Effects of Physico-Chemical Properties of Sodium Exchanged Zeolites on the Fate of Malathion in Waste Water

Abstract

Adsorbents are applied in the removal of organic pollutants from wastewaters. One 0 f the main adsorbents that have been widely used is activated carbon. However, activated carb on is associated with high operational costs, hence the need to design. low cost alternatives. Various materials such as magnetic nanoparticles and zeolites have been used in. the purification of polluted waters with varied merits and demerits. Among the well-studied water pollutants are pesticide residues. Considering the great potential of zeolites, this study examined its utility for the removal of a model pesticide, malathion, from wastewaters, The overall objective of this study was to explore the effects of physico-chemical properties of sodium exchanged zeolites on the fate of malathion in fresh waters. The effects of Si/Al ratio, diffusion dimensionality, pore/channel size and particle size of the zeolites mord enite (MOR), ferrierite (FER), ZSM-5 (MFI) and USY (FAU) on the adsorption and degradation kinetics of malathion were studied. Water samples for treatments were collected from Monjolinho River in Brazil. The zeolites were characterized by XRD, FTIR, AAS, SEM, and 27Al-MAS-NMR, and then used to treat 500 mL of water sample in the ratio of one unit cell of zeolite to one molecule of pesticide in triplicates in the laboratory and analyses done at selected intervals up to 72 h. The concentrations of the remaining pesticides and their metabolites in solutions were determined using a GC-MS while the means and standard deviations were obtained by SPSS. Malathion degradation was enhanced in Na-zeolites with half-life (tYz) in fresh water of 49.5 h. Additionally, the tYz of 16.5, 30.3, 24.8, and, 29 _7 h were realized in faujasite, mordenite, ZSM and ferrierite, respectively. The degradation kinetics of malathion in fresh water was pseudo-first order (R2 =0.996) with rate constant ofO.144±0.0IO h-I compared to other zeolites. Na-faujasite had the highest percentage degradation of malathion. High .SiiAI ratio encouraged degradation of malathion. Effectiveness of dimensionality decreased in the order of 3D, 2D ID. Larger channeled zeolites enhanced the dissipation of malathion in water. Major degradation products of malathion in water were malathion mono and dicarboxylic acids and upon introduction of zeolite were eliminated. Analysis of the zeolites after adsorption by XRD showed enhanced stability and crystallinity of the zeolite structure. The decrease in weight below 500°C observed from TGA curves was as a result of malathion thermal decomposition and desorption. The FTIR, NMR, SEM and EDS detected interaction of malathion molecules with the zeolite structure without formation of new chemical bonds between malathion and zeolites