Jor
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brown color in precious metal solution?
I had some dental fillings, and I dissolved them, boiled away 3 times with 6M HCl and diluted with dilute HCl. I then added, while the solution was at
80-90C, a large excess of a solution of Na2SO3 in 1M HCl. The gold precitated and I decanted and washed the gold several times with dil. HCl and dist.
water. I obtained about 5,2g, wich I am going to sell (still have to find a place that buys gold powder).
But my remaining solution is dark brown/red, so i figured there MUST be Pd or Pt in there, AFAIK there are no other metals in such alloys that give
these colors. I bubbled in chlorine at RT, but after some times the bubbles came through so I concluded (wich might be stupid afterwards) that all Pt
and PD were oxidised to 4+ oxidation state. Next a solution of 4g NH4CL in 25mL of water was added. Also a mistake, as I shouldve boiled first, so
Pd(IV) goes back to Pd(II) (wich does not precitipate with ammonium-ions). A small amount of precitipate formed (wich seems to be reddish (like
(NH4)2PdCl6)) but this could also be due to the still brown color of the solution. I think there is still Pd/Pt in there, so I think I haven't bubbled
in enough chlorine.
What would be the most practical way to go from here. I think I should accept that the Pt and Pd are mixed, or is boiling still effecient to decompose
the solid ammonium hexachloropalladate(IV) to the soluble ammonium tetrachloropalladate(II) ? If the compounds of these metals are mixed, it's no big
deal, as I can dissolve the Pd later (when I have decomposed those compounds to the metals) with nitric acid leaving the Pt (if there is any).
Just to be sure, i can still bubble in chlorine right? Or does this react with ammonium-ions to form some extremely hazardous NCl3? I am never sure if
chlorine reacts with ammonia or ammonium to this compound, but I think it is not so stable in water, but I'm not sure. I could use other oxidisers if
necessary, such as bromine (wich is easier than setting up a chlorine bubbler).
All in all a lot of hassle for I think quite small amounts of these metals (I guess less than gram of Pt+Pd), but I think it's quite fun.
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woelen
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If you bubble in chlorine while there is quite some ammonium ion in it, then you certainly will make NCl3. A well-known demonstration experiment is
electrolysing a solution of NH4Cl under an alkene layer or turpentine layer with platinum or graphite anode. In that demo, bubbles of Cl2 are formed,
which quickly react with the ammonium ions in solution, giving NCl3 and HCl. When the NCl3 touches the alkene or turpentine layer then it explodes
giving a bright flash. This demo is not dangerous because only tiny amounts of NCl3 are formed, which go upwards together with the bubble of Cl2, but
in your case you could collect quite some NCl3.
On the other hand, at very low pH, NCl3 is said to decompose, but I do not know how fast it decomposes. Do some research on that before you add
chlorine. Adding another oxidizer also might be risky if a lot of chloride is present. You must be sure that that is not oxidized to Cl2.
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Jor
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In that case I think I should use bromine, as no NBr3 exists, at least at RT.
I think this does not have any effect on the outcome of the experiment, other than that I'm not sure if it will quantively oxidise all Pt and Pd to
4+. Any bromide-ions in (NH4)2MX6 should make it decompose even more easily to the metal. Any more ideas anyone?
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watson.fawkes
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I would recommend a qualitative test for mercury, a common amalgamate in old dental
fillings generally, even with gold.
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JohnWW
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The brown color definitely indicates the possibility of mixed lower-valence states of platinum group metals alloyed with Au. Also, besides the
possibility of Hg used in the Au alloy to lower its melting-point, another likely constituent of Au alloys used as dental fillings would be Ag, as
used in jewellery to harden it and reduce the cost.
BTW Where did you get those Au (or Au alloy) dental fillings from? Had they been removed in favor of white composite fillings or porcelain crowns?
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Jor
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I did get them from someone I know.
What would be a qualitive test for mercury in this case, considering the other metals wich may be present? I never realised these gold fillings could
contain mercury. that worries me, having a large volume of mercury waste. I didn't have a lot of AgCl precitipate during the procedure, so didn't
contain much Ag.
