Mineralization and stabilization of toxic Pb2+ ions using CMC loaded S/P co-doped biochar composite

Abstract

Creating more stable chemical precipitates containing lead using biochar composite represents a significant and promising strategy for the treatment of lead contamination. Biochar, a porous and carbonaceous material, was fabricated by pyrolyzing plant biomasses (i.e., soybean straw) under anoxic conditions. In this research, a high capacity of adsorbent called carboxymethyl cellulose-loaded sulfur-phosphorus co-doped biochar composite was prepared, and the optimal lead adsorption parameters and mechanism were also investigated. The experimental results showed that CMC@SP2BC exhibited excellent Pb2+ removal capacity, reaching 829.3 mg/g maximum adsorption under optimum conditions (dosage 0.5 g/L, temperature 308 K, initial pH 5, initial lead concentration 2000 mg/L), which was in agreement with the Langmuir and second-order kinetic models. Moreover, the sequential extraction results indicated that the predominant passivation mechanism for Pb was chemical precipitation, followed by ion exchange, complexation, and physical adsorption. In addition, structural characterization revealed that the passivated lead was mainly in the form of minerals such as PbSO4, Pb3(PO4)2, Pb5(PO4)3OH, and Pb5(PO4)3Cl, which was also further confirmed by PHREEQC model simulation at different pH value and Pb2+ concentrations. Finally, Pb2+ was effectively removed from actual ground water by CMC@SP2BC to achieve Class I and Class II ground water standard. The current work offers an efficient solution for immobilizing Pb2+, which has enormous promise for stabilizing heavy metals.