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The finishing.com Hotline -- Serious Education ... plus the most fun you can have in metal finishing

Reverse electroplating for gold recovery


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(2006)

Q. How profitable is the aqua regia gold refining project? I am much interested in setting up a gold & platinum recovery project here in South Africa. I have read a lot about aqua regia technique from the material I got from SHOR INTERNATIONAL. As of now I really understand how it works and all the safety precautions to be honored when refining the boards. I also have a large quantity of scrap 486 mother boards. All I really want to know before I invest a lot of money purchasing the necessary chemicals is, is it a project I can rely on? Is it worth the risk? Somebody please advise me before I waste my money.

SMART CHIRERU
GOLD FEVER - DURBAN, SOUTH AFRICA


(2006)

Q. I have the same question but I would like to know a bit more detail. What's the average recovery or what kind of recovery can I expect from refining gold circuit boards? I am also curious about the gold that is used on these boards. What is the gold alloy used? What percentage of gold does it contain?

Jared Thibeau
- Toronto, Canada



A. Hi Jared. The gold plating on circuit boards will usually be 24 kt, or very close, but the issue is that the plating is very very thin. On reasonably current computers it's probably something like 20 millionths of an inch on the tabs -- and half of that in other areas. Calculate how many square feet of gold plating it takes to get a worthwhile amount of gold.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

(2006)

Q. I am interested in the method of gold recovery from mix metal gold using a salt solution and a high current DC source (both of which I have available). Can anyone tell me more or exactly how to go about it? Does it leave the copper, lead and tin behind or are there more steps to the process? What is GC salt?

Yogesh Soni
- Ahmedabad, Gujarat, India


August 2013

A. Hi Yogesh. "GC" probably means gold cyanide, or more exactly, potassium gold cyanide.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

(2006)

Q. Most electronic chips have a ceramic enclosure. Gold wiring sits inside this enclosure.
Ceramic is a Ca or Si compound with a bonding agent. Temperature hardens ceramic.

Now, how do I get the ceramic to dissolve effectively (quickly) in order to process the precious metal? What substance do you recommend?

Thanks in advance.

Eduardo Garcia
research - Cordoba, Argentina

Recovery And Refining Of Precious Metals


(2006)

A. You must crush the chips in order to get inside of them, a rock crusher works quite well for this, I understand that you can recover between 1/20 and 1/100 of a gram per chip depending on what chips you are processing.

Donald Franson
- Tulsa, Oklahoma


(2006)

A. Hello, these following (non business) hobby websites mention the same article dealing with the security of microprocessors, and details how one might dissolve the packaging materials (using fuming nitric acid) I think.
Now, I don't know how this might affect the following processes for gold extraction, in fact I think it might dissolve everything EXCEPT the silicon wafer - wasting acid and leaving you with a messy sludge! which is why I probably won't be using a method similar. You want to expose as much gold as possible. crushing preferred...

my personal chip website:
http://www.chips.5u.com/idxhck.html

http://www.chips.5u.com

and from whence the article came:
http://www.cl.cam.ac.uk/~sps32/mcu_lock.html

My process has been to heat the chip cover over a Bunsen flame, and pop off the gold plated (both sides!) cover. Now very careful - ceramic gets VERY HOT and retains heat for a few minutes! In small 286, and larger 386 and 486 chips, there are many pure gold bonding wires, easily seen and accessible. In ALL gold-top pentiums, and pentium pros, and IBM etc/other CPU's there is the same. Later CPU's have less and less. See my website to view some nice gold-tops. The smaller black chips generally have no gold content worth the trouble. i.e., if you can't see it on the outside, there isn't much on the inside! but if you are dealing in millions of chips, this becomes a differing story!
I initially scraped the fine gold bonding wires off with a fine blade onto a glass plate for collection. Now, there is more gold in them there chips, however it is plated on the pins, it is on both sides of the cover, and it is also internal to the ceramic, you can see the plated traces running into a layer of ceramic, actually many layers.
What I intend to do is crush/grind/pulverize the complete ceramic chip, and extract the gold with the aqua-regia method. I would like to try the electroplate salt-water and ceramic tray method and have finally figured all the steps and chemicals involved. However just trying to source the ceramic dish/tray/cup and chemicals in new Zealand is proving to be a royal pain in the ears!

