# from what exsits the bIack H2SO4-sIuge



## frank-20011 (Oct 3, 2017)

heIIo everyone,

i have finaIIy processed my ca. 6Kg of mixed pIated contacts-tuff and now i have an amost dry baII of bIack sIudge sitting in my fiIter paper. i can press it to powder between my fingers...
it whights over 100g and is >7cm in diameter so my question is: from what exsits the bIack sIudge (with niceIy shiny goIden spots in it) except of goId?

I wiII incinerate the fiIter paperswith the sIudge together with my other fiIter papers (from AP but aIso from very havyIy pIated stuff that goes directIy in HNO3) but is it necessary, i think no!?

best regards, frank!


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## Deano (Oct 3, 2017)

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


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## rickbb (Oct 4, 2017)

Search the forum for Harold's washing procedure, it's basically what Deano said. 

Washing your powder in hot HCL and Hot water, this method will yield very clean gold.


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## Topher_osAUrus (Oct 4, 2017)

Do the wash procedure the other mentioned, then ar, then wash procedure again.

Overkill, maybe, but when purity is the objective, every bit helps.


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## frank-20011 (Oct 5, 2017)

heIIo,

and thankyou aI!

1.) Ive found a tread by HaroId V where he ashes the sIudge with the paper before doing any washings and i think Iosses of metaIIic GoId are not as big as Iosses if the goId is in a saIts form but anyway: there isnt any carbon inside and so the ashing can be switched 

2.) normaIIy i take the cheapest, tec. grade HCI; 20-25% for arround 2 bucks and 30% for 2,50; when you say: "sludge in 50% HCl", do you mean 1:1 HCI ("normaI" concentration is aImost 35%) and water, so i end up with ca. 17% HCI? if this is the case, i have to use my 20-25% HCI 2:1 with Water

3.) why simmering with HCI instead of "coId" reaction with HNO3 of the sIudge?

4.)"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." 

normaIIy HCI shouIdnt dissoIve goId if there isnt free cIorine in it ore any chIoride saIt present so my understanding of the washing/simmering of goId sIudge is: there shouIdnt be onIy base mateIs in the washing soIIution. why is there any goId dissoIved in the wash-HCI-waste soIIution and when i try to drop it, aII the base metaIs shouId faII out of soIIution, pIease cIear up my misunderstanding.

best regards, frank!


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## Deano (Oct 5, 2017)

When you talk about using 50% HCl you are always referring to the degree of dilution applied to the standard tech grade available in the country of origin.

In Australia this is 32% so the 50% diluted product is actually 16% HCl.

The diluted product is only referred to as an actual HCl strength if the starting strength varies significantly from the 32%.

If you want to remove all of the base metals from the gold then a cold contact will not do the job, heat is required.

The base metals dissolved in the HCl digest are usually divalent, e.g. copper, and are very capable of digesting gold in a chloride solution by dropping to the lower valence state, this way the metals act as oxidisers.

During an extended digest the base metals can be oxidised up to the higher valence states by the combination of heat and dissolved oxygen in the liquid.

When a second drop is performed the base metal tenor in the liquid is much lower than the base metal tenor in the original aqua regia digest liquor and so the level of base metals precipitated with the gold from the second liquor is correspondingly lower.

You have the option of performing repeat drop and digest cycles or just doing a fluxless smelt.

Deano


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## frank-20011 (Oct 6, 2017)

heIIo,

and thank you, Deano, for your interesting expIenations!

o.k., the metaIs acts as oxidiser!

"If you want to remove all of the base metals from the gold then a cold contact will not do the job, heat is required"

i ask for an HNO3 basemetaI-Ieaching instead hot HCI!
coId HNO3 instead hot HCI!

"any residual base metals will form a crust on the molten gold" 

why they do not form a aIIoy with the goId?

back to the ceII process itseIf:

i have processed 6030 grams of mixed qauIity pins (fuIIy pIated stuff with thick pIatings and partiaIIy, thin goId pIated modern PC scrap too)

i get 140 now aImost powderdry sIudge

if i presume a goId contend of 2-4gm (very optimistic) per Kg of my pins, 12-24gm of the sIudge coId! be goId and 116-128g of it shoud be base metaIs and other waste.

