Highly selective removal of nitrate and perchlorate by organoclay

Abstract

An organoclay was prepared using montmorillonite and hexadecylpyridinium chloride (HDPyCl) and tested for the removal of nitrate and perchlorate anions from aqueous solutions. The cationic surfactant modified organoclay was prepared at room temperature using HDPyCl corresponding to 4 times the cation exchange capacity (CEC) of Na-montmorillonite. Powder X-ray diffraction (XRD) analysis of the above organoclay showed a large basal spacing of 40.27Å with the intercalation of HDPy cations in the interlayers probably as a result of a paraffin-type bilayer arrangement. The adsorption data of nitrate and perchlorate were fitted to the Langmuir and Freundlich adsorption isotherms and pseudo-first order and pseudo-second order kinetic models to better understand their adsorption mechanisms. The nitrate and perchlorate uptakes by this organoclay could be described well using the Langmuir isotherm while their uptake kinetics fitted well to the pseudo-second order model. The maximum adsorption capacities of nitrate and perchlorate by the organoclay, HDPy-montmorillonite were calculated at 0.67 and 1.11mmolg−1, respectively. Nitrate and perchlorate uptake kinetics were found to be fast as equilibrium was reached within 4h. Furthermore, the uptakes of nitrate and perchlorate by HDPy-montmorillonite were found to be highly selective in the presence of Cl−, SO42− and CO32−, the most abundant naturally occurring anions. Therefore, the HDPy-montmorillonite could be used as a highly efficient adsorbent for the separation of nitrate and perchlorate from drinking or waste water and ground water.