Study On Mechanism Of High Temperature Cyanide Removal From Pretreated Cyanide Tailings

At present,China’s gold reserves are close to 12,000 tons,ranking the second in the world.In 2019,the gold output reached more than 380 tons,the consumption exceeded 1,000 tons,the output of the world was the first for 14 consecutive years,and the consumption of the world was the first for 8 consecutive years.At present,more than 95%of gold is produced by cyanidation.A large number of cyanidation tailings are produced in the process of gold production.In 2016 "National hazardous waste list" will be"Cyanide cyanide tailings produced in gold ore dressing process"as hazardous waste.Cyanide tailing occupies a large amount of land,causes pollution to the environment,especially to the water body when it is washed into the river by the rain water,which brings great harm to the human and the nature.In this paper,the mechanism of cyanide removal and the products of high temperature gas phase decomposition are studied.The main conclusions of the study are as follows:(1)thermodynamic analysis of cyanidation residue shows that when oxygen is used as oxidant alone,cyanide ion is easy to be oxidized in the range of smelting temperature,and can be decyanded.The products of the optimum reaction under the specified conditions contain no nitrogen oxide and no carbon monoxide.The kinetic analysis of sodium cyanate shows that the activation energy E calculated by Kissinger method is 102.708 kj/mol and the correlation coefficient R2 is 0.965.The correlation coefficient r2(0.4≤α≤0.9)obtained by Flynn-wall-ozawa method is almost above 90%.(2)the results of orthogonal experiment of total cyanide removal from cyanidation tailings show that the effect of decyanation factor is as follows:temperature>time>oxygen concentration.The single factor experiment shows that the optimal conditions are time 2h,oxygen concentration 9%,sulfur dioxide concentration 10%and temperature 400℃,and the total cyanide removal rate of cyanidation tailing is over 99.9%.The kinetic analysis shows that the control of the decyanation process of cyanidation tailing is mainly chemical reaction control.The activation energy is 48 kJ/mol.A single factor experiment was carried out to remove free cyanogen from cyanidation tailings.The results showed that free cyanogen completely decomposed at 350℃ when the time was 3 h,the concentration of oxygen was 9%,and the concentration of sulfur dioxide was 10%.(3)the experimental results on the removal of thiocyanate from cyanidation tailings show that the thiocyanate can be completely removed when the temperature exceeds 500℃.it is also found that simply changing the concentration of oxygen and sulfur dioxide has no obvious effect on the removal of thiocyanate.(4)A study of the gaseous decomposition products of cyanide tailings showed that the formation of nitrogen oxide was mainly influenced by the concentration of oxygen.When the oxygen concentration is less than 10%,the amount of nitrogen oxide can be controlled in a lower range at the smelting temperature,and the content of nitrogen oxide decreases with the increase of the temperature in a certain range.