Studies on the Influence of Mercaptoacetic Acid (MAA) Modification of Cassava (Manihot sculenta Cranz) Waste Biomass on the Adsorption of Cu²⁺and Cd²⁺from Aqueous Solution

Abstract

Cassava peelings waste, which is both a waste and pollutant, was chemically modified using mercaptoacetic acid (MAA) and used to adsorb <TEX>$Cu^{2+}\;and\;Cd^{2+}$</TEX> from aqueous solution over a wide range of reaction conditions at <TEX>$30^{\circ}C$</TEX>. Acid modification produced a larger surface area, which significantly enhanced the metal ion binding capacity of the biomass. An adsorption model based on the <TEX>$Cu^{2+}/Cd^{2+}$</TEX> adsorption differences was developed to predict the competition of the two metal ions towards binding sites for a mixed metal ion system. The phytosorption process was examined in terms of Langmuir, Freundlich and Dubinin-Radushkevich models. The models indicate that the cassava waste biomass had a greater phytosorption capacity, higher affinity and greater sorption intensity for <TEX>$Cu^{2+}\;than\;Cd^{2+}$</TEX>. According to the evaluation using Langmuir equation, the monolayer binding capacity obtained was 127.3 mg/g <TEX>$Cu^{2+}$</TEX> and 119.6 mg/g <TEX>$Cd^{2+}$</TEX>. The kinetic studies showed that the phytosorption rates could be described better by a pseudo-second order process and the rate coefficients was determined to be <TEX>$2.04{\times}10^{-3}\;min^{-1}\;and\;1.98{\times}10^{-3}\;min^{-1}\;for\;Cu^{2+}\;and\;Cd^{2+}$</TEX> respectively. The results from these studies indicated that acid treated cassava waste biomass could be an efficient sorbent for the removal of toxic and valuable metals from industrial effluents.