Harmless Treatment Of Cyanide Leaching Residue From Oxidized Gold Ore

The extract gold by the cyanide process occupies a dominant position in the current gold industry due to its simple process and high gold recovery rate.The current cyanide tailings produced in the domestic gold industry except a few used in cement plant for coordination,most of the rest are stored in the tailings pond by means of a filter press dry heap.The "technical specification for pollution control of cyanide leaching residue in the gold industry(TSPC)"(HJ943-2018)promulgated and implemented on March 1,2018,stipulates that the total cyanide in the leachate prepared by cyanide tailing shall not exceed 5 mg/L before it can enter the tailings pond for disposal.Otherwise,hazardous waste tax of 1000 yuan/ton will be levied.However,current harmless treatment technology of cyanide tailings still has disadvantages such as high cost,poor treatment effect and secondary waste generation,which limit its popularization and use in the gold industry.Therefore,harmless disposal of cyanide tailings urgently requires a more environmentally friendly,efficient,and low-energy-consumption treatment process.This study is committed to the realization of economic,efficient and environmentally friendly harmless disposal of cyanide tailings.The feasibility study and mechanism analysis of two new processes,"filter press backwash-sulfide precipitation copper-Na2S2O5 cyanide breaking-RO membrane system" and "filter press backwash-acidification precipitation copper-gaseous membrane system" were carried out.The main research contents and results of this paper are as follows:(1)Firstly,XRD,SEM,leaching toxicity test and chemical element analysis were used to show that the toxicity of cyanide tailings mainly comes from the copper-cyanide complex in the water contained in the cyanide tailings.The basic route of this study was determined:cyanide tailings press filter backwashing-elution water purification cycle.(2)Exploratory experiments were carried out under laboratory conditions to verify the feasibility of filter press backwash to treat cyanide tailings.The effect of sulfide precipitation copper and Na2S2O5 cyanide breaking on the treatment of copper cyanide wastewater was studied,the copper recovery was 98.12%and the total cyanide removal rate was 99.19%under the optimal conditions.The effect of acidification on the treatment of copper cyanide wastewater was studied,it is concluded that the copper recovery was 98.58%under the optimal condition.(3)On the basis of laboratory research,the feasibility and stability of the treatment of cyanide tailings by filter press backwash-sulfide precipitation copper-Na2S2O5 cyanide breaking-RO membrane system were verified under expanded experimental conditions,and the mechanism was analyzed.By studying the effect of filter press backwash on the harmless treatment of cyanide tailings,it is concluded that under optimal conditions,the cyanide tailings after treatment can meet the requirements of being stored in the tailings pond.Five cycles of experiments were carried out on the process and the backwashed cyanide tailings in the five cycle experiments can be stored in the tailings pond.The average recovery rate of copper ion in eluted water was 98.03%,the removal rate of total cyanide was 98.96%,and the removal rate of thiocyanide reached 80.07%,which meets the requirements of recycling use.Mechanism analysis showed that:the filter press backwashing process is essentially a replacement process between the backwash water and the high-concentration cyanide-containing water in the cyanide tailings;Cu2S and CuSCN are the main Cu-containing products in the sulfide precipitation copper reaction;the cyanide-breaking reaction is essentially the SO2/O2 oxidation method;the RO membrane uses the pressure difference as the driving force and relies on the semi-permeable membrane to separate water molecules from the copper-cyanide complex and inorganic salt ions in the cyanide water.(4)On the basis of the previous experiment,aiming at the problem of low recovery rate of cyanide in elution water,the combined process of acidification precipitation copper and gaseous membrane absorption HCN was adopted to recover cyanide in the form of NaCN.The feasibility and stability of the treatment of cyanide tailings by filter press backwash-acidification precipitation copper-gaseous membrane system were verified under expanded experimental conditions,and the mechanism was analyzed.Through the study of the treatment of cyanide-containing wastewater by gaseous membrane,it is concluded that the cyanide recovery in cyanide-containing water was 99.87%under the optimal conditions.Five cycles of experiments were carried out on the process and the backwashed cyanide tailings in the five cycle experiments can be stored in the tailings pond,the average recovery of copper ion and cyanide in cyanide-containing water were 98.20%and 99.81%,and the removal rate of thiocyanide reached 94.09%,which proves the feasibility and stability of the new process.Mechanism analysis showed that:copper ions are recovered mainly in the form of CuCN and CuSCN in the acidizing reaction,the principle of gaseous membrane absorption of HCN is essentially the acid-base neutralization reaction between HCN and NaOH.