Dissolving gold deposits for analysis
A discussion started in 1999 but continuing through 2018November 20, 2008
Q. 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!
hobbyist - Herzogenaurach, Bavaria, Germany
April 12, 2009
A. Dear Reader,
In response to an article by Giancario B.
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.
- Braidwood NSW Australia
WARNING! The internet is a giant one-room schoolhouse where people will read or overhear details about operations that they are not equipped or qualified to attempt. Some things you read here may be intended for qualified chemists with haz-mat training, and working in fully equipped labs.
January 5, 2010
Q. This question is directed to Don B.,
of Braidwood NSW Australia who seemed to have some very good ideas re metals processing. RE your technique to recover silver from silver chloride via smelting. Is the soda ash and AgCl mix pH adjusted or is the smelting done at the natural solution pH. Is there any benefit to washing the results of the AgCl + soda ash mixture i.e. AgO to remove the resultant NaCl prior to smelting?
Do you have any experience with palladium recovery? I am trying to recover Pd from a nitric acid solution. My plan is to neutralize the nitric acid through either boiling off or addition of urea and then reduce the Pd using either SO2, oxalic acid or Zn metal. Do you have suggest re techniques. Thanks Marc - USA
precious metal recovery - Waukesha, Wisconsin
I usually drop my silver from nitric with salt water. You might call it brine water over there. You can use hydrochloric but I prefer salt. It will drop the silver as a chloride. Filter and dry.
Some of the literature on the subject suggests taking the dry white powder up with ammonia; say 25%. Other literature on this Site say ammonia and silver chloride can form an explosive mixture. I have never had that experience. There are many single chemicals that are quite neutral until mixed with another. Always be careful. You do these things at your own risk.
I flux my silver chloride with 2 1/2 parts soda ash by weight. The chloride is expelled during smelting and you finish up with your silver metal.
I have had limited experience with Palladium. The product used to precipitate it some years ago was very expensive. The price of Palladium and the products cost made it uneconomical. There are other precipitates. After recovery of gold I simply dropped all metals with aluminium,filtered and dried and sent the powder of for assay . A Refiner might smelt this down with silver,and re-assay a drilling.
There is also a test using Stannous Chloride (could be wrong) as you would to detect gold and Platinum?
- Braidwood NSW Australia
April 16, 2009
Q. Dear all, I need help!
First, I'm sorry if my English is bad, but this would be the only way that may help me out.
I have a 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.
pharmacist - Bangkok, Thailand
August 25, 2009
Q. 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 200 mesh, leaching it with 50% HCl (1 HCl : 1 water) for 3 hours, filtering and wash 3 times with water. I assume most base metal is dissolves, I use HCl because Cr will not dissolve in HNO3. Next the filtrate ore leach with straight aqua regia (5 HCl : 1 HNO3) with the process : boiling the ore with HCl for 30 minutes, and add HNO3 partially for a period 1 hour, and keep boiling it for another 1.5 hours. 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 positive/negative view), AgCl still remains in the ore.
fans - Jakarta, Indonesia
August 3, 2010
Q. My family and I live in Colorado and found a placer which definitely has some gold. It is in an area which has historically had tellurides and sulfated golds. Our problem is in not knowing how to remove the clays and prevent the super fine flakes from getting lost.
We are quite worried about the aqua regia with its associated health and environmental risks. We don't know about smelting but feel that it may be a safer way to reduce the material. The x-ray florescence assay proved gold with four times as much silver, but with some lead, (about one third the gold assay), strontium, and loads of iron. In fact the iron reads so high the assayer was quite excited to have a reading of gold at all.
We have used some nitric acid, some sulfuric acid on another batch. We have pulled as much iron and hematite, etc., with some super strong magnets, but don't know how to get it down further without doing aqua regia or smelting. The hydrogen peroxide fascinates me (for many reasons) but I haven't found how it works or what it is used in combination with, or even if it will work for this process. Any information would be greatly appreciated.
hobbyist with potential placer - pagosa springs Colorado usa
January 12, 2011
Q. I filtered my aqua regia and added my urea then my smb there was nothing at first but 30 min later a choc-brown stuff formed at the bottom -- is this my gold?cj lykins
student - colorado
February 15, 2011
Q. Running my first batch of gold recovery from a combination of many different types of gold plated jewelry, all my material it put into the mixture turned a copper color. Of course I thought the acid dissolved all the plating off the jewelry until I realized the copper color slime that covered all my metal rubbed off and and all the old plating was still on the jewelry. What is that copper residue, how did it get there, how do I remove it from the metal and how can I avoid it happening again?Jimmy Reece
hobbyist - Rocklin, California, USA
March 15, 2011
Q. HELLO. I am a student in iran. I have a question for you. please guide me about this problem (with detail and step by step). I work about the recovery of gold and silver from circuit board computer. I dissolved the board in nitric acid for separation of copper from precious metal. Later dissolved the board in aqua regia to obtain the precious metal. I cannot precipitate gold by urea and SMB. please guide me about this problem by step to step.
