PURPOSE: To remove a metalloid or a noxious anion, by a method wherein alkali is added to a heavy metal-containing waste liquid having a ferrous salt added thereto to adjust the pH thereof to 8W12 and a soluble alkaline earth metal salt is further added to said waste liquid before a ferrous ion is oxidized.

CONSTITUTION: A ferrous salt is added to a heavy metal-containing waste liquid and alkali is added thereto to adjust the pH thereof to 8W12. After a soluble alkaline earth metal salt is added, the treated waste liquid is brought into contacted with oxigen-containing gas or receives the addition of an oxidizing agent to oxidize a part of a ferrous ion and a spinnel ferrite precipitate is formed. After a heavy metal ion is taken in the aforementioned precipitated particle or adsorbed therewith, solid-liquid separation is performed. As the aforementioned soluble alkaline earth metal salt, there are halides represented by calcium chloride, strontium chloride or barium chloride or nitrate.