Adsorption and transport of polymaleic acid on Callovo-Oxfordian clay stone: Batch and transport experiments

• Published in: Journal of contaminant hydrology 2014-08, Vol.164, p.308-322
• Main Authors: Durce, Delphine, Landesman, Catherine, Grambow, Bernd, Ribet, Solange, Giffaut, Eric
• Format: Article
• Language: English
• Subjects: Adsorption; Aluminum Silicates; Carbon - chemistry; Chemical Physics; Clay; Clay (material); Desorption; Diffusion; Dispersion; Earth sciences; Earth, ocean, space; Exact sciences and technology; Groundwater; Hydrogeology; Hydrology. Hydrogeology; Hysteresis; Irreversibility; Kinetics; Maleates - analysis; Maleates - chemistry; Mathematical models; Migration; Models, Chemical; Organic Chemicals - chemistry; Organic matter; Physics; Polymaleic acid; Sorption; Transport; Two-box model
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2014.06.015

Dissolved Organic Matter (DOM) can affect the mobility of radionuclides in pore water of clay-rich geological formations, such as those intended to be used for nuclear waste disposal. The present work studies the adsorption and transport properties of a polycarboxylic acid, polymaleic acid (PMA, Mw=1.9kDa), on Callovo-Oxfordian argillite samples (COx). Even though this molecule is rather different from the natural organic matter found in clay rock, the study of its retention properties on both dispersed and intact samples allows assessing to which extent organic acids may undergo sorption under natural conditions (pH7) and what could be the impact on their mobility. PMA sorption and desorption were investigated in dispersed systems. The degree of sorption was measured after 1, 8 and 21days and for a range of PMA initial concentrations from 4.5×10−7 to 1.4×10−3mol.L−1. The reversibility of the sorption process was estimated by desorption experiments performed after the sorption experiments. At the sorption steady state, the sorption was described by a two-site Langmuir model. A total sorption capacity of COx for PMA was found to be 1.01×10−2 mol.kg−1 distributed on two sorption sites, one weak and one strong. The desorption of PMA was incomplete, independently of the duration of the sorption phase. The amount of desorbable PMA even appeared to decrease for sorption phases from 1 to 21days. To describe the apparent desorption hysteresis, two conceptual models were applied. The two-box diffusion model accounted for intraparticle diffusion and more generally for nonequilibrium processes. The two-box first-order non-reversible model accounted for a first-order non-reversible sorption and more generally for kinetically-controlled irreversible sorption processes. The use of the two models revealed that desorption hysteresis was not the result of nonequilibrium processes but was due to irreversible sorption. Irreversible sorption on the strong site was completed after 1day and represented 96% of the total sorption on this site. On the weak site the irreversible uptake was slower and completed only after 16days but it also dominated the sorption. 85% of the PMA sorbed on the weak site was not desorbable after 21days of sorption. The migration of PMA was studied by applying a hydraulic gradient to a clay core inserted in a stainless steel cell. Breakthrough of polymaleic acid, simulated with a 1D transport model including the two-box first-order non-reversible model