Ammonium nitrate wastewaters treatment by an electromembrane process

Abstract

A process is set up to treat ammonium nitrate wastewaters. It couples membrane electrolysis and electrodialysis. Membrane electrolysis regenerates nitric acid and ammonia while electrodialysis is suitable to extract a depleted stream from the salt circuit and to recycle a concentrated stream. The membrane electrolysis current efficiency of acid production decreases when acid concentration in the anolyte increases and does not depend on the ammonium nitrate concentration in the tested range (0.25–2.5 mol L⁻¹). The average value is about 58% when acid concentration runs from 1 to 8 mol L⁻¹. Ammonia is stripped in situ in order to avoid loss of efficiency due to its back-diffusion. The ammonia efficiency values obtained are higher than those for acid production (between 70 and 85%). Electrodialysis produces a depleted stream containing less than 3.5 10⁻³ mol L⁻¹ and a concentrated stream containing more than 2 mol L⁻¹ of ammonium nitrate. This is achieved with 95% current efficiency. An example of process design is given.