Since the Soviet Union began research on thiourea immersion gold in the 1940s, thiourea leaching has become one of the most promising alternatives to cyanidation. Thiourea (HzNCSNH 2 ) is an organic compound. In the presence of acidity and oxidant, thiourea forms a cationic complex with gold. The reaction is: thiourea as a ligand and ionic bonding of metals. The bond may be selectively selected by a lone electron pair or a sulfur atom of a nitrogen atom. In the immersion gold process, thiourea oxidized to various products, Mr. Cheng is a formamidine disulfide, which serves as a selective oxidant gold and silver. If the solution potential is too high, dithiocarbamate will be further oxidized to cyanamide, cyanide sulfide and elemental sulfur, so the leaching solution must be strictly controlled by thiourea leaching.
According to the literature, France began to extract gold and silver from zinc baking sand by thiourea in 1977; the Colorado Colorado mine used thiourea to treat gold-bearing tailings since 1982; Australia's New England antimony ore began to use thiourea in 1984. The method deals with gold-containing antimony concentrates; Russia and other countries have also begun to use the thiourea method in gold production in recent years. After China's development of thiourea iron plate replacement process after numerous industry tests, has been transferred to industrial production through the national identification of a mine in Guangxi. Therefore, it can be considered that the new process of thiourea gold extraction has begun to enter the industrial production stage from the research stage, and the process is also improving day by day.
Thiourea characteristics are: â‘ nontoxic; â‘¡ selective than cyanide, copper sensitive elements such as antimony, arsenic, zinc was significantly lower than cyanide; â‘¢ dissolve gold fast speed, 4-5 times faster than cyanide leaching Above; 4 thiourea dissolved gold is carried out in an acidic medium, which is suitable for leaching of refractory minerals which have been subjected to pretreatment which can produce acid; 5 thiourea gold complex formed in solution is cation in nature, suitable for solvent Extraction and ion exchange methods. Recover gold. However, thiourea is expensive and consumes a large amount (20% oxidized by itself, 80% is absorbed by ore), not as stable as cyanide, and it is easy to corrode equipment due to immersion in gold in an acidic medium. In recent years, some materials have classified thiourea as a suspected carcinogen. Therefore, it can be said with certainty that the thiourea method is difficult to replace the cyanidation method in the near future.
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