Alkaline Sulfide Solutions Research Articles

Selective recovery of antimony from Sb-bearing copper concentrates by integration of alkaline sulphide leaching solutions and microwave-assisted heating: A new sustainable processing route

The technical feasibility of leaching antimony from an antimony-bearing copper sulphide concentrate, using alkaline sulphide solutions and microwave-assisted and non-assisted heating technology, is investigated at a laboratory scale. The leaching test examines the influence of selective leaching reagent (Na2S and NaOH) concentrations, solid/liquid ratio, and temperature. The results indicate that antimony dissolution is highly selective (e.g. only Sb and As are leached), depending on the concentrations of leaching reagents and the leaching temperature. The influence of temperature on the mineral's dissolution, in the range 25–140 °C, is analysed from a thermochemical point of view using equilibrium databases. Under the optimal conditions: leaching agent: 250 g/L Na2S, 60 g/L NaOH, 2 h, 140 °C, with microwave assisted, the leaching efficiency of Sb reached 95.7 %. The antimony content in the copper concentrate is successfully reduced from 1.1 wt% to <0.2 wt% Sb, making it suitable for copper concentrate metallurgical processing. The study demonstrates that increasing temperature and NaOH/Na2S concentrations collectively enhance leaching efficiency, with a statistical significance, reducing both leaching time and the required temperature, compared to non-microwave-assisted leaching. Furthermore, it is established that excess free hydrogen sulphide ions ensure the efficient dissolution of the main impurities associated with penalties, such as antimony and arsenic, with limited copper and iron dissolution from the copper concentrate, predominantly chalcopyrite. Finally, an integrated hydrometallurgical process flowsheet for antimony removal and recovery from a sulphide copper concentrate is proposed.

Mechanisms of passivation and chloride-induced corrosion of mild steel in sulfide-containing alkaline solutions

The pore fluid within many concretes is highly alkaline and rich in reduced sulfur species, but the influence of such alkaline-sulfide solutions on the surface film formed on steel reinforcement is poorly understood. This study investigates the critical role of HS− in defining mild steel passivation chemistry. The surface film formed on the steel in alkaline-sulfide solutions contains Fe(OH)2 and Fe–S complexes, and the critical chloride concentration to induce corrosion increases at high sulfide concentration. However, this behavior is dependent on the duration of exposure of the steel to the electrolyte, and the nature of the sulfidic surface layer.

Selective leaching of antimony from tetrahedrite rich concentrate using alkaline sulfide solution with experimental design: Optimization and kinetic studies

Antimony dissolution from tetrahedrite concentrate obtained from froth flotation experiments was investigated with Na2S-NaOH as lixiviant agent. Min. Run Res. V and CCD methods were applied for the first time, to identify and optimize the effects of Na2S concentration, NaOH concentration, stirring speed, leaching time, temperature and solid percent on antimony recovery. Temperature was identified as a key factor for antimony dissolution while stirring speed and Na2S concentration slightly affected it. Kinetic studies demonstrated that antimony dissolution data fit well to the chemically controlled shrinking core model ([1−(1−α)13]=7.95×105×exp(−61.94RT)×t) with Ea=61.94 kJ.mol.−1, A=7.95 × 105 min.−1 and R2=95.65%. Maximum antimony recovery was obtained 29.52% under optimal conditions as: stirring speed of 495.8 rpm, Na2S concentration of 151.52 g/l, leaching temperature of 89.92 ○C, solid percent of 0.3%, leaching time of 60 min and NaOH concentration of 60 g/l. Moreover, leaching residue observations proved the formation of insoluble covellite and chalcocite minerals during antimony dissolution.

