Biosorption Of Cr³⁺ And Cd²⁺ By Acidithiobacillus Ferrooxidans BY-3

Acidithiobacillus ferrooxidans is a bacterium of the genus Thiobacillus, which are distributed in rivers, lakes and soil widely. It is a chemolithotrophic bacterium, which takes in ferrous or reduced inorganic sulfur compounds as energy source, can grow under extremely low pH environment. Numerous studies showed that Acidithiobacillus ferrooxidans is resistant to a variety of metals and had the potential as a biosorbent for various metals.In this paper, the form of Acidithiobacillus ferrooxidans BY-3 (BY-3) was examined by Scanning electron microscope (SEM), it was rod-shaped, with rounded ends, the bacteria was well distributed. The effect of the gradient of Cd2+(0、40、60、80、100 mM) and Cr3+(0、40、60、80、100 mM) on the growth of BY-3 was investigated, the results showed that both of the metals can inhibit the growth of BY-3 in various degrees, when the concentration of Cr3+ and Cd2+ is high enough. The inhibition concentration of Cr3+ and Cd2+ were 60 mM and 80 mM respectively.The biosorption of Cr3+ and Cd2+by BY-3 were also studied in this paper, the effect of several physicochemical factors including pH、contact time、the initial concentration of metals、biosorbent dose and temperature on the biosorption were observed. The results showed that the state of equilibrium was reached in 40min for the biosorption of Cr3+ and Cd2+, the maximum biosorption capacity of BY-3 for Cr3+ and Cd2+ were 11.24 and 4.29 mg/g respectively. The optimum pH for Cr3+ was 5.0 and 6.0 for Cd2+. The biosorption capacity increased as the temperature increased in a certain range of temperature. Analysis of kinetic data showed that the biosorption of Cr3+ and Cd2+ fitted the pseudo second-order model both. The data obtained indicated that biosorption of Cr3+ and Cd2+ fitted Langmuir model and Freundlich model well, but fitted Langmuir model better. Thermodynamic parameters showed that the adsorption of Cr3+ and Cd2+ onto BY-3 were spontaneous and exothermic under the examined conditions. Fourier transform infrared spectroscopy (FTIR) analysis showed that -OH and-NH on the surface of BY-3 were involved in the biosorption process.