Method of treating nickel-containing etching waste fluid

A method of regenerating an etching waste fluid, includes the steps of dissolving HCl gas in an etching waste fluid at a temperature falling within a range of 20 DEG C. to 50 DEG C. and crystallizing NiCl2 and FeCl2 crystals, the etching waste fluid containing NiCl2, FeCl3, and FeCl2 and being obtained by etching Ni or an Ni alloy with an etching solution consisting of an aqueous solution containing FeCl3, distilling a mother liquor at the atmospheric pressure after crystallization and separation thereof to reduce the HCl concentration in the mother liquor, and distilling, at a reduced pressure, a concentrate obtained upon distillation at the atmospheric pressure to further reduce the HCl concentration, thereby obtaining an aqueous solution containing FeCl3, or bringing the concentrate obtained by distillation at the atmospheric pressure into contact with an iron oxide to cause HCl in the concentrate to react with the iron oxide to further reduce the HCl concentration in the concentrate thereby obtaining the aqueous solution containing FeCl3 with little HCl.