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Highlights • The three polycarboxylic acids effectively inhibit calcite flotation. • The inhibition abilities decrease in the order of PASP > HPMA > PESA. • The depressant prevents the adsorption of sodium oleate on calcite surface. • PASP exhibits best selectivity in the flotation separation of fluorite from calcite. Abstract As a common gangue mineral, the inhibition of calcite is very important to enrich the valuable minerals by flotation. With the increasing complexity of mineral properties and higher requirements for environmental protection, developing a newly eco-friendly depressant for calcite flotation is necessary. In this study, the effects of polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), and hydrolytic polymaleic anhydride (HPMA) on the flotation performance of calcite using sodium oleate as the collector were investigated through flotation experiments. The results showed that all the three depressants exhibited strong inhibition to calcite, and the inhibition capabilities decreased in the order of PASP > HPMA > PESA. The results of zeta potential measurement, contact angle measurement and X-ray photoelectron spectroscopy indicated that the adsorption of sodium oleate on calcite surface was greatly decreased as the addition of the depressant. To investigate the inhibition selectivity, three depressants were used in fluorite flotation, and the results suggested that sodium oleate could still adsorb on fluorite surface in the presence of PASP. The flotation separation of fluorite from calcite could be therefore realized with PASP on the basis of the best selectivity among the three depressants. [ABSTRACT FROM AUTHOR]

The flotation and adsorption of sodium oleate (NaOL) on spodumene with four different particle size fractions (45–75 μm, 38–45 μm, 19–38 μm and 0–19 μm) were investigated. The flotation recovery increases upon slightly decreasing the size fraction, reaching a peak value at a size fraction of 38–45 μm. The recovery then decreases gradually upon further decreasing the particle size over the entire investigated range of solution pH values. The specific chemisorption sites for the anionic NaOL collector are the Al sites on the surface of negatively charged spodumene, which is confirmed by FTIR and zeta potential measurements. Anisotropic surface energies and broken bond densities are calculated based on density function theory (DFT) to characterize the surface chemistry of spodumene crystal planes. The anisotropic adsorption behavior of NaOL on different crystal planes of spodumene is studied in terms of adsorption conformations and interaction energies by molecular dynamics (MD) simulations. It is demonstrated that NaOL prefers to bind in a monodentate chelating complex configuration to the most stable surface plane, the (1 1 0) plane, which has two broken Al O bonds. The (1 1 0) plane of spodumene is more favorable for chemisorbing NaOL than the (0 0 1) plane, which has one broken Al O bond. The flotation behavior of spodumene with different particle sizes is well explained by the surface crystal chemistry. Based on the findings of this work, further improvement in spodumene flotation is possible if a selective comminution or grinding process is used that favors the production of (1 1 0) planes. [ABSTRACT FROM AUTHOR]

The synergistic effect of the mixed cationic dodecyl amine-hydrochloride (DDA) and anionic collector sodium oleate (NaOL) at the air/water interface was investigated by the surface tension measurements. Various physicochemical properties such as surface activity parameters (CMC, γ CMC , Γ max , A min ), the micellar and interfacial compositions ( X 1 m , X 1 σ ) and interaction parameters (β m , β σ ) were evaluated according to the theory of regular solutions. It is observed that the mixed DDA/NaOL at α DDA = 0.5 exhibit a maximum synergistic interactions at the air/water interface. The flotation and adsorption of DDA/NaOL at the solid–liquid interface was investigated by flotation tests with muscovite, contact angle measurements and adsorption measurements. The flotation results indicate that the recovery of muscovite could be achieved a maximum value (98.45%) by the mixed DDA/NaOL at α DDA = 0.25 at pH 7.0. Contact angle measurements further confirm that the DDA/NaOL exhibit more superior hydrophobicity and collecting property than the individual DDA and NaOL. And a more pronounced synergistic effect of DDA/NaOL on muscovite surface at α DDA = 0.25 is observed, which could be attributed to a favourable arrangement of adsorbing species. The adsorption results show that the individual cationic DDA can be adsorbed strongly onto the muscovite, but no significant adsorption of anionic NaOL can be detected. However, in the mixed systems, the adsorption amounts of both DDA and NaOL are enhanced due to co-adsorption. It is proved that there is also a remarkable synergistic effect of mixed DDA/NaOL collectors at the solid–liquid interface. [ABSTRACT FROM AUTHOR]

The performance of the mixed dodecylamine chloride (DDA)/octanol (OCT) surfactants on muscovite flotation was investigated using flotation tests, and their adsorption mechanisms on muscovite and air/water interface were clarified using contact angle measurement, surface tension and molecular dynamics (MD) simulations. The flotation results indicate that the recovery of muscovite rapidly decreases when the pH increases in the presence of only DDA, whereas the recovery of muscovite is high (> 77%) over a wide range of pH in the presence of the mixed DDA/OCT surfactants with a ratio of 2/1. Contact angle measurements further confirm that the mixture displays a stronger collecting power than DDA and is a superior collector for the muscovite flotation. The surface tensions of DDA, OCT and their mixture indicate that the mixture is more efficient than DDA at decreasing the air–water interfacial tension and exhibits much better surface activities. MD simulations show that the mixture interacts with the muscovite mainly through electrostatic attraction and hydrogen-bonding. DDA ion is dominant in the interaction between the mixture and muscovite. OCT molecules are co-adsorbed onto the muscovite through the hydrogen-bond interaction and hydrophobic association with DDA ions. Compared with DDA, a well-compacted monolayer is formed on the muscovite surface in the presence of mixed surfactants, indicating a much stronger hydrophobic character of muscovite. [ABSTRACT FROM AUTHOR]

