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Reverse electroplating for environment-friendly gold recovery / refining

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Q. I am about to embark on scrap circuit board recycling, primarily for the gold and platinum content. I am about to set myself up with an acid solution [aqua regia], that dissolves the precious metals, but is very dangerous to handle. It was recently brought to my attention that I could use a rectifier and salt solution to dissolve the metals , where a ceramic cell of some kind in the vat prevents the gold from transferring itself , and remains suspended until another chemical is added which causes the gold or platinum to solidify and sink to the bottom. I would appreciate some help, as I would like to avoid the messy dangerous route.

Thanks

Allan Chiasson
- Bathurst N,B. Canada


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A. Recycling gold plated circuit board scrap is not a simple process that can be set up using only e-mail/bulletin board responses.

Hire a reputable consultant who can spend the time showing you processes that will:
1. recover the metals
2. be economical to operate
3. be safe for the operators
4. not violate environmental regulations

You will find that aqua regia or chloride-based electrowinning/refining are not going to work on "raw" scrap.

Bill Vins
microwave & cable assemblies
Mesa (what a place-a), Arizona

Secrets of Gold Recovery from Electronic Scrap
[Kindle Edition /ebook]


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A. I have a simplicity refiner from Shor at home and use it to refine karat gold. The alloy is dissolved into a saltwater solution by using either a rectifier or battery charger amazoninfo (12 v 10 amp+) then the gold is precipitated by adding a powdered chemical (I believe is sodium metabisulfite). The "mud" is collected rinsed and dried and melted back to 999.5+ purity. I know of a guy in the USA who uses one to refine the amalgam he gets from stripping the gold plating off circuit boards.

hope this helps.

Regards
Jeremy

Jeremy Scott
- United Kingdom


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A. YOU NEED A HIGH CURRENT, LOW VOLTAGE UNIT FOR ELECTRODEPOSITION, A SOLUTION OF GOLD CHLORIDE, A FIBERGLASS OR CERAMIC SINK (BLANK ALL METAL), AND TWO WEEKS OF THEORY, SAFETY IN HANDLING, AND PROTECTIVE CLOTHING. I AM SENDING YOU A SCHEMATIC FOR THE UNIT. GOOD LUCK. HAVE FUN !

2.5 V, 20 A. CIRCUIT FOR ELECTROPLATING

http://www.maxim-ic.com/appnotes.cfm/appnote_number/2040/ln/en

PRODUCTS SOLUTIONS DESIGN APPNOTES SUPPORT BUY COMPANY 50W Current-Mode Forward Converter Design with the MAX8540 This application note details the design of a 50-watt, isolated, forward converter, using the MAX8540 synchronizable, high-frequency, current-mode PWM controller. Design procedures for both the power stage and controller are presented, along with actual performance measurements. The converter delivers 20 A of Load current at an output voltage of 2.5 V. It employs synchronous rectifiers for secondary rectification. The input voltage range for the converter is 36-75 VDC. This design is available as an evaluation board. The evaluation board demonstrates how easy it is to implement the features network and telecom applications require. The design methods can easily be adapted to the design of high performance, full featured off-line power supplies. Key features: 300 kHz switching frequency, Programmable input UV/OV Protection Programmable hiccup current limit or latch mode overcurrent protection, Programmable maximum duty cycle clamp with feedforward, Programmable slope compensation with single resistor, Synchronization to external clock, Adjustable current limit threshold, Active low-enable feature for easy turn on/off of converter, Internal leading edge blanking on the current sense pin, Output overvoltage protection Space-saving 16 pin QSOP. Description of Application Circuit Operation Figure 1 shows the circuit diagram of a 2.5 V, 20 A isolated forward converter that uses the MAX8540 current mode controller (U1). At startup, the total capacitance at the Vcc pin is charged through MOSFET Q7 and the parallel combination of resistors R30 and R22 from the dc input voltage VIN. When Vcc exceeds the undervoltage lockout threshold of the MAX8540, it goes through the soft-start mode and pulses of gradually increasing duty cycle are applied to the gate drive IC, U8. The MOSFET Q1 therefore starts to switch the input DC voltage across the power transformer T1, used to provide isolation and to step down the input DC voltage to the required level. (Selection of power transformer turns ratio is dealt with in the following section.) Since the energy for driving Q1 comes from the capacitance at Vcc, the Vcc voltage falls. The hysteresis of the MAX8540 undervoltage lockout feature allows this to happen. Pulses on the bias winding of transformer T1 are rectified by D1, regulated, and applied to the Vcc pin. The rectified and regulated bias circuit voltage builds up and prevents the Vcc pin from falling below the undervoltage lockout threshold. The primary side control continues to operate from the bias winding. The MAX8515 (U2) is configured to sense the Vcc pin and turn off Q7 at a voltage slightly higher than the worst-case startup voltage for U1. This avoids unnecessary power dissipation in Q7, R30, and R22. Figure 1. Circuit diagram of 2.5 V, 20 Amp, Isolated Current mode Forward Converter using the MAX8540.

