Montmorillonite modified with hexadecylpyridinium chloride as highly efficient anion exchanger for perchlorate ion

Details of the anion-exchange properties of Na-montmorillonite modified with hexadecylpyridinium chloride (HDPyCl-montmorillonite) for perchlorate ions are reported herein. The perchlorate uptake on HDPyCl-montmorillonite from 0.01 mmol/dm(3) or 0.10 mmol/dm(3) solution rapidly attained equilibrium within 4 h. The perchlorate uptake on HDPyCl-montmorillonite followed the Langmuir isotherm model with capacity of 1.02 mmol/g. The perchlorate uptake of 0.70-0.80 mmol/g on HDPyCl-montmorillonite persisted in a wide pH range of 4-10. High selectivity of HDPyCl-montmorillonite for perchlorate ion was reflected in the high distribution coefficient values (>10(4) cm(3)/g) with selectivity sequence of HPO42- < SO42- < NO3- <ClO4- from multi-anion solution of 0.10, 1.0, or 2.0 mmol/dm(3). This selectivity sequence corresponded to the sequence of increasing hydration energy of anions. These data revealed that the anion uptake on HDPyCl-montmorillonite accompanied with release of chloride ion into solution through anion-exchange processes. (C) 2012 Elsevier B.V. All rights reserved.