Registration Dossier

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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

Si/FeSi silicate is an odourless, solid substance in form of lumps, granules, fines and dust. The colour varies from white to dark grey. Si/FeSi “sculls” and “slags" are formed in the production of ferrosilicon and silicon. No specification exists as such for these products as they are mixes of silicon/ferrosilicon, various silicates, oxides, etc. normally in undefined ratios. The surface of ferrosilicon slag is covered with silicon, calcium, aluminium and magnesium rich oxide phases.


Surface and phase characterisations show silica, oxidized calcium (possibly CaO), magnesium and aluminium to be main surface components of FeSislag for both particle sizes. No iron was detected on the surface. No detectable amounts of quartz or fibres have been observed in X-ray diffraction and scanning electron microscope analyses.

The solubility of Si/FeSi slag in water is very low. Main elements released from Si/FeSi slag in different fluids are silicon, aluminium and calcium. The release is significantly higher in acidic fluids than observed at neutral conditions. The release of other elements present in Si/FeSi slag is usually low.