Cheaper to build, and, Oh, might learn something new.

Paul T. Knisely
- Kenmore, Washington


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thumbsup2Hey, thanks for all the response to my thread. I have yet used any method posted, as I am still collecting gold scrap and squirreling it away. Aqua regia, is still my first choice for the simple reason that I only harvest clean gold, free from any circuit boards or other contamination, except what the gold is plated with. Any input on this would be appreciated.

Allan Chiasson
- Penticton B.C., Canada



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Q. Scrap recovery using Aqua Regia. I also do scrap recover as a hobby and for learning the silver and gold work fair in this process but we have no luck in the recovery of platinum from catalytic convertor honey combs can anyone please comment on this.

Eddie Kiswani
- Chicago, Illinois


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A. Hi Eddie,

The book I'm reading uses sodium sulfite for the precipitation of Gold. At the end of there is an article describing Platinum recovery. If you'll share, where are you finding Platinum?

Extracted from a link:

Platinum-

If you had platinum in your gold, it will not dissolve, to any appreciable degree, in the room temperature aqua regia. It will be left behind when you pour off the aqua regia, prior to precipitation. To insure high purity of the platinum, you will need to re-refine this material. Put this material in a fresh aqua regia bath. This time, however, heat the acid to simmering. Continue heating until all the platinum is dissolved (that may take 1-2 hours). When completely dissolved add 1 ounce of ammonium chloride for every ounce of dissolved platinum. The platinum will precipitate as a red mud. If you want to leave the iridium in the platinum, then wait for it to precipitate before recovering the platinum. Iridium will precipitate as a blue-black mud after the platinum precipitates. Platinum group metals will also show up on the stannous chloride test. Platinum turns red, palladium turns orange and iridium turn blue-black.

Good Luck,

Scott Rae
- Harare, Mashonald, Zimbabwe


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A. Hello Eddie, as a chemist working in the recovery of precious metals from electronics scraps I advise you to keep away from the aqua regia process. It's very dangerous because of it's toxic fumes and time expensive. Furthermore, the aqua regia process attacks the resins of the boards compounds leaving you with an insoluble mud. In fact, most of the operators in this sector prefer to use a basic process composed of cyanide (2% solution) and other components. This process is safer because there are no toxic gas involved, as long you take care not to originate some hydrocyanic gas. Search for literature on this matter.

I can only tell you that the process I have developed, based on cyanide, recover all precious metals from any board in about 15 minutes time. Unfortunately I can't give you other indications, it's a company secret. Good luck

Oscar Gagliardi
scraps treatment - Sevilla, Andalucia, Spain


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A. Hi Eddy

If you live in the USA and you want to use the (process composed of cyanide (2% solution) and other components) that the guy from Spain recommended. You will find that there are tons of environmental laws concerning the use of cyanide leach. I have chatted with several people on a few forums that are using AR and they are recovering the gold. They work outside so the fumes won't cause problems. Do your home work on it before messing with it because it is dangerous if you don't know what you are doing with it. Shor International has a page that describes the process and they have a list on the site of tools and safety tools.

