Sulfide Ions In Solution Research Articles

Effect of sulfide and hydroxide on the removal of heavy metal ions from hydrometallurgical zinc effluent

ABSTRACT Heavy metals removal from Specialized Industrial Park of Zinc of Zanjan effluent was tested using sulfide, hydroxide, and the combination precipitation. The initial effluent includes 200 ppm of zinc, 55 ppm of cadmium, 113 ppm of manganese, 0.85 ppm cobalt, 0.65 ppm nickel, 0.2 ppm iron, and 0.55 ppm lead. Sulfide precipitation using Na2S as a sulfide source is inefficient in the precipitation of manganese except in high concentrations of sulfide, while hydroxide precipitation using lime is not successful in cadmium removal. Combining these two methods in one and two steps is helpful in the precipitation and settling of all heavy metal ions. The optimum temperature, pH, sulfide concentration, and time were determined. The concentration of zinc, cadmium, manganese, cobalt, nickel, and iron were reduced to 0.1, 0.1, 0.14, 0.23, 0.19, and 0.16 ppm, while lead was not detected in the solution in optimum condition. The experiments were repeated for effluent with higher amounts of lead, iron, and nickel, and its success in efficient removing of these ions is also confirmed. Scanning electron microscope (SEM) images and X-ray diffraction (XRD) patterns were used to study morphologies and structures of precipitation. The concentration of Na2S plays a crucial role in removal efficiency. Excess sulfide causes the increment of ions such as manganese in the solution and decrements the efficiency discussed in this research. The lower use of lime, almost no excess sulfide ions in solution, fast kinetics, and precipitating of a wide range of metal ions are some advantages of this method.

Can hydrogen sulphide gas be produced during alkaline leach of enargitic copper concentrates?

The usual answer to the question stated in the title of this manuscript would be a definitive no due to the high stability of dissolved sulphide ions in water under strong alkaline conditions; nevertheless, experimental results presented in this research shows the opposite. Two arsenic-bearing copper concentrates coming from two different Chilean mine sites were used to carry out alkaline sulphide leach experiments. One of them (Concentrate 1) exhibits a P80 of 45 μm and 3.8% arsenic while the other (Concentrate 2) has a P80 of 98 μm and 2.3% arsenic. The arsenic extractions at 60 and 90 °C after 2 h reaction for concentrates 1 and 2 are around 10 and 80% and 14 and 93%, respectively.More relevantly, notwithstanding the strong alkaline conditions used in the experiments, the production of toxic hydrogen sulphide gas was detected and measured in tests performed at 90 °C. The molar ratio between the arsenic leached and the formation of hydrogen sulphide is 20:1 and 5:1 for concentrate 1 and 2, respectively. Stoichiometric computations associated to the mechanisms of carbonation of alkaline solutions and to the thermodynamic predominance of H2S at high pH values cannot fully explain the significant quantity of gas formed during the leaching process. One hypothesis to explain the formation of the gas is mineralogy related. It involves the occurrence of specific parallel secondary reactions taking place at the solid-liquid interface triggering the increase of the local acidity and producing the gas. Due to the high concentration of sulphide ions in solution and the high temperature conditions, the gas is not fully scrubbed by the strong alkaline solution. Looking at the mineralogy of the gangue material in both concentrates, the mass ratio of the gas produced between both concentrate matches the mass ratio of galena, haematite, goethite and kaolinite present in both concentrates suggesting that these minerals would be responsible for producing the gas. Reactions associated to each one of the mentioned species are presented suggesting two different mechanisms for local acidification. This finding would have a strong impact on the implementation of the process at large scale safety-wise.

Synthesis of bovine serum albumin-protected high fluorescence Pt16-nanoclusters and their application to detect sulfide ions in solutions

Highly fluorescent (quantum yield, QY = 17%) Pt16-nanoclusters (Pt16-NCs@BSA) have been prepared via a one-step ultrasonic-assistance method by using cheap and easily available ascorbic acid as reductant and bovine serum albumin (BSA) as a stabilizing agent in aqueous solution. The fluorescence properties of the Pt-NCs@BSA can be easily controlled by optimizing conditions, and the products are extremely stable and could be used for the detection of sulfide ions (S2−) in solutions as a specific luminescence sensor. The present synthesis method is performed in one step, being cost-effective with a particularly short reaction time, which could be extended to the synthesis of other kinds of protein-protected Pt-NCs.

Development of semi-industrial synthesis of calcium polysulfide solution and determination of the content of sulfide ions in solution

Semi-industrial synthesis of a calcium polysulfide solution, a good demercurizing reagent in the technology for utilization of mercury-containing wastes, was developed. The development of a technology for utilization of wastes of this kind with the use of a calcium polysulfide solution is primarily associated with choosing the Hg: CaS n ratios. The Hg: CaS n ratio was found from the concentration of sulfide ions in the CaS n solution because the composition of the CaS n solution, where n = 4–6, is not constant. A photocolorimetric method was developed for determining the concentration of sulfide ions in the CaS n solution. The method was used for rapidly finding the content of sulfide ions in the CaSn solution on batches of industrial solutions in refinement of the technology for waste demercurization. The results obtained in determining the content of sulfide ions in a CaS n solution were confirmed by the independent titrimetric method.

