Recycling of waste of alum industry in manufacturing of porous mullite: microstructure and physico‑mechanical properties

Dealuminated kaolin (DK), a by-product of alum synthesis is utilized to obtain mullite. The stoichiometric composition of mullite is satisfied by α-alumina and DK. The prepared mixture is fired at different temperatures. A porogen material is added with the following proportions; 5, 10, and 15 wt.% to obtain a porous body.The effects of sintering temperature on the formation of mullite phase composition, physical properties and compressive strength as well as the microstructure of the processed bodies are investigated. The addition of the porogen graphite influences both the microstructure and the crystallization reaction of mullite. The study shows that the sample containing 10 wt.% graphite displays the highest mullite content all over the studied sintering temperatures. This effect is attributed to those impurities present in graphite besides that in DK. Thus, enhancing the dissolution of corundum and contributing to the formation of mullite.