1467-4866-9-2 1467-4866 Research article <p>Surface complexation model for strontium sorption to amorphous silica and goethite</p> Carroll A Susan carroll6@llnl.gov Roberts K Sarah roberts28@lllnl.gov Criscenti J Louise ljcrisc@sandia.gov O'Day A Peggy poday@ucmerced.edu

Chemistry, Materials, Earth, and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, USA

Geochemistry Department, Sandia National Laboratories, Albuquerque, New Mexico, USA

School of Natural Sciences, University of California, Merced, California, USA

 Geochemical Transactions 1467-4866 2008 9 1 2 http://www.geochemicaltransactions.com/content/9/1/2 18205927 10.1186/1467-4866-9-2 05 7 2007 18 1 2008 18 1 2008 2008 Carroll et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Strontium sorption to amorphous silica and goethite was measured as a function of pH and dissolved strontium and carbonate concentrations at 25°C. Strontium sorption gradually increases from 0 to 100% from pH 6 to 10 for both phases and requires multiple outer-sphere surface complexes to fit the data. All data are modeled using the triple layer model and the site-occupancy standard state; unless stated otherwise all strontium complexes are mononuclear. Strontium sorption to amorphous silica in the presence and absence of dissolved carbonate can be fit with tetradentate Sr2+ and SrOH+ complexes on the β-plane and a monodentate Sr2+complex on the diffuse plane to account for strontium sorption at low ionic strength. Strontium sorption to goethite in the absence of dissolved carbonate can be fit with monodentate and tetradentate SrOH+ complexes and a tetradentate binuclear Sr2+ species on the β-plane. The binuclear complex is needed to account for enhanced sorption at hgh strontium surface loadings. In the presence of dissolved carbonate additional monodentate Sr2+ and SrOH+ carbonate surface complexes on the β-plane are needed to fit strontium sorption to goethite. Modeling strontium sorption as outer-sphere complexes is consistent with quantitative analysis of extended X-ray absorption fine structure (EXAFS) on selected sorption samples that show a single first shell of oxygen atoms around strontium indicating hydrated surface complexes at the amorphous silica and goethite surfaces.

Strontium surface complexation equilibrium constants determined in this study combined with other alkaline earth surface complexation constants are used to recalibrate a predictive model based on Born solvation and crystal-chemistry theory. The model is accurate to about 0.7 log K units. More studies are needed to determine the dependence of alkaline earth sorption on ionic strength and dissolved carbonate and sulfate concentrations for the development of a robust surface complexation database to estimate alkaline earth sorption in the environment.

Background

Ion sorption to mineral and amorphous solids has long been recognized as a process that controls the composition of trace elements in water. This process is particularly important for the transport of contaminants in the Earth's surface environment where sorption may retard transport by removing the contaminant from a mobile aqueous phase to a more stationary solid phase. Efforts to describe sorption in complex geological settings has evolved from a purely empirical approach in which distribution coefficients (Kd) are a measure of the total amount of specific ion between the solid and aqueous phases for a complex solution and solid matrix specific to a contaminated site. Although this approach provides a direct measure of the ability of the solid matrix to sequester the contaminant from a specific solution, its empirical nature does not allow it to be applied outside of the specific parameters of the contaminated site. Another approach measures thermodynamic surface complexation constants which describe sorption as a series of specific reactions between dissolved ions and surface sites. In principle, thermodynamic data from several single mineral and element experiments can be combined to build a model that represents the complex systems found in nature, especially when coupled with aqueous speciation, mineral solubility, and kinetic databases. However an internally consistent surface complexation database for a wide range of ions and solids found in natural waters that capture the surface charge is still lacking 1 . Databases tend to adopt surface complexation models that account for surface charge if only one solid is available for uptake 2 and non-electrostatic models that ignore surface charge if multiple solids are available for uptake 3 4 5 .

It is also important to be able to estimate adsorption constants for reactions between aqueous components and substrates for which data are lacking both so that surface complexation models can be applied to complex geochemical systems and to build a robust database. Towards this effort, Sverjensky and colleagues have applied the Born solvation and crystal-chemistry theory together with a site-occupancy standard state to develop a predictive triple layer surface complexation model for surface protonation, alkali, alkaline earth, heavy metal and anion sorption for aluminum, iron, manganese, silica, and titanium oxides/hydroxides 6 7 8 9 10 11 12 13 14 15 16 .

