The gold industry has been seeking alternative reagents for leaching gold from lowgrade ores for the past 25 years. Description online access for this thesis was created in part with support from the institute of museum and library services imls administered by the nevada state library, archives. Improvement of thiosulfate stability in gold leaching. A method for leaching or dissolving gold from ores or. The dissolution of the gold can be described as follows where oxygen is the oxidant and thiosulfate the. 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.
A kinetic study that compares the leaching of gold in the. Unlike cyanide, which is highly toxic, the chemicals used in the thiosulfate leaching process are benign. Leaching of gold and silver from printed circuit boards pcbs with cyanide, nitric acid and thiosulfate has been performed with reaction times greater than 2 hours 6. They found that the profit of the thiosulfate leaching process was similar to that of the traditional cyanide method. Leaching of a selected gold ore using thiosulfate solutions for 24 hours suggested the optimum conditions to leach the ore to be 0. Effect of galena on thiosulfate leaching of gold request pdf. The complexity of thiosulfate leaching of gold is exemplified in figure 1 14. High consumption of reagents and the lack of a cheap process for recovering gold have made thiosulfate leaching. Associated sulfide minerals in thiosulfate leaching of. Thiosulfatecopperammonia leaching of pure gold and. The effect of concentration of different reagents, applied potential, ph, temperature, and electrode rotating.
The results show that the reduction in gold dissolution did not originate from the. Thiosulfate leaching thiosulfate leaching is an alkaline. Leaching of gold from the waste mobile phone printed circuit. Leaching of gold occurs at appreciable dissolution rates. Six variables were investigated in fractional factorial screening tests, including thiosulfate s2o23, sulfite so23. Bureau of mines as a potentially economical and environmentally safe method for heap leaching or in situ leaching of lowgrade oxidized gold ores. Barrick thiosulfate leaching of double refractory ore. In addition, the leaching team analyzed the thiosulfate leaching process compared to the traditional cyanide process. The role of ligands and oxidants in thiosulfate leaching. Solidification of sulfur and arsenic in gold concentrate.
The major chemical components of thiosulfate are common fertilisers which include ammonium thiosulphate and ammonium sulphate. The models predicted 90pct gold extraction and a consumption of 0. In the case of the gold leaching process using thiosulfate, copper oxidation by thiosulfate deserves special attention because it is a thermodynamically favored reaction. The results show that solidification roasting oxidation is an efficient and environmentally friendly pretreatment method, and the gold in the calcine can be effectively leached out via the green copper. 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. Mineralogical studies on the concentrate showed that very fine gold grains 10. Recovery of gold from thiosulfate leaching solution. 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. 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.
Also getting the gold out of the precipitates seems to be a real pain. Leaching of gold and silver from printed circuit board of. The mechanism that tetrathionates retarded gold dissolution during the anodic process of gold thiosulfate leaching was studied with the help of electrochemical and spectroscopic techniques. The recovery of gold from thiosulfate will only be maximized through a complete understanding of the chemistry of thiosulfate leaching of gold. A new methodology was established that allowed for the measurement of the leaching currents from currentpotential curves with minimal interference of the.
Gold and silver leaching in thiosulfate solution is preferable kinetically and environmentally if conducted in a closed vessel system. Gold leaching, thiosulfate, additives, leaching kinetics, thiosulfate stability. 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. For clarity, the different components in the thiosulfate leaching system are discussed separately. Biooxidationthiosulfate leaching of refractory gold. Two models were generated from the data for predicting gold extraction and low thiosulfate consumption within the experimental region. Gold recovery from refractory gold concentrates by pressure. A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. 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. In alkaline or near neutral solution of thiosulfate, gold dissolves slowly in the presence of a mild oxidant white, 1905. A comparison of thiosulfate with cyanide leaching of gold from carbonaceous ore showed that thiosulfate is chemically better and economically more advantageous.
