Registration Dossier
Registration Dossier
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EC number: 273-761-1 | CAS number: 69012-64-2 Amorphous silicon dioxide particles from the volatilization and vaporization of furnace feed materials in the manufacture of ferrosilicon and silicon.
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Silica fume is a solid inorganic amorphous substance which may undergo transformation processes in the environment.The vapour pressure of silica fume is extremely low and the alloy and constituents are in practice in-volatile (at NTP).Abiotic (non-biological) degradation of particulate silica fume typically occur by physico-chemical processes and primarily by hydrolysis.
The surface of amorphous silicon dioxide is known to be covered with silanol (–Si–OH) and siloxane (–Si–O–Si–) groups (Iler, 1979). Silanol groups are proton donors and undergo acid-specific reactions. Hydrophilicity of the silanol groups makes the surface wettable. The stable form of dissolved silica in the environment is mono silicic acid Si(OH)4.Thedissociation constants of silicic acid are pKa1 9.9, pKa211.8, pKa3,4 12 & 12 at 30 °C and therefore it is present in the typical environmental conditions and dilute solutions as a non ionizedmolecule.The solubility and hydrolysis rate of sIlica in water is relatively low. Maximum reported equilibrium concentration of amorphous silica is ca. 100-300 mg/l. The solubility increases as temperature or pH increase.
Particulate silica is immobile in soil and sediments. Dissolved silica is relatively mobile in soil.Sorption of dissolved silica in soil is controlled primarily by solid phase constituents like clay minerals and oxides and in the lesser extent by solid organic matter.
Silica is not biodegradable. Silica and dissolved Si(OH)4are generally known to have no or very low potential for bioconcentration and bioaccumulation.
Iler RK (1979) The Chemistry Of Silica - Solubility, Polymerization, Colloid And Surface Properties And Biochemistry, Wiley-Interscience Publishers: New York, NY
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