Utilisation of Magnesium Phosphate Cements to Facilitate Biodegradation within a Stabilised/Solidified Contaminated Soil

摘要

Stabilisation/solidification (S/S) of heavy metals and a parallel biodegradation of an organic contaminant using magnesium phosphate cements (MPC) was investigated under laboratory conditions. The study was aimed at improving the robustness of S/S technology by encouraging biodegradation in order to bring about some form of contaminant attenuation over time. A silty sand soil, amended with compost was spiked with an organic contaminant, 2-chlorobenzoic acid (2CBA), and two heavy metal compounds, lead nitrate and zinc chloride. Two formulations of the MPC grouts based on different proportions of the cement constituents, with paste pH of approximately 6.5 and 10, were utilised for S/S treatment. The study involved treating the organic contaminant present in the soil with and without the heavy metals by employing the low and high pH MPC grout mixes, and using 10% and 25% compost content. Microbial activity was monitored using dehydrogenase assay, whilst the tests pertaining to the performance criteria such as contaminant concentration, unconfined compressive strength, elastic stiffness, permeability and batch leaching tests were evaluated at set periods. Contaminant recovery analysis after 140 days indicated a similar reduction in 2CBA concentration to approximately 56% in the different grout mixes. The cement constituents exhibited stimulatory and inhibitory effects on soil dehydrogenase activity. Heavy metal leachability as well as the engineering behaviour of the treated soils conformed to acceptable standards. The results of the investigations show considerable promise for the application of MPC in contaminated land remediation.