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Bill Vins |
Thanks for your response Bill. I am familiar with the technique you referred to. The problem is (as you alluded to) when you're talking about actual product and much thinner gold the foil is very hard to handle. I am interested in quantitative gold and not impurities. With impurities it is ok to lose a little gold as all you are interested in is the ratio of impurity to gold. The xray technique is fine for thickness but I'm looking for usage on the part. We do routinely perform thickness by XRF to check functional areas of the part. JDK
JD Kronicz, again
- Hanover, Pennsylvania
JD, If you can strip the part using aqua regia, using care to minimize attack on the base metal, the gold can be precipitated form the aqua regia as follows: 1) Boil aqua regia down to incipient dryness- till only a few mls. of liquid remain. 2) Reconstitute using 100-200 mls. deionized water. 3) Adjust pH to 2.5 and bring solution to boil. 4) Add 10% sodium nitrite a few mls. at a time. The gold will precipitate first as a fine powder and with further boiling will begin to agglomerate. When adding sodium nitrite no longer produces any precipitate, filter out the gold, wash with HCl then DI water and oven dry. Determine the gold content gravimetrically. The precipitate will be 99.99% pure, so if your deposit is a Type 1 or 2, the alloying elements will not be present in your precipitate. Good luck.
Keith Wicklund, CEF-SE
avionics - Minneapolis, Minnesota
Another method for precipitating the gold from aqua regia which doesn't involve boiling away the nitric acid and generating toxic nitrogen oxides is as follows:
After dissolving your gold or base metal/gold into the aqua regia, add granulated or prilled urea to the acid/gold complex until the fizzing stops. This will destroy the nitric acid without boiling. The fizzing isn't violent nor are any disagreeable fumes released. A slight excess of urea at this point is ok. Next, slowly add a solution of sodium bisulfite (sodium metabisulfite in water) to the HCL/gold/urea mixture. When you start to smell sulfur dioxide being released, that is a good indication that all of the gold is reduced. Any further addition of sodium bisulfite will begin to reduce copper chloride to cupric chloride, which will precipitate along with your gold. This can discolor the gold, release clouds of noxious fumes when the gold is melted and generally screw up your assay. The gold will precipitate over the course of several hours as a chocolate brown powder which melts to the yellow color we all know and love. Add a few ml of Isopropyl Alcohol [link is to product info at Amazon] of other ! non-acid labile surfactant to free the finer particles which are floating atop the surface tension. After the solution becomes a transparent green, decant off the remaining HCl/copper chloride solution, cover the gold with concentrated HCl and swirl. This will dissolve out any precipitated cupric chloride. Wash the gold several times in distilled water until the water shows neutral to litmus. You can substitute concentrated ammonium hydroxide solution for the HCL wash since it too will dissolve cupric chloride with the added feature that cupric chloride will turn aqua ammonia blue. Repeat the ammonia rinse until no more blue is seen, and then do it once more. One caution here: If there is any possibility that silver salts have been precipitated along with the gold, do not use ammonia. Ammonia will form explosive acetylides such as silver fulminate, especially with insoluble silver chloride or silver oxide. When these dry, they will violently detonate if you even look a! t them too hard. This hazard can be completely avoided if you filter your acid after the urea step since this would trap any insoluble silver chloride and keep it out of your gold. I know this post is long, but the beauty of this process is in the details. I will post a second, even easier method in a followup post so that I won't choke the server with this one.
Frank
Frank Roberts
- Austin, Texas
As promised, here is another simpler method for precipitation of gold from aqua regia:
After dissolving your gold/base metal in the aqua regia, allow the acid to cool and then add an excess of sulfurous (not sulfuric) acid to the pot. This both destroys the excess nitric acid and reduces the gold in one step. Unlike the urea/sodium bisulfite method, no cupric chloride will be precipitated, only your gold. Since sulfurous acid is a water solution of sulfur dioxide gas, you can also bubble SO2 gas through your acid, although this method takes a few hours of slow bubbling to precipitate all of the dissolved gold.
Frank
Frank Roberts
- Austin, Texas
Hi,
Langford and Parker, Analysis of Electroplating and Related Solutions indicates that sulfuric acid, with careful additions of Hydrogen Peroxide [link is to product info at Amazon], will precipitate the gold from a cyanide solution. Other reducing agents listed are ferrous sulphate, Oxalic Acid [link is to product info at Rockler], and potassium nitrite. Regards, Tom
Tom Pullizzi
Platronica.com
Falls Township, PA
How to make luster gold powder form real gold?
