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

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−, SO42- and HCO3- 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 Rmax. at equilibrium (Rmax(%) = 100 × (Ci − Ce)/Ci, where Ci and Ce   are the initial and equilibrium NO3- concentrations in solution) of about 80% for initial nitrate concentrations ([NO3-]i) in the 0.08–2.42 mmol/L range. For higher concentrations (4.83 and 8.06 mmol/L), Rmax. 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 Rmax. value decreases with the increase of adsorbent mass. Under the used experimental conditions, the presence of competing anions does not change the nitrate Rmax.value, but slows down the exchange kinetics, the increasing affinity order towards the SMZ being the following: Cl− ≪ HCO3-#SO42-