Crayfish shell waste as safe biosorbent for removal of Cu2+ and Pb2+ from synthetic wastewater

Crayfish shell is an abundant natural waste and is also a potential biosorbent for pollutants, especially, heavy metals. In this study, the safety of the use of crayfish shell as a biosorbent was first assessed by release experiments involving primary heavy metal ions, such as Cu2+, Zn2+, and Cr3+, in aqueous solution under different environmental conditions. The release concentrations of heavy metals were dependent on pH, ionic strength, and humic acid; and the maximum release concentrations of heavy metals were still lower than the national standard. Specifically, Cu2+ and Pb2+ removal by crayfish shell in synthetic wastewater was investigated. The removal process involved biosorption, precipitation, and complexation, and the results indicate that crayfish shell is an excellent biosorbent for Cu2+ and Pb2+ removal. The precipitation step is particularly dependent on Ca species, pH, and temperature. The maximum removal capacities of Pb2+ and Cu2+ were 676.20 and 119.98 mg/g, respectively. The related precipitates and the generated complex products include Cu2CO3(OH)2, Ca2CuO3, CuCO3, Pb2CO3(OH)2, CaPb3O4, and PbCO3.