hobbyist - IRAN-SEMNAN
July 5, 2011
Q. Ok, I dissolved my gold in aqua regia and the liquid is blackish brown. I added urea to neutralize the nitric acid. got no fizzing at all. then added my precipitate and let sit for a day. and I'm still not seeing the brown mud as you would call it on the bottom. is the liquid supposed to be really dark? What did I do wrong?John Krise
hobbyist - Hamburg, Pennsylvania
February 18, 2012
A. I use oxalic acid to drop the gold; it leaves the platinum metal in solution.jesse peterson
- black hawk colorado
February 28, 2012
Q. Hi, I am a Nigerian. My home town has a good gold deposit. I extract some gold in my first experiment using sodium cyanide to leach the gold out, then use zinc powder to precipitate the gold out. I dissolve the precipitate in aqua regia and add urea (first in dry powder and in another case in solution) but no visible reaction of fizzing as expected and the filtrate drop no gold when ferrous sulphite is added for over 30 hours. Please, any help on how to add the urea or another way of getting rid of the nitric acid. Thanks.Nafiu muazu
- Jos, Plateau state, Nigeria
May 3, 2012
Q. Dear all,
I'm from Greece and I have a project in Refining gold using Aqua Regia. My problem is:
In the Reaction kettle I put 160 ml Nitric acid (58%), 420 ml HCl (33%) and 124,70 gr scraps of metals (50,6% Au, 14% Ag and others metals). I allowed reaction to continue for 2 hours and then I put 18 gr NaCl and 200 ml urea after 1/2 hour.
When I recovered silver from silver chloride powder I found that there are 4 gr of gold which means that all gold from the scrap of metals did not dissolve. I don't know the reason, so I need your help please.
a) I put the Nitric acid in a 1/2 hour. Is it too fast?
b) Should I use Nitric acid 69-72%?
c) Is the % of Ag in my scrap of metal to high?
I'm very thankful for any response because I'm really confused.
- Thessaloniki, Greece
A. There are too many methods of pgm recovery from e-waste but problem is if you want economical processes you should go by illegal methods (cyanidation mainly); and if you want eco-friendly processes these are not economical.Mahender singh
- Agra, Utterpradesh, INDIA
Yikes, that's a sad commentary, cousin Mahender.
Ted Mooney, P.E.
Pine Beach, New Jersey
April 25, 2013
Q. Hi Please help!!!
I have dissolved gold using Aqua Regia; however I might have used way too much SMB, I was so exited I went crazy with it!
I'd like to know if there is any gold left in the solution now, and how will I go about retrieving it now?
- South Africa
April 26, 2013
A. The recovery and refining of precious metals is really not that difficult. For the inexperienced, beginners, hobbyist I would suggest you obtain a copy of the e-book "Refining precious metal waste, by CM Hoke" it is free and can be downloaded at gold refining forums, Google it.
Now to answer your question: to test your solution to determine if there is gold left in the solution do a stannous chloride test. Stannous chloride solution is easy to make, and the recipe is readily available on line. Dip a cue tip in your solution and put a drop of stannous chloride solution on it. If it turns purple-ish you have gold, if it turns orange-ish well you have some Platinum in the solution waiting to be precipitated. To precipitate PT, simply condense the solution until it starts to become like a syrup and add ammonium chloride solution; you'll see immediate precipitation. Read Hoke, it will answer all questions.David Singleton
- Tibro Sweden
Hi, David. Thanks, good response!
But can you or anyone tell me if this CM Hoke e-book is legitimately available for free? Even better, does anyone know of a good list of which e-books are legitimately available and which aren't?
I'm not not saying that Hoke isn't legitimately available for free, but I see so many industry textbooks being distributed as free e-books which I know for sure have been stolen from the legitimate copyright holders, that we's like to be careful against possibly playing a part in it. Thanks again.
Ted Mooney, P.E.
Pine Beach, New Jersey
May 5, 2013
You seem to infer that the ebook by CM Hoke may not be free or it may be illegal. Given the fact it has been available at this site for many years, one would think that if the download violated anyone's copyright that the holder of the copyright would have taken action. If you do not believe it is free, download it yourself. There is a statement regarding copyright in the opening of the book. It is a valued resource for many refiners.
