The Experts below are selected from a list of 12657 Experts worldwide ranked by ideXlab platform
David Dreisinger - One of the best experts on this subject based on the ideXlab platform.
-
eco friendly leaching of gold from a carbonaceous gold concentrate in copper citrate Thiosulfate solutions
Hydrometallurgy, 2020Co-Authors: Jian Wang, Wei Wang, Feng Xie, Yunlong Bai, David DreisingerAbstract:Abstract Thiosulfate is considered to be one of the most promising alternative reagents to cyanide due to its non-toxicity and excellent leaching efficiency. However, the use of ammonia as the additive and high reagent consumption have severely limited the development and commercial application of the traditional copper-ammonia-Thiosulfate leaching system. In this work, the potential use of an environmentally friendly copper-citrate-Thiosulfate leaching system for gold leaching from a refractory carbonaceous gold concentrate has been examined. The experimental results showed that when citrate served as the stabilizer, the copper-citrate-Thiosulfate system exhibited similar extraction capability for gold with a significant decrease in Thiosulfate consumption compared to the traditional copper-ammonia-Thiosulfate system. Thiosulfate consumption increased with Cu2+ and S2O32− concentration, leaching time and temperature, but decreased with citrate concentration and initial pH. The mechanism of the catalysis of gold dissolution in copper-citrate-Thiosulfate solutions by the binuclear cupric-citrate complex (Cu2Cit2H−24−) is presented based on the thermodynamic analysis. The stability of the Cu2Cit2H−24− complex decreased with increasing Cu2+ and S2O32− concentration, increased with an increase of citrate concentration. Moreover, the microwave roasting process applied to concentrate facilitated the subsequent gold leaching process probably by exposing encapsulated gold to Thiosulfate solutions.
-
silver sulfide leaching with Thiosulfate in the presence of additives part i copper ammonia leaching
Hydrometallurgy, 2013Co-Authors: Jared L. Deutsch, David DreisingerAbstract:Abstract Thiosulfate is a promising alternative for the hydrometallurgical treatment of silver sulfide ores. In this study, the copper–ammonia catalyzed Thiosulfate leaching of a silver sulfide rotating disk is investigated. The leaching of silver sulfide by a copper–ammonia Thiosulfate solution occurs either by the substitution of cupric or cuprous for silver. The cupric reaction is favored due to a thermodynamic barrier to the cuprous reaction. At 1 mM copper, there is evidence of partial chemical control for copper–ammonia leaching with a maximum silver dissolution rate achieved when cupric is stabilized in solution with ammonia and for solutions with high Thiosulfate availability. The addition of ethylenediaminetetraacetic acid decreased the leaching rate of the silver sulfide disk due to decreased cupric reactivity, although this comes with the benefit of increased cupric stability.
-
Silver sulfide leaching with Thiosulfate in the presence of additives Part II: Ferric complexes and the application to silver sulfide ore
Hydrometallurgy, 2013Co-Authors: Jared L. Deutsch, David DreisingerAbstract:Abstract Ferric complex alternatives to the cupric–ammonia catalyzed Thiosulfate system including ferric–EDTA, ferric–oxalate and ferric–citrate were studied with a silver sulfide rotating disk. Of these complexes, ferric–EDTA and ferric–oxalate were the most promising alternatives. All ferric complexes tested were unreactive towards Thiosulfate, but are reduced by sulfides present in the ore. When leaching a silver sulfide ore, the most effective lixiviants were ferric–EDTA and the cupric–ammonia Thiosulfate systems. None of the Thiosulfate alternatives were able to recover as much silver as cyanide leaching, likely due to the presence of other silver minerals which may not be amenable to Thiosulfate leaching. Although less silver was recovered, less than 1% of mercury in the ore was leached by Thiosulfate complexes compared to 50% mercury recovery by cyanide.
