Development of novel and suitably tailored adsorbents for chromium and mercury detoxification

Abstract

The detoxification of chromium and mercury from industrial effluents at various levels (ppb newlineto and#956;g) assumes considerable importance. A variety of methods such as precipitation, newlineextraction, reverse osmosis, membrane separation/filtration, etc. have been utilized for this newlinepurpose. Each of these methods possesses their own merits and demerits. In order to newlineovercome some of the inadequacies in some of the existing techniques, it is imperative to newlinedevelop newer and eco-friendly methods. The first work presented in the thesis deals with an newlineefficient approach for the removal of chromium based on the impregnation of trioctylamine newline(TOA) on a macroporous Amberlite XAD-1180 polymeric matrix. Chromium(VI) could be newlinequantitatively adsorbed in an acidic medium (pH 2-3), while chromium(III) could be newlineretained on the resin matrix at alkaline pH. The comprehensively characterized adsorbent newlineshowed a high adsorption capacity of 171.82 mg g-1 in accordance with the Langmuir newlineisotherm model. The adsorption follows second order kinetics and a study of the various newlinethermodynamic parameters such as Gibbs energy, entropy and the enthalpy changes showed newlinethat the adsorption decreases with an increase in temperature. Column studies and newlineregeneration data validated the performance efficiency of the adsorbent with large sample newlinevolume tolerance (1 Litre) and high preconcentration factor (100). The resin column could newlinebe regenerated using NaOH after the removal of total chromium without any loss in the newlineperformance efficiency for nearly 15 cycles. Chromium could be effectively separated from newlinea synthetic mixture of various ions, thus making it a viable proposition for the detoxification newlineof chromium from industrial effluents. newlineAnother green methodology is developed for the effective adsorption for chromium(VI) newlineusing aliphatic primary amine as a guest in Amberlite XAD-4 polymeric sorbent host. The newlineadsorption of chromium was quantitative at pH 2.5. The adsorption process was in newlineaccordance with pseudo second order kinetics and the maximum adsorption capacity.