Hg(II) Adsorption By Alginate-guar Gum Templated Titania Spheres: Kinetic And Isotherm Studies

Abstract

In present communication we report on the kinetic and isotherm studies on Hg(II) removal using our recently reported material, the millimeter sized hollow titania spheres (TSP). The mesoporous spheres with high surface area (11.75 m 2 /g) and bimodal pore size distribution were fabricated by a facile sol-gel approach using alginate-guar gum hybrid beads as the structure directing agent. In order to investigate the utility of TSP for Hg(II) adsorption, the batch adsorption experiments were conducted at various pH values (2–7), initial Hg(II) concentrations (50–300 mg/L), and TSP doses (20-100 mg) at 150 rpm, and 30 °C temperature. The spheres exhibited good capacity to adsorb Hg(II) in wide pH range (pH 3 to pH 7). It was possible to remove >95 % Hg(II) from 100 mg/L synthetic Hg(II) solution at pH 5, and 50 mg TSP dose in 10 h. The adsorption equilibrium data were better fitted to Langmuir model at low temperatures while Freundlich model become favored as the temperature was increased to 40 ºC. Langmuir adsorption isotherm study indicated that the monolayer adsorption capacity of TSP was 62.5 mg/g 62.5 mg/g 78.7 mg/g and 100 mg/g at 10, 20, 30, and 40 ºC respectively, which suggested good Hg(II) adsorption capacity of TSP. The calculated RL values evidenced the feasibility of the adsorption. Adsorption kinetic data well accorded with pseudo-second order kinetic model with the rate constant k, equal to 2.5 x 10 -4 g/mg.min 1.99 x 10 -4 g/mg.min and 0.28 x 10 -4 g/mg.min at 100, 150 and 200 mg/mL initial Hg (II) concentrations, indicating chemisorption taking place in the rate determining step. At high initial Hg(II) concentration (200 mg/mL), the adsorption was exclusively controlled by intraparticle diffusion. The study revealed the suitability of TSP for the mercury removal from wastewater.