I was thinking of using iodide as a reagent, but I think this will get oxidised by the Pd(IV), making it useless.
I was also thinking of adding NaOH, as this gives no precitpate with precious metals AFAIK, and it does with Hg(II).
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garage chemist
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There is no mercury in your gold fillings.
Gold fillings never contain mercury, and amalgam fillings never contain gold. My father makes artificial teeth and he knows for sure.
You would know whether you had amalgam fillings in your HCl + HNO3 solution by the slimy precipitate of hydrous metastannic acid (SnO2) from Sn in the
amalgam. Amalgam fillings consist of ca. 50% Hg and the rest Ag, Cu and Sn.
The metastannic acid is very difficult to filtrate as it clogs most filters. You would really know it if you accidentally dissolved amalgams.
Amalgam fillings must be treated by distilling off the Hg at up to 600°C (dull red glow) in a bent test tube, as I have done:
http://www.versuchschemie.de/hartmut.php?t=5748&postdays... Click on the image links in the posting, you don't need to read the german text.
After dissolution, separation of Hg is very difficult. I have failed to separate Hg from Ag (which is always present in amalgams) by wet chemical
methods, and I've tried a lot.
The distillation, on the other hand, went perfectly and the residue is entirely free from Hg if enough heat is applied.
Your gold still needs to be purified- the gold from the coarse separation by precipitation with SO2 is impure.
Bromine does not work for the oxidation of Pd to +4, it's too weak. Even chlorine only works in the cold- in hot HCl, chloride is oxidised back to Cl2
by Pd(IV), which is the principle behind the separation from Pt.
NCl3 can only start forming once all Pd is precipitated.
Normally, one precipitates most, but not all Pd by adding chlorine to the NH4Cl-containing solution, filters the precipitate, and treats the filtrate
again with Cl2 until the brown color just disappears and all Pd has precipitated.
If your solution is still brown after making it 1-2M in NH4Cl, it contains Pd.
Filter the precipitate (Pt + Pd), and add chlorine to the filtrate in the cold. All Pd should now precipitate. Wash the precipitate with 1M NH4Cl.
Combine the precipitates, dissolve in hot HCl + HNO3 (don't convert to the metals first, the Pd and Pt might form an alloy with unknown dissolution
behavior in HNO3) and evaporate 3x with HCl.
Now add NH4Cl to a concentration of 2M, collect the Pt precipitate (wash with 1M NH4Cl), and treat the filtrate with Cl2 in the cold to precipitate
the Pd (also wash with 1M H4Cl). The brown color should be absent in the filtrate, if not, slowly add more chlorine.
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Fleaker
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garage chemist gave good advice, for he has done this.
The brown colour you see is indeed palladium--it is a very potent yellow upon dilution with water.
That is quite a bit of chloropalladic acid, produced by the action of aqua regia on palladium and then boiling to remove excess nitrates before being
precipitated as the ammonium hexachloropalladate.
You have added sulfite to precipitate gold. I should mention to you that sulfites/SO2 also precipitate palladium, so I suggest you dissolve your gold
powder into HCl by adding hydrogen peroxide in small increments until it dissolves, then boil and add oxalic acid to it with small amounts of ammonia
until the gold precipitate as a brown mud). This will significantly improve the purity of your gold.
You should have added more nitric acid or hydrogen peroxide after the gold was precipitated, and then boiled. Do not worry about NCl3 as it will not
form in strongly acid conditions (and if it does, I have never seen it nor had any problem with all the metals I've dissolved using Cl2-HCl). If you
have ammonium ion present, add nitric acid to the solution and boil--the ammonium cation will be oxidized and you'll eventually be left with only a
chloride/metal acid chloride solution. Make certain you've removed all oxidizer so that there is no free chlorine present, now you may add saturated
ammonium chloride to your chilled Pt/Pd containing solution and look for a canary yellow precipitate (ammonium hexachloroplatinate). If it does not
form but instead the solution slightly reddens, add in sodium hypochlorite or sodium chlorate crystals and you should immediately see a brick red
precipitate of ammonium hexachloropalladate.Filter this, dissolve it in strong ammonia, and precipitate it again with HCl as a voluminous yellow salt.
