In the presence of sodium sulphite, the effective concentration of thiourea is increased and the dissolution rate. Bioleaching, chlorination, aqua regia, bromine, thiocyanate, thiosulfate and thiourea leaching. In the leaching test on the reference gold ore, about 93% of gold was extracted within 3. Nov 29, 2007 gold and silver leaching and recovery process with partially oxidized thiourea characterized as consisting of the thiourea oxidation by the application of an electrical current in a membrane cell, where the anodic and cathodic compartments are separated, before sending the product to the leaching stage and that once concluded the leaching time. The present communication deals with the leaching of gold and silver from the printed circuit boards pcbs of waste mobile phones using an effective and less hazardous system, i. An innovative thiourea gold leaching process sciencedirect. Study on mechanism of gold leaching by thiourea in the. With depletion of the oxidized freemilling gold reserves close to the earths. The study showed that acid washing is essential prior to thiourea leaching fig. The dissolution of gold in thiourea solutions was reported for the first time in 1941, and it was continued in 1960 1. The process design of gold leaching and carboninpulp circuits 14 januaryfebruary 1999 the journal of the south african institute of mining and metallurgy figure 2the carboninpulp cip process figure 1computeraided process engineering cape. These leach modifying additives are a unique and key component in the effectiveness of this process. A leaching agent for gold leaching and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting.
Leaching with a relatively concentrated thiourea solution 1mcs nh 2 2 resulted in 83% gold and 75% silver extraction in four hours. International journal of the society of materials engineering for resources 2014, 20 1, 2934. Leaching goldsilver ores with sodium cyanide and thiourea. Although not as aggressive a leaching agent as cyanide, thiosulphate offers several technological. Leaching gold silver ores with sodium cyanide and thiourea under comparable conditions by j. Gold electrowinning from thiourea solutions, minerals. Optimizing and evaluating the operational factors affecting.
However, the processes of gold recovering from thiourea solutions have received little attention, particularly the electrowinning process. In the method, the gold and silver are extracted from the precious metal bearing materials with a thiourea solution to form a thiourea leach, and the thiourea leach is contacted with carbon to adsorb the gold and silver. Laboratory testing of this reagent has indicated that a thiourea process for gold extraction has. In the presence of sodium sulphite, the effective concentration of thiourea is increased and the dissolution rate of gold in thiourea solution is greatly increased. Other minerals, such as arsenic can react with the oxygen and slow the rate of gold. In situ leaching tests with thiourea as the lixiviant were carried out in two workedout stopes at the no. Pdf gold leaching by use of an n,n disubstituted thiourea. L amps shire abstract there is currently mch interest in how extraction of gold and silver from ores with acidic.
Leaching of a gold bearing partially roasted sulphide. Leaching process involves time consuming stages to reach the total metal dissolution. There are a few wellreputed leaching methods using a variety of different reagents. Report of investigations 9022 recovery of silver, gold, and lead from a complex sulfide ore using ferric chloride, thiourea, and brine leach solutions. Pdf leaching of ovacik gold ore with cyanide, thiourea and. Because the leach ing of gold in acidic thiourea solutions is a redox reaction, useful. An overview of the enviroleach gold recovery process. Another common application for use of thiourea is a common sulfur source for making semiconductor cadmium sulfide nanoparticle. N2 the hydrometallurgical application of thiourea in processing precious metal ores and concentrates has reached the development stage.
However, in actual leaching systems, some sulfide minerals significantly catalyze the redox reaction between thiourea and ferric ion, causing high thiourea consumption if ferric ion is present in excess. Alternative lixiviants to cyanide for leaching gold ores. The behaviour of gold was examined with electrochemical tests and weight loss measurements a using. Eighteen experiments were used to create a model which describes the leaching of gold on the basis of selected factors. This research was carried out on aghdareh gold ore. While a large number of studies have been carried out on gold leaching in acidic thiourea solutions,48 the mechanism of the process has received little attention. The use of cyanide for the extraction of gold from ores and. Pdf an innovative thiourea gold leaching process stefano.
The process design of gold leaching and carboninpulp. Spectroelectrochemical investigations of gold leaching in thiourea media spectroelectrochemical investigations of gold leaching in thiourea media parker, g. The process design of gold leaching and carboninpulp circuits. These are removed by thermal regeneration of the eluted carbon, typically in a rotary kiln at temperatures of 650750c. Lead metal was recovered from the brine solution in an electrolytic cell with. Process for gold and silver leaching with thiourea solutions. With the treated flue dust residue, gold extraction was about 60%. The use of thiourea scnh 2 2 tu has been studied extensively, mainly because it is not harmful to the environment, nontoxic to human beings, and the dissolution of gold in thiourea solutions is much faster than in cyanide solutions. The method comprises a step of leaching the raw material in leach solution comprising thiosulphate anions. The only difference being in the recovery percentage. Pdf leaching of gold and silver from crushed auag wastes. Electrochemical oxidation of gold and thiourea in acidic. Thiourea leaching of gold and silver technology update.
