Removal of Cd and Pb with biochar made from dairy manure at low temperature

Biochar (BC) derived from waste products is a cost-effective sorbent for remediation of metal-contaminated soils. We studied the kinetics and adsorption mechanisms for removal of metal ions, such as lead (Pb2+) and cadmium (Cd2+) with biochar. The adsorption capacities of BC for Pb2+ and Cd2+ increased after alkaline treatment. The highest sorption capacities were 175.53 and 68.08 mg g(-1), for Pb and Cd, respectively. The Langmuir adsorption isotherm and pseudo second kinetic equation could well fit the adsorption processes, revealing that the sorption mechanisms of Pb2+ and Cd2+ by BC are complex and predominantly controlled by chemisorption. BC has a higher affinity for Pb than Cd, due to easy hydrolysis of Pb at low pH. Furthermore, precipitation as carbonate minerals (2PbCO(3)center dot Pb(OH)(2) and CdCO3) and complexation with functional groups (carboxyl and hydroxyl) were also important for adsorption of Pb and Cd by BC.