Improvement of thiosulfate stability in gold leaching. Leaching of gold occurs at appreciable dissolution rates. Has anyone here actually used thiosulfate for leaching gold ore,and had positive results,that can be repeatable as a real leaching process. Therefore, a method for leaching or dissolving gold from ores or precious. Gold recovery from refractory gold concentrates by pressure. Gold leaching was primarily limited by the volume of lixiviant contacting the carbonaceous. The gold bearing sample was identified as a highsulfur finesized wrappedtype refractory gold. Thiosulfate leaching to recover gold from ores is known for several decades but extensive researches have been started only for the past two decades. Solidification of sulfur and arsenic in gold concentrate and leaching of the gold by thiosulfate. Temperature had the greatest effect on the gold leaching rate. The recovery of gold from thiosulfate will only be maximized through a complete understanding of the chemistry of thiosulfate leaching of gold.
It is currently the main gold leaching process in the world. 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. In the testing, thiosulfate consumption was 30 kgt of ore. The subsequent leaching tests using reqcm showed that the gold leach rate in the oxygenthiosulphate system without any additives is in the. Most published studies on gold leaching with thiosulfate focus on gold ores. 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 conventional cyanidation process in gold leaching has been used since 1887. 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. The effect of tetrathionate on the anodic process of gold. Ammonium thiosulphate is an alternative gold leaching laaviant used to replace cyanide. They found that the profit of the thiosulfate leaching process was similar to that of the traditional cyanide method. In addition, the leaching team analyzed the thiosulfate leaching process compared to the traditional cyanide process.
The complexity of thiosulfate leaching of gold is exemplified in figure 1 14. Pdf thiosulphate leaching for gold hydrometallurgy. Faculty of science, kunming university of science and technology, kunming, china. Thiosulfate leaching offers a number of benefits related to gold recovery yields and environmental concerns. Fundamental aspects of gold leaching in thiosulfate. The present work deals with the recovery of gold using ammonium thiosulfate as a leaching agent from waste mobile pcbs containing 0. In addition, thiosulfate can be cheaper than cyanide. 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. Ammoniacal thiosulphate solution allows the solubilization of gold as stable anionic complex. Improved recovery of gold and silver from thiosulfate solution on. Pdf thiosulfate leaching of gold from waste mobile. Solidification of sulfur and arsenic in 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. The oxidized ore slurry is mixed with a thiosulfate salt lixiviant, which mixture is maintained at a ph between 7 and 8.
Barrick thiosulfate leaching of double refractory ore. Ammonium thiosulfate nh 4 2 s 2 o 3 is a leachant which is nontoxic as well as economical. Leaching of gold from the waste mobile phone printed. Many researchers have identified that thiosulfate leaching is the most likely alternative to cyanidation due to nontoxicity, low cost and other benefits. Study on gold extraction from thiosulfateethylenediamine. Leaching process involves time consuming stages to reach the total metal dissolution.
Leaching of gold from the waste mobile phone printed circuit. A study of thiosulfate leaching of gold from carbonaceous. 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. 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 effect of concentration of different reagents, applied potential, ph, temperature, and electrode rotating. Gold leaching in thiosulfate solutions and its environmental. Gold recovery from electronic waste by pressure oxidation. 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.
Recovery of gold from thiosulfate leaching solution. 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. Mineralogical studies on the concentrate showed that very fine gold grains 10. Us5536297a gold recovery from refractory carbonaceous. 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 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. Associated sulfide minerals in thiosulfate leaching of gold. Six variables were investigated in fractional factorial screening tests, including thiosulfate s2o23, sulfite so23.
In the case of the gold leaching process using thiosulfate, copper oxidation by thiosulfate deserves special attention because it is a thermodynamically favored reaction. Pdf gold dissolution in nonammoniacal thiosulphate solutions. Bureau of mines as a potentially economical and environmentally safe method for heap leaching or in situ leaching of lowgrade oxidized gold ores. 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. One such ewaste, the mobile phone printed circuit boards pcbs contain various precious metals which can be extracted by different hydrometallurgical routes. It is less destructive and toxic, and has a higher efficiency with pregrobbing ores as a leaching agent. 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. 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. Effect of additives on thiosulfate leaching of a gold ore s. The role of ligands and oxidants in thiosulfate leaching of gold. In a resinin leach system, full gold recovery was also achievable with sufficient resin after 24 h leach with 0.
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. Thiosulfate is one of the most promising green gold leaching reagents that can replace cyanide. To leach a mildrefractory copperbearing gold ore, the authors used a reagent combination of 0. Coppercatalyzed thiosulfate leaching is being investigated by the u. Cyanide alternative leaching reagents for gold recovery. Gold leaching, thiosulfate, additives, leaching kinetics, thiosulfate stability. The current problem of thiosulphate gold leaching is the high reagent. Leaching of a selected gold ore using thiosulfate solutions for 24 hours suggested the optimum conditions to leach the ore to be 0. 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 mechanism that tetrathionates retarded gold dissolution during the anodic process of gold thiosulfate leaching was studied with the help of electrochemical and spectroscopic techniques. A study of thiosulfate leaching of gold from carbonaceous ore. Such a process strategy is very attractive for leaching certain difficulttotreat ores and presents lessened lixiviant toxicity compared to cyanide. Its advantage is that it can form stable complexes with gold.
It has the advantages of fast gold leaching speed and nontoxicity. The general consensus is that the optimum conditions for leaching gold depends on the nature of the ore to be treated. Effect of galena on thiosulfate leaching of gold request pdf. Ammoniacal thiosulfate and sodium cyanide leaching of preg. Pdf thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high. This instrument allows the mass of a gold sample to be measured in situ, with a sensitivity of less than 10 ng. 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.
