The specific steps for high-temperature calcination activation of magnesium oxide include pretreatment, heating and calcination, heat preservation and decomposition, and cooling and sealing. This method is suitable for moderately moisture-absorbing and degraded magnesium oxide, and can partially restore its activity.
1. Raw Material Pretreatment
Crushing and Sieving: Crush the agglomerated and degraded magnesium oxide using a mortar and pestle or a crusher, and pass it through an 80-mesh sieve to ensure uniform particle size and improve heating efficiency.
Preliminary Drying: Dry in a 110℃ oven for 2 hours to remove surface free water and prevent cracking or steam splashing during calcination.
This step can improve the heat transfer efficiency of subsequent calcination and reduce energy consumption.
2. Heating and Calcination
Equipment Selection: Use a muffle furnace or rotary kiln to ensure controllable and uniform heating.
Heating Program: Increase the temperature to 500℃ at a rate of 10–15℃/min to prevent sudden heating and powder scattering. Once the target temperature is reached, stabilize the furnace and begin timing the calcination.
Key Temperature Control: Below 500℃, Mg(OH)₂ decomposes incompletely; above 800℃, sintering is likely to occur, reducing the specific surface area.
3. Holding and Decomposition
Calcination Temperature: Maintain between 500–800℃ (700℃ recommended);
Holding Time: Continue for 2–4 hours to ensure complete decomposition of magnesium hydroxide:
Mg(OH)₂ → ΔMgO + H₂O↑
Atmosphere Requirements: Maintain ventilation inside the furnace, promptly remove water vapor, and promote the forward reaction.
Experimental data shows that holding at 700℃ for 3 hours can restore the activity rate to over 80%.
4. Cooling and Sealing
Natural Cooling: After turning off the power, cool the material in the furnace to room temperature (approximately 6–8 hours) to avoid stress cracking caused by rapid cooling;
Sealed Packaging: Immediately after removal, place in a double-layer moisture-proof bag (inner PE film + outer aluminum foil bag), and vacuum or nitrogen-filled seal;
Moisture Protection: Place silica gel desiccant inside the packaging and label it "Activated".
Exposed to humid air during the cooling process is strictly prohibited, otherwise it will immediately reabsorb moisture.
5. Activation Effect Verification
|
Test Item |
Standard Requirements |
Test Method |
|
Activated Magnesium Oxide Content |
≥60% |
Hydration method (HG/T 3928-2012) |
|
Moisture Content |
≤1.5% |
Loss on drying method or Karl Fischer method |
|
Physical State |
Loose white powder |
Visual inspection + flowability test |
It is recommended to send the sample to a professional laboratory to ensure it meets the usage standards.
