Triiron bis(orthophosphate)

Endpoint summary

Additional information

Triiron bis(orthophosphate) (CAS 14940-41-1) is an inorganic phosphate substance. Biotic degradation is therefore not relevant for the substance. Furthermore abiotic degradation processes like photolysis in air, water and soil are not likely. In water, soil and biological systems, dissolved Triiron bis(orthophosphate) dissociates to orthophosphate and ferrous ion (Fe2+).

“Redox transformation of iron, as well as dissolution and precipitation and thus mobilization and redistribution, are caused by chemical and to a significant extent by microbial processes (see attachment Fig. 1) (Kappler A. and Straub K. L. 2005).”

Transformations of iron by microorganisms are often much faster than the respective chemical reactions. They occur in most soils and sediments, both in freshwater and marine environments (Thamdrup 2000; Straub et al. 2001; Cornell and Schwertmann 2003).

The iron transport and distribution depend on pH, Eh (redox) and the presence or absence of other dissolved constituents which form with FE(II) or FE(III) dissolved complexes, colloids or poorly soluble mineral phases (Boyd and Ellwood 2010; Konhauser et al. 2011a; Radic et al. 2011; Raiswell 2011). With increasing Eh and pH the amount if iron dissolved in groundwaters, rivers and seawater decreases (see attachment Fig. 2) (Kendall 2012).

Ferric iron (Fe3+) is the stable form in oxygenated waters, which forms at neutral pH highly insoluble oxides and hydroxides (Wang 1998; Simpson 2002; Zhang 1999). In anoxic waters ferrous iron (Fe2+) is stable. As dissolved ion it occurs usually in many freshwater systems. Insoluble salts will be formed in the presences of high carbonate, sulphide and orthophosphate levels (Stumm, W. and Morgan, J. J. 1981).

Orthophosphate is available for biological metabolism without further breakdown. Besides of chemical precipitation phosphate can be biologically removed from waste water. Biological phosphate removal process is relies upon microorganisms to uptake phosphate into their cells either via anaerobic or anaerobic pathways, which is subsequently removed from the STP process as a result of sludge wasting.

 

References:

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