-
the treatment of copper gold ores by ammonium Thiosulfate leaching
Hydrometallurgy, 2002Co-Authors: Ellen Molleman, David DreisingerAbstract:Abstract The application of ammonium Thiosulfate for the treatment of copper–gold ores has been investigated. Copper minerals and copper–gold samples were leached in an ammonium Thiosulfate solution under varying experimental conditions, i.e. aeration, temperature and reagent addition. The behaviour of Thiosulfate, tetrathionate and sulfate in solution was studied using ion chromatography. Experiments showed that both gold extraction and Thiosulfate stability are affected by a combination of aeration and cupric ions in solution. It is important to establish a balance between providing sufficient air and cupric ions for fast gold dissolution, and at the same time minimize the amount of air in the presence of cupric ions to prevent excessive Thiosulfate degradation. Promising results, i.e. high gold extractions and low Thiosulfate consumption, were obtained during a 24-h leach without forced aeration.
Yannick Combet-blanc - One of the best experts on this subject based on the ideXlab platform.
-
Hydrogen production by the hyperthermophilic bacterium Thermotoga maritima part I: effects of sulfured nutriments, with Thiosulfate as model, on hydrogen production and growth
Biotechnology for Biofuels, 2016Co-Authors: Céline Boileau, Richard Auria, Sylvain Davidson, Laurence Casalot, Pierre Christen, Pierre-pol Liebgott, Yannick Combet-blancAbstract:Background Thermotoga maritima and T. neapolitana are hyperthermophile bacteria chosen by many research teams to produce bio-hydrogen because of their potential to ferment a wide variety of sugars with the highest theoretical H_2/glucose yields. However, to develop economically sustainable bio-processes, the culture medium formulation remained to be optimized. The main aim of this study was to quantify accurately and specifically the effect of Thiosulfate, used as sulfured nutriment model, on T. maritima growth, yields and productivities of hydrogen. The results were obtained from batch cultures, performed into a bioreactor, carefully controlled, and specifically designed to prevent the back-inhibition by hydrogen. Results Among sulfured nutriments tested, Thiosulfate, cysteine, and sulfide were found to be the most efficient to stimulate T. maritima growth and hydrogen production. In particular, under our experimental conditions (glucose 60 mmol L^−1 and yeast extract 1 g L^−1), the cellular growth was limited by Thiosulfate concentrations lower than 0.06 mmol L^−1. Under these conditions, the cellular yield on Thiosulfate ( Y X/Thio ) could be determined at 3617 mg mmol^−1. In addition, it has been shown that the limitations of T. maritima growth by Thiosulfate lead to metabolic stress marked by a significant metabolic shift of glucose towards the production of extracellular polysaccharides (EPS). Finally, it has been estimated that the presence of Thiosulfate in the T. maritima culture medium significantly increased the cellular and hydrogen productivities by a factor 6 without detectable sulfide production. Conclusions The stimulant effects of Thiosulfate at very low concentrations on T. maritima growth have forced us to reconsider its role in this species and more probably also in all thiosulfato-reducer hyperthermophiles. Henceforth, Thiosulfate should be considered in T. maritima as (1) an essential sulfur source for cellular materials when it is present at low concentrations (about 0.3 mmol g^−1 of cells), and (2) as both sulfur source and detoxifying agent for H_2 when Thiosulfate is present at higher concentrations and, when, simultaneously, the pH_2 is high. Finally, to improve the hydrogen production in bio-processes using Thermotoga species, it should be recommended to incorporate Thiosulfate in the culture medium.
Matthew I Jeffrey - One of the best experts on this subject based on the ideXlab platform.
-
a kinetic study of rearrangement and degradation reactions of tetrathionate and trithionate in near neutral solutions
Inorganic Chemistry, 2010Co-Authors: Hongguang Zhang, Matthew I JeffreyAbstract:The kinetics of reactions of trithionate and tetrathionate via different reaction pathways were studied in near-neutral solutions. In the case of trithionate, the predominant degradation reaction is hydrolysis to Thiosulfate and sulfate. The pseudofirst-order rate constant is independent of pH and measured to be (6.2 ± 0.2) × 10−7 s−1 for the pH range of 5.5−10.5. With tetrathionate, the reaction in both neutral and alkaline solutions occurs via a Thiosulfate catalyzed rearrangement reaction to trithionate and pentathionate followed by their further reactions. The data suggest that when Thiosulfate is completely absent, this first step will not occur, and in the presence of Thiosulfate, the rate of the first step is independent of pH in the pH range 6−8. The secondary reactions include the hydrolysis of trithionate and the further rearrangement and degradation of pentathionate. This mechanism explains the dominant reaction products for both neutral and alkaline solutions. In the presence of Thiosulfate an...
