Removal performance and mechanism of cadmium and zinc from aqueous solution by crayfish shell biochar

Abstract

Biochar is an efficient and inexpensive material that can be used to remove heavy metal pollutants in water. In this study, crayfish shells were pyrolyzed to produce biochar (CBC) at 800°C, and the CBC effectively removed cadmium and zinc from water. BET and SEM-EDS revealed that CBC was porous and contained a large amount of Ca elements. The mesoporous pore volume accounted for 98.56% of the total pore volume, and the specific surface area was 20.0701 m²/g. After adsorption of Cd²⁺ and Zn²⁺, the content of C, O, and Ca elements significantly decreased. The adsorption process of CBC was consistent with quasi-second-order kinetics and the Freundlich isothermal model, and the maximum adsorption amounts of Cd²⁺ and Zn²⁺ were 1,152.5 mg/g and 1,135.0 mg/g, respectively. In the composite heavy metal system, Zn²⁺ can promote the adsorption of Cd²⁺. FTIR and XRD revealed that the main components of CBC were CaCO₃ and Ca(OH)₂, which mainly comprised hydroxyl radicals, π bonds in phenol hydroxyl groups, and halides. Our findings indicate that CBC is a highly efficient adsorbent for Cd²⁺ and Zn²⁺ in water and can be used to remove heavy metals in composite systems.