (basic condition). On the contrary, the adsorption of silicate species at the silica surface is so strong that the adsorbed species cannot be removed at the whole pH range. This finding agrees with flotation results showing that SS can be used as a dispersant for fluorite at pH = 6–8, but it behaves like a depressant at higher pH. Also, SS effectively depresses the silica floatability at the whole range of pH due to its strong interaction with the mineral surface. This work provides the molecular details about the SS adsorption onto the mineral surface which is complementary to the previous macroscopic studies such as FTIR, zeta potential, and XPS measurements.

To cope with the increase of sulfate gangue minerals in fluorite ores, flotation separation of fluorite from calcite and celestite using Al2(SO4)3 and acidified water glass (AWG) as mixture depressants was studied in this paper. The flotation separation performance and underlying mechanism were studied by flotation experiments, zeta potential measurements, microcalorimetric analysis, adsorption measurements, and X-ray photoelectron spectroscopy (XPS). The flotation results show that under optimum conditions, the inhibition effect of AWG on celestite is more remarkable with the assistance of Al2(SO4)3, but has no obvious effect on the flotation of fluorite. Zeta potential measurements show that both positively charged Al species and negatively charged Si species are adsorbed on the surface of the minerals. Microcalorimetric analysis confirms that the interaction between Al2(SO4)3 and celestite is more intense than that of calcite and fluorite, while AWG is more likely to be adsorbed on the calcite surface. Adsorption measurements reVeal that there is competitive adsorption between the depressant and collector and that the adsorption of the depressant AWG prevents the collector NaOL from adsorbing on the surface of the minerals. The XPS results show that Al species and Si species are chemically adsorbed on the surface of the minerals and change the chemical surroundings of the elements on the mineral surface. Moreover, compared with fluorite, Al species can more clearly enhance the adsorption of Si species on the celestite surface.

In the flotation of copper sulfides, pyrite is often activated by Cu2+ ions dissolved from copper-bearing minerals in alkaline media (pH ˃ 9), which results in pyrite entering the copper concentrate. To reduce the floatability of pyrite, we designed a novel functionally modified biopolymer, tricarboxylate sodium starch (TCSS), that showed superior depression selectivity towards pyrite in low pH solutions when employed in Cu–Fe flotation separation in the presence of sodium butyl xanthate (SBX) as a collector. TCSS depressed the floatability of pyrite more strongly than that of chalcopyrite in single mineral flotation in the pH range 4–6. The most selective separation was achieved at pH ∼ 6; the recovery of Cu in the concentrate was over 77%, and the grade was improved to 24.50% compared to the initial feed grade of 12.50%. Surface characterization analyses, including zeta potential, X-ray photoelectron spectroscopy (XPS) analysis, and Fourier transform infrared (FTIR) spectroscopy, confirmed the different degrees of interaction of TCSS with the two minerals. TCSS was adsorbed on the pyrite surface, possibly via a chemisorption mechanism, as reflected in the FTIR and XPS analyses. The adsorption of TCSS passivated the pyrite surface, which inhibited the adsorption and oxidation of the collector. On the other hand, the adsorption and oxidation of the collector on chalcopyrite surface were effective even in the presence of TCSS, attesting to the weak interactions between chalcopyrite and TCSS.

In current COD measurement method, we found that sodium chlorate (NaClO3) can effectively reduce the chemical oxygen demand (COD) of minerals processing wastewater (MPW). However, the reduction in COD via the present COD method was only achieved through the interference of NaClO3 with COD measurement. A series of laboratory-scale experiments demonstrated that the COD reduction is independent of NaClO3 reaction time, reaction pH and reaction temperature, but only related to NaClO3 dosage, and a higher NaClO3 dosage leads to a lower COD. Results further showed that the addition of NaClO3 didn’t affect the initial concentration of the total organic carbon, chloride ions and the benzohydroxamic acid (BHA); their concentration remained unchanged after the addition of NaClO3. Moreover, the residual concentration of NaClO3 also remained same as the initial value. However, COD in both MPW and BHA solution decreased. Furthermore, when added reducing agent to consume the residual NaClO3 before COD measurement, and then the COD was determined to return to its initial value. All these observations clearly shown that NaClO3 doesn’t react with the reducing substances in wastewater under the experimental conditions; it only reacts with reducing substances under the COD measurement conditions. From all these evidences, we concluded that NaClO3 can interfere with the determination of COD. In fact, the interference of NaClO3 is not specified in the standard method, which is a defect of the present COD measurement method. Residual NaClO3 remains in wastewater may cause secondary pollution to the environment. This study, therefore, suggest the government revise and improve the COD measurement method in order to avoid the interference of NaClO3 and prevent the industrial use of NaClO3 for COD reduction of wastewater.

