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Non-cyanide gold recovery chemicals refers to the environmental-friendly gold recovery chemicals used to replace sodium cyanide in gold recovery process. At present, many countries have enacted relevant laws to limit the use of sodium cyanide because of its high toxicity and great harm to the ecological environment. Therefore, more and more gold processing plants have begun to choose non-cyanide gold recovery chemicals for gold recovery. The currently used non-cyanide gold recovery chemicals mainly include the following types:
Thiourea is formamide disulfide. Using thiourea as the non-cyanide gold recovery chemical is a new technology in gold recovery industry. Generally, the reaction is performed in an acidic medium (pH <1.5) and in the presence of oxidant Fe3 +. The reaction equation is: Au+2cs(NH2)2+Fe3+→Au[cs(NH2)2]2+Fe2+
The advantages of using thiourea as gold recovery chemical are :(1)no toxicity, (2)fast leaching speed, high leaching rate, (3)good selectivity, (4)certain advantages in the processing of other gold-laden carbon, such as anode mud, acid leaching residue and bacterial leaching residue. However, the disadvantage is that thiourea is easy to decompose, resulting in high thiourea consumption and great cost. Besides, because the leaching process is completed in acidic medium, the corrosion to the equipment is relatively large.
In recent years, research on the process of gold recovery using thiourea as non-cyanide gold recovery chemical has made great progress, and has gradually shifted from the experimental stage to the industrial production stage.
Under certain conditions, gold in the ore can react with ammonium thiosulfate or sodium thiosulfate to form a soluble thiosulfate complex. The reaction equation is generally:
The method using thiosulfate as non-cyanide gold recovery chemicals is usually carried out at 50-60 ° C, and Cu2+, SO2 and sulfite are added as stabilizers to prevent the decomposition of thiosulfate ions. The pH of the leaching solution was adjusted by ammonia solution.
The characteristics of using thiosulfate as a gold recovery chemicals are: (1) non-toxic, (2) fast leaching speed, generally only takes 3 hours to achieve the best economic effect, (3) can process refractory gold ores containing copper, arsenic, antimony, selenium, etc. (4) the price of this non-cyanide gold recovery chemical is low and it has no corrosion to the equipment.
The Bcrly Company in the United States has studied a method of extracting gold from gold ores that are difficult to be recovered with cyanide, especially gold ores containing copper and manganese, and applied for a patent.
The reason why halogens and their compounds can be used as non-cyanide gold recovery chemical is that the oxidation potential when halogens become halogen ions is high enough to dissolve gold. In acidic medium (pH <1), sodium chlorate or chlorine gas is used as oxidant to dissolve gold. The reaction formula is: 3/2Cl2+Au+Cl-→AuCl4-
Since gold should be oxidized to trivalent, and some reductive impurities such as sulfides will affect the process, resulting in large consumption of chlorine gas. Therefore, in order to save chlorine gas and increase the recovery rate of gold, gold ore can be roasted at 800 ° C to achieve a sulfur removal rate of more than 97%, and then used to recover gold as non-cyanide chemical. At this time, the recovery rate of gold in the chlorinated solution can reach 99%.
The advantages of the use of halogens and their compounds are :(1) the dissolution rate of gold is fast; (2) gold processing plant can directly produce gold with purity above 99% without refining; (3) the processing cost is lower than that of pyrometallurgy.
There are many types of processes using halogens and their compounds (chlorine, bromine, etc.) as non-cyanide gold recovery chemicals, which are promising gold recovery methods.
CNLITE gold recovery chemicals is a kind of environmental protection high-tech compound gold recovery products, mainly composed of sodium oxide, ammonia, ammonium, calcium oxide and iron oxide. The gold recovery principle of CNLITE gold recovery chemicals is the same as that of sodium cyanide, which should be dissolved in water at room temperature and adjusted to the pH value of 11.5 by adding lime or caustic soda to the pulp. CNLITE gold recovery chemicals can used for CIP, CIL, heap leaching, pool leaching and agitation leaching process of sulphide gold, oxidized gold and silver, gold cyanidation slag.
The characteristics of CNLITE gold recovery chemical are: (1) environmental protection and low toxicity, (2) strong stability, (3) high leaching rate and recovery rate, (4)100% replacement of sodium cyanide without changing the original leaching process and equipment, (5) wide range of application, (6) easy transportation and storage.
At present, CNLITE gold recovery chemical has been widely used in many gold processing plants and has achieved good economic benefits.
Thiourea, thiosulfate, halogens and their compounds, and CNLITE gold recovery chemicals are four common non-cyanide gold recovery chemicals in gold processing plants. They are less harmful to the environment than sodium cyanide and have good development prospects. Actually, there are many non-cyanide gold recovery chemicals such as amino acids, hydroxynitrile and other substances can also be used as non-cyanide gold recovery chemicals for gold extraction. As people attach more and more importance to ecological protection, the use of non-cyanide gold recovery chemicals will be more and more extensive.