Strontium distribution coefficient

The depth distribution of the Sr/Ca ratios of the recrystallized calcites in these sediments was calculated from the Sr2+/Ca2+ concentrations in the pore waters and appropriate values of the strontium distribution coefficient as a function of temperature from 5-25°C, where... 

Robin M. J. L., Sudicky E. A., Gillham R. W., and Kachanoski R. G. (1991) Spatial variability of strontium distribution coefficients and their correlation with hydrauhc conductivity in the Canadian forces base bordon aquifer. Water Resour. Res. 27(10), 2619-2632. 

Bunde RL, Rosentreter JJ, Liszewski MJ, et al. 1997. Effects of calcium and magnesium on strontium distribution coefficients. Environ Geol 32(3) 219-229. 

It may be noted that, since the distribution coefficient is smaller than unity, the solid phase becomes depleted in strontium relative to the concentration in the aqueous solution. The small value of D may be interpreted in terms of a high activity coefficient of strontium in the solid phase, /srco3 38. If the strontium were in equilibrium with strontianite, [Sr2+] 10 3-2 M, that is, its concentration would be more than six times larger than at saturation with Cao.996Sro.oo4C03(s). This is an illustration of the consequence of solid solution formation where with Xcaco3 /caC03 -1 ... 

The lonsiv ion exchange resins are extraction technologies used to separate radionuclides from alkaline wastewater in the presence of competing cations. These resins include lonsiv IE-910 and lonsiv IE-911, which are manufactured using a new class of crystalline silicotitanates (CSTs) invented by researchers from Sandia National Laboratory (SNL) and Texas A M University. CSTs demonstrate high distribution coefficients in acidic, neutral, and alkaline solutions with high concentrations of competitive ions such as sodium and potassium. The affinity of CSTs for strontium in neutral or alkaline wastes is also high. 

Figure 1. Strontium(ll) distribution coefficients as a function of pH in 0.9% sodium chloride.

Therefore, the preliminary investigation described herein examined several aspects of the behavior of the equilibrium distribution coefficients for the sorption of rubidium, cesium, strontium, barium, silver, cadmium, cerium, promethium, europium, and gadolinium from aqueous sodium chloride solutions. These solutions initially contained one and only one of the nuclides of interest. For the nuclides selected, values of Kp were then... 

Therefore, based on available literature, the following sorption results were expected (l) as a result of the smectite minerals, the sorption capacity of the red clay would be primarily due to ion exchange associated with the smectites and would be on the order of 0.8 to I.5 mi Hi equivalents per gram (2) also as a result of the smectite minerals, the distribution coefficients for nuclides such as cesium, strontium, barium, and cerium would be between 10 and 100 ml/gm for solution-phase concentrations on the order of 10"3 mg-atom/ml (3) as a result of the hydrous oxides, the distribution coefficients for nuclides such as strontium, barium, and some transition metals would be on the order of 10 ml/gm or greater for solution-phase concentrations on the order of 10 7 mg-atom/ml and less (U) also as a result of the hydrous oxides, the solution-phase pH would strongly influence the distribution coefficients for most nuclides except the alkali metals (5) as a result of both smectites and hydrous oxides being present, the sorption equilibrium data would probably reflect the influence of multiple sorption mechanisms. As discussed below, the experimental results were indeed similar to those which were expected. 

The distribution coefficients determined for strontium (at U c) and for barium (at ll C for 3 0 < -log < U.5 and at for all other values of -log Ci) are summarized in Figure 2. Due to the relatively high concentration of strontium in seawater (and hence the relatively high concentration initially in the clay-phase) only limited data for strontium were obtained. The distribution coefficients which were obtained appear to behave similarly to the respective coefficients for barium but are somewhat smaller in magnitude. For solution-phase concentrations on the order of 10"3 mg-atom/ml, the barium coefficients appear to be between 10 and 100 ml/gm, and for solution-phase concentrations on the order of 10 ", the barium coefficients appear to be on the order of 10, as was expected. Furthermore, the coefficients for both strontium and barium are generally consistent with the corresponding data obtained for similar oceanic sediments and related clay minerals found within the continental United States (6,758 13) The... 