We illustrate the need for a predictive surface complexation model by considering the role that strontium sorption may play for the safe disposal of radioactive waste. 90Sr is one of several fission products that are concentrated in nuclear weapon and energy reprocessing waste and may interact with several different oxides depending on the waste form and disposal environment. At the Hanford (Washington, USA) site, caustic liquid waste with high 90Sr concentrations was disposed in tanks buried below the subsurface. Some of these tanks have leaked into the subsurface, where the migration of strontium is dependent on both its interaction with natural minerals and the reaction products formed from the interaction of the waste liquid with the subsurface fluvial-glacial sedimentary deposits 17 18 19 20 . Future disposal of 90Sr may include solid waste forms of cement, glass, or ceramics 21 22 23 24 . The long-term disposal of 90Sr depends not only on the stability of the waste form, but also on the sorption of strontium leached from the waste form to possible secondary phases, such as calcite, amorphous silica, iron hydroxides and rutile produced by the degradation of the waste form and corrosion of steel canisters containing the waste.

In this paper new strontium sorption data to amorphous silica and goethite collected over a range of total strontium concentrations, pH, and dissolved carbonate concentrations are described using a surface complexation model that builds on and further calibrates Sverjensky's 16 predictive model for alkaline earth sorption. Surface complexation reactions are constrained with structural information inferred from spectroscopic analysis of strontium at the mineral-solution interface (this study, 25 26 27 28 ).

Experimental methods

Starting materials

For experiments conducted in the absence of CO2, all reagents were prepared with freshly distilled and deionized water collected under a nitrogen atmosphere using a portable microwave still. The water was then transferred to a nitrogen atmosphere glove box and used to make FeCl3, SrCl2, KOH, and NaOH stock solutions from solids that were purged for 20 to 30 minutes under a nitrogen stream and weighed in the nitrogen atmosphere glove box.

For experiments conducted in the presence of CO2, stock solutions were made by dissolving reagent grade NaCl, SrCl2, FeCl3 and Fe(NO3)3 solids in distilled and deionized water. Commercial high purity NaOH, HNO3, and HCl stock solutions were also used to adjust the pH of the sorption experiments. Solutions were stored in sealed containers and were not continually exposed to the atmosphere. We define dissolved carbonate as the sum of dissolved aqueous carbon species in this paper. Sources for dissolved carbonate in the sorption experiments include diffusion of atmospheric CO2 when the suspensions were prepared, dissolved carbonate present in the NaOH stock solution used to adjust solution pH, and possibly carbonate sorbed to goethite when synthesized at atmospheric pCO2.

The amorphous silica used in the sorption experiments was synthetic silica gel (Mallinckrodt Silica), 100–200 mesh, (lot # 6512), with an average pore diameter of 150 Å. The gel was repeatedly cleaned ultrasonically with distilled and deionized water until the suspension yielded a clear supernatant after 10 minutes of settling. Cleaned gel was dried at 40°C for 24 hours and stored in a plastic container at room temperature. Surface area was 277 m2 g-1 determined by BET nitrogen gas adsorption. No effort was made to exclude atmospheric CO2 in the cleaning and drying procedure for amorphous silica.

Four lots of goethite were synthesized following protocols outlined in Schwertmann and Cornell 29 . For CO2-free sorption experiments, goethite (Lot 1) was synthesized using KOH and FeCl3•6H20 in a nitrogen atmosphere from reagents dissolved in CO2-free distilled and deionized water. After initial formation of iron hydroxide, the suspension was purged with nitrogen for 60 hours at 70°C to transform the hydroxide to goethite. It was then rinsed repeatedly to remove chloride using dialysis tubing and CO2-free distilled and deionized water. Goethite was dried under a nitrogen stream at 40°C and stored in a nitrogen atmosphere glove box. Mineralogy was confirmed by XRD. For sorption experiments prepared in atmospheric CO2, goethite (Lots 2 and 3) was synthesized following the same protocol except that no effort was made to exclude CO2. For Lot 4, goethite was prepared from Fe(NO3)3 instead of FeCl3•6H2O and no effort was made to exclude CO2. Surface areas determined by BET nitrogen gas adsorption were: Lot 1 = 37.9 m2 g-1; Lot 2 = 38.2 m2 g-1; Lot 3 = 37.9 m2 g-1; and Lot 4 = 27.7 m2 g-1. An average surface area of 37.8 m2 g-1 was used to model the strontium sorption to goethite in NaCl solutions.

