Non-Chemical Help on dirty Aqua Regia solution with Clorox

[robertpdickson]

First off....I read Hoke so I am asking for advice and not being lazy.

Stupid me; I tried removing gold plating from CPUs and plated pins from circuit boards. My first batch is small to allow for errors like this. First I added HCL and sodium hypoclorite to the beaker of scrap. Second I added Nitric Acid and let it react. I let it react for 24 hours and removed the garbage scrap. Third I added 1 part water to solution and I am left with a dark blue-green solution with dark sediment in the bottom of the beaker. Does anyone have a suggestion on how to rid the solution of the unwanted base metals and convert to a clear yellow auqa regia solution to drop the gold? Thanks in advance for any help.

 

[gold4mike]

First question:

When you removed the "garbage scrap" was there any metal left undissolved?

 

[maynman1751]

Where did you get the idea to run HCl/Cl and then add nitric? HCl/Cl is a refining process and not for recovery. You could have used the nitric by itself to start and been farther ahead. I'll let the more seasoned members handle it from here.

 

[robertpdickson]

GoldMike: When I removed the scrap there was very little metal not dissolved. 99% was gone.

Maynman: Because I took someone's advice and didn't listen to my own brain.

 

[jimdoc]

What exactly was in this small batch?

Jim

 

[robertpdickson]

RAM chip "fingers" and CPU and several cell phone keypad contacts.

 

[maynman1751]

I suppose that you could try cementing with copper. Take all of your solutions and add a piece of copper sheet or busbar to see if any values will cement out. Do you know if all of the nitric was used up. Depending on the quantity of materials you may not have much to recover!
Use the advice that you get here and you won't go wrong!

 

[gold4mike]

Since you had some undissolved metal your gold is most likely no longer in solution. It has most likely cemented back out.

Question #2: Have you made Stannous Chloride yet? If so, what did the test of your liquid show?

If you haven't made it yet - why not?

You're working blind if you don't have Stannous Chloride.

 

[jimdoc]

RAM chip "fingers" and CPU and several cell phone keypad contacts.

I should of worded that "and how much of that stuff?" grams a pound?

Jim

 

[Geo]

i hope you didnt throw away the "garbage scrap". there was no gold in the solution you were working on. the first thing you should have learned about the way metals dissolved (if you did read Hoke's book) is that the most reactive metal will dissolve first. if you have an excess amount of oxidizer in solution, gold will dissolve alongside the base metal. as soon as a point is reached where the oxidizer is depleted enough, gold with stop being dissolved and will start cementing out of solution on whatever base metal is left. this happens faster in a warn solution. when you dissolve PM bearing scrap that has mixed metal (which should never be done unless you understand what i just typed) all of the metal has to be dissolved to completion.

 

[robertpdickson]

I will test with Stannous Chloride tonight. The amount that I "practiced" on was a small amount because I was suspicious of the "ease" to remove gold plating via this method. I really appreciate the feedback and help. Thank you.

Yes, I did retain the "garbage" as well just in case it did cemet to the scrap. The amount of scrap total was 50.15 grams.

 

[robertpdickson]

Okay guys this is unbelievable but....It seems that there was some method to the gentleman's madness in the HCL Clorox bleach foil removal. To answer some questions posed by the folks on here. A Stannous Chloride check of the solution proved to be negative for gold. I poured off the mixture and left the fine mud at the bottom of the beaker....which low and behold contains the gold foil from the computer parts....undissolved. At this point I will further clean the mud then apply the Aqua Regia process and drop the gold with sodium bisulphite.

Apparantly for dirty computer parts the HCL and Clorox releases the foil from the pins, cpus, and plated fingers without dissolving the plating. My fault was adding Nitric to the solution before I neutralized the solution and poured it off.

Fascinating stuff and will I continue this thread until the end of my processing for you info. Again, thanks all for your help and advice.

 

[jeneje]

Okay guys this is unbelievable but....It seems that there was some method to the gentleman's madness in the HCL Clorox bleach foil removal. To answer some questions posed by the folks on here. A Stannous Chloride check of the solution proved to be negative for gold. I poured off the mixture and left the fine mud at the bottom of the beaker....which low and behold contains the gold foil from the computer parts....undissolved. At this point I will further clean the mud then apply the Aqua Regia process and drop the gold with sodium bisulphite.

Apparantly for dirty computer parts the HCL and Clorox releases the foil from the pins, cpus, and plated fingers without dissolving the plating. My fault was adding Nitric to the solution before I neutralized the solution and poured it off.

Fascinating stuff and will I continue this thread until the end of my processing for you info. Again, thanks all for your help and advice.

Why would you use AR to process the foils, It would be better to wash with water to remove any contaminates and then disolve in HCL/CL then drop i would think, if i'm wrong here i will be corrected.
Ken
edited; if you use AR you will have to denox your solution, using the HCL/CL you only have to allow the CL to evaporate from the solution say 24hrs.

 

[NobleMetalWorks]

Sounds like to me you didn't have enough oxidizer in solution so the gold foil was never able to dissolve fully, and whatever might have dissolved ended up cementing out again, thus your "mud". As Geo said, other metals will dissolve before Au, and if this is the case, the base metal under the gold foil could have dissolved before the Au, but there was not enough oxidizer to then attack the Au. Not having the base metal to hang onto, it then foils off. This does not mean that HCl/Cl will foil gold, it means if you don't have enough oxidizer, there is a possibility that Au will foil off without dissolving. But this is only a possibility, and you would have to have the perfect amount of oxidizer to do this without dissolving Au into solution. It almost sounds like you expect the HCl/Cl method to act like AP, but even AP will dissolve gold if there is enough oxidizer present in the solution. It's all about observation, understanding, and craft work.

