Buff Bauxite (also known as bauxite ore or bauxite) is an important raw material for the production of alumina, refractory materials and high-alumina products. Vertical kiln is one of the key equipment for calcining bauxite. It is mainly used to produce calcined bauxite clinker and is widely used in refractory materials, ceramics, building materials and other industries. The following is a detailed introduction from the aspects of bauxite characteristics, vertical kiln calcination process, product application, etc.
1. Basic characteristics of bauxite
(1) Chemical and mineral composition
The main component of bauxite is aluminum oxide (Al₂O₃), and contains impurities such as SiO₂, Fe₂O₃, TiO₂, etc. According to the mineral composition, it can be divided into:
Monohydrate type (Al₂O₃·H₂O): high aluminum and low silicon, suitable for the production of high-purity alumina.
Gibssite type (Al₂O₃·3H₂O): easily soluble in alkali, mainly used for the production of alumina by the Bayer process.
Kaolinite type (Al₂O₃·2SiO₂·2H₂O): high silicon content, requires ore dressing and purification.
(2) Bauxite classification
Grade Al₂O₃ content (%) Application
Special grade ≥85 High-purity refractory materials, corundum products
First grade 75-85 Refractory bricks, ceramics
Second grade 65-75 Cement, ordinary refractory materials
Third grade 50-65 Aluminum smelting, building materials
2. Vertical kiln calcination process of bauxite
Vertical kiln is a vertical continuous calcination equipment, suitable for large-scale production of calcined bauxite clinker, with high thermal efficiency, low energy consumption and large output.
(1) Vertical kiln structure
Kiln body: 10-20m high, 2-4m in diameter, lined with refractory bricks.
Feeding system: top distributor, evenly distribute the ore.
Combustion system: coal gas, natural gas or coal powder combustion, the temperature can reach 1500℃.
Cooling system: bottom blast cooling, discharge temperature <100℃.
(2) Calcination process
Crushing and screening
The raw ore is crushed to 30-80mm block size and soil impurities are removed.
Preheating (200-600℃)
Remove free water and crystal water (the dehydration temperature of diaspore is about 450℃).
High temperature calcination (1200-1500℃)
Al₂O₃ is converted into α-Al₂O₃ (corundum phase) to improve volume stability.
The impurity SiO₂ reacts with Al₂O₃ to form mullite (3Al₂O₃·2SiO₂), which enhances refractoriness.
Cooling and discharging
Slow cooling to avoid thermal shock cracking, the clinker has high hardness and density.
(3) Key process parameters
Parameter Control range Influence
Calcination temperature 1400-1500℃ Determines Al₂O₃ crystal transformation
Residence time 8-12 hours Influences sintering degree
Fuel type Natural gas/coal gas Influences impurity content
Cooling rate <50℃/min Prevents clinker explosion
3. Performance of calcined bauxite clinker
High refractoriness: ≥1770℃ (when Al₂O₃>85%).
Volume stability: shrinkage after calcination <3%, suitable for high temperature environment.
Corrosion resistance: Acid and alkali erosion resistance, suitable for metallurgical furnace lining.
4. Application of calcined bauxite
(1) Refractory materials (main use, accounting for more than 70%)
High alumina bricks: used in blast furnaces, electric furnaces, cement rotary kilns.
Casting material: combined with aluminate cement, used for ladle lining.
Mullite products: high temperature kiln furniture, ceramic kilns.
(2) Ceramic industry
As a whitening agent for ceramic glaze (Fe₂O₃ content is reduced after calcination).
Production of wear-resistant ceramics (such as ball mill linings).
(3) Other applications
Abrasive industry: manufacture of brown corundum and white corundum.
Building materials industry: raw materials for high-alumina cement.
Chemical industry: production of aluminum sulfate and polyaluminum chloride (PAC).
5. Vertical kiln vs. rotary kiln: calcination method comparison
Comparison items Vertical kiln Rotary kiln
Thermal efficiency High (>60%) Medium (40-50%)
Suitable particle size Lump (30-80mm) Powder/small particles (<10mm)
Temperature uniformity Slightly worse (needs uniform distribution) Better (rotation and uniform heating)
Investment cost Lower Higher
Applicable products Medium-high aluminum clinker (Al₂O₃>70%) High-purity alumina (Bayer process raw materials)
6. Industry development trend
Energy-saving transformation: adopt heat storage combustion technology to reduce energy consumption (<100kg standard coal/ton clinker).
High purification: reduce the content of Fe₂O₃ and TiO₂ through flotation and magnetic separation to meet the demand for electronic grade alumina.
Environmental protection upgrade: flue gas desulfurization (SO₂) and dust removal (PM<10mg/m³) meet emission standards.
