Use of CV- and TPP-montmorillonite for the removal of priority pollutants from water

Abstract

The term “priority pollutants” is used to define chemicals hazardous to aquatic life or human health. Thus, it is essential to remove such pollutants from water and try to reduce their impact. Clay minerals might be helpful in the removal of hazardous chemicals, due to impressive adsorption properties. Natural clay minerals adsorb cations and non-charged hydrophilic compounds, but almost do not interact with anions and hydrophobic pollutants as most organic pollutants, including naphthalene and phenolic derivatives. By pre-treating clay minerals with a suitable organic cation, the surface properties of the adsorbent may be adapted, and fast sorption is observed, removing large amounts of such pollutants. In this study we present efficient sorption of naphthalene and several phenolic derivatives to organoclays prepared by adsorption of crystal violet or tetraphenylphosphonium ions on montmorillonite, until a charged-neutralized surface is obtained. The amounts of pollutant adsorbed are at least of the same order of magnitude of those measured for high quality activated carbon, but the adsorption proceeds almost immediately, whereas for activated carbon it takes tens of minutes. The proposed organoclays were mixed with sand and tested in column filters, showing complete removal of high concentration of pollutant at several pore volumes. The adsorbents can also efficiently be applied in “sequential batch” reactors due to the fast adsorption kinetic, followed by flocculation that allows easy separation of the purified effluent. A volume of 150 ml of a 1000 μM TCP solution was completely purified to levels below 3 μM, by means of 0.25 g organoclay.