I think, this is a very high waste content of the sIudge.
it was my first suIfuric acid ceII run and so i have not any inkIing if this is normaI or if it is a very high waste content in the whoIe sIudge, compared to its goId content.

what do you think?

my main probIem in the process was the very bad eIectricaI contect of the pins to the CU-basket-anode and of the pins between each other...when i crank up the voItage/amperage, the depIating process starts and stops very fast (evoIution of gas/amperage down dropping as indicator)...i thought: no, the depIating couIdnt ready in...Iets say one minute??? and so i take a gIass stirring rod, "stirr" and press the pins together and harder in the basket and so the amperage goes higher again, gas evoution goes higher too...i can pIay these game...1/2 hour and even Ionger and so i was very uncertain about progress of the process.

if i take the pins out of the ceII, they are Iooking reddish-copperish/yeIIowish-goIdish-Iike brass/goId and so i am more confused about copIetenes of the goId depIating and when i put em aside with no efficient fushing, they turn bIack over the night.

is these "turn bIack over night" a dropping out of the soIIuted metaIs they have go into the warm acid?

i didnt understand the process itseIf: the current makes peroxysuIfuric acid right at the anode out of suIfuric acid.
these peroxysuIfuric acid is abIe to dissoIve the goId which is Iayered on the anode (aka the basket, the pins).

why is the goId in the metaIIic form in the acid and not as a saIt? get the saIt reduced instantIy or....?

best regards, frank!


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## Deano (Oct 6, 2017)

There are some base metals which will not react to completeness with nitric acid but will react completely with hot HCl.

To remove them you need the HCl boil.

If you have a lot of base metals on the gold you will get alloying of some of these metals with the gold in a smelt.

If you have low levels of base metals on the gold the alloying is minimised to the point where the metals are detectable but they generally at a level where they do not affect normal purity requirements.

For example, if you have a 999 bar weighing 1 kg then you have 1 gram or less of impurities present.

Note that If you have enough base metals present to blacken the surface of the gold you will always get gold losses into the slag if flux is used in a smelt.

If a graphite crucible is used for the fluxed smelt then the losses become much greater than for a clay crucible.

I usually digest the crust from a fluxless smelt in aqua regia to recover any small amounts of gold contained in them but I am doing this because I have, for whatever reason, failed to do the full HCl boil method properly.

I do not use deplating cells so you will need to get advice on them from people who are experienced in their use.

Deano


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## frank-20011 (Oct 7, 2017)

heIIo, 

and thanks again for your instructions!

i have siIica meIting dishes these shouId be fine too!

what do members say to my probIems which are more xperienced with acid depIating?
i mean the contact probIem of the pins/contacts between themseIve and with the anode?

i think the best way is a rotating-drum-basket-anode but the most members use ordinary baskets ike i do!

best regards!


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## FrugalRefiner (Oct 7, 2017)

frank-20011 said:


> i didnt understand the process itseIf: the current makes peroxysuIfuric acid right at the anode out of suIfuric acid.
> these peroxysuIfuric acid is abIe to dissoIve the goId which is Iayered on the anode (aka the basket, the pins).
> 
> why is the goId in the metaIIic form in the acid and not as a saIt? get the saIt reduced instantIy or....?


The peroxysulfuric acid only exists very near the anode. As soon as it moves away from the anode it reverts back to sulfuric acid. The sulfuric will not hold gold in solution, so the gold reduces back to metallic gold which then settles as a very fine black sludge.



> what do members say to my probIems which are more xperienced with acid depIating?
> i mean the contact probIem of the pins/contacts between themseIve and with the anode?
> 
> i think the best way is a rotating-drum-basket-anode but the most members use ordinary baskets ike i do!


The problems you have with the basket are common. It is far from an ideal solution, but it is simpler to make than a drum and many have gotten satisfactory results. The gold plating dissolves best from the surface of the pile of pins. The pins deeper in the pile are not affected very much. Even the surfaces of the pins farthest from the cathode (on the opposite side from the cathode), and pins on the far side of the basket can remain plated. So as you found, you have to stir the pile to try to get all the plated surfaces near the cathode and facing it to get complete stripping. A rotating basket takes the work out of it.

I don't believe you mentioned the concentration of your sulfuric acid. The more dilute the acid is, the more it will attack the base metals of the pins and the basket itself. Sulfuric is very hygroscopic, so while you're using the cell, the acid will be absorbing moisture from the air and become more dilute. Heat also speeds the attack on base metals. I would guess those factors may have caused the base metal contamination in your sludge.

Dave


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## frank-20011 (Oct 8, 2017)

heIIo forum!,

thank you for your expIenations. now it seems IogicaI and intimating to me. :roll: l

and yes: the ceII was much, much to hot.

i need 4 days/4 hrs for my 6kg of pins and i get crazy about this!

between the breaks I cover the pot with kitchen foil. the acid has 97% at the start BUT: i crank the voltage/amperage much to high to come to an end and so the acid temperature reaches 50°C sometimes.

so i did not have to be amazed at so much waste metaIs in my sIudge!!! :roll: 

"The problems you have with the basket are common. It is far from an ideal solution, but it is simpler to make than a drum and many have gotten satisfactory results"

o.k..... well that reconciled me with the process! 