Rob Harvey
- Scottsboro, Alabama


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A. I agree that the Cyanide treatment is a lot more hazardous than the AR method. Cyanide will kill you in 15 minutes or less, it takes less than 1 teaspoon of 2% cyanide solution to cause death. Also you will have toxic waste compared to the Aluminum Hydroxide that you can turn your AR into which has relatively no impact on the environment.

If you aren't careful working with acids they can kill you also but, with a little common sense you will be safer (do it outside). I developed a fume abatement apparatus for my lab out of PVC piping, some sealed plastic buckets and an air compressor. The fumes that are lighter than air rise out on their own and if the condense on the way out to the exhaust system (about 8 ft) then they fall into an acid collection container. If they are heavier then when I use the pump to push the fumes off they run through the activated carbon filter and fall into the acid condensing tank. I don't remove this tank for about a week to allow the acids to turn into a liquid then I neutralize them and dispose of them properly.

With a little time you can figure out how I made this as I sell the plans in my online stores and sometimes on auction sites. I am not going to attempt to advertise here as this is an informative site which I have a lot of respect for!

THE POINT IS DO NOT UNDER ANY CIRCUMSTANCES USE CYANIDE IN THE US. MINES MAKE ENOUGH POLLUTION WITH IT ALREADY!

Shawn Anderson
- Bellwood, Pennsylvania


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Shawn,
Cyanide can be destroyed using sodium hypochlorite (bleach). As long as you neutralize the cyanide before you dispose of the waste water (into the nearby crystal clear mountain stream crammed full of salmon) then I don't see what the fuss is all about.

See this page on how to do that: www.shorinternational.com/cyanodestruct.htm

Alan Jacobson
- Eugene, Oregon


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You are certainly welcome to voice your opinion, Alan, and we thank you for it. But if you don't see what the fuss is about, maybe you should find out :-)

Neutralization of cyanide waste is NOT trivial. A man in a local retirement village here died doing so in the last couple of years. Sewer workers have died as a result of such disposal. 6 employees in a plating shop in Indiana (Bastion Plating) died twenty years ago, and numerous individual workers since. Without careful pH control, not only will the salmon be dead from cyanogen chloride, but perhaps a person as well. Once the cyanide has complexed with nickel or iron, you can't destroy it via simple alkaline chlorination either. It amazes me that the government demands that any employees who work with this receive annual professional safety training; but hobbyists, often dealing with larger quantities under far more dangerous circumstances, sometimes feel that a paragraph of internet advise from a stranger (whose name may even be fictitious) is the only armor they need against their ignorance when working with an instantaneous-acting, airborne poison like hydrogen cyanide.

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


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Q. I am interested in the method of gold recovery from electronic scrap 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?

Also, does anyone here have experience using Butyl Diglyme in recovering gold from acid solutions?

Gary Boehm
- Hamilton, Ohio

Recovery And Refining Of Precious Metals


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A. Butyl Diglyme, available from FERRO and others, takes a bit of getting used to, but delivers 99.9 Gold as a final product.
Route is not too difficult.
Dissolve gold with straight HCl or HC + Chlorine (use fume hood or stay upwind outside...serious fumes)
In a separatory funnel, pour the strained HCl- Gold Chloride.
Add 1/4 measure or volume of Butyl Diglyme. Agitate until all the gold has transferred to the BD.
Separate out the stripped water/HCL portion.
Rinse and repeat until aqueous portion is clean.
Pour the Butyl Digyme portion into a heatproof beaker, place over warm heat,on a sand-filled pan. Add a small amount of Oxalic acid, dissolved in DI water, gently heating to simmer.
The gold will form clean flakes and fall out as it precipitates.
Alternate procedure once you have separated the Butyl Diglyme portion is to add H2O2 to precipitate.
Results may be melted with a bit of Borax Flux in a crucible by torch or furnace to solidify to a 99.5 % Gold button.
Butyl Dyglyme can be strained thru a coffee filter to clean it, and used endlessly, over and over.