I hope I may have enlightened and educated some. And please please, take notes of all the concerns of the experts - this isn't really a home hobbyist project, nor is it a great earner for a home hobbyist either. Try and work with a simple cup of water, practicing not to spill a drop in transferring, filtering etc - and see if you can! Remember that simple microscopic drop could mean a serious burn, or blindness from a miss-wiped face.
Also, personally, I would not attempt the cyanide processing method unless you are prepared to invest into a serious refinery, requiring serious people with serious knowledge and expertise, the cutting of lots of red-tape, lawyers, legalities, zoning, health and safety, etc etc....

Tony Wallace
elements collector - Auckland, New Zealand



(2006)

Q. I have several thousand small bus-bars that were apparently used in a 1960's era PBX telephone system.The base metal is magnetic, but they are 24 carat gold plated.
I would like to remove the gold in the most economical, efficient , and safest possible method.
Any suggestions will be appreciated.

TEE SIM
hobbyist - Dublin, North Carolina


(2006)

Q. TEE SIM,

I also have gold plated computer/telephone system parts. It seems very difficult for hobbyist like us to find a cheap, safe way to remove the gold. I have cleaned about 50 pounds worth of pure gold parts. Clean meaning just the gold part itself. If you find an answer please let me know please, and if I find anything I'll do the same for you.

Thanks,

David A. Hartness
- Blythewood, South Carolina


(2007)

A. Hey TEE SIM & DAVID A. HARTNESS

I have idea for you just strip the isolation and keep the core inside sale those to the people who making jewelry , they can use that to make gold plating necklace etc. Easier and better for you

Gary chow
- San Jose, California



(2007)

Q. Does anyone know how much gold is in a average desk top computer and what percent can be recovered. thanks

Bill Walden
hobbyist - Burleson, Texas


(2007)

Q. Hi everyone, I've been refining my own gold from computer scrap for years now. I use a nitric digest on gold pins and components that are gold plated, that puts almost all the other metals into solution (except the gold), which I pour off most of, then filter the rest. What is left on the filter is "dirty gold". Then I take that and put it into aqua-regia solution. Makes a pretty bright yellow solution. Then I drop the gold out of the solution with sodium sulfite. That leaves the gold looking like a nice reddish brown dirt on the bottom of the jar. I filter this out using Whatman ashless filter paper. Then I burn off the filter paper and I'm left with 99.999% pure gold! Some times, however, I have to deal with "the blue goo" which plugs up my filtering, (in the nitric digest phase).This happens when I haven't gotten all the solder off the parts. You can't have solder on anything. That's my method in a nutshell. Any feed back is welcome.

Yvonne Torburn-Clark
- Mountain Ranch, California

Chemistry of Gold Extraction


(2007)

Q. In response to Yvonne's post, Question: What is the composition of your nitric "digest". Your post seems the most sane for my hobby pursuit and quest for a solution to all this stuff laying on my workbench.
Thanks

Dennis Nichols
- Springfield, Illinois


(2007)

A. In response to Dennis Nichols question; I just use nitric acid and distilled water, about 60-40 ratio. Eats up almost (but not all) metals but the gold. And thanks for the compliment, Yvonne

Yvonne Torburn-Clark
- Mtn. Ranch, California



(2007)

Q. Hey all, just looking at the thread and see a lot of interesting information. Very informative. I work/volunteer at the local computer recycling center here in Oregon and was looking for a way to boost profit margins. Currently we are stripping computers and shipping parts (by the 4x4x4 foot pallet) to various locations for precious metal recovery. My questions is, what is the #1 recommended way for the average hobbyist to recover the gold. Is that method something that can be used as a lesson for a class? Say 2-4 hours? What is the average amount of AU in the average processor? Easiest method of recovering gold scrap? Shall I scrape gold fingers off of circuit boards? What should I store those scrapings in? Glass, plastic, or metal container? Recommendations? Is it really worth all the time and expense? What is the average ROI for example if I use the aqua regia method? Any input would be nice as I really am interested in the recovery process (and keeping e-waste out of the landfills) and also the end product... GOLD. Any input would be nice. Thank you.

