Process And Mechanism Of Selective Chlorination Of Gold Leaching Tailings In Microwave Field

The output of difficult-to-treat gold leaching tailings in my country is large,and the slag contains valuable elements such as gold,silver and copper,which are important secondary resources.Traditional chlorination roasting can efficiently extract valuable elements,but it has disadvantages such as high roasting temperature,natural gas or coal as energy,large carbon dioxide emission and difficulty in flue gas washing.This paper presents a new method of microwave chlorination roasting with low temperature and low emission.This paper presents a new method of microwave chlorination roasting with low temperature and low emission.The process mineralogy characteristics of refractory gold ore leaching tailings were studied.The variation law of the dielectric properties of different components in tailings with temperature and the effect of chlorination agent on the dielectric properties of tailings were researched.The effects of different components in different temperature zones on the decomposition of solid chlorination agents and the mechanism of selective chlorination of gold in the conventional and microwave chlorination roasting were studied.The effects of microwave power,type and dosage of chlorination agent,atmosphere and flow rate on the process of chlorination roasting were systematically studied.The removal rate of cyanogen,chlorine and heavy metals from roasted tailings and its potential impact on environment were evaluated.The specific research conclusions are as follows:(1)The tailings are mainly composed of Si,Fe,Al,O and S,and contain valuable elements such as Au,Cu,Pb and Zn.The mineral granularity is fine,and the gangue mineral composition is complex.The gold in the tailings occurs in the form of fine grained mono-gold,sulfide encrusted gold and quartz encrusted gold.The high content of cyanide is hazardous waste.(2)During the chlorination roasting process,the four selected chlorinating agents are decomposed into chlorine-containing gas,and gold escapes in the form of Au Cl₃ gas after selective chlorination roasting.Among the four chlorinating agents,the decomposition reaction of Ca Cl₂ is the most prone to occur,and it can provide enough chlorine-containing gas in the temperature zone where the gold inclusions are opened to strengthen the volatilization of gold and chlorine.In the conventional chlorinated roasting,the volatilization rates of gold and chlorine reached 81.23%and 89.17%,respectively,under the conditions of Ca Cl₂ addition amount of 5%,air flow rate of 100L/h,roasting temperature of 1273K and roasting time of 15min.(3)The main components Fe₂O₃ and SiO₂ in the gold leaching tailings have great differences in the dielectric properties,and the micro-hot spots and micro-cracks between the components are formed in the microwave heating process,which can strengthen the reaction kinetics of chlorination roasting.The volatilization rates of gold and chlorine were 81.87%and 94.85%,respectively,under the optimal conditions of microwave chlorination roasting temperature 1173K,roasting time 15min,Ca Cl₂ content 5%and air flow rate 100L/h.Compared with conventional chloridizing roasting,the temperature of microwave chloridizing roasting can be reduced by 100?.The reaction activation energy of the conventional and microwave chlorination roasting process were40.9k J/mol and 27.62k J/mol,respectively.Compared with the conventional roasting process,the reaction activation energy of the microwave roasting process was r educed by 32.47%.(4)After conventional and microwave chlorination roasting,the cyanogen content in gold leaching residue decreased from 515g/t to 4.00g/t and 2.45g/t,respectively,and the toxicity of microwave chlorination roasting residue was lower.The chlorine content in the conventional and microwave chlorination roasting tailings was 1.2%and 0.22%,respectively,indicating that more chlorine-containing gas volatilized into the flue gas during microwave chlorination roasting,which strengthened the chlorination volatilization of elements such as Cu,Pb and Zn.In the process of microwave chlorination roasting,chlorine element can be recycled after the higher concentration of volatile chlorine-containing gas is washed by flue gas,which can reduce the amount of Ca Cl₂.