| Carlin-type gold ore is a kind of arsenic,sulfur,and carbonaceous matter containing gold ore,which is a typical double refractory gold ore.The gold in these oresis mainly present as "invisible" Au1+ in gold-bearing minerals,especially arsenian pyrite.The Carlin type gold deposits in China are about 1000 t,but most of them are lean,fine ores,and the exploitation and utilization rate is very low.The pretreatment process for these ores including oxidation roasting,pressure oxidation and chemical oxidation,and bio-pretreatment.Bio-pretreatment which has the characteristics of green,clean,mild conditions and widelyuse,have been rapidly developed in recent years.This study takes a Carlin type gold ore in Guizhou as raw material,which flotates with one roughing and three cleaning steps for bio-pretreatment.Conventional bio-pretreatment,step bio-pretreatment,the kinetics of bio-desulfurization are carried out.However,the gold recovery rate is rarely greater than 85%,even if the oxidation rate of sulfide sulfur exceeds 80%.Mineralogy liberation analysis(MLA),formation of secondary product during the bio-pretreatment,and the preg-robbing capacity ofthe carbonaceous matter in the ore are investigated from mechanism level,which provides the theoretical basis for the utilization of this kind of gold ore.Furthermore,for the large amount of waste acid in the step bio-desulfurization process and low gold recovery rate,a new pretreatment process,which consists of arsenic bio-reducing followed by roasting step has been put forward.The results show that,in the condition of grinding-37 ?m 90%,pulp density of 15%,45?,inoculum 10%,a stirring speed of 120 r/min,5d-3d-2d oxidation 10d in 2.0 L system,this pre-treatment method can effectively solve the problem of excessive amount of acid which seriously affects bacterial activity.The sulfur and arsenic oxidation rate of 80.22%and 91.27%is obtained.And the subsequent CIP cyanidation leaching rate of Au can reach 80.17%,about 60%?70%more than that of direct cyanidation of gold concentrate.The bio-desulfurization efficiency is controlled by chemical reaction for this ore.The desulfurization process is affected by temperature,inoculum,grinding and pulp density,among which grinding is the most important,followed by pulp concentration.The Ea of bio-desulfurization is 31.24 kJ/mol calculated by fitting,when the temperature is range from 30?-45?.The correlation coefficients of inoculum,grinding,pulp density to desulfurization rate constant are 0.003,0.458 and-0.206,respectively,calculated by linear fitting of empirical model of surface chemical reaction.A semi empirical kinetic model of bio-desulfurization for high sulfur gold concentrate is established.Illustrating the limited rate of gold recovery from mechanism level in the following four aspects:1)the gold was presentmainly in solid-solution Au in the bearing minerals,which cannot be direct leached by cyanide;2)the concentrate contains organic carbonaceous matter such as kerogen,which was highly preg-robbing and the addition of activated carbon can not radically solve the problem;3)the secondary product from bio-pretreatment,which was mainly jarosite,interfered with the subsequent cyanidation by coating the non-oxidized pyrite and reducing its contact with cyanide;4)in cyanide residue,the content of gold in kerogen is up to 493g/t,accounting for 56.60%of total gold,while the gold wrapped by sulfides in cyanide residue is 5.87%,accounting for about 1.16%of total gold,therefor,prolonging the pre oxidation time could not significantly improve the subsequent gold recovery.Combined with practice,a new pretreatment process of arsenic bio-reducing followed by roasting step has been preliminarily explored.In the condition of grinding-37 ?m 90%,pulp density 15%,45?.,inoculum 10%,2d-1d-1d oxidation 4 d in 2.0 L system,the content of arsenic in gold concentrate can be reduced to 0.71%,and the removal rate of arsenic can reach 56.59%.The subsequent gold recovery rate can reach 92.03%followed by 600? roasting for 1h and 900? roasting for 1h,which close to the theoretical maximum recovery rate.The new process only takes 4 d for pretreatment,which is much shorter than that of bio-desulfurization.It has important reference value and guiding significance for gold extraction for this kind of gold ore. |
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