Lead complexes of benzohydroxamic acid (Pb-BHA complexes) have been successfully applied to the industrial separation of scheelite from calcite and fluorite minerals. However, the separation of scheelite from calcite using Pb-BHA complexes in the absence of fluorite is difficult. In flotation tests, both sodium fluoride and fluorite particles have been shown to depress calcite but not scheelite. Therefore, fluoride ions from the dissolved fluorite particles play an important role in the flotation separation of scheelite from calcite. In the current study, the results of zeta potential analysis confirmed that fluoride ions are strongly adsorbed on calcite surfaces and that the point of zero charge for calcite shifts to that of fluorite. X-ray photoelectron spectroscopy and atomic force microscopy analyses clearly indicated that the fluoride ions are adsorbed on the calcite surface to form a fluorite film. Thus, this type of surface transformation shows promise as a strategy for the flotation separation of semi-soluble minerals.

Molybdenum ore flotation techniques are constantly challenged by the emergence of complex sulfide minerals, such as bismuthinite, in the mineral processing industry. Conventional flotation depressants, such as sodium sulfide, used in Mo–Bi-containing ore flotation require high dosages, which leads to high cost and low selectivity. Therefore, in this study, pyrogallic acid (PA), a widely distributed organic source, is tested as an alternative depressant to selectively depress bismuthinite in Mo–Bi sulfide ores from Shizhuyuan. Results show that PA has a minimal effect on molybdenite recovery; by contrast, PA has a high depressing effect on bismuthinite amelioration. At 500 g/t PA, molybdenum recovery slightly decreases by 2 percentage points, and bismuth content in molybdenum concentrate sharply declines by 34 percentage points, with respect to samples floated without PA. Batch flotation tests demonstrate that PA addition affects froth stability, as indicated by the variations of solid and water recoveries. The superior selectivity of molybdenite over bismuthinite is promoted by increasing the PA dosage. On the basis of these findings, PA is a feasible option and thus can be used as a depressant for bismuthinite in the flotation of sulfide minerals.

Lead(II)-benzohydroxamic acid (lead-BHA) is a metal-organic complex system used as a highly selective collector in the flotation separation of oxide minerals. In the current study, the surface microstructures and adsorption mechanism of lead-BHA on mineral surfaces were comprehensively investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Raman spectroscopy, atomic force microscopy (AFM) and first-principles calculations. The characteristic Raman peak indicated that lead-BHA adsorbs on mica surfaces. The AFM topography of a mica surface (0 0 1) treated with lead-BHA at a ratio of 1:1 showed many local adsorption layers, but no obvious adsorption layer was observed for the same surface treated with lead-BHA at a ratio of 1:2, which suggests that Pb(BHA)+ might be the effective species for mineral flotation. First-principles density functional theory (DFT) calculations indicated that the lowest unoccupied molecular orbital (LUMO) of Pb(BHA)+ was mainly localized on the lead atom, while the LUMO of Pb(BHA)2 was distributed over the whole molecule, implying that Pb(BHA)+ exhibits better affinity to the mica surface than Pb(BHA)2, and further suggesting that Pb(BHA)+ might be an effective specie. The further first-principle calculation, from the molecular level on mica surface, showed that the Pb(BHA)+ could produce a higher adsorption energy than Pb(BHA)2, revealing that the Pb(BHA)+ should be an effective specie that can efficiently adsorb onto the mica surface. This work may shed new light on the effective species of metal-organic complex collectors on oxide mineral surfaces in flotation separation.