Optimization of Alkaline Sulfide Leaching of Gold-Antimony Concentrates

This article covers a hydrometallurgical method for processing of a gold-antimony flotation concentrate in alkaline sulfide solutions. Thermodynamic analysis of the reaction stibnite with sulfide sodium and sodium hydroxide was performed. The chemical and phase compositions of the investigated material, mainly represented by compounds of antimony, silicon, calcium, sulfur and iron are studied. Phase composition: quartz, stibnite, quicklime, pyrite, dolomite and arsenopyrite. The dependences of the influence of sulfide sodium and sodium hydroxide concentration, and the liquid to solid ratio on antimony extraction into solution were determined by methods of mathematical experiment planning. The calculated values ​​of the determination coefficients testify to the adequacy of the chosen two-level model. The optimum parameters of the process were obtained: L/S ratio = 4,5; the nitric acid sulfide sodium concentration was 61.09 g/L; sodium hydroxide concentration was 16.47 g/

A review of gold extraction using noncyanide lixiviants: Fundamentals, advancements, and challenges toward alkaline sulfur-containing leaching agents

Alkaline sulfur-containing lixiviants, including thiosulfate, polysulfides, and alkaline sulfide solutions, stand out as a promising class of alternatives to cyanide because of their low toxicity, high efficiency, and strong adaptability. In this paper, we summarized the research progress and remaining challenges in gold extraction using these noncyanide reagents. After a brief introduction to the preparation method, the transformation process of various sulfur-containing species in alkaline solutions was discussed. Thereafter, some insights into the mechanism of gold leaching in alkaline sulfur-containing solutions were presented from different aspects, including thermodynamics analysis, electrochemical dissolution, and leaching kinetics. Moreover, recent progress in in-situ generation of sulfur-containing anions from gold-bearing sulfide minerals was outlined as well. Gold passivation caused by sulfur species was discussed in particular because it is considered the greatest challenge facing sulfur-containing leaching systems. Alkaline sulfur-containing lixiviants are expected to serve as alternatives in industrial applications of gold extraction, particularly for refractory gold ores containing copper and carbonaceous matter.

The influence of sulphide, bicarbonate and carbonate on the electrochemistry of carbon steel in slightly alkaline solutions

The influence of sulphide on the electrochemistry of carbon steel in neutral to slightly alkaline sulphide solutions was investigated using electrochemical and surface analytical techniques. Small concentrations of sulphide were found to promote anodic dissolution as FeII carbonate complexes and to destabilize FeIII oxides leading to the loss of passivity, especially at pH ≤ 9. The dominant phase formed was mackinawite, while reactions between FeIII and sulphide led to the formation of oxidized S species (elemental Sand sulphate), polysulfides, and pyrite.

Fundamental Electrochemical Behavior of Antimony in Alkaline Solution

Even though electroplating has been applied to extract antimony from the relevant mines, such as stibnite (Sb2S3) and valentinite (Sb2O3), there are still some unclear points which need to be clarified: in alkaline sulfide solution, S2− can help increase the solubility of Sb(III) ions. In the present study, cyclic voltammetry (CV) and chronoamperometry (CA) tests were employed to investigate the electrochemical behavior of antimony ions in KOH solution (20 wt%), and the results revealed that Sb(III) ions have much higher electrochemical activity than Sb(V) ions. However, Sb(V) ions are not completely inactive at the potential before H2 evolution reaction, as previous studies reported, and part of Sb(V) ions can be electroplated in the KOH solution. The contradictions between the present and previous studies are due to the impurity caused by Sb(III) ions, which are speculated to play a role in Sb(V) ion reduction. Ions such as As3+, Si4+, CO32−, Al3+, and Sn2+ show no interference on the electroplating of antimony. Other electrochemical and chemical behaviors are clarified in this study as well: (1) the Sb(III)/Sb(0) couple is more electrochemically reversible at the interface of antimony metal/KOH solution than that at the interface of a glass carbon/KOH solution; (2) in a sulfide alkaline solution system, S2− ions can coordinate with Sb(III) ions and lower the reduction potential of Sb(III) ions to antimony metal, thus leading to a lower current efficiency of antimony electroplating. The reducing reagents, including KI, K2SO3, and KBH4, can reduce Sb(V) ions to Sb(III) ions in an acid solution, but these chemical reduction reactions cannot happen in the KOH solution. These fundamental studies can provide knowledge on antimony refining from the relevant secondary resources.

