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