Comparative studies of flotation of oleate on diaspore and kaolinite in different particle size fractions (0.075–0.038 mm, 0.038–0.01 mm, 0–0.01 mm) are presented to investigate the influences of particle size. The flotation results show that the kaolinite recovery increases with a decrease in particle size, while the case of diaspore is the opposite. Chemisorptions of anionic oleate collector on the surface Al sites of the negatively charged diaspore and kaolinite are confirmed by zeta potential and FTIR measurements. Anisotropic surface broken bond densities are calculated based on surface crystal chemistry to characterize anisotropic wettability of mineral crystals. The increasing order of broken bond densities ( D b ) and hydrophobicity for different crystal planes of diaspore and kaolinite correlate well with increasing the number of broken Al O bonds. The anisotropic adsorption of oleate on different crystal planes of diaspore and kaolinite are studied in terms of interaction energies computed by molecular dynamics (MD) simulations. The oleate is adsorbed more readily on (0 1 0) than (0 0 1) for diaspore. As for kaolinite, the oleate adsorption is considerably less on (0 0 1) as compared to (1 10 ). The conclusions drawn from purely theoretical computations are in good agreement with our experimental contact angle results. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropic surface broken bond densities and surface energies of six surfaces of scheelite were calculated with density functional theory (DFT). The calculation results show that its surface energy is directly proportional to its surface broken bond density. {112} and {001} surfaces are the two predominant cleavage or exposed planes. The prediction of morphology is well consistent with our experimental observations based on XRD. Anisotropic adsorption behaviors and wettability of these two surfaces after being immersed in sodium oleate and DDA solutions were studied by means of contact angle measurement, AFM and flotation test. The contact angle values at a given NaOl concentration decreased in the order {112}>{001}. As for DDA, similar wettability for the two surfaces was observed. The results were interpreted by AFM and interaction energies for the adsorption of surfactants on each surface calculated in accordance with molecular dynamics (MD) simulation. [Copyright &y& Elsevier]

Abstract: The flotation behavior of kaolinite was investigated using a series of tertiary amines (DRN, DEN, DPN and DBN). Maximum recoveries of kaolinite were 93%, 88% and 84% for DEN, DPN and DRN, respectively. The recovery for DBN was very low. On the basis of the Zeta potential and FT-IR spectra, the ionization of surface hydroxyl and the isomorphic exchange of surface ions accounts for the charging mechanisms of the kaolinite surface. The adsorption mechanism of tertiary amines onto the kaolinite surface was mainly electrostatic. We determined that the IEP of kaolinite increased from 3.4 to higher values after the interaction of kaolinite with the four tertiary amines. FT-IR spectra of kaolinite changed to include sharp peaks of tertiary amines. Inductive electronic effects and space-steric effects of –CH3, –C2H5, –C3H7 and –C7H7 bound to the N atom result in different collecting powers for the four tertiary amines. [Copyright &y& Elsevier]

Abstract: The electrokinetics and flotation behavior of kaolinite have been investigated through flotation experiments, zeta potential measurements, and FTIR spectral analysis. These results have been explained based on crystal structure considerations and quantum mechanical calculations. It has been shown that the PZC of kaolinite is at pH 4.2. Kaolinite exhibits good floatability in weakly acidic solution with dodecyl amine (DDA) collector. The negative zeta potential of kaolinite increases with an increase in pH, and hence the adsorption of DDA on kaolinite increases. However, the flotation of kaolinite decreases with an increase in pH and an increase in DDA adsorption. This anomalous flotation behavior is rationalized based on crystal structure considerations and particle aggregation phenomena. It is considered that the silica (001) and the alumina (001¯) basal planes of kaolinite are negatively charged. From quantum chemistry calculations, the interaction between DDA and the (001) plane was found to be stronger than at the (001¯) alumina plane due to the difference in the structure at the (001) and (001¯) planes. The self-aggregation between (001¯) faces and the edge planes and the adsorption of DDA at the silica (001) plane make the kaolinite aggregates hydrophobic, and good floatability is achieved in acidic solution. In alkaline solution, the kaolinite particles are dispersed. In the presence of DDA, hydrophobic aggregation appears to occur in alkaline solution between the (001) planes due to adsorbed DDA, and thus the hydrophilic (001¯) faces are exposed and flotation is not achieved. [Copyright &y& Elsevier]

