China gold purification process

China gold purification process

            The gold purification process involves dissolving gold-bearing

materials in aqua regia (HNO₃:HCl =1:3), where gold reacts to form soluble

[AuCl₄]⁻ complexes, followed by filtration to separate insoluble residues.

                            Au+HNO₃+4HCl = HAuCl₄+NO↑+2H₂O

           In the gold purifying process, selective reduction is achieved through

a two-stage approach: Primary reduction employs sodium sulfite (Na₂SO₃) u

nder acidic conditions (pH 1-2) to generate SO₂ and H₂SO₃, which preferentially

reduce gold ions to 99.9% pure metallic gold while suppressing impurity precipitation.

                           Na₂SO₃ + 2HCl = 2NaCl + H2O + SO₂↑

                 2HAuCl₄+3SO₂+6H₂O = 2Au↓+ 8HCl + 3H₂SO₄

          The gold purifying concludes with thorough washing of the precipitated gold

powder. Sequential rinsing with 5% HCl removes adsorbed metal ions, followed by

deionized water to eliminate chloride residues. Vacuum drying at 80–100°C prevents

oxidation and maintains powder consistency. Finally, high-purity gold (≥99.99%) is

produced by induction melting under a borax flux to inhibit surface oxidation, yielding

market-ready ingots. Modern adaptations of this gold purification methodology

emphasize environmental sustainability through closed-loop gas recovery systems

(converting SO₂ to H₂SO₄) and effluent treatment for heavy metal removal, aligning

with industrial-scale efficiency and ecological compliance standards.

           This gold purifying method optimizes purity, efficiency, and environmental safety

through controlled pH, temperature, and closed-loop gas treatment systems.

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