Mike Voro
- Lehi, Utah


September 23, 2008

Q. I just happened upon butyl diglyme as a solvent extraction for gold. I'm wondering if butyl diglyme would be a suitable substitute for diisobutyl ketone?

Jim Oleson
Chemist - Fairbanks, Alaska



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!! I really cannot believe that NO-ONE knew of an feasible cheap way to reclaim gold and Platinum from circuit boards. In order to do so cheaply you need an exhausted gold bath and an exhausted platinum bath and an rectifier. You also need the type of electrode used to initially put the platinum ions into the bath, The concept is to put an Positive high voltage low current bias on the metal you want stripped of platinum or gold in the correct bath, the positive ionizes the gold or platinum and the electrolyte simply maintains the metal ions in liquid form.
Now, off hand I don't know what electropositive metal is currently used for Platinum as this is a trade secret, but I suggest trying beryllium as the negative cathode. Good Luck all you scrappers!
Lawrence A Cronce
- Stevens Point, Wisconsin


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Thanks Lawrence. Yes, de-plating is well recognized as a recovery technology. In fact, the title of this thread is "Reverse electroplating for gold recovery".
The anodes for gold & platinum plating are typically platinized titanium, so that material can certainly be used as the cathode in the setup you are describing -- but stainless steel is usually good enough, depending on the particular plating bath. Note, though, that platinum does not deplate from these platinized titanium anodes, so I don't share your confidence that it will easily deplate from the scrap, although I admit that I can't advance the specific reason why, except possibly that being so noble, efforts to put it into solution uncover underlying metal which dissolves into solution preferentially :-)
Thanks again.
pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Actually Sir in response to your response, I can see, that you are not entirely aware of the PhysicalElectroChemistry of How Platinum is initially collected for refining! See, any Platinum Plating electrolyte is initially formed with an base electrolyte and a reverse electroplating process. The concept is that if you have an small surface area anode, say platinum, and you put say 100 volts on it. Then you take your cathode, and you put the opposite voltage on it in a hull cell rectifier. Now, IF the cathode is the same surface area as the anode, it will be at the same voltage. However, let us consider what then will happen at 100 volts in an empty electrolyte, the Platinum will ionize and transfer atom by atom to the cathode, until there is nothing left in the anode. This basic principle is how every bit of Platinum refining is done. However as this is an closely guarded multinational trade secret, it is not taught at colleges. Now, it is for advanced techniques of my own methods that this principle can be used for Platinum electrolyte recharging!
Basically what we have is an small surface area of Platinum that you wish deplated, and you put this into an electrolyte which is known to be able to hold platinum, typically alkaline. The Platinum anode would in a chunk of scrap circuit board be at say 100 volts in the hull cell rectifier. The Cathode, however would have an surface area 1000 times larger. Hence the voltage on the cathode is .1 volts. This voltage while it allows deplating on the anode scrap, does NOT allow replating on the cathode. Hence the electrolyte charges with pure platinum! This in turn can be used to electroplate ANY hunk of metal with pure platinum. My consideration here is that you can do this method selectively and in the correct order bathing the circuit board in consecutive baths of differing electrolytes to recover one metal at a time in the nearly pure form in an electroplating solution for making extra money via electroplating articles of an metal type with virtually any metal. Thus you are saved the problem of selling scrap metal which MUST be assayed before it can be sold for anything near what it is worth.
Now, an further note is that EVERY electrolyte that can hold a metal ion will work for these systems, either in recovering metal in the nearly pure form to making electroplating solutions in the nearly pure form.
You might be able to use an electroplating solution a thousand times before it finally will not do an excellent job of electroplating! Simply recharging it off of scrap.

