Activated carbon as an alternative fuel. Effect of carbon ash on cement clinkerization

• A waste material (Spent activated carbon) is proposed as alternative fuel in cement production.
• Incorporation of new fuel ashes in raw mixes improved its burnability.
• Modification in composition and microstructure of clinker phases due to the new fuel ashes has been established.

Spent activated carbon is a by-product of potabilization plants. The present study explored the feasibility of valorizing this waste as an alternative fuel to replace oil coke in portland clinker furnaces. This involved determining its composition, calorific value, and ash and heavy metal content. Since the ash generated by spent activated carbon firing is taken up by the clinker, the possible effect of such uptake on clinkerization or the properties of the clinker obtained were also ascertained.Although spent activated carbon has an 18% lower calorific value than oil coke, one of the traditional cement kiln fuels, it was found to be apt for the purpose envisaged. Its ash content (10 wt%) is one order of magnitude higher than the ash content in coke.Spent activated carbon ash contains substantial proportions of anhydrite and quartz, hematite and augite, but consists primarily of amorphous matter (59 wt%).The effect of this ash on clinker phases was studied by clinkerizing raw meal in which it was used as a replacement for clay. Such meal exhibited high burnability and yielded clinkers with a composition and mineralogy comparable to the properties found in the industrial product. The sulfate present in the ash induced substantial alite crystal growth in the clinker. The loss of minority elements during clinkerization was likewise studied.