The rejection of pyrrhotite and pyrite has become a long-standing problem in the copper ore industry. This paper describes the first successful depression and adsorption mechanism of a novel and non-hazardous reagent, polyglutamic acid (PGA), on pyrrhotite in the selective flotation of chalcopyrite with xanthate as the collector, making use of various laboratory-scale measurement techniques. The addition of PGA inhibited the flotation of pyrrhotite much more strongly than that of the chalcopyrite in a wide pH range. The prior addition of PGA achieved an improved selective flotation of chalcopyrite from pyrrhotite at pH 8, at which the grade and recovery of chalcopyrite in concentrate were over 80%. Surface measurement techniques including XPS spectral, IR spectral, zeta potential, and reagent adsorption analyses indicated that the PGA interacted differently with the two minerals, and had much greater affinity towards pyrrhotite than chalcopyrite. The presence of PGA blocked the electrochemical activity of the collector on the pyrrhotite surface and thus depressed its flotation, whereas the adsorption of the collector and its oxidation to dixanthogen were more effective on the chalcopyrite surface, indicating a weaker interaction of PGA with chalcopyrite. Our results suggest that the application of PGA could replace the toxic inorganic depressants in flotation technology, and could significantly reduce the environmental impacts of processing. [ABSTRACT FROM AUTHOR]

A scientific and rigorous study on the adsorption behavior and molecular mechanism of collector sodium oleate (NaOL) on a Ca2+-activated hydroxylated α-quartz surface was performed through experiments and density functional theory (DFT) simulations. The rarely reported hydroxylation behaviors of water molecules on the α-quartz (101) surface were first innovatively and systematically studied by DFT calculations. Both experimental and computational results consistently demonstrated that the adsorbed calcium species onto the hydroxylated structure can significantly enhance the adsorption of oleate ions, resulting in a higher quartz recovery. The calculated adsorption energies confirmed that the adsorbed hydrated Ca2+ in the form of Ca(H2O)3(OH)+ can greatly promote the adsorption of OL− on hydroxylated quartz (101). In addition, Mulliken population analysis together with electron density difference analysis intuitively illustrated the process of electron transfer and the Ca-bridge phenomenon between the hydroxylated surface and OL− ions. This work may offer new insights into the interaction mechanisms existing among oxidized minerals, aqueous medium, and flotation reagents. [ABSTRACT FROM AUTHOR]

• SFG provides molecular details about the adsorption of sodium silicate (SS). • SFG signal shows the change in surface charge and adsorption. • SS physically adsorbs at CaF 2 surface at pH < 7 and is removed by water flow. • SS chemically adsorbs at CaF 2 surface at pH > 7 and is unremoved by water flow. • SS penetrates the innermost water layer at SiO 2 surface and adsorbs on it chemically. 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. [ABSTRACT FROM AUTHOR]

Mixed cationic/anionic surfactants are generating increasing attention as effective collectors during the flotation of muscovite, feldspar and spodumene ores. Many papers have been published focusing on the flotation mechanisms of these valuable minerals. However, the depression mechanisms on gangue minerals such as quartz have rarely been reported. In this study, mixed dodecylamine (DDA)/sodium oleate (NaOL) surfactants were used in the flotation separation of muscovite and quartz, and their depression mechanisms on quartz were investigated. Compared to DDA alone, the use of mixed surfactants resulted in a significantly higher adsorption amount of surfactants on the quartz but a lower flotation recovery and contact angle with the quartz. This is attributed to the different molecular self-assembly mechanisms between solely DDA and mixed surfactants at the quartz/water interface, as revealed by molecular dynamics simulations. A hydrophobic monolayer coating forms for solely DDA, with the head groups adsorbing on the quartz via electrostatic interactions. In the case of mixed surfactants, DDA preferentially interacts with NaOL via electrostatic interaction through the oppositely charged head groups and hydrophobic interactions between their carbon chains. As a result, most DDA and NaOL molecules form hydrophilic spherical-like micelles near quartz, whereas only a few DDA molecules adsorb directly on the quartz via hydrogen bonding. These act as a bridge linking the rest of the surfactants, leading to a relatively lower flotation recovery and contact angle for the quartz. This study is beneficial for complementing the flotation theories and mechanisms of mixed cationic/anionic surfactants on minerals. [ABSTRACT FROM AUTHOR]

In this work, molecular dynamics simulation was used to examine the effect of solution pH on the adsorption behavior and self-aggregation of dodecylamine hydrochloride (DDA) on the muscovite (0 0 1) surface. The properties of surfactants are assessed in terms of density profiles in the direction perpendicular to the muscovite surface. Results show that although DDA can adsorb at muscovite at all pH we discussed, the self-aggregation of DDA varies significantly at different pH values. At pH 10, a compact hydrophobic monolayer forms on the muscovite surface. At pH 3, hemi-micelle aggregated structure forms with several DDA cations far away from muscovite surface. At pH 12, it has been confirmed that adsorption of DDA neutral molecules occurs with only a few DDA molecules adsorbing on muscovite directly and acting as a bridge linking the rest DDA molecules, which exists nearby muscovite surface irregularly. Density profiles revealed that at pH 10, DDA cations play a dominant role in the interaction between DDA surfactants and muscovite. While DDA molecules have difficulty in forming a hydrogen bond with the oxygen atom on the muscovite surfaces, and they co-adsorb onto muscovite through the electrostatic interactions with muscovite and hydrophobic force with DDA cations. Therefore, the hydrophobization of muscovite in the presence of DDA are higher at pH 10 than that at pH 3 and pH 12. Our results indicate that molecular dynamics simulation can be a power tool in charactering adsorption behavior of surfactants onto mineral surfaces at different pH values. [ABSTRACT FROM AUTHOR]

