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YT2095
International Hazard
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but what material is the substrate for this honeycomb catalyst?
if it`s an "ordinary metal" wouldn`t making cracks in it then dissolving it in dillute nitric acid leaving the precious metals to fall off to the
bottom be just as good?
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Jdurg
Hazard to Others
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I think the honeycomb is a ceramic material and not a metal.
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
requires wiping afterwards.\"
http://maddox.xmission.com. |
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YT2095
International Hazard
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aha, thnx !
in that case forget my idea 
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Fleaker
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It's actually called gamma alumina-silica (if you're referring to what the
honeycomb is made of). Some type of mullite derivative...
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Till_Eulenspiegel
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RECOVERY OF Pt & Pd FROM CATALYTIC CONVERTERS
Here's what C.W. Ammen has to say about this:
"The metallic composition of catalytic converters varies, some are palladium, some are platinum, and some are platinum-palladium. Some operators
advocate simply crushing the material up, boiling it in 1:3 hydrochloric acid: distilled water, washing the residue, soaking it in aqua regia for 72
hours, filtering the solution, boiling off the nitric acid, diluting the thickened solution with water, precipitating metallic platinum (with ammonium
chloride) and palladium (with potassium iodide or sodium chlorate) and converting each metal to sponge.
This method is widely circulated, but is sketchy to say the least and much too costly to undertake without more definite information. Your first
move should be to assay the material to determine exactly what you have. You basically have 3 Pt group metals to contend with: platinum,
palladium and rhodium.
Catalytic converters usually take one of two forms: pellets that carry a deposit of Pt, Pd, or Rh on a substrate of gamma alumina; or a monolith of
some combination of Pt, Rh, and Pd deposited on a honeycomb (usually made of a ceramic material) with a wash coat of gamma alumina.
Some converters are 2-way (those that oxidize carbon monoxide and hydrocarbons), some are 3-way (those that aside from oxidizing carbon monoxide and
hydrocarbons, also remove nitrous oxides, NOx).
The effort required to get a good representative assay depends on the type of catalyst, whether it is fresh or spent, and other factors. Fresh
catalysts can usually be decomposed with hot HCl and chlorine, hydrogen peroxide, or sulfuric acid and phosphoric acid. Because the catalysts in the
support media contain some silica, you have to use hydrofluoric acid to dissolve the silica. (!)
Platinum - rhenium catalysts are usually decomposed by heating the crushed material in dilute sulfuric acid that contains some sodium formate. The Pt
being insoluble in sulfuric acid and sodium formate, is filtered off, while the rhenium remains in solution in the filtrate. The platinum is then
dissolved in aqua regia and precipitated with ammonium chloride.
The bulk of the catalytic converters that you are likely to process are spent converters and this material, whether in honeycomb or in pellet form --
is usually about 95% by weight gangue (reaction by-products, carbon, organics, ceramics).
The only practical way to deal with this melange of gangue is to incinerate it, burning the carbonous material to carbon dioxide. The incineration
prodict is then ground to a fine powder. The collected ash (residue) after grinding, should be blended (mixed) in a suitable mixer such as a "Y"
blender.
If the material is not incinerated properly, leaving behind carbonous materials that have not been converted into carbon dioxide, the excess carbon
can cause reprecipitation of the values when you get to the dissolving stage of your process.
The next problem is how to concentrate the values in a suitable solvent. One consequence of incineration is that some of the palladium is converted
to palladium oxide, a black, green. or amber solid that is resistant to chemical attack, but must be reduced.
Many reducing agents easily reduce palladium oxide to metallic palladium. Sodium formate in a carbonate-buffered aqueous solution is a good one to
use. The reduction is carried out at aprox. 190 deg. F. , with the solution at a pH of 10. The reduced palladium is washed & filtered, then the
residue from the incineration and the reduced palladium are extracted and refined in the usual wet chemical manner.
The above processes are carried out in the standard manner using expensive reagents. If your operation is not efficient enough to recover a very
high percentage of the values, you may find that catalytic converters are a losing proposition.
