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EC number: 231-130-8
CAS number: 7440-21-3
After oxygen, silicon is next abundant in the earth’s crust in the
form of silicate minerals. Silicon is not known to be present naturally
in the environment in its reduced elemental form. If released in the
environment as its elemental metallic form Si (0), it is oxidized by
atmospheric oxygen or hydrolysed to Si (IV) silica species (SiO2,
in aq. solution Si(OH)4). The rate of these transformations
to oxidized forms is highly dependent on particle size/surface area of
released silicon particles and environmental conditions.
Oxidized silicon as Si(IV) in fresh water or seawater can occur in
both suspended and dissolved forms and is partitioned over a number of
chemical species. In dilute solutions (< 100 mg/L) silicon is as
dissolved Si(OH)4, and in more concentrated solutions as
dimerized, trimerized, colloidal or in the form of aggregated colloids
of different physical size or entirely as insoluble solid particulate
Silicon is practically non volatile in the environment. Amorphous
silica in its solid particulate form is completely non volatile and
immobile substance. Dissolved silica is also non volatile and partitions
mainly in aquatic and soil compartments.
Adsorption of dissolved silica to soil and sediments is not strong
and it is relatively mobile in soil. Adsorption takes place primarily to
inorganic materials and in lesser extent to organic material. A dynamic
adsorption/desorption equilibrium between soil/sediment particles and
water keeps the surface water aquatic concentrations of dissolved silica
relatively constant (ca. 2-15 mg/l). Higher concentrations can be found
in ground waters. Very strong binding of silica to soil materials may
takes place if dissolved silica species form precipitates with other
elements like Al and Mg and forms several types of clay minerals with
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