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Mineral roasting

Mineral roasting can be divided into calcination, oxidation roasting, reduction roasting, chlorination roasting, and sulfation roasting based on the different chemical processes that occur. Roasting not only causes chemical changes in minerals, but also makes the physical form of the material loose and porous, making it easy to leach or separate through beneficiation. Roasting can also remove (recover) volatile components (impurities) and serve as a process or refining for enrichment, impurity removal, metal powder preparation.


       The main types of roasting furnaces include multiple hearth furnaces (MHF), rotary kilns, fluidized roasting furnaces, floating roasting furnaces, sintering machines, and vertical roasting furnaces. The MHF was developed by Nichols Corporation in 1890 for roasting pyrite. In 1931, China imported the first MHF used for roasting tungsten ore. Subsequently, more than 70 fields were gradually expanded, including calcination of kaolin, magnesium oxide, activated aluminum, nickel ore, molybdenum ore, and tungsten ore, production and regeneration of activated carbon, and thermal treatment of sludge, forming a series of furnace types.


       Company is committed to environmental protection and environmental engineering industry, the technology research and development team of the international advanced technology digestion and re-innovation, cooperation with domestic and foreign equipment manufacturers, the formation of its own core equipment- MHF. Master more than 30 corresponding patents, more than 80 sets of MHF engineering experience.

The characteristics of MHF roasting are as follows:

  • Suitable for various types of roasting (calcination, oxidation, reduction, chlorination, sulfation)

  • Acceptable feed moisture content > 50%

  • Long service life

  • Low maintenance costs 

  • Application temperature up to 1100 ℃

  • Good product quality and high activity

  • High flexibility and precise control of temperature curve (± 5 ℃)

  • Wide range of roasting particle size and uniform roasting.

  • Insensitive to fluctuations in the chemical and physical properties of materials

  • Suitable for liquid and gas (including low calorific value gases) fuels

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1. Preparation of lithium hydroxide
       Under the trend of carbon neutrality, future energy consumption will shift towards electricity, leading to a rapid growth in demand for energy storage batteries. To achieve carbon neutrality, both in terms of energy storage and electric vehicles, lithium batteries are indispensable. Lithium hydroxide, as an important strategic material for lithium batteries, has a broad future prospect influenced by the concept of carbon neutrality. The one-step method of roasting lithium ore to produce lithium hydroxide has high product quality and low conversion cost, making it one of the main production methods for lithium hydroxide in domestic enterprises.

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Nanshi Lithium: pilot test of lithiumite roasting

2. Recycling of neodymium iron boron waste
       
The widespread application of neodymium iron boron magnetic materials has promoted the rapid development of the magnetic material industry. In the production process of neodymium iron boron, a large amount of waste is generated, containing a large amount of rare earth metals such as praseodymium and neodymium. Therefore, the recycling and reuse of rare earth metals in neodymium iron boron waste is of great economic significance. The separation and extraction method of oxidation roasting hydrochloric acid dissolution is mostly used in China. Oxidative roasting changes iron into ferric iron, and rare earth is also oxidized. After hydrochloric acid leaching, adjust the pH value to separate rare earth from other metal elements.

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Huazhuo :60000t/y NdFeB recycled material roasting

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Shenghe: 30000t/y NdFeB recycled material roasting

3. MgO synthesis
       
MgO is an important chemical with many special uses. MHF are mainly used to produce active light-burned MgO. The quality of light-burned MgO (i.e. reactivity, specific surface area, loss on ignition, residual CO2) can be adjusted by controlling and changing the temperature. The temperature control of the MHF is precise within ± 5 ℃. Each furnace is equipped with a maximum of four burners, and the combustion conditions can vary independently. Automatic ventilation and oxygen monitoring equipment closely control power consumption and fuel demand to ensure clean combustion. The processing time of materials is controlled by the adjustable speed of the central axis, and the feeding speed controls the depth of the material layer. The dust collected by the dust collector can be returned to the furnace, reducing product loss and exhaust gas.

Calcined magnesium hydroxide
Mg(OH)2 + Heat → MgO + H2O
The total energy requirement to calcine 1.0 kg of 55% solids filter cake, which will yield 0.38 kg MgO is the sum of 2412 kJ

Calcined magnesite
MgCO3 + Heat → MgO + CO2↑
The total energy required to calcine 1.0 kg of magnesite (to produce 0.48 kg of MgO) is approximately 2415 kJ

       The first stage, the preheating zone, magnesite is preheated from the ambient temperature to around 650 ℃ using high-temperature gas inside the furnace.
       The second stage, the calcination zone, when the temperature reaches about 750 ℃, the surface of magnesite begins to decompose and produce carbon dioxide. The temperature further increases beyond the decomposition temperature, and the partial pressure exceeds one atmosphere. The decomposition process can take place inside the particles.
       The third stage, the cooling zone, the calcined magnesite is cooled to around 650 ℃.

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