Questions, ask!
Good luck
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Jor
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Both Fleaker and GC thank you very much for the help. I'm will go your way from here with my problem.
However, in a few hours I am going on vacation for a week and I still have some things to do, like packing bags and stuff 
So next week I'll continue.
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Jor
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Previous time I added only 4g of ammonium chloride, and the solution was still reddish. After adding a solution of about 7g of ammonium chloride in
20-25mL of water, to make a concentration of more than 1M NH4Cl. Now a yellowish precitipate formed, and a greenish solution was obtained. Is this
just copper or palladium in a lower oxidation state (I should mention that the solution has standed for a week, so maybe in that time the palladium
slowly oxidises chloride) ?
the precitpate is settling, I will post further results if I have the time.
EDIT:
I have now filtered, washed twice with a few mL 1M NH4Cl, and twice with a few ml of acetone., Im now waiting for it to dry.
[Edited on 27-2-2010 by Jor]
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Jor
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I added some NaClO solution to the filtrate and some more red precitipate formed, the ammonium hexachloropalladate(IV). I mixed all these precitipates
of the ammonium salts of the chlorocomplexes of Pt and Pd, and added about 15mL of aqua regia, and heated to 90C. There is some foaming and gas
evolution, but even after half an hours, just a little bit has reacted. How long does the complete oxidation of ammonium-ions take? I am leaving it
overnight on the hotplate at about 80-90C (hot-plate temp, solution will be about 60C, because the air-flow of hood will cool it).
After adding NaClO, there is no more Pt or Pd present. I now have light green solution, wich contains no precious metals I guess, so ready to throw
away. Is it true that i can test for PGM with acidified SnCl2-solution, I have heard this.
Another question, according to one source:
(NH4)2PdCl6—ammonium hexachloropalladate (IV)—355.21 g/mol. Brick red hygroscopic crystals. Soluble in hot water, concentrated ammonia. Reduce to
sponge with heat or hydrazine, Pd black with formic acid or borohydride.
Would it be possible to dissolve ammonium hexachloropalladate(IV) in aq. NH3 and add hydrazine (hydrate or sulfate, i have both). Would this give a
nice spongy powder, like the next says, or an extremely fine hard to filter powder? I would trust the source, but I would like confirmation of someone
who tried (Fleaker?). Btw Fleaker have you gotten my PMs? 
[Edited on 28-2-2010 by Jor]
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Fleaker
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Some helpful advice
Yes, you can test with acidified stannous chloride--gold is purple (of Cassius), palladium is nickel-green (may confirm with alcoholic DMG,
dimethylglyoxime), and platinum is blood red. A good test for rhodium is a sulfuric acid boil--if, upon boiling until SO3 fumes are given off, the
metal powder develops a brown-yellow colour, it is likely rhodium. Any colour before that and it probably has palladium or organics on it. There are
other tests.
ALWAYS check before throwing solution away!!!
This is a useful snippet (I have some for Pt and Pd and Rh as well) For very pure gold:
All acids and reagents used must be of trace metal grade. Recommended is the Trace Metal line of products from J.T. Baker. Under no circumstances
should any metal containing object or apparatus contact the gold or solution; only aqua regia boiled quartz and PTFE apparatus should be used.