Moreover, thiosulfate can be used for leaching of gold from carbonaceous gold ores as gold thiosulfate complex which is not pregrobbed by the. Gold recovery by catalytic copper ammonium thiosulphate solution has been studied. Effect of additives on thiosulfate leaching of a gold ore. Within the tanks, the slurry interacts with thiosulfate and a fine, beadlike material called resin that collects the gold. 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. Leaching of gold and silver from printed circuit board of. Ammonium thiosulfate is a noncyanide lixiviant for gold leaching. Thiosulfatecopperammonia leaching of pure gold and pressure. The gold leach rates were measured using a rotating electrochemical quartz crystal microbalance reqcm.
The process of thiosulfate leaching of gold were researched by employing the response surface methodology rsm. Has anyone found a real working precipitation process to recover the gold,that works well,and is dependable. After roasting and oxidizing, the gold leaching rate increases substantially. Importance of solution chemistry for thiosulphate leaching. Us6632264b2 gold recovery from thiosulfate leaching.
Thiosulphate stability in gold leaching process bibliotheque et. A fundamental study on the use of ironiiioxalate thiosulfate thiourea for gold leaching. However, the major problem with this leaching method has been the high consumption of reagents. Gold and silver leaching in thiosulfate solution is preferable kinetically and environmentally if conducted in a closed vessel system. For clarity, the different components in the thiosulfate leaching system are discussed separately. The models predicted 90pct gold extraction and a consumption of 0.
Thiosulphate is a more effective lixiviant of pregrobbing and highcopper ores than cyanide because ammoniacal thiosulphate leaching is less sensitive than cyanidation to. The processes include subjecting the gold bearing and copperbearing thiosulfate solution to a ph andor temperature adjustment to reduce tetrathionate concentration in the. 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. Also getting the gold out of the precipitates seems to be a real pain. Thiosulphate leaching an alternative to cyanidation in gold processing alternatives to cyanide in gold processing thiosulphate leaching thiosulphate leaching is a process that removes gold from gold bearing ores without the use of cyanide.
The analysis of the pox process could supplement the past research results, and the data for. Thiosulphate leaching is a process that removes gold from gold bearing ores without the use of cyanide. Thiosulfate leaching thiosulfate leaching is an alkaline process which removes gold from carbonaceous ores instead of using cyanide. The major chemical components of thiosulfate are common fertilisers which include ammonium thiosulphate and ammonium sulphate. The results for leaching gold with alternative reagents, sodium thiosulfate and ammonium hydroxide, show that the best extraction was achieved at 0. Study of the goldthiosulfate interface under leaching. Solidification of sulfur and arsenic in gold concentrate and. 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. 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.
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. However, in alkaline solutions, oxidization of copper by thiosulfate is much slower zhang, 2004. 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. A kinetic study that compares the leaching of gold in the. Cyanide alternative leaching reagents for gold recovery from electronic waste. Thiosulfate leaching thiosulfate leaching is an alkaline. Gold recovery from ammoniathiosulfate leaching solution. In alkaline or near neutral solution of thiosulfate, gold dissolves slowly in the presence of a mild oxidant white, 1905. Fundamental aspects of gold leaching in thiosulfate solutions. Thiosulphate leaching for gold hydrometallurgy sciencedirect. Thiosulfate leaching of gold from waste mobile phones. Anodic polarization, cathodic polarization and leaching experiments were included in this study. However, gold cyanidation process has serious environmental risks if an accident occurs in the process because of the toxicity of cyanide.
Jm ammonium thiosulphate, 40 mm copper sulphate, ph. Biooxidationthiosulfate leaching of refractory gold concentrate. The block flow diagram process steps of this study is shown in. 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.
Newmont gold company has evaluated the ammonium thiosulphate heap leach process for gold recovery from low grade carbonaceous sulphidic refractory ores following. Pdf thiosulfate leaching of gold from waste mobile phones. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological. Jul 16, 2016 leaching by thiosulfate decreases interference from these foreign cations. At full capacity,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks.
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. The results show that the reduction in gold dissolution did not originate from the. 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. Biooxidationthiosulfate leaching of refractory gold. A comparison of thiosulfate with cyanide leaching of gold from carbonaceous ore showed that thiosulfate is chemically better and economically more advantageous.
This article presents a detailed kinetic study of gold leaching in cyanide, ammonia thiosulfate, and chloridehypochlorite solutions. Thiosulfate leaching of gold ores has great potential to reduce the impact on the environment. 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. A new methodology was established that allowed for the measurement of the leaching currents from currentpotential curves with minimal interference of the. Nioshtic2 publications search 10011646 coppercatalyzed. A process of biooxidation followed by thiosulfate leaching of gold from refractory gold concentrate was investigated. The gold industry has been seeking alternative reagents for leaching gold from lowgrade ores for the past 25 years. Thiosulfatecopperammonia leaching of pure gold and. The role of ligands and oxidants in thiosulfate leaching. Associated sulfide minerals in thiosulfate leaching of. Unlike cyanide, which is highly toxic, the chemicals used in the thiosulfate leaching process are benign. High consumption of reagents and the lack of a cheap process for recovering gold have made thiosulfate leaching. Processes for recovering gold from copper gold ores thiosulfate leaching or gold ores copper catalyzed thiosulfate leaching using ion exchange technology are disclosed.
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