The flotation separation of apatite from calcite is gordian due to the similar surface properties and calcium active sites, which make a poor selectivity in traditional fatty acid system. Pb-BHA coordination collector present great selectivity, and surface transformation by fluoride ions plays an important role in the flotation separation of salt minerals. The application of surface transformation combining with lead nitrate-benzohydroxamic acid (Pb-BHA) coordination collector can achieve the flotation separation of different calcium minerals. This study suggest that the floatability of apatite and calcite is similar without any depressants, and fluoride ions has a strong inhibiting effect on calcite but not on apatite under the Pb-BHA collector system. Zeta potential measurement determine that the surface charge of calcite obviously shift to a negative value with the adsorption of fluoride ions. X-ray photoelectron spectroscopy measurement indicates that fluoride ions is easier to adsorb on surface of calcite than that of apatite, and generate CaF2 films. Atomic force microscopy measurement illustrates the surface morphology of calcite becomes more uneven and the roughness increases obviously after the treatment of F−. Therefore, the surface transformation is meaningful to study and provides a new method for the flotation separation of calcium minerals.

Previous studies on oleic acid systems have shown that calcium dioleate formed during the flotation process plays an important role. Calcium dioleate has been extensively studied as an important intermediate product in sodium oleate flotation of calcium-containing minerals sodium oleate, but its use as a collector to separate calcium-containing minerals remains unverified. The effect of calcium dioleate on fluorite, calcite and scheelite flotation and the adsorption mechanism on the mineral surface were examined using solution chemical analysis, flotation test, adsorption measurement, atomic force microscopy (AFM) and transmission electron microscopy (TEM) in this study. Solution chemical calculations prove that stable calcium dioleate colloid will be the dominant species at certain pH, calcium ion and oleate concentrations. Flotation experiments showed that the calcium dioleate plays an important role in the flotation process using sodium oleate. Calcium dioleate has better flotation effect for fluorite and scheelite but weaker effect for calcite than sodium oleate. Adsorption measurement showed that calcium dioleate is more easily adsorbed on the surface of scheelite and fluorite. AFM and TEM measurements exhibited that the formation of micelle adsorption on the surface of scheelite and fluorite caused by calcium dioleate clearly affects the surface roughness. Calcium dioleate colloids can likely enhance the surface roughness of scheelite and fluorite via selectively adsorption to improve the flotation of scheelite and fluorite.

Metal ions are widely used as activators in the flotation of oxidised minerals. At the same dosage of collector, the recovery of target minerals (cassiterite, scheelite, wolframite and ilmenite) can be evidently improved with the addition of metal ion activator. Adsorption of metal ions and their hydroxides can provide attractive sites for collector attachment, contrary to bare minerals that exhibit considerably low affinity towards the collector. Iron complexes of benzohydroxamic acid (BHA) are formed during the reaction of ferric chloride with BHA in the solution. These complexes also exhibit strong collecting ability towards cassiterite in the flotation, which contradicted the classical theory that the activator must be added before the collector. However, the major active component and the underlying adsorption mechanism of the Fe-BHA complexes are still unknown. In this study, the solution chemistry calculation has been used to identify the major active components of the Fe-BHA complexes. Accordingly, a preferred adsorption model of the Fe-BHA complexes onto the cassiterite surface has been proposed and proven effective, through first-principles calculations based on density functional theory, flotation experiments and adsorption tests. Our results might shed new light on the activation mechanism of metal ions in mineral flotation.

Using microflotation experiments, this study investigated the effect of Pb2+ ions on flotation performance of cassiterite (SnO2) by using benzohydroxamic acid (BHA) as collector. Flotation results showed that floatability of cassiterite significantly improved after addition of Pb2+ ion to the process. Adsorption behaviour and mechanism of BHA on the inactivated and Pb-activated cassiterite surface were further explored by adsorption experiments, zeta potential measurements, X-ray photoelectron spectroscopy analysis and first-principle density functional theory calculations. Experimental and computational results consistently suggested that the adsorbed Pb atoms can coordinate with two O atoms of the two hydroxyl groups on the cassiterite surface. BHA molecules can form two coordination bonds with one Pb ion adsorbed on the cassiterite surface, resulting in a five-membered chelating ring. The proposed adsorption mechanism can be extended to the vast majority of interface assembly systems.

