Efficacy of Agricultural Residue-Derived Biochar for Tackling Cadmium Contamination in an Aqueous Solution

This study aimed to investigate the efficacy of biochar, produced from different agricultural residues varying in lignin and cellulose content and subjected to different pyrolysis temperatures, in removing cadmium ions (Cd (II)) from an aqueous solution. This removal process is crucial for protecting human health and the environment. Specifically, the study focused on the adsorption behaviors of Cd (II) by the biochars made from rice husk biochar (RHB), maize straw biochar (MSB), peanut shell biochar (PSB), cottonseed shell biochar (CHB), and mulberry leaf biochar (MLB), which were prepared at 300 °C and 600 °C. The results indicated that the type of agricultural residue used to produce biochar significantly influenced the adsorption of Cd (II). Notably, mulberry leaf biochar prepared at 300 °C (MLB-300) demonstrated the highest adsorption efficiency, achieving a maximum adsorption capacity of 42.2 mg g^-1. Batch adsorption experiments assessed the impact of various factors, including system pH, NO₃^- concentration, and adsorption duration. The adsorption kinetics were better described by the pseudo-second-order model than the pseudo-first-order model. Moreover, the study found that the lignin content of the biochar plays a major role in determining the adsorption capacity. The surface characteristics of biochar, influenced by the types of agricultural residues and preparation temperature, directly impact its adsorption mechanism and capacity. While biochar produced at 300 °C showed optimal Cd(II) adsorption, those processed at 600 °C were less effective, likely due to the loss of functional groups at higher temperatures.