Abstract: Municipal solid waste incineration (MSWI) fly ash is a particulate matter collected by the air pollution control system, containing pollutants such as heavy metals and dioxins, which was listed in the National Hazardous Waste List (2021 edition). Water washing was required to remove chlorine and other soluble salts before the fly ash was melted or treated in a cement kiln. A small-scale test of water washing was carried out on waste incineration fly ash. The solution after washing was obtained and its composition was detected. According to the test results, the soluble salt content in fly ash and the washing loss rate of fly ash after washing were calculated. The experimental results showed that the soluble salt content in fly ash was 54.6%, and the main component was chlorine salt. The chloride ion content was the highest in the solution, which was about 40 g/L. Washing could remove most of the chlorine salts in fly ash, but the removal of heavy metals was poor. Under the condition of liquid-solid ratio of 6.5∶1.0 （mL/g）, the washing loss rate of fly ash water reached more than 40%. The results of the washing loss rate calculated by the mass loss of dry based fly ash before and after washing and the composition of solution after water washing were consistent, which proved that the method of estimating the wash loss rate of fly ash by the composition of water wash solution was feasible in engineering practice.

Key words: municipal solid waste incineration, fly ash, washing solution, inorganic salt, washing loss rate