Adsorption and sequestration of cadmium ions by polyptychial mesoporous biochar derived from Bacillus sp. biomass

Bacteria-derived biochars from Bucillus sp. biomass under different pyrolysis temperature (250 degrees C, 350 degrees C, 450 degrees C, and 550 degrees C, respectively) were prepared, forming polyptychial, mesoporous graphite-like structure. The adsorption and sequestration efficiencies of Cd2+ by these biochars were evaluated, and the underlying mechanisms were then discussed. Cd2+ sorption data could be well described by Langmuir mode while the pseudo-second-order kinetic model and Elovich model best fitted the kinetic data. The functional groups complexation, cation-pi interactions, and interaction with minerals (including surface precipitation with phosphorus and ion exchange) jointly contributed to Cd2+ sorption and sequestration on biochar, but the interaction with minerals played a dominant role by forming insoluble cadmium salt composed by polycrystalline and/or amorphous phosphate-bridged ternary complex. The maximum sorption capacity of BBC350 in simulated water phase of soil for Cd2+ was 34.6mg/g. Furthermore, the addition of bacteria-derived biochars (1%, w/w) decreased the fractions easily absorbed by plants for Cd in the test paddy soils by 1.9-26% in a 10-day time. Results of this study suggest that bacteria-derived biochar would be a promising functional material in environmental and agricultural application.