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Extracting gold from copper

Q. My name is Tommy. I just got a job at a train yard, we move a lot of copper concentrate through our yard which inevitably spills here and there. Someone at work told me that the concentrate (a granular substance) is copper that has just been taken from the mine and has yet to be refined. They also told me that a percentage of it is gold. How would you get the gold out of the concentrate?

Tommy A. [last name deleted for privacy by Editor] transportation - Arizona, USA

A. Please question your assumptions -- especially when starting a new job! It is NOT inevitable that copper concentrate spills into the ground, and it's probably not acceptable either. Keep stuffing the suggestion box with ideas until the problem is solved.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Dissolve all with aqua regia, then ppt out the copper with NaCl, then filter out the copper chloride and then ppt out the gold as pure with sodium metabisulfite mixed with water. Filter the gold fines and smelt.

You could try dissolution in Nitric acid and that leaves the residue as gold. With excessive Cu, there is a lot of acid gas , brown and irritating so be careful.

Dr Malcolm Mudge
- Perth, Western Australia

Q. Hi sir. I want to know if aqua regia process is applicable to extract gold from the mixture of nickel and copper? Or what is the best way to separate gold from these metals?

Anosha and ali
research worker - Karachi, Pakistan
July 9, 2012

Q. My ore has three metals: gold, copper and iron as a highest concentrate. I tried to extract gold, didn't work out. I prepared hydrochloric acid, sodium hypochlorite solution (bleach), ratio of 2 to 1. After 4 hours added smb expecting precipitation . Where am I going wrong?

Aswell Makando
- Lusaka, Zambia
June 22, 2020

A. Go with nitric acid which will put everything into solution but the gold and you can skip the aqua regia unless you're seeking to refine it to a high purity; but if you're just trying to get rid of your base Metals nitric acid will do that leaving gold untouched and ready to be melted into a button.
Make sure you dispose of the metal Laden nitric acid properly though; put it in a bucket (called a stock pot) dilute it with an equal amount of water and add some iron (piece of angle iron or anything like that) and copper will cement out of solution onto the iron any other metals you have in solution can be dropped using aluminum or zinc so have a few beers and toss the empties in the bucket or toss an old aluminum heat sink from a PC in with it and let it sit somewhere with a lid on it for a month or so and you can even skip the iron if you're not looking to recover the copper then filter that through an old t-shirt or something leaving just the liquid waste that can be neutralized with something like sodium hydroxide (lye) to neutralize the acid to somewhere around pH of 7 so it's not a hazard and then Google can give you the location of your local potentially hazardous materials disposal facility where they'll know what to do with it.

Robert E Lee
- Lakeland Florida
August 24, 2023

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