Remediation of Heavy Metals Contaminated Soil Using Biochar-Modified Kaolin by Stabilization Technique

Abstract

Soil contamination with heavy metals threatens ecosystems and human health. The objective of this paper is to evaluate the remediation of heavy metals (Pb, Cr, Cd, and Zn) contaminated soil using biochar-modified kaolin for the stabilization of Pb, Cr, Cd, and Zn in soils. Scanning electron microscope (SEM) X-ray diffraction (XRD) were used to analyze surface morphologies and phase compositions of remediation materials. Stock solutions of different metals were spiked onto the pre-weighed soil with 1mg/kg Pb, 2mg/kg Cr, 1.5mg/kg Zn, and 1mg/kg Cd concentrations above standards, respectively. This was then allowed for 1month aging period for acclimatization. After the aging period, the spiked soil was then treated with kaolin, biochar and biochar-modified kaolin in a 45 mL polypropvlene centrifuge tube and left for a week period for the remediation process. The toxicity characteristics leachability procedure (TCLP) test was used to assess the leachability tendency of residual metals in the treated soil. Amongst the biochar-modified kaolin, the 7:3 (kaolin:biochar ratio in grams) was the most effective compared to raw kaolin and biochar alone in stabilizing the target metals in the treated soil.  To optimize the whole process, pretesting of the composites was conducted under constant temperature, dosage, contact time and pH. The residual concentrations of the target metals after TCLP were 2.321%, 10.846%, 0.091%, 0.295% and 3.796%, 22.133%, 0.136%, 0.561% after 30 minutes and 1-hour extraction for Pb, Cr, Cd, and Zn, respectively. The research findings demonstrate that biochar modification enhances kaolin's ability to firmly adsorb the target metals. Thus, the research presents a promising approach for the cost-effective and sustainable remediation of heavy metals in contaminated soils.