You should also be wary of auto wrecking firms, who frequently have a very inflated idea of the value of the converters. I have seen claims of from
one to three ounces each of palladium and platinum recovered from ten mixed converters.
The best policy here is to buy the converter guts by the pound, based on an assay."
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garage chemist
chemical wizard
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I have not been able to reply to this thread due to my internet not working at the time.
Precious metal recovery from alloys and jewelry is my kind of thing.
I have successfully recovered 34g of pure gold from dental alloys and also the platinum and palladium.
After dissolution in aqua regia, the solution is diluted to make all the AgCl precipitate. The AgCl is boiled with dilute HCl to extract some
palladium which has coprecipitated.
The combined solutions are boiled down in a still and evaporated two times with concentrated HCl to ensure that no nitrate ions are left (important).
The gold is then quantitatively precipitated by heating the solution to 80°C and bubbling in sulfur dioxide until no more gold (yellow to brown,
crystalline, very dense precipitate) settles out. Don't mess with other reducing agents like dithionite, disulfite, FeSO4 or similar, they intruduce
sodium or Fe(III) ions into the solution which will be a nuisance later.
The gold is washed and redissolved in aqua regia, boiled down, evaporated two times with HCl and precipitated by adding oxalic acid in excess, boiling
and then slowly neutralizing the solution with ammonia until the solution is colorless.
This purification produces almost 999 fine gold. If gold of certainly 999 fineness is desired, it is redissolved, evaporated with HCl as before and
precipitated this time with FeSO4.
The solution from the precipitation of the gold is bubbled with chlorine at room temperature to reoxidise the platinum to IV.
The solution is then boiled for an hour to reduce the oxidised palladium.
Ammonium chloride solution is added, yellow ammonium hexachloroplatinate precipitates which is filtered.
To the solution from before is addedmore ammonium chloride, it is cooled to 10°C and chlorine is bubbled in. Brick-red ammonium hexachloropalladate
precipitates. It is rapidly filtered and washed with chlorine- containing NH4Cl solution (not with water!).
If the filtrate is still brown, the treatment with NH4Cl and chlorine and filtering of red precipitate is repeated.
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Till_Eulenspiegel
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STRIP TANKS -PRECIOUS METALS RECOVERY, CONTINUED
Hi:
Here are a couple of useful US patents on sodium dithionite and gold recovery 3, 271, 135 and 3,271,136 by Charles Davidoff.
Continuing with my post regarding Au recovery from scrap sources including electronic scrap:
Strip tanks often used in the industry usually are low-form solid polymer tanks of maybe 20 - 100 gals or so depending on the scrap availability.
Usually there are 3 tanks, one for stripping, one for rinsing, one for reserve. Suspended above the strip tank via hydraulic hoist or pulley is a
hexagonal or similar perforated drum, equipped with either a belt driven or direct drive electric motor. One of the panels on the drum opens for
access and can be secured.
The plated scrap is mechanically pre-cleaned as much as possible, boards are cut to remove components, etc. Since the reaction is oxygen dependent,
sometimes the tanks are gently aerated. Watch out for any mist.
The cleaned scrap is placed in the drum, and the drum half submerged and very slowly rotated in the solution until all the Au is removed, which is
very rapidly with fresh solutionsalso depending on plating density of course. The drum with spent scrap is rinsed with a spray of DI water over the
rinse tank and the drum reloaded. This is continued until all the scrap for that job is stripped.
The solutions are assayed via atomic absorption (again be sure to matrix match sample and standard. CN- anion can cause an attenuation of half an
order of magnitude.
Au standards are unstable, good for maybe 3 days max. 10 ppm is just about right concentration for older instruments to product a full-scale signal.
Make up the standard in the stripper /CN- solution to the exact same concentration as being run in the plant. Any extra CN- added to the strip tank
later will suppress the signal, causing an erroneously low value to be reported.
Anyhow if the volume of the strip solution is known, the {Au} can be reliably determined to within .1 oz or less.
