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What are the chemical refining methods for gold

     

Answer: The chemical refining of gold mainly adopts processes including concentrated sulfuric acid boiling leaching, nitric acid silver parting, aqua regia gold parting, chlorination gold parting, and reduction with oxalic acid or sodium sulfite.

1、The concentrated sulfuric acid boiling leaching method uses concentrated sulfuric acid for long-term leaching and boiling at high temperatures. It converts base metals such as silver and copper in the alloy into sulfates for removal, so as to achieve the purpose of gold purification.

2、The nitric acid silver parting method features a fast reaction rate and high saturation concentration of silver in the solution. It is generally carried out under autothermal conditions (no heating is required, or heating can be applied at the later stage to accelerate dissolution), so it is widely used in industrial production.

3、The aqua regia gold parting method is suitable for refining crude gold with a silver content of less than 8%. During the process, gold dissolves into the solution, while silver forms silver chloride (AgCl) precipitate and is separated out. The platinum group metals (PGMs) contained in the solution are subsequently separated and recovered.

4、The feedstock for oxalic acid reduction refining is usually crude gold or crude gold powder obtained from the enrichment stage, and a gold grade of around 80% is sufficient. First, the crude gold powder is dissolved to transfer gold into the solution. After adjusting the acidity of the solution, oxalic acid is used as the reducing agent to reduce gold ions into pure sponge gold. Following acid pickling treatment, the sponge gold can be cast into gold ingots with a gold grade of over 99.9%.

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