1. HYDROTHERMAL METAL SOLUBILITY AND SPECIATION

2. THE WATER MOLECULE
Oxygen
Hydrogen
Electrons from hydrogen
Water is a polar molecule, which explains why it is such an excellent solvent, It can form positively directed shells around anions and negatively directed shells around cations.

3. SIMPLE SOLVATION
Simple ion solvation (hydration)

4. SOLVATION AND THE HYDROGEN BOND+ -
H-bond-
Ice crystals
Hydrogen bonds impart structure to water and ice.

5. THE DIELECTRIC CONSTANT
A measure of the capacity of a solvent to solvate ions - high values equal high solvation capacity. + -
External field (capacitor)
Internal field (dipoles)
Charged, oriented dipoles
Uncharged, disoriented dipoles δ+ δ-
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 of the voltage required to align the dipoles in a vacuum over that in water.

6. DIELECTRIC CONSTANT () OF WATER
The dielectric constant of water decreases with increasing temperature and decreasing pressure, leading to a corresponding decrease in its power to solvate ions
200
400
600 50 30 70 90 20 10 5 4 2
L+V Cp
Kbar
T OC
Eugster (1986)

7. Complex molecule solvation (hydration)
COMPLEXATION
As the dielectric constant of water decreases, the water molecule shells around metal ions and anions break down facilitating the formation of complex molecules involving these species, e.g., CuCl42-. These complexes will be surrounded by weaker solvation (hydration) shells. O H H H H O O
Complex molecule solvation (hydration) H 2- H H O H H H H H O O

8. Pearson’s HSAB Principles and Aqueous Metal Complexes
Hard acids (large Z/r) bond with hard bases (ionic bonding) and soft acids (small Z/r) with soft bases (covalent bonding).
Hard
Borderline
Soft
Acids
H+, Na+>K+
Al3+>Ga3+
Y3+,REE3+ (Lu>La)
Mo+6, W+6, U+6
Zr4+,Nb5+
Fe2+,Mn2+,Cu2+
Zn2+>Pb2+,Sn2+,
As3+>Sb3+=Bi3+
Au+>Ag+>Cu+
Hg2+>Cd2+
Pt2+>Pd2+
Bases
F-,OH-,CO32- >HCO3-
SO42- >HSO4-
PO43-
Cl-
HS->H2S
CN-,I->Br-
Pearson (1963)