Abstract

The removal of nitrogen from wastewaters is of great importance due to the harmful effects of nitrogen in the environment. In this study, nitrate removal from two underground mine waters was investigated by strong anion exchange resins (Lewatit MonoPlus SR 7 (referred to as SR7, macroporous), Purolite A520E (A520E, macroporous), Purolite A300E (A300E, gel)) in continuous-flow columns. Both mine waters had similar nitrate concentrations (NO₃-N: Mine A 32 mg/l and Mine B 37 mg/l) but contained different levels of chlorides and sulphates. Overall, all three resins removed nitrate from real underground mine waters effectively. In both mine waters, the earliest breakthrough was registered for resin A300E while resins SR7 and A520E had similar breakthrough points. Chloride was identified as a more competitive ion for nitrate than sulphate with resins SR7 and A520E, as their breakthrough curves shifted from left to right when the water was changed from Mine A (higher concentration of Cl⁻) to Mine B (higher concentration of SO₄²⁻). Resin A300E showed a somewhat higher sulphate uptake than the other two resins, which indicates its lower selectivity. This study provides new insight into how selectively nitrate is removed from real underground mine waters by polystyrene resins with different trialkyl functional groups and porosity.