Removal of various phenoxyalkanoic acid herbicides from water by organo-clays

Dodecylammonium bentonite (DB) and dodecylammonium sepiolite (DS) were used as sorbents for phenoxyalkanoic acid herbicides 2,4-D ((2,4-dichlorophenoxy)acetic acid), 2,4-DP ((RS)-2-(2,4-dichlorophenoxy)propionic acid), 2,4-DB (4-(2,4-dichlorophenoxy)butyric acid), 2,4,5-T ((2,4,5-trichlorophenoxy)acetic acid), and MCPA ((4-chloro-2-methylphenoxy)acetic acid). Langmuir, Freundlich, and the linear Henry's Law isotherm adsorption parameters were calculated from the adsorption isotherms. Langmuir equation showed poor fit for both adsorbents. According to the evaluation using the Freundlich equation, the DS sample showed much higher and stronger sorption capacity than DB. Similar behaviour was also observed in the case of the linear Henry's Law isotherm. The adsorption of the herbicides on both DB and DS decreased in the order of 2,4-DB > 2,4,5-T > 2,4-DP > 2,4-D > MCPA.