Recovery of Zinc from Municipal Solid Waste Fly Ash

Abstract

The availability of many elements is decreasing due to extended use. One possible solution to this problem is the recovery of metals from waste. Fly ash from municipal solid waste (MSW) incineration contains many metals and can therefore be considered a resource. This project focuses on the recovery of zinc from MSW fly ash. A total analysis of the fly ash was performed using ICP-OES after decomposing the sample in a microwave oven. MSW fly ash contains silicates, and the content of the zinc trapped in the silicates was measured. An insignificant amount of the zinc was trapped in the silicates, making it unnecessary to dissolve the silicates for a good yield. Leaching is a common way of dissolving metals from fly ash. In this project, leaching experiments were performed in a process reactor, and the eluate was analyzed with ICP-OES and IC. The fly ash was first pre-leached with water to remove water-soluble salts. Sulfuric acid and ammonia solution were studied as possible leachates for zinc recovery. Using sulfuric acid resulted in immediate formation of gypsum, making this leachate problematic. The leaching experiments with ammonia showed good results, making ammonia solution a possible leachate for recovery of zinc from fly ash.