Off-line coupled electrocatalytic oxidation and liquid phase polymer based retention (EO-LPR) techniques to remove arsenic from aqueous solutions

Abstract

Electrochemistry and membrane ultrafiltration methods ( electro-oxidation and liquid phase polymer based retention technique, LPR, respectively) were off-line coupled to remove As(III) inorganic species from aqueous solutions. Our main objective was to achieve an efficient extraction of arsenic species by associating a polymer-assisted liquid phase retention procedure, based on the As(V) adsorption properties of cationic water-soluble polymers, with an electrocatalytic oxidation process of As(III) into its more easily removable analogue As(V). The electrocatalytic oxidation of As(III) to As(V) was performed in the presence of different water-soluble poly(quaternary ammonium) salts acting also as supporting electrolyte, i.e. poly(vinylbenzyl)trimethyl ammonium chloride, P(ClVBTA), poly[3-(methacryloylamine)propyl]trimethyl ammonium chloride, P(ClMPTA), and poly(4-vinyl-1-methylpyridinium bromide), P(BrVMP). After complete electrocatalytic conversion of As(III) into As(V), the mixtures were introduced into an LPR cell to remove the As(V)-polymer adducts. Using P(ClMPTA), P(ClVBTA), or P(BrVMP) ammonium salts in a 20:1 polymer:As(III) mol ratio at pH 8, complete (100%) retention of the arsenic was achieved. Moreover, the As(V) retention efficiency turned out to be directly related to the net charge consumed during the electrochemical conversion of As(III) to As(V).