Abstract: As a common organic matter in sediments, organic acids have important impacts on the migration behavior of arsenic in groundwater. We investigated the adsorption of arsenic on the main components of sediments in the Kuitun River Basin, Xinjiang, and examined the effects of organic acids on the adsorption of arsenic on goethite. Through XRD characterization and sediment element concentration measurement, we found that the main components of sediments in this area were calcium carbonate, quartz sand, aluminum phosphate, and goethite, with goethite contributing the most to arsenic adsorption. We further investigated the effects of common organic acids (glacial acetic acid, malonic acid, succinic acid, glutaric acid, and citric acid) on the adsorption of arsenic on goethite. The results showed that organic acids inhibited the adsorption of arsenic, with the inhibitory effect being related to the structure of the organic acids. As the increases of the number of carboxyl groups and the decreases of the length of the carbon chain, the inhibitory effect of organic acids on arsenic adsorption was more significant. Citric acid had the strongest effect on arsenic adsorption. The arsenic adsorption process conformed to the pseudo secondorder kinetics and Freundlich adsorption model. The results of infrared spectroscopy showed that citric acid and arsenic had competitive adsorption on the surface of goethite. The results of Zeta potential measurement showed that citric acid formed a negatively charged complex on the surface of goethite.

Key words: adsorption, kinetics, thermodynamics, infrared spectroscopy, surface charge.