Abstract
AbstractThe incorporation of pertechnetate (TcO4–) into feldspathoids produced by alkaline alteration of aluminosilicate clays may offer a potential treatment route for 99Tc-containing groundwater and liquors. Kaolinite was aged in NaOH to determine the effect of base concentration, temperature, and solution composition on mineral transformation and pertechnetate uptake. In all reactions, increased temperature and NaOH concentration increased the rate of kaolinite transformation to feldspathoid phases. In reactions containing only NaOH, sodalite was the dominant alteration product; however, small amounts (6–15%) of cancrinite also formed. In experiments containing NaOH/Cl and NaOH/NO3 mixtures, sodalite and nitrate cancrinite were crystallized (at 70°C), with no reaction intermediates. The addition of SO42– crystallized sulfatic sodalite at 40 and 50°C, but at higher temperatures (60 and 70°C) sulfatic sodalite transforms to vishnevite (sulfatic cancrinite). In experiments where a pertechnetate tracer was added (at ∼1.5 μmol l–1), only 3–5% of the 99Tc was incorporated into the feldspathoid phases. This suggests that the larger pertechnetate anion was unable to compete as favourably for the internal vacancies with the smaller OH–, NO3–, SO42– or Cl– anions in solution, making this method likely to be unsuitable for groundwater treatment.
Highlights
THERE is a global legacy of contaminated land around nuclear facilities, arising from leaking storage ponds and containers (Mon et al, 2005; Perdrial et al, 2011; Wang and Um, 2012)
Preliminary investigation of alkaline alteration of kaolinite in NaOH solutions There was no evidence of new phases in the X-ray diffraction (XRD) patterns where kaolinite was aged in 0.05 M and 0.5 M NaOH at room temperature for 35 days
A partial phase transformation to sodalite, occurred when kaolinite was aged in 5 M NaOH; kaolinite peaks were still dominant at day 35
Summary
THERE is a global legacy of contaminated land around nuclear facilities, arising from leaking storage ponds and containers (Mon et al, 2005; Perdrial et al, 2011; Wang and Um, 2012). At the Sellafield nuclear facility, UK, ∼20 million m3. Kaolinite (Al2Si2O5(OH), (Grim, 1968) is commonly found in sediments and soils around nuclear sites (Huertas et al, 1999), and has a simple. 1:1 sheet silicate structure (Bauer et al, 1998). Kaolinite dissolves, releasing Al3+ and Si4+ into solution, leading to the formation of secondary feldspathoid and zeolite phases (Mashal et al, 2004; Qafoku et al, 2003; Zhao et al, 2004; Wallace et al, 2013). The exact phase precipitated depends on the solution composition, base concentration, Si:Al ratio and temperature (Deng et al, 2006b). Important features of the internal structure of these neo-formed minerals, such as cancrinite ([(Ca,Na)6(CO3)1–1.7][Na2(H20)2][Si6Al6O24])
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