Closed-loop process for Zn and Cu selective recovery from MSWI bottom ash fine fraction

Abstract

In 2019, 224 Mt of Municipal Solid Wastes (MSW) were produced in Europe. A significant proportion of this MSW is treated by incineration producing each year 20 Mt of Municipal Solid Waste Incineration (MSWI) Bottom Ashes (BA). While the coarsest fraction (>2mm) can be reemployed in construction field, this is not the case for the finest fraction <2 mm (30% wt.) which is intended to be landfilled. The challenges of the treatment of this solid residue are multiple. The metals of interest are dispersed within this complex matrix and the gangue is composed by a large proportion of carbonate based minerals which reduces the choice of possible leaching agents. Moreover, the large amounts of iron and aluminum imply to choose a highly selective recovery method and the economic constrains steer the process towards low-cost technologies. The aim of this work is to study the feasibility of a selective copper and zinc recovery, whose contents in the bottom ash fine fraction are comparable to low-grade ores. A four-step process was designed consisting of a flushing, a leaching, a precipitation and an electrowinning. A selective leaching step using ammonia-ammonium chloride solution was carried out to avoid an iron co-leaching. After the leaching step, the precipitation of zinc was achieved by addition of aluminum nitrate followed by an electrodeposition of copper from ammonia medium. Up to 70% of Cu and Zn could be recovered with minimal modifications of the leachate composition allowing thus its reuse. The developed process enables the recovery of metallic copper and zinc in a spinel form from a waste originally intended for landfilling.