Regarding the composition of the strip solutions, commercially available products work really well. Here’s the specs for one:
(Technistrip) (there are others):
Strip rate: .0001” in 5-10 minutes
Au stripped per gallon up to 2.5 troy ounces
“will strip gold by immersion, (no current), from nickel, nickel alloys, copper, copper alloys, silver and iron with no basis metal attack.”
(Experience has shown there is some basis metal attack, however –ed. )
“10 lbs of stripper product per 20 gals”
Anyhow the strip tanks don’t have to be heated unless it’s below 15 deg or so. . The reaction is oxygen dependent, so aeration can help. Monitor
the pH continuously. Keep above 10. Always keep the place ventilated. Use all proper safety equipment and observe all environmental requirements.
Safety first!.
For quantitative precipitation of the Au refer to my earlier post.
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Till_Eulenspiegel
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STRAIGHTFORWARD PURIFICATION OF GOLD
“Off the boards and into the tank, right from there –straight to the bank”.
No tedious triple boildowns , no nonsense here. Industrial method:
Depending on your source of gold, your strip technique and technologies, assuming you derive the aurium from plated scrap, as well as your cyanide
reduction conditions, the crude sludge at the bottom of the hydrolysis (reduction) unit contains: Au, Ag probably as Ag2O, Cu, and Ni as Ni(OH)2.
Collect in a Buechner funnel and wash thoroughly with DI water in situ with vacuum.
Perform all these operations in the hood. Use eye and respiratory protection throughout.
One prepares a 50:50 HNO3 I water mixture; and places the crude sludge in a 4
liter beaker, (again subsequent to through DI wash to remove any trace of CN-.)
Also you better make sure that your nitric acid is clean reagent grade and contains no HCl! Otherwise you will lose some gold in this pre-leach
steep. Designed to remove the silver and base metals prior to purification of the gold to better than 999 purity.
After you have made up some 50% nitric, now add the dilute acid a few cc’s at a time –be alert to the impending exotherm and possible boilover
-- have a beaker of DI nearby or a squirt bottle. Always use a secondary containment vessel in case the primary vessel with the sludge cake boils
over or fractures.
Cover ½ of the sludge cake by volume at first with the dilute nitric and place on a warm hotplate. Be alert, use heat only to initiate the
reaction. You will see that it takes off by itself pretty quick. Don’t leave this reaction unattended! After the reaction subsides somewhat,
really boil the contents for at least 15 min. The function of the nitric pre-leach is of course to remove any nitric acid soluble base metals.
Unfortunately, any Ni(OH)2 is scarcely soluble in nitric, and seriously inhibits efficiencies timewise and purity wise in this procedure. It’s
tough to filter and mechanically retains the gold in its intractable green gel from hell clutches. Try adding celite or diatomaceous earth silica to
help filtration. Your best bet is to avoid any nickel like the plague, don’t let your stripping go so long as to dissolve the nickel in the first
place. It displaces useful solution solvation capacity that might just as well be utilised for gold or platinum atoms. One has to strike a balance
between getting all the gold off the substrates, and removing a lot of useless nickel. Some commercial strip products are worse than others in this
regard.
When you feel that all the base metals are in solution, cool, then filter in the Buechner thru small pore filter paper. Keep the solution off your
skin, acid gold chloride, HAuCl4 stains skin purple, is absorbed and may have immune system modulating properties.
Reason for using 50% instead of conc. nitric is that, depending on the initial sludge composition, conc. nitric acid will dissolve around 1000 ppm of
gold or more. You probably suffer sufficient losses already without any further ones. 50% nitric only dissolves about 10-20 ppm Au, as shown by
atomic absorption analysis.