Cationic flotation is a promising method for separating scheelite from calcite at room temperature, because of the significant difference between their surface charges. Three quaternary ammonium salts, i.e., didecyldimethylammonium chloride (DDAC), trioctylmethylammonium chloride (TOAC), and dodecyltrimethylammonium chloride (DTAC), were investigated as cationic collectors in the flotation of scheelite from calcite. The flotation behaviors of scheelite and calcite with the three quaternary ammonium salts were studied using single-mineral and mixed-mineral flotations; flotation with oleate was used for comparison. The results show that flotation of scheelite from calcite was possible around pH 8 with DDAC and TOAC as collectors. The collecting powers and selectivities of these compounds for scheelite were higher than those of oleate. The molecular structures, Fourier-transform infrared spectra, and zeta potentials indicated that when quaternary ammonium salts are used as collectors, electrostatic interactions play a primary role in the flotation of scheelite from calcite. The adsorptions of the three quaternary ammonium salts fitted a general adsorption isotherm well, but the Langmuir isotherm only fitted the adsorption of DDAC well. It can be concluded from the adsorption isotherm parameters that the role of van der Waals forces is as significant as that of electrostatic forces in the interactions of quaternary ammonium salts with the two minerals, and that the selectivities of the quaternary ammonium salts for scheelite result from their large van der Waals forces, as well as the opposite charges on scheelite and calcite. The van der Waals forces of quaternary ammonium salts significantly affect the adsorption processes and consequently the isotherm plots. [ABSTRACT FROM AUTHOR]

In this work, the adsorption behavior of dodecylamine (DDA) on scheelite and calcite mineral surfaces were investigated by molecular dynamics (MD) simulation, zeta potential measurement, AFM observation, contact angle measurement, and flotation test. The results implied that, the different adsorption behavior of DDA on scheelite and calcite surfaces was mainly attributed to cationic species RNH 3 + of DDA. The adsorption of neutral species RNH 2 and complex precipitates produced by the reactions between RNH 3 + and anionic species released by both mineral surfaces, also played important roles. In a DDA solution (1 × 10 −4 mol/L, pH 7.5–8.0), a handful of RNH 2 of DDA adsorbed on both scheelite and calcite surfaces through N–Ca bonding and hydrogen bonding between hydrogens of –NH 2 group and mineral surface oxygens. On positively charged calcite surface, RNH 3 + adsorbed on a moderate number of CO 3 2 − sites through electrostatic attraction and hydrogen bonding, which caused a moderate zeta potential increase for calcite. On negatively charged scheelite surface, a large number of cationic species RNH 3 + could easily adsorb on abundant WO 4 2 − sites, which caused a significant increase of zeta potential for scheelite. The different adsorption behavior led to a heavier monolayer coverage of DDA species on scheelite surface, and thus a more hydrophobic surface and a better flotation recovery of scheelite. The present work helps propose a new adsorption model of DDA on scheelite and calcite. [ABSTRACT FROM AUTHOR]

Abstract: The main waste product generated during the bauxite flotation in China is the aluminosilicate tailings. It is desirable to develop an application of these aluminosilicate tailings for the treatment of waste streams containing dissolved heavy metals. The Cr(VI) adsorption capacity and mechanisms of the bauxite tailings modified by FeCl3 ·6H2O are investigated in the present study. A maximum removal rate of Cr(VI) by the modified bauxite flotation tailings is obtained at 99.3% in batch experiments. The IEPs of the unmodified and modified bauxite tailings are 3.6 and 5.0, respectively. The IEP of the modified bauxite tailings shifts to lower pH value in the presence of Cr(VI), which indicates that an adsorption of anionic species happens on the modified bauxite tailings. A new band of appears in the FTIR determination of the modified bauxite tailings, which shows that Cr(VI) adsorbs on the modified bauxite tailings in the form of chemical adsorption. Furthermore, the adsorption data of Cr(VI) on the modified bauxite tailings are well described by both Langmuir and Freundlich models. The pseudo-second-order kinetic model also fits experimental data for the adsorption of Cr(VI). [Copyright &y& Elsevier]

Graphical abstract Highlights • Mixed DDA/NaOL showed the better flotation recovery than single collectors. • Angles in mixed DDA/NaOL were bigger and the bubble was adhered more easily. • DDA/NaOL were uniformly adsorbed on muscovite surface as tight multilayer bulks. • The attraction in DDA/NaOL was stronger with the jump-in distance at around 15 nm. Abstract A new approach 'dynamic contact angle analysis' has been used in the present investigation to characterize the hydrophobization mechanisms of single and mixed surfactants on muscovite surface. The hydrophobization of muscovite surface was achieved by anionic NaOL (sodium oleate), cationic DDA (dodecylamine) and combined DDA/NaOL surfactants. Besides dynamic contact angle analysis, AFM and flotation tests were carried out to gain detail information about the wettability of muscovite, adhesion ability of bubbles towards muscovite surface and adsorption of single and mixed DDA/NaOL surfactants on the muscovite surface. From flotation results, the highest recovery (>90%) was obtained by the mixed DDA/NaOL when they were used at a ratio of 1:3 and the concentration of 2 × 10−4 mol/L. The dynamic contact angle tests showed that the angles achieved by DDA/NaOL were bigger and the bubbles were adhered more easily, which are in agreement with the flotation results. AFM imaging indicated that, as compared to single collectors, the combined surfactants adsorbed uniformly on the muscovite surface as bulks and formed a tight adsorption multilayer. The attraction in mixed DDA/NaOL was stronger than that in single DDA with the same jump-in distance at around 15 nm and the long-range repulsion was observed in single NaOL. [ABSTRACT FROM AUTHOR]