Gold of 99,995% purity (20 g.) well rinsed in ether and then in HCl is dissolved in aqua regia in an 800-ml. acid washed quartz jointed flask, and the
solution is concentrated to a thick syrup at 80 degrees Centigrade, removing the most part of the nitric acid. It is then boiled 5 times further and
periodically 20 ml. of hydrochloric acid (4:1) is added to expel nitrogen oxides. The residue is taken up in 650 ml. of hot 18.2 MΩ water and
digested until all soluble material is dissolved. It is then allowed to settle for eight days in a dust-free atmosphere, preferably in a closed
system. The precipitate consists of AgCl containing small amounts of Au, Pd, SiO2, etc. The gold solution is vacuum filtered through a micron quartz
frit via decanting (do not disturb the precipitate). This and all later precipitates are not worked up further to obtain gold. Gold refined by use of
SO2 still contains some Pd, while that precipitated with oxalic acid contains Cu, Pb and other metals. Therefore both of these procedures must be used
to obtain gold of the desired purity. Ultra high purity sulfur dioxide is passed through the warm gold solution (80°C) obtained above; the gold
precipitates quantitatively on careful neutralization with ammonia (1:1). The product is allowed to settle overnight and the deposit of spongy gold is
washed by decantation (7 times) with 200 ml hot 18.2 MΩ water; it is then heated for four hours on a steam bath with concentrated hydrochloric
acid and washed free of acid with hot 18.2 MΩ water. Then it is redissolved in aqua regia in a quartz flask, the nitrogen oxides removed,
filtered, and reduced. The entire procedure above is repeated seven times in order to remove all Ag, Cu, Ni, Zn and Pb. It is no longer necessary for
the gold solution to sit. The precipitated gold product is then digested for 12 hours with ammonia (1:1), washed free of ammonia with 18.2 MΩ
water, heated for four hours on a steam bath with hot concentrated nitric acid, and decanted. Ammonia (1:1) is again added and later removed by
washing with 18.2 MΩ water . The gold sponge is dissolved in dilute aqua regia; after addition of HCl, the solution is concentrated by
evaporation, diluted with UHP H2O, decanted and filtered. The gold is precipitated by careful addition (there is a danger of foaming over) of small
portions of powdered, UHP crystalline oxalic acid (ACS grade may be resublimed twice). If the solution retains a yellow colour, it is carefully
neutralized with ammonia and more oxalic acid is added; the addition of the acid is continued until the solution remains colorless. The resultant gold
sponge is again dissolved and reprecipitated with oxalic acid. It is then Pd-free. Finally the gold is redissolved, precipitated with sulfur dioxide
and heated with concentrated hydrochloric acid, and washed with 18.2 MΩ water. The residual traces of HCl are removed with ammonia and it is
again washed with UHP water. The product is transferred to a quartz dish and dried at 110°C. Yield 75-80%. The gold prepared in this manner is
spectroscopically and analytically pure (free of metallic Cu, Ag, Ni, Pd, Fe, Zn and Pt) and is above 99,9999% in quality.
That source you have sounds like something I have written!
You can purify your ammonium hexachloropalladate by dissolving it in ammonia and precipitating it with HCl. Take this yellow salt and redissolve in
ammonia, warm, and add in hydrazine sulfate. With platinum and palladium both, you will notice with any reducing agent a greenish tone to the solution
(I presuppose this is from it being in its divalent state during its reduction).
You can purify your platinum via bromate hydrolysis (ask if you're curious), else you may keep reprecipitating it...
As far as reducing agents go:
Do not use borohydride! Too expensive, and the precipitate is very fine. So too are the palladium, platinum, and rhodium precipitates so obtained with
ammonium formate, which works well, but is bothersome to filter. Also, steer clear of using alcohols as reducing agents, methanol and ethanol both
make blacks upon reduction. Hydrazine, and its salts work very well and give a heavy gray sponge which does not blow away in the torch. They are also
cheap and readily available. Cheapest still is pyrolysis--slow and steady heating til decomposition will give a nice sponge product, but it melts with
mass loss (usually a percent or so).
I did get your PMs, but I've not heard back??
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Jor
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It's a bit late, I couldn't sleep but a quick reply. I send PMs 13 and 24 februari, maybe you have not recieved them?
When dropping gold out of solution with sulfite, I have not neutralised with ammonia, like your source reference mentions. Does this mean the filtrate
still contains gold?  I will test tomorrow.
I am not too interested to make extremely pure Pt. I only have a really small amount of Pt I think, and purifying would introduce mechanical losses. I
think there is no more than maybe 200mg Pt at most. There is more Pd however, I think.