OK. After filtration and washing in situ in the Buechner, at least 3 times with DI water, test the combined filtrates for silver by diluting 1:1 again
with DI and adding sodium chloride to precipitate the silver chloride, which is extremely insoluble in aqueous solution. The solubility product
constant is 1.0 x 10 exp –23. (You knew that already). AgCl is a lot more soluble in HCl or aqua regia however. Collect the precipitated silver,
if any after settling overnight. Obtain pure silver metal by reducing the silver chloride with zinc and 5% sulfuric acid. (Add the acid first, a
volume sufficient to cover the silver chloride, then the zinc a little at a time, with major stirring, or you’ll be in for a surprise). (Hydrogen
gas evolves, which can ignite via its own heat of evolution.)
Now take the leached metals cake and quantitatively transfer it into another clean 4 l beaker (or one of appropriate size) Add filter papers and all.
Use a rubber policeman and your finest quant technique.
You’ll next digest the gold in aqua regia and remove the contaminants, and finally precipitate the gold as a fine pure powder. To carry on, you
need to add about 150cc AR per pure ounce troy of Au, in theory. In any event use 4:1 AR, estimate the number of oz. you have and add the requisite
amount of hydrochloric acid all at once. Cautiously, (fortune favours the brave) add the calculated amount of nitric slowly. In between additions
warm the unit on a hotplate to initiate the exothermic reaction. Beware boilovers, always use secondary containment.
The reaction exotherm is often delayed. Warm the stuff slightly and stir using magnetic stirring. Don't use your rubber policeman here. Remember you
want to minimise the amount of nitric you use since it delays the reduction reaction later on. When you think all your metal is dissolved, then add a
few drops of HBr and H2SO4 to your beaker. The first precipitates silver as silver bromide, and the sulfuric precipitates any lead as lead sulfate.
Presence of any silver, in form of AgCl is a major problem in gold refining. It’s one of the primary principal contaminants in gold bullion. It’s
a problem. Silver chloride is pretty soluble in concentrated Ar and HCl. Thus, dilute your gold in AR solution with DI water about 30% at this point.
Cool the beaker to zero degrees C, and vacuum filter through #42 Whatman, perhaps twice. To remove the precipitated silver salts, cellulose, nickel
hydroxide, lead salts, debris, etc.
Wash the filter cake of crap several times with DI water until it stops dripping yellow. HauCl4 is reddish orange-yellow when concentrated. When
dilute, it can resemble the colour of iron chlorides, sort of yellow.
Now for the final finale. Place a teflon coated stirbar in your beaker with the H AuCl4 solution in AR, and dilute the clear solution at least another
1:1 with DI. Don’t dilute your AR solution of Au down to less than 3 gms per liter or you may have a bit of trouble with the final precipitation.
Add slowly with mag stirring, small amounts of sodium meta bisulfite or sodium sulfite, about a table spoon at a time, Don’t stir with excessive
speed, The idea is to generate sulfur dioxide gas at a controlled rate. Take your time.
Dense red toxic fumes are evolved! You better do this in a hood, and wear a respirator too, especially if you are sensitive to sulfur dioxide. Keep
adding the powder until all the NOx is evolved and dissipated from the solution. Now the reduction of the gold begins. Remember, minimizing the
amount of nitric you use in dissolving the gold makes this reduction a snap. When to stop adding the sodium sulfite? When all the yellow color is
gone from the solution.
If your solution is contaminated by base metals, over addition can make the precipitate appear black. Normally it is light brown, the colour of a
blonde lebanese. Sometimes it is dark chocolate brown. Occasionally it’s brown, with a coating of yellow, bright yellow. The supernatant can be
various colors, depending on what base or trace metals are present. Just collect the precipitate and wash with:
1. DI water
2. Conc. or strong HCl
3. DI
4. 25% ammonia
5. DI water
6. Alcohol
7. Dry the gold powder prior to firing. Any trace impurities can be removed very effectively by adding a small pinch of potassium nitrate to the gold
powder during the firing process. This drives off the less dense impurities as volatile nitrates. Very pure gold can be distinguished by any of
several macroscopic characteristics . One salient example is the appearance of concentric rings on the surface of the refined gold.
You can actually fire your gold powder without an oven. More next time.
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