A process is intended to allow simple and particularly reliable electrolyte generation and conditioning from metal-containing used electrolytes and/or used process solutions and/or pulverulent metal wastes. For this purpose, waste products containing metal ions from metal surface treatment processes are to be treated by producing and/or using a metal ion mixed solution, replacing anions contained in the metal ion mixed solution with anions selected for an intended use selected and selectively removing metal ions which are categorized as unsuitable for the intended use selected from the metal ion mixed solution prepared in this way.