In previous studies, by regulating the Pb/BHA ratio and pH, lead complexes of benzohydroxamic acid (Pb-BHA) have been proven to be selective for the separation of scheelite from calcium minerals. In this study, sodium silicate (Na2SiO3) and Al-Na2SiO3 polymer were used as depressants for the further separation of scheelite from calcite. Flotation results indicated that both scheelite and calcite were depressed by Na2SiO3, while Al-Na2SiO3 polymer gave good selectivity. The depressing ability of Na2SiO3 for calcite was significantly improved due to the formation of some Al-Na2SiO3 species with aluminum ions, while the reverse was true for scheelite. Zeta potential results indicated that both colloidal Na2SiO3 and Al-Na2SiO3 particles were negatively charged and difficult to adsorb on the negative scheelite surface through electrostatic attraction, especially for Al-Na2SiO3. X-ray photoelectron spectroscopy analysis results showed that the Al-Na2SiO3 adsorbed amount on the scheelite surface was less than the Na2SiO3 adsorbed amount, while the reverse was true on the calcite surface. Binding energy analysis results indicated that calcium cations of scheelite and calcite surfaces could bond to oxygen atoms of Na2SiO3/Al-Na2SiO3 through chemisorption. However, compared with Na2SiO3, Al-Na2SiO3 showed weaker chemisorption on the scheelite surface, but adsorbed more powerfully onto the calcite surface. Therefore, Al-Na2SiO3 showed excellent selectivity for scheelite and calcite, which has been successfully applied at the Shizhuyuan mine.

To improve the floatability of tungsten minerals, lead ions (lead nitrate) were used to modify the surface properties of the minerals and benzohydroxamic acid (BHA) was used as a collector in the flotation system. Pb 2+ -BHA complexes are inevitably present in this process and the role of it is unclear. This investigation is going to describe a new approach and the mechanism of catalyzing BHA adsorption onto scheelite by lead ions. Chemical speciation, zeta potential, FTIR, and XPS studies were conducted to establish the important role of lead ions. Indeed, Pb 2+ -BHA complexes were shown to be the active species responsible for flotation. The speciation and zeta potential results showed the presence of the adsorbed Pb 2+ -BHA complexes on the scheelite. The XPS results for atomic composition and binding energies confirmed Pb 2+ -BHA species adsorbed on the scheelite surface, which contributed to more adsorption of BHA. The new method would increase the recovery of scheelite, simplify the flowsheet and reduce the processing cost.

Pb2+ ions are commonly used as the activator in the flotation of cassiterite. However, lead pollution of surface water has attracted more concern and attention. In this study, the effect of Fe3+ ions as an activator on the flotation performance of cassiterite using benzohydroxamic acid (BHA) as the collector was investigated by the micro-flotation tests. The results of the flotation experiments showed that the addition of Fe3+ ions significantly increased the recovery of cassiterite in the presence of BHA collector. In the BHA flotation of cassiterite, there was a direct relationship between the recovery of cassiterite and the adsorption amount of BHA on the cassiterite surface. The adsorption mechanism of BHA on un-activated and Fe-activated cassiterite surfaces was studied by the adsorption experiments, zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) analysis. The results of the adsorption and zeta potential experiments indicated that the adsorption amount of BHA on the cassiterite surface increased significantly in the presence of Fe3+ ions. The XPS analysis also revealed that terminal hydroxyl group oxygen atoms of the cassiterite surface were the dominant reactive sites for Fe3+ ion adsorption. Furthermore, BHA anions can react with Fe atoms adsorbed on the cassiterite surface to form Fe-BHA complexes, thus improving the hydrophobicity of the cassiterite surface.

Goethite (α-FeOOH) and calcium sulfate (CaSO4·2H2O) are the main solid constituents of the iron oxide residues in zinc hydrometallurgy by the goethite process. Impounding these residues in tailings ponds is costly to maintain and causes a great threat to the local environment. In this study, magnetic separation was applied to separating goethite from calcium sulfate with maghemite (γ-Fe2O3) fine particles as the carrier, which were prepared by roasting −1 μm pure magnetite mineral particles. The SEM images and XRD patterns indicated the precipitation of goethite on maghemite fine particles in the goethite process, which made the goethite aggregates magnetic, while the calcium sulfate formed nonmagnetic bulk precipitates. The magnetic goethite–maghemite aggregates were then separated effectively from calcium sulfate precipitates using a magnetic drum separator. The recovery of Fe and Ca to their corresponding products was 93.2% and 91.9%, respectively. The removal of S and As from goethite precipitates was...