The distribution coefficients determined for cadmium (at ll C) are given in Figure 3- The coefficients appear somewhat less than the corresponding data for strontium and barium. Such results could be due to either anionic complex formation (22) and/ or a less favorable sorption equilibrium. 

The distribution coefficients evaluated for silver (at C) are also given in Figure 3 The silver coefficients determined in 0.68 N NaCl solutions are somewhat less than the corresponding coefficients for cesium and rubidium, and also for strontium and barium. Such results are probably due to either anionic complex formation (22) and/or a less favorable sorption equilibrium. (FurthermoreJ the experiments done using silver in sodium chloride solutions required equilibration times on the order of 90 days, as opposed to two to four days for most other experiments, and it appears that processes, which may or may not be important, are involved which are not understood.)... 

For the nuclides studied (rubidium, cesium, strontium, bariun silver, cadmium, cerium, promethium, europium, and gadolinium) the distribution coefficients generally vary from about 10 ml/gm at solution-phase concentrations on the order of 10 mg-atom/ml to 10 and greater at concentrations on the order of 10 and less. These results are encouraging with regard to the sediment being able to provide a barrier to migration of nuclides away from a waste form and also appear to be reasonably consistent with related data for similar oceanic sediments and related clay minerals found within the continental United States. 

Wahlberg, J. S., and Dewar, R. S., "Ion Exchange on Minerals Comparison of Distribution Coefficients for Strontium Exchange from Solutions Containing One and Two Competing Cations," U. S. Geol. Surv. Bull., (1964), 1140-D. 

Sorption Prediction Equations. Equations predicting radioelement distribution coefficients, K s, as arithmetic functions of component concentrations were obtained for sorption of strontium, neptunium, plutonium, and americium on two Hanford sediments. These equations, presented in Table VH and derived from statistical fits of Box-Behnken experimental designs, were generated for strontium in terms of sodium ion, HEDTA, and EDTA concentrations. Prediction equations for neptunium and plutonium sorption were derived from NaOH, NaA102, HEDTA, and EDTA concentrations. Americium sorption prediction equations were based on NaOH, HEDTA, and EDTA concentrations. 

Using the solubility product constants for calcite and strontianite and assuming a calcium activity of 1.6 mmol/L, a distribution coefficient of 0.8 for strontium and 0.98 for calcite, and a ratio of 50 1 (=0.02) in the solid-solution mineral, the following equation gives the activity of strontium ... 

The other clay mineral, illite, also has some strontium sorption, but the distribution coefficient is about one order of magnitude lower than that of montmorillonite and rectorite. Since, in illite, the layer charge is compensated by non-exchangeable cations (Chapter 1, Table 1.2), cation sorption can takes place only on the deprotonated edge sites. This is the case for tectosilicates (quartz, cristobalite). 

Adsorption of Strontium in Equilibrium-Type and Column Experiments. Laboratory batch equilibrium experiments were used as a rapid method for selecting ion exchangers for testing in columns. Distribution coefficients were obtained for strontium adsorption by equilibrating 1 g of resin or zeolite in 100 ml of basin water and agitating for 24 hr at ambient temperature. After centrifuging, the concenti ation of strontium-90 in the supernate was determined. Table VI shows the measured dis-... 

Table VI. Strontium-90 Distribution Coefficients for Various Ion Exchange Materials...

Several attempts have been made in order to correlate the values to physico-chemical properties of soils however, not much success has been accomplished. Carlon et al. [26] reported a correlation between pH and soil-water distribution coefficient (K ) for Pb log = 1.99-1- 0.42pH. The EPA [19] collected values for cadmium, cesium, chromium, lead, plutonium, radon, strontium, thorium, tritium and uranium in soils. The variability in values can be many orders of magnitude as shown in Table 2. 

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