Determination of release of organic cations from micelle-clay complexes and their re-adsorption in sand/clay columns

Release of organic cations from cationic micelle-clay complexes in slow release herbicide formulations or in column-filters for water purification may pose a problem. In this study we determined the release of octadecyltrimethylammonium (ODTMA) or benzyldimethylhexadecylammonium (BDMHDA) from micelle-clay complexes, and devised a method to retain the released cations by using a column filled with sand/clay mixtures. The adsorption of 5 mM ODTMA or BDMHDA on montmorillonite added at 5 g/l clay was complete. The release was examined at different times and complex concentrations. The percents of release of ODTMA after 24 h were 13.2, 3.8 and 0 for 0.1, 1 and 5 g/L, respectively, whereas for BDMHDA the corresponding values were 31.2, 19.4 and 7.2. Measurements of dissolved organic carbon (DOC) yielded the amount of the released organic cation from micelle-clay complexes in column-filters for water purification after adding a layer (13 cm) of quartz mixed with clay (150:1 w/w ratio) at the bottom of the column. The amount of the released organic cation from columns including the micelle-clay complexes was less (or equal within the experimental error) than the amount released from those including quartz alone or a quartz-clay mixture. Hence, the carbon analysis showed that in the ppm range all the released cations (ODTMA or BDTMA) were retained by the column-filter. The water passing through a 25 cm column filled with quartz mixed with micelle-clay was also passed sequentially through three columns filled with quartz-clay (150:1) and was concentrated 1000-fold. Measurements by GC-MS showed no traces of the organic cations. The conclusion is that the released organic cations from micelle-clay complexes can be completely retained by adding quartz-clay layers.