With an appropriate liquid cation exchanger, ammonia can be extracted selectively from sour waters, thereby greatly reducing the energy requirement for stripping the acid gas(es) from the water. The ammonium form of the liquid cation exchanger is then decomposed thermally, yielding product ammonia and the ion exchanger for recycle. Such a process purifies the water and provides the ammonia and acid gases as separate products. For energy efficiency it is desirable to use a liquid cation exchanger of optimal acidity, strong enough to form the ammonium ion pair, but weak enough to allow ready regeneration. Di-2, 4, 4-trimethylpentyl phosphinic acid (DTMPPA) in the form of Cyanex 272 (American Cyanamid Co.) has been confirmed as an effective extractant through measurements of extraction equilibria and vapor-liquid equilibria for ammonia solutions of as-received and purified Cyanex 272. Preliminary evidence has also been obtained on thermal stability of DTHPPA at regeneration temperatures.