Kaolin, especially ultrafine calcined kaolin, as a very important inorganic non-metallic materials, by virtue of its excellent physical properties in the paper industry has always occupied a very important position. Calcined kaolin paper industry using a high whiteness structural features of a porous material, this material is mainly used to replace expensive senior pigments such as titanium dioxide. Calcined kaolin for paper industry quality requirements mainly for the calcined kaolin particle size, whiteness and opacity, oil absorption, sticky concentration, pH value, abrasion value and other indicators of requirements. In recent years, many of our departments to "double 90" as the goal,has made some attempts and some progress on the technology of paper&coating grade kaolin by coal gangue.
A.Process principles
The technology of paper&coating grade kaolin by coal gangue are mainly include two part : ultrafine grinding process and calcination whitening process.
a.Ultrafine grinding process
The ultrafine grinding process is an important part to determine the quality of the kaolin.Although the function of various equipment , crushing range and energy consumption varied, but the main principle of their crushing crushing extrusion, impact method , grinding stripping method and the splitting method.Different types of shredders has different crushing method.And there are not only one method in one crusher,generally two or over two method combined together to crush.
Ultrafine grinding existing kaolin crushing process , the process is generally used to broken or impact extrusion method based grinding equipment , and equipment used in the process of ultra-fine grinding stripping method based places . The existing ultrafine grinding kaolin crushing process,coarse crushing、medium crushing general use in extrusion method based or impact crushing equipment,but the Ultra fine process usually used grinding stripping method.
b.Calcination whitening process
In view of the kaolin’s Diagenetic features, which contains part of the organic matter , making it ore whiteness only 6 to 40 percent , the paper industry can not meet the quality requirements of the coating grade kaolin , calcined decarbonization must therefore whitening process . In order to avoid the formation of harmful mineral crystalline ( mullite and cristobalite ) , paper grade kaolin production process, controlling the calcination temperature is generally below 1000 ℃. According to the different requirements of quality kaolin , calcined kaolin can be divided into medium temperature and high temperature calcined kaolin two products. Currently the calcination process can be divided into molding powder calcination process and calcining process , and each with distinct characteristics .
B.Process description and characteristics analysis & discussion
According to the ultra-fine process is the use of a dry process or a wet process and superfine technology and calcining process,the production process can be combined into four,namely,calcined after wet ultrafine technology , calcined after dry ultrafine technology,wet after calcined ultrafine technology,dry after calcined ultrafine technology.Because different people's awareness of superfine material,and thus in different enterprises in selected process route are not the same .
a.Wet after calcined ultrafine technology
The flowchart is ：ore→crushing→break up→calcination→wet ultrafine→dry→scattering→product
The main advantage of this process is less ultrafine materials and the ultrafine material are easy to day and scattering.
The main disadvantage of this process is a wet ultrafine grinding media more difficult to solve ; higher quality requires kaolin ; process requires a separate drying equipment to complete dispersion of ultrafine materials processing wet , thus drying equipment high quality requirements , in order to prevent pollution of the material is three .
b.Dry after calcined ultrafine technology
The flowchart is ：ore→crushing→break up→calcination→dry ultrafine→product
The main advantage is short process、less ultrafine handling materials and small energy consumption.
The main disadvantage is high quality requirements of raw materials,difficult to produce -2μm up to 90% ultrafine products,high requiring in ultrafine grinding equipment,only can the use of air- grinder,etc.In terms of the current equipment level,this process is not a viable manufacturing process,because there is no suitable ultrafine mill .
c.Calcined after dry ultrafine technology
The flowchart is ：ore→crushing→break up→dry ultrafine→calcination→product
The main advantage is short process and rational use of energy.
The main disadvantage is difficult to improve product quality and there are strict requirements for products fusible mineral content.For this process doesn’t exist in another part of the burning pulverized material,and therefore suitable for a resource advantages but do not have the financial strength of the business as a process starting .
d.Calcined after wet ultrafine technology
The flowchart is ：ore→crushing→break up→wet ultrafine→dry→calcination→reduction→product
The main advantage is use the wet ultrafine process to make the particle up to 90% within -2μm,reliable technology and easy to solve the problem of impurities such as iron and titanium.
The main disadvantage is long process and need the reduction process
In summary , the use of coal kaolinite to produce coating grade calcined kaolin of paper industry is undoubtedly an effective way of rational utilization of coal gangue.