Kinetics of silver electrodeposition from thiocarbamide solutions at a regular surface coverage with sulfide ions

Kinetics of silver electrodeposition in the presence of sulfide ions is studied on electrodes renewed by cutting off a thin surface layer, at a controlled time of contact of the “fresh” surface with the electrolyte. Solutions containing 10−2 M AgNO3, 0.1 M thiocarbamide, 0.5 M HClO4, and from 2 × 10−6 to 1.5 × 10−5 M Na2S are studied. It is shown that under the studied conditions, the effect of silver electrodeposition on the surface concentration of sulfide ions is insignificant. As the concentration of sulfide ions in solution and their coverage on the electrode surface θ increase, the cathodic polarization decreases. Tafel curves plotted for θ = const are used in estimating the exchange current i0 and the transfer coefficient α. It is shown that α ≈ 0.5 and weakly depends on θ, whereas the exchange current increases with the increase in θ by an approximately linear law from 10−5 A/cm2 at θ ≅ 0 to 10−4 A/cm2 at θ = 0.43. The obtained data are compared with the results of kinetic studies of silver anodic dissolution in similar solutions.

The effect of sulfide minerals on the leaching of gold in aerated cyanide solutions

The effect of galvanic interactions and sulfide mineral dissolution on the gold leaching kinetics in aerated cyanide solutions is investigated. Gold leaching kinetics were measured using a rotating electrochemical quartz crystal microbalance (REQCM), which measures the leaching rates in-situ. When the mineral is electrically in contact with gold, the gold dissolution rate increases as a result of the extra surface area available for oxygen reduction. However the leaching behavior of gold in the presence of soluble sulfide minerals is complicated. It is shown that the formation of sulfide ions in solution results in the passivation of the dissolution of gold. The addition of lead was found to be an effective means of alleviating this problem, as lead promotes the removal of sulfide by precipitation as PbS.

Anodic behavior of gold in acid thiourea solutions: A cyclic voltammetry and quartz microgravimetry study

It is shown that at potentials E 100 μA cm−2) starts at E ≥ 0.65 V, with the primary process being the oxidation of thiourea, which gives rise a current peak at E ≃ 1.0 V. The thiourea oxidation at E ≥ 1.1 produces the appearance of catalytically active species, which drastically accelerate the gold dissolution process in the potential region extending from a steady-state value to 0.6 V, where the current efficiency for gold approaches 100% and a peak emerges at E ≃ 0.55 V. The peak’s height is commensurate with the value of the limiting diffusion current associated with the ligand supply. The species in question make no discernible impact on the thiourea oxidation process. Formamidine disulfide, which forms during the anodic oxidation of thiourea or which is added in solution on purpose, exerts no noticeable catalytic influence on the anodic gold dissolution. The catalytically active species is presumably the S2− ion, product of decomposition and deep oxidation of thiourea and formamidine disulfide. Indeed, adding sulfide ions in solution has a strong catalytic effect on the gold dissolution, whose character is identical to that of the effect exerted by products of anodic oxidation of thiourea at E ≥ 1.1 V μA cm−2.

An electrochemical study of the effect of lead and sulphide ions on the dissolution rate of gold in alkaline cyanide solutions

The presence of impurities in cyanide solutions may either accelerate or retard the dissolution of gold within the potential range typically encountered in conventional gold leaching, i.e. from −600 to 0 mV (SCE). By using potentiostatic and potentiodynamic techniques, it was found that lead species in solution increased the dissolution rate of gold from E corr up to approximately −380 mV (SCE); in contrast to this, sulphide species decreased the dissolution rate of gold and also counteracted the accelerating effect of lead species. At more positive potentials, sulphide species accelerated the dissolution of gold. It is therefore possible to increase the dissolution rate of gold in cyanide solutions containing small amounts of sulphide by maintaining more oxidizing conditions on the gold surface. This finding may be put to practical use in the treatment of sulphide concentrates for which the gold leaching rate should be enhanced by increasing the oxygen concentration while the presence of sulphide ions in solution should prevent passivation of the gold at the higher potentials that would typically be obtained for these conditions.

Influence of sulphide ions on the cathodic behaviour of copper in 0.1 M borax solution

The presence of sulphide ions in solution greatly influences the cathodic behaviour of copper in borax solutions (pH9.2), even when this contaminant is in low concentration. Cyclic voltammograms, polarisation curves and Tafel plots are compared for polluted and unpolluted solutions. Prereduced and aged copper electrodes are investigated. The presence of sulphide ions in solution increases the rate of oxygen reduction on copper, thus having a detrimental effect on the global corrosion process. The transformation of the surface film into one with better conductive properties is suggested.

