The efficient recovery of acids from iron-based electrolytes using graphene oxide (GO) membranes was demonstrated for the first time. The results revealed that the amount of H⁺ permeating the GO membranes and reaching drains was two orders of magnitude larger than that of Fe³⁺. Notably, when the FeCl₃ source concentration was reduced to certain extent, Fe³⁺ could be completely blocked by GO membranes. The mechanism for the effective separation of H⁺ from Fe³⁺ was studied, suggesting that the molecular sieving effect of GO nanocapillaries and the coordination between Fe³⁺ and GO were responsible for the effective blockage of Fe³⁺ while the rapid propagation of H⁺ through hydrogen-bonding networks along water layers within the interlayer spacing was responsible for the fast migration of H⁺. These properties made GO membranes promising cation-exchange membranes for applications of wastewater reuse and membrane separation.