1156 posts
Raw materials Question 31
We are facing a problem in bringing the whiteness of material that is close to cement composition in our R&D trials. We would like to know the effect of each oxide and cooling method on whiteness of the material.
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1156 posts
Re: Raw materials
The principal colouring oxides are those of the first row of the transition metals. In cement the most likely to cause problems are iron, manganese and chromium in that order. The cooling of the clinker is absolutely fundamental to achieving the desired whiteness. You must
(i) burn the clinker as close to the nose ring as possible to eliminate the possibility of oxidation ofFeO to Fe2O3 in the kiln, and
(ii) immediately quench cool the clinker in water.
Air-cooled blast furnace slag can be added to the inlet of the cement kiln in the patented Cemstar process developed by TXI cement in the USA. I know a number of US cement companies are doing this. This is in the manufacture of cement powder. Another use is as an aggregate in the manufacture of concrete.
1156 posts
1156 posts
Re: Raw materials
It is possible to use Ca(OH)2 as a corrective source of CaO. I do not believe you would want to use CO2 as this is one of the exhaust products from the cement manufacturing process rather than making a contribution to the final product. I have not heard of the use of molasses in cement manufacturing and can envisage two problems with this material: (i) it is likely to be sticky and present handling problems, and (ii) there will be some organic material in the molasses. This organic material will smoulder and burn in the upper stages of the preheater, or in the chain systems of long kilns and will give rise to CO and hydrocarbon emissions in the exhaust gases. To add this material safely to a cement kiln would require some means to add the molasses to the hotter sections of the process such as the precalciner or the kiln inlet of a preheater kiln or some mid-kiln firing system of a long kiln.