Effect Of Crystalline Characteristics Of SiO₂ In Siliceous Raw Materials On Clinker Calcination

Clay is one of the main raw materials for Portland cement production.As the exploitation of natural clay resources is limited,cement industries are exploring other raw materials that can provide SiO₂ components.Large amounts of inert siliceous raw materials such as sandstone,silica stone and various industrial solid wastes are more widely used in cement production.Therefore,it is of great significance to improve the quality of clinker calcination and reduce the energy consumption of cement production by optimizing the quality of siliceous raw materials.The influence of Si-O bonding forms,polymorph and crystallinity of quartz on the burnability of raw mixes and microstructure and properties of clinker were analyzed by X-ray powder diffraction combined with the Rietveld method,scanning electron microscopy,thermal analyzer,reflection microscope and isothermal calorimeter.Furthermore,the influence of 14 different kinds of siliceous raw materials from different region in China on the calcination and properties of clinker were deeply studied.The results are shown as follows:1.Siliceous raw materials with simple Si-O bonding form are easier to depolymerize,so it is easier to react with CaO to form C₂S in the process of solid phase reaction.However,wollastonite with chain Si-O bonding form is mostly converted into high-temperature crystal form at about 1200?,and its reactivity decreases,which hinders clinker calcination.2.The relative density is an important factor affecting the reactivity of siliceous raw materials with high silica.Compared with?-quartz,?-cristobalite has higher reactivity and better quality of clinker because of loose structure.Quartz glass also has loose structure.However,due to the high melting temperature of quartz glass,its reactivity is low before the liquid phase appears.Above 1350?,the reactivity of quartz glass is gradually improved,and the quality of clinker is getting better.3.In the clinker with siliceous minerals with high reactivity,such as silicate minerals with chain or layer Si-O bonding form,alite tends to be long column-like and smaller in size.In the clinker with less reactive siliceous raw minerals,such as?-quartz,alite tends to be polygonal plate-like with larger size and more C₂S inclusions.4.The influence of siliceous raw materials on clinker calcination is quite different.The content of C₃S can be decreased and the f-CaO content will be increased in the clinker resulting from the decrease of simple silicate minerals in the siliceous raw materials,and also the increase of either quartz content or its crystal size.5.The minor elements which are associated with the siliceous raw materials have more obvious influence on the clinker formation than the added ones.Associated K₂O can cause a decrease in C₃S content and an increase in its crystal size.For the siliceous raw materials with high silica,the associated MgO in the form can better promote the formation of alite.