The bioleaching of chalcopyrite was investigated using a pure and mixed culture consisting of iron-oxidizing Leptospirillum ferriphilum （L. ferriphilum） and sulfur-oxidizing Acidthiobacillus thiooxidans （.4. thiooxidans）. The electrochemical tests were conducted to investigate the bioleaching behavior of chalcopyrite by various bacteria. Bioleaching efficiency of chalcopyrite in mixed culture is higher than that in the pure culture of L.ferriphilum alone. The iron-oxidizing L.ferriphilum plays a dominant role during bioleaching of chalcopyrite in the mixed culture of L. ferriphilum and A. thiooxidans. During bioleaching, certain values of redox potential are beneficial to the decomposition of chalcopyrite. Jarosite and sulfur are observed as products of bioleaching. The addition of A. thiooxidans during leaching by L. ferriphilum can change the electrochemical control steps of leaching. The corrosion current density is substantially promoted in the culture involving bacteria, especially in the mixed culture.
Electrochimcal behaviors of rusticyanin （Rus.） isolated from Acidithiobacillus ferrooxidans were investigated through Rus.-ZnS-QDs/L-Cys/Au electrode. The cyclic voltammetric results indicate that rusticyanin immobilized on the surface of Rus.-ZnS-QDs/L-Cys/Au electrode can undergo a direct quasi-reversible electrochemical reaction. The immobilized rusticyanin is not denatured and still retains its activity in the temperature range of 19-43 ℃. The reduction ability of the protein increases and its oxidation ability becomes weak with the increase of pH from 6.0 to 7.8. Fe^2＋ ions in the solution can promote the electron transfer kinetics of the immobilized rusticyanin and make its peak potentials （φp） markedly move negatively.
In order to determine the mechanism of bacterial tolerance to fluorine,Acidithiobacillus ferrooxidans ATCC 23270 was domesticated and studied under the conditions of different fluorine concentrations and pH values with or without treatment by Proteinase K.The bacterial activities were observed through measuring the changes of solution potentials by platinum electrode with Ag/AgCl reference electrode and the intracellular fluorine was determined by-uorine ion-selective electrode.The results indicated that the tolerance of Acidithiobacillus ferrooxidans ATCC 23270 to fluorine could be obviously improved by domestication,HF was the effective form of fluorine to affect the bacterial activity,and pH increase or concentration change of ions of strong complex ability with fluorine ions in solution could result in false appearance of high fluorine-resistant strain.Some proteins located in cell wall or cell membrane were intimately relative with the bacterial fluorine tolerance.
Chalcopyrite oxidation rates were examined under various conditions in the presence of Leptospirillum ferriphilum,in which the effects of different pulp content,inoculation amount,external addition of Fe3+ and initial pH value were studied.The bioleaching residues were investigated by X-ray diffractograms(XRD),scanning electron microscopy(SEM) and energy dispersion spectrum(EDS) analysis.The results show that low pulp concentration increases the leaching rate of copper,and external addition of Fe3+ is also beneficial to leaching chalcopyrite.The changes of inoculation amount and initial pH from 1.6 to 2.5 have a little effect on the final leaching rate.The results also imply that Fe3+ ions are important for bioleaching of chalcopyrite.At the end of bioleaching,jarosite and sulfur are observed on the surface of chalcopyrite residues by using XRD,SEM and EDS.With the passivation layer formed by jarosite and sulfur,the continuous copper extraction is effectively blocked.
The electrochemical oxidation behavior of pyrite in bioleaching system of Acidthiobacillusferrooxidans was investigated by cyclic voltammetry （CV）, polarization curve and electrochemical impedance spectroscopy （EIS）. The results show that in the presence or absence of A. ferrooxidans, the oxidation reaction of pyrite is divided into two steps： the first reaction step involves the oxidation of pyrite to S, and the second reaction step is the oxidation of S to SO4^2-. The oxidation mechanism of pyrite is not changed in the presence of A. ferrooxidans, but the oxidation rate of pyrite is accelerated. With the extension of reaction time of A. ferrooxidan with pyrite, the polarization current density of pyrite increases and the breakdown potential at which the passive film dissolves decreases. The impedance in the presence ofA. ferrooxidans is obviously lower than that in the absence of A. ferrooxidans, further indicating that microorganism accelerates the corrosion process of pyrite.
The bioleaching of pyrrhotite was investigated using Sulfobacillus thermosulfidooxidans.The effects of pH,pulp concentration,inoculation amount,external addition of ferrous and ferric ions were examined.The pH is found to exert a profound effect on the leaching process for controlling the bacterial activity and precipitation of ferric ions mainly as jarosite.The results show that low pulp content increases the leaching rate of iron.The inoculation amount from 1×107 cell/mL to 1×108 cell/mL has positive effects on the leaching rate.The results also imply that addition of ferrous sulfate(1 g/L) is required for the bacteria to efficiently drive the extraction of iron,however,the leaching efficiency has no obvious enhancement when 2 g/L ferrous sulfate was added.Comparatively,addition of ferric sulfate(2 g/L) significantly inhibits the bioleaching process.At the end of bioleaching,jarosite and sulfur are observed on the surface of pyrrhotite residues by using XRD and SEM.With the passivation film formed by jarosite and sulfur,the continuous iron extraction is effectively blocked.
Chalcopyrite dissolution was evaluated by bioleaching and electrochemical experiments with thermophile A. manzaensis（Acidianus manzaensis） and mesophile L. ferriphilum（Leptospirillum ferriphium） cultures at 65 ℃ and 40 ℃, respectively. It was investigated that the bioleaching of chalcopyrite was stepwise. It was reduced to Cu2 S at a lower redox potential locating in the whole bioleaching process by A. manzaensis at high temperature while only at initial days of bioleaching by L. ferriphilum at a relative low temperature. No reduced product was detected when the redox potential was beyond a high level（e.g., 550 m V（vs SCE）） bioleached by L. ferriphilum. Chalcopyrite bioleaching efficiency was substantially improved bioleached by A. manaensis compared to that by L. ferriphilum, which was mainly attributed to the reduction reaction occurring during bioleaching. The reductive intermediate Cu2 S was more amenable to oxidation than chalcopyrite, causing enhanced copper extraction.
Acidithiobacillus caldus plays an important role in commercial bioleaching.To understand how NaCl stress adaptation occurs in A.caldus,we grew A.caldus strain SM-1 in media containing high NaCl concentrations.SM-1 grew at concentrations of up to 1.0-mol L^(-1)NaCl,but growth was severely inhibited at higher concentrations.Proteomic analysis showed that SM-1 used multiple strategies to respond to NaCl stress.In addition to several heatshock proteins,enzymes involved in proline biosynthesis increased under NaCl stress.In addition,two DNA-binding proteins and a third protein of unknown function(Atc_(1291)),which was subsequently identified as a putative single-stranded DNA-binding protein,were up-regulated in the presence of NaCl stress.These DNA-binding proteins might play a role in response to osmotic stress.Atc_(1291)was cloned and expressed in Escherichia coli.Surprisingly,we found that E.coli BL21/pET28a-atc_(1291)grew to higher cell densities than E.coli BL21/pET28a,regardless of NaCI stress.Homologs to Atc_(1291)were identified in several groups of Proleohacleria.The role of Atc_(1291)in enhancing cell growth needs further investigation.
Xu GuoChengying JiangYuanming LuoMingjiang ZhangAnsgar PoetschShuangjiang Liu
