Refining of Gold from Mines

[ashapura refinery]

@ 4Metal
The calculation for the sulfamic acid addition gives a clear idea thank you so much for that. I have noted it down. And what you said about employees well yes we just got a slight taste of it. And definitely learnt - Less Nitric Always.

Now the Sulphur Dioxide (No we have not given up either ) - In order to use sulphur dioxide gas we cannot use it right away here in the place where we are located. We need to inform The Pollution Control Board Department of our State that we will be using sulphur dioxide gas and they have to come and inspect our premises for this, to make sure that all the safety measures have been taken and that the entire process would be carried out properly provided that the neutralization of the fumes is done well before it is let out in open air. We have already informed the department. Once we get the green signal we will use this method.

@ Lou

Yes we did learn that patience is always important and in this particular process, to carry it out properly, less nitric is one of the keys.
As for the chemist no he has not worked at Kaloti, it was another refinery.

 

[Palladium]

I'm not a chemist by any means and don't understand all the chemistry involved, but I do think more water is your friend with smb.

Pull a 1 lt sample and dilute it by half after filtering and see if that helps. It won't take but a min to see! I'm a firm believer in water and smb. I used to have problems with my solutions wanting to redissolve when I added smb even though the nitric was neutralized. It was like when the nitrate ion left the gold for precipitation it would act with the smb to redissolve the gold because it didn't have a place to go. Not sure in chemistry terms how that would work, but I figured it was because there wasn't enough water to buffer the reaction. With more water I've learned I have less problems.

 

[Barren Realms 007]

Something that might you might want to consider adding to your process is a heating mantel for your reaction vessel to be used during your primary reaction. A warm or hot solution will utilize your nitric more and allow you to get closer to completely using all of the nitric in your solution. This would also aid in having a warm solution when adding the sulfamic acid to denox the solution.

I am not sure if this would help him or not in his process but I have been guilty at times of adding 32% hydrogen peroxide to my reaction vessel to give the nitric acid some added oxygen for the process and allow a more complete use of the nitric acid that is added. This should be commented on by Lou and the others before it is added because it might cause some problem that I am not aware of.

Another train of thought is that after he has added the sulfamic acid and the endothermic reaction has dropped the temperature of the solution. Not being sure of how much ice he is using at this point in his process to cool the solution to help remove the silver chloride from the solution, I will generally add enough ice to bring the temperature down in the solution to where the outside of the reaction vessel starts condensing the water vapor from the surrounding ambient air and sometimes even creates frost on the side of the vessel.

Another trick to consider that I use is I add crushed ice to my filtering vessel to keep the solution cold during filtering and I have found that I have better success at removing the silver chloride from the solution when doing this. I have found that sometimes but not always this will also trap the silver chloride in the ice and not allow it to clog the filter during the filtering process, but he has not stated he has a problem with this aspect of the procedure.

Another note to be added here is after that filtering is if he uses ice in the filtering vessel is that it gives him a super cooled solution in his precipitation vessel. This is an aid in one part in that when he adds his sodium metabisulphate to the solution is that it will allow more of the SO₂ gas to stay in the cold solution to precipitate the gold, and prevent some gassing off of the SO₂ gas out of the solution during the exothermic reaction that takes place from the precipitation of the gold out of solution. There is a drawback to doing this with a cold solution as well, if he reads enough on the forum he will find that ice is recommended by some in the precipitation vessel to counter react the exothermic reaction during the precipitation of the gold to allow better usage of the SO₂ gas created, if he gets over confident in doing this he can set up a scenario where he adds a lot of sodium metabisulphite solution to the vessel and as the temperature raises quickly that the SO₂ gas can try to gas off and cause a boil over reaction in the precipitation vessel.

Another point that needs to be addressed is that if he uses a large excess of sodium metabisuphite in the solution is that as the gold drops out of the solution it will trap SO₂ bubbles in the powder and as the solution warms up these bubbles will try to escape the powder and bring some of the gold up into the solution with them. I will generally boil my gold powder in water a couple of times to remove any excess SO₂ gas.

Another point to make is that during the denoxing of the gold chloride is that if he has not denoxed all of the excess nitric out of the solution he will have some minor carry over of nitric to his precipitation vessel and after he removes his precipitated gold from the vessel and then tries to wash it with hot HCl that he will have some of the gold go back into his washing solution. One way to counter react this is after the boils in water as mentioned in the paragraph above is to make sure the gold is in fine particles after the water boils and instead of going to an HCl wash is to go to an ammonia wash a couple of times to remove any traces of silver chloride and copper that might have gotten through the procedure.

