Abstract: Crayfish shells are a common type of kitchen waste, and their transformation into biochar for the purpose of adsorbing heavy metal pollutants in water can mitigate pollution and facilitate resource utilization. The various processing methods applied to the raw materials may exert an influence on the adsorption of heavy metals by crayfish shell biochar. A comprehensive understanding of these underlying mechanisms can contribute to the optimization of crayfish shell biochar production and application, thereby offering valuable insights into the management of kitchen waste. In this study, crayfish shells were employed as the primary raw materials, and three types of biochar were obtained through diverse processing methods: raw crayfish shell biochar (CB), cooked and washed crayfish shell biochar (WCB), and cooked and unwashed crayfish shell biochar (CCB). Subsequent batch adsorption experiments were conducted, with a comprehensive exploration of biochar characteristics and adsorption mechanisms through analytical techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The findings revealed a hierarchy in specific surface area and equilibrium adsorption capacity as CB>WCB>CCB, while the maximum adsorption capacity displayed a sequence of CB>CCB>WCB. The adsorption kinetics of Ni(II) by all three biochar types conformed to the Elovich model, pseudo-first-order and pseudo-secondorder kinetic model. The adsorption isotherms followed the Langmuir and Freundlich models. The adsorption mechanisms included physical adsorption, ion exchange, and surface functional group complexation. Notably, cooked crayfish shells proved to be less conducive to resource utilization compared to their raw counterparts, and washing treatments had a negligible impact on adsorption capacity. Consequently, the utilization of unwashed cooked crayfish shells for biochar production emerges as a more economically and environmentally viable alternative.

Key words: pbiochar, crayfish shell, kitchen waste, Ni(II), heavy metal adsorption