Effects Of Surfactant On Chalcopyrite Leaching By Acidithiobacillus Ferrooxidans And Its Mechanisms

Chalcopyrite?CuFeS₂?,the most abundant copper-containing mineral in the Earth's crust,is extremely recalcitrant to hydrometallurgical processing.The main hindrances facing its commercial application in bioleaching are low copper recovery and slow dissolution kinetics,but up to now these problems have not been adequately resolved.Application of surfactants has recently proven a feasible way to improve chalcopyrite bioleaching.However,most research focuses only on polysorbates?Tweens?,whose catalytic mechanism is still unclear.In this paper,effects of different surfactants on chalcopyrite leaching by Acidithiobacillus ferrooxidans were investigated.Effect mechanisms of Triton X-100 and polyethylene glycol?PEG?on chalcopyrite bioleaching were also studied.Acidithiobacillus ferrooxidans strain XZ11?Accession number KJ573102 in GenBank?was isolated from an acid mine drainage in Tibet by an improved method.At.ferrooxidans XZ11 had a high iron-and sulfur-oxidizing ability,and its optimal cultivating conditions were set at 30?,the initial pH value at 2.0.The copper extraction from a low-grade copper ore?containing 0.12%of Cu?reached 72.15%after 15 days leaching by At.ferrooxidans XZ11.The effects of surfactants,such as cetyltrimethylammonium bromide,sodium dodecyl sulfate,sodium p-toluenesulfonate,sodium ligninsulfonate,Tween 20,Triton X-100,polyvinyl alcohol and polyethylene glycol on growth of At.ferrooxidans XZ11 and At.ferrooxidans DB,and on dissolution and bioleaching of chalcopyrite with and without addition of Fe²⁺were investigated.The relationship between effects of surfactants on chalcopyrite leaching and its molecular structure characteristics was clarified.The effects of Triton X-100 on At.ferrooxidans XZ11's oxidation activity and chalcopyrite bioleaching were investigated.Chalcopyrite bioleached in the absence and presence of Triton X-100 were also characterized by XRD,SEM-EDS and XPS,respectively.Results showed that the addition of Triton X-100 had little negative effect on ferrous-oxidizing activity of At.ferrooxidans XZ11,but it was favorable for that of sulfur,and therefore accelerated the biooxidation and dissolution of So generated in leaching process.The results also showed that the copper extraction yield of chalcopyrite with 30 mg/L Triton X-100 increased by 52.15%compared with the bioleaching without Triton X-100 after 21 days.PEG2000 was selected based on investigating influences of PEG with different relative molecular mass on growth of At.ferrooxidans XZ11 and on chalcopyrite bioleaching.The promotion mechanism of PEG2000 on sulfur biooxidation was discussed by contact angle measurements and absorption tests.The influence of PEG2000 on interface between minerals and solution was examined by means of surface tension tests,Zeta potential determination and contact angle measurements.It was found that PEG2000 could render chalcopyrite more hydrophilic and increase the permeability of cracks in the chalcopyrite particles to leaching solution,thereby contributing to development of etched pits.A model of enhanced dissolution of chalcopyrite by PEG addition was established basing on the above results.Furthermore,the effects of PEG 2000 on parameters such as solution pH,bacterial density and metal ion concentration during chalcopyrite bioleaching,and on characteristics of bioleached chalcopyrite surfaces were investigated combining with XRD,SEM and XPS.PEG2000 could promote the sulfur oxidation by At.ferrooxidans XZ11 due to an increase in bacterial attachment.It was found that PEG2000 could remove inhibitory jarosite and elemental sulfur from the chalcopyrite surface,resulting in an increase in copper extraction yield by 1.19 times after 21 days.