Purification method widely used in industrial production of cyanide-containing wastewater treatment

Has been widely used in the industrial production and purification of mature technology with a bleaching oxidation method, liquid chlorine oxidation method, the latest and most promising method is the purification of Ozonation and Inconel SO ₂ ^- air oxidation method or the like.
1. Bleaching powder method: oxidation treatment of cyanide by using bleaching powder. That is, the cyanide-containing sewage is oxidized by a solution such as bleaching powder (CaOCl ₂ ), bleaching powder [Ca(OCl) ₂ ], or sodium hypochlorite (NaOCl) in an alkaline medium (pH=8 to 9).
The first stage is local oxidation:

ClO ^- +H ₂ O+CN ^- → CNCl+2OH ^- (1)

CNCl+2ClO ^- → CNO ^- +3Cl ^- + H ₂ O (2)

The second stage is complete oxidation:

CNO ^- +2H ₂ O ^- → CO ₂ +NH ₃ +OH ^- (3)

2CNO ^- +3ClO ^- → CO ₂ ↑+N ₂ ↑+3Cl ^- +CO ₃ ^2- (4)

The reaction formulas (1) and (2) oxidize the cyanide to a highly toxic silver cyanate (cyanate) CNO. When Ph < 8.5, a highly toxic CNCl is formed, and when the pH is >10, the reaction is slow; (3) The cyanate of formula (4) continues to oxidize to carbon dioxide and nitrogen. The reaction is carried out in an alkaline medium according to the formula (4), and is instantaneously completed at pH < 7; when pH = 8.5, it takes 30 minutes. Thus, the reaction rate is pH dependent, the method is better, it has been adopted by many domestic and foreign gold mine.
2. The liquid chlorine method is similar to the bleaching powder oxidation method, that is, it is carried out under the condition of adding alkali (lime or sodium hydroxide) and chlorine gas, and the bleaching powder method is cheaper and most preferable.
3. Natural purification method Discharge the sewage with low cyanide concentration into the tailings, rely on hydraulic dilution, sunlight decomposition, O ₂ , CO ₂ oxidation and acidification in the air to reduce the pH value of the sewage, causing cyanide in the sewage. CN ^- converted to HCl for volatilization, as well as biodegradation and solid medium adsorption precipitation to achieve the purpose of removing cyanide. This method is more common in the Soviet Union and Canada.
4. Activated carbon adsorption oxidation method The cyanide is oxidized to cyanate and then decomposed into ammonia and carbon dioxide. This method requires the use of copper as a catalyst, and adsorption and oxidation of cyanide by blasting oxygen.
5. Ozone Oxidation Process Ozone (O ₃ ) is generally prepared by high-voltage discharge of air or oxygen. The raw materials are wide and easy to use, easy to manage, and do not require storage. Its dosage is only 40% of the liquid chlorine method, and the cost is low. In addition, O ₃ is easily decomposed into oxygen in water, which not only increases the dissolved oxygen in the water, but also does not leave harmful components. But the investment is bigger.
6. Inco SO ₂ ^- Air Oxidation Method Invented by the Canadian Institute of Technology, in the early 1980s, it has been industrially applied in some US and Canadian smelters, with good results. The method uses SO ₂ ^- oxidant air mixture, and adjusting the pH with lime, with copper as a catalyst. It removes various oxides and ferricyanide complexes and removes them in the form of sparingly soluble ferrocyanide, while other metals are removed as hydroxides. It has the characteristics of simple operation, safe and reliable, low reagent consumption and low cost.

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