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Recovery of ammonia/ammonium
sulphate from synthetically prepared effluent streams
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. |
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