Rian Smith
hobbyist/e-waste recycler - Portland, Oregon


(2007)

My short answer is that mechanical separation & sorting sound worthwhile and may extend to such measures as smashing plastic connectors to get to the gold, cutting circuit boards to separate gold contact areas from the bulk of the board, etc. But please remember that all of the major environmental organizations are begging you not to do this for two reasons: first, amateur recycling is a wrecking ball that spreads the e-waste toxins everywhere instead of keeping them in manageable units like a computer or TV; second, when people "cherry pick" the waste, the recovery of the balance of the equipment becomes economically prohibitive which means it will not be recycled, but these toxins will be left to contaminate the earth.

Any operation which involves burning or chemical treatment should be left for a real refinery anyway. Proper refineries cost tens to hundreds of millions of dollars.

I realize that others may disagree, but in viewing pictures from China and India, you see the human toll and environmental toll of e-waste recycling by amateurs; you also realize that your competition works almost for free.

The best long-term solution to e-waste (as far as I can see, and not taking into account the law of unintended consequences) seems to be laws that require the manufacturer to take it back at no charge for disposal at end of life.

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

(2007)

thumbsup2Wow... after reading all this, I've decided to pay someone else to do it!

Mark Sullivan
- San Jose, California


(2007)

The subject of do-it-yourself gold refining has raised it's ugly head on this forum many times. With the present high gold prices, interest in this subject is building and isn't going to go away. There is very much dangerous misinformation on the internet. On Ebay, there is a fair sized cottage industry providing gold refining info, some good and some bad - mostly overpriced. Several months ago, a gold refining forum was set up (not by me) to provide honest, free information, keep amateurs safe, and properly handle waste. In 6 months, there are over 700 members and over 8,000 posts. There are 2 or 3 of us on the forum who have been professional gold refiners for many years, that attempt to act as a stabilizing factor. Personally, I feel that refining should be done by the pros but, if amateurs are going to do it, they should do it right: goldrefiningforum.com. I would imagine that this forum has already taken some of the burden off of finishing.com.

Chris Owen
- Missouri

Ed. note: Chris has been a great responder at finishing.com and we thank him for his efforts and the education! Also a number of people have been very complimentary about his forum.


February 23, 2008

Q. I found 1/2 pound of white color of gold salt, from an old plating company. How can I recover the gold from this formation

Harry Kaspar
melter - Los Angeles, California


March 3, 2008

Q. Yvonne's method sounds good, how do you retrieve other metals, like silver? Bill.

bill douglas
gold prospector - gold beach, Oregon


May 12, 2008

THANK YOU BROTHERS AND SISTERS,
I've got it. I've been reading this page and others to figure out the process and I've got gold from old e-scrap that I collected for 3 years and got a nugget the size of a quarter and 3/16 of an inch thick. Well here's your answer: titanium metal, a white flame heat source and Borax [linked by editor to product info at Amazon] is all you need, these chemicals. Please work in fresh air also butane don't waste your time and money, think hot heat and even consistent heat does a nice easy job.

THANKS
THE CLYDE
PS. I've got gold so let this economy go to double tooth picks RRRReal money!

Scott Conley
- St. C., Ohio


June 3, 2008

A. This is Very Simple and is the basis of all Chemical Gold recovery in the Au gold mines in the early days.

Take the gold coated item , (we do this with gold tailings in exploration) Boil it in a solution of Concentrated household bleach,50% water to bleach 50% for 45 Min.

Drain off the solution

Put in plastic pail

Put in stainless Steel rod (one side)

Put in roll of wire wool (other side)

get a powerful battery charger [linked by editor to product info at Amazon]

Attach (plus) to wool and minus to SS rod.

Turn on Battery Charger .

leave 40 mins, Gold will be converted from solution to the wire wool.

Take wire wool and dissolve in crucible in hydrochloric acid, carefully drain off the acid and keep sludge at bottom.

Place crucible over Bunsen burner and melt.

Small gold nugget will form in the bottom.

Thank you

PS be careful to vent off the hydrogen gas with the electrowinning stage.

Mark Strologo
- Fremantle, West Australia


November 23, 2008

Q. To the gentleman from Australia- will this process (boiling in bleach solution) work to strip/recover the gold from gold plated items such as jewelry? Thank you in advance for your answer.

