Poor mans AR curious observation

[alexander the Swede]

Hi all,
I´m new to this forum but have been doing some recovery and refining in small scale for the fun of it.
Up until now i have used the well proven metode of HCL and bleach to dissolve my gold foils.
But last time when dissolving gold bond wires recovered from IC chips i found the process taking forever.
So i wanted to try Poor mans AR for a change.

Now, i first added 60 ml of 30% HCL and sodium nitrate to a few grams of foils and they where quickly dissolved leaving a nice yellow solution. I then added 3 grams of bond wires and let it bubble away.it was seemingly working ok and the solution was showing a nice dark yellow color going towards orange/red.
I tested the solution with stannious along the way in the process and it was getting more and more loaded with gold. All of a sudden the AR turned pitch black, This was NOT what i expected, i thought the digestion would slowly come to an end when the nitric or the gold was used up. It looked like the gold was dropping out of solution so i added some more( 40 ml) HCL and sodium nitrate and the color changed back to yellow(not as Orange/red as before but still a rich yellow color) and again it started to dissolve the remaining gold (aprox 1,5 grams left). A quick test with stannious shows lots of gold in solution.Now what happened? i have not seen this before and in many cases when using HCL/ bleach i have even had a lot of copper in solution so the color was green but it still digested all the foils and i dropped the gold from the dirty solution with Smb and then purified it a second time.
Hope someone has an answer, now i am waiting for the last gold to dissolve and it will be interesting to see if it completely dissolves or even better if some of the gold remain so i have an easier time dropping the gold out of the solution.

Regards
Alex

 

[Refining Rick]

I use poor man's A/R exclusively for refining. I too have seen this. I have found a bit of HCL and peroxide (mixed first, then added) will help get things right. I think it has much to deal with lack of O2 and maybe to many other metals in the mix (I do a lot of e-scrap). A little heat helps here also. Do not boil.
As always, more knowledgeable people then I live here, so listen to them first. I am interested to see if I have been doing the right things when I have encountered this.

 

[kernels]

I too have seen the exact same thing happen with AR, HCl and HNO3.

I have noticed this happens when the solution starts running low on oxidizer (Nitric in my case), I have always assumed that because I too have E-scrap (usually bond wires) mixed with other metals, when the oxidizer starts running out, the gold cements out on the remaining base metals, but because the solution is hot, the gold powder gets 'dispersed' through the liquid making it look black.

Usually adding a bit more Nitric makes the solution return to yellow very rapidly (like within a second or two)

 

[alexander the Swede]

Thanks for the replies guys,

Nice to hear i am not the only one that has seen this happen. Although it is not much of a problem since it is easily fixed with some extra addition of in my case HCL and some sodium nitrate. At this point almost all of the gold is dissolved and i am left with a very nice Auric chloride solution.Since there is still some bond wires left i can assume that all nitric in solution is used up. To be on the safe side i will let it sit for a day extra in that case i will not need to denox the solution.

I believe that i had too little Poor mans AR solution to start with, i did this intentionally since i don´t want to use excess chemicals when not needed.I have seen a lot of videos where people use far to much and end up with 500 ml of solution for just a small amount of gold. This is also why i did not add any extra water, having only 30% HCL i thought it was diluted enough.

In any way, i will definitely be using poor mans AR in the future since it was very effective dissolving those bond wires.

 

[FrugalRefiner]

At this point almost all of the gold is dissolved and i am left with a very nice Auric chloride solution.Since there is still some bond wires left i can assume that all nitric in solution is used up.

It's possible that there are still nitrates left, but no HCl. Since an excess of HCl does no harm, when a reaction stalls it's always a good idea to add a bit of HCl just to make sure that's not the cause.

Dave

 

[alexander the Swede]

Thanks Dave,

I will definitely add some more HCl to be on the safe side and see if the reaction is complete.I have not checked the PH but will do so as well to be sure.Thanks for pointing that out, it is easy to miss that detail and just assume there is enough HCL in the solution.

As they say Assumption is the mother of all f--ups

And since i plan to drop the gold with SMB i definitely need excess HCL to give me that So2 gas to precipitate the gold.

I have to say that i am very glad to have found this forum, so much knowledge in one place. Truly amazing.
I found Hookes book a bit "dry" reading it even though it is very informative.
But combined with this forum you have all you need to be successful in this nice hobby
.
Keep up the good work.

Regards
Alex

 

[anachronism]

At this point almost all of the gold is dissolved and i am left with a very nice Auric chloride solution.Since there is still some bond wires left i can assume that all nitric in solution is used up.

It's possible that there are still nitrates left, but no HCl. Since an excess of HCl does no harm, when a reaction stalls it's always a good idea to add a bit of HCl just to make sure that's not the cause.

Dave

Dave's got this right. It's a lack of HCl rather than a lack of Nitrate. Your solution going black was precipitation.

A solution with a lack of Nitrate stops working, a solution with a lack of HCl immediately precipitates a load of material out. Adding HCl will clear it almost instantaneously.

Edit: a Tip - Always add more HCl rather than more Nitric/Nitratres first. It may take a short while but when the reaction re-starts it's nowhere near as vicious as adding more Nitric. If you do it the other way around, you can make a real mess. 8)

 

[alexander the Swede]

Dave was spot on, there was to little HCL in solution.
I added some extra HCL and the remaining gold was quickly dissolved.
I even had to add some more gold foils ( more than i thought) to take care of the remaining nitric.

Thanks all for good tips, i am amazed how little Nitric/ nitrate is actually needed to dissolve
gold and i certainly won´t be over doing my nitrate additions in the future.

I am definitely going to use Poor mans AR next time as well, If i had used HCL/bleach i would not have been able to dissolve the same amount of gold in such a low volume of solution.
Now i am left with a very rich concentrated gold solution and every drop will be dealt with very carefully