MSWI fly ash steam washing, aimed to reach a condition of non-hazardous waste and to their possible reuse.

Due to the high content of heavy metals and soluble salts, municipal solid waste incineration fly ash (MSWI FA) is classified as hazardous waste and its reuse is limited for their environmental risks. This work analyzes the steam washing application, to remove chlorides and heavy metals from MSWI FA, in order to reach a condition of non-hazardous waste, making them more suitable for stabilization as geopolymers or cement. The target of the steam application is both a sustainable and optimized utilization of water, to reduce the waste-water, and to take the advantage of the heat generation to dissolve most of the soluble salts; moreover, the steam is a resource that can be generated directly at the incineration plant. Steam washing experiments were performed under different conditions of flux and humidity, continuously monitored by sensors, keeping a low enthalpy steam (T< 100°C) for some cycles of washing; a vacuum pressure was applied to remove rapidly the superficial water in the washing chamber. Pre-treated (washed by water) samples of fly ash were also tested with steam washing for comparison. The steam washing was seen to be efficient in removing water-soluble chlorides including sodium chloride, potassium chloride, sulfates as well as heavy metals. The best efficiency of chlorides and sulfates removal was seen to be by 85%, using a steam flux of 2L/min and humidity of 40% v/v; while for heavy metals, like Cd, Zn, Pb the removal was up to 80% at the same conditions.