Treatment of Cyanide from Gold Leaching Wastewater.pdf

1、Due to its high ability to dissolve gold, cyanide has been used to leach gold from ores (gold cyanidation process).the wastewater discharged from this process that often contains cyanide compounds at high concentrations.

2、 Hydrogen cyanide (HCN), salt cyanide like Sodium cyanide (NaCN) and potassium cyanide (KCN) are the main compounds of cyanides that are present in these wastewater. Due to the toxic property of these cyanide compounds,

3、this wastewater has to be treated in order to reduce the concentration of cyanide. Most of gold leaching plants have established treatment process of these cyanide containing waste water, most of these treatment process

4、work on principle of converting cyanide compounds to the less toxic ones. The standard levels of cyanide in wastewater vary from country to another. In China, the level of cyanide in wastewater to be discharged in efflue

5、nts and pond tailings must not exceed 0.5mg/L. In recent years, cyanide removal from gold leaching wastewater technology has strengthened and improved.
　　Now days, alkaline chlorination, INCO process and bio treatment

6、 are the dominant methods used for the cyanide removal from gold leaching wastewater. However, the use of many of these methods results in generation of toxic byproducts which also require additional and special handling

7、, without ignoring the high cost of them. It is in this regard that research on new technologies and methods for the cyanide removal from these wastewater must be enhanced. In this project treatment of gold leaching wast

8、ewater was performed using new oxidation method where, Sodium peroxide (Na2O2), Hydrogen Peroxide (H2O2) and Sodium Hypochlorite (NaClO), were used as oxidizing agents. The effect of different parameters (oxidants dosage

9、s, temperature, and time) have been investigated and their optimumconditions were determined. Laboratory based experiments were conducted. After data analysis, the results showed that the destruction of cyanide compounds

10、 was successful. In most case CNO-, NH3, CO3- were the forms of the products. The results showed that in 60 min, at 40℃,and 8 ml of Sodium peroxide, cyanide concentration was reduced from 14.8mg/L to 1.5mg/L. The same fo

11、r Hydrogen peroxide, At 65℃, 20ml of Hydrogen peroxide, in 7hoursthe cyanide concentration was reduced from 14.8mg/L to 0.5mg/L. the results also showed that cyanide concentration was reduced also using Sodium hypochlori

12、te. In this case, the dosage was 1.5ml of sodium hypochlorite, 45℃ and 2hours cyanide concentration was reduced to 0.05mg/L.These results shows that the removal of cyanide in gold leaching wastewater can be achieved usin

13、g the chemicals mentioned previously without generating toxic byproducts. Cyanide removal using Hydrogen peroxide is very efficient as it can remove about 90％ of total cyanide and this method is environmental friendly as

14、 no toxic byproducts are generated. However, the reaction is very slow when no catalyst is used and it took longtime to react. But when the copper sulfate was added, the reaction was quick and showed good results. Result

15、s show that Cyanide wastewater treatment by Sodium hypochlorite is more efficient that the two other methods as it can remove almost 100% of the total cyanide. However further study can be conducted to assess the cost of