Kaolin bleaching methods are the following:
First, chemical iron removal and whitening
The so-called chemical iron removal is a chemical method that selectively dissolves iron-containing minerals in materials and then removes them.
Second, the reduction method
1, the insurance powder reduction method
This method has limitations. One of the reasons for the poor bleaching effect is that the powdered powder is easily decomposed and its reducing ability is reduced.
The insurance powder reduction method is very demanding in terms of conditions, and two problems must be solved in order to achieve industrial production:
1 strictly control the acidity, temperature, etc.;
2 How to get the product clean as soon as possible.
2. Acid-soluble hydrogen reduction method
In order to make the impurity Fe in kaolin more easily convertible into a colorless and easily soluble state, it is necessary to add a reducing agent at the time of acid dissolution.
When kaolin contains pyrite and organic matter, the mineral is often gray. These materials are difficult to remove using pickling and reducing bleaching. This requires the use of oxidation bleaching.
The oxidative bleaching method uses a strong oxidant to oxidize pyrite in a reduced state in an aqueous medium to ferrous ions of soluble dry water; at the same time, the dark organic matter is oxidized to make it washable. The oxidizing agents used in the oxidative bleaching of the color oxides include sodium hypochlorite, hydrogen peroxide, potassium permanganate, chlorine, ozone, and the like. Taking sodium hypochlorite as an example, pyrite is oxidized.
Four, microbial (T.f.) oxidative whitening method
Many non-metallic ores contain harmful impurities in pyrite. At present, the mining site uses chemical whitening, but the cost is high.
V. Organic acid iron removal and whitening
Can be divided into in situ biobleaching and two-stage biobleaching:
(1) In situ biobleaching refers to the addition of kaolin at the beginning of the fermentation.
(2) Two-stage biobleaching means that Aspergillus niger is first cultivated in a shaking flask.