Terry Larson
- Evansville, Indiana


February 11, 2009

Q. My question goes along with Mark Strologo of Fremantle, West Australia --

I already have my gold (as gold chloride) in a salt solution (as in sea salt). Do I go ahead and electroplate the gold out and skip the boiling procedure?
Any help is appreciated.

harry freeman
hobbyist - the woodlands, Texas



November 2, 2008

Q. I HAVE BEEN USING NITRIC ACID TO RECOVER MY GOLD AND HAS WORKED GREAT FOR YEARS I COLLECT 100% OF ALL MY GOLD. NOW WHERE I BUY MY NITRIC ACID HAS DECIDED TO TAKE THE PRICE UP TO WHERE IT IS NO LONGER EVEN CLOSE TO BE PROFITABLE. I WANT TO USE REVERSE ELECTROPLATE SINCE I HAVE THE MACHINE ANYONE KNOW WHAT ACID I USE FOR THIS? THANKS ANDY

ANDY BOYTOR
HOBBYIST - HOUSTON, Texas


December 1, 2008

Q. May I have the following questions and thank you for your kindly answer and suggestion
1. How many percentage of gold can be recovered from electronic scrap?
2. How many miligram contents of gold in separated CPU per kilogram?
3. How many miligram contents of gold in PCB?
4. What are the needed tools to start the recovery job?
5. What kind of scrap can be recover the precious metal except computer parts or cell phone?

Lin Chuan Wang
hobbyist - Bangkok, Thailand


December 29, 2008

The answer to most of those questions are trade secrets of sorts, so it seems. If you discovered a gold vein, would you go broadcasting it and start a stampede to it?

In short, it's worth going for if you know what you're after. Computers for instance, the older the better, cause back in the 286,386,n P1 days the manufacturers were using heavy but expensive plating. So go after those sources and you won't go wrong. You would be surprised at the amount of old Gold Rich abandoned units sitting in basement rooms of schools, office bldg's, Hospitals, etc.:)

Allan Chiasson
- Penticto BC, Canada


May 9, 2009

Q. What are your feelings on using a solution of 1/3 muriatic acidamazoninfo, 2/3 Hydrogen Peroxide [linked by editor to product info at Amazon] and taking the gold flake recovered and superheat it with a butane minitorch and some flux. I am having difficulties with the flux (how to make it/utilize it} any suggestions?

James Franklin
- Indianapolis, Indiana


June 20, 2009

Q. Hi Guys,

Just a quick question for you all and being totally naive:

Recovering metals such as gold & copper from circuit boards, can electrowinning be used? If so, how does the process work? Do you crush and pulverize the PCB's, put them in the electrolyte solution, then that solution is processed by sending a charge through the cathodes and anodes. Finally you pull out either the plating or the powder and discard the electrolyte solution after neutralizing it?

Is this correct or am I way out?

Thanks for your replies in advanced

Jason M.
student - New Zealand


July 11, 2009

Hello, will the Aqua Regia method work with gold filled jewelry to extract the gold? If not, how would I go about that?

Thank you!

Felicia Espinosa
- Gilbert, Arizona



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November 6, 2009

A delightful blog but I am concerned about the cyanide phobia evinced here. Certainly a serious substance but, in the matter of science, exaggeration is unwarranted.

Cyanide is a naturally occurring chemical. In the open it decomposes nicely without any human intervention. Its short Chemical Persistence is the reason it was considered safe for use by skilled technicians in executions.
Electricity and water kill far more people each year than cyanide. When you do hear of cyanide death, it is usually through peripheral chemistry.

The stuff is reasonably difficult to handle and I laud the idea of leaving it alone but never restrict yourself from valid scientific inquiry.

EPA in Coeur d'Alene, Idaho misunderstood cyanide and caused the death of a fine man through some of the most complex of legal wranglings. The subsequent coverup is devastating!

What you know won't kill you. What you don't can kill you.

Jack Wiegman
- Missoula, Montana

November 6, 2009

Thanks, Jack. Whether concern about cyanide is legitimate or a phobia depends on the circumstances. While it is true that cyanide is in almonds, lima beans, apple pips, etc., here is some food for thought --

The owner and plant manager of Film Recovery Systems in Chicago made the front cover of the national news magazines some years ago when they were convicted of 1st degree murder over the death of one of their employees. They claim the man (59 years old) simply had a heart attack; the prosecution claimed a reckless death from cyanide.

