| Presently,many Carlin-type gold ores have been found worldwide.Carlin-type gold ores are a kind of refractory gold ores.The gold leaching efficiency of Carlin-type gold ores is low.This is due to the micro-disseminated structure of the gold ores,the inclusion of sulfide minerals and the "preg-robbing" of carbonaceous matter.Recently,bio-oxidation pretreatment process has received more attention,because of the advantages such as operation at mild conditions,simple process,low energy consumption and environmental friendliness.Phanerochaete chrysosporium can degrade the carbonaceous materials,such as lignite,coals,activated carbon and graphite.In addition,it oxidizes sulfides.Thus,P.chrysosporium was chosen as an experimental strain.The focus of this study was to evaluate the capability of P.chrysosporium to pretreat the carbonaceous matter and sulfide minerals of Carlin-type gold ores.In addition,the fungal oxidation mechanism was studied.The aim was to solve the technological bottlenecks of "preg-robbing" caused by carbonaceous matter and the inclusion of sulfide minerals in the gold ores.Elemental carbon,organic acid and hydrocarbons are important carbonaceous matter which can disturb the gold leaching by cyanidation from Carlin-type gold ores.Thus,the experiments were conducted as follows.Firstly,elemental carbon,organic acid and hydrocarbons were extracted from Carlin-type gold ores.And then,the physico-chemical property and the interference degree of carbonaceous matter for the cyanide leaching gold were investigated.Results showed that elemental carbon was the mixture of graphite and activated carbon.And the degree of crystallinity of elemental carbon was low.The organic acid,as a kind of humic acid analogue,was detected to have the aromatic rings skeleton.Hydrocarbons contained alkanes,aromatic hydrocarbons and oxygen-containing groups.In addition,these hydrocarbons mainly consisted of the aromatic nucleus with 1-4 rings,therefore,the condensation degree was low.The interference degree of carbonaceous matter for the cyanide leaching gold was proven as follows:elemental carbon>organic acid>hydrocarbons.P.chrysosporium could decompose elemental carbon,organic acid and hydrocarbons in Carlin-type gold ores.In shake flask experiments with P.chrysosporium,the degradation amount of elemental carbon,organic acid and hydrocarbons were 34.09 wt.%,31.63 wt.%and 47.24 wt.%after treatment for 14 d,16 d and 24 d,respectively.P.chrysosporium could cause the surface exfoliation of elemental carbon in the form of layers and its pore structure was destroyed.The average pore diameter,the pore volume,the BET specific area and the micropore area were decreased.The microcrystalline structure of elemental carbon was altered by the attack of P.chrysosporium.The macromolecular structure was destroyed.The number of aliphatic structure and oxygen-containing groups were increased.The number of aromatic rings and the condensation degree of aromatic nucleus were reduced.After treatment with P.chrysosporium,some of the macromolecular structure was destroyed in organic acid.The amount of aromatic structure and aliphatic structure,the grade of maturity and the condensation degree were decreased.The amount of oxygen-containing groups and the humification degree were increased.After fungal treatment,some of the macromolecular structure was destroyed in hydrocarbons.The isomerization degree,the amount of oxygen-containing groups and aliphatic structure were increased.The amount of aromatic hydrocarbon and the condensation degree were decreased.The treatment by fungi also had an effect on the thermal property of elemental carbon,organic acid and hydrocarbons.The amount of low-stability compounds was increased.The degradation of elemental carbon,organic acid and hydrocarbons mainly depended on Lignin peroxidase(LiP),Manganese peroxidase(MnP),Laccase(Lac)and Cytochrome P450.The organic acids,which are generated by P.chrysosporium,played an indirect role by influencing the pH during the fungal degradation process.P.chrysosporium could reduce the interference of elemental carbon,organic acid and hydrocarbons with the cyanide leaching gold.This improvement was ascribed to the combined effect of degradation and passivation with enzymes.P.chrysosporium was shown to be able to oxidize arsenopyrite and chalcopyrite.In shaking flask experiments with P.chrysosporium,after treatment for 24 d,the pitting corrosion was observed,featured with a lot of visible corrosion pits on the arsenopyrite and chalcopyrite surface.Meanwhile,12.30 wt.%of iron,26.48 wt.%of sulfur and 25.03 wt.%of arsenic were dissolved from arsenopyrite.The oxidization layer on the arsenopyrite surface mainly consisted of polysulfides,iron oxides,iron hydroxides,mycelia and their secretions.Thus,the results showed that P.chrysosporium could accelerate the oxidation corrosion of arsenopyrite by decreasing the pitting potential,the corrosion potential and the polarization resistance plus increasing the polarization current,the corrosion current density,the cathodic and anodic electronic transmission coefficients.After fungal treatment for 24 d,43.61 wt.%of copper,18.05 wt.%of iron and 44.68 wt.%of sulfur were dissolved from chalcopyrite.The red brown oxidation film on the chalcopyrite surface was mainly composed of the iron deficiency sulphides,S0,Cu2O,CuOOH,FeOOH,mycelia and their secretions.Thus,P.chrysosporium could accelerate the oxidation corrosion of chalcopyrite by decreasing the corrosion potential and the polarization resistance plus increasing the pitting current,the polarization current,the corrosion current density and the anodic electronic transmission coefficient.The degradation of chalcopyrite with P.chrysosporium was related to the anodic dissolution and the immediated cathodic reaction.The oxidation of sulfide minerals with P.chrysosporium was the combined effect of enzymes,hydrogen peroxide and organic acids.Under the sterilization degradation system,after P.chrysosporium treatment for 24 d,the content of total carbon of Carlin-type gold concentrate was reduced from 3.18 wt.%to 2.59 wt.%.The dissolved amount of iron,sulfur and arsenic were 21.36 wt.%,35.43 wt.%and 43.72 wt.%,respectively.Under the non sterilization degradation system,after fungal treatment for 12 d,the content of total carbon of the fungal degradation residue-? was reduced from 2.59 wt.%to 1.98 wt.%.The dissolved amount of iron,sulfur and arsenic were 18.59 wt.%,24.86 wt.%and 35.14 wt.%,respectively.The fungal degradation residue-? and the fungal degradation residue-II are from the sterilization and non sterilization degradation systems,respectively.The gold cyanide leaching efficiency of Carlin-type gold concentrate,the fungal degradation residue-I and the fungal degradation residue-? were 12.19 wt.%,52.79 wt.%and 87.53 wt.%,respectively.These suggest that P.chrysosporium can improve the cyanide leaching gold of Carlin-type gold ores.Finally,the new fungal pretreatment technology including the two sections,sterilization and non sterilization of Carlin-type gold ores with P.chrysosporium,has been developed. |
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