Sorption experiments

Strontium sorption was measured in amorphous silica and goethite suspensions prepared in the presence and absence of atmospheric CO2 at 25°C from pH 6 to 10. Tables 1, 2, 3, 4, 5, 6 list total surface area, sorption atmosphere, ionic strength, and initial and final solution composition for each experiment. Amorphous silica or goethite was mixed with a freshly prepared SrCl2/NaCl or Sr(NO3)2/NaNO3 solution of the desired concentration in polycarbonate test tubes. After the pH was adjusted, the tubes were sealed, shaken vigorously by hand, and then reacted for 2 or 14 days in a constant temperature orbital-shaker water bath at 200 rpm. The 14-day experiments were conducted in goethite suspensions to see if additional reaction was needed to precipitate strontium carbonate at higher pH. At the end of the experiment, the final pH of each solution was measured, a sample (2.5 ml) was taken, filtered (4.1 nm pore size), acidified with high purity HCl or HNO3 to prevent SrCO3 precipitation, and analyzed for strontium by inductively coupled plasma atomic emission spectrometry (ICP-AES) (detection limit = 10-7 molal; precision ± 2%). For many of the experiments prepared in the presence of atmospheric CO2, total dissolved carbonate was measured from a filtered sample using a carbon analyzer with an IR detector (detection limit = 5 × 10-5 molal). With this technique, dissolved carbon is purged with 11 N phosphoric acid and nitrogen gas. The resulting concentrations are under saturated with respect to atmospheric CO2 at higher pH. Additional control experiments with no solid present were done to check for strontium sorption to vessel walls and for precipitation of SrCO3(s). Strontium sorption uncertainty is calculated from the analytical uncertainty of the initial and final solution concentrations and the uncertainty associated with a small amount of strontium inherent in the substrate measured from substrate control experiments. For the experiments prepared in the absence of CO2, preparation, sampling, and reagent storage were done in a nitrogen atmosphere glove box.

<p>Table 1</p>

Solution analyses for strontium sorption to amorphous silica in nitrogen atmosphere, I = 0.1 M NaCl and T = 25°C.

