Kaolin, also known as dolomite, is a clay and clay rock mainly composed of kaolinite clay minerals. It is white and fine in texture and is more common in nature.

In industrial applications, kaolin is a mineral raw material required for many industries such as paper making, ceramics, rubber, chemicals, coatings etc, and is widely used.

In actual production, the whiteness and brightness of kaolin will directly affect the quality of the finished product, so we have a more stringent standard for the whiteness of kaolin. Usually, the mineral composition and content of iron and titanium in kaolin is the main factor affecting the whiteness of kaolin. Then, how to remove iron from kaolin and increase the whiteness of kaolin?

Kaolin grinding mill

In modern industry, the method of removing iron and whitening of kaolin can be divided into three categories: physical method, chemical method and biological method. So let us take a look at the chemical removal of iron in kaolin:

Acid leaching

The acid leaching bleaching method uses a suitable acid solution such as hydrochloric acid, sulfuric acid, nitric acid or the like to treat the kaolin, and converts the impurities in the kaolin into a soluble compound, thereby separating from the kaolin and achieving the purpose of whitening.

Oxidative bleaching

It is a bleaching effect by oxidizing impurities such as pyrite to a water-soluble ferrous ion by using a strong oxidizing agent and oxidizing other dark organic substances into a colorless substance.

Reductive bleaching

In the reduction bleaching method, ferric iron which is hardly soluble in water in kaolin is reduced to divalent iron which is soluble in water under the action of a reducing agent, and then washed and filtered to remove it. 

Redox combined bleaching

Since in practice, kaolin mostly contains both ferrous iron and ferric iron, the oxidation method or the reduction method alone is not satisfactory. It is necessary to oxidize the ferrous iron in the kaolin with a strong oxidant by an oxidation-reduction combination method. The ferric iron is reduced, and the ferric iron is reduced to divalent iron by a reducing agent, followed by removal with the filtrate.

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28th Nov 2018