What would cause my AR solution to only drop part of the gold powder?

[Mountain Man]

I have a very consistent problem that I could you help with. When using the A.R. process I can and do consistently get the gold to drop. However, not all of it. After I drop the gold I retest with stanous chloride and it still shows gold in the solution. I have 2 theories. 1. Did not use enough smb, however adding more does not drop any more gold. 2 The ph level is off not allowing the remainder of the gold to drop.

Could there be other causes that I am unaware of and if so could you enlighten me on this. I have over 10 gallons of ar solution that is still showing significant gold in the solution.

MtnMan.

 

[Geo]

If you test the solution immediately after the drop, it could be a false positive. A false positive is more brown. The SO2 is reacting to the tin in the solution. After the drop, decant the solution to another container without disturbing the dropped powder. Place the solution on heat. Heat to near boiling and observe the solution. There should be small bubbles coming from the solution as if there was a reaction going on. This is the excess SO2 escaping the solution. When the bubbles stop being emitted, the SO2 is gone. Remove the solution from the heat. There is a good possibility that some gold powder has settled to the bottom. Allow the solution to cool completely. Now you can test the solution and get a true reading on the test without the excess SO2 messing with the results.

 

[Mountain Man]

Thank you for your help. I am going to try what you said to do. One thing though. The test after the first drop is after I have poured the remaining solution into another clean glass jar the size is around 4 gals.. The stanous test shows deep black that turns to deep purple. Brown is usually not present. That is why I think there is gold still remaining in the solution. I have had brown before but it was clear it was as you said and not gold. This is the same color as the test prior to dropping the gold which is why I was wondering if my ph is wrong. I am going to try what you said though and see what results present itself. I will post my results.

Thank you for your help. I really appreciate it.

 

[Lino1406]

On the other hand real cause to worry if precipitated gold was more then what is in

 

[Geo]

Take 1000ml and place it in a 2000ml beaker. Place the beaker in a catch basin. Start adding aluminum foil in small amounts and stir. Only add a small amount at a time or the solution will boil over. Keep adding the aluminum foil and stirring until the solution is very black and the beaker is hot to the touch. Let the solution cool and decant the solution to another container being careful not to decant any solids remaining. Take this sample and dissolve it in HCl and bleach. Test this solution. Sometimes, a solution does not like giving up the excess nitric acid that stops the precipitation and you have to cement the metal and start over.

 

[anachronism]

Take 1000ml and place it in a 2000ml beaker. Place the beaker in a catch basin. Start adding aluminum foil in small amounts and stir. Only add a small amount at a time or the solution will boil over. Keep adding the aluminum foil and stirring until the solution is very black and the beaker is hot to the touch. Let the solution cool and decant the solution to another container being careful not to decant any solids remaining. Take this sample and dissolve it in HCl and bleach. Test this solution. Sometimes, a solution does not like giving up the excess nitric acid that stops the precipitation and you have to cement the metal and start over.

I don't think you should do this with a solution containing mixed metals in the first instance. All you are achieving is dropping all the metals below Al out and then having to dissolve them again. Assuming your tests for gold are correct you are far better firstly trying a small solution and using a different precipitant first. Ferrous Sulphate works great for dirty solutions containing multiple metals. You can also use Ascorbic acid. Worst case you can use the copper bar/copper powder approach.

Remember this is the product of ore- it's got a boatload of metals and whilst the theory of HCl washing out all the base metals is good it doesn't need to be done as the first step.

Take a small sample (500ml) and work on getting THAT to be free of gold rather than using a sledgehammer to crack a nut because you're just doing all the work again unneccessarily.

Finally if you're worried about your pH then test it (your small sample as above.) If your SMB sits on the bottom and does nothing then try adding a small amount of HCl and see what happens. A pH tester is cheap and a great tool to invest in.

 

[Geo]

What I suggested is just for a test and not for the entire amount. I have a suspicion that there may be PGM's present and may be giving the dark colored stannous test. Dropping all metal from a small sample and then redissolving an even smaller amount of the cemented metal without nitric acid and then diluting with HCl should give a more accurate visual with stannous chloride of what metals he is dealing with. If it were mine, I would simply cement everything onto solid copper and work with what ever comes out. But it's not me and not mine. If someone is to learn, they should learn with what they have first.