The use of thiourea as an alternative lixiviant to gold cyanidation for processing goldbearing ores or concentrates was first developed by soviet metallurgists in the 1940s. The thiourea process of gold and silver extraction from ores, concentrates or secondary raw materials con sists of gold and silver leaching into the thiourea solution and the consequent precipitation of these metals from the solu tion. Thiourea is easily oxidized to formamidine disulphide, which reduces the leaching efficiency and increases reagent consumption. Recovery of silver, gold, and lead from a complex sulfide ore. Is any free how to for thio leaching guide on the internet. Following the biooxidation, gold has been leached in acidic thiourea solutions, under different ph1 2.
While awareness of the use of biohydrometallurgical techniques in metal mining industries is increasing, the knowledge on microbiological precious metal solubilization is still. The interac tion of leach variables with thiourea consumption and gold extraction was established. For the thiourea process to compete industrially with cyanidation, it is essential to develop efficient processes to recover the gold from solution. Thiourea is a reducing and complexing agent and can be used for the processing of gold and silver. A lixiviant for gold and silver leaching can be created by selectively oxidizing thiourea, bypassing the steps of cyanide use and smelting. Research on the leaching of gold by thiourea has been reported extensively in the literature, but research on the recovery of gold from leach solutions has not been well documented. It has also been used in the production and modification of synthetic resins. In this regard, leaching studies focus on the use of strong acids hcl, hno 3, h 2 so 4 and oxidative reagents cyanide, thiourea, halide, nitrate, iodide, and thiosulfates 35.
Thiourea leaching of gold concentrates and recovery of gold. May 01, 2008 spectroelectrochemical investigations of gold leaching in thiourea media spectroelectrochemical investigations of gold leaching in thiourea media parker, g. Gold and silver extraction with cyanide was sensitive to. Thiourea leaching of gold concentrates and recovery of. Dissolution behavior of gold in alkaline media using thiourea. Recovery of silver, gold, and lead from a complex sulfide. Thiourea leaching of gold au from ewastes can be considered an alternative to highly toxic cyanidation, provided that its reagents consumption can be largely reduced. Auag noble metal wastes represent a wide range of waste types and forms with various ballast elements and components. A method for leaching or dissolving gold from ores or. Several other cyanidefree methods have been studied, such as chloridehypochlorite 5, cupric chloride 6, ferric chloride 7, thiourea 8, and glycine 9, along.
Thiourea bioleaching for gold recycling from ewaste. Therefore, a method for leaching or dissolving gold from ores or precious. Two of the main advantages of cyanidation are the selectivity of free cyanide for gold dissolution and the. Since cls is different than cyanide or any other leach solution now in use, this new technology must, in some manner, be exported for the potential use of cls. The application of novel thiourea leaching technologies to the extraction of gold from a bioleached pyrite concentrate was investigated. The aim of this experimental work was devoted to the preliminary evaluation of the feasibility of thiourea leaching for the extraction of gold from a domestic gold bearing ore 4 gt au, at laboratory scale. Gold recovery from nonmetallic secondary raw materials by leaching with thiourea and adsorption on ion exchangers. Recycling and reuse of electronic wastes ewastes are becoming an increasingly critical strategy for securing metal resources as well as for minimizing environmental impacts. Leaching goldsilver ores with sodium cyanide and thiourea under comparable conditions by j.
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. Reaction mechanism of gold dissolving in alkaline thiourea solution was studied by electrochemical methods, such as cyclic voltammetry, chronopotentiometry, ac impedance, linear sweep voltammetry. No passivation of the gold surface is observed in simple acidic solutions. Cls almost always recovers 10% to 25% more gold than thiourea. Thiourea leaching of a coppergold ore using statistical.
The aim of this experimental work was devoted to the preliminary evaluation of the feasibility of thiourea leaching for the extraction of gold from a domestic goldbearing ore 4 gt au, at laboratory scale. Gold electrowinning from thiourea solutions gold electrowinning from thiourea solutions juarez, c. Sep 01, 2000 the use of thiourea as an alternative nonpolluting reagent for gold leaching is very well known. The addition of small concentrations of thiourea in thiosulfate and thiocyanate systems has been shown to enhance the anodic oxidation of gold, as discussed in other sections. Mechanism of gold dissolving in alkaline thiourea solution. Us4561947a process for the recovery of noble metals from. In order to determine the maximum size to which an ore may be ground for cls leaching, thiourea leaching, or any kind of leaching, a number of tests should be run. Link with starting formulation testedphoto golddissolving in 3 days.
