Decomposition Of Thiosulfate Research Articles

Improvement of thiosulfate stability in gold leaching

Ammonium thiosulfate is a noncyanide lixiviant for gold leaching. However, the major problem with this leaching method has been the high consumption of reagents. To leach a mild-refractory copper-bearing gold ore, the authors used a reagent combination of 0.3M (NH 4 ) 2 S 2 O 3 , 0.03M CuSO 4 and 3M NH3 at pH 10.2 for 24 hours. In the testing, thiosulfate consumption was 30 kg/t of ore. Dissolved oxygen and copper species were found to be responsible for the rapid decomposition of thiosulfate. The thiosulfate consumption could be reduced to around 17 kg/t by the addition of an equivalent amount of a chelating agent, by reducing the copper sulfate addition to 0.001M or by replacing CuSO 4 by NiSO 4 . An increase in pulp density from 28.6% to 61.5% also reduced the thiosulfate consumption to around 17 kg/t. Thiosulfate consumption could be further reduced to 10 kg/t by regulating the dissolved oxygen concentration.

Effect of sulfides on gold dissolution in ammoniacal thiosulfate medium

To understand how various sulfide minerals affect the dissolution behavior of gold in the ammoniacal thiosulfate leaching system, an extensive study has been carried out on gold leaching in the presence of sulfides using pure gold plates. Special emphasis has been placed on gold leaching in association with sulfide dissolution, thiosulfate decomposition, and dissolved oxygen depletion in leach solutions. The results demonstrated that the leaching behavior of gold depended strongly on the solubilities of the sulfides, the thiosulfate decomposition, and the oxygen concentration in slurries. Gold dissolution was enhanced or diminished, depending on the sulfide types and the sulfide concentrations in slurries. An increase in the stirring speed accelerated the gold dissolution rates due to the improved mass transfer occurring in the gold leaching process and the increased dissolved oxygen content in leach solutions. The addition of sulfate in the sulfide slurries increased the gold leaching rates because of the depression of the sulfide dissolution in the leaching systems. Topological studies by scanning electron microscopy (SEM) demonstrated that the existence of passivating layers at the leached gold surfaces could result in the retardation of gold dissolution in the presence of sulfide minerals.

Rapid reaction of sulfide with hydrogen peroxide and formation of different final products by freezing compared to those in solution

AbstractThe reaction of sulfide with hydrogen peroxide in an aqueous solution at pH 9 produces thiosulfate, sulfite, and an unknown sulfur compound as intermediates, and, finally, all sulfides convert to sulfate (Chen and Gupta, Environ Lett 1973, 4, 187–200; Yokosuka et al., Nihon Kagaku Kaishi 1975, 11, 1901–1909; Hoffmann, Environ Sci Technol 1977, 11, 61–66; Ràbai et al., J Phys Chem 1992, 96, 5414–5419). This reaction was found to be accelerated by freezing. The decomposition rate of sulfide by H2O2 in freezing at −15°C was about 5 times faster than the maximum decomposition rate in solution at 25°C. The decomposition of sulfide by freezing obeys zero‐order kinetics, and the rate coefficient was 11.9 mol dm−3 min−1 at a freezing rate of 0.83 cm3 min−1. Zero‐order kinetics is one of the characteristics of freezing rate‐controlled reactions. Thiosulfate, sulfite, and an unknown sulfur compound were also observed as intermediates in the reaction by freezing. The decomposition of thiosulfate obeys first‐order kinetics, and the rate coefficient was 0.0496 min−1 at −15°C. The rate coefficient in freezing at −15°C is about 47 times faster than that in solution at 25°C. Sulfide, thiosulfate, and sulfite were consumed after 90 min. However, the unknown sulfur compound was not oxidized and was preserved in ice for a long time even in the presence of an excess of hydrogen peroxide. The concentration of an unknown sulfur compound in the frozen sample can be changed by changing the concentration of H2O2 and the pH of the solution. Freezing could be used for rapid preparation and preservation of unstable substances in solution. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 198–205, 2003

Thermal Analysis of a Hydrated Silica–Sodium Thiosulfate–Sulfur System

A system formed by concerted action of orthosilicic acid gelation and decomposition of sodium thiosulfate to afford highly dispersed elemental sulfur was studied by simultaneous methods, DTA, TG and DTG. A typical curve has been found to be an outcome of thermal processes associated with desorption of physically adsorbed water, condensation of surface silanol groups and thermal degradation of sodium thiosulfate. A large loss in mass over the lower temperature range was assigned to the loss of physically adsorbed water and condensation of silanol groups of the gel as indicated by accompanying strong endothermic effects. Subsequent strong exothermic effects were attributed to combustion of elemental sulfur embedded in the gel. Experiments were also conducted to control the extent of decomposition of the thiosulfate and generation of elemental sulfur by varying pH of thesilicic acid solution. These have shown that acidification of the silicic acid - sodium thiosulfate system with sulfuric acid fostered decomposition of the thiosulfate and raised the quantity of elemental sulfur.

