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Monazite ((Ce, La)PO4) is one of the major types of light rare earth minerals from which the light rare earth elements cerium (Ce) and lanthanum (La) are economically extracted. Flotation is extensively used to recover fine-grained monazite. Sodium oleate (NaOL) is considered as the collector with the strong collecting ability for monazite flotation. However, this study shows that its collecting ability is still limited. In this paper, a phosphonic acid, nonane-1,1-bisphosphonic acid (C9-BPA), was employed as the novel collector in place of NaOL. Flotation experiments show that even when the C9-BPA dosage is less than one-fifth of the NaOL dosage, the monazite recovery using C9-BPA as the collector is approximately 22 wt% higher than that using NaOL. The mechanism by which C9-BPA adsorbs on monazite was investigated using zeta potential, infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements as well as first-principles calculations. Zeta potential measurements show a more significant decrease in the zeta potentials of monazite after the addition of C9-BPA compared to those after the addition of NaOL. For C9-BPA-treated monazite, the characteristic peaks of C9-BPA were observed in the IR and C 1s XPS spectrum, whereas for monazite treated by NaOL, no characteristic peak of NaOL was observed. Experimental results show that C9-BPA has a stronger affinity towards the monazite surface than NaOL as confirmed by the higher adsorption energy of CP-BPA on the monazite surface (‒204.22 kJ/mol) than NaOL (‒48.48 kJ/mol). This study demonstrates an extensive application value and prospect of C9-BPA in monazite flotation and helps design novel collectors with strong collecting ability for monazite flotation.

Utilization of large doses of inorganic reagents in mineral industry not only leads to high cost but also increases the toxicity in the environment. This research provides a new, environmentally friendly, biodegradable, and cost-effective depressant reagent, namely tricarboxylate sodium starch (TCSS), in chalcopyrite and pyrrhotite flotation systems. The selective depression and adsorption mechanism of TCSS on the two minerals were studied through the laboratory based measurements such as microflotation experiments, XPS spectral analysis, IR spectral analysis, adsorption amount analysis and zeta potential measurements. The addition of TCSS exhibited a much better depressive performance towards pyrrhotite than chalcopyrite in a wide pH range. Binary mineral flotation experiments indicated that an effective separation between the two minerals could be possible at a low concentration of TCSS, at which an improved recovery and grade of chalcopyrite of more than 75% could be achieved. All of the analytical measurements justified the flotation results and revealed that TCSS behaved differently with the two minerals. TCSS showed significantly much greater affinity towards pyrrhotite, the reason of which may be the presence of large amount of metal hydroxyl species on its surface. Keywords: Organic depressant, Flotation, Pyrrhotite, Chalcopyrite, Tricarboxylate sodium starch

Since the excessive dosage of Pb2+ ions could facilitate the gangue mineral quartz activation and cause serious environmental problems, this work has an attempt to examine the performance of cupferron as a new alternative collector in selective separation of cassiterite from quartz with low dose of Pb2+ ions. Microflotation results show the improved selectivity of cupferron towards cassiterite as compared to quartz. Accordingly, its selective adsorption mechanism has been investigated by zeta potential measurements, X-ray photoelectron spectroscopy (XPS) analysis and first-principle density functional theory (DFT) calculations. The results of zeta potential measurements demonstrate the stronger adsorption of cupferron on cassiterite surface than quartz whether Pb2+ ion was added or not. The XPS analysis and first-principle DFT calculations consistently show that Sn4+ ions on the hydrated cassiterite surface exhibit much stronger reactivity towards cupferron adsorption than Si atoms on the hydrated quartz surface, resulting in a remarkable difference between the collecting ability of cupferron towards cassiterite and quartz. This work should shed new light on the discovery of cleaner flotation reagents for cassiterite beneficiation.

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.

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.

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.

