Other
Scientific paper
Feb 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53..303w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 2, pp.303-312
Other
6
Scientific paper
The solubility of crystalline WO 3 was measured in pure water and solutions of HCl (0.5-5 molal), NaOH (0.01-1 molal), NaCl (1-6 molal) and KCl (1 molal) at 500°C and approximately 1 kbar in order to determine the speciation of tungsten in hydrothermal solutions in the presence of Cl - , Na + and K + . The average solubility of WO 3 in pure water was measured to be 515 ppm W under the above conditions. No significant increase in solubility was observed in the presence of up to 5 molal HCl implying that Cl - complexing of W is not important in natural solutions. A log K value for the reaction WO 3 (s) + H 2 O(l) = H 2 WO 4 (aq) of -2.55 ± 0.2 was derived. WO 3 solubility was considerably increased by the addition of NaCl and even more so by the addition of NaOH. The dependence of W concentration on NaCl and NaOH concentrations, together with quench pH measurements, suggest the importance of a cation-tungstate ion pair such as NaHWO 4 0 , but the possibility of a polymeric tungsten species cannot be excluded. A value of log K = 1.0 ± 0.1 was derived for the reaction WO 3 (s) + NaOH 0 (aq) = NaHWO 4 0 (aq) and a value of log K = -4.22 ± 0.09 was derived for the reaction WO 3 (s) + NaCl 0 (aq) + H 2 O(1) = NaHWO 4 0 (aq) + HCl 0 (aq). The solubility of assemblages containing WO 2 was also investigated. These solubilities were higher than those measured for WO 3 alone. This combined with the intense blue color of the solutions indicates the presence of a significant amount of a reduced (W(V) species.
Vlassopoulos Dimitrios
Wood Scott A.
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