Investigation of Hydrogen Production from Alkaline Sulfide Solution with Nanosized CdS/ZnS-PdS Photocatalyst of Various Compositions

Hydrogen sulfide is highly toxic to humans and harmful to the environment. On the other hand, H₂S is produced in large quantities in some industrial processes like the refinery of crude oil and the sweetening of natural gas. Nowadays, H₂S is usually burned to sulfur and water in the Claussprocess wasting the energy of hydrogen stored in H₂S. Progress in the area of photocatalysis results in considerable development of the heterogeneous photocatalytic conversion of hydrogen sulfide into hydrogen gas. In this work, photocatalytic hydrogen production from alkaline sulfide solutions was investigated, utilizing various ZnS/CdS composites modified with PdS as cocatalyst. The highest photocatalytic activity was found at 1:1 molar ratio of CdS and ZnS. At this catalyst content the optimal PdS-loading was investigated in the range of 0-0.4% (n/n); the 0.05-0.10% (n/n) PdS content proved to be most efficient. The catalyst consisted of the agglomerates of 80-150 nm size particles. During long time illuminations (10 days) the size of the agglomerates increased, but the diameter of the individual particles and the photocatalytic activity did not noticeably change. The dependence of the rate of hydrogen production on the concentration of sulfide, sulfite, and thiosulfate ions was also studied. An increase of the amount of reactants resulted in an enhancement of the reaction rate, while the presence of thiosulfate ions lowered the catalytic activity. One of the possible reasons of this effect is the side reaction of thiosulfate ions by the conduction band electrons.

Leaching kinetics of tellurium-bearing materials in alkaline sulfide solutions

ABSTRACTLeaching of tellurium from tellurium-bearing materials is of significant importance. A novel alkaline sulphide leaching process for tellurium-bearing materials was developed. It was found that 94.92% of tellurium and 95.70% of antimony were extracted under optimum conditions: 200 g/L of Na2S concentration, 80 °C of temperature, 10:1 mL/g of L/S and 60 min of leaching time. The kinetic data for the dissolution of tellurium and antimony followed the Avrami equation. The calculated activation energies indicated that tellurium dissolution was controlled by the mixed regime of both the diffusion and chemical reaction, while antimony dissolution was controlled by chemical reaction.

Antimony(III) sulfide complexes in aqueous solutions at 30 °C: A solubility and XAS study

Stibnite solubility experiments and ambient temperature X-ray absorption spectroscopy (XAS) measurements of antimony in solution were undertaken to determine the aqueous speciation of Sb(III) in sulfide solutions having reduced sulfur concentrations from 0.001 to 0.1molkg−1S2−total over the pH range of 3.5 to 12. At 30°C, stibnite solubility curve was defined by a scheme of five species: Sb2S42−, HSb2S4−, H2Sb2S52−, H3SbS2O, and Sb(OH)3(aq). Equilibrium constants were determined for the following heterogeneous solubility reactions:Sb2S3s+HS−⇋Sb2S42−+H+Sb2S3s+HS−⇋HSb2S4−Sb2S3s+2HS−⇋H2Sb2S52−0.5Sb2S3s+0.5HS−+1.5H++H2Ol⇋H3SbS2O0.5Sb2S3s+3H2Ol⇋SbOH3aq+1.5HS−+1.5H+The Sb K-edge XAS measurements of antimony in alkaline (pH=10.9 to 12) sulfide solutions gave average first shell coordination environments for strongly alkaline solutions that were consistent the speciation model derived from solubility experiments (i.e., Sb2S42− and Sb(OH)3(aq)). XAS data enabled the elimination of a speciation model involving only Sb-S monomers at strongly alkaline pH. Antimony speciation in near neutral to strongly alkaline pH's is dominated by dimeric antimony sulfide complexes at sulfide concentrations>0.001molkg−1S2−total. Calculations of stibnite solubility and aqueous antimony speciation for conditions in anoxic marine basins indicate that sulfide species comprise a significant part of the total dissolved Sb(III) when molkg−1S2−total>~0.00005molkg−1 and that stibnite is close to saturation in some anoxic basins.

