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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Kdsoil (aluminium): 3700 L/kg

Key value for chemical safety assessment

Other adsorption coefficients

Type:
other: soil Kd
Value in L/kg:
3 700

Additional information

Aluminium dihydrogen triphosphate (CAS 13939-25-8) is an inorganic phosphate compound. The substance can be transformed by hydrolysis forming aluminium species and soluble orthophosphate (PO43-) in sewerage systems, sewage treatment plants and in the environment. The mobility of aluminium species is very complex and difficult to predict. The formation of speciation of aluminium and adsorption and desorption of aluminium on suspended particles can be affected by a number of geochemical factors. The relative mobility of aluminium species depends upon on many factors, especially pH, alkalinity, temperature, dissolved organic carbon, dissolved inorganic carbon and anion concentration. At low pH, (less than 5.5), aluminium is predominantly present as Al3+ species, which is highly mobile. As pH increases above 5.5, aluminium-hydroxide complexes and organically complexed aluminium are formed by hydrolysis and combined with organic matters. Above pH 7, anionic aluminium hydroxide predominates. Kaplan (2005) published several Kd values based on measured Al concentration in groundwater and sediment and suggested Al Kd values for soil, grout, gravel, clay to be 3700 mL/g and 5000 mL/g for concrete, respectively. Furthermore, colloidal aluminium species play also an important role in the adsorption of other trace metals and anions in soils and sediments.

Phosphorus retention in soils is influenced by the form of P released. Triphosphate is a condensed phosphorus species with three phosphate units. Busman studied the adsorption of polyphosphate by soils and clay minerals and indicated that affinity of polyphosphate increased with increasing length of phosphate units, and adsorption of triphosphate was more strongly adsorbed than orthophosphate, whereas mobility and solubility of triphosphate increased by hydrolysis in soils to orthophosphate (Busman 1984). 

Reference

Kaplan D.I. (2005) Recommended Distribution Coefficients, Kd Values, for Special Analysis Risk Calculations Related to Waste Disposal and Tank Closure on the Savannah River Site (U), Westinghouse Savannah River Company Savannah River Site,

Busman, L.M. (1984) Behavior of polyphosphates in soils . Retrospective Theses and Dissertations. Paper 8979.