Recovering Volatilized Salts from MSWI Fly Ash into Different Metal Species with High Purifies

Thermal sintering/melting technology is a hot topic for the treatment of municipal solid waste incineration with fly ash (FA) nowadays. Most attention is focused on the safety of the treated FA, but seldom focus is put on the separation of thermally volatile metal salts. In this work, we investigated a thermal-sediment control method for effective separation of Zn, Pb, Cu, Cd, K, and Na from FA. Volatilized solids collected from different sediment zones (according to their distances from the FA source) are compared in detail under controlling gas flow rates and heating temperatures. As a result, 52 wt % of Cd and 54 wt % of Pb are first separated in different zones, and 53 wt % of Zn and 52 wt % of Cu are second separated in different zones. Finally, Na and K are recovered together. Pb and Zn purities are as high as 93–94 wt %. What is more, recovery rates of metals from FA follow the order of 90 wt % (Pb) > 83 wt % (Zn) > 81 wt % (Cd) > 77 wt % (Cu) > 73 wt % (Na) > 66 wt % (K). A volatilization-condensation mechanism is put forward to explain the separation of different metal salts. The main result of this work helps the development of the “zero-waste city” concept, which is also in favor of green development and circular economy.