Effect of Electrolytes on the Adsorption of Nitrite and Nitrate from Aqueous Solutions by Activated Carbon

Abstract

Nitrite and nitrate levels were quantitatively adsorbed to wood-derived activated carbon in aqueous system and the effects of electrolytes investigated in this study using batch sorption process. The data showed that nitrate adsorbed nearly 1.5 times higher than that of nitrite. The adsorption is adequately explained by Freundlich and Langmuir isotherm models (r=0.99) with parameters indicative of a beneficial adsorption.. However, the adsorption is markedly reduced in presence of electrolytes (P<0.01). A greater reduction in mean adsorption of the anions occurs in presence of alkaline salts (Na₃PO₄, CH₃COONa; 95.5 per cent) and neutral chloride salts (NaCl, MgCl₂; 90.4 per cent) compared to those observed in presence of neutral sulfate salts (Na₂SO₄, MgSO₂; 67.8 per cent) and acidic salts (ZnSO₄, NaH₂PO₄; 52.2 per cent). Acetic acid increases adsorption of nitrite by about 26 per cent (P<0.01) and decreases that of nitrate by ca. 30 per cent (P<0.01). The study reveals that nitrite and nitrate are beneficially adsorbed to the charcoal, and presence of electrolytes in general causes greater reduction, over 50 per cent, in their adsorption to the charcoal.