The process flow for activating magnesium oxide using the high-temperature calcination method includes four core steps: raw material pretreatment, heating and calcination, heat preservation and decomposition, and cooling and sealing for preservation. It is suitable for moderately moisture-absorbing and degraded magnesium oxide, and can partially restore its activity.
1. Raw Material Pretreatment
Crushing and Screening: Crush the agglomerated and degraded magnesium oxide using a crusher or mortar and pestle, 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 moisture and prevent steam splashing or powder scattering during calcination.
This step improves heat transfer efficiency, reduces subsequent energy consumption, and is a key pretreatment to ensure uniform activation.
2. Heating and Calcination
Equipment Selection: A muffle furnace (for small batches) or a rotary kiln (for continuous industrial production) is recommended to ensure controllable temperature and uniform heating.
Heating Program: Slowly increase the temperature to 500℃ at a rate of 10–15℃/min to avoid sudden heating that could cause material cracking. After reaching the target temperature, stabilize the system and begin timing the holding phase.
Key Temperature Control Points: Below 500℃, Mg(OH)₂ decomposes incompletely; above 800℃, sintering is likely to occur, reducing specific surface area and activity.
3. Incubation and Decomposition
Calcination Temperature: Maintain between 500–800℃, with 700℃ being the optimal balance point, balancing decomposition rate and prevention of sintering;
Holding Time: Continue for 2–4 hours to ensure complete dehydration and decomposition of magnesium hydroxide:
Mg(OH)₂→ΔMgO+H₂O↑
Atmosphere Control: Maintain good ventilation inside the furnace, promptly remove water vapor, and promote the forward reaction.
Experimental data show that holding at 700℃ for 3 hours results in an activity recovery rate of over 80%.
4. Cooling and Sealing
Natural Cooling: After turning off the power, allow the material to cool to room temperature inside the furnace (approximately 6–8 hours) to avoid stress damage to the crystals caused by rapid cooling.
Sealed Packaging: Immediately after removal, place in a double-layered moisture-proof bag (inner PE film + outer aluminum foil bag). Vacuum sealing or nitrogen filling is recommended.
Moisture Prevention: Place silica gel desiccant inside the packaging and label it "activated" to prevent secondary moisture absorption.
Exposed to humid air during the cooling process is strictly prohibited; otherwise, it will immediately reabsorb moisture and become ineffective.
5. Activation Effect Verification
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>=60% |
Hydration method (HG/T 3928-2012) |
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<=1.5% |
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Visual inspection + flowability test |
It is recommended to send the sample to a CNAS-accredited laboratory to obtain authoritative data to ensure that it meets the requirements of high-precision application scenarios.
