Synthesis and Characterization of Biopolymer Coated Particles for the Removal of Tungsten from Drinking Water

This study investigates the removal of tungsten from simulated water using biopolymer coated particles (i.e. chitosan coated clay) and natural clay. The effects of initial tungsten concentration (from 20 to 500 ppm) and water pH (4, 5.5 and 6.4) on zeta potential and tungsten removal were studied for both chitosan coated clay and natural clay. It was found that the net surface charge of natural clay shifts from negative to positive upon coating with chitosan as confirmed with zeta potential measurements. The point of zero charge (PZC) of natural clay and chitosan coated clay are 2.8 and 5.8, respectively. The chitosan coating on clay was found to be stable over seven days. Zeta potential measurements show that the net surface charge of chitosan coated clay decreases with increased tungsten concentration in feed water since the positively charged sites are consumed due to adsorption of tungsten anions. Chitosan coated clay was found to be much more effective than natural clay for the removal of tungsten. The initial tungsten concentration and water pH significantly affect the removal of tungsten for both the use of chitosan coated clay and natural clay. High initial tungsten concentration and high pH decrease the tungsten removal efficiency of coated and natural clay.