Calcium Oxide[4]
Overview
Calcium oxide (CaO), produced by thermal decomposition of limestone (calcium carbonate), is a fundamental industrial chemical with centuries of use. Its high reactivity with water and strong alkalinity make it indispensable across multiple sectors, from metallurgy to environmental remediation. Modern production typically involves kiln calcination at 900–1200°C to drive off carbon dioxide. As a key intermediate in lime cycles, CaO readily converts to calcium hydroxide (slaked lime) upon hydration. This transformative property underpins its role in pH adjustment, waste treatment, and construction chemistry. Industrial-grade material often contains minor impurities like silica or magnesium oxide, depending on the source limestone.
Physical and Chemical Properties
Calcium oxide appears as a white, odorless solid with a cubic crystal structure in its pure form. It exhibits extreme hygroscopicity, rapidly absorbing atmospheric moisture to form calcium hydroxide. The exothermic reaction with water releases approximately 63 kJ/mol of heat, requiring careful handling to prevent thermal burns or steam explosions. With a Mohs hardness of 3.5 and melting point exceeding 2500°C, CaO maintains stability under high-temperature industrial processes. Its basic nature (pH ~12.5 in solution) enables acid neutralization, while the refractory properties suit furnace linings. Notably, it reacts with acidic oxides (e.g., SiO₂) to form slag phases in metallurgy.
Main Applications
In steelmaking, calcium oxide serves as a flux to remove impurities (phosphorus, sulfur) by forming slag. Approximately 50-100 kg of quicklime is consumed per ton of steel produced. The construction industry utilizes it in cement clinker production (60-65% of global demand), where it reacts with silicates to form calcium silicates. Environmental applications include flue gas desulfurization (FGD) to remove SO₂ emissions and wastewater treatment for heavy metal precipitation. Smaller-scale uses encompass soil stabilization, glass manufacturing, and as a desiccant in chemical processes. Emerging applications involve CO₂ capture through calcium looping cycles.
Safety and Storage
As a Category II alkaline corrosive substance, CaO requires stringent handling protocols. Workers must wear acid-resistant gloves, face shields, and dust masks to prevent contact with skin or inhalation of particles. Storage areas should be well-ventilated, dry, and separate from acids or organic materials. Bulk storage in silos requires humidity control below 50% RH to prevent premature slaking. Fire hazards exist when contacting water—small leaks can generate enough heat to ignite nearby combustibles. Spills should be contained with dry sand or vermiculite, never water. Transport typically follows UN1910 classification for corrosive solids.
B2B Procurement Guide
Industrial buyers should specify parameters like available lime (≥90%), reactivity (measured by slaking rate), and particle size distribution (80-150 mesh common). Packaging options range from 25kg moisture-proof bags to bulk tanker trucks for large consumers. Regional suppliers near limestone quarries often offer competitive pricing. Key procurement considerations include: verifying certificates of analysis for purity/contaminants, evaluating supplier capability for consistent large-volume delivery, and confirming compliance with local hazardous material regulations. Just-in-time delivery minimizes storage risks, while long-term contracts (1-3 years) typically secure better pricing in volatile markets.
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