7.2 Reactions involving Phosphorus Minerals
Four reactions involving phosphorus minerals are relevant to the fate of phosphorus in septic system plumes, including precipitation of hydroxyapatite, variscite, strengite and vivianite. These reactions are as follows:
- hydroxyapatite precipitation as shown in Equation 22;
|
5Ca2+ + 3HPO42– + H2O → Ca5 (PO4)3OH + 4H+ |
(22) |
- variscite precipitation as shown in Equation 23;
|
Al3+ + PO43– + 2H2O → AlPO4·2H2O |
(23) |
- strengite precipitation as shown in Equation 24;
|
Fe3+ + PO43– + 2H2O → FePO4·2H2O |
(24) |
- and, vivianite precipitation as shown in Equation 25;
|
3Fe2+ + 2PO43– + 8H2O → Fe3 (PO4)2·8H2O |
(25) |
There is a greater assimilation capacity for phosphorus in the unsaturated zone below a septic system at locations where conditions promote the precipitation reactions presented in Equations 22 through 24.
