Unlike cyanide, which is highly toxic, the chemicals used in the thiosulfate leaching process are benign. The topics of this work are gold ores and their suitability for leaching processes, pretreatment of concentrate, leaching chemistry and reagent consumption, leaching kinetics, gold recovery from leaching liquors and environmental and safety aspects. In batch reactor experiments the best yield was 88 %. The gold industry has been seeking alternative reagents for leaching gold from lowgrade ores for the past 25 years. Processes are provided for recovering precious metals from refractory materials using thiosulfate lixiviants. Feng university of science and technology, liaoning, anshan, china received august 15, 2017, revised november 15, 2017 the effect of additives on gold leaching was investigated using ammonium thiosulfate or calcium thiosulfate. The combined effect of temperature and ammonia concentration. At the highest thiosulfate ions concentration the leaching recoveries of ag and cu were 60 and 35%, respectively. A development of in situ gold leaching using ferric edta.
Bioleaching, chlorination, aqua regia, bromine, thiocyanate, thiosulfate and thiourea leaching. The complexity of thiosulfate leaching of gold is exemplified in figure 1 14. Ammonium thiosulfate will react differently,with different ores. Gold sodium thiosulfate is a fairly common sensitizer with elicitation of symptoms linked to gold in jewelry, occupational exposure to gold, dental restorations, gold plated intracoronary stents and previous rheumatoid arthritis treatment. The current problem of thiosulphate gold leaching is the high reagent. Silver sulfide leaching with a copperthiosulfate solution in. Electrochemical study of the gold thiosulfate reduction.
The effect silver alloyed with gold was evaluated and the result showed that the dissolution rate of pure gold is higher than that form 4 and 8 wt% ag alloys. For this pro pose, the gold leaching reagents are described and discussed in terms of their environmental and economical points of view. Effect of additives on thiosulfate leaching of a gold ore. If you let your leach run too long,and let the ph drop too much during run time,it will then pull in some iron. Alternative lixiviants to cyanide for leaching gold ores. There exist encapsulated materials and gold present in microscopic pyrites and arsenopyrites. Thiourea is not stable in base solution, but it was found that gold dissolution rates can be increased with a little thiourea,the mechanism is still unclear. Industrially, barrick gold has implemented a calcium thiosulphate retro.
Leaching of gold from the waste mobile phone printed. I have edited this to include some information that may help the forum members in the future, and one in particular. Kohl school of chemical engineering, georgia institute of technology, atlanta, georgia 303320100, usa abstract the electrochemical reduction of gold thiosulfate has been studied and compared to the reduction of gold cyanide. Thiosulfate leaching can be considered a nontoxic process, the gold dissolution rates can be faster than conventional cyanidation and, due to the decreased interference of foreign cations, high. Gold cyanidation also known as the cyanide process or the macarthurforrest process is a hydrometallurgical technique for extracting gold from lowgrade ore by converting the gold to a watersoluble coordination complex. Based on the comparative analysis for five common recovery techniques of rarenoble metals from pregnant leach solution, ionexchange resin. A process for recovering a precious metal from a precious metalcontaining material, comprising. Thiosulfate leaching to recover gold from ores is known for several decades but extensive researches have been started only for the past two decades. Ammonium thiosulphate is an alternative gold leaching laaviant used to replace cyanide. High consumption of reagents and the lack of a cheap process for recovering gold have made thiosulfate leaching. Optimizing the thiosulfate leaching of gold from printed. Even though thiosulphate leaching has a potential in gold leaching, there is one major problem remaining and that is a high consumption of thiosulphate during gold leaching. It is the most commonly used leaching process for gold extraction production of reagents for mineral processing to recover gold, copper, zinc and silver represents. Thiosulfatecopperammonia leaching of pure gold and pressure.
Adsorption of copper from an ammoniathiosulfate media using. Comparisons are also made with other recovery processes, including carbon adsorption, solvent extraction, electrowinning and precipitation. In alkaline or near neutral solution of thiosulfate, gold dissolves slowly in the presence of a mild oxidant white, 1905. Recovery of gold was found to be highly dependent on the concentration of copper sulfate, ammonium thiosulfate, ph and pulp density. Mar 26, 2011 the effects of thiosulfate concentration, copper to thiosulfate ratio, agitation vigorousness, ph values, and dissolved gases on the leaching of silver sulfide with the copper thiosulfate solution were studied. Coppercatalyzed thiosulfate leaching is being investigated by the u. Improvement of thiosulfate stability in gold leaching. To avoid the losses of ammonia a closed leaching system is recommended. Thiosulfate leaching thiosulfate leaching is an alkaline process which removes gold from carbonaceous ores instead of using cyanide.
