Improved heavy metal immobilization of compacted clay by cement treatment

This study examines the use of cement treatment in improving the lead immobilization properties of a compacted clay liner for sanitary landfill applications. The compaction and strength characteristics of the cement treated clay at cement contents of 0%, 3%, 6%, 9%, 12%, 15% and 18% by weight of dry soil are studied via standard compaction and unconfined compressive strength tests. The lead immobilization characteristics of the cement treated clay are also investigated using atomic absorption spectroscopy. The cement contents of 6% and 9% significantly affect the permeability coefficient and lead absorption of the clay. The permeability coefficient of the cement treated clay meets the requirement for a waterproof material in landfill, i.e., <1.49 × 10^-11 m/s. Lead immobilization is shown to increase with increasing cement content. When the lead nitrate solution in the form of Pb²⁺ ions seeps through the cement treated clay, the hydrolysis reaction results in the formation of Ca²⁺ and OH^- ions. The solution with high alkalinity from this reaction dissolves SiO₂ and Al₂O₃ in the clay. The Pb²⁺ ions are therefore absorbed by SiO₂ and Al₂O₃ and Pb₃SiO₅ is formed. As a result, the lead content in the effluent from the cement treated clay is significantly lower than that from untreated clay. The results from this research can be translated into a regulatory framework for managing the contamination dissipation of industrial waste from landfill.