Within the tanks, the slurry interacts with thiosulfate and a fine, beadlike material called resin that collects the gold. Leaching process involves time consuming stages to reach the total metal dissolution. It has the advantages of fast gold leaching speed and nontoxicity. The current problem of thiosulphate gold leaching is the high reagent. Jul 16, 2016 leaching by thiosulfate decreases interference from these foreign cations.
Its advantage is that it can form stable complexes with gold. The present work deals with the recovery of gold using ammonium thiosulfate as a leaching agent from waste mobile pcbs containing 0. Thiosulfate leaching thiosulfate leaching is an alkaline process which removes gold from carbonaceous ores instead of using cyanide. Improved recovery of gold and silver from thiosulfate solution on. Thiosulfate leaching of gold ores has great potential to reduce the impact on the environment. Faculty of science, kunming university of science and technology, kunming, china. Most published studies on gold leaching with thiosulfate focus on gold ores. Thiosulfatecopperammonia leaching of pure gold and pressure. Gold leaching was primarily limited by the volume of lixiviant contacting the carbonaceous. May 27, 2017 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. This article presents a detailed kinetic study of gold leaching in cyanide, ammonia thiosulfate, and chloridehypochlorite solutions. 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. Thiosulfate leaching of gold from waste mobile phones. A study of thiosulfate leaching of gold from carbonaceous ore.
Us5536297a gold recovery from refractory carbonaceous. Pdf thiosulfate leaching of gold from waste mobile phones. Fundamental aspects of gold leaching in thiosulfate. Ammonium thiosulphate is an alternative gold leaching laaviant used to replace cyanide. It is less destructive and toxic, and has a higher efficiency with pregrobbing ores as a leaching agent. In the testing, thiosulfate consumption was 30 kgt of ore. Study on gold extraction from thiosulfateethylenediamine. Gold recovery from electronic waste by pressure oxidation. Importance of solution chemistry for thiosulphate leaching. Anodic polarization, cathodic polarization and leaching experiments were included in this study. Thiosulfate leaching offers a number of benefits related to gold recovery yields and environmental concerns.
Thiosulphate leaching is a process that removes gold from gold bearing ores without the use of cyanide. Ammoniacal thiosulfate and sodium cyanide leaching of preg. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological. Temperature had the greatest effect on the gold leaching rate. A process for recovering gold in which an ore slurry of refractory sulfidic and refractory carbonaceous ore having pregrobbing characteristics due to the presence of organic carbon is subjected to pressure oxidation in an autoclave.
The subsequent leaching tests using reqcm showed that the gold leach rate in the oxygenthiosulphate system without any additives is in the. Coppercatalyzed thiosulfate leaching is being investigated by the u. Leaching of gold from the waste mobile phone printed circuit boards pcbs with ammonium thiosulphate literature reveals that only limited studies have been carried out to recover the metals from waste mobile phonepcbs. The analysis of the pox process could supplement the past research results, and the data for. Nioshtic2 publications search 10011646 coppercatalyzed. Has anyone here actually used thiosulfate for leaching gold ore,and had positive results,that can be repeatable as a real leaching process. 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. Study of the goldthiosulfate interface under leaching. 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. Thiosulfate leaching to recover gold from ores is known for several decades but extensive researches have been started only for the past two decades. Gold recovery from ammoniathiosulfate leaching solution. Pdf thiosulphate leaching for gold hydrometallurgy.
A fundamental study on the use of ironiiioxalate thiosulfate thiourea for gold leaching. Thiosulphate leaching for gold hydrometallurgy sciencedirect. Moreover, thiosulfate can be used for leaching of gold from carbonaceous gold ores as gold thiosulfate complex which is not pregrobbed by the. Ammoniacal thiosulphate solution allows the solubilization of gold as stable anionic complex. 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 gold from the waste mobile phone printed. 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. The oxidized ore slurry is mixed with a thiosulfate salt lixiviant, which mixture is maintained at a ph between 7 and 8.
