Rotary Kiln Dead-Burned Magnesite Process​

The core of the rotary kiln dead-burned magnesite process is to decompose magnesite (main component: MgCO₃) into light-burned magnesia (MgO) through high-temperature calcination, followed by further calcination to obtain high-density, high-purity dead-burned magnesia (dead-burned magnesite).

This process is mainly used for producing high-purity dead-burned magnesia, a key raw material for manufacturing refractory materials, which is widely applied in high-temperature industrial fields such as iron and steel, cement production.

I. Core Process Steps

The entire process is divided into three main stages: raw material pretreatment, calcination, and cooling. The specific steps are as follows:

Raw Material Pretreatment

Crushing: Mine-run magnesite is crushed into 20-50mm lumps to remove large impurities.

Screening: Vibrating screens are used to separate ore lumps of different particle sizes, ensuring uniform particle size of feedstock to the kiln and avoiding uneven calcination.

(Optional) Water Washing / Magnetic Separation: If the ore has high impurity content (e.g., silicon, iron), water washing (to remove sludge) or magnetic separation (to remove iron) is required to improve raw material purity.

Rotary Kiln Calcination (Core Link)

Feeding: Pretreated ore lumps are evenly fed into the feed end of the rotary kiln.

Preheating Zone: Ore lumps are first preheated at 300-800℃ in the kiln to evaporate moisture and initially decompose part of the carbonate.

Calcination Zone: Entering the high-temperature zone (1600-1800℃), MgCO₃ is completely decomposed into MgO and CO₂, with the reaction formula: MgCO₃ → MgO + CO₂↑; meanwhile, MgO grains grow and densify to form dead-burned magnesia.

Cooling Zone: Calcined magnesia enters the cooling zone at the kiln tail, where the temperature drops to 800-1000℃ before discharge.

Post-Treatment

Cooling: The discharged high-temperature magnesia is further cooled to below 100℃ using a cooler (e.g., single-cylinder cooler) to facilitate subsequent processing.

Crushing and Screening: According to customer requirements, the cooled magnesia is crushed and screened into products of different particle sizes (e.g., 0-1mm, 1-3mm).

Inspection and Packaging: Test indicators such as MgO content and bulk density of the products; qualified products are packaged and stored.

II. Key Process Parameter Control

Parameter control directly affects the quality of dead-burned magnesia. The core control indicators are as follows:

Calcination Temperature: Stable control at 1600-1800℃ is required. Insufficient temperature leads to incomplete decomposition of MgCO₃, resulting in low purity and density; excessive temperature may cause over-sintering of MgO and kiln ringing.

Kiln Atmosphere: Oxidizing atmosphere (excess air is introduced) is adopted to avoid the formation of low-valent magnesium compounds from MgO under reducing atmosphere, which affects product quality.

Material Residence Time: Adjusted according to ore particle size, usually controlled at 2-4 hours to ensure sufficient internal and external calcination of ore lumps and uniform grain growth.

Kiln Rotational Speed: Generally 0.5-2r/min. Excessively high speed results in insufficient material residence time and incomplete calcination; excessively low speed may cause local overheating.

III. Process Advantages and Precautions

1. Process Advantages

High Automation Level: PLC system can control parameters such as temperature and rotational speed, stabilizing product quality and reducing manual intervention.

Large Processing Capacity: A single rotary kiln can handle hundreds of tons per day, suitable for large-scale industrial production.

Stable Product Quality: Uniform temperature in the high-temperature zone ensures high magnesia purity (MgO content ≥95%) and bulk density (≥3.3g/cm³), meeting the requirements of high-end refractory materials.

2. Precautions

Raw Material Control: Strictly control the MgO content (≥42%) and impurity content of ore fed into the kiln to avoid impurities affecting product performance.

Kiln Ringing Prevention: Regularly clean kiln rings; the risk of ringing can be reduced by adjusting raw material particle size, controlling temperature and rotational speed.

Energy Consumption Optimization: Waste heat recovery devices (e.g., preheaters) are used to utilize the heat from kiln tail flue gas, reducing fuel consumption (e.g., natural gas, coal powder).