Efficient Removal of Lead and Arsenic from Groundwater Using Thiourea-Modified Biochar and Nano Zerovalent Zinc

Sidra Chaudary1 and Hafsa2

1Department of Botany, University of Agriculture, Faisalabad, Pakistan 2Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan

Abstract

Groundwater contamination by heavy metals such as lead (Pb) and arsenic (As) is a critical environmental and public health issue due to their toxicity and persistence. This study investigates a sustainable and low-cost approach using rice husk-derived biochar modified with thiourea (TMBC) and combined with nano zerovalent zinc (nZVZn) to enhance removal efficiency through adsorption and redox reactions. Batch experiments assessed the effect of pH (3–9), contact time (5–180 min), adsorbent dosage (0.05–0.5 g), and initial metal concentration (10–100 mg/L) on removal performance. The nZVZn–TMBC composite achieved over 90% Pb and 85% As removal at optimal pH values of 5 and 6–7, respectively, reaching equilibrium within 90 minutes. Adsorption followed Langmuir isotherm behavior, indicating monolayer coverage, and pseudo-second-order kinetics suggested chemisorption as the dominant mechanism. Material characterization confirmed successful thiourea functionalization and uniform nZVZn deposition, providing increased surface area (215 m²/g) and abundant active sites. The approach demonstrates effective heavy metal remediation, utilizing agricultural waste and a green synthesis strategy, offering a practical solution for groundwater treatment in resource-limited settings. Future studies should focus on field-scale application, adsorbent regeneration, and multi-contaminant treatment.