-
an electrochemical study of gold leaching in Thiosulfate solutions containing copper and ammonia
Hydrometallurgy, 2002Co-Authors: P L Breuer, Matthew I JeffreyAbstract:The electrochemistry of gold in Thiosulfate solutions containing copper and ammonia was studied using a combination of standard electrochemical techniques and the rotating electrochemical quartz crystal microbalance. It was found that the cathodic half reaction, the reduction of copper(II), occurs readily in the potential region where gold should be oxidised to gold Thiosulfate. However, the gold oxidation half reaction in Thiosulfate solutions alone is hindered; the presence of ammonia is required for the reaction to occur at an appreciable rate. It was also shown that copper(II) affects the gold oxidation half reaction; this is why copper(II) is more effective than other oxidants at leaching gold in Thiosulfate solutions. One complication with using copper(II) as an oxidant is that it also reacts with Thiosulfate, which results in a decrease in copper(II) concentration. Such a decrease in [Cu(II)] was shown to cause a decrease in the rate at which the gold oxidation half reaction proceeds. The effect of temperature and Thiosulfate concentration on the oxidation of gold was also investigated.
Yongbin Yang - One of the best experts on this subject based on the ideXlab platform.
-
an eco friendly and efficient process of low potential Thiosulfate leaching resin adsorption recovery for extracting gold from a roasted gold concentrate
Journal of Cleaner Production, 2019Co-Authors: Zhonglin Dong, Tao Jiang, Yongbin YangAbstract:Abstract Thiosulfate is a promising alternative lixiviant to cyanide for leaching gold from its ores/concentrates due to increased environmental and public concern over the use of poisonous cyanide. However, high Thiosulfate consumption and high cost for gold recovery from pregnant solution have limited its industrial application. In this work, an innovative process for extracting gold from a roasted gold concentrate is proposed: firstly, gold leaching with Thiosulfate under a low mixed potential; then, gold separation and enrichment with an ion-exchange resin to produce concentrated gold solution that can be refined to metallic gold by electrowinning. Compared with traditional Thiosulfate leaching, the mixed potential of stable stage of low potential leaching decreased around 30 mV through using low concentrations of reagents and limiting oxygen supply, a slightly higher gold extraction was obtained, whilst Thiosulfate consumption substantially reduced from 34.6 kg/t-concentrate to 15.8 kg/t-concentrate. The amount of undesirable anions particularly cuprous Thiosulfate and polythionates in the pregnant solution significantly dropped owing to the mild leaching conditions. This considerably weakened their competitive adsorption with gold (I) Thiosulfate onto the resin, contributing to the decrease of resin dosage used for gold recovery. The eluent dosage also declined because of the less interfering ions on resin surface. Based on these results, low potential Thiosulfate leaching followed by resin adsorption recovery is put forward, providing an eco-friendly and efficient process for gold extraction from roasted gold concentrate.
-
study on the oxygen pressure alkaline leaching of gold with generated Thiosulfate from sulfur oxidation
Hydrometallurgy, 2018Co-Authors: Qiang Zhong, Yongbin Yang, Tao JiangAbstract:Abstract Thiosulfate leaching is a promising alternative to cyanidation, but high Thiosulfate consumption has restricted its wide commercial application. In this study, the simultaneous gold extraction by generated Thiosulfate deriving from the oxidation of added sulfur during oxygen pressure alkaline leaching (OPAL) without cupric-ammonia catalysis was investigated, and the results were encouraging. It has been proven that the sulfur can be produced from the oxidation pretreatment of sulfide gold ores or concentrates. Thus, this study provides an enlightenment to solve the problem of high Thiosulfate consumption by a two-step process consisting of an appropriate oxidation pretreatment for sulfide gold ores or concentrates and OPAL. The gold extraction from an ore and terminal Thiosulfate concentration after the OPAL in this study reached 78.0% and 0.28 M, respectively, and they were further improved to 83.6% and 0.31 M by the addition of humic acid (HA). The function of HA was proposed that it not only prevented passivation species from coating gold surface but also weakened the decomposition of generated Thiosulfate. It can also be concluded that the improvement of temperature and oxygen partial pressure can substitute the cupric-ammonia catalysis for Thiosulfate leaching.
