How to convert some weak magnetic iron minerals such as hematite, limonite, siderite and pyrite into ferromagnetic minerals?
Weak magnetic minerals can be converted into ferromagnetic minerals by roasting, which is customarily called magnetization roasting. However, due to the different types of calcined minerals, the chemical reactions occurring during calcination are also different, so the principle of calcination is also different. According to the roasting principle, it can be divided into reduction calcination, neutral calcination and oxidative roasting.
   In the heating process, the limonite first removes the crystal water and turns into hematite which does not contain water, and then proceeds according to the above reaction.
Second, neutral roasting
This kind of roasting is suitable for siderite. When roasting, it can be heated to 300~ without introducing air or introducing a small amount of air.
   Third, oxidative roasting
Oxidation roasting is suitable for pyrite. It is calcined in a short time in an oxidizing atmosphere (or a large amount of air) and is oxidized to pyrrhotite. The reaction is as follows:
7FeS 2 +6O 2 → Fe 7 S 8 +6SO 2 ↓
The calcination time is extended and the pyrrhotite is converted into magnetite by the following reaction.
3Fe 7 S 8 +38O 2 → 7Fe 3 O 4 +24SO 2 ↓
   This method is commonly used in the separation of the metal concentrate with pyrite roasting from rare metals.
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