# no precipitation?



## gear-golem (Aug 31, 2010)

hey, ive been using aqua regia to dissolve gold off old circuit boards and computer parts and its been removing the gold off the boards but when i add the precipitant i get no results, ive tried both ferrous sulfate and sodium metabisulfite and still no results. anyone got any ideas why this is happening ?


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## qst42know (Aug 31, 2010)

Unless you are dissolving all the base metal the gold is cementing to them in a form you don't recognize. 

AR is a very poor way to remove gold plate from circuit boards.

Keep reading the forum to find effective methods.


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## Lino1406 (Sep 2, 2010)

After you dissolve the gold in aqua regia, you have to
displace HNO3 with HCl. This is done by adding HCl, vaporizing
3 times, to get a syrup form. Then add the FeSO4


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## gear-golem (Sep 6, 2010)

for vaporizing it, just heat it?? and is it better to use the feso4 in a powder or dissolved?


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## dtectr (Sep 6, 2010)

Lino1406 said:


> After you dissolve the gold in aqua regia, you have to
> displace HNO3 with HCl. This is done by adding HCl, vaporizing
> 3 times, to get a syrup form. Then add the FeSO4


 Correct - Hoke also advises: 
"As in Chapter V, you must remove the excess nitric acid by evap-
orating the solution to a syrup, adding hydrochloric acid, and boil-
ing down again, *finally diluting with considerable water *and getting
rid of all sediment. This procedure is necessary when you use cop-
peras, or sulphur dioxide, or any other precipitant. Be sure that
the resulting solution is perfectly clear and free from sediment or
cloudiness."

Regarding the use of sulfur dioxide gas, which is essentially what SMB introduces, she says:
"The beginner sometimes finds that the gold is very slow to come down.
Usually the trouble is that the liquid contains *too high a concentration of
acid*; that is, maybe he failed to evaporate of f all his excess nitric acid;
or maybe he used too much sulphuric or hydrochloric acid in previous
steps. *One remedy is to add water to dilute the liquid and reduce the
concentration of acid; another is to add pinches of sodium carbonate, a
very small quantity at a time, stirring well.* When the acid concentra-
tion is right, the dark cloud of precipitated gold will appear promptly."

Those with more experience with different precipitants will need to weigh in, 
but remember that lazersteve diluted his AuCl 4:1, forcing dissolved Ag out of solution, 
but perhaps also lowering the ph enough to allow easier precipitation?. I just did a small batch 
wherein I evaporated off the excess chlorine, but failed to dilute the remaining solution, 
I believe thereby *concentrating* the acid - it took twice as much SMB to drop & took over a day to settle.

Again, I'm just a beginner, so others with more experience can weigh in with real world info, but thats what I found in Hoke.


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## Lino1406 (Sep 6, 2010)

Should best be dissolved by adding a part of concentrated HCl
and pouring the resulted solution to drop Au. Then part water
and continue dropping. Then part HCl again etc.etc.
Of course SMB is wasted by high acidity, since SO2 will exit
without reacting. Also SMB has unwelcome smell (SO2). On
the other hand, the volume of SMB solution needed is 1/5
that of FeSO4 solution


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## Oz (Sep 6, 2010)

Despite Hoke's caution as to too high a concentration of acid I have had no problem in precipitating gold from concentrated HCl. I chill my solution to remove the silver and lead chloride so my solution starts cold when I add dry SMB. The SMB powder goes to the bottom of the solution and reacts to form SO2 gas in a controlled manner. If the gold chloride solution is room temperature or warm, the SMB is wasted easily by reacting on the top of the solution too rapidly. 

Just my experience.


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## Barren Realms 007 (Sep 6, 2010)

Oz said:


> Despite Hoke's caution as to too high a concentration of acid I have had no problem in precipitating gold from concentrated HCl. I chill my solution to remove the silver and lead chloride so my solution starts cold when I add dry SMB. The SMB powder goes to the bottom of the solution and reacts to form SO2 gas in a controlled manner. If the gold chloride solution is room temperature or warm, the SMB is wasted easily by reacting on the top of the solution too rapidly.
> 
> Just my experience.



Works pretty good on a stir plate and to add some ice just before you add the SMB the container should be sweating(not sweeting). 8)


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## dtectr (Sep 7, 2010)

excellent advice. i've been dropping usually after heating to evap extra chlorine. 
Oz - does chilling drop silver & lead as precipitate, then filter, then drop? i have had problems with fairly dirty gold at times.
edited "precipitant" to "precipitate"


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## Oz (Sep 7, 2010)

Dtectr,

My experience is that yes it does. I do still add a bit of sulfuric acid after chilling in a freezer to scavenge any lead as lead sulfate but it seems redundant. You can see a bit more detail in this thread starting on page 6 http://goldrefiningforum.com/phpBB3/viewtopic.php?f=72&t=7349&p=72837#p72837 where I talked about it, and 4metals shared some commentary. 

I am not claiming a quantitative removal of silver and lead, but on your next batch you may wish to split it and try a side by side comparison to see if it helps with your particular contaminates that are leaving you with a dirty gold.


