A cooperative bioleaching(Acidithiobacillus ferriooxidans and Acidithiobacillus thiooxidans)and single bioleaching(Acidithiobacillus ferriooxidans or Acidithiobacillus thiooxidans)of sphalerite were investigated by X-ray diffractometry,energy dispersive spectrography and scanning electron microscopy.The experimental results show that the leaching rate of zinc in the mixed culture is higher than that in pure culture and the sterile control.In these processes,two kinds of bacteria perform different functions and play a cooperative role during leaching of sphalerite.The bioleaching action carried out by Acidithiobacillus ferriooxidans(A.ferriooxidans)is not directly performed through Fe2+ but Fe3+,and its role is to oxidize Fe2+ to Fe 3+ and maintain a high redox potential.Moreover,the addition of an appropriate concentration of ferric iron to the leaching systems is beneficial to zinc dissolution.In the leaching systems without Acidithiobacillus thiooxidans(A.thiooxidans),elemental sulfur layers are formed on mineral surface during the dissolution of zinc and block continuous leaching.Acidithiobacillus thiooxidans,however,eliminate the passivation and cause the bioleaching process to continue in the leaching systems.At the same time,protons from the bacterial oxidization of the elemental sulfur layers also accelerate the leaching of zinc.
According to physiological and biochemical characteristics of Leptospirillum ferriphilum, a strain of object bacteria was isolated successfully. Bacteria were enriched by selective liquid medium and plated on designed single-layered agar solid medium. Colony was cultured and bacteria were collected. The morphologies of the object bacteria were observed using crystal violet staining, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The result of 16S rDNA identification shows that this bacterium belongs to Leptospirillum ferriphilum and it is named as Leptospirillum ferriphilum strain D1. These results indicate that this new single-layered agar solid medium is efficient and physiological-biochemical characteristics show that the optimum simple for isolation of Leptospirillum ferriphilum. Additionally, initial pH value and its growth temperature are 1.68 and 40℃.
Zeta potentials of pyrite and Acidithiobacillus ferrooxidans cultured by sulfur in different levels of ionic strength and pH values were measured by Coulter Delsa 440SX zeta potential determinator. Meanwhile, the effects of bacterial adhesion and bacterial concentration on zeta potential of pyrite after adsorption were investigated. The results show that with the increase of ionic strength, zeta potentials of pyrite decrease in the range of pH 2.5?10.5 and the isoelectric point(IEP) of mineral shifts to the left. It is also found that the specific adsorption on pyrite of chloride ion can affect zeta potentials of pyrite sharply. As bacterial adsorption occurs, IEP of pyrite shifts towards that of Acidithiobacillus ferrooxidans; as bacterial concentration is increscent, this tendency is even larger and more obvious. Finally, a reasonable explanation for above-mentioned experimental phenomena was given by electrical double layer model and surface ionization model.
The adsorption mechanism of cysteine on pyrite was studied by amounts adsorbed, FTIR and XRD measurements. The results obtained by adsorption experiment suggest that as the mass ratio of mineral to cysteine mp/mc is greater than 5, the amounts adsorbed on mineral is stable after adsorption for 15 min and cysteine adsorbing with mp/mc shows the same tendency. It can be inferred by its Langmuir-type adsorption isotherm that chemical interaction governs the entire adsorption process. The results from FTIR and XRD prove that the functional groups of cysteine appear with blue shift of their characteristic adsorption peak in FTIR spectrum; meanwhile, the lattice constant obviously decreases and the widening of crystal planes such as (210), (220) and (211) is found after cysteine adsorbing on mineral.
