The Effects of Water Washing on Cement-based Stabilization of MWSI Fly Ash

Abstract

Municipal solid waste incineration (MSWI) fly ash is classified as a hazardous waste due to its high content of leachable heavy metals. Currently, cement-based stabilization process before landfill has attracted much attention since it can transform the hazardous waste into non-hazardous waste. It is known that MSWI fly ash in China has high-level of soluble chlorides, which has a negative effect on the stabilization of the solidified matrix. In this study, therefore, a water washing pre-treatment process was applied to remove chlorides as much as possible. Experiments were conducted at the conditions of liquid-to-solid (L/S) ratio of 10, 20, 30, 40 and 50 and washing time of 0.5, 1, 2, 3 and 4h for the washing process. Based on the analysis, the MSWI fly ash with L/S ratio of 10 and washing time of 2h was selected for the subsequent experiment. The washed fly ash and raw fly ash were then mixed with different amounts of cement and placed into the mould for 7, 14 and 28 days, respectively. The results showed that cement-based solidification process exhibited the maximum compressive strength of 7.87MPa when the addition of cement was 67% and the maintenance period was 7 days. Besides, toxic characteristic leaching procedure (TCLP) tests showed that the solidified matrix can meet the requirement of landfill.