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. Pdf thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high. Many researchers have identified that thiosulfate leaching is the most likely alternative to cyanidation due to nontoxicity, low cost and other benefits. Biooxidationthiosulfate leaching of refractory gold concentrate. Newmont gold company has evaluated the ammonium thiosulphate heap leach process for gold recovery from low grade carbonaceous sulphidic refractory ores following. Effect of additives on thiosulfate leaching of a gold ore. Fundamental aspects of gold leaching in thiosulfate solutions. Gold recovery from refractory gold concentrates by. Therefore, a method for leaching or dissolving gold from ores or precious. However, the major problem with this leaching method has been the high consumption of reagents. The block flow diagram process steps of this study is shown in. After roasting and oxidizing, the gold leaching rate increases substantially. The processes include subjecting the gold bearing and copperbearing thiosulfate solution to a ph andor temperature adjustment to reduce tetrathionate concentration in the thiosulfate solution prior to contacting with an ion.
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. The conventional cyanidation process in gold leaching has been used since 1887. At full capacity,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks. However, in alkaline solutions, oxidization of copper by thiosulfate is much slower zhang, 2004.
Effect of additives on thiosulfate leaching of a gold ore s. In addition, thiosulfate can be cheaper than cyanide. Has anyone found a real working precipitation process to recover the gold,that works well,and is dependable. The processes include subjecting the gold bearing and copperbearing thiosulfate solution to a ph andor temperature adjustment to reduce tetrathionate concentration in the. In a resinin leach system, full gold recovery was also achievable with sufficient resin after 24 h leach with 0. The process of thiosulfate leaching of gold were researched by employing the response surface methodology rsm. Gold recovery by catalytic copper ammonium thiosulphate solution has been studied. 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. Solidification of sulfur and arsenic in gold concentrate and. One such ewaste, the mobile phone printed circuit boards pcbs contain various precious metals which can be extracted by different hydrometallurgical routes. To leach a mildrefractory copperbearing gold ore, the authors used a reagent combination of 0. 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. Cyanide alternative leaching reagents for gold recovery from electronic waste.
The percentage of gold leached by ammoniacal thiosulfate was found to depend on the initial gold content of the carbonaceous matter since an equivalent, small amount of gold was taken up by all carbonaceous matters examined. Sweep voltammetry, chronocoulometry and surface enhanced raman spectroscopy sers were employed in this research program to characterize the gold electrolyte interface under leaching conditions in alkaline thiosulfate solution. The general consensus is that the optimum conditions for leaching gold depends on the nature of the ore to be treated. This instrument allows the mass of a gold sample to be measured in situ, with a sensitivity of less than 10 ng. A study of thiosulfate leaching of gold from carbonaceous. Thiosulphate stability in gold leaching process bibliotheque et. Thiosulfate is one of the most promising green gold leaching reagents that can replace cyanide.
The kinetics and mechanism of gold leaching in the ammonia thiosulfate copper atscu system have been studied using the rotating electrochemical quartz crystal microbalance reqcm. Gold leaching in thiosulfate solutions and its environmental. The results for leaching gold with alternative reagents, sodium thiosulfate and ammonium hydroxide, show that the best extraction was achieved at 0. The cost and transport of cyanide, the poor recovery of gold from carbonaceous ores, the lack of selectivity of cyanide towards copper minerals and the cost of waste treatment are real factors which can make cyanide unattractive in some circumstances. Jm ammonium thiosulphate, 40 mm copper sulphate, ph. Thiosulphate is a more effective lixiviant of pregrobbing and highcopper ores than cyanide because ammoniacal thiosulphate leaching is less sensitive than cyanidation to. Pdf gold dissolution in nonammoniacal thiosulphate solutions. 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. Ammonium thiosulfate nh 4 2 s 2 o 3 is a leachant which is nontoxic as well as economical. The gold bearing sample was identified as a highsulfur finesized wrappedtype refractory gold. Cyanide alternative leaching reagents for gold recovery. However, gold cyanidation process has serious environmental risks if an accident occurs in the process because of the toxicity of cyanide. Ammonium thiosulfate is a noncyanide lixiviant for gold leaching. Associated sulfide minerals in thiosulfate leaching of gold.
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