Jul 01, 1990 thiourea dioxide 30%, in leaching of gold and silver ores 25%, in diazo papers blueprint papers 15%, and as a catalyst in the synthesis of fumaric acid 10% iarc 2001. L amps shire abstract there is currently mch interest in how extraction of gold and silver from ores with acidic thiourea solution compares with extraction using. Other uses of thiourea are as a photographic toning agent, in hair preparations, as. Gold and silver leaching and recovery process with partially oxidized thiourea characterized as consisting of the thiourea oxidation by the application of an electrical current in a membrane cell, where the anodic and cathodic compartments are separated, before sending the product to the leaching stage and that once concluded the leaching time. An overview of the enviroleach gold recovery process agents have been identified that improve the gold leach kinetics as well as the stability of the gold that has leached into solution. Nowadays the most popular industrial processes include cyanide, thiourea, and thiosulfate leaching methods. Hence, the application of thiourea to gold leaching may lie in improving other alternative lixiviant processes where only small dosages are used. Gold electrowinning from thiourea solutions was studied by linear sweep voltammetry and chronopotentiometry. The present invention provides a process for the hydrometallurgical recovery of noble metals from materials containing them by treatment with thiourea in an aqueous, acidic medium in the presence of an oxidation agent, wherein the aqueous medium simultaneously contains an oxidation agent and a reduction agent. Apparent activation energy of anodic process of gold electrode dissolving in alkaline thiourea solution is 14. Response of lowgrade gold ore to cyanidation and thiourea. 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 extraction of gold from bioleached pyrite using novel. The cls leaching solution was action minings first product, but just as important is the technology attached to this leach solution. A method is provided for recovering gold and silver from precious metal bearing materials including ores, leaching residues, flue dust, electronic scrap, jewelry scrap, etc. In addition to cyanide being hazardous, metal cyanide species derived from cyanide leaching e. Several other cyanidefree methods have been studied, such as chloride hypochlorite 5, cupric chloride 6, ferric chloride 7, thiourea 8, and glycine 9, along. Optimizations of overall gold extraction and thiourea usage were the goals. The process design of gold leaching and carboninpulp circuits contaminants. Pdf thiourea leaching gold and silver from the printed. However, the interest for thiourea leaching of gold mainly came during the 1980s and 1990s to establish a parallel process.
Influence of thiourea concentration on gold dissolution. I have been using hclcl to remove the gold then dropping it with smb. Pdf a novel reagent for gold leaching was synthesized and the leaching conditions investigated. The modelling results indicated that the factors influencing the degree of cyanide leaching of gold were in the order of leaching time nacn concentration 2. The aim of this paper is to study leaching of gold with cyanide replacing alternatives such as ammonium thiosulfate, chloridehypochlorite, thiourea and thiocyanate to provide new cases for the tool. Thiourea leaching interest in the thiourea process for leaching gold occurred mainly during the 1980s and early 1990s. There is currently much interest in how extraction of gold and silver from ores with acidic thiourea solution compares with extraction using alkaline cyanide solution. The redox potential of gold i and silveri thiourea complexes in acidic thiourea solutions are 0.
According to the label on the consumer product, the liquid silver cleaning product tarnx contains thiourea, a detergent, and sulfamic acid. A process for recovering gold from goldbearing raw material is provided. But with this method i end up with a lot of hcl, which i reuserecycle in a variety of ways. In the method, the gold and silver are extracted from the precious metal bearing materials with a thiourea solution to form a thiourea leach, and the thiourea leach is. Associated sulfide minerals in thiosulfate leaching of. Us4778519a recovery of precious metals from a thiourea. The best result on gold thiourea leaching was obtained under a nitric acid concentration of 2 n, thiourea concentration of 2 %, and oxidant fe2so43 concentration of 3 %, solid. Discussion this work has adopted a factorial design approach to the assessment of thiourea leaching of the copper gold ore. The acidic leaching using thiourea, required more chemical reagents and maximum gold recovery of 90. Assessing the similarity of cyanidefree gold leaching processes.
Agitation leaching tests were performed by the bureau of mines on 14 precious metal ores using sodium cyanide nacn and thiourea nh22cs as extractants. Thiourea leaching has been applied to a refractory gold concentrate previously treated by bacterial oxidation. Spectroelectrochemical investigations of gold leaching in. Gold recovery from electronic waste by pressure oxidation. Gold occurs in this concentrate as free particles in the range of. Gold leaching is the key stage in process of gold mining. Regeneration is carried out in a steam atmosphere to minimize carbon degradation due to oxidation. Bureau of mines on 14 precious metal ores using sodium cyanide nacn and thiourea nh22cs as extractants. The influence of thiourea concentration on the leaching of gold was investigated by varying csnh 2 2 in the range from 10 to 100 gkg. The aghdareh mine and gold processing plant is located 32 km from takab city in the western azerbaijan province, iran, at 4658. Since the initial report of thiourea as a complexing reagent for gold leaching. Recently, there has been mch interest in the min ing and metallurgical processing indus tries in thiourea as an extractant for gold and silver, 614. For this propose, the gold leaching reagents are described and discussed in terms of their environmental and economical points of view. Gold recovery from its flotation concentrate using acidic thiourea leaching and organosilicon polymer.
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