Adsorption of chromate/organic-acid waste mixtures in aquifer materials. Technical progress report, July 1, 1989-June 30, 1990.

摘要

Chromate and organic acids are widespread contaminants at DOE contamination sites. These anionic compounds are often found as co-contaminants, along with other anions such as nitrate, cyanide, and fluoride. The mobility of anionic contaminants depends strongly on the extent of adsorption, which occurs primarily to positively charged oxide minerals. Unfortunately, most studies of anion adsorption were conducted on single adsorbates and there has been little examination of the interactive effects of combinations of anionic adsorbates. Furthermore, the adsorptive behavior of many organic acids, even as isolated adsorbates, is poorly understood. This project addresses these problems by elucidating the binding mechanisms of organic acids on mineral surfaces. A combination of wet-chemical and spectroscopic methods are being used. The first year of the project has focused on the adsorption of oxalate, one of the most important organic acids at DOE sites. Goethite has been used as model adsorptive mineral because it is known to be among the most important adsorptive phases in subsurface environments. High purity goethite has been synthesized and the physical properties fully characterized. Acidic surface functional groups and the corresponding surface charge development of the goethite have been quantified by CO(sub 2)-free acidimetric titrations. Accurate isotherms and pH adsorption edges have been determined for oxalic acid on goethite. In the remain out-years of the project, we will focus on the competitive interactions of chromate and organic acids, applying a combination of conventional titration methods and in-situ FTIR surface spectroscopy. Experimental procedures will be expanded to studies of natural aquifer materials found at DOE sites. 12 figs.