Kinetics and Mass Transfer Studies on the Adsorption of Arsenic onto Activated Alumina and Iron Oxide Impregnated Activated Alumina

The present investigation deals with the uptake of As(III) and As(V) ions from aqueous solution by activated alumina and a new laboratory-prepared sorbent—iron oxide impregnated activated alumina. Iron oxide impregnation onto activated alumina significantly increased the percent arsenic removal and adsorption capacity for As(III) and As(V) ions. The maximum As(III) and As(V) removals were 96.8% and 98.4%, respectively, by iron oxide impregnated activated alumina (IOIAA). Maximum As(III) and As(V) removal of 94.2% and 96.1% was observed over activated alumina. Kinetic studies were performed at different initial sorbate concentrations to determine the mechanism of mass transfer of sorbate onto this sorbent. The maximum removal of As(III) and As(V) by activated alumina and iron oxide impregnated alumina takes place within 6 h and attains equilibrium within 12 h. First-order Lagergren kinetics explained the adsorption of arsenic over activated alumina whereas a pseudo-second order rate equation explained the behaviour of As(III) adsorption over iron oxide impregnated activated alumina. Diffusional effects in solid pellets were also investigated to understand the mechanism of adsorption. These results indicate that the mechanism of arsenic adsorption is complex on both sorbents as both pore diffusion and surface diffusion contribute to the arsenic removal. During the initial period, surface diffusion was predominant but as the adsorption progresses, pore diffusion dominated the rate of adsorption.