The
JEB Tailings Management Facility (TMF) is central to reducing
the environmental impact of the uranium ore processing operation located
at the McClean Lake facility and operated by AREVA Resources Canada
(AREVA). The geochemical controls of this facility are largely designed
around the idea that elements of concern, such as Mo, will be controlled
in the very long term through equilibrium with supporting minerals.
However, these systems are far from equilibrium when the tailings
are first placed in the TMF, and it can take years, decades, or centuries
to reach equilibrium. Therefore, it is necessary to understand how
these reactions evolve toward an equilibrium state to understand the
very long-term behavior of the TMF and to ensure that the elements
of concern will be adequately contained. To this end, the Mo speciation
in a series of samples taken from the JEB TMF during the 2008 sampling
campaign has been analyzed. This analysis was performed using powder
X-ray diffraction (XRD), X-ray fluorescence mapping (μ-XRF),
and X-ray absorption near-edge spectroscopy (XANES). These results
show that only XANES was effective in speciating Mo in the tailings
samples, because it was both element-specific and sensitive enough
to detect the low concentrations of Mo present. These results show
that the predominant Mo-bearing phases present in the TMF are powellite,
ferrimolybdite, and molybdate adsorbed on ferrihydrite.
Two precambrian greywackes GW1A and GW1C with different structures were investigated to describe their reaction behaviour in concrete. A portlandcement CEM I, 32,5 with a high alkali content (Na2O-eq. = 1,4 %) was used. The soluble constituents of the greywackes in the alkaline pore solution of the concrete were determined by using a special method of chemical concrete analysis. The concrete samples were storaged in a special fog chamber at 40 °C and 100 % rel. humidity until to 9 month. The following conclusions can be given:
1 The concrete samples which were made with greywacke GWIA show a damage value of about 4 to 5 by means of rifts observed. Analogeous to the damage it can be found that the concentration of the soluble constituents which were release from greywacke begins at zero and increases continual}· until the end of the investigation. A specific discussion of several soluble oxides shows enormous differences between the reactivity of certain constituents investigated.
2 The concrete samples which were manufactured with greywacke GWIC show a damage value of about 1...2 only. But the quantity of the soluble constituents which come from the greywacke is higher. Characteristically here is a shoot up of the soluble constituents after beginning of the cement hydration process. After this the content of the soluble constituents decreases again. This behaviour in chemical reactivity of greywacke investigated can be declared by different structures. The mainly differences between both the GWIA and the GWIC were the size of the greywacke constituents. The chemical reactivity which was determined immediately after the alkali attack of the pore solution of the hardened cement and the macroscopical reactivity observed by means of rifts after 9 month are not the same.
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