Solvation (Hydration) The polar nature of the water molecule causes separation of ionic species. The number of water molecules surrounding an ion (hydration number ) depends on the ionic radius.
Water molecules may be considered to be a simple electrical dipoles Dielectric constant of water. Determined by creating an electrical field between two capacitor plates and measuring the voltage. The oriented dipoles create an internal field that opposes the external field. The dielectric constant is the ratio voltage in a vacuum over that in water. The Dieletric Constant of Water
24681012 -3 -4 -6 -7 -8 -9 -2 -5 pH mNaCl = 2 (12 Wt%) mNaCl = 0.2 (1 Wt%) mNaCl = 0.01 log m Zn total Zn-HS species Zn-Cl Zn 2+ 24681012 -3 -4 -5 -6 -7 -8 -9 pH mNaCl = 2 (12 Wt%) mNaCl = 0.2 (1 Wt%) mNaCl = 0.01 log m Zn total Zn-HS species Zn 2+ Zn-Cl Tagirov and Seward (2010) Relative Importance of Chloride and Bisulphide complexation
350 300 250 200 150 100 50 12345678910 Temperature ºC pH 10 ppm 100 ppm 1000 ppm 10000 ppm Solubillity of Sphalerite as a Function of Temperature and pH 2m NaCl 0.01 mΣS SVP (Based on data of Ruaya and Seward 1986; Tagirov and Seward, 2010) Soluble Insoluble
Gold solubility T = 250 o C P = 500 bar 1 m NaCl S = 0.001 m
REE Complexation REE forms very stable fluoride complexes, and less stable chloride complexes The LREE are much more mobile than the LREE Migdisov et al. (2009)
REE-fluoride solubility and REE Complexation Association of HF at low pH and low solubility of REE Precludes transport of REE as fluoride complexes. Williams-Jones et al. (2012).
References Williams-Jones, A.E., and Heinrich C.A., 2005, Vapor transport of metals and the formation of magmatic-hydrothermal ore deposits. Economic Geology 100: 1287-1312. Eugster, H.P., 1986, Minerals in hot water. American Mineralogist, v.71, 655- 673. Crerar, D., Wood, S.M., Brantley, S., and Bocarsly, A., 1985, Chemical controls on solubility of ore-forming minerals in hydrothermal solutions. Canadian Mineralogist, v. 23, p. 333-352 Seward, T.M., and Barnes, H.L., 1997, Metal transport by hydrothermal fluids in Geochemistry of Hydrothermal Ore Deposits H.L. Barnes (ed), p. 235-285. John Wiley and Sons Inc. Williams-Jones, A.E., \midisov, A.A. and Samson, I,M, 2012. The hydrothermal mobility of the rare earth elements – a tale of “ceria” and “yttria”. Elements, 8, in press.