Refining of Gold from Mines

[nickvc]

4metals I agree about the OP been in a fairly lucky position with their materials but I would still want to know every last trace of values were been recovered and that the incoming weight and the final weght recovered were within the correct expectations.
Running a successful refinery needs constant attention and professional attitude letting anything slip will allow discrepancies to be made by employees if they so decide.

 

[4metals]

Nick,

Not sure I would call it luck that they are in the position they are in, they set up a buying operation, managed it well, and obviously were able to set up a refinery to process the material themselves based on their profitability.

But I agree, every refiner needs to be certain that their operation is running within their own defined and acceptable parameters. The numbers don't lie, and if you see the numbers slipping, the ability to go into the plant and start asking questions from an informed perspective will generate respect from your employees. Being aware of your losses and sharing that awareness with your staff makes anyone thinking of stealing think twice. (Share the awareness, not your techniques!)

As many people smarter than me have noticed, gold makes people do weird things!

 

[ashapura refinery]

Very sorry for replying back so late. The entire process is finally over, including the cleaning of pipes, filter bags, etc and the balance quantity (loss) now comes up to 28gms. The leftover solutions have been checked with stannous chloride for gold and nothing was found.

However we were happy with the gold bars as their finishing was really good compared to the older times.

Hopefully our next batch will have much lesser losses, but before we go for the next batch, we are going to make sure we have the right chemist and right stuff in hand.

We will keep you all posted and a very very big thank you to each one of you for helping us through and making us understand where we had been going wrong so far.

Will definitely come back with some good news on starting again ... :lol:

 

[artart47]

Hi Friends!
Following this thread has been so interesting! I'm amazed at the expertise and problem solving abilities that some of our members have, ( 4metals,lou ...) This is an example of how full co-operation can achive great results that benefit everyone involved. As a newb working with mason jars, Goodwill stainless and Home depot chemicals, it's nice to have great teachers!
Good luck with your refinery and hope you prosper!
artart47

 

[sugianto]

I think I will start small and do it as simple as possible.
Many knowledge acquired from reading this.

 

[nikhil1300]

We are also refining gold from mine using Aqua Regia process but the final product is not satisfactory,posting pic....we are getting some kind of crystal formation on the final gold bar 999/995 .How to avoid this.We are melting in inert atmosphere induction melting .

 

[Geo]

I am by far the least qualified to help with this but from everything I have ever seen, it looks like gas bubbles escaping as the metal cools.

 

[4metals]

The OP from Ashapura refinery posted the details of her process and equipment. As a result we were able to help her solve her issues and, as you can see from reading the entire thread, the entire process benefitted from our assistance.

In order for us to help you we will need to know the details of both your refining process and your melt process. Without specifics we can only guess, you are the eyes on site so you need to help us if you would like us to help you.

 

[nikhil1300]

1)Once we get the dore bar from the mines we melting the Dore bar in the induction melting furnace and take a dip sample.
2) Assaying of the gold is done through fire assay method and X-ray method.
3) The Dore bars are then re melted for making the grains in the induction melting furnace.
4) The grains are then put in the mixing reactor (titanium vessels with steerer and suction into Scrubber)
5) We then added Nitric Acid 10 lts and HCL - 30 Ltrs for every 12kg of dore gold 93% Au 6%Ag 1%cu
6) After the completion of the aqua regia process,we add sulfuric acid for lead precipitation
7 ) Then we filtered the aqua regia solution and removed the silver chloride and then in the gold chloride we added Urea ash to kill the excess Nitric Acid. Then we added sodium metabisulfite for precipitation of gold and chk with stannous chloride for any gold left in the solution,wash the gold power with hot distilled water 3 to 4 times till the ph comes to 7,filtered the fine gold powder. We dry the gold in steel vessels under the flame, then the power is melted in gas furnace to make a bar(approx 8kg each)
8) These bars are rolled blanked and then melted in Induction melting to make 1kg bars
9 ) The washing solution is then stored in the pvc tanks (200 Ltrs)

 

[nikhil1300]

few picture of our unit and process

 

[nikhil1300]

gold power 999 melting in gas furnace

 

[Lou]

Ok. We will get to it.