Barrick thiosulfate leaching of double refractory ore. The role of ligands and oxidants in thiosulfate leaching of gold. Gold recovery by catalytic copper ammonium thiosulphate solution has been studied. Adsorption of gold from thiosulfate solutions with. The proposed method of the gold recovery comprises leaching with a solution of a mixture of sodium and ammonium hydrosulfite and thiosulfate, by sorption of the thiosulfate gold complex on a highly basic anion exchanger and by isolation of the highly basic anion exchanger, the sorption being carried out 210 hours after the leaching. Associated sulfide minerals in thiosulfate leaching of. Biooxidationthiosulfate leaching of refractory gold concentrate. Crush your ore to the consistency of fine sand in a rod mill, then transfer it into a large vat with a strong solution of sodium thiosulfate and agitate it with paddles for a day to a week, depending on the size of your vat. Application of thiosulphate leaching in gold recovery. Gold sodium thiosulfate is a fairly common sensitizer with elicitation of symptoms linked to gold in jewelry, occupational exposure to gold, dental restorations, goldplated intracoronary stents and previous rheumatoid arthritis treatment.
Electrochemical study of the gold thiosulfate reduction anne m. Many researchers have identified that thiosulfate leaching is the most likely alternative to cyanidation due to nontoxicity, low cost and other benefits. At full capacity,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks. The models predicted 90pct gold extraction and a consumption of 0. Gold extraction was found to be enhanced with solutions containing 1520 mm cupric, 0. Adsorption of copper from an ammoniathiosulfate media. The observed leaching results show that with increasing thiosulfate ions concentration the leaching efficiency increases for both ag and cu. Recently, thiosulphate leaching of gold in the absence of ammonia has shown to be one of the most promising alternatives to cyanide, as evident. Leaching of gold, silver and accompanying metals from circuit. Cyanide alternative leaching reagents for gold recovery from electronic waste. Anodic polarization, cathodic polarization and leaching experiments were included in this study. The study showed that the leaching rate of gold and silver in the closed vessel was greater than that obtained in the open vessel by 30% and 45% respectively. It confirms the possibility of thiosulfate leaching application for silver extraction.
Leaching of sludge from the avr process with ammonium. Effect of additives on thiosulfate leaching of a gold ore s. Gold and silver leaching in thiosulfate solution is preferable kinetically and environmentally if conducted in a closed vessel system. Thiosulfate leaching thiosulfate leaching is an alkaline. Gold leaching in thiosulfate solutions and its environmental. Gold and silver leaching in thiosulfate solution is preferable kinetically and environmentally if. Such a process strategy is very attractive for leaching certain difficulttotreat ores and presents lessened lixiviant toxicity compared to cyanide. It is currently the main gold leaching process in the world. Leaching and recovery of gold using ammoniacal thiosulfate. Review gold leaching by copperii in ammoniacal thiosulphate solutions in the presence of additives. The dissolution of the gold can be described as follows where oxygen is the oxidant and thiosulfate the. These chemicals represent health and safety risks for workers and a serious threat for the.
Cyanide alternative leaching reagents for gold recovery from. Feng university of science and technology, liaoning, anshan, china received august 15, 2017, revised november 15, 2017 the effect of additives on gold leaching was investigated. The thiosulfate leaching of gold from waste pcbs exhibits that gold could be leached with good recovery under specific conditions. A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated.
In the testing, thiosulfate consumption was 30 kgt of ore. Sep 01, 2000 thiosulfate leaching kinetics of gold in the presence of copper and ammonia thiosulfate leaching kinetics of gold in the presence of copper and ammonia breuer, p. Bits and pieces of information are what is dangerous with any process. Chlorination, aqua regia, bromine, thiocyanate, thiosulfate and thiourea leaching. This study was performed using agfcimpregnated activated carbon acagrfc. Mineralogical studies on the concentrate showed that very fine gold grains 10. The influence of thiosulfate, ammonia and copper sulfate concentrations on the leaching of gold from pcbs of waste mobile phones was investigated. The leaching results of different types of gold ores including oxide, sulfide. Thiosulphate stability in gold leaching process bibliotheque et. Within the tanks, the slurry interacts with thiosulfate and a fine, beadlike material called resin that collects the gold.
