Study of lead (II) adsorption onto activated carbon originating from cow bone

In this study, the adsorption of lead (Pb2+) onto activated carbon (AC) originating from cow bone, chemically modified with HNO3, was investigated. Physico-chemical carbon characterization assays and the determination of the optimum pH conditions and contact time, as well as studies on the kinetic and isothermal equilibrium and adsorbent reuse, were carried out. The AC presented a greater amount of acid functional groups than basic groups at the surface, making it efficient for cationic exchange. The pHPZC was 4.0 and the minimum contact time required for the assays to be performed was 6 h. It was observed that the time required to reach kinetic equilibrium decreased with increasing initial metal concentration in solution and the values found for qexp were 32.1, 50.1 and 42.3 mg g−1 for concentrations of 100, 150 and 200 mg L−1, respectively. The pseudo-second-order kinetic model best represented the experimental data for all initial lead concentrations studied, presenting good linear correlation coefficients. The Langmuir and Freundlich models were used to fit the experimental data and these showed good correlations, with the Langmuir model providing a better description of the equilibrium (higher R² value). It was verified that the HCl desorption showed the highest efficiency; the minimum time to reach the desorption equilibrium was 3 h and the recovery was approximately 50%. The proposed adsorption process efficiently removes lead present in aqueous solution and can be used in industrial processes.