Another tool he might want to consider putting in his arsenal is an infrared temperature reader to keep up with judging the temperatures of his reactions since glass is a good thermal conductor of temperature.

 

[Lou]

Frank, if the gold is gone out of the solution with sulfur dioxide and no more red NO_x is fumed off, the nitrates are gone.

One can safely wash the gold precipitate with muriatic if one has a quantitative precipitation and negative stannous.

Should mention that after stirring and the first negative stannous, give it some time to settle and when it's settled, then check again with stannous just to be sure.


Lou

 

[Barren Realms 007]

Yes I agree. About the only time I have had the gold go back into the solution is when I have left the gold powder on the hot plate in HCl over night. So I have learned not to leave it on the hot plate over night. 8)

 

[ashapura refinery]

We did the process again properly this time. I am sending the pictures of the left over solution after the precipitation.

Now we took a bit of the solution in a beaker and tested it with a little stannous chloride and this is what it looks like. There is some left over gold in the solution. Now how should we go about this? Should we be adding more SMB?

The drying of the fine gold powder, the melting and the assaying is still pending though so we yet do not know the exact amount pending.

And we have understood the need of a heating device for the mixing reactor. Will get it done as well so that next time we work with Sulfamic Acid we get the proper result.

 

[Palladium]

You should test before you filter the gold powder to make sure the drop is complete. That way you don't have to filter and drop it twice. You should test with stannous using a spot plate or a piece of paper. If it still tests positive add more smb until you get a negative reaction with stannous.

 

[Palladium]

[youtube]http://www.youtube.com/watch?v=Hz8odRIqtuQ[/youtube]

 

[Palladium]

Every time I see you add SnCl to liquid I cringe!

[youtube]http://www.youtube.com/watch?v=CGBrsfn0ouM[/youtube]

 

[4metals]

Ralph is right. Putting stannous chloride into your acid forms the colloid we spoke of earlier. It is so fine that in low concentrations it is difficult to even see. Using a spot plate, paper towel, or Q Tip wet with a few drops of solution and applying a single drop of stannous chloride test solution will detect less gold in solution. I prefer paper towels because they go with the burnable recoverable materials and you get your gold back down the line.

Please remember that stannous chloride goes bad. Faster if you do not add tin metal to the solution. Always keep a small volume of solution you know contains gold to test the solution when you get a negative test. It is an easy way to screw up and lose gold. Take a few milliliters (maybe 2) of gold dissolved in your reactor with the next lot and add about 20 ml of water and keep it in a vial so you have a sample to compare to.

Your acid after the drop is as clean as the Hydrochloric often is before we start refining! If this mining doré is the type of material you set up to refine, why did you buy a filter press? At the concentration of metals in the waste you have shown us, it will take thousands of treated gallons to fill the press with hydroxides. What other gold or silver material do you process?

 

[Palladium]

Silver Silver Silver !!! You're right 4metals with that waste stream after recovery of the silver he could use an evaporator in his waste process to concentrate the solutions. He could run a long time between waste treatments with a lot less trouble!

 

[Palladium]

http://www.chemteksys.com/Evaporators.html

 

[Palladium]

As for the recovery we have done so far:
1) We had used cpvc pipes earlier and we found fine gold particles in the pipes, we then removed these pipes and cleaned them out.

Where were these pipes located? Was it between precipitating vessels and settling vessels or after the settling vessels and before waste disposal?

 

[g_axelsson]

We did the process again properly this time. I am sending the pictures of the left over solution after the precipitation.

Now we took a bit of the solution in a beaker and tested it with a little stannous chloride and this is what it looks like. There is some left over gold in the solution. Now how should we go about this? Should we be adding more SMB?

That could be a false positive due to an excess of SMB. Correct me if I'm wrong as I've only worked with smaller lots, but the pale liquid after the drop and the brown color of the colloid after adding stannous to the liquid looks like a complete drop to me. Stannous reacts with a brown color on excess SO₂ or SMB.

And I agree with the others, your 100 ml test sample for stannous is as big as my larger lots. You only need drops of the liquid to do a test with stannous.

