Valorization of Agroindustrial Waste as Biosorbent of Lead (II) in Solution and its Reuse in the Manufacture of Building Bricks

Lead is a non-biodegradable toxic heavy metal. Biosorption is a simple, cost-effective and eco-friendly method for remediating lead-contaminated environments. Additionally, rice husk is a highly available residual biomass that can be used as a biosorbent. This study aimed to analyze the biosorption of Pb<sup>2+</sup> using both natural and chemically treated rice husk and to evaluate the incorporation of the resulting biomass-contaminant residue into ceramic matrices to immobilize the removed Pb<sup>2+</sup>. Natural and alkaline-activated rice husks were characterized and used as biosorbents for Pb<sup>2+</sup> in solution. Experimental results demonstrated that the maximum removal occurred at pH 5 and equilibrium was reached in 30 minutes. The chemical modification caused a significant increase in the removal efficiency, from 7.08 ± 0.59% to 94.51 ± 1.17% at room temperature and a biosorbent dosage of 3 g/L. The Langmuir isotherm model was the most appropriate for representing Pb<sup>2+</sup> biosorption onto rice husk. The maximum adsorption capacities (q<sub>m</sub>, mg/g) were 8.464 for natural rice husk and 27.450 for the chemically modified form. Biosorption data followed a pseudo-second-order kinetic model. Ceramic pieces were prepared by mixing commercial clay and rice husk containing adsorbed Pb<sup>2+</sup>, with the residue added at 10% by volume. Pb<sup>2+</sup> fixation was assessed through ecotoxicity and leaching tests, which confirmed that ceramic pieces immobilized Pb<sup>2+</sup> within their structure. In conclusion, the use of alkaline-treated rice husk as a Pb<sup>2+</sup> biosorbent, combined with the incorporation of the biomass-Pb<sup>2+</sup> residue into ceramic matrices for Pb<sup>2+</sup> immobilization, provides an eco-friendly alternative for detoxifying lead-contaminated environments.