Caustic scrubbing neutralises acid gases such as HCl, SO₂ and H₂S into a sodium hydroxide solution. The reaction is fast, so the limiting factor is rarely chemistry — it is keeping the bed clean and evenly irrigated as reaction products build up in the circulating liquor.

As salt concentration rises, precipitation becomes a real risk. Packing choice and distributor design decide whether the column runs for years or blocks in months.