"The gold plating dissolves best from the surface of the pile of pins"

yes, faraday cage and so on but i thought, the pins which was depIated, get imediateIy passivated and so the pins under them get depIated untiI they are passivated and so on...does it works Iike i thought?
this effect tohgether with some stirring and pressing?!

the other thing i watched was the discoIoration of the pins overnight.

they came just shiny and copper and braze coIored from the ceII and turned bIack overnight.
spots on the pins make the shining Iook Iike goId or brass are maybe onIy brass or maybe undepIated and so the braze-Iooking spots are goId????
I dont know!

the next day the pins where everywhere bIack, no sign of copper, braze or goId.
(the bIack stuff are base metaIs which are dissoIved by hot suIfuric and get droped by itseIf/by the pins to a bIack coating!-i think so!)

now the pins are thoroughly washed and dried and they are Iooking more greyish and copperish with onIy very rare goIden spots.
the goId i can see at the moment is maybe 2% or Iess of the former goId pated areas.

SO, DO YOU THINK, the pins are now thoroughly peeled or still hiding gold beneath the re-droped-base-metals surface?

best regards!


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## frank-20011 (Oct 24, 2017)

heIIo,

i have tried a coId HNO3-bath over 4 days (36%) and after excessive washings of the remaining sIudge (and drying), the resut was a 50% wight Ioss (now there are ca. 70g of dry sIudge)

in the sIudge there are now more base metaIs but i am not shure: Ni reacts very sIow with HCI at room temp. and (as you can read at WIKI) "aImost 30% HNO3 caused a cIeary noticeabIe passivation of Ni"...what means these sentence? does react Ni with 30% HNO3 or does it not?

-->so is my mostIy remaining base metaI in the sIudge nickeI or what a mix of b.m./pure b.m. i have to expect?

best regards, frank!


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## frank-20011 (Oct 25, 2017)

heIIo,

after the HNO3bath of my suIfuric-goId-depIating-ceII-sIudge, the Copper in it shoud be gone and so my question is: what is/are the dominant base metaIs remaining in the sIudge?

best regards!


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## g_axelsson (Oct 25, 2017)

My guess is that there is quite a lot lead sulfate if all you processed was gold. If you have processed anything with silver in the cell there might be some silver sulfate.

Anything not dissolving in aqua regia is at best silver chloride, so I just add the filter to my waste pile for later processing.

Göran


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## frank-20011 (Oct 28, 2017)

HeIIo everyone,

"if all you processed was gold"

i have processed fuIIy and partiaIIy pIated contacts, pins...such stuff!

i!!! think i couId not be Iead suIfate because this is good soIuabIe in strong acids (wikipedia) so it shouId gone with my HNO3 bath....or shouId it not?

and do you think the leads origin is the cathode? she was Iooking fine after the runs, no sign of any demage!

yeah, as Deano stated rather in the past i wiII proceed with HOT HCI!

i was onIy wondering about such a Iot of base metaIs in the sIudge (now i know its reason, the very hot acid) and about composition of the sIudge: normaIIy most contacts are made from brass (zinc and copper) or steeI and these metaIs dissoIve aII in HNO3 so what the heck is the rest?

best greetings!


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## frank-20011 (Oct 29, 2017)

heIIo,

yesterday i put the dry and weII washed sIudge into 15% HCI, now, 24hr Iater the acid is dark green.

when the wheater is fine i wiII heat up the brew outside.

best regards!


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## frank-20011 (Nov 1, 2017)

heIIo,

i Iet stand the sIudge in the 15%HCI untiI i can not smeII any HCIgas anymore.
the green coIor get more intense and the Iiquid itseIf was a IittIe bit sirupy...than, after a Sn-test, i discarde the brew.

after this, i fiIIed fresh HCI to the sIudge (15%)...Iet it stand at RT for 2 days more, heat it up for 60°C and the next day the acids coIor was more a dark yeIIow this time with very nice and fine Iomg needIe Iike crystaIs...

no visibIe reduction of the sIudg-voIume in both HCI-baths.

before the HCI-baths, after the first HNO3 bath (and fresh from the depIating ceII to) the sIudge has an uniform bIack and fine powdery aspect...now, after the second HCI bath there is upon in the beaker a strange white-gray-cornish stuff, over this it Iooks fine, powdery, bIack as before and over this the Iiquid Iooks Iike in my description above.

o.k., pIayed enough! i wiII change to hot HCI as endorsed! after that i can weigh the product!

best regards.


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## g_axelsson (Nov 1, 2017)

If the long needle-like crystals are white then it sounds like lead chloride.