I try to use HCl/Cl for as much recovering as possible, with the exception of things I can enter into an AP tank. Like people have posted before, you just have to drive off the Cl. HCl/Cl readily dissolves Au so long as you have enough Cl to complete the process. If you have a piece of china, or a glass, coffee mug, etc with gold around the rim, make up a small batch of HCl/Cl then put your item with the gold trace in the solution and watch how incredibly fast it dissolves right off. It works perfectly so long as you have enough oxidizer ( Cl ).

If I were you, I would wash everything you have, really well, retaining and testing the rinse solution for values with Stannous Chloride before wasting it. Then I would make up a fresh batch of HCl/Cl and enter your material into the solution, or rather carefully and slowly pour without splashing, your HCl/Cl solution into your cleaned/washed material. Then observe, half of what we do when recovering and refining is observing. If you have read Hoke, and you have done your familiarity tests, you will have learned how to observe reactions, and if you have read enough about HCl/Cl, you will be able to observe and understand what your solution is doing, and how much more oxidizer you need to add, in small increments, to achieve a total dissolution of the Au. It is the same exact thing when you use AR, and you slowly add Nitric Acid. You would make small additions of Nitric waiting and observing the reaction, until you observe that all the PMs have been dissolved into solution. Nitric acts as the oxidizer, the same as bleach does in HCl/Cl.

Scott

 

[robertpdickson]

Well sadly I must say I am now stumped. I took my Au solution used UREA and distilled water at 1 parts to 2 and tried to drop....no success the sodium bisufite dissolves. So I added more until the solution would no longer take anymore and let it sit.

The next day I filtered the solution again to rid the white colored sodium bisulfite out and retested with stannous. With a more highly diluted solution it turn dark brown to almost purple.

I've included a photo of the solution. If there is any hope of recovery; I would appreciate any advice? A picture of the solution is attached.

Thanks again all!

 

[butcher]

The solution looks to contain gold (although iron compounds can also be yellow),

Your stannous chloride may not be able to tell you much if there is excess oxidizer in solution (the stannous chloride reduces the gold dissolved in solution to metal, to give the violet color, if there is oxidizer in solution like chlorine gas or nitric acid, then the stannous chloride cannot reduce the gold to the violet looking metal),

Too much SMB can also give a brown reaction to the stannous chloride test.

At this point you have several options to try and determine if oxidizers are involved (use the evaporation method to remove nitric in solution,using Harold's trick of adding a gold button will help here you would not have to evaporate the solution so much), or if all else fails you can always cement the values from the acidic solution using a copper buss bar.

I would try to rid nitric and then retest, if you wish you can take a small portion from the main batch in a test tube and experiment with it on a small scale, add a foil of gold and heat solution to use up any nitric acid (if the gold foil dissolves add another until it does not dissolve the gold with heating), then the try the stannous test, if the stannous chloride test then works, you know several things gold will reduce to metal, you did have gold in solution, oxidizers were the problem.

 

[goldpete]

my comment is to robert.
at no time have i seen you say you have evaporated the nitric or cl . i was having the same problem youve had , and i had the same result youve had , untill i learned that i needed to add sulfuric aid then evaporate using the proess in hokes book.

i am now getting fine black sediment which i assume is gold but i wont know until i try to melt it , im waiting till i get enough because i only do small batches at a time

 

[robertpdickson]

To the last post....the sulfuric acid and evap. Going back over my notes I realize now that I did not use sulfuric after adding more Nitric to speed reaction. (Suffering from newbie acid usage I guess) I will add about 10 drops of sulfuric and evaporate in a sand bath and post the results.

Again thanks for everyone's help. It is much appreciated.

 

[goldpete]

ok buddy , good luck .and please becareful you dont add too much nitric because it is the nitric you need to evaporate off.

id like to also find out , when you evaporating off the nitric , did you let it heat untill it becomes a syrup , then add some hcl and evaporate again? and repeat that adding hcl untill you get nop reaction ?
then adding 3 times your solution in water ?

also you might need more than a few drops of sulfuric , you need one ounce of sulfuric to each quart of solution.
please be careful because as soon as you begin to add it , it will violently react and splash back at you

do you remember i said to you earlier that i have made your mistakes before ? . well here is a pic of my solution at that time , i hope this helps you.
this pic is a solution that had been evaporated but i didnt have any sulfuric at the time . i had added SMB and gold didnt drop , i didnt know why , but a week later when i got some sulfuric , i pour some in there and the sediment you can see dissapeared and i was left with gold at the bottom

 

[robertpdickson]

Man that is/was identical to my solution. I filtered off the excess SMB and washed the powder with water.

I'm now going back to add Sulfuric and evaporation to rid the solution of Nitric acid. I will perform the HCL addition(s) to the syrup and then water and report back.

Thanks again!!!

Well, I just don't know what to say. After using the sulfuric to burn off the nitric I condensed the solution to a syrup and added HCL and repeated until I observed no more reaction. The last batch of syrup I added a 10mL amount of HCL and no reaction. I diluted the syrup with a 3 to 1 ratio with distilled water and I now have a clear green solution...not the golden yellow which I started with. And now my tests with Stannous are negative which leads me to believe that my test on the original AR solution was reacting to other metals vs. gold. I assume I lost the gold in my various washings and unorthox ways that I approached this. Now I will back up and try again. Practice makes perfect.

Any thoughts or advice?

UPDATE: It seems to have worked. Because my processes were a bit backwards the murky green solution (I made a mistake above) the sediment has settled into the black gold powder. Unbeilieavable.

Thanks again.