I already have some precititipate of the mixture of ammonium salts on my filter wich i can't remove. I am not sure how to remove it, I'm thinking
about burning it, but maybe some Pt and Pd are lost as smoke? I have heard a solution of copper hydroxide in ammonia dissolved cellulose, so maybe I
can use this to dissolve the filter paper, but this might be very slow and require large volumes of this 'solvent'.. Otherwise I will extract it out
of the filter with warm ammonia.
I will do the reduction soon, I think tomorrow, using hydrazine sulfate.
I need to find some oxalic soon! I have about 10 grams left 
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Jor
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Ok, last week I was not able to dissolve the ammonium salts in aqua regia, even after boiling once with aqua regia, and next evaporating to dryness at
60C. I boiled again with a new portion of aqua regia, vigorously, but it seemed some dissolved, but most did not. As I thought the ammonium ion would
react more readily with lower oxidation state nitrogen (for example it quickly reacts with nitrite to form nitrogen), I added some more aqua regia,
and about 1g (not weighed) of sodium nitrite in 5mL of water, and started to heat the solution to vigorous boiling. There was, when the solution was
boiling, very vigorous gas evolution, a mixture of HCl, NO2 and nitrogen I think (+some chlorine). I kept a watch glass on the beaker to keep most NO2
inside, wich would definately assist oxidation of ammonium-ion. After brief boiling I got a clear, dark red solution.
Im now going to start the process of boiling down 2 or 3 times with 6M HCl.
Then I will add ammonium chloride to about 1,5M, look for any yellow precitipate of the platinum salt, filter, and add in 5% sodium hypochlorite
solution, and filter red ammonium hexachloropalladate(IV).
EDIT:
I have boiled the solution to about 10mL everytime, and adding in a new 10-15mL of about 4M HCl. I repeated four times. After last time of boiling
down:
Next, this was diluted with dilute HCl, and a solution of 6,8g of ammoniumchloride in 35mL of water was prepared. In the solution containing palladium
and platinum, some precitpate formed when cooling down. i was not sure what is it, it can't be NaCl as the HCl is too dilute. Na-ions were introduced
before as sodium nitrite. I warmed the solution to dissolve everything, and added this to the ammonium chloride solution. A yellow precitipate of
(NH4)2PtCl6 formed!
http://i405.photobucket.com/albums/pp133/Joris12345/P1130007...
But as I think fillings don't contain much platinum, I think the precitate just has a high volume. We will see, I'l leaving it to settle now.
[Edited on 7-3-2010 by Jor]
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Jor
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I filtered the yellow precitpate without suction (don't have vaccuum), washed twice with 1M NH4Cl, and dried at 100C. I obtained about 1,25g of
ammonium hexachloroplatinate(IV), wich is a good 0,55g Pt, say in worst case 0,5g because of some remains NH4Cl. I am going to heat this in a
procelain crucible later to obtain Pt sponge.
http://i405.photobucket.com/albums/pp133/Joris12345/P1130011...
After the filtering I added some more HCl and bleach. I expected a red precitipate of (NH4)2PdCl6, but got a brown precitate! Why is this? I want to
dissolve this in ammonia and reduce with hydrazine to sponge palladium.
It is already filtered, washed twice with 1M NH4Cl and once with acetone.
Edit:
I don't understand it... When i precitpated the Pd for the first time (together with the Pt) I had a large amount of precitipate, I guess certainly 1g
worth, and I think more. Now after seprating the Pt and Pd, and reduding the red compound with hydrazine in ammonia, I got only about 100-150mg of
Pd!!! 
I still have a red solution (from wich the palladium was precitpated, I thought completely), evolving chlorine slowly from excess hypochlorite+acid,
the solution is still acidic, and vertainly contains 1 or more M NH4(+). But why is it still red? From all other solution where i precitipated Pd, I
got a green supernatent, this is red, indicating presence of Pd, at least that's what I think. But the Pd does not precitipate. Does anyone know why?
I am thinking about boiling this solution to volatise all chlorine, and then adding hydrazine to this acidic solution to precitipate any remaining Pd.
However, there will also be precitipated copper in the Pd.
