# help...white insoluble salt after denox



## Sucho (Jan 5, 2011)

Hi all!

i processed 600 grams of old ISA and PCI fingers from graphics and network adapters

first i treated fingers with diluted nitric ( 1 part nitric 65 %, 1 part H2O) heated to 70-80 degrees for a couple of hours

then i filtered nitric/nitrates solution and wash foils/cuprex with water

then i have added AR solution(3:2:1 HCL:H2O:HNO3) into the beaker with foils/cuprex

all foils and visible gold flakes have been dissolved - nice yellow solution

when i was denoxing my AR solution , white salt dropped (about 3-5 grams)
i filtered the salt and try to drop out gold using water solution of SMB(both heated to 60 degrees)
there was only 0.1- 0.2 g of gold powder dropped
i think that there must be much more gold in 600 g of fingers
what is the white salt ? its insoluble in H20, HCl, AR, slightly different from AgCl, not UV active
ist it a kind of auric complex salt or some other compound of gold ?

thanks for all answers

// sorry about my english


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## Juan Manuel Arcos Frank (Jan 5, 2011)

I do not think so....it seems to be an insoluble chloride,CuCl,(copper chloride I),lead or mercury...

Since you have added HCl then CuCl is discarded.

Add boiling water,if it dissolves then it is lead chloride...if do not then must be mercury chloride,to probe it add some ammonia,if it turns to a black mud then it is mercury chloride.

I hope it helps.

Regards.

Manuel


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## Sucho (Jan 5, 2011)

i have added hot water to eliminate lead chloride because of its increasing solubility in hot water after process that time...it is not lead chloride
i dont have ammonia to test mercury, may i use any ammonium salt ? or something like that ? 

my question is, is it possible that 600g of fingers contains only 0.1 - 0.2 g of gold?
is it possible that my white salt is a gold compound ?


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## Platdigger (Jan 5, 2011)

"i filtered the salt and try to drop out gold using water solution of SMB(both heated to 60 degrees)
there was only 0.1- 0.2 g of gold powder dropped"

How long did you wait for the gold to precip?
This small amount of gold may take even a day or two, or more, to settle out completely.
Also, if there was any nitric left in the solution, you may need more smb.

I say this because you did get a small amount of gold, and if there was some residual nitric still in the solution the bulk of your smb could have been used up by the nitric.


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## Sucho (Jan 5, 2011)

i let it settle for a week

i have used enough SMB,after 2 days i added another SMB, after 4 days another...

there is not problem...i tested it on AES machine
there was only tracks of gold in the solution after settling


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## samuel-a (Jan 5, 2011)

Sucho said:


> when i was denoxing my AR solution , white salt dropped (about 3-5 grams)


how did you denoxed? evaporation/urea/adding volume ?


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## Sucho (Jan 5, 2011)

evaporating to a syrup (overloaded solution-first crystals formed) two times
adding a bit of HCl and water each time


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## dtectr (Jan 5, 2011)

Sucho said:


> evaporating to a syrup (overloaded solution-first crystals formed) two times
> adding a bit of HCl and water each time


 If your nitric wasn't killed first, you may be making aqua regia which could be redissolving your gold. 
also, check this thread for other ideas: 
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=34&t=8780


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## Harold_V (Jan 6, 2011)

Sucho said:


> evaporating to a syrup (overloaded solution-first crystals formed) two times
> adding a bit of HCl and water each time


Don't add water. It serves no purpose and prolongs the evaporation period. Add HCl until there are no signs of nitric remaining---then dilute with water as appropriate. 

Harold


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## Sucho (Jan 6, 2011)

to Harold_V : I have to add a bit of water each time, because i dont want to fry dryed crystals-when its hot and almost evaporated, HCl added evaporates rapidely
frying dryed crystals is not good because of thermal decomposition of Au I-III compounds

to dtectr : i know that NO3- is oxidizer agent in AR........if i had some excess nitrate ions in my solution, i thing i killed them with SMB overloading

i can test my solution with DPA to know, if theres any residual NO3-/NO2- ions


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## dtectr (Jan 6, 2011)

sucho
I apologize for missing the fact that you had evaporated to syrup twice. 

This is all academic to me thus far, and welcome a critique &/or observations.

Hoke addresses the tin paste issue:
"Repeat the nitric treatment if necessary, then wash
the residue well, but *do not let it dry*. The residue is gold, plus tin
paste, plus such base metals as were not reached by the nitric acid.

"Next, mix up a little sulphuric acid and water, half and half (pour
the acid into the water, slowly, and stir all the time) and cover
your residue with this solution. Warm gently. This dissolves the
tin paste, dissolves any remaining tin metal that the acid can reach
and changes any remaining lead into white insoluble lead sulphate." (p.72)

you'll notice that to tin compounds, except metastannic acid, I would assume, sulfuric is the key here. 
CHEMIST ALERT: And maybe, not letting it dry? 
Harold's usual admonition of roasting to red heat may be key in resolving metastannic acid problems?
"and at a red heat, into anhydrous stannic oxide."
[which is soluble in concentrated sulfuric acid.]
"According to Weber, nitric acid of specific gravity 1-2 converts tin, at ordinary temperatures, into stannous nitrate, stannic acid, and metastannic acid, which is coloured yellow by admixed stannous metastannate. With nitric acid of specific gravity 1-35, the products, if the liquid is well cooled, are metastannic acid [? stannic] and stannic nitrate; by dilution and heating, the stannic acid is converted into insoluble metastannic acid, which indeed is always produced under the influence of heat." both quotes _A dictionary of chemistry and the allied branches of other sciences, Volume 5 By Henry Watts_
http://books.google.com/books?id=cUcsAAAAYAAJ&pg=PA820&img=1&zoom=3&hl=en&sig=ACfU3U0jbYvLKniNgjoiYnWeRo-BAqLAsg&ci=142%2C349%2C804%2C298&edge=0

I imagine because of the tin issue, that Hoke advises:
"Thus, when making up aqua regia, add some sulphuric acid, say
an ounce of the concentrated acid to each pint of aqua regia, more
or less. As we said in Chapter V, this sulphuric acid serves two
purposes: it hastens the expulsion of the excess nitric acid, and it
also helps to get rid of lead. You will now see how it does this:
by converting the lead into the insoluble white lead sulphate, which
will remain with the mud of silver chloride that is left after the
other metals dissolve in aqua regia, and which is filtered out at
the same time."
CHEMIST ALERT: thus eliminating some, if not all, in initial AR digest?

This could also be why the absolute cleanest drop & digest I had was residue from the sulfuric cell, incinerated, then dissolved with HCl-Cl & dropped with SMB.

Again, only academic until someone with real-life experience weighs in.

good luck, though, & keep us posted!


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