The adsorption behaviors and the activation mechanism of calcium ions (Ca 2+ ) on sericite surface have been investigated by Zeta potential measurements, Fourier transform infrared spectroscopy (FT-IR), Micro–flotation tests and First principle calculations. Zeta potential tests results show that the sericite surface potential increases due to the adsorption of calcium ions on the surface. Micro-flotation tests demonstrate that sericite recovery remarkably rise by 10% due to the calcium ions activation on sericite surface. However, the characteristic adsorption bands of calcium oleate do not appear in the FT-IR spectrum, suggesting that oleate ions just physically adsorb on the sericite surface. The first principle calculations based on the density functional theory (DFT) further reveals the microscopic adsorption mechanism of calcium ions on the sericite surface before and after hydration.

In this study, the effects of reagent addition order on the flotation behavior of calcite and fluorite, as well as the influence of acid on the floatation behavior of the calcite, were investigated. Results showed that when the calcite surface had adsorbed the collector, the depression of calcite became increasingly difficult. The presence of acid significantly enhanced the selective depressing effect of depressants on calcite. Actual ore flotation and artificial mixed ore flotation experiments demonstrated that the addition of acid can significantly reduce the calcite content in the concentrate. This phenomenon can be explained by the exposure of the new calcite surface due to the surface dissolution, which facilitated the reaction of calcite with the depressor.

The separation of scheelite from other calcium-containing minerals via flotation is problematic because of their similar surface properties and response to conventional anionic collectors. Herein, we report, to the best of our knowledge, a new type of metal–organic complex collector prepared via self-assembly of benzohydroxamic acid (BHA) ligands and Pb(II). A new Pb(II) complex [Pb6L8(NO3)3]NO3 (HL = BHA) is synthesized using coordination reactions and structurally characterized using single-crystal X-ray diffraction. Further, its flotation behavior and adsorption mechanism at the solid–liquid–gas interface were investigated via flotation experiments, zeta potential, XPS, TOF–SIMS, AFM, SFG-VS, adsorption capacity, froth-stability testing, etc. The results show that the developed complex exhibited good collecting ability and absolute specificity for scheelite. The complex was chemically adsorbed on the scheelite surface by combining the lead functional group and oxygen atoms of scheelite to form multilayer adsorbents, rendering the scheelite particle surface strongly hydrophobic. The complex collector and frother assembly are co-adsorbed at the gas–liquid interface, which significantly reduced the solution surface tension, forming a stable foam layer. Therefore, selective flotation was achieved through the targeted adsorption at interfaces. A simplified flotation process for scheelite using complex collector has been successfully applied in industry, significantly improving the recovery of scheelite. This high selectivity makes metal–organic complex a novel and promising collector for high-efficiency mineral flotation and contributes to the efficient and clean development of mineral resources.

Sulfate minerals have gradually become the main gangue minerals of fluorite deposits, and the flotation separation of fluorite and sulfate minerals is difficult with commonly used depressants. In this paper, the high selectivity of a novel depressant sodium polynaphthalene formaldehyde sulfonate (SPS) for the flotation separation of fluorite and celestite both in single mineral and artificial mixed ore experiments was studied, and the underlying separation mechanism was investigated by zeta potential measurement, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) analysis, and Atomic force microscopy (AFM) imaging analysis. Flotation results showed that, in the presence of sodium oleate (NaOL) and SPS, the flotation recovery difference between fluorite and celestite reached 76.26% and the grade of fluorite concentrates increased by 32.11% at pH 6.0. The analysis results showed that the adsorption of SPS on the fluorite surface was limited at pH 6.0, and the adsorption was most likely be through electrostatic interaction. For celestite, the adsorption of SPS on the surface significantly changed the chemical surrounding of celestite surface inhibiting the chemical adsorption of NaOL, and the chemical adsorption of SPS was more significant at pH 6.0.

