Development of a simple technique for selective removal of cesium in wastewater in the presence of mixed alkali metals

Thumbnail Image
Pholosi, Agnes
Journal Title
Journal ISSN
Volume Title
Vaal University of Technology
Amongst treatment technologies, adsorption is rapidly gaining prominence because it can remove metal pollutants at low concentrations, economical, ease of operation, and the adsorbent can be regenerated for reuse. This study therefore, aimed at developing a simple material for selective removal of cesium from wastewater. An agricultural waste material (pine cone) was used as a cheap solid support for transition metal hexacyanoferrate and applied as biosorbents for cesium removal. The preparation and characterization of biosorbent for cesium removal in the presence of alkali metals is reported. The experimental procedure was carried out in three phases; the first phase described the sample preparation. Toluene-ethanol mixtures of different ratios were investigated as surface treatment method for pine cone and the optimum treatment ratio determined by measuring the improvement in surface properties of the pine cone such as bulk density, iodine number, and surface negative charge. The modification of pine cone with iron hexacyanoferrate was examined in the second phase. The preparation of potassium iron(III) hexacyanoferrate (KFeHCF) supported toluene-ethanol modified pine cone powder was studied in order to consider its application for cesium removal from aqueous solution. The biosorbent was designed to incorporate the hexacyanoferrate ligand which is known to have a high affinity for cesium ions in aqueous solution. Fe(III) was loaded onto the toluene-ethanol treated pine cone powder followed by hexacyanoferrate ligand incorporation on the biosorbent producing the potassium iron hexacyanoferrate supported toluene-ethanol treated pine cone. The modified pine cone was characterized by FTIR, XRD and TGA analysis. The influence of solution pH and adsorbent dose were studied. The application of potassium iron hexacyanoferrate for the selective removal of cesium in the presence of sodium and calcium was investigated in the third phase. Batch adsorption kinetic studies were performed to determine the effect of modification on cesium removal. Coefficient of correlation, r2, and Chi-square, χ2, methods were applied in the determination of the best fit kinetic method. Increasing the ratio of toluene in the extractant mixture increased formation of esters and iodine capacity of the material, but reduced carboxylate ions and surface charge. Maximum cesium adsorption was observed for the 2:1 toluene-ethanol treated sample. Structural characterization using FTIR, XRD and TGA confirmed the successful modification of KFeHCF pine cone powder. Cesium adsorption experiments indicate that KFeHCF supported toluene-ethanol modified pine was more efficient for cesium removal than the raw pine cone powder. Kinetic modeling of Cs+ adsorption was done using the pseudo-first, pseudo-second order and diffusion chemisorption kinetic models. The pseudo first order kinetics could not accurately predict the experimental data. The kinetics data fitted the pseudo-second order and diffusion-chemisorption models. The chemisorption diffusion model only accurately describes the experimental data after 5 min of contact whereas the pseudo second order describes the experimental data over the range of contact time. The application of the FeHCF modified pine cone for cesium removal from aqueous solution revealed that the FeHCF modified pine was less affected by the presence of competitive cations than the toluene-ethanol treated sample and the raw pine cone sample.
M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology.
Adsorption, Metal pollutants removal, Cesium removal, Wastewater, Heavy metal pollution, Biosorption and biosorbents, Chemical composition