Ferrosilicon - reaction mass of iron and iron disilicide and iron silicide and silicon

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Additional information

The vapour pressure of different FeSi grades are extremely low and the alloy and constituents are in practice in-volatile (at NTP). Solubility and hydrolysis rate of FeSI in water is low.Dissolved metal/metalloid fraction of each (smelted) grade was less than 1 % which means in all cases < 1 mg/l dissolved at initial 100 mg/l load. The dissolved metals were primarilySi, Fe, Ba, Mg, Sr, Cu, Zn. The solubility and solubility rate to saline and alkaline water seems to be slightly increased, but the solubility may still be regarded low since the grades of FeSi clearly have a character of an alloy.FeSi is not biodegradable. Phototransformations are not regarded as important environmental fate processes of FeSi alloys.

Particulate FeSi is immobile in soil and sediments. Environmental fate of different grades of FeSi is for relevant parts connected to fate of its dissolution and transformation products. Dissolution, dissociation and speciation of dissociation products of FeSi is influenced by concentration of especially Si(OH)₄and Fe(II/III)-complexes and depending on grades, concentrations of other dissolved metal ions. All transformation products have different physical-chemical properties and their ecotoxicity is different.

Si and Fe are typically immobilized for clay mineral synthesis, whereas other metals/metalloids will be adsorbed by soil colloids and minerals by non specific or by more specific mechanisms (Tan 1998). Sorption of dissolved silica in soil/sediments is known to be controlled remarkably by solid phase constituents like clay minerals and oxides and in the lesser extent by solid organic matter.

In soil, noncrystalline aluminosilicates (allophones), oxides, and hydroxides of Fe, Al, and Mn, and even the edges of layer silicate clays to a lesser extent, provide surface sites for the chemisorption of transition and heavy metals. All these minerals present a similar type of adsorptive sites to the soil solution: a valency unsatisfied OH^-or H₂O ligand bound to a metal ion (usually Fe 3+ , Al 3+ , or Mn 3+ 4+ ) (McBride 1994).

FeSi grades and constituents are all inorganic elements. Testing of these alloys for bioaccumulation is not seen relevant. Information of bioaccumulation potential of constituents is available, even if some of the datasets may still be quite limited.

The major FeSi constituents are not known to bioaccumulate at harmful levels in species living in aquatic, sediment or soil. Certain species may actively concentrate Si and Fe in their body and both elements are essential elements or beneficial nutrients. Some species may still be naturally sensitive to harmful effects caused by too high or too low background levels of certain elements (e.g. silicon or iron). These issues may be documented in the CSA report but these findings need not to be considered further under FeSi alloy registration.

McBride, M. B. (1994), Environmental chemistry of soils, ISBN 0-19-507011-9, Oxford University Press.

Tan, K.H., (1998) Principles of soil chemistry, third edition, NY, 1998, ISBN 0-8247-0147-X