Process Flow for Producing Calcium Carbonate from Dolomite
Introduction
Dolomite, a calcium magnesium carbonate mineral (CaMg(CO3)2), serves as a crucial raw material for producing high-purity calcium carbonate (CaCO3) through specialized processing techniques. This article details the comprehensive process flow for transforming raw dolomite into refined calcium carbonate products, emphasizing critical stages such as calcination, hydration, carbonation, and grinding. The selection of efficient processing equipment is vital for achieving desired product quality and operational economics. We will explore how advanced milling technology, particularly our SCM Ultrafine Mill, optimizes this production chain.
Raw Material Preparation
The process begins with the mining and primary crushing of dolomite ore. The raw dolomite is first crushed using jaw crushers or hammer mills to reduce its size to below 50mm, facilitating subsequent handling and processing. This stage may include washing to remove impurities like clay or silica.
Calcination Process
Calcination is a thermal treatment process where crushed dolomite is heated in a rotary kiln or shaft furnace at temperatures ranging from 900°C to 1100°C. This process decomposes dolomite into calcium oxide (CaO), magnesium oxide (MgO), and carbon dioxide (CO2):
CaMg(CO3)2 → CaO + MgO + 2CO2
The resulting mixture, often called “dolime,” is then cooled and prepared for the next stage. Efficient calcination requires precise temperature control to ensure complete decomposition while minimizing energy consumption.
Hydration and Slaking
The calcined product (CaO + MgO) is mixed with water in a hydrator or slaker. This exothermic reaction produces calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2):
CaO + H2O → Ca(OH)2
MgO + H2O → Mg(OH)2
The hydration process is carefully controlled to achieve a slurry of consistent viscosity and particle size. The resulting milk-of-lime slurry is then screened to remove any unreacted particles or impurities.
Carbonation Reaction
The carbonation stage is where calcium carbonate is precipitated. The hydrated slurry is transferred to a carbonation tank, and carbon dioxide gas (often recovered from the calcination stage) is bubbled through it under controlled conditions of temperature and pressure. The primary reaction is:
Ca(OH)2 + CO2 → CaCO3 + H2O
This reaction precipitates fine particles of calcium carbonate. The process parameters, such as CO2 flow rate, temperature, and agitation speed, are critical for determining the final particle size, morphology, and brightness of the CaCO3 product. The magnesium hydroxide typically remains as a by-product and can be separated if needed.
Filtration and Drying
The precipitated calcium carbonate slurry is then fed into filter presses or rotary vacuum filters to remove excess water. The filter cake, with a moisture content of around 10-20%, is subsequently dried in rotary dryers or flash dryers to reduce moisture to less than 0.5%. Drying conditions must be optimized to prevent agglomeration and preserve the particle size distribution achieved during precipitation.
Grinding and Classification
The dried calcium carbonate cake often requires further size reduction to meet specific market requirements for fineness and particle size distribution (PSD). This is where advanced grinding technology becomes indispensable. For producing high-value, ultra-fine calcium carbonate grades, our SCM Ultrafine Mill is exceptionally well-suited.
This mill is engineered to handle the brittle nature of calcium carbonate efficiently. Its vertical turbine classification system ensures precise cuts without coarse particle contamination, delivering consistent product quality. With an output fineness range of 325-2500 mesh (D97 ≤ 5μm) and a capacity of up to 25 tons per hour (depending on the model, e.g., SCM1680), it significantly outperforms traditional grinding systems. Key advantages for CaCO3 production include:
- Energy Efficiency: Consumes 30% less energy compared to jet mills while offering double the output capacity.
- Precision Grinding: Intelligent control systems automatically adjust operational parameters to maintain the target fineness (D97).
- Durability: Specially hardened grinding rollers and rings ensure extended service life when processing abrasive materials like CaCO3.
- Environmental Compliance: Integrated pulse dust collector ensures emissions are well below international standards, and the low-noise design (<75dB) promotes a better working environment.
The ground product is then classified using air classifiers to ensure the final product meets the exact customer specifications for top-cut particle size.
Surface Treatment (Optional)
For specialized applications in plastics, paints, or coatings, the calcium carbonate may undergo surface modification. This involves coating the particles with stearic acid or other coupling agents in a high-speed mixer to improve compatibility with organic matrices and enhance dispersion.
Packaging and Storage
The final calcium carbonate product, whether untreated or surface-treated, is conveyed to automated packaging systems. It is packed in 25kg bags, big bags (1 ton), or stored in silos for bulk shipment. Proper packaging is essential to prevent moisture absorption and contamination.
Conclusion
The production of calcium carbonate from dolomite is a multi-stage chemical and mechanical process that demands precision and efficiency at every step. From calcination and carbonation to the critical final grinding stage, the choice of technology directly impacts product quality, operational cost, and environmental footprint. Integrating high-performance equipment like our SCM Ultrafine Mill into the process flow ensures the production of consistent, high-purity ultra-fine calcium carbonate that meets the stringent demands of modern industries. For larger capacity requirements or coarser grinding stages, our MTW Series Trapezium Mill, with its robust construction and high transmission efficiency, also presents an excellent solution for intermediate size reduction tasks within this flow.