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## qst42know (Sep 7, 2010)

gear-golem said:


> hey, ive been using aqua regia to dissolve gold off old circuit boards and computer parts and its been removing the gold off the boards but when i add the precipitant i get no results, ive tried both ferrous sulfate and sodium metabisulfite and still no results. anyone got any ideas why this is happening ?



Before you proceed, and this is important, down right vital.

Have you tested this solution with stannous chloride?


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## dtectr (Sep 7, 2010)

Oz said:


> Dtectr,
> 
> My experience is that yes it does. I do still add a bit of sulfuric acid after chilling in a freezer to scavenge any lead as lead sulfate but it seems redundant. You can see a bit more detail in this thread starting on page 6 http://goldrefiningforum.com/phpBB3/viewtopic.php?f=72&t=7349&p=72837#p72837 where I talked about it, and 4metals shared some commentary.
> 
> I am not claiming a quantitative removal of silver and lead, but on your next batch you may wish to split it and try a side by side comparison to see if it helps with your particular contaminates that are leaving you with a dirty gold.


Oz,
what are you using to dissolve your gold? I had a batch of pins that I had run earlier but i believed 
i'd left some values behind & used poor man's AR, with incremental additions of Potassium Nitrate, so little excess nitric to expel.
Worked like a charm & "yes" - I'd left a significant amount, though still a very small drop. The recipe i used 
called for adding HCl to expel excess nitric - Hoke, using real AR, called for addding a little sulfuric to expel nitric,
didn't she? So i was wondering if you were getting "double duty" out of your addition of sulfuric, zapping pb & nitric in one fell swoop?


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## Oz (Sep 7, 2010)

Dtectr,
I put most of my gold into solution with HCl and Cl2 (chlorine gas) but also use aqua regia, it depends on the scrap. I have little experience with the making and use of the poor man's AR, Lazersteve would be best in that department. 

I have a copy of Hoke somewhere but not at hand so I cannot check, but I can't imagine her saying to use sulfuric acid to expel nitric (perhaps you are thinking of removing the last traces of lead from chloride solutions). SMB will also displace nitric before it starts precipitating your gold. If you see red gas come off of your solution when using SMB, you know nitric is your problem (it is not always visible even with nitric present). 

To be clear, sulfuric would displace your nitric (as well as your HCl) if you used it for triple boiling down to syrup each time. You would not like the results however as your gold would come out of solution as a fine precipitate along some of your base metals. Those base metals that were soluble under heat would form a crystalline mass of their salts encapsulating the bulk of your values as your now concentrated sulfuric cooled. 

Free Cl2 and nitric have already been removed from my solutions before I chill them. I am simply using the sulfuric as a redundant and simple precaution to remove all traces of lead from my solution before precipitating.


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## dtectr (Sep 7, 2010)

oz
you're right - wrong process! it is the triple-boil-down - 1 oz of sulfuric/qt helps drive off acids easier/quicker 
to avoid becoming crusty.AND dissolves lead.

And you're right - Lazersteve's recipe for Poor Man's AR is one i used - I believe he mentioned elsewhere that by 
adding the nitrate in small amounts you avoid the excess NOx fumes problem. 

hoke must have been a card:
"(5) REMOVING EXCESS NITRIC ACID
You were told to use no more aqua regia than was required. Be-
ginners always use too much. Experienced workers often do the
same thing, especially when in a hurry, because fresh acids work
more rapidly than those that are partly exhausted.
Sooner or later you must get rid of the unused nitric acid."

i love that: "You were _told_ to use ..." or, more liberally: "Now since you didn't listen, we gotta clean it up!"

thanks for your patience.

dtectr


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## Oz (Sep 7, 2010)

I see little reason to have/need 1 fluid ounce of sulfuric per quart in triple boiling to remove nitric, but I guess it wouldn't hurt. I am confused however if Hoke is saying the sulfuric helps dissolve lead. Lead is rather insoluble in sulfuric. When sulfuric is added to gold chloride it scavenges the lead and forms a solid whitish lead sulfate. 

Could you please type the paragraph or 2 where she describes this. 

She had to be a pistol in her day to do what she did. It was a different world for women in business and science back then. All the more reason to respect her.


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## dtectr (Sep 7, 2010)

Chapter 5 The Commonest Case
(5) REMOVING EXCESS NITRIC ACID
You were told to use no more aqua regia than was required. Be-
ginners always use too much. Experienced workers often do the
same thing, especially when in a hurry, because fresh acids work
more rapidly than those that are partly exhausted.
Sooner or later you must get rid of the unused nitric acid. Most
workers think it pays to do so right away, as follows:
Put the aqua regia solution into a big evaporating dish. It will
contain some sediment, mostly silver chloride; this does no harm at
this point, so do not filter it yet. Now add a little sulphuric acid,
stirring all the time, and working slowly, as it might spatter. Use
about an ounce or less of the sulphuric acid to each quart of liquid.
Now boil the solution down gently, to a syrup, being careful not to
spatter. The purpose of the sulphuric acid will be explained later.

