Calcination of Hydromagnesite in a Rotary Kiln

Hydromagnesite (brucite) calcination in a rotary kiln primarily yields light-burned magnesia. The core process comprises raw material pretreatment → sealed feeding → segmented calcination in the rotary kiln → rapid cooling → grinding and classification → finished product packaging, with integrated waste-heat recovery and environmental control systems to ensure compliance with indices and product reactivity. 

Ⅰ. Full-Process Technology

1. Raw Material Pretreatment Section (Control impurities, uniform particle size, reduce moisture)

Coarse crushing → fine crushing → screening: Raw ore is coarsely crushed by a jaw crusher to 30–50 mm, then shaped and further crushed to 10–30 mm by a hammer crusher; vibration screening ensures uniform particle size.

Impurity removal and purification: Remove red veins and waste rock, and wash with water to remove clay; for high-silica/iron feedstock, magnetic separation is applied to remove iron and enhance purity; alternatively, wet ball milling combined with carbonation can be used for impurity removal.

2. Sealed Feeding Section (Prevent air leakage, ensure stable metering)

Belt-scale conveyor → sealed screw feeder → kiln head sealed hopper, achieving slightly positive-pressure feeding to prevent cold air ingress, which could disrupt the temperature field inside the kiln.      

3. Rotary Kiln Calcination Section (Core section, five-zone temperature control)  

Total residence time: 60–90 min (matched to particle size).

Heating method: direct heating with natural gas/coal gas.

4. Rapid cooling section (activation locking)

Discharge from kiln head → single-cylinder cooler; rapid cooling below 100℃ to prevent activity loss and pulverization.

Waste-heat recovery: cooling hot air is recycled for preheating in calcination, saving 15%–20% energy.

5. Post-processing and packaging (quality enhancement)

Milling and classification: ball mill / vertical mill to 325 mesh–5 μm (based on customer particle-size requirements); air classification controls particle size D50.

Inspection and packaging: measure MgO content, activity, and whiteness; pack in moisture-proof lined bags to prevent moisture absorption.

II. Key process parameters and control points:

Feed particle size: powder 100–325 mesh, lump 10–30 mm.

Decomposition temperature: 700–780℃ (core range for light calcination).

Atmosphere: Slightly oxidizing, O₂ ≥ 5%, to avoid reduction causing iron contamination.

Kiln speed and slope: Rotational speed 1–3 r/min, slope 2%–4%, matched to material residence time.

III.  Environmental protection and compliance highlights:

Dust control: Baghouse dust collectors at kiln head and kiln tail, emission ≤ 30 mg/m³.

Desulfurization and denitrification: Gas-fired desulfurization tower + SCR, SO₂/NOₓ compliant; natural gas does not require treatment.

Noise: Soundproof enclosures installed on equipment, boundary noise ≤ 60 dB(A).

IV.  Common issues and countermeasures