Oxidation of hydrosulphide ions on gold Part I: A cyclic voltammetry study

The results of an investigation to determine the mechanism(s) of oxidation of sulphide ions on a gold electrode are discussed. The cyclic voltammetry results are presented in Part I and characterization results after various electrochemical pretreatments are to follow in Part II. The cyclic voltammetry studies show that several stages are involved in oxidation of sulphide ions to form elemental sulphur. Initially, sulphide ions undergo underpotential deposition to form chemisorbed sulphur as isolated atoms. As oxidation proceeds, a monolayer of chemisorbed atoms is formed which reacts with sulphide ions in solution to form polysulphides at higher potentials. As the potential for oxidation is further increased elemental sulphur is produced. The reduction of polysulphide to hydrosulphide ions occurs by a 2-electron transfer process whereas the reduction of elemental sulphur occurs by a l-electron transfer process. The latter reaction involves the formation of an activated complex which is a relatively slow process.

Role of sodium sulfide in the flotation of oxidized copper, lead, and zinc ores

This paper reviews uses of sodium sulfide in the flotation of oxide minerals of copper, lead, and zinc. The activation and depression effects of sodium sulfide are of particular importance because of their applications with oxidized lead and copper ores. In spite of its industrial importance, the nature of the heterogeneous reactions between sulfide ions in solution and the surface of oxidized minerals has not been fully understood. Hence, proposed mechanisms of the sulfide action in flotation, methods of measuring and monitoring sodium sulfide in flotation pulps, and variables influencing the sulfide addition are analyzed. Recent studies on sodium sulfide addition to flotation pulps, monitoring its concentration, and the optimum dosage control using platinum and/or sulfide specific ion electrodes are discussed.

Use of Reactive Iron Oxide To Remove H2S From Drilling Fluid

During a gas kick in a Wyoming wildcat well, blowout prevention procedures were complicated by equipment failure and the presence of H2S. This paper describes the use of a specially prepared magnetic iron oxide to remove the H2S chemically from drilling fluids. This mud treatment protected the drillpipe from corrosion and prevented the release of toxic gases, allowing the well to be killed successfully. Introduction Drilling a well in an area where gas containing hydrogen sulfide (H2S) can escape poses grave risks. The complications of dealing with H2S at the surface, as indicated by Goolsby, emphasize the importance of good blowout prevention procedures and of precipitating out any H2S entering the wellbore. The combination of treating the drilling fluid with NaOH to absorb H2S and with zinc compounds to precipitate H2S has proven successful. The combined treatment has disadvantages, particularly the relatively large quantities of treating particularly the relatively large quantities of treating chemicals required and the harmful effects on drilling fluid properties, especially those of low-solids, nondispersed polymer muds. These disadvantages encouraged us to search for an alternative sulfide scavenger. Reactions H2S reacts with water and is extremely destructive to steel. Typically, in basic drilling fluids, H2S is neutralized by this reaction: H2S + NaOH NaHS + H2O This reaction theoretically requires 1.174 kg NaOH to neutralize each kilogram of H2S. The reaction is essentially complete at pH higher than 9, but lowering the pH below 9 would allow free H2S to escape.Zinc carbonate reacts with sulfide ions in solution to form insoluble zinc sulfide: ZnCO3 + NaHS ZnS + NaHCO3 This reaction theoretically requires 3.679 kg zinc carbonate to precipitate each kilogram of H2S. Zinc sulfide (wurtzite or sphalerite) has a specific gravity of about 4.0. Commercial zinc compounds are either basic zinc carbonate, which contains up to 50 wt% zinc, requiring 3.8 kg material to precipitate each kilogram of H2S, or organic zinc chelates, which may require 10 kg or more for each kilogram of H2S. Precipitated zinc sulfide has an extremely low solubility in water and does not pose any hazard in neutral or basic drilling fluid, but zinc sulfide is soluble in dilute acids. Muds containing zinc sulfide could release H2S at any time if the mud should become acidic (Table 1).While searching for a more effective material, we noted that ferrous hydroxide reacts with H2S under the fight conditions to form iron pyrite, which is insoluble even in concentrated hydrochloric acid. The proposed reaction is Fe(OH)2 + 2 H2S FeS2 + 2 H2O + H2 This reaction requires 1.32 kg ferrous hydroxide to precipitate each kilogram of H2S. This reaction appeared precipitate each kilogram of H2S. This reaction appeared to be almost three times as effective on a weight basis as zinc compounds are in removing H2S from solution in mud. The precipitate is a naturally occurring, stable compound that would not have adverse environmental effects. However, ferrous hydroxide is not readily available nor very soluble in drilling fluids and it reacts slowly with H2S. JPT P. 797