There are many immersion gold processes today, and the dominant cyanidation process is still dominant, but the acute toxicity of cyanidation is seriously endangering the environment and human health. In order to reduce environmental pollution and increase the recovery rate of gold, metallurgists have proposed a variety of new immersion gold methods. These methods can be roughly divided into two types. One is to develop a pretreatment process based on the traditional cyanidation method; The second is non-cyanide immersion gold. The following is a review and review of the cyanide-free leaching method and process during the gold leaching process. 1. Water Chlorination The industrial application of this method precedes the cyanidation process, but the application of the cyanidation process has made the process undesired. With the development of non-cyanide immersion gold research, water chlorination has been re-emphasized by metallurgists. The chemical reaction equation for immersion gold is as follows: 2Au+3Cl 2 +2HCl→2HauCl 4 It is known from the reaction that gold is oxidized by chlorine and complexed with chloride ions, so it is called water chlorination immersion gold. The main oxidizing agent for water chlorination is chlorine and its oxyacid salt. Due to the high activity of chlorine, there is no passivation problem on the surface of the gold particles. Therefore, the leaching rate of gold is much faster than the cyanidation process. The above is an early chlorination process, followed by many improvements. Newment used a chlorination process similar to the Tervitt Canyon goldworks and converted it into a "flash" chlorination system in April 1988. Studies have shown that the "flash" chlorinated gold leaching rate is increased by 6% and the chlorine consumption is reduced by 25%. Peru and France have reported a new process of gold brine leaching (Brine leaching), which uses high concentrations of sodium chloride solution and sulfuric acid as medium, and manganese dioxide as oxidant to produce elemental chlorine in solution. Leach gold. From the available data, there are few reports on improvements in leaching with chlorine. Chlorine gas leakage problems in water chlorination methods have led researchers to seek alternative oxidants to replace chlorine. More research is done by leaching gold from the chloride salt system with oxidants such as sodium chlorate, sodium hypochlorite and potassium permanganate. A method for treating refractory ore with one-step pressure oxidation of sodium hypochlorite is described in the literature. While silver sulfide is decomposed gold dissolution, and while recovering carbon adsorption or other methods. It has also been reported in the literature that the extraction of gold from black sand by using sulfur chloride and sulfur dichloride has a high efficiency and can achieve complete dissolution and extraction of gold. In the literature, the cyanidation method, the thiourea method and the water chlorination method were compared. The unit consumption of the cyanidation reagent was 1.5 times that of the chlorination method, and the unit consumption of the thiourea reagent was 25 times that of the chlorination method. The water chlorination process has the lowest cost. The process is characterized by fast leaching rate, low energy consumption, simple equipment, low cost and high recovery rate. The biggest problem is that Cl 2 is easy to leak. The current research trend of the water chlorination system is to seek to replace the chlorine oxidant and the enhanced water chlorination method to develop into a non-polluting direction. Second, bromination and iodization The dissolution of gold in bromine -bromide is as follows: 2Au+3Br 2 +2Br - → 2AuBr 4 - The bromine-bromide leaching mechanism is similar to chloro-chloride. Shaff applied for a patent on bromine gold extraction in 1881 (US Patent No. 267723), but it has not received much attention in recent years due to environmental and mineral nature changes. In recent years, there have been many foreign studies, and many articles have been published, claiming that the bromination leaching method such as bioleaching-D method and K method should compete with cyanide leaching method, and emphasize that this method does not pollute the environment. The study of gold extraction from Zimuyu original ore by immersion in bromine-sodium bromide solution showed that the leaching rate of gold was 90% after soaking for 15-20 days, and chlorine could be used to regenerate bromine. The sulphur-containing gold ore was leached by sodium chloride-bromine water method, and the gold recovery rate was over 97%. The Xinjiang Institute of Chemistry of the Chinese Academy of Sciences used bromide as a catalyst to accelerate the leaching rate of sodium hypochlorite-sodium chloride system, and achieved satisfactory results. For gold leaching kinetics of bromine have been reported, under saturating conditions bromo, dissolution rate of the gold is 0.73mg · cm -2 · h -1, and is 0.63mg · cm -2 · h -1 under saturating conditions chloro . Bromine is selective for the dissolution of gold in the reaction. When the gold ore contains metal elements such as iron , copper , lead and zinc , bromine can dissolve >88% of gold, while the leaching rate of other elements is <30%. The bromination method is a new process conducive to environmental protection. It is characterized by short leaching time, high gold recovery rate, similar chemical cost to cyanidation, low pollution, and bromine recycling, consistent with the direction of green metallurgy advocated. The iodine immersion gold process has not been reported in domestic research, and it is mainly used in the recovery of industrial waste gold. Frinkel Stein et demonstrated AuI 2 - 4 complex than AuCl - more stable complexes, iodides gold leaching is a good complexing agent. A. Davis's research shows that in the two systems of Au-I - I 2 -H 2 O and Au-I - -ClO - -H 2 O, I 3 - is the main oxidant, and points out that ClO - and I - I 2 (s) is generated when they meet. QI.PH used rotating disk technology to study the factors affecting the dissolution rate of iodine-iodide system, and gave the reaction rate equation: The reaction activation energy Ea = 34.4 kJ·mol -1 was calculated. When c(I 2 )=5×10 -3 mol·L -1 and c(NaI)=10 -2 mol·L -1 , the dissolution rate of gold is 2.1×10 -9 mol·cm -2 ·s -1 . The immersion gold process of iodination is generally carried out in a weakly alkaline medium, and the equipment is easy to solve in anticorrosion. In addition, the amount of the agent is small and the pollution is light, which is a very promising gold leaching method. Third, thiosulfate method The chemical reaction equation for thiosulfate leaching gold is as follows: 2Au+4S 2 O 3 2- +H 2 O+0.5O 2 =2Au(S 2 O 3 ) 2 3- +2OH - S 2 O 3 2- can be oxidized in an acidic solution, the product of which is S 4 O 6 2- →H 2 SO 3 →S 2 O 6 2- →SO 4 2- , but under alkaline conditions S 2 O 3 2- is very stable. Tests have shown that copper ions and ammonia have a catalytic effect in the thiosulfate immersion process. In order to keep S 2 O 3 2- stable in solution and to make the copper in the solution a copper ammonia complex ion, a certain amount of free ammonia must be maintained, and the leachate must also maintain a pH > 9.2. When there is free ammonia in the solution, copper is mainly in the form of Cu(NH 3 ) 2 + and Cu(NH 3 ) 4 2+ . When there is no free ammonia in the solution or leaching with sodium thiosulfate alone, Cu is Cu. (S 2 O 3 ) 3 5- is present. Jiang Tao's research further reveals the anodic dissolution mechanism of gold: NH 3 preferentially diffuses to the surface of gold particles and cooperates with gold ions to form ammonia complex ions into solution and is replaced by S 2 O 3 2- to form more stable gold thiosulfuric acid. Roots with ions. In the study of thiosulfate immersion gold kinetics, copper and ammonia have been catalyzed during the gold leaching process. Thermodynamic studies and experiments have confirmed that the thiosulfate leaching process needs to be carried out in an alkaline medium and therefore does not corrode the equipment. The leaching rate of the process is high, and the reagents used are not very toxic, but the thermal stability of the thiosulfate system is relatively poor, the consumption of the immersion gold agent is large, the temperature fluctuation range is allowed to be narrow, and the use thereof is limited. Fourth, thiourea method In the past ten years, there have been many reports on the research of thiourea at home and abroad. The main processes are thiourea carbon slurry method, thiourea resin method, thiourea iron slurry method and thiourea electrowinning method. The extraction of precious metals with thiourea has great advantages. Because of its low toxicity, fast leaching rate and easy regeneration of reagents, it is not sensitive to the mineral composition of arsenic , antimony , copper and sulfur which affect cyanide leaching. . When thiourea is present, the electrode potential of the Au + /Au pair is reduced from 1.68 V to 0.38 V. Clearly, gold is easily oxidized and dissolved in the thiourea solution. Since the electric pair is close to the standard electrode potential of SC(N 2 H 3 ) 2 /SC(NH 2 ) 2 and Au[SC(N 2 H 4 ) 2 + ]/Au (0.42V and 0.38V), it is necessary to make gold To oxidize and dissolve without oxidizing thiourea, it is necessary to select a suitable oxidant and adjust the concentration of the relevant substances as appropriate. The oxidizing agents commonly used in the thiourea process are Fe(III) salts and air oxygen. Under acidic (pH < 1.5) conditions, using Fe 3+ as the oxidant, the immersion gold reaction is as follows: Fe 3+ +SC(NH 2 ) 2 +Au→Au[SC(NH 2 ) 2 ] + +Fe 2+ The thiourea itself is also partially oxidized to form dithiomethane, and the reaction is: 2SC(NH 2 ) 2 E 0 =0.42V The intermediate product, dithiocarbam, decomposes at a rate resulting in irreversible consumption of thiourea. In the acidic medium, thiourea itself also undergoes side reactions such as decomposition and hydrolysis, which increases the amount of thiourea. According to reports, in 1977, France began to extract gold and silver from zinc baking sand by thiourea method. The Colorado Colorado mine has been producing gold from thiourea since 1982. After many industrialization tests in