Complex Gold Ore Roasting-acid Leaching-fluorine Salt Pretreatment-cyanide Process Research

In this paper,“roasting-acid leaching copper-fluorine salt pretreatment–cyanidation leaching”process was developed,among which fluorine salt pretreatment was benefit to destroy the structure of silver-containing compact inclusions,and further increase the leaching rate of silver.The thermodynamic calculation data of roasting process shows that when temperature exceeds 773K,the metal oxides can be converted into MeO·Fe₂O₃,MeO·SiO₂ and other substances,which may wrap around gold and silver.Adding sodium hydroxide during roasting process promoted the formation of Na₂O·Fe₂O₃ and Na₂O·SiO₂,while inhibited the formation of ferrite and silicate,and further avoided the coating effect of these substances on gold and silver.The results of the roasting process show that the roasting atmosphere has the most significant effect on the cyanidation leaching of gold and silver,followed by the amount of additive NaOH.The optimum roasting conditions were as follows:rich oxygen atmosphere,sodium hydroxide dosage of 6 g?per 100g gold concentrate?,roasting temperature of 903K,roasting time of 3 h.Under this optimal condition,the leaching rate of gold,silver and copper can reach 95.92%,57.57%and 92.57%,respectively.Through the sulfuric acid leaching process,copper in the calcine can be completely leached,and gold and silver were enriched in the slag.Consequently,the separation of copper from gold and silver was achieved.The optimal acid leaching conditions obtained by the experiment were:temperature of 363 K,time of 3 h,stirring speed of 300 rpm,liquid-solid ratio of 4:1,and sulfuric acid concentration of 1mol/L.Under this condition,the leaching rate of Cu can reach 95.57%.The leaching rates of Au and Ag were 93.21%and 63.25%respectively,through sulfuric acid leaching–cyanidation leaching process,demonstrating that additional sulfuric acid leaching process did not present significant effect on the leaching rate of Au and Ag compared with direct cyanidation leaching of calcine.Properly increasing the concentration of ammonium hydrogen fluoride and sulfuric acid can obviously improve the pretreatment effect of fluorine salt and then increase the leaching rate of silver.The optimum pretreatment of fluorine salt conditions were as follows:reaction liquid to solid ratio of 10:1,rotational speed of300 r/min,ammonium hydrofluoride concentration of 1.5 mol/L,sulfuric acid molar concentration of 1.5 mol/L,reaction temperature of 30?,and reaction time of 90min.Under these conditions,the leaching of gold and silver was significantly improved,reaching 99.43%and 96.9%,espectively.The mineralogy analysis shows that the distribution of gold and silver in the gold concentrate was complex.The natural gold showed fine grain size and mainly embedded in silver-gold ore and silver-bearing gold ore.After roasting process,the silver-bearing gold particles embedded in pyrite.The acid fluoride system has an erosion effect on the dense wraps of gold and silver,promoting the exposure of gold and silver components.After fluoride salt pretreatment,the gold and silver on the surface did not change much,but the silicon content decreased from 7.11%to 1.61%,which laid a good foundation for subsequent cyanide leaching of gold and silver.