It will be nice to see the final yield of this lot, both in purity and quantity. I'm eagerly awaiting the results.

Göran

 

[4metals]

Ralph,

Waste treatment from acid refining never benefits much from atmospheric evaporators. The most concentrated you can get the acid is down to its azeotrope concentration so there is still a lot of volume you will not evaporate easily.

The other option is break the acid with caustic. In this case there is a lot of chloride in the waste and caustic adds a lot of sodium so the salt concentration is very high. The salt will clog the evaporator quickly.

As much as Shawn from Chem Tec would love to sell you an evaporator, they are made for electroplaters rinse waters where the majority of the waste is water. Chem Tec also makes a line of scrubbers, hoods and vacuum equipment specifically for refining http://www.goldrefiningequipment.com/Index.html

 

[kurtak]

This time we told our chemist that we are not going to use the Soda Ash procedure and will be using Sulfamic Acid and then precipitate by using only SMB. Apparently he was not very happy with this idea. Later in the evening he gave up saying I cannot do this process anymore and left.

ashapura

If your chemist was unable to understand &/or follow the instructions being passed on to you by Lou & 4metals you are better off with out him --- He was clearly taught wrong methods when it comes to refining ( I could not believe what I was reading when I first read the methods you were using they were so wrong) & does not want to accept that his methods are wrong & therefore is not open to learning what is right & what works

You are currently being advised by 2 of the very best in the world when it comes to large volume refining of PMs - about the only thing I can think of that would be better then getting this advise from them here on the forum - would be to actually "hire" 4metals to come over & do an actual on sight walk through of your operation (if he is willing to do so as that is what he does/did but I believe he is now retired &/or semi retired)

A heating mantle on your reaction vessel would be a good thing as that will help to drive the reaction of the acids to completion especially as the reaction nears the end which means you will use less nitric which in turn means less free nitric to de-NO_x

I have been following this thread with much interest & you are being "very well advised" by those commenting on your problems & if you follow what is being said you should start seeing much better results

Kurt

 

[justinhcase]

I agree, You may just find you precious metal leak has just walked out your door.
Big alarm bells when an employee throws his toys out of the pram for you improving your system.
Make a good offer to a refiner with a good reputation who you like and get on.
I can not take any one who suggests you try to run a lab with out heating vessels seriously.
Just

 

[Anonymous]

I agree with Kurt.

You'd be well advised to engage Lou or 4metals professionally, they really do understand what this is about and their fees would likely be recouped in short order. As others have mentioned I think you may have the wrong team around you and that is a road to nowhere. As a point of reference for you I also run a company which is over 18 years old and employ many people so I do understand business, and from my perspective you need to stop the problems right now or you could lose a lot of money and possibly all the investment.

Good luck, and take the good advice that has previously been given.

Jon

 

[4metals]

Gentlemen,

While there is appeal in visiting far off exotic places all in the name of employment, there would be little to gain on the part of forum members who rarely see this degree of detail in an operation like Ashapura's refinery.

I applaud Ashapura's willingness to share the details of his operation in order to get valuable advice to aid his company. Hopefully others will learn to give detailed descriptions and photos of their operations in order to get meaningful and helpful advice. Then the true spirit of the forum, Refiners helping refiners, can show through.

 

[ashapura refinery]

Firstly saying thank you will never be enough when it comes to the amount of help we have received. After reading everything and understanding things we have learnt a lot. As for the amount of money we have lost - we have no idea where to begin from. Today in the afternoon we were calculating on how much money we could have saved in doing the entire setup.

Coming to the process - we completed the batch how much ever we could. The washing of the refined powder was done well as per the instructions of Lou in our filtration vessel itself. There was no problem with that at all. Sadly everyone was so tired from working for hours continuously that we forgot to take pictures (Sorry about that.)
Now for the leftover solution - the pictures of which we had put up in our last post - we added SMB to a small batch of it but there was no reaction in that. Then we collected another small part of the solution in a beaker and added zinc to it and got black color.

For now we have kept that solution aside as it is. ( Pictures of the solution with SMB and with Zinc addition have been put up.)
Now for the purity - we dried the fine gold powder, melted a sample and did an assay and got the purity of 9992, the same as the previous batch. So yes the purity of the gold did come out to be good.

We next moved on to making a large bar and then making the grains of the bar and started the melting process for the Kilobars. This time we are moving on with 999.0 and not converting it to 995.0 as this was the request of the client.