Quick question--how do you assay for the final purity?

 

[rickbb]

While there is appeal in visiting far off exotic places all in the name of employment, .

My current employment requires me to visit far off exotic places from time to time and I can tell you, it's not that great. 1 place out of 10 is ok, 1 out of 100 is really nice and I'm glad to be there. The rest, lets just say, not so much.

 

[4metals]

Two things jump out in my mind, first is the surface appearance of the molten gold in the gas furnace. Refined gold should have no flux on it, you didn't say if the melt was fluxed but usually refined gold reflects like a mirror with no streaks or haze on the surface of the pool. yours appears to either not be fully melted yet or to have flux on the surface. The first bar picture you posted also has the appearance of a faint green borax flux residue.

Second is the quantity of gold doré you are digesting and the amount of acid you are using. The rule of thumb is for every 7.5 ounces of metal you start with you need 1 liter of Aqua regia. You used considerably less acid than that, and you stated that your refined gold bar is roughly 8 kg. Well 93% (your gold assay) times 12 (your starting weight of doré) should yield 11.16 kg. So, can you please post a few photo's for us to see.

First I would like to see the aqua regia before you add urea or drop the gold. It should be a bright red with white like snow silver chloride settled on the bottom.
Second, I would like to see the insolubles. (the silver chloride when it is filtered out) These should be smooth and white with no chunks as they pour on to the filter.
and Third, I would like to see the result of your stannous chloride test on the paper or spot plate.

Your method, as stated, will not produce gold of .9999 purity.

 

[g_axelsson]

Impressive plant, as an amateur I can only dream of working with equipment as yours.

I noticed two things about your process though.
1. Before filtering off the silver chloride, add a bit of sulfuric acid to eliminate any lead present.
2. Washing seems to lack a few steps. If there is a drag down of copper chloride and silver chloride, pure water have a hard time to remove it. A boil in HCl removes any copper traces and some silver chloride too.

You got an XRF system, does it show any traces in the finished bar? Is it possible to analyze a spot just at the crystal formation? What is the main contamination in the finished bar?

Göran

 

[4metals]

The most likely impurity, based on the stated assay of the feed doré, is silver. Dilution and chilling of the solution before filtration will go a long way to increase purity by simply enhancing the natural insolubility of the silver chloride in the loaded aqua regia.

With the concentration of copper at or below 1% in the feed, unless an awful lot of sodium metabisulfite was added the chances of copper chloride dropping out is slim. SO₂ would be my choice to reduce the gold as well.

 

[nikhil1300]

Impressive plant, as an amateur I can only dream of working with equipment as yours.

I noticed two things about your process though.
1. Before filtering off the silver chloride, add a bit of sulfuric acid to eliminate any lead present.
2. Washing seems to lack a few steps. If there is a drag down of copper chloride and silver chloride, pure water have a hard time to remove it. A boil in HCl removes any copper traces and some silver chloride too.

You got an XRF system, does it show any traces in the finished bar? Is it possible to analyze a spot just at the crystal formation? What is the main contamination in the finished bar?

Göran

Thank you very much,we are adding sulfuric acid after dissolution of gold and also washing the gold with Hcl,the xrf shows Gold 999 if the lazer is pointed on the crystal formation.

 

[nikhil1300]

The most likely impurity, based on the stated assay of the feed doré, is silver. Dilution and chilling of the solution before filtration will go a long way to increase purity by simply enhancing the natural insolubility of the silver chloride in the loaded aqua regia.

With the concentration of copper at or below 1% in the feed, unless an awful lot of sodium metabisulfite was added the chances of copper chloride dropping out is slim. SO₂ would be my choice to reduce the gold as well.

Getting SO2 gas is very difficult in India there most of them use Sodium Metabisulfite
We wash the gold powder with hot distilled water just in case if we have added excess of sodium metabisulfite so it gets dissolved in hot water.

 

[butcher]

Maybe you can just build yourself an SO2 generator.

 

[nikhil1300]

Maybe you can just build yourself an SO2 generator.

can you share details about the SO2 generator drawing technical details etc