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park, Wyoming, USA. II. Formation and decomposition of thiosulfate and polythionate in Cinder Pool

Cinder Pool is an acid-sulfate-chloride boiling spring in Norris Geyser Basin, Yellowstone National Park. The pool is unique in that its surface is partially covered with mm-size, black, hollow sulfur spherules, while a layer of molten sulfur resides at the bottom of the pool (18m depth). The sulfur speciation in the pool was determined on four different days over a period of two years. Samples were taken to evaluate changes with depth and to evaluate the importance of the sulfur spherules on sulfur redox chemistry. All analyses were conducted on site using a combination of ion chromatography and colorimetric techniques.Dissolved sulfide (H2S), thiosulfate (S2O32−), polythionates (SxO62−), and sulfate were detected. The polythionate concentration was highly variable in time and space. The highest concentrations were found in surficial samples taken from among the sulfur spherules. With depth, the polythionate concentrations dropped off. The maximum observed polythionate concentration was 8μM. Thiosulfate was rather uniformly distributed throughout the pool and concentrations ranged from 35 to 45μM. Total dissolved sulfide concentrations varied with time, concentrations ranged from 16 to 48μM. Sulfate was relatively constant, with concentrations ranging from 1150 to 1300μM. The sulfur speciation of Cinder Pool is unique in that the thiosulfate and polythionate concentrations are significantly higher than for any other acid-sulfate spring yet sampled in Yellowstone National Park. Complementary laboratory experiments show that thiosulfate is the intermediate sulfoxyanion formed from sulfur hydrolysis under conditions similar to those found in Cinder Pool and that polythionates are formed via the oxidation of thiosulfate by dissolved oxygen. This last reaction is catalyzed by pyrite that occurs as a minor constituent in the sulfur spherules floating on the pool's surface. Polythionate decomposition proceeds via two pathways: (1) a reaction with H2S, yielding thiosulfate and elemental sulfur; and (2) by disproportionation to sulfate and thiosulfate.This study demonstrates that the presence of a subaqueous molten sulfur pool and sulfur spherules in Cinder Pool is of importance in controlling the pathways of aqueous sulfur redox reactions. Some of the insights gained at Cinder Pool may be relevant to acid crater lakes where sulfur spherules are observed and variations in polythionate concentrations are used to monitor and predict volcanic activity.

Zinc plating

Although nickel has a lower standard electrode potential than copper, nickel-sulfur coatings were successfully deposited on copper through one-step immersion plating method, which was carried out in the aqueous solution consisting of NiSO4·6H2O and Na2S2O3·5H2O at room temperature. The open circuit potential tests demonstrated that copper had a more negative potential than nickel in Na2S2O3·5H2O solutions, which made the deposition of nickel on copper through immersion plating feasible. Because of the decomposition of sodium thiosulfate, sulfur could be codeposited with nickel and the nickel-sulfur coatings were finally obtained. The surface morphology and composition of the coatings were characterized with SEM, EDS, XPS and XRD analyses, and the results indicated the coatings were mainly composed of metallic nickel and Ni3S2. The deposition process of the nickel-sulfur coatings was investigated by analyzing the morphology evolution of copper substrates. The as-prepared nickel-sulfur coatings possessed good anticorrosion ability for its compact structure and could lower the corrosion current density of copper in 3.5 wt% NaCl solution to its 1/20.

Oxidation of arsenopyrite (FeAsS) in acid Part II: Stoichiometry and reaction scheme

The electrochemical oxidation of arsenopyrite (FeAsS) in 0.01 iv1 chloride solution at pH 2 has been investigated and the effect of electrode potential, temperature and arsenopyrite mineral composition on the reaction stoichiometry studied. Iron, arsenic and sulfur products were formed in the ratio 1 : 1 : 1, for all conditions for arsenic deficient and stoichiometric arsenopyrite. Product speciation was dependent on temperature and potential, but not on arsenopyrite composition. At 25°C, Fe(ii), Fe(iii), As(iii), As(v), S, SO42−and S(x) (which could be a polythionate such as tetrathionate or pentathionate) were formed and ∼9e− produced per mol of arsenopyrite oxidized. At 75°C, practically no S(x) was formed and 7.5 e− produced per mol of arsenopyrite oxidized. A qualitative reaction scheme, based on the decomposition of thiosulfate to polythionate in the presence of As(iii), is outlined.