Nioshtic2 publications search 10011646 coppercatalyzed. In addition, thiosulfate can be cheaper than cyanide. Thiosulfate is also used to extract or leach gold sodium thiosulfate and silver from their ores as a less toxic alternative to cyanide. Bureau of mines as a potentially economical and environmentally safe method for heap leaching or in situ leaching of lowgrade oxidized gold ores. All, i did the search on thio leach and read all 304 results, but in none of them there is an explanation of how it is done on escrap. Nov 21, 2014 ammonium thiosulfate ecological alternative to replace sodium cyanide in gold and silver dissolution in lowgrade ores, m. However, the major problem with this leaching method has been the high consumption of reagents. Associated sulfide minerals in thiosulfate leaching of gold. Recovery of the gold dissolved in the rich leaching solution can take place by acti. At the end of the leaching process two goldthiosulfate complex solutions were obtained, with gold concentrations of 336.
The processes include subjecting the goldbearing and copperbearing thiosulfate solution to a ph andor temperature adjustment to reduce tetrathionate concentration in the thiosulfate solution prior to contacting with an ion. However, gold cyanidation process has serious environmental risks if an accident occurs in the process because of the toxicity of cyanide. The hydrometallurgical leaching of native gold from goldbearing ores or the dissolution of gold metal during the recycling of electronic and precious metal scrap is performed every day using hazardous chemicals such as sodium cyanide or aqua regia. Pdf ammoniacal thiosulfate leaching of gold from a. Ammonium thiosulfate ecological alternative to replace sodium. Similar trends were obtained for the leaching of gold from two different types of scraps and pcbs of waste mobile phones. Thiosulfate leaching of gold ores has great potential to reduce the impact on the environment. Comparison of cyanide and thiosulphate leaching for gold production. For the barrick gold goldstrike thiosulfate plant, the leach tanks have been constructed out of 2205 stainless steel because of the corrosive nature of thiosulfate in the leaching system.
Fundamental aspects of gold leaching in thiosulfate. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological advantages including its lower toxicity and greater efficiency with gold deposits associated with pregrobbing ores. Thiosulphate leaching is a process that removes gold from gold bearing ores without the use of cyanide. At best, leaching achieved 2,98 mghcm2 with ammonium thiosulfate and 2,68 mghcm2 with sodium thiosulfate. Ammonium thiosulfate is a noncyanide lixiviant for gold leaching. Pdf gold dissolution in nonammoniacal thiosulphate solutions. All of my observations are with sodium thiosulfate. As result of this comparison, thiourea stands out as the most promising alternative gold leaching reagent to cya nide. The effect of cuii ions addition on silver leaching from solid residue after pressure leaching was investigated at thiosulfate and ammonia concentrations of 0. The conventional cyanidation process in gold leaching has been used since 1887. The effect of concentration of different reagents, applied potential, ph, temperature, and electrode rotating. The role of ligands and oxidants in thiosulfate leaching.
The ammoniathiosulfate system with copper offers high gold leaching rates compared to the cyanide system, because the reaction is catalyzed by cupric ions. Two models were generated from the data for predicting gold extraction and low thiosulfate consumption within the experimental region. Dec 01, 2002 read thiosulfate leaching of gold from a mechanically activated cupbzn concentrate, hydrometallurgy on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. It is the most commonly used leaching process for gold extraction. Is it possible members with more knowledge on this matter to post here to discuss this method of leach in details, like thio solution concentration. Thus, the use of thiosulfate with autoclaveprocessed double refractory ores does not result in the loss of the gold complex in the tails. In thiosulfate and thiourea leaching, some metal surfaces may need to be coated to prevent cementation of gold from gold bearing solutions. Therefore, a method for leaching or dissolving gold from ores or precious. I would like to hear the facts,from someone that has used it in a real mining situation.
Adsorption of the goldthiosulfate complex ion au s 2 o 3 2 3 on silver ferrocyanide agfcimpregnated activated carbon in aqueous solution has been studied in order to find an effectual adsorbent for the thiosulfate extracting gold from ores. Newmont gold company has evaluated the ammonium thiosulphate heap leach process for gold recovery from low grade carbonaceous sulphidic refractory ores following. The current problem of thiosulphate gold leaching is the high reagent consumption, to understand the decomposition chemistry of thiosulphate, solution stability tests were conducted in open and sealed vessek mder ambient temperature. Leaching by thiosulfate decreases interference from these foreign cations. Au s o present in the solutions produced by leaching gold ores in an ammoniathiosulfate media, where copper is the main impurity in the system. Gold is recovered from the eluate by precipitation with sulfide ions, cementation or electrowinning. A process for recovering gold from thiosulfate leach solutions and slurries in which gold is loaded onto an ion exchange resin. Ammoniacal thiosulfate leaching of gold from a refractory ore using a full factorial design.