Any know what I should do? I think I messed it up somewhat 
[Edited on 7-3-2010 by Jor]
[Edited on 7-3-2010 by Jor]
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Jor
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I have now heated my ammonium hexachloroplatinate in a porcelain crucible, and a lot of white smoke was produced. After this ceased, I let cool and
collected the grey powder. It is about 0,5-0,55g of Pt, nice element sample. Adding hydrazine to the red solution (mentioned in the post before, wich
i suspected had Pd in it) did not precitpate any metal, just made the dirty orange solution turbid
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Jor
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I first thought of making a new topic, but my question perfectly fits in this topic.
I recently obtained about 17g of gold fillings (100 EUR), of wich I think 2 grams or so is ceramic/teeth. The alloy is supposed to be Orion GX alloy,
wich is according to my source about 84% gold, 8% platinum and 5% palladium. The alloy looks silvery, and is not magnetic. I put a single piece (4,7g)
in 30mL aqua regia (1:4 HNO3:HCl) and nothing happened when it was cold (wich I expected). When heating some bubbles appeared. I heated until boiling
and the solution became blood red and there was vigorous bubbling, starting on the piece of metal. I boiled for 10 minutes. After coming back 1 hour
later (left the solution on the hotplate, solution was very hot but not boiling, 80C?) no reaction was taking place. So I decanted the solution,
rinsed the metal with some water, and heated in a flame to evaporate the water. Then I weighed, and it weighed 4,65g! There might be a slight error,
but sill I expected a much lower weight, it seems that almost nothing reacted (at least some did, there was a strong red color (PdCl6(2-) I think)).
The vigorous bubbling can be explained as simple decomposition/boiling of the aqua regia.
But why does the alloy react so slowly? Gold quickly dissolves in hot aqua regia, palladium as well, and platinum quite slowly. Can an alloy become
quite inert, even if the neat metals it is made of are much more reactive?
I am leaving the reaction mixture at 70-80C overnight, I hope some more will have dissolved.
I am very positive the seller did sell me real precious metal containing alloys, as this is a real dentist (selling al kinds of dentist-related items
on the local ebay site), but it really puzzles me how slowly the metal reacts. I have dissolved gold teeth before (3 times now) and always the alloys
quickly dissolves (especially the gold colored ones, the silvery ones dissolve slower, but not this slow in my experience).
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Ephoton
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not sure about using hydrazine for precitating Pd but I have used formic acid with gold and Pt.
some times when I had to little metal in a large amount of solution it would go coloidal and I would get
a very turbid solution that threw light all over the place.
still had the right colors for what ever I was precipitating but sometimes it would not drop at all.
I used to think it was left over calcium from the calcinite that I used to make the aqua regia.
but on making the aqua regia from pure acids I still got this some times.
dropping the gold with hydroquinone after stripping all acid and adding more HCl then stripping this repeatadly
three times fixed this. then I would use the formic to drop the Pt group.
I never seperated the Pt group though.
[Edited on 15-5-2010 by Ephoton]
e3500 console login: root
bash-2.05#
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Jor
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I had to bump this.
I recently had a mixed precitipate of (NH4)2MCl6 (M= Pt and Pd) in some dilute aqua. This was due to forgetting to boil the solution to reduce Pd(IV)
back to Pd(II). Now after a month I decided to process this to the pure metals.
I made the solution alkaline by adding NaOH. Next I boiled this solution for 20 minutes to remove all NH3 from the solution. Then the solution was
made acidic again with 37% HCl. There was a very small amount of red precitipate. The solutionw as decanted, the precitipate dissolved by adding some
hot NaNO2 solution (nitrite reacts with ammonium-ions to form N2) and this was added to the main solution.
I had a deep red solution, still containing some free nitrate. I boiled the solution completely down at hotplate temp. 90C overnight. This resulated
in a large amount of solids (including NaCl). To this was added some 4M HCl, it was boiled down to a syrupe and 150mL of 2,5M HCl were added. Boiling
this gave no brown NO2 (when a watch glass was on the beaker and a white paper behind the beaker). I assumed at this point that all Pt was oxidised to
the 6+ oxidation state. To be sure I added about 10mL of 4% bleach, resulting in some bubbling.