Mahendra Bir Singh
- Kathmandu, Nepal
What doing if the gold came from electronic scrap (from contacts) and the concentration is too poor? Something to do first ?
Eric Tordeur
- Belgium
+
Thank you Frank Roberts.
Your method Recovering Gold from Aqua Regia worked well for me. However, I found at first with high quantity of copper from circuit boards I had problems with precipitation. I solved this problem by first dissolving most of the copper etc with nitric acid and pouring it off before Aqua Regia process. I now have this nitric copper etc solution. Can you suggest the best way to recover silver and copper from this?
Tony Plummer
- Harare, Zimbabwe
Dear Keith .W
I read your suggestion for determining the gravimatically in reply to
JD. You have not mentioned that, what will have happened to silver
chloride which get settled in gold chloride solution (aqua regia
solution)?
Does silver chloride remain as it is after boiling the aqua regia?
Kindly reply for this.
Rajesh
- Vellore, TamilNadu, India
Dear Sir,
I want to refine gold from Scrape and I use aqua regia reaction to
dissolved gold. now for precipitation I use SODIUM METABISULFITE
solution (300 Grams per Liter) and added as 1 Gram Gold = 3 ml of
SODIUM METABISULFITE solution.
I find some amount of precipitation but it dissolved again with the
solution.
How I can recover my gold from this solution?
MAX PANCHAL
GOLD SMITH - INDIA
Talk about precipitating gold from the solution but nowhere I read the easy way to determine if any or all gold is precipitated out. I use a little tin ( from lead-free tin solder for water pipes) dissolved in Hydrochloric acid. Put a drop of this on absorbent paper and then add a drop of the solution where the gold is from precipitated. If any gold remains in the solution the drop turns black. When all gold is precipitated the color stays neutral. This detects 4 parts in a million.
Alexander Baldal
- Philipsburg, Saint Maarten, Netherlands Antilles
+++++++
I AM IN THE MIDDLE OF CONFUSION WHEN I MAKE MIXTURE OF AQUA REGIA,
I REALIZE THAT OUR NITRIC ACID SUPPLIER SUPPLY ME WITH ONLY 68%
CONCENTRATED NITRIC ACID SO WHAT WILL BE THE RATIO OF MIXING IT WITH
HCl I WONDER AND I HAVE BEEN GETTING PINK COLOUR MIXTURE WHEN I MIX
THE NITRIC AND HCL WITH RATIO OF 3 TO 1 (3 HCL TO 1 NITRIC)NEEDED
ADVISE AND ALSO THE WAY TO NEUTRALIZE NITRIC BEFORE EXTRACTING
THEM,
MY VERY MUCH THANK TO WHO EVER CAB HELP AND ADVISE ME ON THIS
MATTER
JIMI LIM
Jimi Lim
Singapore
April 1, 2008
Hi I am working in gold refining plant.we dissolve 12.5 kilos of gold in approx.50 lt. aqua regia.after filtration of silver chloride we bring the pH to 7 to destroy the excess nitric acid by adding soda ash solution.we precipitate the gold using sodium metabisulfite solution.can anybody give me full chemical reaction taking place in the whole process. thanks,
Vijay Pillai
chemist - UAE
June 16, 2008
Hai,
I'm from Indonesia need help.
Note : Nitric acid 68%, HCL 30% (sold in the store)
I use Aqua regia (450 ml. HCL, 150 ml. Nitric Acid, 200 grams scraps
of metals).
I wait one night (the color of solution is yellow-brown), then
tomorrow I added 450 grams sodium bicarbonate and some of lime to
neutralize the acid. The reaction is :
Bottom precipitate is metals, middle precipitate is orange-brown
mud.
I pour off the container with filter. I get the clear solution. The
orange-brown mud in the filter when dried is change to brown. The
metals color is cloudy brown-grey.
1. How to neutralize the solution (HCL, Nitric Acid, Sodium
Bicarbonate) pH 1.
2. How to find out the brown mud if is indicate of gold.
3. How to cleans the metals cloudy brown-grey.
I'm very thank's for any response because I'm really confusing.
