What are the main methods for non-cyanide gold extraction?


Cyanide is the most common method and the most stable way to gold and silver ore extraction material, however, there are also time leaching (leaching cycle) long (one week to one year heap leaching, agitation leaching is 24 to 72 hours), and the organic Carbon, antimony , arsenic , copper , zinc and other harmful elements are quite sensitive, which causes a significant reduction in the leaching rate of gold and silver, and a significant increase in production costs. In particular, the cyanide is highly toxic and harmful to the environment. Therefore, how to improve the leaching rate of gold and silver, reduce the cost, and find new technologies and processes that are non-toxic or less toxic to replace highly toxic cyanide is an important research topic. Non-cyanide leaching agents include thiourea, oxygen, bromine , iodine , ammonia, thiocyanate, and stone sulphur.

(1) Thiourea method This method dissolves gold under acidic conditions with high speed, no toxicity, selectivity is better than cyanide, and is not sensitive to base metal impurities. It is used to treat some gold-containing materials, such as anode mud and gold-bearing uranium ore. Dipping and sulfuric acid slag have certain advantages, but the consumption of the medicinal agent is high, the leaching equipment is easy to corrode, and the effective method for recovering gold from the thiourea solution is lacking.

In 1997, it was found that sodium sulfite can inhibit the irreversible decomposition of alkaline thiourea to a certain extent, promote the dissolution of gold, and can selectively dissolve gold from gold-containing waste. It is considered that sodium silicate is an efficient way to extract gold from basic thiourea. stabilizer.

(2) Halogen and its halogen salt method The reagents used in this method are mainly chlorine, bromine, iodine, chloride salt, iodide, bromide, etc., for example, chlorine gas, hypochlorite, chloride salt method, K reagent, Geobrom 3400 An oxidizing agent such as Bio-D reagent. Chlorine is used both as an oxidant and as a complexing agent in the leaching process.
Halide ions (X-) and Au + Au2 + is a strong ligand chloride leaching arsenic-containing carbon material suitable for processing gold ore, slag, antimony, gold concentrates reselection, arsenic pyrite gold ore. The bromination method is one of the most promising leaching processes for replacing cyanide gold. It has the advantages of low price, high leaching rate, fast leaching speed, non-toxicity, no corrosion, recycling of chemicals, and recovery of gold from precious liquid. Convenient and so on. There are many studies on iodide in foreign countries. The leaching of iodine-iodide solution can obtain a higher gold leaching rate than the cyanide method. It is also possible to directly deposit gold from iodine-iodide.

(3) Nitrile method This method extracts gold using three nitriles of malononitrile (also known as acyl cyanide), cyanoacetamide and acetonitrile. When treating carbonaceous gold ore, the nitrile gold leaching rate is much higher than the cyanidation method. When oxidizing ore and sulfide ore are treated, the gold leaching rate is as effective as cyanide leaching, but the price is higher.

(4) The biological preparation method, that is, the microorganism can leach gold, which is related to the microbial cell component protein, the metabolite amino acid of the microorganism (glycine, histidine, aspartic acid, etc.). The protein and gold form a negatively charged complex that is linked by the nitrogen atom of the amino acid group to form a stable gold complex.

(5) Coal gold agglomeration method This method utilizes a flotation agent to improve the hydrophobic character of the surface of the gold particles, and the hydrophobic gold particles enter the agglomerate by the collision action during the stirring process. The gold-bearing agglomerates undergo secondary recycling, enrichment and ashing, and the obtained toluene is subjected to smelting or other methods to obtain finished gold.

(6) Polysulfide method and stone sulphur mixture method This method uses gold and silver to leach the reagent formed by the reaction of sulfur and lime, and the polysulfide chelate ion has
Like, which have a strong complexing ability of metal ions in a suitable oxidizing agent (e.g. potassium permanganate, etc.) with the next, or by means of disproportionation polysulfide ions, can effectively dissolve gold and silver.

(7) Other methods Other methods include a humic acid method, an FM reduction reagent method, a thiosulfate method, and the like.

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