Final pH

Surface Area m 2 L -1

Initial [Sr] M

Final [Sr] M

%Sr orbed

Γ Sr sorbed Mol m -2

Total Sr = 10-3 M aged for 2 days

± 5%

3.14

10934

9.99 × 10-4

9.71 × 10-4

2.8

2.57 × 10-9

3.89

10983

1.00 × 10-3

9.90 × 10-4

1.3

1.17 × 10-9

3.89

10983

1.00 × 10-3

9.88 × 10-4

1.5

1.38 × 10-9

5.42

11037

1.01 × 10-3

9.86 × 10-4

2.0

1.86 × 10-9

6.02

11075

1.01 × 10-3

9.83 × 10-4

2.5

2.32 × 10-9

6.33

11115

1.01 × 10-3

9.78 × 10-4

3.4

3.06 × 10-9

6.55

11095

1.01 × 10-3

9.97 × 10-4

1.5

1.40 × 10-9

7.12

11101

1.01 × 10-3

9.80 × 10-4

3.2

2.92 × 10-9

7.04

11035

1.01 × 10-3

9.74 × 10-4

3.4

3.15 × 10-9

7.42

10855

9.95 × 10-4

9.33 × 10-4

6.3

5.74 × 10-9

7.95

10705

9.80 × 10-4

8.40 × 10-4

14.2

1.30 × 10-8

8.62

10415

9.54 × 10-4

6.23 × 10-4

34.7

3.18 × 10-8

9.12

10088

9.21 × 10-4

4.16 × 10-4

54.8

5.00 × 10-8

9.52

9720

8.88 × 10-4

2.64 × 10-4

70.3

6.43 × 10-8

Total Sr = 10-4 M aged for 2 days

± 5%

4.20

11019

1.00 × 10-4

9.85 × 10-5

2.0

1.80 × 10-10

4.89

11005

1.01 × 10-4

9.88 × 10-5

1.7

1.60 × 10-10

5.50

11034

1.01 × 10-4

9.92 × 10-5

1.6

1.42 × 10-10

6.22

11013

1.01 × 10-4

1.01 × 10-4

0.4

3.93 × 10-11

6.33

11057

1.01 × 10-4

1.01 × 10-4

0.5

4.92 × 10-11

6.71

11110

1.01 × 10-4

9.97 × 10-5

1.7

1.56 × 10-10

6.62

11087

1.01 × 10-4

1.01 × 10-4

0.7

6.64 × 10-11

7.01

11086

1.01 × 10-4

9.84 × 10-5

2.5

2.30 × 10-10

7.46

10912

9.96 × 10-5

9.38 × 10-5

5.8

5.31 × 10-10

7.82

10809

9.86 × 10-5

8.75 × 10-5

11.3

1.03 × 10-9

8.54

10475

9.56 × 10-5

6.42 × 10-5

32.8

2.99 × 10-9

8.95

10257

9.39 × 10-5

4.89 × 10-5

47.9

4.38 × 10-9

9.43

9888

9.05 × 10-5

2.84 × 10-5

68.7

6.29 × 10-9

Total Sr = 10-5 M aged for 2 days

± 5%

6.82

11081

1.06 × 10-5

1.06 × 10-5

-0.5

-4.60 × 10-12

6.57

11086

1.06 × 10-5

1.04 × 10-5

1.5

1.41 × 10-11

6.57

11044

1.06 × 10-5

9.30 × 10-6

12.1

1.15 × 10-10

6.84

10939

1.05 × 10-5

1.03 × 10-5

1.5

1.42 × 10-11

7.22

10842

1.04 × 10-5

9.47 × 10-6

8.6

8.19 × 10-11

7.88

10672

1.02 × 10-5

8.33 × 10-6

18.3

1.74 × 10-10

7.91

10481

1.00 × 10-5

7.53 × 10-6

24.7

2.35 × 10-10

9.16

9584

9.14 × 10-6

2.40 × 10-6

73.8

7.03 × 10-10

9.74

8484

8.13 × 10-6

8.33 × 10-7

89.8

8.60 × 10-10

Total Sr = 1.5 10-6 M aged for 2 days

± 10%

6.32

11056

1.51 × 10-6

1.60 × 10-6

-5.5

-7.55 × 10-12

6.53

11013

1.51 × 10-6

1.56 × 10-6

-3.4

-4.65 × 10-12

6.82

11000

1.51 × 10-6

1.59 × 10-6

-5.0

-6.85 × 10-12

6.83

11032

1.51 × 10-6

1.55 × 10-6

-2.8

-3.86 × 10-12

7.06

10988

1.50 × 10-6

1.39 × 10-6

7.3

9.99 × 10-12

7.29

10900

1.49 × 10-6

1.45 × 10-6

2.7

3.74 × 10-12

8.65

9964

1.37 × 10-6

6.96 × 10-7

49.1

6.74 × 10-11

9.10

9534

1.31 × 10-6

3.77 × 10-7

71.2

9.76 × 10-11

9.16

9562

1.31 × 10-6

3.65 × 10-7

72.1

9.87 × 10-11

6.62

11041

1.52 × 10-6

1.51 × 10-6

0.6

7.93 × 10-13

6.59

11092

1.52 × 10-6

1.51 × 10-6

0.6

7.89 × 10-13

6.52

11036

1.52 × 10-6

1.48 × 10-6

2.7

3.71 × 10-12

6.77

10957

1.51 × 10-6

1.59 × 10-6

-5.6

-7.65 × 10-12

7.30

10831

1.48 × 10-6

1.37 × 10-6

7.4

1.01 × 10-11

9.62

9014

1.24 × 10-6

1.26 × 10-7

89.8

1.23 × 10-10

Total Sr = 6 × 10 -7 M aged for 2 days

± 20%

6.34

11073

6.10 × 10-7

6.91 × 10-7

-13.3

-7.33 × 10-12

6.65

11058

6.09 × 10-7

6.70 × 10-7

-10.0

-5.53 × 10-12

6.78

11046

6.08 × 10-7

6.41 × 10-7

-5.4

-2.99 × 10-12

6.83

11028

6.07 × 10-7

6.20 × 10-7

-2.1

-1.13 × 10-12

7.29

10862

5.98 × 10-7

6.01 × 10-7

-0.6

-3.08 × 10-13

7.2

10841

5.97 × 10-7

6.20 × 10-7

-3.8

-2.07 × 10-12

8.66

9955

5.48 × 10-7

2.50 × 10-7

54.4

3.00 × 10-11

9.06

9417

5.19 × 10-7

1.21 × 10-7

76.7

4.22 × 10-11

9.62

8977

4.94 × 10-7

4.34 × 10-8

91.2

5.02 × 10-11

<p>Table 2</p>

Solution analyses for strontium sorption to amorphous silica in air, I = 0.1 M NaCl and T = 25°C.

Final pH

Surface Area m 2 L -1

Initial [Sr] M

Final [Sr] M

%Sr sorbed

Γ Sr sorbed Mol m -2

Total Dissolved Carbonate M

Total Sr = 10-3 M aged for 2 days

± 5%

6.67

11073

9.98 × 10-4

1.01 × 10-3

-1.5

-1.31 × 10-9

not measured

6.72

11098

1.00 × 10-3

1.02 × 10-3

-1.6

-1.43 × 10-9

not measured

6.80

11086

9.98 × 10-4

1.03 × 10-3

-3.6

-3.27 × 10-9

not measured

6.90

11060

9.94 × 10-4

1.02 × 10-3

-2.5

-2.21 × 10-9

not measured

7.19

11012

9.91 × 10-4

1.05 × 10-3

-6.1

-5.46 × 10-9

not measured

7.89

10724

9.66 × 10-4

9.35 × 10-4

3.2

2.89 × 10-9

not measured

8.32

10522

9.45 × 10-4

8.00 × 10-4

15.4

1.38 × 10-8

not measured

8.65

10237

9.23 × 10-4

5.28 × 10-4

42.7

3.85 × 10-8

not measured

9.58

9224

8.33 × 10-4

3.22 × 10-5

96.1

8.68 × 10-8

not measured

6.54

11016

1.00 × 10-3

1.02 × 10-3

-1.5

-1.36 × 10-9

1.72 × 10-5

6.61

11026

1.00 × 10-3

1.01 × 10-3

-0.4

-3.41 × 10-10

3.61 × 10-5

6.70

11004

9.97 × 10-4

1.01 × 10-3

-0.9

-8.38 × 10-10

3.34 × 10-5

6.73

11003

9.99 × 10-4

9.99 × 10-4

0.0

1.79 × 10-12

3.69 × 10-6

7.14

10961

9.93 × 10-4

9.69 × 10-4

2.4

2.19 × 10-9

2.67 × 10-5

7.72

10758

9.77 × 10-4

8.82 × 10-4

9.7

8.76 × 10-9

1.72 × 10-4

8.65

10327

9.36 × 10-4

5.85 × 10-4

37.5

3.40 × 10-8

3.52 × 10-4

8.98

10019

9.04 × 10-4

4.33 × 10-4

52.1

4.70 × 10-8

4.44 × 10-4

9.57

9565

8.65 × 10-4

2.20 × 10-4

74.6

6.75 × 10-8

5.64 × 10-4

7.98

10670

9.68 × 10-4

8.49 × 10-4

12.2

1.11 × 10-8

1.04 × 10-4

8.06

10590

9.68 × 10-4

8.60 × 10-4

11.1

1.01 × 10-8

8.95 × 10-5

8.82

10187

9.27 × 10-4

5.25 × 10-4

43.3

3.95 × 10-8

1.05 × 10-4

8.84

10272

9.27 × 10-4

5.05 × 10-4

45.5

4.11 × 10-8

1.54 × 10-4

8.85

10228

9.28 × 10-4

5.30 × 10-4

42.8

3.89 × 10-8

1.46 × 10-4

8.91

10160

9.27 × 10-4

5.14 × 10-4

44.6

4.07 × 10-8

2.13 × 10-4

9.16

9992

9.05 × 10-4

3.86 × 10-4

57.3

5.20 × 10-8

1.53 × 10-4

9.19

9967

9.06 × 10-4

3.91 × 10-4

56.8

5.17 × 10-8

1.52 × 10-4

9.26

9767

8.88 × 10-4

3.77 × 10-4

57.5

5.23 × 10-8

3.47 × 10-5

9.38

9961

9.00 × 10-4

3.40 × 10-4

62.2

5.62 × 10-8

2.40 × 10-5

9.44

9849

8.96 × 10-4

3.24 × 10-4

63.8

5.81 × 10-8

9.92 × 10-5

9.53

9822

8.88 × 10-4

2.83 × 10-4

68.2

6.16 × 10-8

7.95 × 10-5

9.54

9787

8.88 × 10-4

2.72 × 10-4

69.4

6.30 × 10-8

1.85 × 10-4

9.72

9461

8.58 × 10-4

2.29 × 10-4

73.3

6.65 × 10-8

1.82 × 10-4

Total Sr = 10-4 M aged for 2 days

± 5%

7.08

11079

1.00 × 10-4

1.04 × 10-4

-3.5

-3.15 × 10-10

not measured

6.41

11063

1.01 × 10-4

1.06 × 10-4

-5.1

-4.57 × 10-10

not measured

6.92

11002

1.00 × 10-4

1.09 × 10-4

