Fly ash, a by-product from the combustion of coal or other materials, is collected and processed. This may include drying, crushing or screening the fly ash to prepare it for further processing steps.
Leaching: In this step, the prepared fly ash is treated with an acid solution. This solution dissolves the zinc out of the fly ash and forms a zinc-containing solution. Sulphuric acid is often used as it effectively dissolves zinc and is a relatively inexpensive option.
Solid-liquid separation: The mixture of fly ash and acid is separated in this step. The liquid phase, which contains the zinc solution, is separated from the solid residue (the undissolved components of the fly ash). This can be done by filtration, sedimentation or centrifugation.
Zinc extraction: The purified zinc is then extracted from the solution. This is often done by electrolysis, where an electric current is passed through the solution to deposit the zinc at a cathode. The result is pure metallic zinc.
Recycling and disposal of residues: The solid residues from the solid-liquid separation and the remaining solutions after zinc extraction must be disposed of in an environmentally friendly manner.
