The Screening Of Leptospirillum Ferriphilum And Its Adhersion Charaterisics On The Refractory Golden Pyrite Ores

As a dominant gold-producing country, there was a large amount of refractory golden pyrite ore reserves in China. Bio-oxidation technology had been widely used to pre-treat the refractory golden pyrite ores. There were several kinds of bio-oxidation strains in nature. However, Acidithiobacillus ferrooxidans had been treated as the main commercial strain long time ago. However, now it was discovered that Leptospirillum was the dominant iron-oxidation strain when the temperature was about 40℃. As Leptospirillum was always used with other bioleaching strains in the bio-oxidation process, the research about the pure Leptospirillum strain was rare. Currently, there were several problems in isolating and screening iron-oxidation strains. By summarizing previous researches, the double-layer plate technique was modified and adopted to isolate and screen bio-oxidation strains from acid mine drainage (AMD) in this study. The isolated strain was applied to pretreat the refractory golden pyrite. The effects of the operating parameters, such as temperature, initial pH and the inoculum amount on the biooxidating of the refractory golden pyrite ore were studied. Moreover, the effect of adhesion characteristics and the passivation layer on the bio-oxidation process were also studied.In this paper, there were totally eight iron-oxidation strains isolated from AMD. And five of them could oxidize the refractory golden pyrite efficiently. Among them, one strain with the best oxidation ability was characterized by the morphological observation, the biochemical and physiological identification, and 16S rRNA sequence analysis. Finally, it was identified and named as Leptospirillum ferriphilum LJ-02.In order to determine the basic operating conditions of the bio-oxidation process, the single factor shake flask experiments and the classical Hansford logic equation fitting were carried out to analysis the effect of the basic operating parameters. The ore oxidation ratio increased with the temperature when the operating temperature were increased from 36℃ to 41℃. And the ore oxidation ratio decreased with the temperature increased from 41℃ to 46℃. Low pH could be also conductive to improve the biooxidation efficiency and the ore oxidation ratio. Considering the factor of the process cost, the optimum operating initial pH for the biooxidation refractory golden pyrite was determined as 1.4. When the inoculum was less than 10%(V/V), the ores oxidation ratio increased with the inoculum amount,. Thus, the optimum culture temperature, initial pH and the inoculum amount for the bio-oxidation process were determined as 41℃, pH 1.4 and 10%(Ⅴ/Ⅴ), respectively.The adhesion characteristics of Leptospirillum ferriphilum LJ-02 was important for the oxidation process, and the relationships between the adsorption ratio and the oxidation ratio were researched in this study. The results showed that LJ-02 could oxidize the refractory golden pyrite rapidly when the bacteria adhered to the surface of the ore. However, when LJ-02 was suspended in the solution, the pyrite was rarely oxidized. The results of SEM showed that LJ-02 did adhere to the surface of the ore. And the surface turned to be crude and full of wrinkles as well as some "wormhole" appearred. Due to the correlation analysis, the adsorption ratio and oxidation ratio was highly correlated under different temperature, and significantly correlated under different pH.The results also shown that the passivation layer outside the ores, which was produced gradually during the bio-oxidation process, had the negative impact for LJ-02 on the refractory golden pyrite bio-oxidation process. The passivation layer of the ore residue could be removed partly by using a kind of washing solution. The washed and non-washed ore residues were used in LJ-02 bio-oxidation experiment. After a long time biooxidation process, the Fe3+concentration of former was 7.20 g/L, while that of the later was 3.96 g/L. Compared to the results of the non-washed ore residues, the oxidation ratio in washed residues was improved by 81.82%, as well as the adsorption ratio improved by 38%.