Boboy
Boy Raynolds
hobbyist - Jakarta, Indonesia
August 9, 2008
I've yellowish gold chloride solution. In it I've added half the quantity very strong HCl acid. Then i dissolve melted gold alloy as an anode while the cathode is pure gold strip. Expecting pure yellow gold to sponge around the cathode, instead only a coffee brown sponge is formed. No reaction to HCl but fizzes to HNO3. Result is pure gold. But expected gold weight to karatage ratio is below calculation. Where am i wrong?
For example if a kilo of gold scrap has the karat fineness of 875/1000 then after refinery shouldn't the gold recovered weigh 875 grams since the remainder 125 grams of base metals, other than Pt, Pl, etc, should be gone as chlorides. I always seem to accumulate a few grams lesser than expected. I don't even transfer any liquids or solids to other containers. I'm stuck me mateys.
Balasaravanan Palanirajh
employee - Colombo, western province, Sri Lanka
September 24, 2008
How can we dissolve gold in HCL using hydrogen peroxide and in
what amount should we add these solution, and how to recover
dissolved gold in the solution the method should be easy and without
fumes??
Can anyone help me please???
Jazz Smith
university student - Australia
November 20, 2008
Dear all, I know my English is very bad but Please HELP!!!
I am an Italian living in Germany hobby goldsmith that after years of
melting is gold decided to refine it.
I looked up in internet and then I started
After dissolving my gold into the aqua regia and allowed of the acid
to cool down, I filtered the solution (a grey powder remain in the
filter).
After adding granulated urea to the acid/gold complex (until the
fizzing stopped) I left for two days in an acid bottle because I did
not receive the sodium bisulfite (as previously announced from my
pharmacy) and I had to find one other way to precipitate the
gold.
I found in Internet that I could use Oxalic acid and I did.
After mixing the Oxalic acid to the mixture, the mixture turned light
green.
After short time the solution was separate in two colors (bottom
light green and top brown).
I stirred often for the next two days but nothing different
happened.
I told maybe the gold sponge will be in the light green creamy
result. I filtered to separate the light brown solution from the
light green one.
I rinsed the creamy stuff in the filter with hot distilled water and
the result that came out was a black solution in the cup and a white
salt looking powder with some brown spots in the filter.
I tried to rinse the salt looking powder with ammonia and turned
light blue. By continuing rinsing, the liquid is clear but the powder
is very light gray.
Now I have 3 cups with:
1. light gray powder,
2. light brown solution,
3. Black liquid.
What is going on??? I have seen all the colors but not a brown
sponge.
Is the gold still in the solution or in the salt looking
powder?
Can I still get the gold out of it?
How can I do that?
Help me, please!!!
Best regards
Gc.
Giancarlo Balisciano
hobbyist - Herzogenaurach, Bavaria, Germany
Dear Reader,
In response to an article by GB (Giancario Balisciano) dated 20th
November 2008.
Hope this helps. Not knowing how you undertook the process it could
be that your light blue solution was Silver or Tin or Copper. With
the latter two this depends upon the valance (or its pH above or
below 7). These problems occur when trying to recover metals from
electronic boards etc because of the base metals such as tin in
solder. It could have been Platinum or Palladium? The light grey
powder could also have been silver chloride which would have darkened
on exposure to light. It could also have been other metals which the
Tin precipitated out.
The light brown solution could have been gold. I would add aluminium
foil to this after filtering and after adding say about 5% (by
volume) a solution of Hydrochloric Acid. This (adding aluminium) will
bring down all metals leaving a clear solution. It will produce a
rotten egg gas smell as hydrogen is released.
The black liquid (again not knowing how you did this or if the
process was complete before precipitation) could have been Nitric
Acid which could have caused your problems from the beginning if it
was not boiled out of the Aqua Regia. It will in fact prevent
precipitation of your gold. Many of the more notable writers on this
subject suggest adding boiling water to this (use a plastic bucket)to
expel the Nitric or in the alternative reboil the solution and
neutralize the Nitric/expel it with Urea in solution.
What I have suggested in the past is that if all else fails add
aluminium foil to your solution. It should reduce or recover all
metals which will be a fine black or brown powder.