In this work, the flotation performance of separately added Pb 2+ ions and benzohydroxamic acid (BHA) was compared with that of Pb 2+ /BHA (Pb-BHA) complexes, and the possible adsorption mechanism on the ilmenite surface was investigated by conducting single-mineral flotation tests as well as zeta potential, ultraviolet (UV) spectroscopy, microcalorimetry, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. The results of mineral flotation testing revealed that Pb-BHA complexes exhibited better flotation characteristics as compared to those of their sequentially dosed components, while the collection properties of these complexes depended on their compositions. Thus, the complexes with Pb 2+ /BHA molar ratios equal to 1:2 and 1:1 exhibited much higher ilmenite collection efficiencies and wider effective pH ranges than those of the complexes with Pb 2+ /BHA ratios of 2:1 and 3:1. Furthermore, the obtained zeta potentials indicated that the resultant Pb-BHA complexes with a Pb 2+ /BHA molar ratio of 1:1 were slightly positively charged. After increasing its magnitude, the zeta potential of ilmenite shifted toward positive values. Large amounts of Pb 2+ ions in solution were possibly adsorbed on the surface of ilmenite, which suppressed the adsorption of Pb-BHA species. The obtained UV spectra showed that varying the Pb 2+ /BHA ratio strongly affected the compositions of the produced complexes. The results of microcalorimetry analysis indicated that the adsorption heats (−Δ ads H) of the utilised reagents could be ranked in the order of Pb 2+  < BHA < Pb-BHA, suggesting that Pb-BHA species exhibited the highest affinities to the ilmenite surface. Finally, the obtained FTIR and XPS spectra revealed that Pb-BHA complexes were adsorbed on the ilmenite surface more strongly than their individual components. [ABSTRACT FROM AUTHOR]

Collecting performance and adsorption behaviors and mechanisms of two quaternary ammonium salts, dodecyltrimethyl ammonium chloride (DTAC) and cetyltrimethyl ammonium chloride (CTAC), on illite particles have been investigated through flotation tests, adsorption analysis, zeta potential, FTIR measurements and fluorescence spectroscopy. Adsorption analysis revealed that the adsorbed amount of surfactants on mineral surface increases by increasing the pulp pH or by increasing the length of carbon chains of surfactants. Therefore, at same concentrations, CTAC due to its longer carbon chains has a larger adsorption density on illite surface than DTAC, which was measured by FTIR analysis and zeta potential measurements. As compared to DTAC, CTAC showed much better collecting properties as it has higher I 3 /I 1 value and a lower critical micelle concentration (CMC) value, which was analyzed by pyrene fluorescence observations. However, decrease in recovery by CTAC in an alkaline solution was mainly due to the complete adsorption of CTAC molecules on mineral particles, hence, its insufficient concentration in the pulp was unable to stabilize the flotation froth. From the results of flotation behaviors and adsorption mechanisms, it is concluded that CTAC is much more efficient surfactant than DTAC in relation to flotation separation of illite. [ABSTRACT FROM AUTHOR]

Fluorite, a chief source of fluorine in the nature, usually coexists with calcite mineral in ore deposits. Worldwide, flotation techniques with a selective collector and/or a selective depressant are commonly preferred for the separation of fluorite from calcite. In the present study, an attempt was made to use benzhydroxamic acid (BHA) as a collector for the selective separation of fluorite from calcite without using any depressant. Results obtained from the flotation experiments for single mineral and mixed binary minerals revealed that the BHA has a good selective collecting ability for the fluorite when 50 mg/L of BHA was used at pH of 9. The results from the zeta potential and X-ray photoelectron spectroscopy (XPS) indicated that the BHA easily chemisorbs onto the fluorite as compared to calcite. Crystal chemistry calculations showed the larger Ca density and the higher Ca activity on fluorite surface mainly account for the selective adsorption of BHA on fluorite, leading to the selective separation of fluorite from calcite. Moreover, a stronger hydrogen bonding with BHA and the weaker electrostatic repulsion with BHA − also contribute to the stronger interaction of BHA species with fluorite surface. [ABSTRACT FROM AUTHOR]

The efficient separation of scheelite from calcium-bearing minerals, especially calcite, remains a challenge in practice. In this work, a novel reagent scheme incorporating a depressant of sodium hexametaphosphate (SHMP) and a collector mixture of octyl hydroxamic acid (HXMA-8) and sodium oleate (NaOl) was employed in both single and mixed binary mineral flotation, and it proved to be highly effective for the separation. Furthermore, the role of the pH value in the separation was evaluated. Additionally, the mechanism of the selective separation was investigated systemically via zeta potential measurements, fourier transform infrared (FTIR) spectroscopy analysis, X-ray photoelectron (XPS) spectroscopy analysis and crystal chemistry calculations. It turns out that the selective chemisorption of SHMP on calcite (in the form of complexation between H 2 PO 4 − /HPO 4 2− and Ca 2+ ) over scheelite is ascribed to the stronger reactivity and higher density of Ca ions on the commonly exposed surfaces of calcite minerals. The intense adsorption of HXMA-8 on scheelite over calcite due to the match of the O O distances in WO 4 2− of scheelite and CONHOH of HXMA-8 holds the key to the successful separation. We were also interested in warranting the previous claim that NaOl is readily adsorbed on both minerals via chemisorption. Our results provided valuable insights into the application of mixed collectors and an effective depressant for flotation separation. [ABSTRACT FROM AUTHOR]

