The development of arsenic adsorption isotherms for G2 media

Abstract

Arsenic is a contaminant which is known for its toxicity in high concentrations. Arsenic can be naturally occurring and affects drinking water in many parts of the world. ADI has developed G2 media, ferric hydroxide coated sand which is effective in the removal arsenic. The Canadian Drinking Water Guidelines suggest an interim maximum allowable concentration of 0.025 mg/L for arsenic. The development of arsenic adsorption isotherms for G2, media will allow for estimation of arsenic removal per unit weight of media. Batch adsorption studies and column testing was conducted at a pH of 7.0 and 22 degrees Celsius. The data showed that the Langmuir isotherm was the best fit for the data collected in this study. From the Langmuir isotherm model, it was determined that for an equilibrium concentration of 0.025 mg/L, the X/m ratio of the media is 107 ug/g of G2 media. A column study to develop a breakthough curve was started, however there was not adequate time to complete the study. The data collected, the X/m ratio is 1080 ug/g of G2 media. This contradicts the value obtained by batch testing. This is most likely due to the change of pH during batch testing. The adsorptive capacity of G2 media changes as arsenic is adsorbed as pH increases. Further batch tests with highly buffered solutions, and desorption studies for G2 media are recommended.