Kaolin is widely used in ceramics, paper making, coatings and other fields. Kaolin generally contains iron, and too high iron content will affect the whiteness of kaolin, thereby affecting the added value of products. The whiteness of high-grade kaolin is required to be more than 92%. How to remove iron from kaolin to a greater extent has become an urgent problem to be solved. Here we introduce kaolin iron removal equipment and kaolin iron removal and whitening methods.
There are two main occurrence states of iron in kaolin, one is in kaolinite and accessory minerals (such as mica, titanium dioxide and illite), which is called structural iron; The other is in the form of independent iron minerals, called free iron (including surface iron, fine crystalline iron and amorphous iron). The independent free iron removal method is simple, and physical methods such as magnetic separation and flotation can be used, while the removal method of structural iron is more complex, requiring chemical methods, such as oxidation reduction method, acid dissolution method, chlorination method, microbial method, etc.
The physical iron removal methods, magnetic separation and flotation, are mainly introduced here.
Removal of iron by magnetic separation is to remove iron element from kaolin with an iron remover There are two traditional methods of iron removal from kaolin, namely, dry iron removal and wet iron removal. Customers can choose the iron removal process according to different requirements. Strong magnetic minerals such as magnetite or iron filings impurities in kaolin can be removed by ordinary magnetic separation; If the iron mineral is weakly magnetic, the high gradient strong magnetic separation method can be used or the weakly magnetic mineral can be transformed into strong magnetic iron oxide after roasting, and then the common magnetic separation method can be used to remove it.
There are three main methods to remove iron from kaolin by flotation: carrier flotation, double liquid flotation and selective flocculation.
The carrier flotation method refers to the use of a carrier to absorb Fe2O3, for example, the use of calcite to adsorb the extremely fine impurity mineral Fe2O3 onto the carrier minerals. With the help of collectors or the hydrophobic adhesion of the carrier itself to the bubbles, the iron containing carrier foam and kaolin concentrate products are obtained, thus achieving the separation of kaolin and Fe2O3.
The double liquid flotation method is to add fatty acids (or other hydrophobic collectors capable of capturing impurities of iron minerals) into the kaolin slurry for stirring, static and stratification to form organic liquid (containing Fe2O3) and kaolin suspension double-layer liquid, and then use gravity separation equipment for separation.
The selective flocculation method is to add flocculant to the fully dispersed pulp, and selectively flocculate the free harmful iron impurities dispersed in the pulp through the bridging effect between the flocculant and the mineral particle surface, and then separate the flocculent from the pulp. There is a large amount of water (pulp concentration is less than 20%) in the production of this method that needs to be removed in the subsequent process. At the same time, the residual flocculant in the kaolin concentrate also affects the quality of the final product.
Above, we introduced two physical methods to remove iron from kaolin, namely magnetic separation and flotation.
Equipment used for magnetic separation method: if the particle size of kaolin is relatively coarse, the grinding and classification equipment shall be used to grind the kaolin to a certain fineness, and then the magnetic separator shall be used to remove the iron element. If it is weakly magnetic iron, the high gradient magnetic separator shall be used.
Equipment used in flotation method: ball mill is also required to grind large particles of kaolin ore, and then mechanical stirring flotation machine is used to separate iron and kaolin, such as BF flotation machine, SF flotation machine, JJF flotation machine, etc. Mixing equipment is also used in double liquid flotation method, because mixing strength is an important factor affecting the method, and insufficient mixing strength will reduce the probability of collision between iron minerals and kaolin; If the stirring intensity is too high, it is easy to form the intermediate phase of emulsion turbidity.
The above describes the kaolin iron removal equipment and two methods of kaolin iron removal and whitening. There are also some chemical methods, which are not introduced here because we do not cover them. Compared with the flotation method, the magnetic separation method is simpler, easier to operate and lower in cost, but requires higher magnetic separation equipment; The flotation process is complex and costly. The specific method for iron removal should be determined according to the beneficiation test.