Aluminosilicate minerals (e.g., spodumene, albite) have complex crystal structures and similar surface chemistries, but they have poor selectivity compared to traditional fatty acid collectors, making flotation separation difficult. Previous research has mainly considered the mineral crystal structure as a whole. In contrast, the surface characteristics at the atomic level and the effects of different crystal interfaces on the flotation behavior have rarely been investigated. This study focuses on investigating the surface anisotropy quantitatively, including the chemical bond characteristics, surface energies, and broken bond densities, using density functional theory and classical theoretical calculations. In addition, the anisotropy of the surface wettability and adsorption characteristics were examined using contact angle, zeta potential, and Fourier-transform infrared measurements. Finally, these surface anisotropies with different flotation behaviors were investigated and interpreted using molecular dynamics simulations, scanning electron microscopy, and X-ray photoelectron spectroscopy. This systematic research offers new ideas concerning the selective grinding and stage flotation of aluminosilicate minerals based on the crystal characteristics. [ABSTRACT FROM AUTHOR]

The effects of Pb 2+ ions on ilmenite flotation and adsorption of benzohydroxamic acid (BHA) as a collector were investigated using microflotation tests, zeta potential measurements, adsorption analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The microflotation results indicate that the addition of Pb 2+ significantly improves the recovery of ilmenite using BHA as a collector. A maximum recovery of 88.46% is obtained at pH 8.12 in the presence of Pb 2+ ; a maximum recovery of 45% is obtained at the same pH using BHA alone. At pHs below 8.0, lead nitrate are mainly present in the solution as Pb 2+ and PbOH + , while at pHs above 8.0, the predominant components are Pb(OH) 2(s) and Pb(OH) 3− . The adsorption of these lead species influences the zeta potential of ilmenite and the number of activated sites on the ilmenite surface. FTIR and XPS analyses reveal that lead species and BHA react with the metal sites on the ilmenite surface. The lead species in solution are either adsorbed onto the ilmenite surface, which increases the surface activity of ilmenite, or react with BHA in solution to form complexes of lead and BHA. [ABSTRACT FROM AUTHOR]

The analysis of flotation and adsorption of mixed collectors on oxide and silicate minerals is of great importance for both industrial applications and theoretical research. Over the past years, significant progress has been achieved in understanding the adsorption of single collectors in micelles as well as at interfaces. By contrast, the self-assembly of mixed collectors at liquid/air and solid/liquid interfaces remains a developing area as a result of the complexity of the mixed systems involved and the limited availability of suitable analytical techniques. In this work, we systematically review the processes involved in the adsorption of mixed collectors onto micelles and at interface by examining four specific points, namely, theoretical background, factors that affect adsorption, analytical techniques, and self-assembly of mixed surfactants at the mineral/liquid interface. In the first part, the theoretical background of collector mixtures is introduced, together with several core solution theories, which are classified according to their application in the analysis of physicochemical properties of mixed collector systems. In the second part, we discuss the factors that can influence adsorption, including factors related to the structure of collectors and environmental conditions. We summarize their influence on the adsorption of mixed systems, with the objective to provide guidance on the progress achieved in this field to date. Advances in measurement techniques can greatly promote our understanding of adsorption processes. In the third part, therefore, modern techniques such as optical reflectometry, neutron scattering, neutron reflectometry, thermogravimetric analysis, fluorescence spectroscopy, ultrafiltration, atomic force microscopy, analytical ultracentrifugation, X-ray photoelectron spectroscopy, Vibrational Sum Frequency Generation Spectroscopy and molecular dynamics simulations are introduced in virtue of their application. Finally, focusing on oxide and silicate minerals, we review and summarize the flotation and adsorption of three most widely used mixed surfactant systems (anionic–cationic, anionic–nonionic, and cationic–nonionic) at the liquid/mineral interface in order to fully understand the self-assembly progress. In the end, the paper gives a brief future outlook of the possible development in the mixed surfactants. [ABSTRACT FROM AUTHOR]

The anisotropic adsorption of sodium oleate (NaOL) on feldspar surfaces was investigated to elucidate the different flotation properties of feldspar particles of four different size ranges. Microflotation experiments showed that the feldspar flotation recovery of particles with sizes spanning different ranges decreased in the order 0–19 > 19–38 > 45–75 > 38–45 μm. Zeta potential and FTIR measurements showed that NaOL was chemically adsorbed on the Al sites of the feldspar surface. The anisotropic surface energies and broken bond densities estimated by density functional theory calculations showed that, although feldspar mostly exposed (0 1 0) and (0 0 1) surfaces, only the (0 0 1) surfaces contained the Al sites needed for NaOL adsorption. The interaction energies calculated by molecular dynamics simulations confirmed the more favorable NaOL adsorption on (0 0 1) than (0 1 0) surfaces, which may represent the main cause for the anisotropic NaOL adsorption on feldspar particles of different sizes. SEM measurements showed that the main exposed surfaces on coarse and fine feldspar particles were the side (0 1 0) and basal (0 0 1) ones, respectively. A higher fraction of Al-rich (0 0 1) surfaces is exposed on fine feldspar particles, resulting in better floatability compared with coarse particles. XPS and adsorption measurements confirmed that the Al content on the feldspar surface varied with the particle size, explaining the different NaOL flotation of feldspar particles of different sizes. Therefore, the present results suggest that coarsely ground ore should be used for the separation of feldspar gangue minerals. Further improvements in the flotation separation of feldspar from associated valuable minerals can be achieved through selective comminution or grinding processes favoring the exposure of (0 1 0) surfaces. [ABSTRACT FROM AUTHOR]

