An adsorption isotherm for bromide

Abstract

Abstract. Bromide is often used as a conservative tracer in soils and sediments; however, it may be adsorbed onto variably charged sediments such as exist at the Savannah River Site (SRS) in South Carolina. Using a methodology simulating concentration gradients observed during field-scale injection of anionic tracers, a series of column experiments were used to determine the nature of bromide adsorption onto and desorption from a sediment sample from SRS. Bromide concentrations ranged from <0.1 to 700 mg/L. Adsorption and desorption were reversible and repeatable; however, desorption showed tailing. Adsorption followed an apparent Freundlich isotherm (95% confidence interval) having an exponent of 0.906 (_+0.033). A second-order polynomial fit provided a more accurate but less conventional model of the adsorption.

New inorganic (an)ion exchangers based on Mg–Al hydrous oxides: (Alkoxide-free) sol–gel synthesis and characterisation

“…Adsorptive capacities of the conventional and natural adsorptive materials towards bromide are usually lower. Removal capacity of the natural materials towards Br À was 0.01 mg[Br] g À1 [48]. Adsorption of bromide by the new Mg-Al hydrous oxides was pH dependent and ranged 20-25 mg[Br] g À1 dw at pH = 4-5 and 5-7 mg[Br] g À1 dw at pH 8.5 at the initial concentration of 198.5 mg[Br] L À1 .…”

When “Conservative” Anionic Tracers Aren't

“…Organic acids generally display sorption maxima that correspond to their pKa values, and when comparing similar compounds, the bond strength between organic acids and hydrous oxides surfaces generally increases with pKa (Kung and McBride 1989). 3 H 2 O is more conservative than Br − in anion‐sorbing sediments (Seaman et al 1995; Korom 2000). Br − adsorption is nonlinear (i.e., concentration‐ dependent), resulting in greater tailing (i.e., dispersion) than apparent for a “conservative” tracer (Seaman et al 1995; Seaman et al 1996; Korom 2000; Seaman et al 2007).…”

“… 3 H 2 O is more conservative than Br − in anion‐sorbing sediments (Seaman et al 1995; Korom 2000). Br − adsorption is nonlinear (i.e., concentration‐ dependent), resulting in greater tailing (i.e., dispersion) than apparent for a “conservative” tracer (Seaman et al 1995; Seaman et al 1996; Korom 2000; Seaman et al 2007). Korom (2000), in a column study using an undisturbed sand with Br − concentrations from <0.1 to 700 mg/L, found the sorption was best fit by a second‐order polynomial; however, a Freundlich isotherm also described the adsorption within a 95% confidence interval on the regression. Br − sorption increases with increasing concentrations (Korom, 2000), as suggested by Figure 1B with pH < PZC.…”

“…Br − adsorption is nonlinear (i.e., concentration‐ dependent), resulting in greater tailing (i.e., dispersion) than apparent for a “conservative” tracer (Seaman et al 1995; Seaman et al 1996; Korom 2000; Seaman et al 2007). Korom (2000), in a column study using an undisturbed sand with Br − concentrations from <0.1 to 700 mg/L, found the sorption was best fit by a second‐order polynomial; however, a Freundlich isotherm also described the adsorption within a 95% confidence interval on the regression. Br − sorption increases with increasing concentrations (Korom, 2000), as suggested by Figure 1B with pH < PZC. However, given the nonlinear nature of the sorption, the fraction of added Br − sorbed decreases with increasing aqueous Br − concentrations, making anionic tracers appear more conservative (i.e., less retarded) at higher concentrations (Seaman et al 1995; Seaman et al 1996; Korom 2000).…”

Bromine and bromide in rainfall, cloud, stream and groundwater in the Plynlimon area of mid-Wales

“…Although, in nature, bromide is usually considered as a relatively conservative ion, often used as a tracer for water movement, it can also sorb onto sediments and be involved in biogeochemical cycling (Davis et al, 1998;Korom, 2000;Huggenberger et al, 1998;Neal et al, 1990). Bromine can occur in various oxidation states from 1 up to +7 (1, 0, 1, 3, 4, 5, 7) but, of these higher oxidation states, dissolved inorganic bromine is of environmental concern as the ion bromate.…”