Efficient Cadmium(II) Removal from Aqueous Solution Using Microwave Synthesized Guar Gum-Graft-Poly(ethylacrylate)

Microwave induced emulsion copolymerization of ethylacrylate and guar gum resulted in copolymer samples of different % grafting (%G) by changing ethylacrylate and guar gum concentrations at fixed microwave power (100%) and exposure time (15 s). The synthesis was done in the absence of any redox initiator/catalyst, and the adsorption behavior of the copolymer (295%G) was investigated by performing both the kinetics and equilibrium studies in batch conditions. Several experimental parameters such as contact time, initial cadmium concentration, temperature, adsorbent dose, electrolyte amount, and pH of the solution were varied to optimize the adsorption conditions. The most favorable pH for the adsorption was pH 9, and at this pH the adsorption data were modeled using Langmuir and Freundlich isotherms. The data fitted satisfactorily to both the isotherms, indicating that the real heterogeneous nature of the surface sites involved in the metal uptake and overall sorption of Cd(II) on the adsorbent was complex and involved more than one mechanism. On the basis of the Langmuir model, Q(0) was calculated to be 714.28 mg/g for microwave synthesized copolymer (mwGG-g-PEA) in comparison to 270.27 for conventionally synthesized copolymer (cvGG-g-PEA), revealing the advantage of using microwaves in the adsorbent synthesis. The sorption by mwGG-g-PEA followed pseudo-second-order kinetics where a linear plot of t/(qt) versus t was obtained, the correlation coefficient (RI) and rate constant at 100 mg/L Cd(II) being 0.9978 and 4.6 x 10(-4) g/mg/min, respectively. The adsorbent exhibited high reusability and could be successfully recycled for nine cycles where in the ninth cycle 38% adsorption was feasible. To understand the role of PEA grafts (in the copolymer) in the adsorption process, different %G samples were evaluated as adsorbent under optimized conditions.