Studies on the influence of mercaptoacetic acid (MAA) modification of cassava (Manihot sculenta Cranz) waste biomass on the adsorption of Cu 2+ 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 Cu2+ and Cd2+ from aqueous solution over a wide range of reaction conditions at 30°C. Acid modification produced a larger surface area, which significantly enhanced the metal ion binding capacity of the biomass. An adsorption model based on the Cu2+/Cd2+ 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 Cu2+ than Cd2+. According to the evaluation using Langmuir equation, the monolayer binding capacity obtained was 127.3 mg/g Cu2+ and 119.6 mg/g Cd2+. 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 2.04 × 10-3 min-1 and 1.98 × 10-3 min-1 for Cu2+ and Cd2+ 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.