Filter and dry these precipitates and start your dissolution process
again boiling the solutions down to remove the Nitric. Your silver
should naturally because of the Aqua Regia (the use of Hydrochloric
Acid) remain as a white Silver Chloride powder (which should not
redissolve in Aqua Regia) which can be filtered and fluxed after
boiling in water and drying, with 2 1/2 parts by weight of the total
precipitate of just Soda Ash or Sodium Carbonate to reduce the silver
to metal in a crucible. It will expel (as a white smoke) the attached
Chloride during furnacing as Sodium Chloride or salt leaving you with
pure silver.
Again tin could be a problem and it might be taken up with
hydrochloric acid? With your brown solution I would again
re-precipitate using sodium meta bisulphite to recover the gold (that
is if your silver dropped and was filtered) and then add aluminium to
the remaining solution after filtering to recover other PM's. Green
coming to the top of the solution during this process usually
indicates copper beginning to precipitate. You can stop at that or
continue until clear.
There are many ways to skin a cat as they say but never throw
anything out. The use of aluminium is simply using the Periodic Table
and the order of reactivity.
Regards,
DP
Don Buckley
- Braidwood NSW Australia
Dear all, I need help!!
Before, I'm sorry if my English is bad, But this would be the only
way that may help me out.
I have problem with precipitation gold from Aqua regia,
(My raw material is soil that eroded from some kinds of rock and was
proof that there was gold deposited )
- first, I boiled out unwanted metal by nitric acid. mud and gold do
not dissolve,then I filtered the mix solid-solution and discard
solution.
- I put solid from the first step to aqua regia (3 HCl : 1
HNO3)
(gold dissolved in this step and left unwanted mud deposited at the
bottom of a container)
- I filtered the mud out and collected the solution.
- I used urea to get rid of HNO3, after the fizzing stopped I added
Sodium sulfite (Na2SO3), (in this step the solution turn to
yellow.)
- I've waited and waited (several days) but nothing
happened.(Actually in this step the precipitation of gold should
occur)
** Could anyone tell me what is the problem ?? Is that because of the
contamination ?? and what should I do ??
- I used to try with adding KMnO4 to a little amount of sample from
this step. the results began with precipitation of brown - black
solid at the bottom and the solution turned dark-magenta.
- I collected the precipitate and melted it (melting alone would get
black plate of solid,no yellow metal appeared, But melting with
copper the yellow metal would appeared in form of very very small
spot on black plate )
- Is that precipitate collected from this step possibly be gold or
gold + something else?? if not what should it be ????
- If gold precipitate along with something else (unwanted) What
should I do to get pure ???
Now I actually Know that there's gold in my raw material but can't
take it out. Anyone help me please.
Sorry again If this post is too long, but too much detail will help
more.
Your help would be appreciated
PS. If this method is not suitable for this kind of raw material,
please give me suggestions.
THANKS
Patcha Thepsuwan
pharmacist - Bangkok , Thailand opt
August 25, 2009
My name is Budiarto from Indonesia, I am a processing gold from
tailing ex mercury using cyanide. I found an ore looks like a
platinum ore. First I crush the ore to 200mesh, leaching it with 50%
HCl (1 HCl : 1 water) for 3hours, filtering and wash 3times with
water. I assume most base metal is dissolves, I use HCl because Cr
will not dissolve in HNO3. Next the the filtrate ore leach with
straight aqua regia (5 HCl : 1 HNO3) with the process : boiling the
ore with HCl for 30minutes, and add HNO3 partially for a period
1hour, and keep boiling it for another 1.5hours. After cool filtering
with paper filter. The clear solution still have some solid seems
like silica gel & yarn that is flying around and will not settle
down. I start by adding ammonium chloride, but no red mud came out.
Next I try with copper wire (still in straight aqua regia condition)
with warming, a white solid precipitate but it seems very light
because it takes 12 hour to settle down. It also happen the same
thing with aluminum foil.
After filtering the white powder precipitate, I try to dissolve it in
straight HCl it is not dissolve, also in straight HNO3. But it is
easily dissolve in aqua regia in hot condition.
If what I get is platinum, why is ammonium chloride test didn't show
up?
There is still a lot shiny thing in the ore after several times long
hour aqua regia leaching, is this rhodium?
Taking out the gold is easy with zinc dust since there is no other
metal remain in the solution (in electro positif/negative view), AgCl
still remain in the ore.
dessy budiarto
fans - Jakarta, Indonesia
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