Per the plating journals a few years ago, paramedics refused any treatment to a man suffering a heart attack in a plating shop because they were afraid it was cyanide poisoning. Coroners have refused to autopsy people believed to have died from cyanide poisoning, so we'll never know.

The 6 men who died at Bastion Plating in Indiana in 1984 all died of cyanide poisoning, from mixing acid with cyanide, not from drowning or electrical shock.

I've spent my entire career in the plating industry, and until fairly recently, most shops used cyanide plating solutions, many still do. The concept doesn't frighten me at all, but it is SO easy to make a serious mistake. I can't count the times I heard of people accidentally adding dry acid salts to a cyanide tank, or cyanide powder to an acid tank, making the area a California Gas Chamber if not INSTANTLY evacuated.

The stuff can be dangerous, especially if we are talking about untrained people (most of the people here trying to recover precious metals from electronic scrap).
Please give us some info or link about the Coeur d'Alene death. Thanks again.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

November 17, 2009

thumbsdownWOW! Talk about serious fear mongering. While it is true that cyanide is a serious poison, it is far safer than Aqua Regia. Proper safety protocols and common sense allow cyanide to be used quite safely. It is by far the safest and most economical method for extracting gold from most ores and stripping scrap and etching metals for plating. It is easily destroyed by oxidizing with bleach or peroxide and will breakdown rapidly when exposed to sunlight and air. Mining companies use many thousands of tons of the stuff with virtually no problems (except when someone screws up bad). How many people drown in water every year? How many die from gasoline fires and ingestion? Pesticides?
Cyanide does not accumulate in your body like mercury and rarely stays in the environs for very long.

Roger Smith
- Bishop, California


November 19, 2009

Hi, Roger. In addition to working with sodium cyanide and potassium cyanide in electroplating processes for brass, cadmium, copper, gold, silver and zinc plating for 40 years, I designed & installed many wastewater treatment systems for cyanide destruction. I don't fear cyanide, I have proper respect for it.

People who work with cyanide in industry usually:
1. Have received approved Haz-mat training annually.
2. Are required under pain of job loss to wear proper protective gear.
3. Have hydrogen cyanide detectors installed in their plants.
4. Have cyanide antidote kits on hand.
5. Have Scott Airpacs and a fellow worker trained in their use to rescue them and call 911.
6. Have pre-arrangements with hospitals and fire departments to deal with possible cyanide exposures.

This thread includes many entries by amateurs with no appreciation of the hazards of cyanide, and educating them that it is an extremely powerful and fast acting poison, both by ingestion and accidental acidification, is not fear-mongering but a reasonable attempt to instill healthy respect.

You claim it's "far safer than Aqua Regia" but I quoted an actual case where 6 maintenance men died from cyanide vapors in a plating shop, caused by an accidental mixing of cyanide and acid. I feel it's foolish and dangerous to suggest that people can safely work with it without Haz-Mat training and equipment.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

February 16, 2010

What about this Electrolytic action for removing gold from E-Waste. Is this a good process for a small 1 bdrm operation?

Will Davis
Hobbyist - Springfield, Michigan


November 6, 2011

I recently purchased a thumb cell refiner with the intent of refining sterling silver. I am writing this in hopes of shedding some light on there advertised statement "Requires no experience". Lets see, how do I say this...HORSE HOCKEY!
First of all, the 'instructions' which they admit are the heart of the product you are buying, are vague at best. Prior to the purchase, I did a lot of reading and fortunately, am equipped with all the proper safety accessories. That being said, I am going ahead with a run. They say in the massive 2 page instructions (without diagram 1, or photos!) to use "... a flat thin piece of pure silver (your cathode)." 3 paragraphs later they say "...assemble the unit and connect your silver anode and graphite cathode to your rectifier." So, is it best to use pure silver for a cathode, or the graphite rod? They NEVER mention ratio of area between anode and cathode. I might mention the 'kit' comes with a 5/8" x 12" round graphite rod.
Also, if someone would be so kind and would offer some help, they say NOTHING about recovery of the 250 grams of pure silver used to make the bath, nor do they mention anything about neutralizing the bath for safe disposal once it is no longer able to produce pure silver.
Now I know you're all wondering, did I contact the seller for better instructions?....Yes I did, and the resulting 'answers' served to confuse me more than inform me.
I am logging the entire process as I go, and when I complete this process, I'll offer to sell them back a REAL set of instructions, complete with a diagram, suited for the "Requires no experience" crowd. I know, I'm dreaming, but I thought everyone could use a little humor.

mark_purdue
Mark Purdue
- Atascadero, California USA

----
Ed. note: Thanks Mark. For a bunch of reasons we strive to keep the discussion generic and to not slam individual products, so we have removed the name of the thumb cell refiner vendor.



