Water purification from perchlorate by a micelle–clay complex: Laboratory and pilot experiments

Abstract

A technology for purification of water from perchlorate by filters including a complex between micelles of octadecyltrimethylammonium (ODTMA) and a clay-mineral, montmorillonite (Mt), or bentonite is presented. Laboratory filters of lengths of 20 and 40cm were filled with a powdered micelle (ODTMA)–Mt complex mixed with excess sand at ratios of 1:100 to 1:15 w/w. A pilot filter (60cm diameter∙110cm length) was filled with a 1:19 mixture. The complex exhibited a relatively large affinity to adsorb perchlorate; the presence of other anions, such as chloride, nitrate and sulfate at concentrations exceeding 1000-fold those of perchlorate had little effect on its removal from water by filtration. This high affinity was explained by the fact that the positively charged complex has abundance of hydrophobic regions, whereas perchlorate, is characterized by a large bare anionic radius, i.e., a loose hydration shell. A model which accounts for convection, adsorption and desorption was adequate in simulating and predicting the kinetics of filtration for two orders of magnitude variation in concentrations of perchlorate and one order of magnitude variations in concentrations of adsorbing sites, filter length, and flow velocities. Production of a granulated complex enabled to fill the filters exclusively with the complex and make the technology suitable for upscale. Based on the results of pilot experiments and model calculations, it is suggested that in comparison with other technologies, the micelle–clay filter has a relatively large capacity to remove perchlorate in the range of hundreds to thousands μg/l.