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How does a hydrogen-loaded cation-exchange resin convert salts into acids?

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chemical structure of cation exchanger — ion-exchange reaction Figure 1: Chemical structure of cation exchanger. The exchangeable ions are marked ⁺. The whole structure is permeated by solvent molecules, usually water (not shown).

A hydrogen-loaded cation-exchange resin converts salts into acids through a process of ion exchange. When a solution containing dissolved salts is passed through a column of this resin, the resin releases its bound hydrogen ions into the solution while simultaneously capturing the metal cations from the salt.1

As the resin exchanges its hydrogen ions for the metal cations present in the salt, the anions originally associated with those metal cations are left to pair with the newly released hydrogen ions, effectively forming their corresponding free acids. This process is a fundamental step in the deionization of water, where the resulting acidic solution is typically passed through a second column containing an anion-exchange resin to neutralize the acids and remove the remaining anions.1