Electrochemistry from what exsits the bIack H2SO4-sIuge

[Beginner lee]

Hi All,
I guess I'm on time for this.
I just try my first run on H2SO4 de-plating on gold coated copper piece.
My run is steel cathode, after deplating, i didn't wash very well on the black sluge, with sulfuric in it, then go for AR, HCL in it then slow increment with HNO3. Then i have same problem with this unknown gray sluge which not dissolve in AR, filter it off, boil with dissolute HCL & HNO3, nothing happen to it. What it is?

Is there any problem if too much sulfuric in AR.

My AR after is little greenish, but, after heat it up , it become yellow/gold color as usua(Why?).
Just adding SMB to my AR solution, waiting to see the result tomorrow.
After AR, the gold appear in-normal as picture, golden color, let see how the gold powder form tomorrow.

The black/gray sluge which not dissolve in AR, boiled HCL & HNO3, as mention above, may be silver chloride.
Will try convert it to solid silver with iron and melt.

Thanks

 

[Topher_osAUrus]

Lead sulphate?

 

[Beginner lee]

Cannot be lead, because deplate item is gold, nickel and copper. Cathode is steel.

 

[Beginner lee]

:x Cannot be lead, because deplate item is gold, nickel and copper. Cathode is steel.

 

[Topher_osAUrus]

You only said "piece", so I'm assuming a jewelry piece, which will have solder on it. That could be the source of your sludge

If you think its silver, filter it off and rinse it well with water. Add some ammonia to it. Any silver chloride will dissolve. Filter the solution, add HCl to the filtrate, the silver will reduce back to silver chloride.

If ammonia or ammonia hydroxide (store bought stuff is trash, 10%-30% is best) is unavailable, just set the washed solids in question in sunlight, it will blacken if its silver.

 

[nickton]

okay I may have missed this but,
going back to the original boiling in diluted HCI process: How exactly does one extract the base metals if some of the gold goes into solution too?

I am referring to Deano's post of course:

"Mostly your black sludge has the colour caused by a mix of fine particle size and base metal contamination.

Remove the base metals by simmering the sludge in 50% HCl until the gold clumps, remove the filter paper before doing this.

Recover any residual gold from the filter paper by including it in your next aqua regia digest.

Ashing filter papers will result in gold losses.

The liquor resulting from the HCl boil will contain gold in solution, if you drop this out with your preferred precipitant it will come down fairly clean.

Put all of the dry recovered gold in a clay crucible and smelt without flux,any residual base metals will form a crust on the molten gold and are easily removed.

I usually put the clay crucible inside a graphite crucible as a safety precaution for the smelt.

Unless the precipitated gold is very, very pure any flux in the smelt step will cause losses into the slag


Deano"

It seems like you can't decant since some of the gold goes into solution, so how really does one separate the gold from base metals after boiling? I have gotten to the black sludge stage and turned it into a fairly gold colored liquid in hci/bleach that got a nice dark stannous chloride reaction, but after dropping with SMB (?)(stumpout by bonide), it all came down as a black powder again that I couldn't seem to melt down into gold. Seemed to be too many impurities still. Maybe my torch just isn't hot enough either.

hmm. I guess the answer to my own question might be: remove the "clumped" gold somehow, or just leave it in the bottom,
then precipitate with Sodium metabisulfide (SP??) and decant after letting settle. Most of the base metals will remain in the solution that is then poured out.

--rank amateur... :mrgreen:

 

[nickvc]

Nickton welcome back.
With the HCl boil if there are certain base metals present some gold will go back into solution but this is a small recoverable amount, either save until you have a large volume or use it for the next digest. The powder in the bottom of the flask after boiling should be clean and clumping together so simply carefully decant add water and boil again decant and do it again until the water is colourless, to dry your powder put a watch glass over your beaker and heat gently to remove the water, to remove I use a small designated paint brush to transfer to the crucible.

 

[frank-20011]

hello,

"I think your loading into much and trying to run to fast"


i agree with you and i know it while i am doing it but almost 7kg...my cell is small, much to small and even with the big heaps of pins in my basket, the hot acid, i need 3 day, ~5hrs a day and i just wanted to qiut the work.

the problem and it's causes have now been resolved and i have to live with it.
i wrote above the HCl leachings of the sludge...the last one i repeat not at room temperature, i let stay the beaker at 50°C at the top of a heating boiler for 4-5 days and again the acid get greenish and thick as with the previous cold-acid bath but not as much.

the volume of the sludge degreased ~3 times...

after it i try to wash the sludge, it settles very badly and even after 2 weeks the water looks black.

i decided to decant it, gold could not stay stirred up 2 weeks.

(stannous tests of the acid baths where always negative)

i repeat water washings until the water stay clear and colorless...strangely the sludge now coatet in different layers: below grey and cornish, above black and fine

i put a drop of the wash water on a watch glass, after its evaporation i get a lot of needle like cristals.

the whole time me sludge was in a 750ml beaker an i have to repeat the water washings ~10-15 times until the evaporation test of the washwater didn't show any cristals on the watch glass.

now the sludge is looking fine, black and uniform, no sign of any stratification and it's volume degreased more to a rate which seems realistic to the amount of pins i worked with.

this is more a report...i haven't any questions at the moment...don't forget: i am doing this the first time and so everything is new and interesting to me and far from being economical.

next time i will do a lot different.

as you can read, even in such a "simple", well-documented process as this, there is still plenty of room for error.
now i think the mud has worked up well enough to continue with AR process.

best regards, frank!