-8.9

-8.11 × 10-10

not measured

7.02

10966

9.99 × 10-5

1.05 × 10-4

-5.3

-4.79 × 10-10

not measured

7.26

10922

9.88 × 10-5

9.88 × 10-5

0.0

4.05 × 10-13

not measured

7.50

10712

9.70 × 10-5

9.10 × 10-5

6.2

5.61 × 10-10

not measured

8.57

10078

9.14 × 10-5

5.30 × 10-5

42.2

3.81 × 10-9

not measured

9.33

9404

8.51 × 10-5

2.15 × 10-5

75.2

6.77 × 10-9

not measured

9.86

8585

7.81 × 10-5

9.13 × 10-6

88.7

8.03 × 10-9

not measured

Total Sr = 10-5 M aged for 2 days

± 5%

6.21

10913

1.05 × 10-5

1.07 × 10-5

-1.4

-1.39 × 10-11

not measured

6.40

11302

1.06 × 10-5

1.04 × 10-5

1.2

1.13 × 10-11

not measured

6.70

11458

1.06 × 10-5

1.03 × 10-5

2.0

1.88 × 10-11

not measured

7.15

11367

1.05 × 10-5

1.01 × 10-5

3.8

3.54 × 10-11

not measured

6.95

10918

1.05 × 10-5

1.04 × 10-5

1.0

9.75 × 10-12

not measured

7.60

10844

1.03 × 10-5

9.45 × 10-6

8.5

8.10 × 10-11

not measured

7.91

10811

1.03 × 10-5

8.71 × 10-6

15.1

1.43 × 10-10

not measured

8.92

10175

9.72 × 10-6

4.36 × 10-6

55.2

5.27 × 10-10

not measured

9.58

9544

9.12 × 10-6

1.85 × 10-6

79.7

7.62 × 10-10

not measured

Total Sr = 10-6 M aged for 2 days

± 10%

6.52

11049

1.59 × 10-6

1.65 × 10-6

-3.9

-5.60 × 10-12

not measured

6.64

11038

1.59 × 10-6

1.53 × 10-6

3.4

4.84 × 10-12

not measured

6.71

11025

1.58 × 10-6

1.50 × 10-6

5.4

7.78 × 10-12

not measured

6.81

11019

1.58 × 10-6

1.48 × 10-6

6.7

9.56 × 10-12

not measured

6.88

11030

1.58 × 10-6

1.51 × 10-6

4.5

6.42 × 10-12

not measured

7.62

10867

1.56 × 10-6

1.42 × 10-6

8.8

1.26 × 10-11

not measured

8.39

10590

1.52 × 10-6

1.13 × 10-6

25.3

3.64 × 10-11

not measured

9.06

10235

1.47 × 10-6

7.21 × 10-7

50.9

7.32 × 10-11

not measured

9.59

9873

1.42 × 10-6

3.89 × 10-7

72.5

1.04 × 10-10

not measured

Total Sr = 7 × 10-7 M aged for 2 days

± 20%

6.89

11022

6.81 × 10-7

6.46 × 10-7

5.1

3.14 × 10-12

not measured

6.50

11070

6.83 × 10-7

6.57 × 10-7

3.8

2.31 × 10-12

not measured

6.70

11016

6.80 × 10-7

6.82 × 10-7

-0.3

-2.12 × 10-13

not measured

6.43

11013

6.80 × 10-7

7.18 × 10-7

-5.6

-3.44 × 10-12

not measured

7.56

10685

6.59 × 10-7

5.63 × 10-7

14.7

9.05 × 10-12

not measured

7.73

10508

6.49 × 10-7

5.15 × 10-7

20.6

1.27 × 10-11

not measured

8.52

9978

6.16 × 10-7

3.34 × 10-7

45.7

2.82 × 10-11

not measured

9.05

9538

5.89 × 10-7

1.71 × 10-7

70.9

4.38 × 10-11

not measured

9.53

8920

5.50 × 10-7

8.10 × 10-8

85.3

5.26 × 10-11

not measured

 <p>Table 3</p>

Solution analyses for strontium sorption to amorphous silica in air, I = 0.005 M NaCl and T = 25°C.