January 11, 2012

Hello have you tried a PCB etching solution like ferric chloride this will dissolve the copper under the gold leaving the gold flakes. The bad thing is that this will dissolve other metals like the lead silver and it will exhaust itself very quickly but if you protect the other metals with a lacquer leaving the gold exposed this would result very cheap
Eduardo uribe

Adrian Uribe
- Albuquerque, New Mexico


March 10, 2012

I'm new here, stumbled on this site looking for a simple way of collecting Gold off of plated jewelry ...
I do not want some big production... a small and simple procedure would be fine. I am not a chemist but I've worked with some nasty stuff, I know how to be safe and environmentally friendly.

It seems Reverse electroplating is the answer... the chemicals seems to be expensive and needs to be purchased in large amounts and some are hard to find. The aqua regia process seems dangerous and tricky, there has got to be a simpler way... I've seen it on YouTube, a glass dish Reverse electroplating jewelry... What is needed for that?

Bill Kaetz
- Paramus, New Jersey, USA


May 2, 2012

Q. Lately, several plating companies tell me they DO NOT do reverse deplating. I am suspicious but don't know what else to ask. I have quite a bit of gold plated objects, and I don't want to start a new business just to sell it. Can anyone tell me who buys gold in plate form, or who will strip it and buy the gold?

Al Pelletier
- Sekiu, Washington, USA


May 3, 2012

A. Hi Al.

In these days of prolonged recession there are "We buy gold!" stores on every other street corner in the cities and suburbs. If none of them are uninterested in buying it, it should give you a sense of its value vs. the cost of recovery. Modern gold plating tends to be from 10 to 40 millionths of an inch thick, often even thinner. You will see many costume jewelry manufacturers rejecting the idea of "micron gold" (coatings of 40 millionths thick) as being much thicker than they are willing to apply. Please do a simple volume calculation of how much gold you actually have. Good luck.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

August 20, 2012

I have reversed plating of gold in an acid bath; now how do I get it to gold bullion?

toni parker
- TUCSON, Arizona, usa


September 17, 2012

Q. Where can I buy the acids for the extraction of gold from computer/cell phone parts. I have so many cell phones and would be willing to sacrifice them but would not do me any good if I can't extract the gold, and would it be worth it? Any help or info would be appreciated.

sam serna
- san jose ,california u.s.a.


September 18, 2012

A. Hi Sam.

Acids are readily available =>

But cell phones are new technology with the thinnest possible gold plating. Please calculate how much gold you have before investing in acids, and before undertaking the required education and the risks of gold recovery.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

Muriatic Acid

Nitric Acid


October 29, 2013

A. Firstly, I am not an authority on this subject. That said, is abrasion an option? A firearms cartridge tumbler with an aggressive abrasive. Pan the residue, then melt it. Gold will be at the bottom, won't it? Perhaps just skip to the melting. Even the copper will have value.

Jonathan Cochran
- Pyeongtaek, S.Korea


Thanks, Jonathan. I understand that some people concentrate on the gold plated tabs of circuit boards, scraping the gold off with a razor blade (don't forget safety glasses or goggles for this). But if this has any practicality at all, it's only for very old (50 year old or more) boards. With today's gold plating of 20 millionths of an inch or less, if you were able to scrape off 100% of it, you'd need 5 layers just to equal the thickness of a human hair; 100 layers to equal the thickness of your thinnest (0.002") feeler gauge. I'm reminded of the alliterative crude-ism "small as a nit on a gnat's nut" :-)

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



How to refine gold from 10K to 14K?

