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topic 5198

GOLD "BOMBING" PROCEDURES AND REGULATIONS NEEDED


A discussion started in 2000 & continuing through 2017 . . .

(2000)

Sirs,

I am writing this letter in request of any information that your office can provide on case histories and or regulations regarding a chemical gold stripping process known as "bombing".

This process is used by almost every company in the gold manufacturing community especially in smaller and medium sized operations especially in California and Hawaii.

The process involves the use of Potassium Cyanide, Hydrogen Peroxide (35%) and warm water. When Gold is processed in this solution a small explosion occurs releasing a cloud of toxic gas and a quantity of toxic water as well. The gold is stripped and made brighter in appearance (1% gold is lost in the process to the water solution).

Almost all shops using this procedure dump the effluent down a sink and they ventilate the gas cloud outside.

I am aware of only one shop in my area that has an OSHA approved operations procedure for the protection of the employee, but I cannot find any reference to the proper handling, reclamation, and or disposal of the effluent or the emitted gas.

Please help me to find all applicable regulations and procedures to safely and properly handle and dispose of these materials. If there is a small closed loop system for doing this procedure, I would appreciate that information as well. Thanks for your assistance, Dane Musick Field Engineer (If your office cannot directly assist, please refer me to the people who can address these issues technically)

Dane E. Musick
- Honolulu, Hawaii


(2000)

I am acquainted with the "cyanide bombing" procedure but am surprised to hear that it is ubiquitous; I only saw it done once, decades ago, and the demonstrator thought he had something pretty unique.

If it is done primarily in smaller and medium size operations, what process do larger operations use in its stead, and what precludes the smaller operations from doing the same?

You are probably correct that the waste products are harmful and dangerous, but 'toxic' is an overused politicized word and I don't like to see you use it (at least you didn't use 'spew'). In my State the governor reminded everyone that " 'toxic' is a matter of statute not opinion"; but this cuts both ways: a harmless material is toxic if the State defines it as such, and the harmful materials you are complaining about are not 'toxic' unless California and Hawaii so rule.

The plating industry is very heavily regulated and has been for decades, so plating shops don't vent this to the atmosphere nor run it down a drain. Other gold processors may, but I'd presume there is an EPA 40 CFR covering gold and precious metals works. That's where I'd start looking.

You may also want to review letter #182 here. Regards.

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


(2000)

It is true that "Cyanide Bombing" process is the most preferred mass finishing process since it is fast and can be batch treated. I have personally worked with bombing of jewelry and I have to say that the word "toxic " is pushing it a bit too far. When a solution of boiling sodium cyanide is treated with hydrogen peroxide, then a large amount of gas (probably hydrogen ) is released which actually does the scrubbing action on the surface of the jewelry. Cyanide is instantly converted to a cyanate which is not considered toxic and can be easily disposed off after removing the precious metals by plating it out and treating the residual liquid with bleach to ensure proper removal of any cyanide present in the solution.

I am not aware of any specific OSHA regulations for this process but a proper enclosed area like the sand blasting unit with a ventilation leading to a scrubber should suffice the proper precautionary measures. The operator should have proper protective gloves [linked by editor to product info at Amazon] and eye protection (goggles [linked by editor to product info at Amazon]) while working with these chemicals.

The word "bombing" sounds like something very toxic and hazardous but in fact the reaction causes some frothing and bubbling causing some liquid to jump out of the container due to rapid release of gas. Please let me know if you need anymore information. I would be happy to direct you to somebody who actually uses this process and help you in this matter.

Ajit Menon
- Rapid City, SD


(2004)

I have recently started to use potassium cyanide to clean my gold and silver before soldering. Unfortunately, I am not familiar with the process. I have been told that combining hydrogen peroxide with the cyanide solution will enhance the results. I wonder if someone out there can give me precise mixing ratios and mixing techniques for good results.

Thanks,

Randy Sainte-foy
jeweler - Montreal, Quebec, Canada


(2005)

I am a 4th generation goldsmith from Sweden, I learned from my grandfather.

We used potassium cyanide with hydrogen peroxide all the time, and this was the process as I recall it. Please forgive me if I don't know the right terms in English, I learned all of this back home in Sweden :)

1) After assembling the piece, put it in heated (diluted) sulfuric acid until all the black spots and all the borax (or whatever you used) is gone. Word of caution: Don't heat the acid at the same time as you're heating the cyanide...

2) Rinse, dab dry, and polish on the wheel with the rougher compound.