Final pH

Surface Area m 2 L -1

Initial [Sr] M

Final [Sr] M

%Sr sorbed

Γ Sr sorbed Mol m -2

Total Dissolved Carbonate M

Total Sr = 10-4 M aged for 2 days

± 5%

6.85

10857

1.14 × 10-4

5.28 × 10-5

53.9

5.62 × 10-9

3.84 × 10-5

6.88

10983

1.16 × 10-4

5.04 × 10-5

56.7

5.94 × 10-9

3.93 × 10-5

7.16

10815

1.12 × 10-4

1.57 × 10-5

86.4

8.87 × 10-9

5.47 × 10-5

7.33

9931

1.05 × 10-4

2.87 × 10-5

72.9

7.64 × 10-9

5.80 × 10-5

7.74

9472

9.72 × 10-5

1.94 × 10-5

80.4

8.21 × 10-9

6.23 × 10-5

7.86

8468

8.92 × 10-5

1.81 × 10-5

80.0

8.39 × 10-9

2.45 × 10-4

7.97

8962

8.89 × 10-5

1.35 × 10-5

85.3

8.41 × 10-9

2.60 × 10-4

8.21

8502

8.41 × 10-5

7.74 × 10-6

91.3

8.98 × 10-9

2.21 × 10-4

8.36

8501

7.97 × 10-5

5.24 × 10-6

94.0

8.77 × 10-9

2.25 × 10-4

8.48

8504

7.40 × 10-5

3.34 × 10-6

96.1

8.31 × 10-9

2.32 × 10-4

8.64

8458

7.07 × 10-5

2.54 × 10-6

97.0

8.05 × 10-9

1.54 × 10-4

8.70

8529

6.91 × 10-5

2.04 × 10-6

97.7

7.87 × 10-9

1.35 × 10-4

8.76

8484

6.65 × 10-5

1.67 × 10-6

98.1

7.65 × 10-9

1.44 × 10-4

6.20

8830

9.69 × 10-5

8.19 × 10-5

15.6

1.70 × 10-9

7.51 × 10-6

6.59

9879

1.03 × 10-4

7.35 × 10-5

29.0

3.02 × 10-9

2.24 × 10-5

7.00

10715

1.14 × 10-4

5.89 × 10-5

48.8

5.18 × 10-9

3.36 × 10-5

7.34

11091

1.06 × 10-4

4.12 × 10-5

61.5

5.85 × 10-9

5.96 × 10-5

7.56

10071

9.88 × 10-5

2.94 × 10-5

70.7

6.89 × 10-9

6.61 × 10-5

7.50

10733

1.02 × 10-4

3.59 × 10-5

65.3

6.20 × 10-9

1.39 × 10-4

7.90

9476

8.96 × 10-5

1.78 × 10-5

80.6

7.58 × 10-9

1.93 × 10-4

8.13

9062

8.45 × 10-5

1.15 × 10-5

86.9

8.06 × 10-9

1.94 × 10-4

8.24

8935

8.04 × 10-5

1.19 × 10-5

85.7

7.66 × 10-9

2.09 × 10-4

8.44

8563

7.28 × 10-5

4.32 × 10-6

94.7

8.00 × 10-9

2.70 × 10-4

8.67

8495

6.37 × 10-5

2.85 × 10-6

96.2

7.17 × 10-9

2.36 × 10-4

8.89

8491

5.66 × 10-5

1.32 × 10-6

98.5

6.51 × 10-9

2.34 × 10-4

8.98

8696

5.34 × 10-5

1.12 × 10-6

98.8

6.02 × 10-9

2.06 × 10-4

<p>Table 4</p>

Solution analyses for strontium sorption to goethite in nitrogen atmosphere, I = 0.1 M NaCl and T = 25°C.