Deposition of Electrically Conductive, Microwave Shielding, and IR-Detecting Inorganic Coatings on Polymer Films

Abstract A simple, inexpensive and pollution free electroless chemical deposition technique was used to deposit thin coatings of inorganic electrically conductive materials (CuxS, x∼2, CuS and Cu2Se), microwave shielding materials (CuS and Cu2Se) and IR-detecting materials (PbS and PbSe) on transparent polyester films. The technique is based on hydrolytic decomposition of thiosulfate and selenosulfate complexes of the corresponding metals in aqueous media.

Role of additive in the physico-chemistry of graphite-based transfer films

Thin transfer films were formed on steel surfaces during friction against graphite-based pins. Sodium thiosulfate Na 2S 2O 3 or sodium molybdate Na 2MoO 4 were added to graphite to improve the film formation. In order to understand the solid lubricant properties of the graphite + additive mixtures, physico-chemical characterization was performed using classical θ−2θ and grazing-incidence X-ray diffraction, thermogravimetry, Raman and micro-Raman spectroscopy and transmission electron microscopy. The graphite + additive pins before and after friction tests and the transfer filsm were analysed. Graphite was shown to become more and more defective during the transfer process. A turbostratic structure was detected. Crystallite size became as small as a few nanometers. Chemical reactions of the additives were observed as soon as the mixtures were prepared. Decomposition of thiosulfate led to the formation of sulfate Na 2SO 4 and free sulfur. No such reaction was seen with molybdate. The results are discussed in terms of disorder in the two- and three-dimensional ordering of the graphitic structure and are related to the role of interstitials between graphite planes.

Dissolution and Reaction of Sulfide Inclusions in Stainless Steel Imaged Using Scanning Laser Photoelectrochemical Microscopy

The in situ scanning laser photoelectrochemical microscopy technique has been used to image heterogeneity of the surface chemistry around sulfide inclusions in stainless steel under anodic polarization. The deposition around inclusions of a ring of material deduced to be sulfur is demonstrated. Evidence is presented that this ring of material has its origin in the decomposition of thiosulfate produced by the anodic dissolution of the inclusions. The evidence supports models of the initiation of pitting corrosion which attribute the effect of sulfide inclusions to the acceleration of anodic dissolution kinetics caused by adsorbed sulfur.

Aspects of the Interfacial Electrochemistry of Semiconductor Pyrite ( FeS2 )

The electrochemical oxidation of has been studied using cyclic voltammetry, EDX, and AES techniques. Cyclic voltammograms reveal one anodic peak and two cathodic peaks on the return sweep. These peaks are attributed to the electroadsorption/desorption of OH groups on pyrite surfaces. It is proposed that the electrocatalytic electroadsorption of OH groups on is due to the presence of Fe 3d electrons in the upper portion of the valence band. Thus, OH− ions are oxidized by holes on Fe 3d states in the first step. These groups are transferred to sites in the second step. Surface analysis reveals preferential release of Fe2+ from the pyrite lattice. A mechanism for the anodic dissolution of pyrite is proposed, according to which S is not an intermediate product, but is rather a stable end product which forms due to the decomposition of thiosulfate . The proposed mechanism is consistent with the observations reported by previous investigators.

Mechanism of thermal decomposition of lead thiosulphate

The thermal decomposition of lead thiosulfate (LTS) was studied by various methods: X-ray phase analysis, IR and ESR spectroscopy, etc. A mechanism of thermal decomposition is suggested, including rupture of the S-S bond and the formation of radicals. According to the mechanism, the reaction rate can be enhanced in the presence of the PbS phase. The formation of PbS is the cause of the topochemical character of the reaction. The composition of the thermolysis products of LTS containing a radioactive isotope of sulfur is predicted.

ChemInform Abstract: Sulfur Compounds. Part 112. The Molecular Composition of Hydrophilic Sulfur Sols Prepared by Acid Decomposition of Thiosulfate.

AbstractHydrophilic sulfur sols, obtained by acid decomposition of Na2S2O3 in water (so‐called Raffo sols) are analytically characterized using chemical analysis, IR and Raman spectra, ion‐pair chromatography, and reversed‐phase HPLC.

