Browsing by Subject "SELENIUM"

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  • Li, Xiaodong; Meng, Shuo; Puhakka, Eini; Ikonen, Jussi; Liu, Longcheng; Siitari-Kauppi, Marja (2020)
    To determine the diffusion and sorption properties of radionuclides in intact crystalline rocks, a new electromigration device was built and tested by running with I- and Se(IV) ions. By introducing a potentiostat to impose a constant voltage over the studied rock sample, the electromigration device can give more stable and accurate experimental results than those from the traditional electromigration devices. In addition, the variation in the pH of the background electrolytes was minimised by adding a small amount of NaHCO3 as buffers. To interpret the experimental results with more confidence, an advection-dispersion model was also developed in this study, which accounts for the most important mechanisms governing ionic transport in the electromigration experiments. Data analysis of the breakthrough curves by the advection-dispersion model, instead of the traditional ideal plug-flow model, suggest that the effective diffusivities of I- and Se(IV) are (1.15 +/- 0.06) x 10(-13) m(2)/s and (3.50 +/- 0.86) x 10(-14) m(2)/s, respectively. The results also show that I- is more mobile than Se(IV) ions when migrating through the same intact rock sample and that their sorption properties are almost identical.
  • Elorinne, Anna-Liisa; Alfthan, Georg; Erlund, Iris; Kivimaki, Hanna; Paju, Annukka; Salminen, Irma; Turpeinen, Ursula; Voutilainen, Sari; Laakso, Juha (2016)
    Background Vegetarian and vegan diets have become more popular among adolescents and young adults. However, few studies have investigated the nutritional status of vegans, who may be at risk of nutritional deficiencies. Objective To compare dietary intake and nutritional status of Finnish long-term vegans and non-vegetarians. Methods Dietary intake and supplement use were estimated using three-day dietary records. Nutritional status was assessed by measuring biomarkers in plasma, serum, and urine samples. Vegans' (n = 22) data was compared with those of sex-and age-matched non-vegetarians (n = 19). Results All vegans adhered strictly to their diet; however, individual variability was marked in food consumption and supplementation habits. Dietary intakes of key nutrients, vitamins B12 and D, were lower (P <0.001) in vegans than in non-vegetarians. Nutritional biomarker measurements showed lower concentrations of serum 25-hydroxyvitamin D3 (25(OH) D3), iodine and selenium (corrected for multiple comparisons, P <0.001), Vegans showed more favorable fatty acid profiles (P <0.001) as well as much higher concentrations of polyphenols such as genistein and daidzein (P <0.001). Eicosapentaenoic acid proportions in vegans were higher than expected. The median concentration of iodine in urine was below the recommended levels in both groups. Conclusions Long-term consumption of a vegan diet was associated with some favorable laboratory measures but also with lowered concentrations of key nutrients compared to reference values. This study highlights the need for nutritional guidance to vegans.
  • Li, Xiaodong; Puhakka, Eini; Liu, Longcheng; Zhang, Wenzhong; Ikonen, Jussi; Lindberg, Antero; Siitari-Kauppi, Marja (2020)
    A surface complexation model of Se(IV) sorption on biotite with one type of strong sorption sites and two types of weak sorption sites were developed based on experimental data obtained from titration, sorption edge and sorption isotherm experiments. Titration data was collected using a batch-wise manner together with back-titration to calibrate the effect of mineral dissolution in 0.01 M KClO4 background electrolytes from pH 3 to 11 in an inert atmosphere glovebox. Further calibrations of the titration curve include proton exchange and cation exchange in which the calculations of cation occupancies on biotite surfaces were taken into account. The sorption edge measurements were determined by measuring the sorption of 10(-9) M total Se with a radioactive Se-75 tracer on converted biotite in 0.01 M KClO4 solution from pH 3 to 11. Se sorption was observed to be strongly dependent on pH. Surface complexation modelling was performed by deriving a set of optimized parameters that can fit titration, sorption edge and sorption isotherm (at pH similar to 7.7) experimental data. A CASTEP code implemented into Materials Studio was used to calculate the site densities and site types on the biotite surfaces. Weak sorption sites with site densities of 3.2 sites/nm(2) and 1.4 sites/nm(2) were derived from the codes and used in the sorption model. A computer code that coupled PHREEQC with Python was developed for the fitting and optimizing processes. The model was validated by sorption data at pH similar to 9.5. The results show that the model can provide quantitative predicts of Se(IV) sorption in groundwater conditions of a deep geological repository and help improve the performance assessments by giving more convincing estimates of the release of radionuclides towards aquifers and biosphere.
  • Li, Xiaodong; Puhakka, Eini; Ikonen, Jussi; Söderlund, Mervi; Lindberg, Antero; Holgersson, Stellan; Martin, Andrew; Siitari-Kauppi, Marja (2018)
    The sorption behavior of Se(IV) on Grimsel granodiorite and its main minerals, plagioclase, K-feldspar, quartz and biotite, were investigated in Grimsel groundwater simulant in a large Se concentration range (from 1.66 x 10(-10) M to 1 x 10(-3) M). Experimental results show that the distribution coefficients (K-d values) of Se (IV) on the rock and mineral samples increased with the decreasing of Se(IV) concentration. The sorption of Se (IV) on biotite has the largest K-d value in low concentration area (<10(-7) M) stabilizing between 0.0595 +/- 0.0097 m(3)/Kg and 0.0713 +/- 0.0164 m(3)/Kg. The Kd value of Se(IV) on K-feldspar was the second largest (0.0154 +/- 0.0019 m(3)/Kg in 10(-9) M) while the sorption on quartz was negligible. The sorption behavior of Se(IV) on Grimsel granodiorite followed the same trend as plagioclase, the most abundant mineral in Grimsel granodiorite, with K-d values of 0.0078 +/- 0.0010 m(3)/Kg for Grimsel granodiorite and 0.0085 +/- 0.0016 m(3)/Kg for plagioclase, when Se(IV) concentration was 10(-9) M. HPLC-ICP-MS results show that all the Se(IV) remained in + IV oxidation state after more than 1 month experimental time and speciation modelling proved that the main species in Grimsel groundwater simulant were HSeO3- and SeO32-. Multi-site surface complexation modelling was performed by PHREEQC with the help of molecular modelling techniques which was performed with the CASTEP code implemented into Materials Studio. The modelling results predict that there are three kinds of sorption sites on the surface of biotite mineral, with sorption site densities differing in three magnitudes.