I note that many try to discourage people from refining at home telling them that this activity is not for the novice, and is very dangerous. Walking in public is dangerous, but we do it anyway. Refining is safe if certain protocols are followed and one employs a little common sense. We learn by reading, by trial and error, by doing. Here is a good example. Some proclaim that to get micron gold out of ore requires the use of very dangerous substances like mercury and cyanide. Anyone who has ever worked with ore knows this is horse hockey, miners in the Phillipines do it all the time by crushing their ore and washing it with plain soap and Borax, neither of which are harmful to the environment. It works, and forces the micron gold to the bottom of the pan. The gold can then be separated, melted with borax flux and poured into buttons for refining. The process is nowhere near as difficult or as dangerous as some want to make it. I do it in my garage on a regular basis, and have for years, and have never had a problem and sir I do not have a degree in chemistry or in engineering. Read the book, follow the formulas, follow safety procedures and it's not unlike baking a cake.David Singleton
- Tibro, Vastragotlands Region, Sweden
May 6, 2013
Hi David. I don't question your statement that Hoke is available for free download: I see it available on many sites including the notorious Pirate Bay.
What I was inquiring after was a list of which e-books are legitimately free versus which were pirated, with the authors being robbed of the proceeds of their efforts. I ask because I know such authors! Even an article I wrote for this site and an auto enthusiast magazine has been reprinted without attribution on more than a hundred websites; advising them & filing DMCA complaints proved to be an impossible game of whack-a-mole; so I learned for myself that it is an unrealistic rationalization to assume that copyrights are expired simply because a book is available for free download :-(
But Goldrefining.com seems to be a very reputable site. Further, I've now checked the Standford and Rutgers copyright renewal databases and don't see the Hoke copyright renewed, so it does seem legitimate. Thanks!
You are getting gold by crushing rocks, and I'm happy to believe it's not dangerous. But others on this page repeatedly advocate aqua regia, cyanide, nitric acid, etc., and I don't think it is inappropriate to warn inexperienced readers that these are dangerous processes. Good luck.
Ted Mooney, P.E.
Pine Beach, New Jersey
September 18, 2013
Q. I'm using the aqua regia method on gold plated computer pins. Now, my understanding is for every ounce use 150 ml 30 ml of nitric and 120 ml of hydrochloric..let sit over night then filter it, then add boiling water to a pound of urea then a quart of boiling water with an ounce of sodium metasulphite. My question: do you have to use boiling water for the urea and sodium? Can you just add those straight to the acids to still get pure gold or do you have to add those with boiling water? And after you add the sodium metasulphite how long does it take to see the gold powder lay at the bottom? If anyone can give me this info I really appreciate it. Thank you.Daniel Schuler
- Struthers, Ohio, America
September 25, 2013
Q. Please help recover gold I put circuit boards off phones and gold pins the tin silver copper went in I put in urea then meta sulfate but all that there is green looking brew and whitish gray goo down bottom. So I filtered the green stuff and took off whitish goo and added water and HCl then I added salt. How do I get gold?Jonathan Harrington
- Down Newly, England, UK
June 9, 2014
Q. Good day.
I have been attempting to refine gold from scrap electronics however I am having a few problems.
I have attempted to extract the gold using nitric acid but was left with a mixture of gold foils and particles and white mud substance... I could not separate the gold from other materials so I dropped the entire amount in aqua regia .
The gold has dissolved into the aqua regia and I then filtered out the rest of the stuff boiled out the nitric from the mix however I am failing to acquire any of the right reducing agents to drop the gold from the solution ... The reason is that I cannot find the reducing agents anywhere.
I hope that somebody could suggest a method for me to drop the gold with an easier to acquire reducing agent
- manhattan, new york, USA
July 15, 2014
Q. Every time I neutralize the Nitric Acid with Urea and then add the Meta bisulphite, it turns my solution clear. How can I drop the gold out of this clear solution...where is my mistake? Thank you!Mike Moore
- Long Beach, California, US
October 5, 2014
A. After dissolving gold you just test the solution using a stannous chloride. If you know about the dissolved quantity of gold, then add FeSO4 after urea neutralisation.bhupesh mulik
cac admixtures - mumbai,maharashtra,india
December 19, 2017
Q. Hi, please help me ...
I have about 5 g in my aqua regia solutions. After cooling the aqua regia then I put urea to de-nox the nitric acid. I put too much SMB and my solution turned dark green from gold color. After 12 hours it's turned to light green but a White Crystal formed, mixed with black mud. After testing with stannous chloride, the result is negative for gold. How can I remove the remaining SMB from the gold dust?
- kuala lumpur, malaysia
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