An enhanced dechlorination method of solid waste incineration fly ash washed by recyclable organic solvent and water mixtures

Abstract

The enrichment of chloride salts in municipal solid waste incineration (MSWI) and hazardous waste incineration (HWI) fly ash seriously restricts the resources utilization of fly ash. Water washing is a convenient means of dechlorination while the large water-to-solid ratio results in large water consumption and high energy consumption for subsequent brine concentration. In the present study, an enhanced method was proposed to reduce the water-to-solid ratio during washing by introducing organic solvents as dechlorination auxiliary solvents. The results showed that the addition of water-soluble solvent formed a new solution system with water, increasing the ability to dissolve salt per unit of water by 25.15 %–94.53 %. The polarity differences between organic solvents and the water affected the dissolution of salts in the mixed system, and the mixture of lower polar water-soluble solvent indicated better dechlorination efficiency. Besides, the mutual solubility of the lower polar organic solvent and the water decreased with the concentration of salts increasing, and the minimum Cl⁻ concentration of the brine layer was 2.68 M after liquid-liquid separation. Finally, the concentration of Cl⁻ in brine layer was naturally concentrated to 2.68–3.53 M, which was increased by 125.63–144.13 %, and the energy consumption of brine concentration was greatly reduced.