Comparative adsorption of Pb2+ and Cd2+ by cow manure and its vermicompost

Organic waste has great potential for use as an amendment to immobilize heavy metals in the environment. Therefore, this study investigates various properties of cow manure (CM) and its derived vermicompost (CV), including the pH, cationic exchangeable capacity (CEC), elemental composition and surface structure, to determine the potential of these waste products to remove Pb2+ and Cd2+ from solution. The results demonstrate that CV has a much higher pH, CEC and more irregular pores than CM and is enriched with minerals and ash content but has a lower C, H, O and N content. Adsorption isotherms studies shows that the adsorption of Pb2+ and Cd2+ onto either CM or CV follows a Langmuir model and presents maximum Pb2+ and Cd2+ adsorption capacities of 102.77 mg g−1 and 38.11 mg g−1 onto CM and 170.65 and 43.01 mg g−1 onto CV, respectively. Kinetic studies show that the adsorption of Pb2+ onto CM and CV fits an Elovich model, whereas the adsorption of Cd2+ onto CM and CV fits a pseudo-second-order model. Desorption studies indicate that CV is more effective than CM in removing Pb2+ and Cd2+. FTIR analysis demonstrates that the adsorption of Pb2+ and Cd2+ onto CM mainly depends on existed aliphatic alcohol, aromatic acid as well as new produced carbonates, whereas that onto CV may be contributed by the existed aliphatic alcohol, aromatic acids as well as some carbonates and phosphates. Thus, vermicomposting disposal of cow manure with destination mineral addition may broaden the way of its recycle and environmental usage.