Removal of Perchlorate Ion in Tap Water with Montmorillonite Modified with Hexadecylpyridinium Chloride

Abstract

Removal of perchlorate ion in tap water with montmorillonite which modified with hexadecylpyridinium chloride (CPC-montmorillonite) was investigated by column chromatography. Almost all anions except Cl− ion in a tap water containing 0.518 and 0.540 mg dm−3 on average of perchlorate ion (ClO4−) and bromate ion (BrO3−), respectively, through the CPC-montmorillonite bed, are adsorbed at the beginning of the column experiment, whereas the Cl− concentration in effluent immediately increases steeply. The anions exhibit breakthrough in the order of F−, SO42−, BrO3−, NO3−, Br− and ClO4−. These results suggest that the anion uptake on CPC-montmorillonite proceeds through anion-exchange process, and the anion affinity of CPC-montmorillonite becomes F− < SO42− < BrO3− < NO3− < Br− < ClO4−. The ClO4− concentration in effluent solution passing through the CPC-montmorillonite bed falls below detection limits of ion chromatography up to 4,500 bed volumes (BV) at the feed solution rate of space velocity (SV) 15 h−1, thus the ClO4− ion in the tap water can be reduced to less than 0.025 mg dm−3 of the target value under consideration as a standard of water-purity for tap water at Ministry of Health, Labour and Welfare of Japan. The ClO4− concentration increases gradually between 5,000 and 10,000 of BV and becomes nearly constant at above near 10,000 of BV. The ClO4− uptake amount on the column experiment can be estimated as 0.04 mmol g−1 from the adsorption breakthrough curve of ClO4− ion. During 37 consecutive days of column experiment, 86 % of hexadecylpyridinium chloride molecules were eluted from an interlayer of CPC-montmorillonite and the basal spacing, (001) plane, of CPC-montmorillonite decreased from 4.05 nm to 2.11 nm.