Chemical stability and adsorption of anionic tracers in an acid environment

Abstract

The effectiveness of anionic compounds as tracers in the environment is determined by factors such as ion chemical stability and adsorption. In extremely acid systems (pH = three) anion adsorption could become significant. This research investigated the role of fluid pH upon anion stability and adsorption in order to identify tracers for field use at a uranium mill in Colorado. Stability, column, and batch tests were conducted to assess anion chemical reactivity and adsorption as a function of varying pH. Three tracers, bromide (Br⁻), thiocyanate (SCN⁻), and chlorodifluoracetic acid (CDF) were tested extensively on standard silica sand and mill tailings soil. Laboratory testing indicated that anion adsorption increased as pH decreased. SCN⁻ was most affected. All anions were relatively stable in acid solution. However, SCN degraded slowly in sulfuric acid solution through oxidation and hydrolysis. Although physical adsorption occured at acid pH, all anions were considered useful as tracers in the environment.