This paper presents an efficient COD reduction from sulfide minerals processing wastewater using Fenton process, and the COD of the tailings dam wastewater is largely reduced from 130 mg/L to 30 mg/L, so as to meet the emission limit (COD

Galena (PbS) is an important and abundant source of lead (Pb) metal. It often coexists with other sulphide minerals such as sphalerite (ZnS). Flotation has been extensively used to separate galena and sphalerite. Herein, a reagent scheme comprising aerofloat collectors and Zn2+ and SO32− depressants is developed for the flotation separation of galena from sphalerite-rich sulphide ore. The flotation results demonstrate that Zn2+ and SO32− provide a synergistic depression effect on sphalerite and the aerofloat collectors exhibit more selectivity towards galena. Static calculations and ab initio molecular dynamics simulations were employed to investigate the mechanism of the adopted reagent scheme on galena/sphalerite flotation separation at the atomic scale. The reagent scheme used here has great potential for beneficiating other galena-containing sulfide ores. The calculation and simulation results can help in the design of novel collectors and depressants exhibiting excellent selectivity for the flotation separation of galena/sphalerite.

Benzohydroxamic acid (BHA) has been widely used as the collector for cassiterite flotation, whereas low collecting ability of BHA need to be improved. It is shown through flotation that BHA exhibits weak collecting capacity to cassiterite even in the case of using lead nitrate as the activator, but the superior floatation performances of lead(II)–BHA complexes is observed. The adsorption isotherms of BHA onto cassiterite reveal a higher adsorption density around pH 9 using lead(II)–BHA complexes as the collector. The complexation of lead(II) by BHA has been studied by differential pulse voltammetry. In weak alkaline solution, [Pb(HL)]+ and [Pb(OH)(HL)] species with significantly collecting power are well predominant. Zeta potential studies demonstrate a stronger affinity to the mineral surface of Pb2+/Pb(OH)+–BHA complexes. XPS and FTIR studies indicate that chemisorption with the similar formation of Sn–O–Pb bond is the main interaction between the two kinds of collector and cassiterite.

The flotation response of chalcopyrite and molybdenite when using a novel compound, acetic acid-[(hydrazinylthioxomethyl)thio]-sodium (AHS), as the depressant was investigated through micro-flotation and batch flotation in this study. The depressing mechanisms were studied by means of zeta potential, FTIR and XPS measurements. The micro and bench flotation results indicated that AHS exhibited a strong influence on the depression of chalcopyrite and had little effect on the flotation of molybdenite minerals; these results might be attributed to the significant improvement of the molybdenite/chalcopyrite selectivity index after the addition of AHS. The results of the FTIR spectra, zeta potential and XPS measurements indicated that AHS chemisorbs onto the chalcopyrite surface through its S and N atoms, forming a five-membered cheat ring. A possible depressant mechanism along with a postulated adsorption mode for the surface interaction between AHS and chalcopyrite are provided.

Sphalerite (ZnS), galena (PbS) and pyrite (FeS2) are the important metallic sulphide minerals. These three sulphide minerals are often associated with each other, and large amounts of sphalerite and pyrite are lost in the galena flotation tailings. In this study, the flotation method was employed to recover sphalerite and pyrite from a galena flotation tailing waste. The reagent scheme, including Cu2+ activator and butyl xanthate (BX) collector, can efficiently recover sphalerite and pyrite to obtain a two-mineral mixed concentrate with the Zn and Fe grades of ∼17 % and ∼26 %, respectively, in the sphalerite-pyrite bulk rough flotation. Quicklime (CaO) depressant in combination with BX collector can efficiently separate sphalerite and pyrite to obtain the two products in the sphalerite/pyrite separation rough flotation: the sphalerite concentrate with the Zn grade of ∼33 % and the pyrite concentrate with the Fe grade of ∼36 %. The first-principles calculations were employed to study the interaction mechanism of the adopted reagents in the recoveries of sphalerite and pyrite from the galena flotation tailing. This study provides an important reference for the recoveries of sphalerite and pyrite from similar galena tailings.

The selective separation of molybdenite from chalcopyrite is difficult because of their similar floatability in the presence of a collector. In this study, rhodanine-3-acetic acid (3-Rd) was first applied in molybdenite flotation as a novel chalcopyrite depressant, and its depression effect and mechanism were systematically investigated by flotation tests, density functional theory (DFT) calculation, zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) analysis. Single mineral flotation results indicated that 3-Rd can selectively depress chalcopyrite flotation, whereas its effect on molybdenite is negligible. Mixed mineral and bench flotation tests further proved that 3-Rd is an efficient chalcopyrite depressant. The first-principle periodic calculations based on DFT predicted that 3-Rd prefers to adsorb onto Fe rather than Cu because of the more negative adsorption energy of the COO or CSS group on Fe in the chalcopyrite surface. Zeta potential measurements demonstrated that 3-Rd is adsorbed on chalcopyrite surface more selectively, and its adsorption strength is higher than that on molybdenite surface. XPS analysis further confirmed that 3-Rd is chemisorbed on chalcopyrite surface by binding with Fe active site and is adsorbed on molybdenite surface through hydrogen bonding and electrostatic interactions.