January 8, 2015

Okay, all very interesting but I'm just looking to raise the gold content of scrap, say 10k to 14k, is there a safe chemical process or physical process (melt for instance) that I can use to remove copper or other metals from the scrap gold I buy for my casting? I'm mostly looking to increase the Karet of the cold and get rid of the copper/rose hue from the final product. I like to cast with a brighter gold and I find a lot of the 10k to be too dulled.

Marie Rosin
- Sierra vista, Arizona


January 31, 2015

A. Refining cannot be done by simply melting it. You might be able to oxidize and remove a small amount of the copper by adding 3 or 4 perls (BBs) of sodium nitrate along with a pinch of borax to the melt. The small amount of copper oxide produced will end up in the slag. This can be repeated. Some of the zinc in the alloy will be oxidized at the same time and this could affect the casting properties.

Gold scrap often contains solder and solder often contains lead. Since it only takes about 5-10 ppm of lead to make the casting brittle, it is usually a bad idea to re-cast scrap gold. Most all reputable jewelers that I know of don't even try to re-cast scrap gold.

There is no safe method to refine (purify) gold. It always requires the use of aqua regia, which is a combination of nitric and hydrochloric acids. Both are quite dangerous and, in combination, they are even more so. When in use, very toxic fumes are emitted and, therefore, a fume hood is an absolute necessity. Also, it takes a lot of hands-on experience and knowledge to successfully refine karat gold.

The only safe way to raise the purity to 14K is to melt the 10K and add pure gold to it. If you have 10 grams of 10K, you would have to add about 4 grams of pure gold to it to raise the purity to 14K. However, you won't know what color you'll end up with until you do it.

Chris Owen
- Nevada, Missouri, USA


February 4, 2015

A. Hi Marie,

Leave chemicals to the chemists.

The earliest method for refining gold is cupellation.

The gold is simply melted, preferably in a bone ash cupel, and the base metals (except silver) are oxidised. If you have a bone ash cupel, the oxides are absorbed by the cupel, otherwise discard the slag. This method produces gold pure enough for assay purposes and then you can add whatever you need to get back to 14 ct.

Or with a bit of calculation, you could refine a small part of your sample and add it to the remaining 10 ct part.

Search the net for "Fire assay cupel" and use an oxidising flame (a kiln is better)

geoff smith
Geoff Smith
Hampshire, England



February 23, 2015

Q. Can someone please tell me what size battery charger I need in sulfuric acid reverse electroplating? I seen somewhere a 12 V 10 Amp, and on here a 12 V 6 Amp. So which one is better?

jared Martin
- Hobbs New Mexico


February 2015

A. Hi Jared. Either will work equally well after a fashion, it just depends on the volume of material you are processing (a 10 Amp unit processes more material faster) -- but neither will be great because they are designed to charge batteries, not as power supplies for electroplating. As Geoff warns, it's really best to leave chemical and electrochemical processes to people who are trained in it because there are dangers at every step in the process.

Regards,

Ted Mooney, finishing.com   Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


February 25, 2015

The gold refining forum that I act as a moderator on [ed. note: goldrefiningforum.com] has done much work with the so-called "reverse electroplating" method of gold stripping using concentrated sulfuric acid as the electrolyte. It can be used to strip gold from most anything, including aluminum, without attacking the substrate metal (unless the solution gets too hot). The gold precipitates as a black powder and settles to the bottom. After settling, the top solution can be siphoned off and reused. It will also strip silver and palladium but separating these from the solution is more difficult than with gold.

The biggest problem with a small cell is regulating the amperage. If too much current is used, the solution will overheat and this can cause big time problems down the line. I once had a 50 gallon cell that I ran at 250 amps. Even in sunny L.A., the solution never exceeded about 110 °F.

I would recommend not exceeding 5 amps per gallon, which will strip most gold plating in just a few minutes. This is difficult to do with a battery charger although I have never used one for this application. I do know that an automatic charger won't work. A manual one will work. Also, unlike an automatic charger, the output of a manual charger can be varied by plugging it into a Variac.

Being an old plater, I prefer the one knob, one ammeter, one voltmeter, and fuse (one or two) type rectifier as a power supply.

Just remember that an electrical connection must be made to each isolated gold-plated portion of the part you are stripping. For this reason, circuit board fingers are not a candidate, since the individual fingers are not connected to each other.

Chris Owen
- Nevada, Missouri, USA


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