Adsorption and reduction of palladium (Pd2+) by Bacillus licheniformis R08

Preliminary study on the mechanism of Pd²⁺ biosorption by resting cells of Bacillus licheniformis R08 biomass has been carried out by means of chemical kinetics and AAS, TEM, XRD and FTIR methods. The results showed that at 30°C and pH 3.5, when dry R08 biomass powder (800 mg/L) was mixed with Pd²⁺ (100 mg/L) for 45 min, the rate constant k of biosorption of Pd²⁺ attained a maximum of 5.97 × 10⁻² min⁻¹ and the half life period of the reaction reached 12 min. The part of Pd²⁺ adsorbed by R08 biomass was reduced to elemental, cell-bound Pd at the same condition. The cell wall of R08 biomass was the primary location for accumulating Pd²⁺, and aldoses, i. e. hydrolysate of a part of polysaccharides on the peptidoglycan layer in the acidic medium, serving as the electron donor, in situ reduced the Pd²⁺ to Pd⁰.