Waste-to-energy bottom ash management: Copper recovery by electrowinning

Abstract

Municipal solid waste (MSW) incineration process generates 0.2 tons of bottom ash (BA) per ton of waste. BA contains significant quantities of potentially harmful and/or value-added metallic species such as Cu, which can be leached and discharged into the environment unless they are conveniently managed. The reduction of metal content in BA would allow its use in different applications (e.g., concrete pavement bases and subbases), thus promoting circular economy schemes. In this work, the feasibility of Cu recovery from BA has been studied for the first time by integrating solid-liquid (SL) extraction and electrowinning (EW). First, the leaching of metallic elements from BA was carried out using H2SO4. The resulting leachate, which contained Cu as well as Al, P, Zn, Ca, Fe, Mg, Na, K and Mn as major elements, served as feed stream in the electrochemical process. The EW parallel-plate cell operated in batch mode was composed of one Ti|IrO2 anode placed between two AISI 304 stainless-steel cathodes (interelectrode distance of 2 cm). The operation parameters under investigation to achieve the maximum electrochemical Cu recovery were: initial Cu2+ concentration (0.1-1 g/L), pH (0.5-1.5), current density (100-300 A/m2) and electrodeposition time (2-7 h). It was possible to extract more than 98 % of Cu from the leached stream by EW and to recover almost 90 % in the cathodes from a 1 g/L Cu solution at pH 1.5, operating at 200 A/m2 for 5 h. Therefore, the integration of SL and EW processes offers an attractive alternative for the valorization of BA from MSW. The recovered high-purity Cu could be used in several high-tech sectors, such as batteries, fuel cells, electric traction motors, wind energy, photovoltaics technology, robotics, drones, 3D printing and digital technologies, in good agreement with current circular economy and waste-to-energy approaches.