Dechlorination of fly ash by hydrolysate of municipal solid waste leachate

Municipal solid waste incineration fly ash (referred to as the fly ash) presents an important environmental problem in China today, but strategies for its treatment have yet to be widely studied and implemented. The currently available methods for the dechlorination of fly ash are not sufficient, given the amounts of fly ash produced each year. To increase the reuse fraction of fly ash as raw material for cement production, we propose an improved dechlorination method. Specifically, fly ash was leached with the hydrolysate of municipal solid waste leachate (HMSWL) to remove the water-insoluble chlorine. Three-step HMSWL leaching removed 94.3% of the total chlorine in fly ash, much more than the 82.7% that was removed through three-step ultrapure water (UW) leaching. X-ray diffraction indicated that three-step UW leaching could remove Cl mainly in the forms of KCl, NaCl, CaClOH and AlOCl, whereas three-step HMSWL leaching could further remove more water-insoluble Cl in the forms of AlOCl. In addition, the experimental results further suggested that the low pH of HMSWL (4.9) contributed little to the water-insoluble Cl removal, whereas the displacement of organic acid radicals (especially by the butyrate radical) was the major cause of water-insoluble Cl removal. Therefore, HMSWL rich in butyrate radical could be an ideal water substitute for fly ash dechlorination.