Now, you may comment again sir.
Lawrence A Cronce
- Stevens Point, Wisconsin


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Voltage is voltage, irrespective of surface area, Lawrence. If the voltage is 100 volts on the cathode, it's 100 volts on the anode no matter the size of either.

An individual can sell scrap metal, but he cannot sell electroplating services nor electroplated parts without complying with 40CFR433 and a whole bunch of other EPA regulations governing electroplating and hazardous wastes. Electroplating is 'categorically regulated', meaning that every drop of rinse water, no matter how innocuous, is regulated hazardous waste which must be manifested and hauled by a licensed disposal facility unless you obtain the disposal licenses yourself. Good luck.
pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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In response to:
"Voltage is voltage, irrespective of surface area. If the voltage is 100 volts on the cathode, it's 100 volts on the anode no matter the size of either."

True but irrelevant. ~ That's not how it works.
Plating (or stripping) action is most certainly affected by the size of the electrode.
The power density (available energy) at the site (molecular) of the plating action is a direct result of the surface area of the electrode. The 'size' of the electrode affects the voltage and current per unit area on the surface. There will definitely be more plating (or stripping) action at a site with a higher voltage and current flow than there will be at a site with a low voltage and current flow.

(Using bogus values to simplify the explanation.)
Assume you have two atoms that will plate (bond) with a potential of 0.5 volts or higher.
If you have 100 volts and you split it up between 100 atom pairs each is going to be at 1 volt and they will bond easily.
If you have 100 volts but 2000 atom pairs. (Larger electrode).. You still have the same voltage and current overall (through the solution and between the electrodes) as with the 100 pairs .. but .. each atom pair is only experiencing 0.05 volts potential and no bonding will occur.
Sam Johnson
Electronic Control Systems (Nuclear Power Plants) - Glendale, Arizona


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Hi, Sam.
What made my assertion relevant is that I made a true statement contradicting Lawrence's inaccurate one. Your terms 'power density' and 'available energy' are incorrect too; you are apparently talking about 'current density'. So, I suppose Lawrence can come back now and say "true but irrelevant" :-)

If you get a chance, please take a look at the discussion between Humpty Dumpty and Alice in Lewis Carroll's "Through the Looking Glass", where Carroll reminds us how silly it is to attempt a discussion if one of the participants tries to assign his own meaning to words. The first step against confusion & obfuscation is recognition that words must be used correctly and with consistent meanings. Voltage, current, power, energy, current density and so on all have established scientific meanings, which let us relate them to each other via Ohm's Law and Faraday's Law, etc. -- and it is absolutely relevant to immediately point out when people have used the terms in a fashion that will lead to erroneous conclusions.
pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

Peter Newell - Through the looking glass and what Alice found there 1902 - page 110

'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean -- neither more nor less.'

'The question is,' said Alice, 'whether you can make words mean so many different things.'

'The question is,' said Humpty Dumpty, 'which is to be master -- that's all.'

Alice was too much puzzled to say anything; so after a minute Humpty Dumpty began again. 'They've a temper, some of them -- particularly verbs: they're the proudest -- adjectives you can do anything with, but not verbs -- however, I can manage the whole lot of them! Impenetrability! That's what I say!'

'Would you tell me please,' said Alice, 'what that means?'

'Now you talk like a reasonable child,' said Humpty Dumpty, looking very much pleased. 'I meant by "impenetrability" that we've had enough of that subject, and it would be just as well if you'd mention what you mean to do next, as I suppose you don't mean to stop here all the rest of your life.'

'That's a great deal to make one word mean,' Alice said in a thoughtful tone.



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thumbsdownOMG (cringe, cringe), I doubt I am the only one praying none of these "hobbyists" live in my town/watershed.

Great candidates for a Darwin Award though...

http://www.darwinawards.com/

...suspect there's a good chance for at least Honorable Mention here, regardless.


Thomas Hanlon, Materials Engineer
aerospace finishing - East Hartford, Connecticut, USA


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