pH = 11 - SKB

PDF rendering: DokumentID 1415884, Version 1.0, Status Godkänt, Sekretessklass Öppen4.2.3 IronSeveral authors reported the formation of a variety of species for the iron-phosphatesystem (Wilhelmy et al., 1985). However, few of these studies reported reliablethermodynamic data for the iron-phosphate species.The CHEMVAL database (Falck et al., 1996) summarized thermodynamic data for fourdifferent Fe-P aqueous species (Table 4-5).Table 4-5. Thermodynamic data for Fe-P aqueous species in CHEMVAL database.Species Reaction Log Kº eqFeHPO 4 (aq) H 2 PO 4 - + Fe 2+ ↔ FeHPO 4 (aq) + H + -3.56FeH 2 PO 4+H 2 PO 4 - + Fe 2+ ↔ FeH 2 PO 4+2.64FeHPO 4+FeH 2 PO 42+H 2 PO 4 - + Fe 2+ ↔ FeHPO 4 + + 1e - + H + -10.26H 2 PO 4 - + Fe 2+ ↔ FeH 2 PO 4 2+ + 1e -8.76Figure 4-6 shows the predominance diagrams obtained for the Fe-P system by usingTable 4-5 thermodynamic data. As can be seen, FeHPO +4 would be the onlyphosphate species that could be relevant under oxidising conditions (Eh>0.5V) and pHconditions (pH