The Molecular Composition of Hydrophilic Sulfur Sols Prepared by Acid Decomposition of Thiosulfate [1

Hydrophilic sulfur sols prepared from sodium thiosulfate and concentrated sulfuric acid and purified by repeated NaCl precipitation and peptization in water have been studied by chemical analysis, vibrational spectroscopy, ion-pair chromatography and reversed-phase HPLC. The composition of the sol is Na1.64S28.6O6 · 5.9/n Sn · 1.0 NaCl. The elemental sulfur Sn (n = 6-14; mainly S 8) accounts for 17% the total sulfur; 83% of the S are present as long-chain polythionates which form micelles in which the Sn molecules are dissolved. On aging of the sol at 20 °C the polythionate micelles decompose to give water-soluble short-chain polythionates and elemental sulfur which precipitates from the solution. The micelle structure of hydrophilic sulfur sols may serve as a model for the so-called sulfur globules (S°) formed intra- or extracellularly by many sulfur bacteria which oxidize reduced sulfur compounds to S°. - ᴛ∙nfrared and Raman spectra of K2SmO6 (m = 3-6) are reported. The photodecomposition of aqueous tetrathionate yields sulfite, thiosulfate, and polythionates with up to 9 sulfur atoms

A low-cost laboratory experiment using a nephelo-turbidity meter

Principle of the nephelo-turbidity meter, description of the apparatus, and application to the kinetic study of the decomposition of sodium thiosulfate by mineral acid.

An improved nephelometric method for the determination of small amounts of thiosulfate in aqueous samples

The procedure is based on decomposition of thiosulfate, with formation of sulfur, in the presence of 0.5 mol l −1 nitric acid. Thiosulfate is determined in the range 15–100 mg l −1, with a relative standard deviation of 5.4% and a mean relative error of 3.2%. These data are of the same order of magnitude as those obtained for the earlier silver/1,10-phenanthroline method. The present method has the advantage of being almost completely free from interferences; the only interference observed (sulfide) is easily eliminated.

Kinetics of decomposition of tetrathionate, trithionate, and thiosulfate in alkaline media

Kinetics of decomposition of tetrathionate, trithionate, and thiosulfate in alkaline media

Genomic and physiological diversity amongst strains of Thiobacillus ferrooxidans, and genomic comparison with Thiobacillus thiooxidans

Twenty-three strains of Thiobacillus ferrooxidans of known pedigree were examined. Thirteen strains survived 65° C for 5 min and 7 of these for 10 min, but sporulation was never observed. All strains grew between 25° C and 35° C and some strains grew at 5° and 40° C. They were genomically diverse, comprising 7 DNA homology groups, and the GC content varied from 55–65 mol %. Correlation between genomic group and growth temperature was noted. All strains grew on ferrous sulfate as energy source, but some failed to utilize elemental sulfur. Acidified thiosulfate supported growth of most of the strains examined but it was judged to be a poor substrate upon which to base taxonomic conclusions because of decomposition of thiosulfate in acid. Six strains of Thiobacillus thiooxidans showed negligible genomic affinity to T. ferrooxidans, and they comprised 2 DNA homology groups and their GC content varied from 52–62 mol%. Anomalies due to contaminants in cultures of T. ferrooxidans were resolved, and the contaminants were identified.

Formation and decomposition of thiosulfate in the ferrous sulfide-sulfur dioxide reaction

Formation and decomposition of thiosulfate in the ferrous sulfide-sulfur dioxide reaction

A study of the metal sulfide-sulfur dioxide reaction in aqueous media by reaction pressure characterization and ultraviolet spectrophotometry

The metal sulfide-sulfur dioxide reaction has been characterized for seven different sulfide ores by using the changes in sulfur dioxide pressure during the reaction and by ultraviolet spectrophotometric analysis of the reaction products. The UV analysis, which showed that thiosulfuric acid is a major product of the metal sulfide-sulfur dioxide reaction, was used to monitor the r rate of formation of thiosulfuric acid during the reaction. Results from a series of base-line experiments using ferrous sulfide showed a high correlation between the rate of change of sulfur dioxide pressure, the rate of appearance of ferrous ion, and the rate of formation of thiosulfuric acid. These results were compared with those obtained in similar experiments with six naturally-occurring sulfide ores. Finally, the UV method was employed to monitor the kinetics of the decomposition of thiosulfuric acid into elemental sulfur. Using these results, in conjunction with the mechanisms previously developed for the Wackenroder reaction and the acid decomposition of thiosulfate, a mechanism is proposed for the acid oxidative dissolution of sulfide ores which accounts for the formation of elemental sulfur.