Acid retardation
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.
Metal ions are from ion exchanger excluded due to Donnan effect.
