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Environmental fate & pathways

Hydrolysis

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Si/FeSi silicate may be regarded as slowly dissolving/hydrolysing material in alkaline, neutral and acidic solutions. Solubility is higher in acidic solutions. Half life for hydrolysis has not been determined. The screening solubility investigation at 100 mg/l load revealed calcium (> 2100 µg/L), silicon and aluminium  (> 1300 µg/L) to be the main elements released  from Si/FeSi silicate at acidic conditions, at significantly higher concentrations than observed for the near neutral pH conditions 
(Si ≈ 160 µg/L, Ca ≈ 60 µg/L, Al ≈ 26 µg/L). These findings are contradictory to the general dissolution behaviour of silicon typically higher at pH neutral conditions compared to acidic conditions. The release of elements such as calcium and aluminium at acidic conditions are believed to enhance the dissolution properties of silicon‐rich phases. Other elements released at significantly lower concentrations were magnesium, sulphur, nickel, copper, iron, barium, manganese, strontium, cadmium, titanium, yttrium and beryllium.
At acidic conditions (pH 1.7), approximately 5.3% of the amount of particles loaded were released/dissolved. Corresponding values were significantly lower (0.3%) at near pH-neutral conditions of PBS (pH 7.2).

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