This evaporation is a tiresome process. It goes rapidly at first, but
soon the liquid begins to spatter and you must lower the flame. Do
not cover the dish, as that merely impedes evaporation. A sand bath
or a steam bath is useful; these have already been described.
When using a sand bath, start work by pushing the sand to the
sides of the pan, so that the heat can quickly reach the evaporating
dish; later, as evaporation has progressed, scrape the sand down
underneath the dish, to lessen the tendency to spatter.

The advantage of the steam hath is that it does not cause spatter-
ing, and a dish can be left on it without supervision, without danger
of overheating.

Let the evaporation continue until the liquid becomes syrupy;
then slowly add a little full-strength hydrochloric acid. Brown
fumes will bubble off ; this is the unused nitric acid being expelled.
Usually this evaporation must be repeated at least once, maybe twice
evaporating to a syrup and adding a little hydrochloric acid in
order to get rid of all the unused nitric acid.

Do not carry the evaporation far enough to form a hard crust.
One reason for the sulphuric acid is that it hastens the expulsion of
the nitric acid, and when it is present there is less tendency for a
hard crust to be formed. The sulphuric acid also serves another pur-
pose to get rid of lead which is described fully in a later chapter."

you know what, Oz? When i re-read that, the HCl drives off the nitric, but the sulfuric is supposed to hasten the evaporation of acids.
I was confused by the sulfuric thing, because later she reccomends a final washing with a caustic (lye) solution to remove lead sulphate.

Sorry - I probably should have Pm'd all this - I'm probably confusing someone right now, besides myself.


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## gear-golem (Sep 8, 2010)

qst42know said:


> gear-golem said:
> 
> 
> > hey, ive been using aqua regia to dissolve gold off old circuit boards and computer parts and its been removing the gold off the boards but when i add the precipitant i get no results, ive tried both ferrous sulfate and sodium metabisulfite and still no results. anyone got any ideas why this is happening ?
> ...




ive been unable to find any or find how to make some stannous chloride (perhaps someone would be able to help with that), so ive just been putting it in the aqua regia as clean as possible and dissolving all of the board pins to ensure the gold is dissolved (kind of a bad idea but its all i could come up with until i get some stannous chloride or make some)


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## qst42know (Sep 8, 2010)

Any post by lazersteve has the instructions in his signature line.


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## Oz (Sep 8, 2010)

dtectr said:


> you know what, Oz? When i re-read that, the HCl drives off the nitric, but the sulfuric is supposed to hasten the evaporation of acids.
> I was confused by the sulfuric thing, because later she reccomends a final washing with a caustic (lye) solution to remove lead sulphate.
> 
> Sorry - I probably should have Pm'd all this - I'm probably confusing someone right now, besides myself.


It is no problem, others may have similar questions and we are all learning. Rest assured that if I misstep here someone better than I will ask for me to clarify and back up my statements. You got me to questioning things in my mind for a bit when you were quoting Hoke and I disagreed so, which is a good thing. It seems she prefers to precipitate the lead while boiling down and I prefer to do it after is all. 

I think you have it in your head now. If anything I was the one confusing some as I have tweaked things a bit to my advantage and situation beyond normal convention in my refining. Perhaps I was the one that should have been quite.


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## dtectr (Sep 8, 2010)

Oz said:


> dtectr said:
> 
> 
> > you know what, Oz? When i re-read that, the HCl drives off the nitric, but the sulfuric is supposed to hasten the evaporation of acids.
> ...


 Not at all, senor. Your questions did the same for me. Never hold back on that. 
that's what's great about this forum - we push each other to be the best we can be. it would be great to someday compile a statistic on what we accomplished, R & R-wise, before & after joining this forum.
thanks


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## gear-golem (Sep 11, 2010)

hey ive just read something and ive wondered if its true. instead of vaporizing off all the excess nitric acid, you can add urea into the acid until it stops fizzing and then filter. anyone heard anything about this before and how effective is it and should i just stick with the vaporizing method


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## glorycloud (Sep 11, 2010)

Most of the pros here recommend staying away from using urea and they
all seem to heartily recommend evaporation for the nitric. What they
really recommend is controlled addition of nitric so that there is no
need to evaporate off anything as no excess was used to start with. 8)


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## gear-golem (Sep 20, 2010)

hey ive got another question, ive read elsewhere that it is possible to use zinc as a precipitant.is this actually true and what colour would the precipitated solids be (im sorry if this has already been asked but i couldnt find a definite answer for this and im still partially learning) and a chemical name for this too would be appreciated

thanks


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## qst42know (Sep 20, 2010)

Zinc would displace all the metals in solution below it on the list. The activity or reactivity series of metals. Keep in mind this is a simplified list.

http://www.files.chem.vt.edu/RVGS/ACT/notes/activity_series.html


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## nickvc (Sep 20, 2010)

Zinc dust is more commonly used in recovering values from cyanide solutions which will need further refining. It will precipitate gold from your solutions but the recovered metal would be far from pure and it's use is limited to recovery from disasters when the intent is to start refining from scratch,the link qst42know explains why.


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