2 posts
2 posts
Re: CaF2 decreasing CaCO3 decarbonation temperature?
Dear all,
I am not a chemist- but as far as i understood - and we have seen that in some cases, the use of Flouride lowers the flam,e temperature. Fluoride-containing additives have a major influence on the liquid phase in a kiln, and act as a mineralizer to accelerate the formation of C3S below the normal stability temperature. Fluorides also act as a fluxing agent and cause the liquid phase to appear at a lower temperature. Since liquid formation is essential in the formation of alite, fluorides allow the appearance of alite in clinker a lower temperature. Regardless of the appearance of the liquid phase, the activation temperature must be sufficient to form alite. Studies indicate that fluoride acts as a mineralizer and that alite can be formed at temperatures, in practice, in the range of ~1100 o C (2012 o F), instead of the normal lower stability limit of 1250 o C (2282 o F) when fluoride-additives are added to the kiln. This, we have seen when adding Spent Cell Liners from the Aluminum smelting Industry in Kilns.May somebody can explain the exact reaction? One Kion has reported a 10% lower energy(fuel)consumption at the kilnburner with te use of SCL. Thanks , Dirk
537 posts
Re: CaF2 decreasing CaCO3 decarbonation temperature?
Hello Dirk,
Yes, you are quite correct. The beneficial effects of fluoride on the clinkerisation process have been widely studied. Fluoride acts as both a fluxing agent and as a mineralizer. The difference being that a flux reduces the temperature at which a melt forms, while a mineralizer is a substance which accelerates the rate of reactions within the burning zone without necessarily changing the melt temperature.
Fluoride acts as a fluxing agent by way of a CaO-SiO2-CaF2 low temperature eutectic which melts at temperatures around 1100 degC, as opposed to the alkali, sulphur and magnesium doped CaO-Al2O3-SiO2-Fe2O3 eutectic which melts at ~1250 degC.
As you mentioned, fluoride also acts as a mineralizer by accelerating the formation of C3S at temperatures well under its normal lower stability range. This is thought to be due to the doping of the C3S crystalline structure with fluorine ions. Fluorine substitutes for O-2 and in the process the symmetry of the C3S crystalline lattice is increased.
Over the past 10 years or so I have had a lot of experience with burning SCL and, as you rightly pointed out, the positive effect on clinkerization is remarkable. You just have to watch now much you burn, because of the potential negative effects of fluoride on cement setting and hydration.
Regards,
Ted.