537 posts
re FeO problem
Hello Raj,
Yes, as you say, white cement production is different and white cement kilns are often operated under reducing conditions to improve the clinker and cement lightness. However, there is so little iron present in the white cement clinker that the effect of such a small amount of FeO on C3S decomposition is negligible.
Raw materials which contain FeO, such as steel slag or mill scale etc. should also not cause problems with regard to C3S decomposition because, as long as the kiln is operated under sufficiently oxidising conditions, FeO will be oxidised to Fe2O3 well before the formation of C3S in the burning zone.
In fact, a small amount of FeO in the raw materials may actually be helpful to the calcination process since FeO is known to accelerate the dissociation of CaCO3 into CaO and CO2. (Ref: http://nopr.niscair.res.in/bitstream/123456789/10069/1/IJEMS%2017(4)%20282-288.pdf)
Regards,
Ted.
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537 posts
re FeO problem
Hello Michael,
Actually, the formation of the ferrites (CF, C2F and C4AF) consumes free CaO. If they were prevented from forming in the clinker, this would increase the availability of CaO which would push the chemical equilibrium towards the formation of more C3S and proportionately less C2S.. (and of course more C3A.)
Regards,
Ted.
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