This guide outlines a standardized gold extraction protocol using aqua regia dissolution and reduction methods, optimized for clarity and operational efficiency.

Step 1: Dissolution of Impure Gold

• Objective: Solubilize gold from ore using aqua regia.
• Conditions:
  • Conduct in a well-ventilated fume hood (critical for safety).
  • Mix 3 parts hydrochloric acid (HCl) and 1 part nitric acid (HNO₃) to form aqua regia.
• Procedure:
  1. Place impure gold in a beaker; add aqua regia slowly to control exothermic reaction.
  2. After reaction subsides, heat the mixture to evaporate until ~1/5 of original volume remains (ensures complete dissolution).
  3. Add concentrated HCl in 3–4 aliquots (max amount = nitric acid in aqua regia) to expel free nitric acid (stop when no reddish-brown NO₂ gas evolves).
  4. Cool, filter to remove insoluble solids, and dilute with distilled water to ~50 g/L gold concentration.

Step 2: Gold Reduction (Precipitation)

• Objective: Convert dissolved gold ions (Au³⁺) to elemental gold (Au⁰).
• Conditions:
  • Maintain solution temperature at 30–40°C.
  • Use 150 g/L sodium bisulfite (NaHSO₃) solution as reducing agent.
• Procedure:
  1. Stir solution vigorously while rapidly adding NaHSO₃ until:
     • Gold powder fully precipitates (solution becomes colorless and clear).
     • pH is neutralized (test with pH paper; match local water pH).
  2. Decant supernatant; wash precipitated gold with boiling water until washings are colorless.

Step 3: Purification of Gold Powder

• Objective: Remove adsorbed impurities (e.g., iron compounds).
• Procedure:
  1. Stir gold powder with 15% hydrochloric acid for 5 minutes to dissolve contaminants.
  2. Decant acid carefully (avoid losing gold); repeat washing until effluent is colorless.
  3. Filter residue to obtain sponge gold (high-purity intermediate).

Step 4: Smelting to Refined Gold

• Objective: Convert sponge gold to 99.9% pure gold via smelting.
• Conditions:
  • Use a crucible with borax (flux) to remove oxides.
  • Heat with a musket furnace (or equivalent high-temperature source).
• Outcome: Solid gold ingot with ≥99.9% purity.

Essential Chemicals and Tools for Gold Extraction

For bulk procurement of reagents (e.g., nitric acid, sodium bisulfite) or specialized equipment, reach out to our team for tailored mining solutions.