Degraded magnesium oxide cannot be completely reactivated because the resulting magnesium hydroxide (Mg(OH)₂) is an irreversible product. However, its activity can be partially restored through high-temperature calcination, suitable for moderately degraded materials.
1. High-Temperature Calcination Method: Limited Reactivation
Applicable Conditions: Only applicable to moderately degraded magnesium oxide (surface hydration, slight agglomeration);
Reaction Principle: Mg(OH)₂ → ΔMgO + H₂O↑ Magnesium hydroxide decomposes at high temperature, regenerating magnesium oxide;
Operating Parameters:
Temperature: 500–800℃ (avoid sintering below 800℃);
Time: 2–4 hours, ensuring sufficient dehydration;
Equipment: Muffle furnace or rotary kiln, well-ventilated;
Post-treatment:
Cool naturally to room temperature after calcination;
Sieve (80–100 mesh) to remove impurities;
Immediately seal the packaging to prevent secondary moisture absorption.
After this treatment, the activity can be restored to 70%–85% of its original value, but the specific surface area and reactivity are still lower than those of fresh, highly active MgO.
2. Activation Effect Evaluation Criteria
|
Indicators |
Recovery Target |
Detection Method |
|
Active Magnesium Oxide Content |
≥60% |
Hydration Method (HG/T 3928-2012) |
|
Moisture Content |
≤1.5% |
Karl Fischer Method or Drying Loss Method |
|
Flowability |
Loose Powder |
Visual Inspection + Pour Test It is recommended to send samples to a CNAS-accredited laboratory to obtain authoritative data to ensure that the application requirements are met. |
3. Cases Where Activation is Not Possible (Do Not Attempt)
Severely hardened, like stone: The interior is deeply hydrated and difficult to completely decompose during calcination;
Contains carbonate impurities (such as MgCO₃): Requires higher temperatures (>900℃) for decomposition, easily leading to sintering deactivation;
Used in high-precision fields (such as electronics and medicine): Even if partially restored, there is still a risk of performance fluctuation.
Forcibly using activated materials may lead to product cracking, insufficient strength, or uncontrolled reaction.
4. Alternative Recommendations: Prioritize Resource Utilization. If activation costs are high or the effect is unsatisfactory, it is recommended to shift to non-critical applications such as agricultural improvement and environmental desulfurization to turn waste into treasure.
Safety Tips: The calcination process should be carried out in a well-ventilated environment. Wear protective equipment and avoid dust inhalation.