In this paper, sodium thiocyanate (NaSCN) has been used for the first time as an activator of heteromorphite. In the flotation of heteromorphite, 93% recovery was obtained at the concentration of collector ODA 0.4 × 10–4 mol/L in the presence of NaSCN, while the concentration of collector should be 2.5 × 10–4 mol/L and 0.6 × 10–4 mol/L for the non-activator or Na2S treatment, respectively. The Micro-flotation results showed that heteromorphite can be effectively activated by NaSCN. Nay, the activation effect was better than sodium sulfide, and was slightly affected by activation time. FTIR analysis, Zeta-potential measurements and XPS analysis were conducted to determine the activation mechanism of sodium thiocyanate on heteromorphite. The result of FTIR analysis showed that after NaSCN treatment, the collector ODA can be chemisorbed on the heteromorphite surface via forming zinc-ammonium complex, and physically adsorbed simultaneously by electrostatic attraction. Note that the physisorption effect is more significant. Zeta-potential measurements and XPS analysis showed that the ambidentate ligand SCN− can chemisorbed on the heteromorphite surface via forming zinc-thiocyanate complex anions by S or N elements. What's more, the value of zeta potential of minerals was more negative, which enhanced the physisorption of collector on the mineral surface. Ultimately, the surface hydrophobicity of the heteromorphite was enhanced, and better flotation recovery effect was obtained. The results of this paper can provide a new idea for the activation of minerals.

The flotation separation of scheelite and barite is difficult because they have the same active sites. The surface transformation of semi-soluble minerals is inevitable in the flotation of salt minerals, but an effective flotation separation can be achieved through the dissolution and surface transformation of fluorite. In the current flotation test, fluorite particles and sodium fluoride are efficient depressants for barite but not for scheelite. These results suggest that fluorite ions released from fluorite are crucial to the separation of barite and scheelite. Zeta potential measurement indicates that fluorite ions can obviously shift the surface charge of barite, but it cannot influence that of scheelite. X-ray photoelectron spectroscopy confirms that fluoride ions are strongly chemisorbed on the barite surface and generate BaF2. Atomic force microscopy measurement directly illustrates the change in the barite surface morphology and the formed BaF2 film. Thus, surface transformation is clearly important for flotation and provides a new strategy for the separation of salt minerals.

Previous studies have shown that Pb-BHA complexes (lead complexes of benzohydroxamic acid) have better collecting ability and can be used in flotation experiments with BHA acting as a collector and lead ions acting as activators. However, the structures of Pb-BHA complexes adsorbed on a mineral surface remain unclear. In this work, the adsorption behavior of Pb-BHA complexes on the scheelite surface was studied by flotation experiments and adsorption capacity measurements, and the structures of the adsorbed Pb-BHA complexes were determined using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The adsorption capacity results showed that more BHA was adsorbed on the scheelite surface in Pb-BHA flotation, and the XPS and TOF-SIMS analysis showed that the species of Pb-BHA complexes adsorbed on the scheelite surface were similar in activation flotation and Pb-BHA flotation. Therefore, the different contents of the complexes on the scheelite surface were responsible for the flotation behavior. XPS and TOF-SIMS showed that BHA combined with lead ions to form complexes with different structures, such as five- and four-membered ring structures. Structure fragment inference based on the measurements indicated that lead ions formed monomer complexes with two BHAs, and that lead hydroxide polymers with a certain degree of polymerization bonded with oxygen atoms in the complexes. The Pb-BHA complexes combine with oxygen atoms on the scheelite surface to form an adsorbate, rendering the surface hydrophobic.

Tin and its compounds have a variety of applications. It is recovered as cassiterite from ore deposit by flotation. Traditionally, the use of fatty acids and their derivatives with limited selectivity of cassiterite over calcite (the main gangue mineral) has been replaced by benzohydroxamic acid (BHA). BHA shows poor collecting ability to cassiterite, even when lead nitrate (LN) is added as the activator. In this work, the flotation results show that cassiterite can be separated efficiently from cassiterite-calcite binary mixed minerals using a mixture of LN/BHA as collector and carboxymethyl cellulose (CMC) as depressant. The separation performance of the mixture of LN/BHA is much better compared with adding LN and BHA in sequence at the same dosage. Zeta potential measurements indicate that the mixture of LN/BHA exhibits much stronger ability to adsorb on cassiterite compared with adding LN and BHA in sequence even in the presence of CMC.

