1 / 6

Speciation

Speciation. Any element exists in a solution, solid, or gas as 1 to n ions, molecules, or solids Example: Ca 2+ can exist in solution as: Ca ++ CaCl + CaNO 3 + Ca(H 3 SiO 4 ) 2 CaF + CaOH +

neila
Download Presentation

Speciation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Speciation • Any element exists in a solution, solid, or gas as 1 to n ions, molecules, or solids • Example: Ca2+ can exist in solution as: Ca++ CaCl+ CaNO3+ Ca(H3SiO4)2 CaF+ CaOH+ Ca(O-phth) CaH2SiO4 CaPO4- CaB(OH)4+ CaH3SiO4+ CaSO4 CaCH3COO+ CaHCO3+ CaHPO40 CaCO30 • Plus more species  gases and minerals!!

  2. How do we know about all those species?? • Based on complexation  how any ion interacts with another ion to form a molecule, or complex (many of these are still in solution) • Yet we do not measure how much CaNO3+, CaF+, or CaPO4- there is in a particular water sample • We measure Ca2+  But is that Ca2+ really how the Ca exists in a water??

  3. Aqueous Complexes • Why do we care?? • Complexation of an ion also occurring in a mineral increases solubility • Some elements occur as complexes more commonly than as free ions • Adsorption of elements greatly determined by the complex it resides in • Toxicity/ bioavailability of elements depends on the complexation

  4. Defining Complexes • Use equilibrium expressions: • cC + lHL  CL + lH+ • Where B is just like Keq!

  5. Mass Action & Mass Balance • 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

  6. 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: • from Gibbs free energies of formation. The IAP could then be determined from a water analysis, and the saturation index calculated.

More Related