Kinetic and Equilibrium Investigations of Cobalt(II), Nickel(II), and Tungsten(VI) Adsorption on Fly Ash Processed by Hydrothermal Treatment in an Alkaline Solution

Abstract

The adsorption of tungsten(VI) from a single solution onto zeolite fly ash (FA60) produced by hydrothermally treating fly ash (FA) in alkaline solution had been reported. However, taking into account practical considerations, the tungsten(VI) adsorption from a complex solution system containing cobalt, nickel, and tungsten should be investigated. In this study, the amounts of cobalt(II), nickel(II), and tungsten(VI) adsorbed onto the FA and FA60 surfaces were evaluated for a complex solution system. It was observed that a higher amount of tungsten(VI) was adsorbed onto the FA60 surface than onto the FA surface. The adsorption isotherms for tungsten(VI) were fitted using both the Freundlich and Langmuir equations. The result suggest that tungsten(VI) was adsorbed onto the FA and FA60 surfaces through electrostatic interactions between the positively charged FA or FA60 surfaces and the tungsten(VI) anions in complex solution. The pseudo-second-order model described the data more accurately than the pseudo-first-order model. The data obtained for various contact times indicated that the adsorption of tungsten(VI) proceeded through a multistep process involving the adsorption of tungsten(VI) onto the external surface and its subsequent diffusion into the interior of the absorbent. These results suggest that FA60 has a promising potential for the adsorption of tungsten(VI) in complex solution.