Cyanide Removal from Gold Tailings

The process of extracting gold with cyanide as the leaching solution is called gold extraction, which is the main method of extracting gold from ore or concentrate in modern times. However, cyanide wastewater will become the main source of water pollution, the discharge of waste gas will directly endanger human beings and biological groups, and the dumping of waste will also cause the deterioration of the ecological environment. Therefore, we need to treat the tailings after gold extraction to eliminate the hazards of cyanide, that is, the removal of cyanide.

There are three main methods of removal:

1) Natural decomposition method

Volatilization method, biological decomposition method, photolysis method.

2) Oxidation method

Alkaline chlorination method: chlorine method, hypochlorite method, electrolytic regeneration method; SO2-air method; ozonation method; hydrogen peroxide method; acidification-volatilization-reneutralization (AVR) method.

3) Adsorption method

Ion exchange and acid regeneration method, ferrous sulfide method, ion flotation method, electrolysis method, conversion precipitation method.

Common methods:

01) Alkaline chlorination method

Alkaline chlorination refers to the oxidation of cyanide in wastewater to non-toxic substances such as carbon dioxide and nitrogen using chlorine gas or liquid chlorine and bleaching powder. It is a common method for treating cyanide-containing wastewater. The method has the advantages of good treatment effect, simple equipment and easy automation, but the reagent cost is high, the cyanide cannot be recovered, and the treatment effect of the ferricyanide complex is not good. According to the different chlorine-based oxidants added, the alkaline chlorination method can be divided into bleaching powder method, liquid chlorine method, electrolytic salt method, etc. The advantage of the alkaline chlorination method is that it is easy to manage and has a good effect. The disadvantage is that some chemicals are not easy to transport and store, and the cost is high and the power consumption is large.

02) Ion exchange purification method

The ion exchange purification method is a method of removing harmful ions in wastewater by exchanging ions in wastewater with exchange ions. The advantage of the ion exchange purification method is that it recovers cyanide and metals, reduces cyanide and heavy metals to very low levels, and removes bisulfate.

However, it also has some disadvantages, for example, HCN gas is dangerous and must be sealed with care. High volume of sulfuric acid used for desorption; possible clogging of resin bed with metal deposits; and high capital cost.

03) Activated carbon adsorption method

The cost of activated carbon adsorption for treating wastewater is low, and it can comprehensively recover precious metals such as gold while removing cyanide in wastewater. The effect is very remarkable, and it has opened up a new way for the transformation from pure domestic sewage treatment to profitable sewage treatment.

The copper, lead, zinc, chlorine and other impurities in the treated wastewater are relatively small, and the drainage outside the tailings dam can be fully recycled, achieving a good effect of "zero discharge". It can not only exempt sewage charges, but also save the cost of using fresh water and solve the problem of water shortage.