 

[anachronism]

What I suggested is just for a test and not for the entire amount. I have a suspicion that there may be PGM's present and may be giving the dark colored stannous test. Dropping all metal from a small sample and then redissolving an even smaller amount of the cemented metal without nitric acid and then diluting with HCl should give a more accurate visual with stannous chloride of what metals he is dealing with. If it were mine, I would simply cement everything onto solid copper and work with what ever comes out. But it's not me and not mine. If someone is to learn, they should learn with what they have first.

Sure it's true that we've got differing opinions.

There's always more than one way to skin a cat as they say. You could always drop the gold and then test for PGMs because the tests would also be cleaner. There's a whole heap of folk who show "positive stannous results" for PGMs who have years later to show any metal recovered so I'm more than a little dubious as to those results because all kinds of things can affect them.

I've always viewed deep black to deep purple to be gold not PGMs. It just means it's good and strong for gold. The next stage is gold plating out on the stannous and that's a gorgeous sight.

 

[goldenchild]

+1 on the copper. It's the surefire way to drop only the "good" metals. It will also simultaneously remove excess nitric. Something like Al will drop everything and make a hell of a mess later on. Cu chloride is easy to filter leaving behind the PMs. No need to overthink this one.

 

[Mountain Man]

Thank you all for your advice. I value all your opinions as I am not even close to being an expert. I have over 20 gals of ar solution all showing gold remaining. I am going to try both methods for the purpose of not only recovering all the gold but to improve my level of understanding and knowledge.
I will post my results.
Again Thank You Both.

 

[Mountain Man]

I have one more question. What PH tester do you recommend? I know that may sound like a silly question but I may have gotten the wrong one.

 

[FrugalRefiner]

I use wide range pH test paper/strips. It's cheap and easy, no calibration or maintenance needed.

Dave

 

[galenrog]

I use wide range pH test paper/strips. It's cheap and easy, no calibration or maintenance needed.

Dave

And that, Dave, is one more reason you are indeed, The Frugal Refiner.

 

[Mountain Man]

Thank You Dave.

I have another question. Before I ask it though I want to say that the material I recovered this gold from is a 3 lb. batch of high grade ceramic cpus. I may be wrong but I have always had a much cleaner recovery processing ceramics than fingers or other items. Having said that, the powder tends to be much cleaner and a medium to light brown in color and has been assayed at 22 to 23 karat so the purity is high. Now for my question. If I were to evaporate the solution down the gold should still be in the remaining solution still. Is that correct? And if so, could I not then wash it to remove the excess A.R. solution and then recover the gold or is there existing problems that I am not aware of doing it that way?

 

[FrugalRefiner]

If you evaporate it down, you'll still have a gold salt. When you try to "wash it to remove the excess A.R. solution", the gold salt will go back into solution.

Dave

 

[Mountain Man]

Okay, that makes sense. Thanks to all of you for sharing your experience and wisdom.

 

[Palladium]

Ar solution needs an excess of hcl for the smb to work correctly.

 

[Mountain Man]

Hello, I'm back.

Okay I tried heating one 1000 ml beaker and nothing dropped from the solution except smb in crystallized form. I tested the solution and it positively shows gold. Black/purple in test. I also checked the ph of all the solution containers I have that show gold. The ph test shows +1 constantly in all containers. To me that means I am very consistent in my efforts to eliminate the nitric acid.

That being said I still have not been able to drop anymore of the gold. I am leaning towards introducing the copper strips unless there is a better way from here. I am open to all suggestions.

Thank you.

 

[Mountain Man]

I have a couple of other unrelated questions. Does anyone know how to recover the gold from gold pyrite and from gold ore?

 

[FrugalRefiner]

The ph test shows +1 constantly in all containers. To me that means I am very consistent in my efforts to eliminate the nitric acid.

I'm not sure I understand that correlation. pH of 1 simply means the solution is fairly acidic. You could get that result from hydrochloric, nitric, sulfuric acids etc.

That being said I still have not been able to drop anymore of the gold. I am leaning towards introducing the copper strips unless there is a better way from here. I am open to all suggestions.

Palladium brought up an excellent point. AR needs some free HCl for the SMB to react and create the SO₂ needed to reduce the gold. I would try adding some HCl to a sample of your solution, and then, if necessary, some fresh SMB.

Dave