Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

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Refining to 999.9% with smooth finish on GOLD bullion (2 replies)

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platinum01786
1 year ago
platinum01786 1 year ago

I Currently have an aqua regia refining plant from italy which refines 15kg Gold at a time.
after our refining process we notice that the gold we refine is normally between 999.6-999.9
however the final surface of the gold has rough edges and has a dull surface area after melting.we are looking for the shiny gold surface which is to be expected on pure gold.
we have tried changing the following variables but have had no luck:
- stop adding metabisulfate at 500mv  to ensure no precipitation of platinum group metals
- ensuring input material is below 5% silver
-Refining material Twice using aqua regia
- using 32% HCL, and 60% nitric. in 0.9L per KG Nitric and 3 Litres per KG HCL 1:3 Ratio
- we also tried using 36% hCL and 68% nitric this made it worse
- wash with HCL after perciptating the powder
- wash with HCL then with hot water 3 times .
- Melt into distilled water for granulation
- Melting the precipitated powder using a vacuum casting machine
- We tried then refining using Electrolysis after aqua regia also no luck

Now we have exhausted all options how do i make it frost free and completely shiny

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Wieslaw Wodecki
1 year ago
Wieslaw Wodecki 1 year ago

Proszek Au po redukcji i trawieniu HCl , wypłukaniu wodą zalać 5 - 10% NH4OH. Następnie dokładnie wypłukać wodą przed granulowaniem.

Prawdopodobnie zmatowienia mogą być spowodowane AgCl który rozpuszcza się w nadmiarze HCl

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Wieslaw Wodecki
11 months ago
Wieslaw Wodecki 11 months ago

Au powder after reduction and digestion with HCl, rinsing with water, pour 5 - 10% NH4OH. Then rinse thoroughly with water before granulating.

Probably the fogging can be due to AgCl which is dissolved in excess HCl.

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