What should be paid attention to in the production of iron oxide red colour by green alum calcination? --1, 2

There are many production processes for common red iron oxide pigments, generally dry and wet. Among them, green alum calcination is a common one, is also the most used one. What aspects should be paid attention to when manufacturing and processing with this method:

The reaction mechanism of the green alum calcination method is to use the heating method to decompose the green alum, and use the oxygen of the air to oxidize the green alum. For the smooth progress of the reaction, dehydration treatment is performed first, otherwise ferrous sulfate will dissolve in its own crystal water during high temperature calcination. Moisture evaporates rapidly through high temperature ,It will cause the ferric sulfate to agglomerate after melting, and finally cause the product to agglomerate and not be in a powder state.

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The calcination temperature has a great influence on the reaction process. Only when the temperature reaches 450~550℃ can the water of the last molecule in the dehydrated green alum be removed.

When the reaction temperature reaches 600℃, the decomposition reaction can only proceed to 50%-60%, and the product contains a large amount of Fe(OH)SO4 basic formula.

Salt remains, which is difficult to remove by ordinary washing methods. This insoluble and soluble substance is decomposed into sulfuric acid after hydrolysis, which will seriously

The corrosion resistance of the pigment is reduced, and the basic ferric sulfate can only be removed by washing with hot water for a long time. In order for the reaction to proceed to the end, the calcination temperature must reach 700 ℃ to completely decompose the green vitriol, but the product still contains a small amount of basic ferric sulfate, and the reaction

Not fast enough. If the reaction temperature is increased to 800°C, the decomposition rate is accelerated and red iron oxide without basic iron sulfate is produced.

The lower reaction temperature can obtain yellow-phase iron red, and the higher reaction temperature can obtain blue-phase iron red, so the determination of the specific temperature depends on the requirements of the product. There are many factors that affect the color of red iron oxide, and the particle size is one of the important ones, and the particle size is controlled by the calcination temperature and time. The hue of the pigment is also related to the amount of air introduced. Too much air will increase the content of manganese oxide, and the presence of manganese oxide will cause the iron red to have a light brown phase and make the color darker. In addition, a small amount of lead sulfate is intentionally added to the green vitriol to generate lead oxide impurities, which reduces the sensitivity of iron oxide to high temperature during the calcination process, and improves the hue of iron red.

It can be seen that there are many places to pay attention to the manufacture and production of iron oxide red pigments, which are related to the color and quality of the pigment. No matter what method is used to manufacture and produce, the quality and performance of the product must be ensured.