Next the solution was boiled for 15 minutes to reduce all Pd(IV) to Pd(II). The solution was then treated with NH4Cl to a concentration of about 1,5M.
Now here is the problem. Instead of a yellow precitipate, wich I got half a year ago, I got a dirty brown precirpate. Does this contain some ammonium
hexachloropalladate(IV)? How long does one need to boil to decompose all Pd(IV)? Also, the supernatant liquid was not greenish, but still dark red,
even though the concentration of NH4Cl is well above 1M.
Why is the solution still red, and can the color ammonium hexachloroplatinate(IV) also be brown (crystal size?) ?
If it contains some Pd, how can i remove this from the precitipate? I know (NH4)2PdCl6 dissolves in ammonia. Does the Pt salt also dissolve in
ammonia?
I also did a test with a dilute SnCl2 solution in dil HCl. When some of this is dropped on a tissue paper, together with some drops from the precious
metal solution (AFTER THE PRECITIPATION OF Pt!) slowly a light green color develops (Pd). When the solution fo precipious metals is put in 2 test
tubes, and to one is added some dilute SnCl2 in HCl, the solution in the test-tube without SnCl2 is brownish, while the one with SnCl2 is brown/red
(not a bright red).
To be sure no Au is present, I boiled a few mL of the solution with some sulfite and HCl. No gold was precitipated.
[Edited on 3-1-2011 by Jor]
[Edited on 3-1-2011 by Jor]
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Fleaker
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I'll help you out Jor!
Start over.
Your failure was improper removal of free chlorine from the solution. Also, you will not get Pt (VI)!
1.) Take all of your values containing solutions and reduce them by adding zinc. pH should be between 2-3.
2.) Remove excess zinc by rinsing the cemented metals with 3M HCl until no more fizzing, then boiling water.
3.) Use 35% nitric acid (warm) free of chlorides to remove any silver and palladium. This is solution A; if palladium is present in
heavy concentration, it will be chocolate brown, if palladium and copper are present together, it will be brown greenish blue, if nickel is present,
it will be similar but with a more pronounced green. If it's dilute palladium with colorless contaminating cations, it will be yellow.
4.) Add 12M HCl (2X volume of nitric you added) to solution A; slowly at first; observe for any white precipitate. If there is, it is probably AgCl
(and you must filter this, use only enough HCl until no more AgCl precipitates). Boil with hot water in case you think it is PbCl2 (it is easily
soluble in hot water unlike AgCl). If you have silver chloride, it is imperative that you keep it as a slurry!
5.) Boil your solution A to remove nitrogen oxides (bear in mind that a beginner's mistake in parting palladium from platinum using nitric acid is
using too much HNO3), adding HCl to it when it becomes syrupy. Do this 2-4X until no more NOx is evolved. If the initial digestion is done properly,
it will not need to be done more than once.
6.) Your solution A is now an HCl solution of H2PdCl6. Make it as concentrated as you may (syrup), then add 30 mL dH2O for every 50 mL solution
concentrate. Place this in an ice bath until quite cold, and add sodium chlorate to it until you see a slight effervescence of Cl2. Thereupon add a
saturated ammonium chloride solution to the chloropalladic acid and sodium chlorate solution. Precipitation of a brick red compound should start
immediately. Add until the supernatant is clear and tests free of Pd(II) or very weak with acidified tin (II) chloride solution (pull an aliquot or
dip a cotton swab in add add a drop of 1M SnCl2 in 2M HCl and look for a green colour).
7.) Filter your (NH4)2PdCl6 washing the cake with saturated cold ammonium chloride solution. If the precipitate is bright brick red like in my thread,
it is very pure. If it is a drab red with brown, then it is contaminated. In that case, dissolve it in ammonia to yield a clear yellow solution that
is quite basic (pH 10). If there is any precipitate, it is an impurity (likely iron). Re-acidify with concentrated HCl in an icebath to obtain a
yellow salt, tetraamminepalladium (II) chloride, a monohydrate. This is filtered (and the supernatant checked for palladium). Alternatively, you can
very effectively precipitate palladium with ethanolic dimethylglyoxime and then calcine that to get very pure palladium.
