Refining Gold From Circuit Boards & Electronic Scrap 
with Muriatic & SubZero (nitric acid Substitute)
Version:  March 09, 2008

Back to:  Refining Precious Metals Page

The acid used in this process is muriatic (also known as hydrochloric) acid.  This acid is corrosive (see warning label on your bottle).   For this reason, this kind of refining is best done outdoors, away from anything that may be damaged by exposure to these fumes. 

Having described it's hazards, it must be pointed out that, like most industrial processes, refining gold in acid is quite safe when performed under controlled conditions.  In addition, the results of doing your own refining can be quite sweet.  Based upon feedback we've gotten from several hundred users, we estimate that the return of gold, when you refine the material yourself, is 10 times the return when sent in to a commercial refining company.

  To refine gold with the SubZero Aqua Regia , you will need the following additional items:

·          protective clothing--minimum requirement: goggles and rubber gloves

·         muriatic or hydrochloric acid

·         baking soda (sodium bicarbonate) to neutralize the acid when finished

·         tap water and distilled water  

·         containers for the boards

Make your aqua regia solution:

In a glass or plastic container, add 1 lb SubZero to ½ gallon of muriatic or hydrochloric acid.  Do not use a metal container.

Before refining:

Cut off those portions of the board that have gold.  Discard the rest.  Chips, which have gold inside as well as outside, must be broken open. On a small scale, one tap with a hammer should suffice.  With lots of chips, you might want to use a cement mixer.

In a glass or plastic container (a 5 gallon, clean white bucket will work well), add 1 lb SubZero to ½ gallon of muriatic or hydrochloric acid.  Do not use a metal container.  Not all the SubZero will dissolve.  This is normal.  Do not discard the undissolved SubZero-  The undissolved SubZero is required to be in the solution  for the gold to complete its dissolution.

Dissolving the gold:

The acid should be at room temperature.  Place your boards in a plastic mesh, or plastic wire basket or a plastic mesh bag.  The acid has to pass through the basket or bag, so make sure it is either plastic mesh or plastic wire.

Add the basket or bag, with your boards, to the acid solution.   The metal will begin to fizz and give off an invisible or slightly brown fume.  You can cover the container, but do not seal it tightly because you don't want a built up of gas pressure.   You can speed up the process by heating your solution, but this creates added hazard-  hot acid fumes more rapidly and is more corrosive.  Dissolving time, at room temperature, dissolving time is usually between ½ hour and 2 hours. Check the boards to make sure all the gold has been removed and dissolved into the aqua regia acid.

Remove the basket from the acid, taking care not to drip acid anywhere.  The aqua regia is not used up yet, so you can use the same acid to dissolve the gold off more boards.  You can continue to use this acid, several times, to dissolve the metal off additional boards until it is no longer effective.  The acidy boards should be rinsed (with water) into another bucket.  Any brown particles are likely to be gold and should be recovered and put into a future refining bath.

Adjusting the pH & Precipitating the pure gold:

When the aqua regia is no longer effective (no longer dissolves the gold on the boards), it is time to recover the pure gold from the solution.

The acid will be a dark, emerald green color and should be clear, like Coca Cola, not murky or muddy looking (nothing floating inside the dark waters).  If the acid is murky, it may contain particles and should be decanted into another bucket or it should be filtered.

Now add a pinch of urea to the dark acid solution.  If it fizzes, add additional urea until it no longer fizzes.  When there is no longer any fizzing, add 1½ tablespoons of Storm Precipitant for every ounce of dissolved metal (dissolved metal content, not just dissolved gold content).  Immediately, the acid will change to a muddy brown appearance as brown particles of gold form in the acid.  This brown "mud" is, despite its appearance, pure gold.   If you want to speed the precipitation process, you can add the precipitant to very hot water before adding to the acid.  This technique will precipitate the gold in only about 5 minutes (30-120 minutes is normal when not using this technique), but be aware that hot precipitant has a very strong, pungent odor.

Once precipitation is complete, test the acid for the presence of dissolved gold with Precious Metal Detection Liquid. 

Testing to make sure no dissolved gold is discarded:

Precious metal detection liquid will detect the presence of dissolved gold down to 4 parts of gold per million parts of acid )detecting the presence of about 1/1,000th of 1 gram of dissolved gold.  Testing for the presence of dissolved gold is absolutely necessary to insure that no dissolved gold is thrown away with the waste acid. 

To test, first immerse the end of the stirring rod in the acid.  Remove it and touch that end to a paper towel to make a wet spot.  Put a drop of gold detection liquid on the wet spot on the paper towel. If any gold is still dissolved in the acid, the wet spot will turn a purple-black or a purple-brown.  If you see this color change then give the precipitant more time to work and/or add more precipitant.

Rinsing the pure gold:

The acid should now be a clear, amber or a green color with a brown mud at the bottom.  Pour off the acid into another container.  If you have a filter, you can use it.  Do not pour off any of the mud.  The mud is pure gold.

When all the acid is poured off, add tap water to the mud.  Stir and let the mud settle.  Pour off the water into the container with the acid.  If you have a filter, you can use it.  Do not pour off any particles of brown. Repeat this rinsing 3-4 times or more.

Testing to insure purity:

Test with aqua ammonia to insure high purity of your gold.  Place a drop of aqua ammonia test liquid on the wet gold mud.  If you see any change in color to blue, even a very pale blue, rinse and test again.

Give the mud a last rinse, this time with distilled water.

Drying and melting:

Rinse the mud into a beaker that is made to be heated or into glass coffee pot.  Put the beaker or pot on a hot plate to dry the mud.  Do not preheat the hot plate or thermal shock may cause the beaker to break.

Melt the dried mud (now a powder).  If using a torch, first wrap the powder in tissue paper and then soak that in alcohol.  Also, use a Burno crucible.  This will keep your gold from being blown away by the gas pressure from the torch.  The gold will again take on the appearance of metal.  If you've followed the instructions carefully, the gold will be 99.95 % pure with virtually no losses.

Platinum-  

 Computer Scrap-  Very few boards have platinum.  Typically, platinum (and other platinum group metals, like palladium) are found on the surface of the hard drive platter (the inside is aluminum).  To dissolve the aluminum, first make cut marks across the disks and then put in a saturated solution of cold water and lye.  Lye is very corrosive, so wear protective gear.   As the solution comes in contact with the aluminum, the solution will become very hot and the aluminum will dissolve.  Discard the solution and recover and rinse the platinum.  The platinum will not be pure.  To make pure and to separate one platinum metal from another, you will need the Simplicity Refining System. 

 Catalytic Converters-  Follow the normal procedure for refining gold, but heat the SubZero aqua regia to simmering.  Remove and replace the catalytic converters after the platinum is dissolved off the surface.  Precipitate the platinum from solution with zinc powder or aluminum foil.  The precipitated metal will not be pure and requires the use of the Simplicity Refining System for further purification.