Comparison of Batch and Column Methods for Determining Strontium Distribution Coefficients for Unsaturated Transport in Basalt

Abstract

Contaminant distribution coefficients determined under saturated conditions are often used to model transport under unsaturated conditions. Although the distribution coefficients are assumed to be consistent under different moisture conditions, this is rarely tested. Column and batch adsorption tests were used to determine strontium distribution coefficients in crushed basalt. Column tests were conducted at saturated and unsaturated moisture contents. Batch tests were conducted at several solid/liquid ratios. Preliminary column tests using bromide as a conservative tracer indicated the presence of immobile water in the column and pointed toward the use of a two-region model to determine the Sr distribution coefficients. Use of a single-region model (no immobile water), however, resulted in an average value (3.09 mL/g) not significantly different than the average value determined using the two-region model (3.41 mL/g). Moisture content had no significant effect on Sr distribution coefficients determined by applying either model to the column test data. The batch test distribution coefficient determined at the recommended standard solid/liquid ratio (0.25 g/mL) was less than the column test values and decreased significantly with increasing solid/liquid ratio. The results indicate that K ds determined with this method will not accurately reflect Sr transport in unsaturated or saturated basalt.

Effects of pH and soil texture on the adsorption and transport of Cd in soils

“…However, the disadvantage of the tests is oversimplified compared with the field conditions. Specifically, batch tests are carried out under conditions of static, overly shaking or stirring and at solid/liquid ratios much lower than those present in the field [4,5] . Column tests have the advantage to simulate the field conditions closely.…”

“…For example, soil in the column can be packed to have bulk densities and porosities similar to those observed in the field, and the advective and dispersive transport processes can be set up in similar patterns in the field. Nevertheless, the disadvantage of column experiments is time consuming and difficult to separate the chemical and physical transport processes involved [5] .…”

Dependence of particle concentration effect on pH and redox for arsenic removal by FeS-coated sand under anoxic conditions

“…At pH 7 and pH 9, the value of K d is essentially independent of the SSR. But, at pH 5, K d increased with the solids concentration, inverse to the commonly reported SSR effect of higher values of K d at lower SSRs (O'Connor and Connolly, 1980;Bajracharya et al, 1996;Benoit and Rozan, 1999;Porro et al, 2000;Phillippi et al, 2007;Wang et al, 2009;Utomo and Hunter, 2010;Leote et al, 2013).…”

“…However, a dependence on the SSR has been observed in systems comprising sorbents as diverse as soils, estuarine and marine sediments, and well-characterized minerals, and sorbates ranging from metals and nutrients to organic compounds and actinides (Leote et al, 2013). The general pattern of the particle concentration effect is higher values of the distribution coefficient at lower SSRs (O'Connor and Connolly, 1980;Bajracharya et al, 1996;Benoit and Rozan, 1999;Porro et al, 2000;Phillippi et al, 2007;Wang et al, 2009;Utomo and Hunter, 2010;Leote et al, 2013). This phenomenon has been explained in terms of: (i) sorption sites with different affinities for the sorbate (Hemming et al, 1997); (ii) an erroneous inclusion of colloidal forms of the sorbate in measuring the dissolved fraction concentration (Benoit and Rozan, 1999); (iii) flocculation of the sorbent affecting specific surface area (Utomo and Hunter, 2010); (iv) competition between the sorbate and like-charged ionic species for sorbent sites ; and (v) complexation among multiple sorbates (e.g., metal cations and ligands) and the sorbent (Phillippi et al, 2007).…”

Comparison of Approaches to Calibrate a Surface Complexation Model for U(VI) Sorption to Weathered Saprolite

“…The pH-dependent sorption (Waite et al 1994, Barnett et al 2000, 2002. The higher R s/w value of 0.25 kg/l was recommended by the ASTM standard sorption protocol (ASTM D4646-03; Porro et al 2000). All experiments were conducted in 50 mM NaNO 3 at equilibrium with atmospheric CO 2 .…”