Study On The Pretreatment Of Refractory Gold Ores By Manganese Dioxide

Gold particles in refractory gold ores are usually occluded or included in the sulfide minerals,in particular pyrite and arsenopyrite.Pre-oxidation is one of the most effective means to decompose the sulfide mineral structure to liberate gold for leaching by conventional cyaniding process.As a main available oxidizing process,chemical oxidation has advantages of simple,quick reaction,no exhaust gas pollution,strong adaptability and development potential.In this paper,the pre-oxidation technique for a refractory gold concentrate in Gansu Province was investigated experimentally,which used manganese dioxide as oxidant.More details are described as follows:(1)some factors affecting the dynamics of single mineral tests were explored;(2)the mechanism research of simultaneous leaching for pyrite-MnO2 was investigated;(3)practical ore pre-oxidation and subsequent cyaniding leaching tests were carried out.The paper systematically studied the leaching behavior of single mineral,the dynamic factors of affecting the rate of pyrite oxidation and the rate of manganese leaching,and determined the optimum extraction conditions.The results showed that the oxidation of pyrite was the rate controlling step,and the oxidation rate strongly associated with redox potential.Sulfuric acid concentration,reaction temperature,reaction time,dosage of manganese dioxide and pyrite grain size had marked influences on the decomposition of pyrite during leaching.The dynamics mechanisms of pyrite oxidation and manganese leaching were investigated through XRD and SEM-EDS.The leaching products mainly included Fe3+,Fe2+,Mn2+,SO42-and a small amount of S0.Elemental sulfur partly attached on the surface of pyrite,causing the flotation of some pyrite particles.But the effect of leaching product on pyrite oxidation was less conspicuous.The results indicated that the oxidation of pyrite may follow "thiosulfate pathway",where thiosulfate was generated firstly.Then thiosulfate detached and reacted,finally formed sulfate and parts of elemental sulfur in acidic conditions.The optimum conditions of practical ore pre-oxidation were determined as follows:FeS2/MnO2 mass ratio of 0.2,reaction temperature of 90?,the total H2SO4/FeS2 mass ratio of 4.0,pre-oxidation time of 12 h.After the pre-oxidation,valuable metals were efficiently extracted,achieving satisfactory test index.The manganese leaching rate reached 96.30%,pyrite oxidation rate reached 90.50%,and the cyaniding leaching rate of gold came to 88.30%.The results of practical ore pre-oxidation tests showed that the interactions between sulphides and manganese dioxide could also applied in the cyaniding leaching of gold from a pyrite concentrate ore.Manganese dioxide is an important component of pyrolusite,which is a kind of abundant mineral.The results of this paper provided more data for further research and comprehensive utilization of refractory gold ore and pyrolusite.