Well the Bars are coming out to be good on the back (picture attached) but on the front (picture attached) we have these reddish spots which generally get removed by Hand Buffing and cleaning with sulphuric acid.

Tomorrow morning we will be marking these bars. Once done we will post pictures of the bars immediately.

Coming to the advice given for improvising:
Heating of the mixing reactor - As 4metal suggested - we will be contacting the company who supplied the glass equipments and check with them if they can take back the cylindrical vessels and provide us with a heating device for the mixing reactor. We will make arrangements for this at the earliest.

Other problems faced:
One small problem we faced during the Aqua regia process was that we had undissolved grains of approx. 302.00 gms. We had the stirring in the mixing reactor going on for nearly 4 hours. What we have noticed during the stirring process is that in the beginning the material starts dissolving very quickly but, like almost 80-85% gets dissolved easily but later the process slows down - is this because of too much of silver chloride being formed?

What other material we process:
We are getting the entire batch of dore gold from West Africa. We get it from one particular supplier in batches of 7-13 Kgs each batch and this dore generally contains gold, silver, copper and iron. Apart from this we do not process any other material at the refinery.

Apart from all this - one thing which is bothering us is that there are bigger refineries than ours in U.A.E wherein they follow the process which we had mentioned in the very beginning. And they say that their losses are way less as compared to ours. It's not like we do not want to go ahead with the method we followed now or anything of that sort. It is just something which we have been wondering about because the place from where they receive their material is also the same place from where we are receiving.

We talked about asking for consultancy by Lou or 4Metals today morning when we completed the process. So yes we will be contacting them to know their fees and the way to go about the entire thing.

And as 4metal said about sharing details, we can share every single detail we have no problems with that because we believe that learning has no end and as he mentioned that our details maybe helpful to the members of the forum – trust us we will be way more happy if anyone else can benefit from all the advice being given in this post.

Some more details about us:

When we decided on setting up this refinery in India (This is our first business in India) we consulted with our friend who is a chemical engineer and had previously helped in the setup of another refinery. We didn’t have 100% knowledge in the topic of refining but we did have some idea on how to go about it because we have previously worked with our friend and seen the process.

Our aim when setting this refinery was to make it one of India’s best refineries and also to reach the acceptance level of LBMA. India is a large consumer of gold and on a daily basis a lot of gold is being imported into the country. We had set this entire unit keeping large quantities in mind. Which is one of the reasons of having so many cylindrical vessels, a big tank for collection, a filter press etc.

But sometimes things do not work as planned, we had a lot of issues in setting up. A lot of delays took place and a lot of problems came as well but we worked our way through and then imported our very first batch. Now in the very first batch we had our friend who took care of the entire process with ease but there was a big loss, along with him we had an assayer who was excellent in assaying and did have some knowledge about refining but again not completely.

The losses remained unexplained and after that we did not get in touch with him, the assayer also left after a month because he was not able to adjust with the environment and also his knowledge in refining was less. We had done two batches of refining before he left.
We kept our search for a good chemist on and waited for sometime till we got somebody better. Upon recommendation we hired another chemist who was earlier in a good refinery. Based on his past experiences we hired him but had the same problem of losses which even he failed to explain.

Well this is just a part of the chemist. Apart from this we faced problems with the chemicals in the beginning. The acids were easy to find but none of them were of good quality, we had to then find a manufacturer in another state whose chemicals are much better percentage and grade wise.

Also the governmental policies changed due to which our importing licenses were cancelled and we had to wait for nearly 2 months without any work going on. So yes we have invested a lot of money in this setup and we have also incurred losses.

Anyhow this was our last big batch. Now we will not be processing big quantities and will instead process with a small quantity to make sure we are getting on the right path.

A small background info on us:
The person managing the entire process now is my father, who has experience in Gold Jewellery manufacturing. He has been in the field for almost about 35 years now. And he loves advancing with the technology and also never says no to learning something new. This refinery was something he wanted to do long time ago and that is how we have started off by getting the support from his friend and everything.
Even though things did not work as planned nor did we become one of the best refineries in India, but we are still glad we got to learn so much .

Tomorrow morning we will be stamping our bars and we will definitely put up the pictures of the final finished goods. Hopefully the finishing would be good. Once we are done with our delivery we will be back on the recovery of the left over gold.