Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Increase the Gold Purity (7 replies and 3 comments)

Bob Mathias
2 years ago
Bob Mathias 2 years ago

Please advice how can I increase the gold purity during smelting from sulphide ore, fluxes used are Borax (dehydrated), Silica, Soda ash and Potassium Nitrate. It is for smelting of EW sludge and I want to reduce the amount of silver and base metal to get above 90% gold purity.

John Koenig
2 years ago
John Koenig 2 years ago

To remove silver ( if not the refinery - whats the point of it?!) blow in chlorine gas. But really, why remove the silver? The dore is shipped to a refinery and they will complete the separation. What is the value of +90% Au in dore if it will be sold to a refinery?

Bob Mathias
2 years ago
Bob Mathias 2 years ago

It is not to remove silver completely but to reduce the amount of it in dore at least 10% Ag and 2% base metal to be contained in dore. Actually we are facing problem of a dore containing high amount of Ag and we're trying to reduce it to increase %Au. What is % Au and % Ag exactly required in dore?

John Koenig
2 years ago
John Koenig 2 years ago

I have shipped dore with 97% silver, 2% gold and 1% base and 93% gold and 7% silver. There are more important things to worry about than lowering the silver content of the dore. Ship the dore to a refinery and let them handle it.

Bob Mathias
2 years ago
Bob Mathias 2 years ago

How did you consider the fluxes ratio to get 97% Ag and 93% Au?

Most of gold mine in my country they want high fines of the gold especially small scale mines because it has more value than Ag and base metal. Please can we share other important things you know on what to do and do not during smelting.

John Koenig
2 years ago
John Koenig 2 years ago

Ok, I can understand the high gold purity if the dore will not be shipped to a refinery. The process you would use is the Miller process. This process involves the use of chlorine gas and can be dangerous. The chlorine gas is blown into the dore melt. The silver and copper will form chlorides and float to the surface. The chlorides are scrapped off the melt. I would suggest a cover of borax during the melt. Once the purple of gold chloride gas forms, turn off the chlorine gas. The silver chloride can be melted with borax and soda ash and flour as a reducing agent. Send a private note with your email and I will send additional information.

The flux calculation I use is to remove base metals into the slag. Trying to move silver into the slag will increase the loass of gold into the slag.

Collin Amonde
1 year ago

Hi, John

I am also interested to see your flux calculation

David
1 year ago

Hello Collin, I have not heard from John in a while... but you may find what you need in looking at https://www.911metallurgist.com/blog/flux and https://www.911metallurgist.com/blog/fluxing-and-smelting-silver-ore

Alan Carter
2 years ago
Alan Carter 2 years ago

It would be nice to see your flux calculation for me too. If you only want a relatively modest amount of dore improved, add silver in 7 to 1 proportion to your molten metal (same as used in fire assay parting) then by granulating poring the molten mix into copiously amount water. Then digest the granulate by Nitric acid. Wash gold residue and re smelt for up to 99% gold purity un less any other precious metals are present in significant amounts. Silver is easily recovered as silver chloride by adding HCl and filtering off. If interesteded I can also advise on recovery high puritive Silver. The above procedure have been by me as as all other comments I offer.

vijay
1 year ago

nice advice

Bob Mathias
2 years ago
Bob Mathias 2 years ago

Thanks for your good advice.

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