A novel process for the desalination of MSWI fly ash via in-situ leachate concentrate washing and residue solution electrolysis

Abstract

Desalination of municipal solid waste incineration (MSWI) fly ash is necessary prior to its disposal. Water washing followed by evaporation crystallization for salt extraction is a popular desalination process for MSWI fly ash, while facing large water consumption, high evaporation energy consumption, and difficulties in crystalline NaCl selling. Leachate concentrate is another hazardous waste produced in MSWI plant which is hard to be degraded. In this work, a novel process for the desalination of MSWI fly ash via leachate concentrate washing and residue solution electrolysis was proposed. The effects of liquid-to-solid (L/S) ratio and washing step were discussed. Low-carbon electrolysis strategy for the high-salt washed leachate concentrate was explored. Results showed that leachate concentrate washing displayed the similar desalination performance to water washing and the preferred L/S ratio was 3. The dissolution of Cl in fly ash exceeded 92 % after its twice washing. The desalination capacity of leachate concentrate decreased sharply with increasing using times while its salinity increased steadily. With CO2 injection in a regulating chamber, stable electrolysis of the washed leachate concentrate was achieved. The findings are expected to provide guidance on the treatment of MSWI fly ash, leachate concentrate as well as high-salt wastewater in other fields.