Recovery of ammonia/ammonium sulphate from synthetically prepared effluent streams

K. Sarangi, N.C. Rout, T. Subbaiah, S. Anand* and R.P. Das

Hydro and Electro Metallurgy Departments, Regional Research Laboratory,
Bhubaneswar 751 013, Orissa, India

Received 5 March 2003; accepted 22 July 2004


Oxidative ammonia leaching of sulphidic ores and reductive leaching of oxidic ores with sulphur based reductants in ammoniacal medium produce effluent streams containing ammonium sulphate. The various options for treating such solutions are: (a) concentration of ammonium sulphate by reverse osmosis or electro-dialysis (b) electrolytic decomposition of ammonium sulphate for ammonia and sulphuric acid recovery and (c) lime boil for ammonia recovery. Experimental data generated for concentrating synthetically prepared ammonium sulphate by reverse osmosis and by electro-dialysis gave maximum concentrations of ~40 and 270g/L respectively. Electro-decomposition studies showed that current efficiency depended on various factors such as initial ammonium sulphate concentration, current density and presence of metal ion impurities. A maximum of 87% current efficiency was achieved with initial ammonium sulphate concentration > 70g/L while keeping the current density as 100mA/cm2. The energy requirement during electro-decomposition of ammonium sulphate for producing ammonia was found to be less as compared to other processes used for its production. Ammonia recovery through lime boil gave ~93% efficiency but the process suffers due to disposal problem of calcium sulphate. A combination of electrochemical decomposition and electro-dialysis operations has been suggested as a viable approach for ammonia and sulphuric acid recovery.

Keywords: Electro-dialysis, Electrodecomposition, ammonium sulphate, ammonia

* Corresponding author
   E-mail : sanand@rrlbhu.res.in