Abstract
	Metal cations can be separated from free acids by a diffusion process which is carried out by feeding the spent solution into a particle bed of a special ion exchange resin. The metal cations are passing the resin bed immediately while the free acid to a high degree is eluated from the resin afterwards just by use of water. Therefore, this procedure has been termed acid retardation.
	Due to the fact, that valuable acids can be recovered in this way, equipments for acid retardation have been applied successfully during the past few years in the metal finishing industry, mainly for the regeneration of solutions for scale removal, pickling, acid dipping, bright dipping, anodizing, chemical machining, etc.
	For the application of this procedure in hydrometallurgy, investigations have been started for the separation of Mg and Mn from electrolytes in zinc winning plants as well as for the removal of As from spent electrolytes in copper refineries. Results of these research projects will be reported under technical and economical aspects.