Final pH

Surface Area m 2 L -1

Initial [Sr] M

Final [Sr] M

%Sr sorbed

Γ Sr sorbed Mol m -2

Total Sr = 10-3 M, aged for 2 days

± 5%

6.53

1412

9.20 × 10-4

9.44 × 10-4

-2.5

-1.65 × 10-8

6.79

1435

9.25 × 10-4

9.26 × 10-4

-0.2

-1.01 × 10-9

6.96

1457

9.26 × 10-4

9.06 × 10-4

2.2

1.37 × 10-8

7.26

1565

9.30 × 10-4

8.47 × 10-4

8.9

5.30 × 10-8

7.40

1449

9.27 × 10-4

8.07 × 10-4

12.9

8.28 × 10-8

7.82

1433

9.23 × 10-4

6.85 × 10-4

25.8

1.66 × 10-7

8.30

1478

9.20 × 10-4

6.23 × 10-4

32.3

2.01 × 10-7

8.91

1479

9.16 × 10-4

5.27 × 10-4

42.5

2.63 × 10-7

9.49

1445

9.12 × 10-4

3.28 × 10-4

64.0

4.04 × 10-7

6.23

1431

9.61 × 10-4

9.45 × 10-4

1.6

1.08 × 10-8

6.74

1494

9.66 × 10-4

8.98 × 10-4

7.0

4.56 × 10-8

7.16

1472

9.68 × 10-4

9.30 × 10-4

3.9

2.58 × 10-8

7.47

1472

9.71 × 10-4

7.87 × 10-4

19.0

1.25 × 10-7

8.19

1491

9.76 × 10-4

7.67 × 10-4

21.5

1.40 × 10-7

8.51

1482

9.73 × 10-4

7.71 × 10-4

20.8

1.37 × 10-7

8.88

1481

9.69 × 10-4

5.56 × 10-4

42.6

2.79 × 10-7

9.25

1462

9.63 × 10-4

3.29 × 10-4

65.8

4.34 × 10-7

10.02

1452

9.55 × 10-4

9.74 × 10-5

89.8

5.91 × 10-7

Total Sr = 10-4 M, aged for 2 days

± 5%

6.43

1570

1.09 × 10-4

1.16 × 10-4

-5.5

-3.85 × 10-9

6.78

1433

1.10 × 10-4

1.10 × 10-4

-0.6

-4.52 × 10-10

7.23

1431

1.10 × 10-4

1.13 × 10-4

-2.7

-2.09 × 10-9

7.49

1442

1.11 × 10-4

1.10 × 10-4

1.0

7.44 × 10-10

7.78

1602

1.11 × 10-4

1.00 × 10-4

9.6

6.63 × 10-9

8.19

1555

1.11 × 10-4

8.76 × 10-5

20.8

1.48 × 10-8

8.89

1511

1.10 × 10-4

4.53 × 10-5

58.7

4.26 × 10-8

9.38

1532

1.10 × 10-4

3.44 × 10-5

68.6

4.90 × 10-8

9.9

1540

1.09 × 10-4

1.88 × 10-5

82.7

5.85 × 10-8

Total Sr = 10-5 M, aged for 2 days

± 5%

6.43

1540

1.08 × 10-5

1.06 × 10-5

1.4

9.51 × 10-11

6.74

1534

1.08 × 10-5

1.05 × 10-5

3.1

2.19 × 10-10

7.30

1501

1.09 × 10-5

1.07 × 10-5

1.8

1.29 × 10-10

7.73

1423

1.09 × 10-5

9.67 × 10-6

11.2

8.54 × 10-10

8.05

1463

1.09 × 10-5

9.31 × 10-6

14.6

1.08 × 10-9

8.42

1503

1.09 × 10-5

7.79 × 10-6

28.4

2.05 × 10-9

9.22

1502

1.08 × 10-5

3.88 × 10-6

64.2

4.62 × 10-9

9.79

1481

1.08 × 10-5

1.61 × 10-6

85.0

6.19 × 10-9

10.21

1416

1.07 × 10-5

7.34 × 10-7

93.2

7.06 × 10-9

<p>Table 5</p>

Solution analyses for strontium sorption to goethite in air, I = 0.1 M NaCl and T = 25°C.

Final pH

Surface Area m 2 L -1

Initial [Sr] M

Final [Sr] M

%Sr sorbed

Γ Sr sorbed Mol m -2

Total Dissolved Carbonate M

Total Sr = 10-4 M aged for 2 days

± 5%

6.43

1299

1.10 × 10-4

1.06 × 10-4

3.9

3.34 × 10-9

not measured

6.85

1304

1.10 × 10-4

1.07 × 10-4

2.5

2.13 × 10-9

not measured

7.23

1307

1.10 × 10-4

1.08 × 10-4

1.8

1.49 × 10-9

not measured

7.62

1311

1.11 × 10-4

1.02 × 10-4

8.4

7.13 × 10-9

not measured

7.97

1309

1.11 × 10-4

1.03 × 10-4

6.8

5.71 × 10-9

not measured

8.29

1305

1.1 × 10-4

1.17 × 10-4

-5.8

-4.92 × 10-9

not measured

8.96

1304

1.10 × 10-4

6.18 × 10-4

43.7

3.68 × 10-8

not measured

9.28

1297

1.09 × 10-4

4.11 × 10-4

62.4

5.26 × 10-8

not measured

9.97

1278

1.08 × 10-4

2.30 × 10-5

78.8

6.68 × 10-8

not measured

Total Sr = 10-4 M aged for 14 days

± 5%

6.52

1478

1.11 × 10-4

1.09 × 10-4

1.9

1.43 × 10-9

1.47 × 10-4

7.03

1513

1.11 × 10-4

1.06 × 10-4

5.0

3.69 × 10-9

2.10 × 10-4

7.50

1523

1.12 × 10-4

1.01 × 10-4

9.5

6.97 × 10-9

3.76 × 10-4

8.12

1491

1.11 × 10-4

8.20 × 10-5

26.4

1.97 × 10-8

5.29 × 10-4

8.18

1507

1.11 × 10-4

6.84 × 10-5

38.4

2.83 × 10-8

6.38 × 10-4

9.19

1478

1.11 × 10-4

4.20 × 10-5

62.0

4.64 × 10-8

7.22 × 10-4

9.84

1484

1.10 × 10-4

2.17 × 10-5

80.2

5.93 × 10-8

8.93 × 10-4

10.59

1453

1.09 × 10-4

7.54 × 10-6

93.1

6.96 × 10-8

9.97 × 10-4

11.32

1416

1.06 × 10-4

2.15 × 10-6

98.0

7.34 × 10-8

1.07 × 10-3

Total Sr = 10-5 M aged for 2 days

± 5%

6.89

1301

1.17 × 10-5

9.81 × 10-6

16.4

1.48 × 10-9

not measured

7.18

1310

1.18 × 10-5

1.00 × 10-5