-
effect of common associated sulfide minerals on Thiosulfate leaching of gold and the role of humic acid additive
Hydrometallurgy, 2017Co-Authors: Bin Xu, Yongbin Yang, Qian Li, Tao Jiang, Xi Zhang, Guanghui LiAbstract:Abstract Compared with the Thiosulfate leaching in the presence of inert quartz, the conclusion was obtained that all studied sulfide minerals including chalcopyrite, galena, sphalerite, pyrite and arsenopyrite could accelerate the Thiosulfate consumption and hinder the gold dissolution in varying degree. The dominant cause for these two detrimental effect of sulfide minerals were inferred separately via the analyses of frontier orbital energy and XPS to be the catalysis of these minerals on Thiosulfate decomposition and the passivation of gold surface. The passivation layer on gold surface mainly consisted of copper and sulfur species. It was also concluded by leaching tests that HA (sodium humic acid) additive could effectively reduce these harmful effect of sulfide minerals. The acting mechanism of HA during Thiosulfate leaching was studied in detail mainly through the analyses of mixed pulp potential, zeta potential and XPS, and was proposed as follows: humic acid radical ions not only weakened the interaction between Cu(II) and Thiosulfate via complexing with Cu(II) at axial coordinate sites and relieved the catalytic effect of minerals on Thiosulfate decomposition by making the affinity of mineral surfaces for S 2 O 3 2 − disappear, but also prevented passivation species from coating gold surface through electrostatic repulsion.
-
effect of pyrite on Thiosulfate leaching of gold and the role of ammonium alcohol polyvinyl phosphate aapp
Metals, 2017Co-Authors: Xiaoliang Liu, Yongbin Yang, Tao Jiang, Xin Min, Xi ZhangAbstract:The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal Thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of Thiosulfate. This detrimental effect became more severe with increasing pyrite content. Further, the presence of pyrite also substantially slowed the gold leaching kinetics and reduced the overall gold dissolution. The reduction in gold dissolution was found to be caused primarily by the surface passivation of the gold. The negative effects of pyrite, however, can be alleviated by the addition of AAPP. Comparison of zeta potentials of pyrite with and without AAPP suggests that AAPP had adsorbed on the surface of the pyrite and weakened the catalytic effect of pyrite on the Thiosulfate decomposition by blocking the contact between the pyrite and Thiosulfate anions. AAPP also competed with Thiosulfate anions to complex with the cupric ion at the axial coordinate sites, and thus abated the oxidation of Thiosulfate by cupric ions. Moreover, the indiscriminate adsorption of AAPP on the surfaces of gold and passivation species prevented the passivation of the gold surface by surface charge and electrostatic repulsion. Therefore, AAPP effectively stabilized the Thiosulfate in the solution and facilitated the gold leaching in the presence of pyrite.
-
a review of Thiosulfate leaching of gold focus on Thiosulfate consumption and gold recovery from pregnant solution
Metals, 2017Co-Authors: Wenhao Kong, Yongbin Yang, Tao Jiang, Xiaoliang LiuAbstract:Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high Thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of Thiosulfate, including the control of reaction conditions, the use of additives, the generation of Thiosulfate in situ, and the replacement of traditional cupric-ammonia catalysis, are introduced and evaluated after the presentation of background knowledge about Thiosulfate consumption. The replacement of cupric-ammonia catalysis with other metals, such as nickel- and cobalt-based catalysts, is proposed. The reason is that it not only reduces Thiosulfate consumption observably via decreasing the redox potential of leach solution significantly but also is beneficial to gold recovery mainly owing to eliminating the interference of cuprous Thiosulfate [Cu(S2O3)3]5−. Based on the comparative analysis for five common recovery techniques of rare-noble metals from pregnant leach solution, ion-exchange resin adsorption is considered to be the most appropriate to recover auroThiosulfate [Au(S2O3)2]3− because the resin can be employed in the form of resin-in-leach/pulp and, furthermore, is able to be eluted and regenerated simultaneously at ambient temperature. At last, how to reduce the process cost of the resin adsorption technique is discussed. In order to simplify the complex two-stage elution process for loaded resins, the traditional catalysis is suggested to be replaced.