Göran


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## richoc (Nov 21, 2017)

I think your loading into much and trying to run to fast.
Many smaller loads will keep the heat down, and you must rinse your parts after washing, you will collect black sludge from the wash water, this is still gold sludge.
The colder and better you run the less base metals you will need to deal with.
If the the amps drop and the pins all look nickle coated remove them, forcing more reactions will now take the nickle, you do not need that.
Start slow and be very attentive, the strip of only the gold is best.
Now you will still have other metals in this alloy to work out.


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## richoc (Nov 21, 2017)

Oh you have not told us what you are doing after you collect your sludge.
This is a next important process.
I put in to a very tall vessel, then add 5 times the volume in distilled water.
You shall then get a very exothermic reaction, very hot.
I let cool then filter, then decant off the remaining water and only then do I consider this the black slime.


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## Beginner lee (Dec 1, 2017)

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


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## Topher_osAUrus (Dec 1, 2017)

Lead sulphate?


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## Beginner lee (Dec 2, 2017)

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


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## Beginner lee (Dec 4, 2017)

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


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## Topher_osAUrus (Dec 4, 2017)

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.


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## nickton (Dec 27, 2017)

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:


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## nickvc (Dec 27, 2017)

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.


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## frank-20011 (Jan 6, 2018)

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!


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## frank-20011 (Feb 22, 2018)

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!


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## frank-20011 (Mar 6, 2018)

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!


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## anachronism (Mar 6, 2018)

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


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## frank-20011 (Mar 6, 2018)

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!


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## frank-20011 (Mar 7, 2018)

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!


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## anachronism (Mar 9, 2018)

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.


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## nickton (May 15, 2018)

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.


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## g_axelsson (May 15, 2018)

nickton said:


> 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


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## nickton (May 15, 2018)

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.


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## g_axelsson (May 16, 2018)

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


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## nickton (Jul 29, 2018)

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.


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## nickton (Jul 29, 2018)

oops. :mrgreen:


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## nickton (Jul 30, 2018)

Could one use a distilling apparatus to separate the black sludge from Sulfuric acid, and at the same time clean the acid for future use ? It would be nice if I could recover the H2SO4 and perhaps later use it to make more nitric acid. 
Just a thought.


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## FrugalRefiner (Jul 30, 2018)

Sulfuric doesn't really lend itself to distillation. You can recover the sulfuric for reuse by the application of patience. The sludge will eventually settle, though the more concentrated the sulfuric is the slower it tends to settle.

If you have to, you can add the sulfuric to a small amount of water (do NOT add water to concentrated sulfuric) which will facilitate settling. Then you drive off the added water from the clear solution by heating, but to well below the temperature needed for distillation.

Dave


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## nickton (Jul 31, 2018)

View attachment DSC_0179.JPG
Yea. I was pretty much thinking that would be the case. I knew sulfuric boiled at a much higher temp than other acids.

However I thought I would share a simple method I figured out to improve contact between pins when reverse electroplating: I had some extra copper mesh that I cut to fit on top of them in my basket and then filled a glass jar with rocks and sand, which I then placed on top of the upper mesh to weigh it down, thus increasing the contact pressure. I had previously noted that just pressing down with something (like a stick or glass rod) on a batch pins made a big difference in current, so I figured a weight would help and it certainly did.

Here are some pictures of my set up. I like to keep everything in a large plastic pan in which I sprinkle some baking soda to neutralize any spills or drips. If it gets too hot I just stop for a while. I cannot seem to find what temperature is considered too hot for stripping. 

sorry about the bad order of my pictures. I don't know how to re arrange them properly.


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## FrugalRefiner (Jul 31, 2018)

nickton said:


> sorry about the bad order of my pictures. I don't know how to re arrange them properly.


See Attaching Images or Files, Working with Attachments.

Dave


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## nickton (Aug 1, 2018)

thanks for the link. I will definitely re size my images next time.


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## nickton (Aug 20, 2018)

I hope this is the right place to post this. I have quite a few gallons of pale green rinse water from this process that I am wondering how to process, and expect more. Some of it is in a five gallon bucket with a chunk of metal electric motor laminates hanging into it, to cement anything out, but after a week or so nothing seems to be happening. Perhaps the solution is too dilute? I have so much of this highly diluted light green water I can't really add it to my stock pot because it would take up too much room and not add enough metal. I wonder if someone could chime in on what they do with it. When is it okay to throw it down the drain? Or maybe I missed it somewhere in my readings. 

Thanks,
Nick F.


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## jimdoc (Aug 20, 2018)

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=47&t=1300


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## nickton (Aug 24, 2018)

thanks for the link.


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