Abstract
Rice straw activated carbon oxidized with HNO3 was studied for thorium removal. It was found that carbon has mesoporosity (82%) greater than microporosity (18%) and high ash content (54.1%). Acidic oxides including carboxyl, lactonic, and phenol ones are formed on the carbon surface during preparation and oxidation. The thorium adsorption process proves that the rate of reaction was fast, requiring short contact time. Optimum values were set as pH of 4.0 and 20 mg/l for thorium at removal time of 100 min. Different models were used to determine the kinetic data among which a pseudo-second-order equation was the best fit (R-2 = 0.999). The mechanism of the adsorption kinetics was investigated by employing intra-particle diffusion, surface mass transfer, and Boyd kinetic expressions. The results show that thorium ions' transportation from solution to the surface of the adsorbent is rapid enough (6.2 x 10(-6) cm/min) to use these residues for the removal of thorium from contaminated wastewater. Particle diffusion is the best operating mechanism to control the sorption kinetics of thorium ions. Used carbon had comparable adsorption capacity for thorium as compared to other adsorbents. The quantitative elution study of thorium can be realized with sulfuric acid. Consequently, this carbon can be considered a potentially cheap and operative scavenger for adsorption of thorium from solution.