Toshiaki Asakai - One of the best experts on this subject based on the ideXlab platform.
-
reliability in standardization of sodium Thiosulfate with potassium dichromate
Microchemical Journal, 2015Co-Authors: Toshiaki Asakai, Akiharu HiokiAbstract:Abstract Sodium Thiosulfate is often standardized with potassium dichromate. In the standardization, iodine (triiodide) liberated by potassium dichromate in an acidic potassium iodide solution is titrated with a sodium Thiosulfate solution. The iodine liberation process significantly affects the titration results. In the present study, the accuracy of the liberation process was examined by assaying potassium dichromate through two different paths: assaying directly by coulometric titration with electrogenerated Fe(II), and assaying by gravimetric titration through the iodine liberation reaction with a sodium Thiosulfate solution of which concentration was standardized by coulometric titration with electrogenerated iodine. The accuracy of the standardization of a sodium Thiosulfate solution by potassium dichromate was discussed from the apparent assays of potassium dichromate under different measurement conditions.
-
Precise coulometric titration of cerium(IV) as an oxidising agent with electrogenerated iron(II) and reliability in cerium(IV) standardisation with sodium Thiosulfate
Analytical Methods, 2012Co-Authors: Toshiaki Asakai, Akiharu HiokiAbstract:Cerium(IV) is a useful strong oxidising agent and is often standardised against Thiosulfate. In the standardisation, triiodide liberated by Ce(IV) in an acidic potassium iodide solution can be titrated with Thiosulfate to determine the concentration of Ce(IV). The accuracy of the standardisation has not been established because the iodine liberation process is not well-understood. In the present study, to evaluate the iodine liberation process, Ce(IV) was assayed through two different methods: precise coulometric titration with electrogenerated ferrous ions and gravimetric titration with Thiosulfate independently determined by precise coulometric titration with electrogenerated iodine. The reliability of Ce(IV) standardisation with Thiosulfate is discussed on an absolute basis by coulometric titrations of both Ce(IV) and Thiosulfate solutions. Finally, the accurate determination of Ce(IV) was achieved by both methods. Information on the stability of Ce(IV) solutions is also presented.
-
Precise coulometric titration of sodium Thiosulfate and development of potassium iodate as a redox standard
Talanta, 2007Co-Authors: Toshiaki Asakai, Mariko Murayama, Tatsuhiko TanakaAbstract:Abstract In this paper, we determine the effective purity of potassium iodate as a redox standard with a certified value linked to the international system of units (SI units). Concentration measurement of sodium Thiosulfate solution was performed by precise coulometric titration with electrogenerated iodine, and an assay of potassium iodate was carried out by gravimetric titration based on the reductometric factor of sodium Thiosulfate assigned by coulometry. The accuracy of the coulometric titration method was evaluated by examining the current efficiency of iodine electrogeneration, stability of sodium Thiosulfate solutions and dependence on the amount of sodium Thiosulfate solution used. The measurement procedure for gravimetric titration of potassium iodate with sodium Thiosulfate was validated based on determination of a reference material of known purity (potassium dichromate determined by coulometry with electrogenerated ferrous ions) using the same gravimetric method. Solutions of 0.2 and 0.5 mol/L sodium Thiosulfate were stable over 17 days without stabilizer. Investigation of the dependency of titration results on the amount of sodium Thiosulfate solution used showed no significant effects, no evidence of diffusion of the sample, and no effect of contamination appearing during the experiment. Precise coulometric titration of sodium Thiosulfate achieved a relative standard deviation of less than 0.005% under repeating conditions (six measurements). For gravimetric titration, the results obtained for the effective purity of potassium dichromate were sufficiently close to its certified value to allow confirmation of the validity of the gravimetric titration was confirmed. The relative standard deviation of gravimetric titration for potassium iodate was less than 0.011% (nine measurements), and a redox standard with a certified value linked to SI units was developed.
