Synthesis of Processes for Recovering Metals from Incineration Fly Ash of Municipal Solid Wastes

Abstract

The purpose of this study is development of separation processes by which metal elements worth using for raw materials of chemicals (for examples Cd, Cu, Mn, Pb, Zn and so on) are recovered from incineration fly ash of municipal solid wastes.
Candidate Process (D) evolved out of Candidate Process (C), which was synthesized with a computer-aided procedure. The process consists of addition of Na₂S to nitric solution as leachate of the fly ash for forming precipitate of sulfides, and consecutive dissolution of sulfides with dil-H₂SO₄, conc-H₂SO₄ and HNO₃ to separate Mn²⁺, Zn²⁺ and Cd²⁺ from each other and to leave CuS insoluble in the acids. For further purification of metals, Candidate Process (D) was modified into Candidate Process (E), in which solvent extraction of Zn²⁺ from Mn²⁺ and Cd²⁺ fractions with bis (2-ethylhexyl) phosphoric acid (D 2 EHPA), and addition of NH₂aq or (NH₄) ₂CO₃ to form [Cu (NH₃) ₄] ²⁺ and to leave PbS insoluble were adopted.