The Sorption of Lead and Cadmium by Hydroxyapatite-Biochar Nanocomposite from Aqueous Solution.

Lead (Pb) and cadmium (Cd)-contaminated wastewater treatment has become a major worldwide problem. The use of hydroxyapatite (HAP)-based composites may be an eco-friendly method for removing Pb and Cd from aqueous solutions. Based on the concept of treating waste with waste, we supported HAP particles on spent mushroom-substrate biochar (SMSBC), creating a new composite (HAP/BC) for removing Pb and Cd from solution. The sorption of Pb and Cd by HAP/BC was systematically studied in single and binary heavy metal systems. A series of characterization analyses were applied to investigate the properties of HAP/BC and explain the Pb and Cd removal mechanisms. The results revealed that the HAP content, reaction time, initial Pb and Cd concentrations, initial pH of the solution and competing cations affected Pb and Cd removal by HAP/BC. SMSBC effectively reduced HAP agglomeration, thereby resulting in HAP/BC with outstanding Pb and Cd removal capacities. The presence of Pb was not conducive to Cd removal, while the Pb removal efficiency was barely affected by the presence of Cd in the binary Pb–Cd system. Combining the results of the bath experiments with the characterization analyses, the reaction between HAP/BC and Pb might be primarily a dissolution–precipitation process, whereas the reaction with Cd was primarily an ion exchange. Additionally, oxygen-containing functional groups and cation-π interactions might also play a role in Pb and Cd sorption. Overall, the eco-friendly HAP/BC demonstrated significant potential for Pb and Cd decontamination and provided insights for the efficient use of SMS resources.Highlights: SMSBC use as a carrier could clearly reduce the clustering effect of HAP particles. HAP/BC exhibited superior Pb and Cd removal capacities in solution. Dissolution–precipitation dominated the reaction process between HAP/BC and Pb. The Cd removal process by HAP/BC was primarily controlled by ion exchange. [ABSTRACT FROM AUTHOR]