8.) Return to your residues from the first parting with nitric acid. This is platinum (unless silver was present, in which case, platinum may
co-dissolve). Digest this in hot (70%) aqua regia. As a cement product from zinc, it should take only a few hours to dissolve, if not less. For every
31 g Pt, I'd put 150 mL of 12 M HCl and add only as much nitric as I need to dissolve it. The amount of nitric acid is variable and depends on the
temperature, the fineness of the platinum, and other factors. Anyway, once it is digested, dilute the solution by half, and filter it if there are
insolubles in the bottom (which may consist of rhodium, iridium, and certain Ru and Os).This is solution B.
9. Boil down the Pt solution to a syrup, add concentrated HCl and repeat until no more NOx are formed.
10. Put concentrated acidic solution in a tall form Berzelius beaker in an icebath and add hot saturated ammonium chloride. The supernatant should be
very clear. Filter this canary yellow ammonium hexachloroplatinate. Rinse the cake well with cold, saturated ammonium chloride solution. If the
precipitate has traces of green in it, then there is rhodium contamination and you will need to perform bromate hydrolysis. If there is orange,
palladium is still present. If there is brown, it is iridium. Hopefully it is yellow.
11. Each pure metal precipitate you obtain you can simply and carefully heat to obtain the gray sponge. Or you may dissolve them in ammonia and add
hydrazine sulfate and heat to 70*C, whereupon they will precipitate with much effervescence of nitrogen gas. This gives a gray heavy sand. You may
also use ammonium formate which gives a blacker, finer product that is more metallic. Just make sure pH is around 5-6 with formic acid being in
excess. This reduction works at 80-105*C.
Or you can do what I do and put them in a dedicated quartz tube and reduce with hydrogen at ~400-600 C, with cooling under a vacuum. The ammonium
chloride produced is rinsed off of the pure metal and out of the tube. Then the metal can be melted inductively or with oxyhydrogen.
I may have made a mistake or two as I have a severe head cold, but I've done this process many times and it works quite well.
Good luck Jor,
Fleaker
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Jor
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Thanks a lot. I will start tomorrow. Instead of sodium chlorate I will use bleach, as sodium chlorate is harder to get and I only have about 20g left.
But can you explain the dark red color of the liquid even after I treated it with ammonium chloride. It's very deep brown/red. I don't understand this
as the precitpate I got was orange/brown instead of yellow.
By the way, can I also use H2O2/HCl or HCl/NaOCl to dissolve the platinum metal powder, or preferably just bring all the metals into solution at once
with one of these mixtures, and then just more carefully decompose ALL the de Pd(IV) to Pd(II) by boiling for much longer? Because i hate to boil away
many times to remove all nitrate.
The small amount of crude ammonium hexachloroplatinate(IV) I have will be reduced to the meta; by dissolving in dilt NaOH, boiling, making the
solution acidic and adding in the zinc.
[Edited on 16-1-2011 by Jor]
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Fleaker
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Don't bother basifying and adding zinc. You can do it with zinc at low pH without boiling. Or you can just simply heat it (calcine it to sponge).
Bleach is acceptable, so long as there is free chlorine in the solution when you go to precipitate the palladium.
You can use peroxide/HCl, chlorate/HCl, even sparged O2 and HCl but nothing works as well as aqua regia used correctly. Avoid bleach in a digestion
solution as you're weakening your acid. You don't have to boil many times if you only use as much nitric as needed. I told you to separate the
platinum from the palladium with nitric acid to avoid you getting co-mingled precipitates of the different ammonium hexachlorometallates.
The dark red colour of the liquid when the platinum is gone may be rhodium. Rhodium does in fact dissolve in aqua regia to give a very red solution.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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HHammerHeadD
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Quote: Originally posted by Jor  | | I bubbled in chlorine at RT, but after some times the bubbles came through so I concluded (wich might be stupid afterwards) that all Pt and PD were
oxidised to 4+ oxidation state. . |
chances are that if you bubbled in clorine...you done just disolved your gold!
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