The flotation behaviors of ilmenite untreated or treated with lead ions using sodium oleate as a collector were studied. The results of micro-flotation experiments reveal that ilmenite shows good floatability at pH 6–8. Compared with the flotation recovery of ilmenite untreated with lead ions, ilmenite floatability can be enhanced, and the resulting increase in recovery can surpass 30% after the addition of lead ions. The results of zeta potential tests show that the isoelectric point of ilmenite can change from 5.2 (untreated) to 7.8 (treated), which is beneficial for the interaction between ilmenite and the collector and increases its floatability. Adsorption measurements show that the adsorption amounts of ilmenite treated with lead ions are higher than those of untreated ilmenite. XPS tests show that after activation with lead ions, the relative contents of iron and titanium on the ilmenite surface, which play leading roles in ilmenite flotation, increase by 5.9% and 4.6%, respectively. At the same time, changes in binding energy are more visible after ilmenite is pretreated with lead ions and subsequently treated with sodium oleate. Within the optimal flotation pH range, oleate species (RCOO − , ( RCOO ) 2 2 - , (RCOO) 2 H − ) can mainly react with iron on the ilmenite surface through chemical adsorption in addition to electrostatic effects. [ABSTRACT FROM AUTHOR]

The mixed anionic collector sodium oleate (NaOL) and cationic collector dodecyl ammonium chloride (DTAC) demonstrate high selectivity for the flotation of spodumene from feldspar, and the optimal molar ratio of NaOL and DTAC is 9:1. To detect the underlying mechanism, surface tension measurements, adsorption measurements, zeta potential measurements and Fourier transform infrared (FTIR) analyses were performed. The surface and thermodynamic parameters (CMC, γ CMC , Γ max , A min , Δ G m 0 ) obtained from surface measurements show higher surface activity and a denser molecular arrangement in mixed NaOL/DTAC than in single NaOL or DTAC. Further analysis of the interaction parameters and activity coefficients ( β m , β σ , f m , and f σ ) obtained from the theory of regular solutions shows that there is a synergistic effect both in the mixed micelle and at the water/air interface. Moreover, the maximum synergistic interaction was found at X DTAC = 0.5 in mixed NaOL/DTAC. The adsorption measurements show that more NaOL is adsorbed on the spodumene surface than on feldspar and that the cationic collector can improve the adsorption of NaOL on the spodumene surface by a small amount, but not for feldspar. The zeta potential measurement and Fourier transform infrared analyses show that in the mixed NaOL/DTAC system, the anionic collector NaOL first reacts with aluminum sites on the mineral surface. Then, the cationic collector DTAC forms an electroneutral complex with the anionic collector NaOL and co-adsorbs on the Stern layer because of the chemisorption of NaOL. Based on these analyses, an adsorption model of the mixed collector NaOL/DTAC on the mineral surface was drawn. [ABSTRACT FROM AUTHOR]

The anisotropic physicochemical properties of calcite, including cleavage nature, surface (free) energy, surface relaxation degree, wettability and adsorption behaviour, were revisited in this paper based on the surface structures and surface broken bonds reported previously. The relationships between these surface properties were also discussed. The analysis indicated that the positive relationship between the density of surface broken bonds and the surface energy of calcite was established, and the former could be used to predict the cleavage nature, commonly exposed surfaces and the degree of surface relaxation. The distribution characteristic and the number of broken (or unsaturated) bonds of surface Ca atoms can be used to explain the anisotropic surface wetting and adsorption behaviour of calcite. This review demonstrated that surface broken bonds could be a fast way to study the surface properties of minerals and materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Trisodium nitrilotriacetate (TN) was a novel depressant during fluorite separation from calcite. • TN showed excellent depressing performance on calcite at pH 7.9. • The multi-dentate neutralization reaction between TN and calcite surface occurred. • An adsorption model is finally obtained. The recovery of fluorite from calcium-bearing carbonate ores by foam flotation is challenging due to low separation efficiency. Herein, we studied the effect of trisodium nitrilotriacetate (TN) addition on the surface properties of calcite and fluorite. For this purpose, we performed micro-flotation tests and carried out zeta potential measurements as well as Fourier transform infrared (FT-IR) and X-ray photoelectron (XPS) spectroscopic measurements to analyze the surface properties of these minerals. The addition of TN as a novel depressor significantly improved the effect of calcite and sodium oleate (NaOl) on the flotation-based fluorite recovery and separation from calcite. TN interacted with fluorite via an electrostatic interaction according to the zeta-potential and XPS analyses. The interaction of TN with calcite was via electrostatic attraction and chemical adsorption. Preferential chemical adsorption of NaOl replaces TN from the fluorite surface. However, calcite preferentially adsorbs TN due to the chemical bonding between carboxyl of TN and the hydrated calcite surface layer, which chemically modifies the original calcite surface. This work also suggests interaction and adsorption mechanisms between TN and calcite. [ABSTRACT FROM AUTHOR]

