Stabilization of Lead-Contaminated Mine Soil Using Natural Waste Materials

Abstract

Stabilization was applied as a remediation option for immobilizing lead (Pb) in contaminated mine soil. Four types of waste materials were used as stabilizing agents, namely waste oyster shells (WOS), calcined oyster shells (COS), natural starfish (NSF), and spent-coffee-grounds-derived biochar (SCGB). The Pb-contaminated mine soil was treated with the stabilizing agents ranging from 0 to 10 wt% and a curing period of 28 days. The toxicity characteristic leaching procedure (TCLP) was employed for evaluating the effectiveness of the remedial process. The Pb immobilization mechanism in the treated mine soil was investigated using scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM-EDX) analyses. The obtained results showed that the TCLP Pb levels decreased as the stabilizing agent dosage increased. The WOS and COS stabilizing agents immobilized Pb effectively in the contaminated mine soil. Application dosages of 4 wt% and 2 wt% for WOS and COS, respectively, were sufficient for compliance with the TCLP regulatory level of 5 mg/L. For the NSF and SCGB treatments, 4 wt% and 10 wt%, respectively, were necessary to meet the TCLP regulatory limit. The effectiveness of Pb immobilization was found to increase in the following order: SCGB < NSF < WOS < COS. The chemical fraction analyses showed that the lower F2 (weak acid soluble) fraction and higher F3 (reducible) and F4 (oxidizable) fractions were most likely associated with the high level of Pb immobilization. Moreover, the SEM-EDX analysis results showed that the most effective Pb immobilization could be strongly associated with the pozzolanic reaction products.