Lead complexes of benzohydroxamic acid (Pb–BHA) are metal-organic complex collectors having excellent selectivity. However, the flotation efficiency of Pb–BHA needs improvement. In this research, we report the introduction of an electron-donating group into the BHA ligand to improve the performance of Pb–BHA in mineral flotation; p-methyl-benzohydroxamic acid (MBHA) was synthesized and used as a new ligand to form the Pb–MBHA complex. The flotation behavior of Pb–MBHA in scheelite flotation was investigated using micro-flotation experiments. The adsorption mechanism of collectors at the solid–liquid interface was investigated via solution chemistry analysis, Fourier-transform infrared spectroscopy (FTIR), zeta potential, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Froth stability tests were used to study the adsorption behavior of the collectors at the gas–liquid interface. Pb–MBHA had stronger collecting ability and pH adaptability than Pb–BHA. The Pb(MBHA)+, Pb(MBHA)2, and Pb(OH)MBHA were the main species of Pb–MBHA in solution. For oxygen atoms on the scheelite surface, Pb–MBHA has stronger chemical adsorption ability than Pb–BHA, and its adsorption made the scheelite surface more hydrophobic. The foaming ability and foam stability of Pb–MBHA were stronger than those of Pb–BHA in solution, and stable foam was more likely to form at the gas–liquid interface.

Pb–benzohydroxamic acid (BHA) (lead complexes of benzohydroxamic acid) exhibits high selectivity but low collecting efficiency in scheelite flotation. Herein, we report the manner in which BHA and sodium dodecyl sulfate (SDS) were employed as ligands to coordinate with the lead ions to obtain a colloidal lead-group multiple ligand complex, i.e., the Pb–BHA–SDS, for improving the collecting efficiency of Pb–BHA. The flotation mechanism of Pb–BHA–SDS with respect to scheelite was investigated from the viewpoint of interface science based on the pure mineral flotation, zeta potential, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and contact angle measurements. The results showed that the BHA and SDS coordinated with Pb2+ to form novel lead-group multiple ligand complexes, this is different from the traditional understanding associated with the mixed collectors. Pb–BHA–SDS was a better collector with stronger collecting ability and excellent selectivity in case of a scheelite flotation than Pb–BHA. The addition of SDS to Pb–BHA enhanced the latter’s adsorption ability on the scheelite surface and improved the hydrophobicity of the collector’s nonpolar groups, rendering Pb–BHA–SDS as a more efficient collector at a low dosage.

Strategic Ca-bearing minerals such as scheelite and fluorite are usually separated by flotation; however, their separation is quite difficult due to the similarity of the Ca active sites on their surfaces. Lead nitrate-benzohydroxamic acid (Pb-BHA) mixtures show better selectivity for scheelite than the conventional strong collector sodium oleate (NaOL), but their high cost hinders their wide application. Therefore, in this work, a novel collector system (Pb-BHA-NaOL) was developed to overcome the above-mentioned drawback. Flotation results using a single mineral and real ore showed that Pb-BHA-NaOL had better selectivity for scheelite than Pb-BHA. When Pb, BHA, and NaOL were sequentially assembled in a 240:120:1 molar ratio at pH 9.0, the selective separation of scheelite from fluorite was successfully achieved without adding depressants. Additionally, the same scheelite recovery could be achieved while using 20% less Pb and BHA by employing the Pb-BHA-NaOL system rather than the Pb-BHA system. Through zeta potential measurements, solution chemistry calculations, and X-ray photoelectron spectroscopy, the major role of the selective chemical adsorption of Pb-BHA+, Pb-BHA-OL, and Pb(OH)-BHA-OL− on the surface of scheelite in the separation of scheelite from fluorite was revealed, along with the role of NaOL as an accelerator to improve the adsorption modes and capacities of Pb and BHA on scheelite.

Ferritungstite ores have great commercial value because of the huge reserve and high content of W, Mo and Fe. But their economic recovery has long been a challenge due to its complex mineralogy and heterogeneous. The current study investigated how reductive roasting of ferritungstite ores with mixed sodium salts affected the phase evolution of W, Mo and Fe through Micro-area XRD and Powder XRD, with the goal of comprehensive transformation of ferritungstite. Reductive roasting with mixed sodium salts at 800 °C transformed ferritungstite to Na 2 WO 4 and magnetite (Fe 3 O 4 ), which were easily recovered by water leaching and magnetic separation. Furthermore, a lot of pores and gaps rather than sintering or agglomeration was observed in the ore particles after roasting by SEM-EDS, which was beneficial for the water leaching of W and Mo. As a result, 96.40% of W and 96.64% of Mo were extracted after water leaching, while an iron concentrate with an Fe content of 55.65% and recovery of 83.30% was obtained after magnetic separation. These results suggested such process would be applicable to the comprehensive recovery of valuable metals from ferritungstite ores, as well as similar tungsten ores and scraps.