Incorporating a molecular co-catalyst with a heterogeneous semiconductor heterojunction photocatalyst: Novel mechanism with two electron-transfer pathways for enhanced solar hydrogen production

Photocatalytic hydrogen production is considered to be a promising solution to the global energy crisis and to environmental pollution caused by fossil fuel consumption. In the present study, a core/shell cadmium sulfide/zinc oxide (ZnO/CdS) semiconductor heterojunction photocatalyst is used with a cobalt–salen molecular co-catalyst for highly enhanced photocatalytic activity. CdS nanorods were synthesized using a simple solvothermal method and a ZnO shell was grown by a solution deposition method. Under optimum conditions, the system exhibited a H2 evolution rate of 725µmolh−1mg−1 with a turnover number of ∼102,700 and excellent stability over 50h in the presence of Na2S/Na2SO3 as the electron donor under visible light. The highest apparent quantum yield of the system was 44% under monochromatic 420nm light. The formation of ZnS during photocatalysis was proved due to surface dissolution of ZnO in alkaline sulfide solution. ZnS can enhance the photocatalytic activity of ZnO/CdS nanorods by providing increased charge transfer interfaces. The molecular cobalt co-catalyst also contributed to the enhanced activity by accepting the photogenerated electrons from the semiconductor photosensitizer. The proposed mechanism suggests that the photogenerated electrons in CdS are transferred not only to ZnO but also to the molecular co-catalysts, leading to highly improved photocatalytic activity for H2 production.

Recovery of tellurium from high tellurium-bearing materials by alkaline sulfide leaching followed by sodium sulfite precipitation

A novel process of tellurium recovering from high tellurium-bearing materials by alkaline sulfide leaching followed sodium sulfite precipitation is developed. The influences of Na2S concentration, leaching temperature, liquid to solid ratio and leaching time were studied during the leaching process while the effects of Na2SO3 excess coefficient, reduction temperature and reduction time on tellurium precipitation from alkaline sulfide solutions were investigated. It was found that 91.24% of Te and 92.51% of Sb were extracted into leaching solution under the optimum conditions: Na2S concentration 100g/L, 80°C of leaching temperature, 10:1mL/g of liquid to solid ratio and 60min of leaching time. 98.85% of Te was precipitated selectively at 30°C for 15min with addition of 1.5-fold excess of Na2SO3 while the antimony precipitation was closed to zero. XRD pattern and chemical analysis indicated that the precipitate was elemental tellurium with a purity of 99.11%. SEM image showed that the shapes of elemental tellurium were spindle with an average particle size of 1–2μm. Antimony in Te-free solution was recovered as NaSb(OH)6 by hydrogen peroxide oxidation.

Corrosion behavior of HVOF sprayed hard face coatings in alkaline-sulfide solution

The paper focuses on the corrosion behavior of high velocity oxygen fuel (HVOF) sprayed WC-17Co, WC-10Co-4Cr, Cr3C2-25NiCr coatings in alkaline-sulfide solution (S2−, 0.2ml/L, pH=10). Eighteen days of immersion test is carried out and corrosion rate analysis shows that the Cr3C2-NiCr coating of low porosity exhibits the best corrosion resistance. In alkaline-sulfide solutions, porosity, passive film and microgalvanic between hard phase and binder phase have significant effect on the corrosion behavior of coatings. The corrosion mainly occurs in binder phase from SEM, though WO3, WS2, Cr2S3 are detected in XPS. In WC-17Co coating, the binder phase Co transforms to Co oxides and serious corrosion can be observed in binder phase. WC-10Co-4Cr coatings suffer localized corrosion since galvanic corrosion occurs between locations with different solubilities of W in Co binder. Cr3C2-25NiCr coating shows slight corrosion with the formation of NiS/Ni2O3/Cr2O3from the binder and Cr2S3 from the hard phase. The results are verified by the polarization curves, which show the longest passive region and lowest Icorrosion of Cr3C2-25NiCr coating.

