Adsorption properties of municipal sludge biochar for soluble heavy metals

Sludge-derived biochars were prepared at 300°C and hypoxia. The effects of addition amount, pH and contact time on adsorption of Pb2+, Cu2+, Zn2+in solution by sludge-derived biochars were firstly investigated, and the influence and adsorption mechanisms were further discussed. The results showed that the removal rate of heavy metals in solution adsorbed by sludge derived biochar was inversely proportional to the hydrated ionic radius of heavy metals. The removal rate of heavy metals increased with the increase of sludge-derived biochars. However, the adsorption amount per unit mass decreased. The adsorption amount of heavy metals increased with the increase of pH in solution, and the maximum value appeared when pH was equal to 6.00. The adsorption capacities of Pb2+, Cu2+and Zn2+were 42.941, 25.769 and 12.484 mg/g respectively. Pseudo second-order model can effectively describe the adsorption process of heavy metal ions on sludge-derived biochar, which was mainly controlled by the chemical reaction. The equilibrium adsorption capacities of Pb2+, Cu2+and Zn2+were 39.747, 6.849 and 10.004 mg/g respectively, and the equilibrium time followed the order: Pb2+>Zn2+>Cu2+.