Benzohydroxamic acid (BHA) is a universal collector for the flotation of oxidized minerals because of its excellent selectivity. However, improving collecting efficiency of BHA still remains a challenge in mineral processing. We report herein the substituted aryl-hydroxamic acids acted as collectors for scheelite flotation to compare the collecting effect with BHA. The collecting performance of BHA, p-methyl-benzohydroxamic acid (MBHA) and p-bromine-benzohydroxamic acid (BBHA) was investigated by flotation tests. Next, the adsorption behaviors of MBHA and BBHA on scheelite surface was studied via zeta potential and X-ray photoelectron spectroscopy (XPS) measurements. In addition, the electronic effect of substituents in MBHA and BBHA molecules were studied by Density Functional Theory (DFT) calculation. On the basis of these studies, bonding groups of MBHA molecule are better electron donors than BHA and BBHA, which are responsible for the superior adsorption effect and collecting performance towards scheelite than BHA and BBHA.

Laurionite is the main highly hazardous lead bearing waste in iron ore sintering dust due to its poor stability and high content, while its flotability and flotation separation have not been adequately investigated. In this study, the flotation behavior of laurionite and its interaction with Na2S were investigated in detail to find an economic and promising way for the separation of lead from sintering dust. The flotability and sulfidization flotation of laurionite were examined by micro-flotation experiments, zeta potential measurement, Fourier transform infrared spectroscopy (FT-IR) analysis and X-ray photoelectron spectroscopy (XPS) studies and solution chemistry calculation. The micro-flotation experiments results indicated that Na2S would improve the flotability of laurionite within a moderate dosage, otherwise decrease its float. The negativity of zeta potential observably increased when adding an appreciate amount of Na2S prior to NaBX, indicating a better adsorption of BX− on mineral surface, which would increase the flotation recovery. To figure out the mechanism behind that, the laurionite surface was analyzed by XPS, which found the formation of PbS films after adding Na2S. The FT-IR analysis showed the BX− absorbance on laurionite significantly decreased after treating with high concentration of Na2S. Moreover, the solution chemistry calculations demonstrated that the proper dosage of Na2S could enhance the flotation of laurionite by reduce free lead ion in solution and covered some part of lead mineral surface, which sharply reduced the demand of collectors in flotation. However, the excess S2− would inhibited the adsorption of BX− on laurionite surface since the formation Pb(BX)2 was weaker than PbS. These results did not only expose that the addition of appropriate amount of Na2S could enhance laurionite’s sulfidization flotation, but also provide an effective way to separate laurionite from iron ore sintering dust.

It is difficult to separate scheelite especially from fluorite with fatty acid collectors because the adsorption mechanism of these collectors occurs through chemisorption of the oleate ion onto the mineral surface. A simplified flotation process using Pb-BHA complexes was developed to replace the energy-inefficient Petrov’s process of using a fatty acid, increasing the recovery of scheelite and reducing the cost. The relationship between surface chemical properties (crystal chemistry, solubility, and Zeta potential) of minerals and flotation by using a fatty acid or Pb-BHA complexes was studied in detail to provide new insights into the selective separation mechanism. The results indicate that the scheelite surface exposes more O atoms than Ca and that they are negatively charged due to the anisometric dissolution of Ca and WO4, which provides the possibility for separation using selective interfacial reaction. The Fourier Transform infrared spectroscopy (FTIR) and Zeta potential results indicate that both chemical and electrostatic adsorption play an important role in the adsorption of Pb-BHA complexes on the scheelite surface. The X-ray photoelectron spectroscopy (XPS) results of the atomic composition and binding energies confirmed the presence of the adsorbed Pb-BHA complexes and that Pb, O and Ca may be the active adsorption sites. Therefore, scheelite was able to be collected by forming either a Ca-O-Pb-collector or W-O-Pb-collector (BHA). However, fluorite was only able to be collected by a fatty acid collector and colloidal [H2SiO3]n−, and a high temperature was needed improve the selective desorption of the adsorbed fatty acid collector by forming Ca-[H2SiO3]n− on the fluorite surface, resulting in serious problems in industry. However, the Pb-BHA complexes significantly contribute to improving the recovery of scheelite minerals, simplifying the flotation process, and circulation of the residual reagents and water.