Remediation of Heavy Metal Contaminated Soil by Using Chemical Stabilization

Abstract

The effectiveness of ordinary portland cement (OPC) in the immobilization of heavy-metal contaminated soil was investigated in this study. Heavy metal contaminated soil was collected from a scrap metal yard within the outskirts of Kuala Lumpur, Malaysia. Metal composition analysis indicated that the predominant heavy metals present in the soil were iron and aluminium with some composition of zinc and lead and little composition of copper and chromium. The contaminated soil was treated with OPC using cement-to-dry soil (C/Sd) ratios of 0.5, 1, 2, 4 and 8. The effectiveness of the treatment was evaluated by performing unconfined compressive strength (UCS) test and crushed block leaching on the treated soil. Crushed block leaching tests were performed in accordance with standard protocols of Method 1311: Toxicity Precipitation Leaching Procedure (TCLP) and Method 1312: Synthetic Precipitation Leaching Procedure (SPLP) of the United States Environmental Protection Agency (USEPA). The treatment results were compared to the solidified waste acceptance criteria which were compiled based on the regulatory waste disposal limit at a disposal site in the United Kingdom (UK) and the maximum concentration of contaminants for toxicity characteristic of solid wastes from USEPA. The UCS values of the solidified samples at 28 days under air drying for C/Sd ratios of 0.5 – 8.0, far exceeded the minimum landfill disposal limit of 0.34 N/mm2 at a disposal site in the UK. Subsequent to leaching of the treated soils by three different leaching solutions (acetic acid, deionized water and nitric/sulfuric acid), metals in the leachates were either undetectable or appreciably below the proposed leachability limits.