Other TYPICAL Purification method of GOLD
Dissolve gold scrap into to aqua regia solution and heat the solution slowly, do not boil. Leave the solution at least 1 hrs then Extra nitric of the gold solution can be neutralized with urea addition till the point where the urea does not react any more. Then use Na2SO4 ( sodium metabisulphite ) is better for dropping the gold (free electrons greater reactivity). Rest solution 24 hours. Then filter precipitate.
Or you can use ferrous sulphate in place of Sodium metsabisulphite. Second, for neutralisation you add urea and add zinc dust to reduce all metals.
Method Precipitate the GOLD with sodium metabisulfite/ zinc :
Recover gold from Filings, Setting, Waste water, Consumables used in production, Emery papers, and sweeps from the production floors then dissolve into aqua Regia solution, Let it work 1 night or simply heat it up for a while to shortened the process and on filtration precipitate it. Filter the solution and neutralize it with Urea or just heat it up until all of the nitric vaporized. Watch out not to lose any precious metal during the heating. Test the pH. Precipitate gold using sodium metabisulfite / ferrous sulphate / zinc.
Gold precipitate from aqua regia solution by using hydroquinone. It was so simple and attaining 99.99% purity after firing was an incredible delight.
Refining the silver chloride left over from the solution was a little more of a chore but I got to within 80%.
Method to precipitate the Gold with Hydrazine Hydrate :
Recovere all gold from working area then dissolve all into Aqua Regia Solution. Leave this solution for 10 -12 hrs to complete precipitation, then Filter it out. And addition of Hydrazine hydrate 64 or 85% (liquid) works well to precipitate gold from acid gold plating baths which contain HAuCl4 solution.
After addition of Hydrazine Hydrate you can practically see big brown spongy ball like gold getting precipitated & once all the gold in the solution has precipitated the solution at the top has lot of white foam, which indicates the end of precipitation. Finally neutralise the solution with 25% urea solution.
This will give you the necessary result in recovering pure gold.
We let the solution stand overnight to settle down & recover gold from it by washing it with water.
Hydrazine Hydrate also used in GOLD purifiaction faxctory. Remember Hydrazine Hydrate does not work well with alkaline solution.
NOTE : You use hydrazine hydrate for gold precipitation. Don't add urea in gold chloride solution.
You can also dilute hydrazine hydrate with five parts of water, that is 1:5. Then you add it in your gold chloride solution. You can get exact value by checking your pH level of gold chloride.
Hydrazine Hydrate Reaction can be easily understand by this reaction :::
Aqua Regia : 3 HCL+1 Nitric Acid.