Municipal solid waste incinerators (MSWI) ashes are being investigated in order to understand recovery opportunities with the final aim of diversifying sourcing and partly overcoming raw materials shortage and improve resource efficiency (Commission, 2014). Strategic tools such as Life Cycle Assessment (LCA) (Astrup et al., 2014) and Substance Flow Analysis (SFA) (Funari et al., 2014) follow through a reliable resource assessment, and a comprehensive investigation on performance characteristics of metals recovery/extraction processes from MSWI ash is required. During the last decades a number of bio- and hydrometallurgical methods are proposed as new directions for the treatment of solid waste, but there is still a limited experience in turning MSWI ash into resource (Meawad et al., 2010). Here we present preliminary results of bio-hydrometallurgical experiments for critical metals recovery from MSWI residual products (i.e., bottom and fly ash) and a comparison of the performance characteristics between acid leaching and acid bioleaching. Different experimental setups were explored; sulphuric acid leaching showed the advantage of reduction and mobilisation of Ca, thus improving the quality of the final product. Conversely, bioleaching experiments were performed in a mixed culture of T. ferrooxidans and T. thiooxidans and their efficiency was evaluated over a period of several weeks; reagents involved are lower than those needed for acid leaching thus making the process economically feasible and more environmental friendly. The influence of the experimental parameters will be discussed for both acid leaching and acid bioleaching procedures. The recovery methods of metals and critical raw materials from MSWI ashes are discussed.
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