Diffusion of organic anions in clay-rich media: Retardation and effect of anion exclusion. (December 2018)

• Record Type: Journal Article
• Authors: Dagnelie, R.V.H.; Rasamimanana, S.; Blin, V.; Radwan, J.; Thory, E.; Robinet, J.-C.; Lefèvre, G.
• Is Part Of: Chemosphere. Volume 213(2018)
• Page Start: 472
• Page End: 480
• Publication Date: 2018-12
• Subjects: Organic anions -- Anion exclusion -- Adsorption -- Diffusion -- Retardation -- Clay rock; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2018.09.064
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: The transport of emerging organic contaminants through the geosphere is often an environmental issue. The sorption of organic compounds slows their transport in soils and porous rocks and retardation is often assessed by extrapolation of batch experiments. However, transport experiments are preferable to strengthen migration data and modelling. In this context, we evaluated the adsorption of various organic acids by means of through-diffusion experiments in a sedimentary clay-rich rock (Callovo-Oxfordian, East of Paris Basin, France). A low diffusivity of organic anions was quantified with effective diffusion coefficients, De, ranged between 0.5 and 7 10 −12 m 2 s −1 . These values indicated an organic anion exclusion. As for chloride, the porosity accessible to organic anions was lower than that of water: εa (organic anions) < ε(water). The partial exclusion of organic anions from rock porosity was linked to both charge and size effects. A significant retardation was observed for organic anions such as oxalate, citrate or α-isosaccharinate. Yet, retardation measured by diffusion experiments was significantly lower than expected from batch experiments on crushed samples. An empirical correction factor is proposed to account for a possible decrease of retardation with accessible porosity of diffusing solute. This feature has significant implications for the estimation of migration parameters of organic compounds in the environment. Graphical abstract: Highlights: Retarded diffusion of organic anions was studied in Callovo-Oxfordian claystone. Carboxylates displayed anion exclusion due to both charge and size effects. Anion exclusion lowered accessible porosity and effective diffusion. Diffusive retardation was correlated with hydrophilicity of sorbates. A possible correlation between anion exclusion and retardation is discussed.