Removal of Ammonium and Nitrate Ions from Mine Effluents by Membrane Technology

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Abstract
Ammonium and nitrate ions could be removed from synthetic and actual mine effluents by using nanofiltration (NF) and reverse osmosis (RO) membranes. RO membranes were found more effective in removing these ions (>99% for NH4 + and about 97% for NO3 −) than NF membranes (about 66% for NH4 + and about 43% for NO3 −). Removal of ammonia from synthetic solutions containing only ammonia and water by both NF and RO membranes was found to be very low (10–30%), indicating that ammonia in mining effluents existed not as free ammonia but as ammonium salt complexes. The degree of separation depends on the size of the ammonium salt molecule. Removal of ammonia in the form of ammonium iron sulfate from a synthetic solution by NF membranes reached more than 98% while the removal of ammonium sulfate compound from an actual effluent by the same membranes reached about 55%. Ammonia separation by membranes assures the production of quality water suitable for recycling in mining operations since the other metal ions and anions, such as Ca and SO4, were also retained in the concentrate. It may be feasible to further process the concentrated product containing appreciable amounts of nitrate and sulfate ions to produce ammonium compounds as fertilizer. During the test, no operating problems were observed such as fouling or scaling. The membrane performance was not affected at the end of the test as proved by NaCl separation before and after the ammonia run. These results justify a laboratory-scale test with real effluents in order to evaluate the effects of various parameters including the effect of concentration on the membrane performance.

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