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EC number: 231-143-9
CAS number: 7440-33-7
The average temperature among all seven- and 28-day tests varied in the
range 21.0-21.6 °C, with 19.9 °C as the single value below 20.0 °C,
which was not expected to affect the reaction kinetics. With the maximum
temperature of 22.0 °C, essentially all temperatures fell within the
20-23 °C proposed for the T/DP. The average D.O. readings met or
exceeded the >70% saturation criterion.
All target 8.5 pH levels in the W-series for the test substance lay in
the range 8.3-8.7, which is the variability proposed from the T/DP.
Similarly, all but 21 of the 480 target 6 pHs were less than the
proposed upper limit of 6.25, and it was not expected that these
variations would have had a significant effect on the T/D kinetics of
the tested substances. The pH levels less than the lower limit of 5.85,
since the variability appears to have been random, are not expected to
have affected the substances’ reaction kinetics.
In the studies designed to examine the effects of other metals on
tungsten (W) dissolution, after 46 days of contact, the W/Ni, W/Co and
munitions grade W reactors contained visible amounts of what appeared to
be undissolved metal powders, while insoluble products and precipitates
were observed in the W/Cu (greenish yellow) and W/Fe (reddish brown)
reactors. The variations in dissolved tungsten concentration over time
for the different powder mixtures are presented in two time periods: 0-7
days and 7-46 days. The trend of dissolved tungsten concentration during
the first week, shown in Figure 3 (attached), suggests that two distinct
kinetic phases occur for all the systems. The systems all start off with
different rates of dissolution for the first day, although W/Ni and W
ammunition grade systems had almost identical slopes. A reduction in the
slopes for all the systems then occurs after the first day and they all
display a constant linear dissolution trend till the seventh day. The
slopes of the two distinct phases for each system are presented in Table
Table 1. Slopes of dissolution
curves in the first week.
In the second period, Day 7 to Day 46 (see attached Figure 4), the
tungsten concentrations in the W/Co, W/Ni, and W munitions-grade systems
continued to increase slowly but almost linearly throughout the
experiment. However, for W/Fe and W/Cu, the dissolved tungsten
concentration reached a maximum value and then decreased. The highest
concentration was measured after 14 days for W/Cu and after 28 days for
The cause of the decrease in tungsten concentration for the W/Fe system
is suspected to be either the precipitation of insoluble tungsten–iron
compounds or the adsorption of tungsten by amorphous iron precipitates
or a combination of both. Attempts to qualitatively identify the
precipitates using X-ray diffraction were unsuccessful. For the W/Cu
system, the formation and precipitation of insoluble WO3.H2O and
WO3.2H2O (confirmed by X-ray diffraction) at low pH, is responsible for
the reduction in the concentration of tungsten in solution.
The most appropriate way to quantify tungsten metal solubility is
through the Transformation Dissolution data. At a loading of 100 mg/L at
a pH of 8.5, 16.51 mg W ion/L were determined by the
transformation/dissolution study. These values will be passed forward to
the risk assessment.
Dissolution of tungsten metal in distilled water is accompanied by the
formation of a non-protective oxide film (Lassner and Schubert, 1999).
Tungsten metal dissolution was found to take several days to equilibrate
(Dermatas et al, 2004), with dissolution slowing after the first 6
hours. The dissolution of tungsten in the presence of dissolved oxygen
was observed to be one order of magnitude larger than the dissolution
rate in the absence of dissolved oxygen (Ogundipe et al, 2009).
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