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Environmental fate & pathways

Hydrolysis

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In theory, both of the main elements in CaSi are hydrolysable at the standard pure elemental stage. Both Ca and Si are strong reducing agents and react with water (decompose water) with evolution of hydrogen gas (Cotton et al. 1999). Ca is oxidized to Ca 2+ and Si is oxidized to Si 2+/4+ states. The reactions produce alkaline aquatic solutions (e.g. for Ca).
Ca (s) + H2O -> CaO + H2 (g)
CaO + H2O -> Ca(OH)2
In the case of binary alloys, the reaction conditions and kinetics for alloys may be very different than those for pure elements. It is known that CaSi alloys do not react violently with water. Gas evolution of CaSi powder with water has been studied applying CaSi powder 0 – 500 μm. The rate of flammable gas development was 6.2 ml/kg h. (Method: Test N.5: Test method for substances which in contact with water emit flammable gases, UN Manual of Test and Criteria Part III – 33.4.1.4). The observed gas evolution rate means that less than 0.1% of CaSi reacted within 24 hours and therefore the reaction rate cannot be described vigorous or high.
In the OECD T/D test (KTH 2009) solutions very small quantities of elements were released from the particle mass in both pH 6 and 8 media. In total, only a very small portion (ca. 0.01 % at pH 6 and less than 0.007% at pH 8) of the loaded 100 mg/l amount of particles sized 1 mm of CaSi was dissolved upon the 24hour exposure in to the OECD T/D test media.
Cotton F.A., Murillo, C.A. and Bochmann, M.,1999. Advanced Inorganic Chemistry, 6th Edition; John Wiley and Sons, New York.

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