Abstract: A method and an apparatus for removing fine-grain silicon material from coarse-grain ground silicon material are disclosed. In the method, ground silicon material is selected that exhibits a predominantly brown color in an aqueous suspension, indicating that a considerable fraction of the ground silicon material has a grain size of less than 0.25 ?m, and the ground silicon material is supplied to a reaction vessel. An aqueous or water-containing solution of a base is added to the ground silicon material, causing an etching process which chemically removes a fine fraction with a grain size of less than approximately 1 ?m. Acid or water is then added to terminate etching and cause rapid sedimentation of a suspension in form of a relatively coarse-grain solid, which can be removed for further processing. The solution formed above the relatively coarse-grain solid can also be withdrawn.