Evidence of Competitive Adsorption of Sb(III) and As(III) on Activated Alumina

The impact of Sb(III) on the removal of As(III) from solution with activated alumina (AA), a widely employed low cost sorbent for various types of water treatments, was assessed. Adsorption isotherms were determined for binary element systems with As/Sb concentration ratios of 5:1, 9: 1, and 12:1 to mimic conditions in water treatment facilities. These were compared to those established for single element systems. There was in increase in Sb(III) adsorption in the binary system compared to the Sb(III) only system. Conversely, in binary systems, As(III) adsorption decreased compared to the As(III) only system. These effects were similar at low and high As(III) concentrations (20 and 240 mu g/mL, respectively) and at low and high pH (7.2 and 9.2). Adsorption in single element systems was well-modeled using Freundlich theory (R-2 >= 0.92). For As: log q(e) = 0.521 log C-e - 0.064; K-f = 1.066, 1/n = 0.52. For Sb: log q(c) = 0.703 loo C-e - 0.258; K-j = 0.552, 1/n = 0.70. The equation and constants determined for As(III) agree well with previous work, while those determined for Sb(Ill) are the first published. However, these equations do not fit for the binary systems, suggesting that other processes become important. This may be explained by the higher pH of As-containing Solutions, leading to changes in both the speciation of the As and Sb and the Surface charge of the AA, and possible competitive behavior between Sb(III) and As(Ill). We Suggest that the concentration of Sb in waters treated for As Should be monitored and further research is required to quantify and understand the impact of low concentrations of Sb oil the removal of As through adsorption.