The composition of municipal solid waste incinerator (MSWI) fly ash is complex, which contains high concentration of heavy metals, dioxins and chloride, was classified as hazardous waste and difficult to be recycled. From the former study, it was found that water-extracted MSWI fly ash (WFA) has the characteristic of pozzolanic property, and the heavy metals leaching potential of WFA are quite low after mechanical milling. Nevertheless, the large amount of chloride in the MSWI fly ash could not be lowed down effectively even after several times of water-extraction, that will impact the utility of the WFA recovery.
In this study, chloride stabilizing ability was explored by mechanical milling and alkali activation for the water treatment plant sludge (CWTPS) blended with WFA, in order to evaluate the feasibility of recovery the MSWI fly ash as cement substitute.
In this study, calcined CWTPS was blended with WFA in different weight ratios, milled and activated by different concentrations of NaOH solution compared with water for different periods to produce the activated powder, replaced a part of the cement, grouted and cured for 7 and 28 days, exam the chloride stabilizing ability of activated powder and the cement paste by FTIR and XRD analysis.
The results showed that, the chloride content of WFA as high as 160,000 mg / kg. When CWTPS blended with WFA in 70% to 30% by weight, milled with water for 96 hours, and then replaced 10% of cement, grouted and cured for 28 days, the chloride leaching concentration of cement paste was non-detectable. The chloride stabilizing rate reached 100%, and the relative compressive strength compared with pure cement reached 96.29%. Both the chloride stabilizing rate and compressive strength presented excellent results.