Leaching studies on cement stabilized wastes

Abstract

This work investigated the environmental compatibility and field application of a cement based Solidified/stabilized product based on its leaching characteristics and engineering properties. In this study, Municipal Solid Waste Incineration(MSWI)flyash is stabilized with ordinary Portland cement(OPC)to determine its suitability for land fill disposal and for use as construction materials by investigating its compressive strength and leaching potential. In order to determine its safe application to the environment, three tests were selected. They were the Unconfined Compression Strength(UCS)test, Toxicity Characteristic Leaching Procedure(TCLP)test and TCLP with further acidification on the leachate. The results show that the minimum strength requirement of 0.5Mpa can be easily achieved with a 90% IFA and 10% OPC mix for land fill disposal and the usage of IFA as an additive for producing high strength concrete produces a final mechanical quality that produces sufficient strength that is acceptable for construction applications. However, the standard TCLP test was unable to differentiate the leachability of metal contaminants in the cement based waste materials due to the high acid neutralizing capacity(ANC)of cement basedS/Swaste product. With acidification, the heavy metal precipitate that was already present in the leachate begins to dissolve, hence increasing the concentration of heavy metals to elevated level. Therefore, TCLP is too conservative a test to assess the toxicity of cement basedS/S products as the results did not truly reflect the leaching potential of the metal constituents. Using TCLP as an assessment of the cement basedS/S product may lead to disposal solutions (in terms of landfill disposal or usage in construction materials)which are less than optimal in terms environmental safety, particularly in the long term.