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Environmental fate & pathways

Adsorption / desorption

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Description of key information

In case of environmental release of LiPF6, the speed of its reaction with water and the subsequent dissociation of the soluble hydrolysis products will be such that only the adsorptive behaviour of the resultant ions has relevance for environmental mobility. 
Fluoride may be strongly adsorbed in acid soils and clays. Lithium may be adsorbed onto certain clays, but is generally expected to show limited adsorption to most soils and to river sediments.
Inorganic phosphate is expected to be fairly mobile in soils.

Key value for chemical safety assessment

Additional information

HF

In the soil compartment, HF itself is not expected to be present: any fluoride introduced via unexpected release of LiPF6 will principally be present in the form of fluoride ion. For this reason, separate assessment of HF mobility is not meaningful or necessary.

 

Fluoride

A soil column of ferruginous lateritic clay was efficient at removing fluoride from aqueous solution: 10 mg F-/l reduced to 0.019 mg/l after 120 minutes: Chidambaram, Ramanathan and Vasudevan, 2003). Wang et al (2002) reported that clay and acid soils can strongly adsorb dissolved fluoride, leading to local accumulation of fluoride in soil; however in alkaline and quartz-sandy soils fluoride is not so well retained and leaches more into groundwater. A more extensive review of fluoride mobility in soil (WHO EHC 227, 2002) notes that the principal determinants of fluoride mobility in soil are pH and availability of aluminium and calcium for complex formation and cites extreme immobility of fluoride in loamy soil in lysimeter experiments. However the introduction of fluoride into the soil compartment through weathering of minerals means that fluoride is often found in groundwater: partitioning of fluoride entering the soil via pollution between soil solids and ground/pore water will depend on the local background concentration in groundwater as well as other soil characteristics.

 

Lithium

Lithium is selectively adsorbed in preference to other cations by certain clays, the extent of its retention in secondary clays is related to the local presence of magnesium (Li+ substituting for Mg2+); however it appears to be only poorly adsorbed onto river sediments (Aral and Vecchio-Sadus, 2008). Lithium also adsorbs slightly to humic soils, but in general lithium compounds are not expected to adsorb strongly to soils or sediments (Webwiser – US NLM, 2012).

 

Phosphate

Concerns arising from phosphate in runoff form agricultural lands indicate high soil mobility in some cases, and addition of inorganic phosphates have been shown to raise water-soluble phosphorus levels. Soil organic content affects phosphorus/phosphate mobility (Tarkalson and Leytem, 2009).