Study On The Optical Properties Of Calcined Cobalt Surported Coal Series Kaolinite

As a kind of important inorganic white pigment, kaolin was used widely in various fields, such as ceramic, papermaking, coating by its excellent light-scatting properties, but the whiteness of calcined kaolin-products is effected greatly to a large extent because of the various impurities, such as iron. The cobalt ion which can weaken the staining behavior of iron ion in kaolin was introduced by liquid phase deposition in this paper. The research indicates that the appropriate cobalt ion addition quantity can improve significantly the color index of calcined products of iron-containing kaolin and the calcined kaolin of low color deviation of which color index is close to zero can be obtained.(1) Compared with kaolin without cobalt, the brightness of kaolin with cobalt increased apparently to an extent of 1%-3% above the temperature of 500℃. Cobalt has a great influence on the a*,b* values and can make transition to coordinate[-1.72,-2.44](blue-green) from [0.79,3.42](red-yellow).The red-yellow which emitted by the iron can be hided well.(2)The effect of holding time on the brightness of kaolin with cobalt is not obvious. The maximum brightness value is acquired at 1000℃and 2 h holding time。The brightness value fluctuates slightly with the increasing of time and descents as a whole. But the a*,b*values can be affected greatly by the holding time and can reach to [-1.1,-3.45]with the increase of holding time.(3) The additional technological conditions of cobalt ions has greatly effect on the color of calcined kaolin. Calcined kaolin which was calcined after pre-registering raw material and then adding cobalt ions can get better result than without pretreatment.(4)The cobalt element does not have an apparent influence on the crystal transformation of kaolin, but can affect the degree of caking greatly.The results show that calcined kaolin of the low color deviation was obtained when the ratio of nFe:nCo=2.75:1～4.81:1, the calcined temperature ranged from 500℃to 1000℃, which the whiteness and lightness were more than 80% and 85% respectively and the value of a* ranged from 0.13 to-1.72 and the value of b* ranged from 1.62 to-3.34.