plating, anodizing, & finishing Q&As since 1989
Trying to recover gold but the orange precipitate explodes as I try to melt it?
June 10, 2010
I have neutralized Aqua Regia solution containing gold with Liquor Ammonia solution ( 25% 0.91 pure)? After adding Ammonia to solution, I got orange ppt. Now to melt it into fine solid form I find troubles, as it explodes. please suggests me , how can I get back gold in solid form from precipitate. please also suggest me any neutralizing agent for Aqua regia solution, so that I could directly furnace( melt) the precipitate into solid gold form. Thank you sir.Mustafa Kantawala
plating shop - Surat, Gujarat, India
Ok...that is funny. A little knowledge is a dangerous thing.
I think the product of the reaction is ammonium nitrate. Good thing you didn't add some diesel fuel to it before you gave the reaction energy (heat). I bet it popped pretty good.
electroplater - Galva, Illinois
You are lucky man-Never try to mix any precious metal solution and ammonia,all that compounds are explosive and very dangerous!I think that simplest way is to slowly evaporate aqua regia solution(very thick sirupy liquid must be result),then mix it with borax and melt.From internet archive website you can download old goldsmith handbook by George Gee(free,000 $)-there you can find good chapter on that subject.Hope it helps and good luck!
- Cerovski vrh Croatia
George Gee:Recovering precious metals from waste
- Cerovski vrh Croatia
Hi Mustafa, I'm Bhupesh Mulik working as refining officer in jewellery company. you neutralised gold dissolved solution of aqua regia using urea.dont use ammonia.than add ferrous sulphate to precipitate gold.Bhupesh Mulik
- Mumbai, India
June 15, 2010
Under favorable conditions, by using ammonia, you could have produced the very explosive fulminate of gold, which can explode from mild shock. Before doing anything, I would read up on this compound on the internet. I think you can re-acidify it, but I would try to rig up a way to do this at-a-distance, outdoors, in an unpopulated area. Keep ammonia away from gold or silver solutions unless you really know what you are doing.
Next time, do things right. After dissolving gold in aqua regia, most people will have a excess of nitric acid in the solution. This must be eliminated before the gold can be precipitated. There are several ways to do this. You can evaporate the solution down to a syrup, dilute 3 times the volume with water, filter out the silver chloride and junk, and then precipitate the gold. Another way is to add small amounts of urea to the aqua regia until the pH is 1. The best way is to not use an excess of nitric to start with.
Besides ferrous sulfate, the most common precipitants for the gold are mainly the sulfite chemicals - sodium sulfite, sodium metabisulfite, or sodium bisulfite. Use these under a fume hood, since SO2 gas will be produced. You can also bubble SO2 gas through the solution. Ferrous sulfate is safer to use, since no fumes are released.
Before doing any more refining, I would strongly suggest reading "Refining Precious Metals Wastes", by C.M. Hoke. Although written in 1940, it is still, by far, the best book for learning how to refine jewelry scrap of all sorts. She primarily uses ferrous sulfate as the gold precipitant.
- Nevada, Missouri, USA
June 16, 2010
Thank you everybody for the suggestions, and now on I will be careful with Ammonia.
Now I still have the orange ppt is the same form which I cannot melt, so what to do with it now ?
- Surat, Gujarat, India