Study On Process Analysis And Oil Absorptive Properties Of Kaolin Modified By Acid And Alkali

Calcined Kaolin was modified separately by hydrochloric acid and sodium hydroxide in this work, the structures and oil absorptive properties of kaolin and modified kaolin were studied by TG-DTA, XRD, BET, SEM, TEM and EDS techniques. The optimum conditions of modified kaolin were determined, the modified processes of acid and alkaline were analyzed, and Al2O3 of the filtrate were recycled. In addition, in order to make industrial kaolin produce and obtain higher surface area of modified kaolin, 31% of industrial hydrochloric acid, first acid and then alkali modification of calcined kaolin were also respectively tried.Experimental results show that, the composition and the structure of kaolin are complex, it has small surface area because the pore is mainly distributed by macropores. In order to improve the surface area, kaolin must be first calcined at a certain temperature, and then modified by acid or alkaline, and the optimum calcination temperature of kaolin was confirmed that 850℃and 1000℃were respectively in acid and alkali modified conditions.When the ratio of liquid to solid is 8mL/g, the reaction time is 2h, the temperature is 90℃and the concentration of acid is 4mol/L, the optimum and high surface area can be obtained, it is 468.1654m2/g, which improved 2 times than the reported of literature. When the ratio of liquid to solid is 6mL/g, the reaction time is 2h, the temperature is 90℃and the concentration of acid is 3mol/L, the optimum surface area of 129.8048m2/g can be obtained. Kaolin after modification have higher surface areas, this is due to Al, Si and other elements leaching from kaolin under acid and alkali modification.Both of the oil absorption and the leaching rate were small, this is because 31% of industrial hydrochloric has shortage of purity, there are some materials such as iron, chlorine and organic impurities, which make Al not be fully leached from calcined kaolin when it was modified by industrial hydrochloric. The oil absorption, the surface area and the pore volume of first acid and then alkali modification are all reduced significantly, this is because Al element can leach from kaolin and leave a lot of holes after acid modified, alkali modification make Si element leach from calcined kaolin and connect these small hole to be expanded at the same time.