Abstract: A process for the treatment of raw materials which contain arsenic and metal to produce a metal-free arsenic product and an arsenic-free metal sulfate is disclosed, in which the raw material is leached by using an aqueous solution of sulfuric acid and then the metals are crystallized as sulfates from the separated aqueous solution, which is separated from the metal sulfate crystals. The leach is performed at elevated temperature under oxidizing conditions, in order to bring the arsenic to a 5-valent form, the metal sulfates are crystallized out from the selectively separated, arsenate-bearing aqueous solution by cooling, and arsenic is removed from at least part of this aqueous solution before the aqueous solution is returned to the leach.