Strong Cation exchange resin are usually regenerated by passing concentrated acid such as HCl, when we pass any monovalent , and divalent metal solution , they show great affinity towards resin, as compared to H+ ions of acid, thus replace them, and occupy their place in the resin, but when we want to use these resin again , how can we regenerate them for use by strong acid washing, because metal ions have greater affinity towards stationary sites in the cation exchange resin as compared to hydrated protons of acid.if we use high concentration of acid, how could the high concentration of protons, replace the metal ions inside the resin.