Batch-wise nitrate removal from water on a surfactant-modified zeolite

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Nitrate adsorption kinetics were determined in batch-wise experiments on a surfactant-modified zeolite (SMZ), prepared by treatment of a clinoptilolite sample by HDTMABr (HDTMA + being the hexadecyltrimethylammonium cation). The influence of various parameters was studied, namely initial nitrate concentration (0.08–8.06 mmol/L), liquid/solid weight ratio (L/S = 5–50 mL/g) and presence of Cl −, SO 4 2 - and HCO 3 - competing anions (at the same equimolar concentration equal to 1.61 mmol/L). The equilibrium time for nitrate uptake is short (0.5–1 h), with a maximal removal value R max. at equilibrium ( R max(%) = 100 × ( C i − C e )/ C i , where C i and C e are the initial and equilibrium NO 3 - concentrations in solution) of about 80% for initial nitrate concentrations ([ NO 3 - ] i ) in the 0.08–2.42 mmol/L range. For higher concentrations (4.83 and 8.06 mmol/L), R max. decreases significantly to 58% and 40% values, respectively. The sorption equilibrium data are in good agreement with the Langmuir isotherm model. On the other hand, the R max. value decreases with the increase of adsorbent mass. Under the used experimental conditions, the presence of competing anions does not change the nitrate R max.value, but slows down the exchange kinetics, the increasing affinity order towards the SMZ being the following: Cl − ≪ HCO 3 - # SO 4 2 - < NO 3 - .