Corrosion behavior of 316L stainless steel anode in alkaline sulfide solutions and the consequent influence on Ga electrowinning

During Ga enrichment by ion exchange, sodium sulfide is an indispensable compound to elute Ga (III) from resin. The effects of residual S2− ions on the corrosion behavior of stainless steel anode and Ga electrodeposition are studied. It is found that 316L stainless steel anode is corroded seriously and Ga is hardly electrodeposited in the presence of 2.17g/L S2−. The adsorption of HS− ions damages the passive film of anode surface, which leads to the formation of soluble and colloidal (NaFeS2)n. After 48h electrowinning, the weight loss of stainless steel anode (7.38mg/cm2) in Ga solution with 2.17g/L S2− is much larger than that (0.23mg/cm2) in solution without S2−. Green-black precipitates are found in Ga (III) solution due to the degradation of colloidal (NaFeS2)n. Meanwhile, the corrosion of stainless steel anode brings iron ions into Ga (III) solution. Iron species are deposited or absorbed on the cathode, which is unfavorable to Ga electrodeposition. At lower S2− concentration, both Fe and O are detected in Ga coatings. When S2− concentration is up to 2.17g/L S2−, Ga electrodeposition is completely inhibited.

The corrosion resistance of Ni anode and Ga electrowinning in alkaline sulfide solutions

In this paper, a nickel anode was used for Ga electrowinning in the presence of S2- ions. The corrosion resistances of nickel and stainless steel electrodes in alkaline solutions of S2- were studied by cyclic voltammetry, XPS, and weight loss measurements. Ga electrowinning was carried out in Ga solutions with high concentrations of S2- at different current densities and NaOH concentrations. The results indicated that the nickel anode showed better corrosion resistance than the stainless steel anode. The corrosion rate of nickel was much lower than that of stainless steel due to the formation of stable passive films consisting of Ni oxide and hydroxide. The corrosion rate of the nickel anode was only 0.28 mg cm(-2) after 48 h electrowinning in the presence of 5 g L-1 S2- ions. The corrosion resistance of the nickel anode was almost independent of the NaOH concentration and the current density. When the nickel anode was used for Ga electrowinning, the current efficiency (QE) decreased in the presence of S2- owing to the reduction of the incomplete oxidation products of S2- on the cathode. The complete oxidation of S2- to SO4 (2-) was accelerated on the nickel anode, which lowered the concentrations of S2- and that of its incomplete oxidation products in solution. Bright, high-purity metallic gallium was obtained when using the nickel anode, even in Ga(III) solutions of 5 g L-1 S2-. Therefore, nickel was a suitable anode material for Ga electrowinning in Ga solutions of S2- ions.

Improved surface and electrical properties of passivated GaSb with less alkaline sulfide solution

The surface quality of HCl-etched and ammonium sulfide [(NH4)2S]-based treated bulk n-GaSb(100) were compared using x-ray photoelectron spectroscopy (XPS) and TOF-SIMS. It has been found that native oxides present on the GaSb surface are more effectively removed when etched with concentrated HCl solution. With additional [(NH4)2SO4+S] substances or hydrogen ions in the passivation solution, the treated samples displayed significant reduction of native oxides and formation of the sulfides compared with pure (NH4)2S solution. The treated samples also result in a noteworthy improvement in the current–voltage (I–V) characteristics of Au/n-GaSb Schottky contacts, as evidenced by the lower ideality factor (n), higher barrier height (Φb) and higher rectification ratio at ±0.2V. The I–V measurement provided definitive confirmation of XPS and TOF-SIMS results, establishing the need for less alkaline solution for greater passivation stability.