For this propose, the gold leaching reagents are described and discussed in terms of their environmental and economical points of view. Despite the fact that the gold mining industry accounts for only % of total cyanide consumption there is growing public concern over the use of toxic cyanide for gold extraction. Leaching of gold from the waste mobile phone printed circuit. Gold is recovered from the resin by elution with polythionate ions and the resin is regenerated with sulfide or sulfite. Gold recovery from ammoniathiosulfate leaching solution. The processes can employ lixiviants that include at most only small amounts of copper andor ammonia and operate at a relatively low ph, reduction of polythionates, inert atmospheres to control polythionate production, and electrolytic solutions which provide relatively high rates of. Us8597399b2 method for thiosulfate leaching of precious.
Thiosulfate leaching of gold from waste mobile phones. Us6632264b2 gold recovery from thiosulfate leaching. The thiosulfategold complex formed in thiosulfate leaching is not attracted to carbon so this failure to remove the carbon is no longer an issue. The proposed method of the gold recovery comprises leaching with a solution of a mixture of sodium and ammonium hydrosulfite and thiosulfate, by sorption of the thiosulfategold complex on a highly basic anion exchanger and by isolation of the highly basic anion exchanger, the sorption being carried out 210 hours after the leaching. Reagent consumption is one of the major factors affecting the feasibility of the process to the actual operation yen et al.
Thiosulfate leaching offers a number of benefits related to gold recovery yields and environmental concerns. The solutions resulting from gold leaching contain gold thiosulfate, copperammonia and copper thiosulfate complexes, plus tetrathionate in different proportions as a function of the concentrations of copper, ammonia, thiosulfate, and ph. Gold extraction was found to be enhanced with solutions containing 1520. Thiosulfate leaching of middlerefractory gold ore with. Method for thiosulfate leaching of precious metalcontaining. Leaching of gold, silver and accompanying metals from circuit boards pcbs waste jana ficeriova1, peter balaz1 and eberhard gock2 auag noble metal wastes represent a wide range of waste types and forms, with various accompanying metallic elements. The goldbearing sample was identified as a highsulfur finesized wrappedtype refractory gold. During this time, gold was dissolved according to reaction 1, and the formation of the goldthiosulfate complex aus 2 o 3 2 3.
The kinetics and mechanism of gold leaching in the ammoniathiosulfatecopper atscu system have been studied using the rotating electrochemical quartz crystal microbalance reqcm. Thiosulfate extensively forms complexes with transition metals hence a common use is dissolving silver halides in film photography developing. Processes for recovering gold from coppergold ores thiosulfate leaching or gold ores copper catalyzed thiosulfate leaching using ion exchange technology are disclosed. To leach a mildrefractory copperbearing gold ore, the authors used a reagent combination of 0. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological advantages including its lower toxicity and greater efficiency with gold deposits. Run time,ph,and temperature are the keys to using thiosulfate. Sodium thiosulphate gold leaching 911 metallurgist. Oct 14, 2003 processes for recovering gold from copper gold ores thiosulfate leaching or gold ores copper catalyzed thiosulfate leaching using ion exchange technology are disclosed. Leaching of middlerefractory gold ore show that both of the consumption of thiosulfate and leaching rate was decreased compare to the traditional copperammonia thiosulfate system. Selected leaching results unlike gold cyanidation, thiosulfate leaching involves relatively high concentrations of reagents, while the gold extraction is largely dependent on the presence or absence of various background reagents. A method for leaching or dissolving gold from ores or. Thiosulfatecopperammonia leaching of pure gold and. There was a distinct disappearance of gold after each batch reactor experiment. Thiosulfate leaching can be considered a nontoxic process, the gold dissolution rates can be faster than conventional cyanidation and, due to the decreased interference of foreign cations, high gold recoveries can be obtained from the thiosulfate leaching of complex and carbonaceoustype ores.
The effects of some associated minerals on thiosulfate gold leaching were studied through thermodynamic analysis and leaching experiments on composite ore samples containing various minerals and a reference silicate gold ore. Ca2698578c method for thiosulfate leaching of precious. It is less destructive and toxic, and has a higher efficiency with pregrobbing ores as a leaching agent. Importance of solution chemistry for thiosulphate leaching. For clarity, the different components in the thiosulfate leaching system are discussed separately. Biooxidationthiosulfate leaching of refractory gold. Gold recovery from thiosulfate leaching the university of. The major chemical components of thiosulfate are common fertilisers which include ammonium thiosulphate and ammonium sulphate. Thiosulphate leaching in gold recovery is an alternative chemical process with several advantages such as, lower cost and relatively harmless nature, faster leaching kinetics compared to cyanide. Pdf thiosulfate leaching of gold from waste mobile.
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