pH = 11 - SKB

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PDF rendering: DokumentID 1415884, Version 1.0, Status Godkänt, Sekretessklass Öppen2. ObjectivesThe objectives of this work are twofold:to address the effect of phosphates on the radionuclide solubility limitscalculated with the Simple Functions Spreadsheet tool, andto study the effect of temperature over the following radionuclides: Ra, Se, Ni,Sm, Ho, Am, Cm, Pu, U, and NpTo this aim, a literature review on the phosphate chemistry (i.e. hydrolysis reactions,major elements complexation and radionuclide phosphate complexes stability) basedon the open literature data and on the specific data generated in tailored national andinternational programs has been conducted.In a second stage, the solubility limits of the selected radionuclides at temperaturesdifferent than 25ºC have been calculated by means of the simplified Van’t Hoffequation.3
PDF rendering: DokumentID 1415884, Version 1.0, Status Godkänt, Sekretessklass Öppen3. MethodologyThe work within this project has been divided in two different and independent tasks:Task 1 – Phosphates chemistry and its role on radionuclides solubility limitsTask 2 – Temperature influence on radionuclide solubility limitsFor the first task, a three-step approach has been followed (Figure 3-1):1) The range of phosphate concentrations in groundwaters of interest to <strong>SKB</strong>(Grivé et al., 2010a) have been investigated and discussed,2) A literature research has been conducted with emphasis on the affinity ofphosphate towards the radionuclides of interest and by considering its majorelements chemistry (hydrolysis, Ca, and Fe interactions),3) An assessment on the relevance of the complexation on the groundwaterconditions obtained in 1) has been performed in order to select a finalthermodynamic data set.12Phosphates concentrations ingroundwatersLiterature data research3AssessmentFinal Thermodynamicdata selectionFigure 3-1. Sketch showing the methodology followed in this work.Task 2 methodology consisted of:1) The selection of the most appropriate approach for doing temperaturecorrections,2) The selection of enthalpy values from <strong>SKB</strong> database (Grivé et al., 2008; Duroet al., 2006a),4
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