Native starch has a complex molecular structure that limits its ability as a selective depressant in sulfide flotation separations. This research study was conducted primarily to develop a series of starch-based molecules of different molecular weights with the aim of obtaining the most selective depressant of pyrite in chalcopyrite flotation. Five low molecular weight molecules were produced by the oxidative treatment of starch using H2O2 as the oxidant and FeSO4·7H2O as the catalyst. Oxidation treatment resulted in molecular modification of starch, producing low molecular weight molecules of grafted polar groups with increased reaction time. The molecules developed were investigated by microflotation to obtain the most selective and effective depressant for pyrite than chalcopyrite. The optimal and most selective depressant was named tricarboxystarch (sodium salt), also known as TCSS, based on the results of characterization measurements. The inhibitory effect of tricarboxystarch on pyrite was far more selective and effective than native starch. Good selective separation between pyrite and chalcopyrite was achieved by adding tricarboxystarch to a low pH solution. Tricarboxystarch contained three –COOH and several –OH groups in the skeleton, providing excellent depression of pyrite. This study is a basic research that sheds new light on the development and optimization of organic polymers for flotation technology.

In this work, the interfacial microstructures and adsorption mechanisms of benzohydroxamic acid (BHA) on Pb2+-activated cassiterite (1 1 0) surface were investigated by means of Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM) and density functional theory (DFT) calculations. AFM images showed that the roughness value of the natural cassiterite surfaces decreased after the treatment of Pb2+ and BHA with respect to the clean surface. The experimental high-resolution XPS spectra and the DFT calculated spectral lines consistently showed that the major surface species was the Pb-BHA complex on the cassiterite surface. The new peak of N1s at 401.88 eV in the X-ray photoelectron spectroscopy of cassiterite surface treated by BHA showed that BHA could be also chemically adsorbed on the surface. The Raman spectra revealed that the peak around 268 cm−1 should be attributed to the Pb-O bonds in the interface bonding structure of BHA-Pb-O≡. HR-TEM images of the clean, Pb2+ and Pb2+||BHA (adding BHA after Pb2+)-treated interfaces further demonstrated the interfacial microstructures. This work showed a new light on the understanding of the interface adsorption mechanism of flotation reagent and the activation mechanism of metal ion on oxidized mineral.

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.

Metal indium (In) and its alloys have been widely used in semiconductor industries. In a Canadian sulfide ore, metal In mainly occurs as substitutes in stannite and sphalerite, and a sulfide mineral (i.e., roquesite), which accounts for 65% and 20% of the total In, respectively. In this work, the flotation method was adopted to pre-enrich the In in the Canadian sulfide ore due to its low cost, simple operation and high separation efficiency for fine particles. The findings of this research can provide a basis for the pre-treatments of In-bearing sulfide ores.

In this work, the activation mechanism of calcium species on the α-quartz surface was investigated. Microflotation, zeta potential measurements, first-principle calculation based on density functional theory (DFT), time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements and atomic force microscope (AFM) were conducted in this investigation. Sample preparation methods for minerals without a complete cleavage plane and reagent adsorption determination were introduced. Results revealed that quartz could be activated by calcium ions at the pH above 10, and calcium ion concentrations at pH below 10 slightly affected quartz recovery. Ca2+ could repel the hydration shell and hydroxylation on the quartz and be preferentially adsorbed onto the quartz surface at an alkaline pH. However, the coverage thickness and density of Ca2+ and the relevant coverage density of sodium oleate increased as the pH increased. The adsorbed amounts in the horizontal and vertical directions were also not uniform. The surface coverage thickness and density of Ca2+ and the corresponding amount of adsorbed sodium oleate played an important role in the activation of quartz. When the pH was above 10, the thickness and density of Ca2+ coverage on the quartz surface was sufficient, and Ca2+ could subsequently react with sodium oleate forming C18H33O2Ca. Thus, the quartz hydrophobicity was improved.

