Magnesium-specific ferro silicon, with FerroSilicon 75 as its core grade, is specifically designed for the Pidgeon process in magnesium production:
Composition Requirements: Si 72%-78% (core reducing element), impurities Al≤1.0%, Ca≤2.0%, S≤0.02%, P≤0.04%, Ti≤0.1%, Mn≤0.3%;
Physical Properties: Melting point 1250-1350℃, density 6.9-7.1 g/cm³, in block form (10-50 mm, accounting for ≥90%), with block integrity ≥95% to avoid breakage and dust generation during transportation and storage;
Core Advantages: High silicon reduction activity (reduction efficiency ≥85%), minimal impurity interference, magnesium recovery rate 5%-8% higher than ordinary ferrosilicon, suitable for large-scale magnesium production.
Core Reduction Mechanism and Quantitative Effect
(1) Core Reaction Principle of Pidgeon Process for Magnesium Refining
Special ferrosilicon is used as the core reducing agent to reduce magnesium oxide to magnesium metal at high temperature. The reaction process is as follows:
Main reaction: 2MgO + Si → 2Mg (gaseous) + SiO₂ (spontaneous reaction under vacuum at 1150-1250℃);
Auxiliary reaction: CaO + SiO₂ → CaSiO₃ (the generated calcium silicate can lower the melting point of the slag and promote separation);
(2) Quantitative Reduction Effect and Key Influencing Factors
Core effect data:
Under standard conditions (Si=75%, impurities meet standards, size 15-30mm), magnesium reduction efficiency reaches 85%-90%, magnesium recovery rate ≥80%, and 1.2-1.4 tons of special ferrosilicon are consumed per ton of magnesium;
Compared with ordinary ferrosilicon: Due to its lower impurities (Al≤1.0% vs. ordinary ferrosilicon Al≤1.5%), special ferrosilicon increases magnesium recovery rate by 5%-8% and reduces production cost per ton of magnesium. 300-500 RMB.
Key Influencing Factors:
Silicon Content: When Si < 72%, reduction efficiency decreases by 10%-15%, and the consumption of ferrosilicon per ton of magnesium increases by 0.2-0.3 tons; when Si > 78%, costs increase but reduction efficiency does not significantly improve.
Impact of Excessive Impurities:
Al > 1.0%: Al₂O₃ inclusions are formed, leading to increased slag viscosity and a 3%-5% decrease in magnesium recovery rate;
S > 0.02%: MgS is formed with magnesium, reducing the purity of the magnesium product (Mg purity drops from 99.9% to below 99.5%);
Ca > 2.0%: Excessive reaction with SiO₂ produces low-melting-point substances, corroding the reduction tank and shortening equipment lifespan by 30%.
Core Quality Standards for Ferrosilicon for Magnesium Production
(1) Composition Quality Standards
| Quality Indicator | Requirement Range | Core Impact |
| Silicon (Si) content | 72%-78% | Directly determines reduction efficiency and magnesium recovery rate |
| Aluminum (Al) content | ≤1.0% | Avoids increased slag viscosity, ensuring smooth reduction |
| Calcium (Ca) content | ≤2.0% | Controls slag composition, protecting the reduction vessel |
| Sulfur (S) content | ≤0.02% | Avoids MgS formation, ensuring magnesium purity |
| Phosphorus (P) content | ≤0.04% | Prevents magnesium product brittleness, improving quality |
| Titanium (Ti) content | ≤0.1% | Reduces side reactions, minimizing magnesium loss |
| Manganese (Mn) content | ≤0.3% | Avoids impacting magnesium's mechanical properties |
(2) Physical Quality Standards
Size Distribution:
10-50mm lumps (10-20mm 30%, 20-30mm 40%, 30-50mm 20%), ≤10mm or ≥50mm particles ≤10%, ensuring uniform contact with magnesium oxide particles;
Block Integrity:
Single block weight 50-500g, breakage rate ≤5%, avoiding dust generation during transportation and storage (dust reduces reaction contact efficiency and increases losses);
Moisture Content:
≤0.3%, preventing decomposition at high temperatures to generate H₂, leading to porosity defects in magnesium products.
Core Selection Principles
Composition Priority: Prioritize high-purity ferrosilicon alloy with 74%-76% Si and ≤0.8% Al to ensure reduction efficiency and magnesium quality;
Size Matching: Select 15-30mm for the Pidgeon process and 10-20mm for continuous processes to avoid efficiency reduction due to particle size mismatch;
Cost Balance: Reject "low-silicon, high-impurity" fesi (although the price is 10%-15% lower, the magnesium recovery rate decreases by 5%-8%, resulting in higher overall costs).
