Municipal solid waste fly ash washing for cement application

Abstract

Waste incineration is general solution to manage of municipal solid waste. However, large amount of municipal solid waste incineration fly ash (MSWI FA) accumulating heavy metals poses problem to the environment. One of the fundamental treatments is called solidification-stabilization of MSWI FA with cement to cap hazardous elements. Elements such as chloride and sulfate are captured in MSWI FA when it is collected in an air pollution control device causing low compressive strength of concrete. Thus, a further treatment of MSWI FA to remove these salts are required. Therefore, this study investigated MSWI FA treatment by deionized water, 0.01M and 0.1M HNO3, and 0.1M and 0.25M Na2CO3 to remove chloride and sulfate. Physical and chemical structures of treated and untreated MSWI FA was studied to understand the chloride and sulfate removal mechanisms. Treated MSWI FA was further used as cement replacement in mortar, and the compressive strength was tested. Results suggested that all of the treated solutions can equally remove chloride, but Na2CO3 can remove sulfate in highest level. In addition, mortar with DI-water-treated MSWI FA gave the highest compressive strength. Moreover, heavy metals in the mortar leached by Toxicity Characterization Leaching Procedure (TCLP) method pass the standard.