3) Put the piece(s) in an enamel pot with enough cyanide mixture to cover it. (I would guess we used maybe half a deciliter of cyanide in about 5 liters of water. We had "the scoop" and "the bucket", and I never had a reason to know the exact measures - sorry! We did mix it beforehand and used only what we needed each time) When the cyanide is boiling, turn off the heat and pour in a dab of peroxide (somewhere in the 30% range concentration-wise, so not the peroxide you get at the grocery store) and QUICKLY move your pan to where it can bubble up and "boil over" safely. We used a drum with a funnel. The contents of the drum were a very pretty blue :)

4) Rinse and dry, and polish on the wheel with the finest compound.

5) Wash in heated ammonia and dish washing liquid (we used Fairy - a squirt into water enough to turn it a light green, and then a bit of ammonia - couple of tablespoons, probably. Here also, just enough liquid to cover the pieces). Don't let the ammonia boil - you'll smell it anyway ;)

Feel free to get back me if you have any questions - or any answers for that matter - I'd love to find out where I could get this stuff, as no polishing method I've tried in this country even comes close...

Thanks,

//Gunilla//

Gunilla Leavitt
- Santa Cruz, California


(2007)

I am head of a jewelry manufacturing unit in India. We use bombing for improving finishing of jewellery. For recovery we were using electrolysis method. However recently there is problem in recovery. it may be due to high silver content in the liquid waste. Someone told me there is another method which uses addition of HCL. Can somebody explain details of the process using HCl for recovery.

Dinesh Kumar Sinha
Jewelry Manufacturing - Noida, UP, India


(2007)

with respectful
sirs

ya I want to know about bombing method,
I am so interesting with bombing method , because I never heard this method
so I need your help to get more information about bombing

the first I want to know :
what I must mix in to bombing method ?
the first I know potassium cyanide
than the second in Hydrogen Peroxide and warm water
but my friends tell me that lack something
so I am confuse ?

and the second I want to know :
what percent I must use to make a 1 liter "bombing" liquid
so I can use well

thanks you very much
and I am before I am sorry
because my English not pretty good ;0

SHANDY PURNAMA
CRAFTSMAN IN PLATING SHOP - SURAKARTA, INDONESIA


May 1, 2009

hello
I need help. how can we recover gold? and for cyanide bomb, we have to add hydrogen peroxide drop by drop or all of it in same time?

Ali Jaff
plating shop employee - Shiraz, Iran


September 17, 2009

Hi , I do the "bombing " method you describe. I too do not have the exact quantity measurements ! Mix about 1/2 - 3/4 cup of cyanide to approx. 5 liters water. The water should be about 70 °C temperature, stir to dissolve cyanide. Put item to be stripped (bombed) into a dish - I use a Pyrex dish - and add about an eggcup full of hydrogen peroxide. Take care to keep your face away as this mixture is volatile and you don't want to be sprayed by the explosion.Wash out with clean water as soon as reaction is complete.If there is any oxidising of your treated item, just soak it in the cyanide solution for a bit and it should come out clean. After a bit of practice, you will work out the method and quantities to best suit your needs . I test the temp of my water so the reaction times are consistent.Good luck.

Mike Gilmeister
- Auckland, New Zealand


September 10, 2010 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Hi,
I have a small jewelry business in the U.K. and have a real problem with firestain.
I've just found this site after trawling through the net, my request is how do you make a chemical bombing/stripping plant for a small jewelry workshop? What are the chemicals to use and what sort of rectifier (I have one for electroplating) do you use, I don't use acid for pickling the jewelry I make, and safety pickle doesn't get the firestain out.
I've tried cyanide and ammonia mix and reversed polarity but it leaves the piece black not shiny.
Can anyone suggest a solution please.

Many thanks,

Nigel Graham
designer goldsmith - Eastbourne, East Sussex, U.K.

April 20, 2017

A. I read a posting talking of combining Cyanide and Ammonia ... I was taught that this combination should always be avoided, cyanide and ammonia should be stored in different rooms.
Bombing [cyanide/peroxide] to the full explosion has been explained in previous posts, but if you require a totally brilliant finish [especially to inner surfaces that can not be polished or tumbled] to item[s] it is necessary to go a step further -complete the full bomb, then 2 or 3 times place item in the hot cyanide, then introduce a small amount of peroxide while giving the container a vigorous swirling motion, then kill the mixture with cold water BEFORE the full explosion is completed.
Practice on an old item to perfect the system.
I have used this extra stripping process after bombing for over 40 years and still have companies send items to me where the gold looks dead and needs some life with never any complaints.

Colin Hanson
- Rotorua, New Zealand



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