Leaching kinetics of enargite in alkaline sodium sulphide solutions

Leaching of enargite samples containing approximately 12% As, 0.5% Sb and 39% Cu was studied in alkaline sulphide solutions containing sodium hydroxide and sodium sulphide. Kinetic parameters studied included temperature, particle size, reagent concentration, agitation rate and stoichiometry in high pulp density experiments. The extraction of arsenic was chemical reaction controlled with an activation energy of 74kJmol−1, indicating the importance of temperature on the process. The relative contributions of total initial sulphide and hydroxide concentrations on leaching kinetics were determined and a new rate equation was developedrAs=−dAsdt=k'As2.37S2−1.83OH−3.31,kgt−1h−1where k′ depends on system activation energy and can be predicted from this parameter (it had a value of 1.63×10−3 in this work). This rate equation was validated against data presented in other similar studies of enargite leaching. It is demonstrated that the hydroxide ion plays a direct role in the leaching reaction, rather than simply ensuring adequate sulphide speciation. Copper, iron, zinc, and silver were not extracted during the leaching procedure. Through chemical analysis, X-ray diffraction and scanning electron microscopy leach residues were characterised. Residues contained copper–sulphur compounds such as digenite, bornite and sodium copper sulphide (NaCu5S3).

Process flowsheet development for recovering antimony from Sb-bearing copper concentrates

The technical feasibility, on laboratory scale, of hydro- and electrometallurgical processes of recovering metallic antimony from an antimony-bearing copper sulphide concentrate has been investigated. The influence of Na2S concentration, temperature and solid concentration was studied during the leaching test while the effect of current density, Na2S concentration, electrolyte temperature and NaOH concentration on antimony electrowinning from alkaline sulphide solutions was investigated. The leaching results showed that antimony dissolution is strongly dependent on the concentration of the leaching reagent as well as the leaching temperature. The antimony content in the concentrate was reduced from 1.7% to less than 0.1% Sb which is desirable for copper metallurgy. Cathode current efficiency is one of the important parameters to evaluate the performance of an electrolytic process. It is revealed in this study that current efficiency of antimony deposition from sulphide electrolytes is highly dependent on the concentration of sodium hydroxide and the current density used. The results illustrate that the combined effect of increasing anode current density (which was 10times higher than the cathode current density) and NaOH concentration enhanced the current efficiency of the electrolytic process. It was demonstrated that excess free sulphide ions impacts the current efficiency of the process detrimentally. An integrated hydro-/electrometallurgical process flowsheet for antimony removal and recovery from a sulphide copper concentrate was developed.

Initial stages of corrosion pits on AISI 1040 steel in sulfide solution analyzed by temporal series micrographs coupled with electrochemical techniques

Abstract This work presents a study of the initial instants in the pitting corrosion of AISI 1040 steel, analyzed by temporal series micrographs coupled to an open circuit potential (Eoc) and polarization curves. During the Eoc measurement, the pit induction time and the initial pit growth in MnS inclusions was detected in alkaline sulfide solution. The pit area behavior has two distinct rate of area changes in specific regions directly associated to current slope changes. Finally, it was possible to create a three-dimensional model of the pit depth evolution on the metal, using Faraday’s law and the bullet-shaped geometry.

Effect of Chloride Ions on Corrosion and Stress Corrosion Cracking of Duplex Stainless Steels in Hot Alkaline-Sulfide Solutions

The resistance of commercial duplex stainless steels (DSS) UNS S32205 and UNS S32101 to corrosion and stress corrosion cracking (SCC) has been studied using immersion tests and slow strain rate tests (SSRT) in hot alkaline-sulfide solution, with and without chloride ions, at 170°C. Weight-loss coupons of austenitic, superferritic, and DSS alloys were used to study the influence of alloy composition. SCC susceptibility of UNS S32205 and S32101 was evaluated in 150 g/L sodium hydroxide (NaOH, 3.75 M) and 50 g/L sodium sulfide (Na2S, 0.64 M) with 0 to 100 g/L sodium chloride (NaCl, 0 to 1.7 M) at 170°C, using SSRT at an initial strain rate of 2 × 10−6 s−1. The results indicate that there is a complex relationship among the chloride concentration, alkalinity, and percent sulfidity of the solution and behavior of the stainless steels. Corrosion resistance of the ferrite phase of DSS was superior to the austenite phase in chloride-containing solutions, which had an important role in SCC initiation. Crack initiation in the austenite phase and at austenite-ferrite phase boundaries of DSS was enhanced by the presence of chlorides. These findings demonstrate that chloride ions have an important role in the corrosion and SCC susceptibility of DSS in hot alkaline-sulfide solutions.