Modification of natural clinoptilolite for nitrate removal from aqueous media

Natural zeolitic tuff from the Zlatokop mine (Vranjska Banja deposit, Serbia) was investigated as the starting material to obtain a low cost adsorbent for the removal of nitrate from aqueous media. The tuff rich in zeolite, clinoptilolite, was modified with several oxides, iron(III), manganese(IV) and magnesium, by simple procedures in order to make the clinoptilolite surface accessible for binding nitrate ions. The obtained oxide-modified zeolite samples were characterized by scanning electron microscopy and energy dispersive X-ray analysis (SEM/EDS), powder X-ray diffraction (PXRD), infrared spectroscopy (FTIR) and by measurement of their specific surface area. The effects of the adsorbent dosage (0.5, 1.0, 1.5 and 2.0 g), temperature (25, 35 and 45 degrees C) and initial nitrate concentration (c(0), 100, 200 and 300 mg dm(-3)) on the binding efficiency were also studied. For all adsorbents, the efficiency increased with temperature. The type of the oxide affected the adsorption mechanism. The Fe(III) oxide-modified zeolite exhibited the best binding ability. For this adsorbent, the adsorption kinetics were studied and it was found that they were best represented by the pseudo-second-order model.