PARAQUAT ADSORPTION ONTO ALGINATE-CLAY BEADS

MARIANA ETCHEVERRY; V. CAPPA; J. TRELLES; GRACIELA P. ZANINI

Buenos Aires

Workshop; II Workshop on Bio-degradable Polymers and Biocomposites III Workshop BIOPURFIL, Bio-based Polyurethane Composites with Natural Fillers; 2015

INTRODUCTIONAlginate beads are well-known support materials in biosciences applications [1], and in the last years they are being used in the environmental field [2].On the other hand, clays have been used in the last decades in the removal of toxic metals or organic pollutants from aqueous solutions due to favorable surface properties, availability, and environmental and economical considerations. The encapsulation of clays in alginate beads can lead to the generation of very practical and effective materials for the removal of pollutants.The aim of this work is to use alginate-clays beads materials to remove paraquat (PQ), a highly toxic herbicide used in Argentina.MATERIALS AND METHODSNa-alginate was supplied by Fluka. The clay used was a Na-montmorillonite (99.4% purity), obtained from Lago Pellegrini (Río Negro, Argentina). PQ, (99.0%) was supplied by Supelco. Preparation of alginate-clays beads: 100 cm3 of a 1% (w/v) Na-alginate solution was mixed with 4 g of montmorillonite and stirred. This mixture was added drop by drop to stirred reservoir containing 0.1 M CaCl2. The beads were allowed to harden in this solution for 10 min. After this time spherical beads containing 4% (w/v) of montmorillonite were obtained. The beads were washed with distilled water and stored in NaCl. Pure alginate beads were prepared in the same way but without mixing with montmorillonite.Adsorption isotherms and adsorption kinetic studies were performed with batch experiments at pH 5.5±0.2. For isotherms, a selected amount of beads were placed in centrifuge tubes, proper volumes of 0.01M NaCl and aliquots of stock solution of herbicide were added in each tubes to cover a wide range of concentrations. The tubes were shaken end-to-end during 24 h to ensure equilibration. The same procedure was followed in kinetic studies, and adsorption was evaluated at different times. The concentrations of PQ in the supernatant were quantified at 257 nm by UV?Vis spectroscopy.RESULTS AND DISCUSSIONThe beads resulted to be spherical with an average diameter of 1000µm, as seen by scanning electron microscopy. The presence of clay particles could be detected within the beads. The clay presence produced hard beads that were easily handled.The adsorption isotherms for alginate clay beads show saturation adsorption values of 0.3 mmol/g, whereas it was 0.1 mmol/g for pure alginate beads. The difference between these two values is highly related to the cation exchange capacity of the clay content (CEC:0.9 mmol/g).The adsorption kinetics was preformed at three PQ concentrations (0.075mM, 0.15mM, 0.2mM). In all cases adsorption was completed after around 7h. The adsorption rate increased as PQ concentration increased. Adsorbed amount vs t1/2 plots were linear, indicating that the process was controlled by diffusion of PQ within the beads.CONCLUSIONSThe encapsulation of clays in alginate beads allowed to prepare a material with high capacity to adsorb the herbicide paraquat. The material isenvironmentally friendly and has potential application in the removal of different pollutant in the environment. REFERENCES[1] Bayramoglu G, Denizli A, Bektas S, Arica M, Microchemical 72 (2002), 63?76.[2] Silva R, Manso J, Rodrigues, J, Lagoa, R., J. Environ. Sci. Health A 43 (2008), 1311-1317.