Processing dolomite (CaMg(CO₃)₂) to produce calcium carbonate (CaCO₃) involves separating the magnesium (Mg) component from the calcium (Ca) component. Here are the key methods used:
1. Calcination & Carbonation Method
This is the most common industrial approach:
– Step 1: Calcination
Dolomite is heated at high temperatures (700–1000°C) to decompose it into calcium oxide (CaO), magnesium oxide (MgO), and CO₂:
\[
\text{CaMg(CO}_3\text{)}_2 \rightarrow \text{CaO} + \text{MgO} + 2\text{CO}_2
\]
– Step 2: Hydration & Separation
The calcined product is mixed with water to form a slurry. Magnesium hydroxide (Mg(OH)₂) dissolves more readily than calcium hydroxide (Ca(OH)₂), allowing selective leaching.
– Step 3: Carbonation
The remaining Ca(OH)₂ is reacted with CO₂ to precipitate pure CaCO₃:
\[
\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}
\]
2. Acid Leaching Method
– Dolomite is treated with a weak acid (e.g., acetic or hydrochloric acid), selectively dissolving Mg while leaving CaCO₃ behind.
– The reaction with HCl:
\[
\text{CaMg(CO}_3\text{)}_2 + 4\text{HCl} \rightarrow \text{CaCl}_2 + \text{MgCl}_2 + 2\text{H}_2\text{O} + 2\text{CO}_2
\]
– The solution is then treated to precipitate CaCO₃ by adding sodium carbonate (Na₂CO₃):
\[
\text{CaCl}_2 + \text{Na}_2\text{CO}_3 \rightarrow \text{CaCO}_3 + 2\text{NaCl}
\]
3. Selective Precipitation Using CO₂
– Dolomite is partially dissolved in water, and CO₂ is bubbled through the solutio.jpg)
– Mg remains in solution as Mg(HCO₃)₂, while Ca precipitates as CaCO₃.