Chemistry questions help

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[Amith0424]

Step 1: Beneficiation (removing silica, SiO₂)​

• Acid leaching method: Treat crushed dolomite with dilute HCl or H₂SO₄.
  • Reaction:
    CaCO3+2HCl→CaCl2+CO2↑+H2OCaCO₃ + 2HCl \rightarrow CaCl₂ + CO₂↑ + H₂OCaCO3+2HCl→CaCl2+CO2↑+H2O MgCO3+2HCl→MgCl2+CO2↑+H2OMgCO₃ + 2HCl \rightarrow MgCl₂ + CO₂↑ + H₂OMgCO3+2HCl→MgCl2+CO2↑+H2O
  • Silica (SiO₂) does not dissolve, so it can be filtered out.
  • Result: solution of MgCl₂ + CaCl₂.

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Step 2: Separate Ca and Mg​

• Selective precipitation:
  Add NaOH or NH₄OH.
  • Mg²⁺ → Mg(OH)₂ (precipitates at higher pH).
  • Ca²⁺ precipitates as Ca(OH)₂ only at very high pH, so with careful control, Mg can be separated.
• Another method: Add sodium carbonate (Na₂CO₃) to selectively precipitate CaCO₃ first, leaving Mg²⁺ in solution as MgCl₂.

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Step 3: Produce Magnesium Compound​

• From the Mg-rich solution, you can get:
  • Mg(OH)₂ (by precipitation with alkali).
  • MgO (calcining Mg(OH)₂ at ~1000 °C).
  • MgCl₂ (by evaporating solution).

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Step 4: Extract Mg Metal (if you want pure magnesium)​

Two main industrial routes:

1. Thermal reduction (Pidgeon process)
   • Start with calcined dolomite (CaO·MgO mixture).
   • Mix with ferrosilicon, heat in vacuum ~1200–1250 °C.
   • Reaction:
     2MgO+2CaO+Si(Fe)→2Mg(g)+Ca2SiO42MgO + 2CaO + Si(Fe) \rightarrow 2Mg(g) + Ca₂SiO₄2MgO+2CaO+Si(Fe)→2Mg(g)+Ca2SiO4
   • Magnesium vapor is condensed into solid metal.
2. Electrolysis of MgCl₂
   • From solution or molten salt (with added NaCl/KCl to lower melting point).
   • Electrolysis gives:
     • Cathode: Mg²⁺ → Mg (metal).
     • Anode: Cl⁻ → Cl₂ (gas).

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Summary:

• Crush → acid leach → remove SiO₂ → separate Mg²⁺ from Ca²⁺ → make Mg compound (Mg(OH)₂, MgO, or MgCl₂).
• For metal magnesium, use Pidgeon process or electrolysis of MgCl₂.