Mass Action Mass Balance c n CL H i c l C HL mCa 2 mCa L mCa2 mCa2 MCaCl mCaCl20 CaCL3 CaHCO3 CaCO30 CaF CaSO40 CaHSO4 CaOH Final equation to solve the problem sees the mass action for each complex substituted into the mass balance equation 2 n x Mineral dissolution precipitation To determine whether or not a water is saturated with an aluminosilicate such as K feldspar we could write a dissolution reaction such as KAlSi3O8 4H 4H2O K Al3 3H4SiO40 We could then determine the equilibrium constant aK a Al 3 a H3 4 SiO4 K aH4 from Gibbs free energies of formation The IAP could then be determined from a water analysis and the saturation index calculated INCONGRUENT DISSOLUTION Aluminosilicate minerals usually dissolve incongruently e g 2KAlSi3O8 2H 9H2O Al2Si2O5 OH 4 2K 4H4SiO40 As a result of these factors relations among solutions and aluminosilicate minerals are often depicted graphically on a type of mineral stability diagram called an activity diagram ACTIVITY DIAGRAMS THE K2O Al2O3 SiO2 H2O SYSTEM We will now calculate an activity diagram for the following phases gibbsite Al OH 3 kaolinite Al2Si2O5 OH 4 pyrophyllite Al2Si4O10 OH 2 muscovite KAl3Si3O10 OH 2 and K feldspar KAlSi3O8 The axes will be a K a H vs a H4SiO40 The diagram is divided up into fields where only one of the above phases is stable separated by straight line boundaries 6 Muscovite Quartz 7 Amorphous silica Activity diagram showing the stability relationships among some minerals in the system K2O Al2O3 SiO2 H2O at 25 C The dashed lines represent saturation with respect to quartz and amorphous silica log aK aH 5 K feldspar 4 3 Gibbsite Kaolinite 2 1 Pyrophyllite 0 6 5 4 3 log aH SiO 0 4 4 2 1 Seeing this what are the reactions these lines represent 2 0 Gibbsite 4 Al 6 Al OH 4 8 2 3 4 5 6 AlOH Al OH 2 10 Diagram Al T 25 C P 1 013 bars a H2 O 1 log a Al 2 25oC 7 pH 8 9 10 11 12 Greg Mon Nov 01 2004 Redox Geochemistry WHY Redox gradients drive life processes The transfer of electrons between oxidants and reactants is harnessed as the battery the source of metabolic energy for organisms Metal mobility redox state of metals and ligands that may complex them is the critical factor in the solubility of many metals Contaminant transport Ore deposit formation
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