 

[frank-20011]

hello,

i let stood the beaker with the black sludge and the AR at the open until the AR had evaporated.
gray mud and yellow christals were the result.

i add hot water and try to dissolve the crystals, the grey sludge stay stirred up in the sollution.

with the stannous chloride test the yellow solution was immediately discolored, like clotted blood: black with a red tint.

i take a few more drops of the gold-chloride sollution and add a few crystals potassiumpyrosulfite but this time nothing happend.
i try to make the sollution more acidic with a drop HCl but this changed nothing also.

why did tin chloride precipitate metallic gold and potassiumpyro/bi-sulfite not?

best regards, Frank!

 

[frank-20011]

Hello,

thorough denoxing by evaporation of the whole sollution, dissolving the residues with dest. aqua, double denoxing by sulphamic acid and the gold precipitated neatly after adjustment of the ph value by a splash of HCI.

puhhh....now i have a test glass with 3,2g dry "gold" powder, i will refine it later with other gold.

3.2g are not what I expected from 6kg pins.

the pins where mixed. partly gold plated pc pins from the 80s, 90s, 2000s and also fully plated pins.
pins from telephons, relays, TV and so on....all different kind of electronic devices the pins came from but also transistors/diodes in fully plated cases sometimes older than 40years but the most stuff is from "modern" pc devices.

3,2g dirty gold from >6kg pins, that's realistic?

i saved the pins after they came out the sulfuric cell and all pins look the same: black-copper nevertheless they consist of different materials.

do you think it makes sense to dissolve part of the pins in hno3 to see if there is still some gold coming out or should I be satisfied with my 3,2grams?


best regards!

 

[anachronism]

Let's see a pic of the pins that are left. It will take a LOT of Nitric to dissolve 6Kg of pins.

 

[frank-20011]

hello,

i will only dissolve a sample in HNO3 (maybe)...not the whole 6kg batch!

i will make a foto...please wait!

thanks a lot, best regards!

 

[frank-20011]

hello,

that's it:

https://abload.de/img/p1030967kfpnh.jpg


as you can see, all pins look the same.
regardless of the material, all of them have evenly discolored.

on the watch glass (top left) are some objects where the gold was visibly not removed, on the right is a relay contact.
even his contact point made of silver is black just like copper, brass, kovar, steel!

but again: 3g of gold from 6Kg pins, is it realistic?


best regards!

 

[anachronism]

If the pins only have 3g of gold on them in he first place yes it's realistic. I've seen pins vary from as low as that but they were pins from newer PCs.

 

[nickton]

I wonder if it's a good idea to leave them in a de-plating bath over night, which is what I think you said you did. Most videos I've observed on the subject show very rapid de-plating. Could keeping pins in a bath too long become a problem? I would think this could cause more contamination for one. When I did it , each batch took not much more than a half hour to an hour perhaps to do. Processed pins looked mostly copperish after washing with water (if I remember correctly).

Also I was wondering if the HCI should be diluted with distilled water when boiling black sludge in it? Or does it matter? Tap water might cause some gold to go into solution I think.

 

[g_axelsson]

Also I was wondering if the HCI should be diluted with distilled water when boiling black sludge in it? Or does it matter? Tap water might cause some gold to go into solution I think.

I would use concentrated HCl unless there is an abundance of lead contaminating the black powder. But diluting with tap water would probably not dissolve any measurable amounts of gold. You need free chlorine or nitrates to dissolve gold, there is already an abundance of chloride ions from the acid.

When diluting nitric acid, tap water could form a weak aqua regia if there is chloride ions in the water.

Göran

 

[nickton]

Okay. So that only happens with nitric acid then. I thought it was with HCl too, where the chlorine in tap water is like a form of bleach mixing with the HCl, making the alternative to traditional AR, which will put some of your gold into solution.

 

[g_axelsson]

The amount of free chlorine in tap water is quite low compared to bleach, so I think that the amount of gold that might dissolve is minuscule.

The amount of chlorine in treated drinking waters is in the range of 0.2 - 1.0 mg/liter.

Chloride ions on the other hand (sodium, potassium, calcium chloride) vary with the levels in the source of the drinking water. For UK the levels were around 11-42 mg/liter between 1974 and 1981 according to a study. In the USA levels in tap water has been between 5 and 460 mg/liter. All numbers from a WHO study I found via google.

I'm lucky to live in a town which doesn't need to treat the water with chlorine and the chloride content is really low, only 1.6 mg/liter. Low enough that I can use tap water to dilute my silver nitrate without any visible silver chloride.

Göran

 

[nickton]

Have you seen Sreetips' you tube videos of sulfuric stripping cells? I just watched them and his yields are incredibly small. I personally think he may have left a bit of gold still on the pins since he simply determined the end of de-plating occurred when bubbling from the cathode stopped during each run. I, like you, noticed that additional stirring and pushing onto different areas of the cage caused considerably more reaction and de-plating. However I do respect the meagre results he had, and am not expecting too much myself. It appears to be a common mistake to over estimate yields from electroplated material.

 

[nickton]

oops. :mrgreen: