Good Morning: we have two quarries in our plant, one of them has a problem with lower StC material (between 70 and 90% of StC); when we use material of this quarry the raw mill tends to stick in the hot cyclones or in the kiln inlet.
We have found that the differences between the quarries in the lower Stc material is in the Al2O3 content, the value is higher in the material of the quarry with problem. We tried to compare XRD diffraction patterns but we did not found any difference in a raw meal with similar StC value; we thought that the background hide the differences.
We are trying to determinate with a secuencial XRF an element comparison, we are going to determinate Cl too., but we don't have this information yet.
Which minerals with Al2O3 are sticky? Which antoher analysis do you recommend us?
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re Sticky Material
Minerals containing Al2O3 have a very high melting temperature (eg refractories), so it's not compounds of aluminium that are causing your problem, so XRD analysis is not likely to help you.
'Stickiness' of hot meal in the cyclones and kiln inlet is generally caused by the recirculation of the more volatile elements such as potassium, sodium, sulphur and chlorine. The stickiness arises because of the lower melting point of their compounds ie potassium and sodium sulphates and chlorides. These compounds (and eutectic mixtures of them) all melt below 1100C, some even as low as 500C, and this is what sticks the hot meal particles together. This is a very well known problem in kilns with high alkali/sulphur/chloride raw materials.
Chloride is the most problematic element since potassium chloride is the most volatile of all the chloride and sulphates that form in the kiln. Chloride therefore has a >99% chance of recirculating between the burning zone and the kiln inlet and can be a major cause of back-end buildups if present in excess.
I recommend that you analyse the K2O, Na2O SO3 and Cl- content of all the different raw materials from the two quarries, especially the clays, shales or volcanics since these elements often occur in higher concentrations in argillaceous materials rather than limestone. Therefore, limestones with lower CaCO3 content (StC?) are more likely to contain higher quantities of alkalis, sulphur and chlorides.