Hard zinc is a kind of zinc-based alloy as the byproduct of certain zinc processing, including waste galvanizing zinc (Zn-Fe alloy) from hot dip galvanizing of steel industry, the zinc residue (containing Zn, Fe/Ge/In/Ag, etc.) from the refining process of crude zinc, zinc-cadmium alloy, zinc-containing slag from waste incineration, etc. Hard zinc can be used to recover zinc as well as other valuable metal.