Effect of organic extractsnt, pH and temperature change,on bioleaching microorganisms during SX treatment

摘要

During the solvent extraction process, the bioleaching solution goes through changes. These changes comprise basically the incorporation of an organic phase, as well as changes in temperature and pH profiles. The resulting conditions have an effect on the following stages and more importantly on the behavior of the microbial community. The influence of the increase in temperature and acidity during solvent extraction on a mixed culture of bioleaching microorganisms was investigated. The effect of both factors was tested separately ( changing just one of them) and together (both at the same time) , where temperature was increased from 20 to 30°C and pH was decreased from 2. 0 to 1. 5 and then to 1.0 ( according to SX plant data) . At the same time, the effect of an organic phase composed of 24% LIX 84IC as the extractant and Oxform SX12 as the solvent on the same microbial community was studied. Quantitative and qualitative changes of the microbial population were investigated using optical microscopy, MPN (most probable number) , and qPCR. Decreasing pH had a stronger negative effect on biomass numbers and activity ( oxidation of ferrous iron) than temperature. Total cell number and activity decreased around an order of magnitude when the pH decreased to 1. 0. Sulfobacillus species showed the smallest decrease in cell numbers of all the species quantified. The number of active iron-oxidizing cells was reduced more by contact with the organic phase than by decrease in pH, and the detrimental impact of both stress factors together was even greater. Relatively constant cell numbers were recovered from the organic phase after contact. Predominately, Acidithiobacillus thiooxidans was recovered from the organic phase. The results gathered in this study show the impact of SX on bioleaching communities, and therefore possible influences on following downstream stages.