The depression of pyrite (FeS2) through an organic depressant is not only ineffective but also nonselective which causes poor selectivity. In this research, the depression effect of an organic polymer ‘poly-γ-glutamic acid (γ-PGA, a widely available class of polysaccharides)’ on pyrite flotation was improved by the addition of lime (CaO). The most encouraging flotation results were received at relatively lower concentrations of CaO and γ-PGA. The addition of CaO and γ-PGA had a synergistic inhibitory effect on pyrite flotation with a minor compromise in terms of the chalcopyrite grade at low alkaline conditions (pH 9). Adsorption studies and zeta potential measurements revealed that both CaO and γ-PGA were greatly adsorbed onto the pyrite surface than chalcopyrite. The addition of CaO and γ-PGA underwent a two-step depression effect on pyrite surface: (1) calcium species dissolved from CaO prefrentially adsorbed onto the pyrite surface and decreasing its negative charges; (2) pre-adsorbed calcium hydroxyl species promoted the adsorption of γ-PGA onto the pyrite surface. The XPS and FT-IR measurements revealed that γ-PGA formed the chemical coordination bonds with Ca-species on pyrite surface. Based on these measurement analyses, a two-step depression mechanism of CaO and γ-PGA on pyrite was also proposed. The envisaged scheme has its own benefits of environmental friendliness and cost-effective characteristics in Cu S flotation systems.

In recent years, benzohydroxamic acid (BHA) has been widely used as a selective collector in the flotation of oxide minerals such as scheelite, wolframite, cassiterite and ilmenite despite its moderate collecting ability. Lead nitrate (Pb(NO3)2, LN) is a commonly used activator for improving BHA flotation. According to the classical activation theory, the pre-adsorbed Pb2+ ion can increase the number of active site on oxide mineral surface, thus increasing the subsequent adsorption amount of BHA collector. In this study, BHA and LN were used, for the first time, in the flotation of spodumene, a valuable silicate and major source mineral for lithium battery materials. Interestingly, the adsorption test results show that the adsorption amount of BHA on spodumene surface was the same whether LN was added or not, while the micro-flotation test results show that the addition of LN helped increase the spodumene recovery from 0 to 80% using 120 mg/L BHA at pH 8. These results seem to be contradictory to the classical activation theory, yet by using density functional theory-based first-principle calculations, X-ray photoelectron spectroscopy and atomic force microscopy theoretically and experimentally, their underlying mechanism is therefore revealed. Those results show that in the absence of LN, a “flat” adsorption mode with the benzene ring of BHA parallel to the spodumene surface, is more inclined to a monodentate mode between O2− ion (attached to N) of BHA and surface Al3+ ion, leading to an adsorption energy of −113 kJ/mol. While with the presence of LN, a “vertical” adsorption mode with the benzene ring perpendicular to the spodumene surface, is favored in a bidentate mode between two O2− ions of BHA and Pb2+ ion of pre-adsorbed solvated Pb(OH)+ complex, leading to a much higher adsorption energy of −270 kJ/mol. Based on coordination chemistry analysis, differences in the adsorption mode and energy of BHA on Pb2+-activated and unactivated spodumene surfaces can be explained by differences in coordination number and bond dissociation energy. This study will provide valuable insights into the activation of Pb2+ ion in BHA flotation of valuable silicate minerals, and help to enrich understanding of activation mechanisms of metal ions in anionic collector flotation of minerals.

Quartz, a common gangue mineral, often coexists with the Ca-containing minerals in natural ore deposits, such as scheelite, apatite, fluorite and calcite. The depression of quartz in the flotation separation of these minerals is normally difficult, especially when the surface of the quartz is activated by Ca2+ ions dissolved from the calcium-bearing minerals. Thus, the search for an efficient depressant for Ca2+-activated quartz is urgent. In this study, citric acid (CA) was employed as a depressant for Ca2+-activated quartz. Microflotation results showed an improved depression efficiency of CA for the sodium oleate flotation of Ca2+-activated quartz. The depression mechanism of CA was evaluated through combined experimental and computational techniques, including zeta potential measurements, adsorption tests, Fourier transform infrared and X-ray photoelectron spectroscopy analysis, solution chemistry analysis, and density functional theory-based first principle calculations.