The flotation and adsorption behaviors of two quaternary ammonium collectors DTAC (dodecyl trimethyl ammonium chloride) and CTAC (cetyltrimethyl ammonium chloride) on diaspore and kaolinite were investigated in this work. The flotation recovery of diaspore increases with the increase of pH and the decrease of particle size, however, the situations for kaolinite are opposite. Furthermore, the influence of pH on flotation of kaolinite decreases with the decrease of particle size, and for the fine particles (undersize 0.045mm), the flotation recovery with CTAC which has a longer hydrocarbon chain and is believed to have a stronger collecting ability is lower than that with DTAC. The dramatic differences of the flotation behaviors between diaspore and kaolinite are correlated to the differences of their crystal structures. The morphologies of diaspore and kaolinite particles in different size were studied by SEM. The kaolinite particles have much larger specific surface areas (about 7 times) than the diaspore particles due to their layered structure. This leads to the differences of collector adsorption behaviors on kaolinite and diaspore and results in the different flotation behavior. [ABSTRACT FROM AUTHOR]

Abstract: Highly branched waxy maize starch (WMS) was used to separate diaspore from artificial mixtures of diaspore and kaolinite by microflotation using dodecylamine (DDA) as collector. It was found that WMS depressed the diaspore flotation while activated the kaolinite flotation more or less. The adsorption of WMS on diaspore was examined through adsorption test, zeta potential measurement, infrared spectroscopy, and atomic force microscopy. It is suggested that both chemical interaction and intermolecular hydrogen bonding by hydroxyl groups of starch with surface Al–OH moieties occurred in the adsorption. Results obtained from the adsorption of DDA and WMS on diaspore showed that starch virtually enhanced the DDA adsorption. The depressant action of WMS can be rationalized primarily by the formation of hydrophilic adsorption layer enveloping the surface of diaspore and covering the collector. [ABSTRACT FROM AUTHOR]

Abstract: The variation of surface properties of pyrrhotite after biological conditioning with Leptospirillum ferriphilum and Acidithiobacillus caldus was evaluated by zeta-potential, adsorption and contact angle measurements. Previous work showed that the pyrrhotite isoelectric point (IEP) shifts towards the cell isoelectric point after interacting with bacterial cells, indicating the adsorption of cells on the pyrrhotite surface. The degree of interaction of pyrrhotite with A. caldus was observed to be much more pronounced than that of L. ferriphilum, because of the different affinity of A. caldus and L. ferriphilum to pyrrhotite. After treatment by A. caldus, the pyrrhotite surface formed a membrane of sulfur, which was shown by X-ray diffractograms (XRD) and the energy dispersion spectrum (EDS), which explains the increasing hydrophobicity of pyrrhotite. However, the contact angle and surface hydrophobicity of pyrrhotite treated by the L. ferriphilum kept decreasing during bioleaching. The results indicate that the energy source for the microorganism growth determines its function mechanism in the bioleaching system. The iron-oxidizing bacteria offer an indirect mechanism function during bioleaching of pyrrhotite and the sulfur-oxidizing bacteria offer a direct mechanism function. [Copyright &y& Elsevier]

• Ultrasound treatment improves separation of ilmenite from titanaugite & olivine. • Treatment condition for maximum difference in floatability was identified. • Effect of ultrasound on different minerals is due to change in mineral dissolution. • Ultrasound converts Fe(II) to Fe(III) and promotes dissolution of Ca and Mg. • Fe(OH) 3 precipitate on ilmenite enhances collector adsorption in floatation. Selective separation of ilmenite from gangue minerals after ultrasonic preconditioning was studied in terms of surface dissolution. After preconditioning, ilmenite exhibited better single-mineral flotation capacity while titanaugite and olivine had lower recoveries. Significant separation could be obtained at pH 6.0 after ultrasonic treatment (500 W, 5 min). Zeta potentials of preconditioned titanaugite and olivine shifted positively compared to those of raw titanaugite and olivine treated with sodium oleate (NaOL), respectively. Meanwhile, the zeta potential of ilmenite was similar before and after NaOL adsorption. Mineral dissolution results indicate that ultrasonic preconditioning promotes the dissolution of Mg and Fe species but not the Ca species. The dissolution of Ca and Mg is much higher than that of Fe. According to solution chemistry calculation, Fe(OH) 3 precipitate is dominant at pH greater than 2.5, and Ca2+, Mg2+, Fe2+, and Fe(OH)+ are dominant under acidic conditions. Microcalorimetric measurements demonstrate that the preconditioned ilmenite releases more heat during NaOL adsorption than titanaugite and olivine do. XPS results reveal that ultrasonic treatment facilitates the conversion of Fe2+ to Fe3+. After preconditioning, Fe species interacted with NaOL to promote the latter's chemisorption on ilmenite and olivine, while Ca2+ was more likely to interact with NaOL on titanaugite. [ABSTRACT FROM AUTHOR]