Preparation Of Calcined Kaolin White Pigment By Modified Mechanochemistry Method

Titanium dioxide is the best white pigment which is widely used in paints,paper,plastics,rubber,cosmetics and other industries.In recent years,due to the obvious contradiction between supply and demand of titanium dioxide,all countries around the world are working to develop a substitute for titanium dioxide,but because the technology of the production is difficult and the product quality cannot compare with pure titanium dioxide,the application of the substitute for titanium dioxide is very limited.In this paper,calained kaolin with big reserves and low price was used as substrates,through the surface activation and titanium dioxide coated of the calained kaolin,calained kaolin/titanium dioxide composite pigments with excellent performance(high whiteness,high covering power,low oil-absorption value)were prepared by oxalic acid modified mechanochemistry method and surface active agents modified mechanochemistry method.The added value of calcined kaolin had been increased and on the other hand,calcined kaolin can be used to instead the titanium dioxide which is expensive.The best technological conditions of preparing kaolin/titanium dioxide compound pigments had been ascertained with the method of oxalic acid modified mechanochemistry method:two-step method was suitable,the concentration of oxalic acid was 1mol/1,the temperature of the pickling was 80?,m(titanium dioxide):m(calcined kaolin)was 3:7,the coating time was 4 hours.Compared with the calained kaolin,the whiteness of the product prepared by modified mechanochemistry method increased from 93%to 96.5%,and the covering power decreased to 27.5g/m2.The coating mechanism was:the ionization of the complex ion was increased and the complex ability of the complex ion and the activation effect had been improved due to the reaction of hydrogen ions in oxalic acid and iron impurities.The best technological conditions of preparing kaolin/titanium dioxide compound pigments had been ascertained with the method of surface active agents modified mechanochemistry method:the amount of surface active agents was 2.5%(accounting for the proportion of the total mass of powder),m(titanium dioxide):m(calcined kaolin)was 3:7,the coating time was 3 hours.Compared with the calained kaolin,the whiteness of the product prepared by modified mechanochemistry method increased from 93%to 96.2%,and the covering power decreased to 29.5g/m2,the oil-absorption value was 29.8.The coating mechanism was:particles of titanium dioxide were coated on the surface of calcined kaolin uniformly,there were only few of the free titanium dioxide particles in the system.