China's thiourea-iron plate replacement process, it has been certified by the state and transferred to industrial production in a mine in Guangxi. The thiourea gold extraction process needs to be further improved. One of the important points is that the amount and price of thiourea are much higher than the cyanidation method. In addition, the promotion of the use of thiourea method also has some technical obstacles, especially under oxidizing conditions, thiourea will oxidatively decompose into dithiomethane. In view of the main problems existing in traditional thiourea leaching gold, it has been proposed to strengthen the thiourea immersion gold by magnetic field, and achieved good results. Literature studies have shown that the addition of SO 2 can improve the efficiency of the thiourea leaching process, and SO 2 can reduce dithiocarbamate to thiourea during the leaching process. It is also reported that the gold concentrate of the Longshui Gold Mine in Guangxi is extracted by the heated thiourea carbon slurry method. The leaching rate of gold is 94.26%, and the recovery rate of gold is 90.2%. Studies have shown that the main conditions for reducing the amount of thiourea and increasing the leaching rate of gold are the organic combination of appropriate temperature, oxidant, adsorbent and other factors. Five, stone sulfur mixture method (LSSS) This method is the first new non-cyanide gold extraction technology in China. The immersion gold reagent used is synthesized from lime or Ca(OH) 2 and sulfur. The reagent has the advantages of being non-toxic, easy to synthesize, fast immersion gold, and used in an alkaline medium, so the requirements on equipment and materials are not high. The active ingredients in LSSS immersion gold are mainly calcium polysulfide (CaSx) and thiosulfate. Since both polysulfide and thiosulfate are suitable for gold leaching, this method has good immersion properties. In the immersion gold process, the polysulfide ion S x 2- has a dual role of oxidation and coordination, and S 2 O 3 - can act as a ligand, and the main gold dissolution reaction is as follows: 6Au+2S 2- +S 4 2- →6AuS - 8Au+3S 2- +S 5 2- →8AuS - 6Au+2HS - +2OH - +S 4 2- →6AuS - +2H 2 O 8Au+3HS - +3OH - +S 5 2- →8AuS - +3H 2 O 2Au+4S 2 O 3 2- +H 2 O+0.5O 2 →2Au(S 2 O 3 ) 2 3- +2OH - In addition, the researchers proposed an electrochemical-catalytic mechanism for the copper-sulfur-containing stone sulfur mixture, that is, the coordination reaction of NH 3 in the anode catalyzed polysulfide ion and thiosulfate ion, Cu(NH 3 ) 4 2+ in the cathode catalytic oxygen Reduction reaction. All in all, the stone sulphur mixture method has the characteristics of low cost and easy availability, fast immersion rate, high leaching rate for difficult refractory minerals, strong adaptability, non-toxicity and no pollution, but the subsequent process is still not perfect and needs further study. 6. Chlorine dioxide method Based on the comparative analysis of various existing gold immersion methods, the authors first proposed a new method for immersion gold from ore by ClO 2 -Cl - -H 2 O system. The immersion gold reaction under neutral and alkaline conditions is: 5Au+17Cl - +3ClO 2 +6H 2 O→5AuCl 4 - +12OH - The kinetic tests show that the leaching reaction is a first-order reaction for ClO 2 and a 0.5-stage reaction for Cl - . The activation energy of the reaction is Ea=28.99kJ·mol -1 , and the reaction is controlled by the diffusion process. The ClO 2 dissolution rate is faster than the cyanidation, water chlorination and bromination processes, but slightly slower than the iodination process. Using this method to leach a typical oxidized gold deposit, the leaching rate of gold is 95.5%, and the leaching rate of the sample by conventional cyanidation method is only 91.4%. ClO 2 has been widely used as a strong oxidizing agent in water treatment, and is widely used as a disinfectant and a bleaching agent in industrial and civil fields. Because ClO 2 is highly oxidizing, economical and practical, and harmless to humans and the environment, chlorine dioxide is a promising green gold immersion process. In addition to the various non-cyanide gold extraction processes described above, there are thiocyanate method, bacterial leaching method, humic acid method, etc., which are limited in length and will not be described again. The western region is rich in mineral resources. Special attention should be paid to the protection of the western environment while developing and utilizing gold resources. The non-cyanide immersion gold process described above emphasizes the resource and environmental themes. Although some new processes are only in the experimental stage or intermediate test stage, from the development trend of gold smelting technology, these harmlessness should be strengthened. Research on the gold extraction process, expanding the scope of the test and conducting industrial practice. Grinding curved lines Rail track grinding car,Polishing car,rail grinding vehicle,Railway track grinding car,Rail grinding vehicles for railways Safe Seal Technology Co., Ltd. , https://www.jolseals.com
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