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Aqua Regia: Dissolving Your Gold


Step 1: Add Your Acid

Get a clean plastic or glass container and place your e-scrap into it, and ensure you have your desired dissolving agent handy.

All aqua regia dissolving methods require muriatic acid, which can be obtained at most paint, hardware and swimming pool supply stores.

 

Refining E-Scrap? Consider using a basket or mesh bag

The purpose of using a basket is to facilitate removing and replacing the circuit boards and to safe dissolving supplies. The circuit boards are quite bulky, even after you have removed as much of the plastic and other non-gold bearing material as possible. As a result, you'll need to use more solution to cover the boards than is required to dissolve the metal.

For the most economical use of the solution, you will want to take the boards out of the solution (after the gold dissolves) and then replace them with fresh boards. A basket or mesh makes this easy to do.

The acid has to pass through the basket or bag, so make sure it is either plastic mesh or plastic wire.

Baskets & Mesh Bags Available

 

If you're using nitric acid:

For every ounce of metal that you are refining, add 30 milliliters of nitric acid and 120 milliliters of muriatic acid to the container.

Be very careful. The acids and the fumes are extremely corrosive. Usually, but not always, the acid reacts slowly at first.

After some minutes have passed, however, the acid will become very hot and brown, and very corrosive fumes (nitric oxides and other fumes) will be generated.

 

If you're using sodium nitrate:

For every ounce of metal that you are refining, add 120 milliliters of muriatic acid and 1 ounce (or 2 tablespoons) of sodium nitrate.

Sodium nitrate is not very soluble, so it is likely that you will have to use more sodium nitrate and muriatic acid than you expect.

Because sodium nitrate is slow dissolving, the metal usually takes longer to dissolve than when using either nitric or MX3.

 

If you're using MX3:

For every ounce of metal that you are refining, add 120 milliliters of muriatic acid and 1 ounce (or 1-1/2 tablespoons) of MX3.

MX3 Dissolving Agent is a very dense, highly soluble mix of chemical compounds and is recommended as the most economical and easiest to use dissolving agent.

Step 2: Dissolving Your Material

Add the basket or bag, with your metal, 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 build-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.

 

Compaison of Dissolving Agents

Dissolving AgentSodium NitrateMX3 ConcentrateNitric Acid
Corrosive? Mildly Mildly Extremely
Toxic? No No Yes
Shelf Life Unlimited Unlimited Unlimited
Requires Heating? No* No* No*
Dissolving into HCl 1-3 hours ~1 hour ~1 hour


*heating not required except when dissolving platinum group metals

Once the procedure's time has passed, check the boards to make sure all the gold has been removed and dissolved into the aqua regia acid. Let any boards with gold still on them continue dissolving until none remain.

 

If you're using a home-built system:

  1. 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.

  2. If you have more items to dissolve, repeat the procedure. You can continue to use this acid several times to dissolve the metal off additional boards until it is no longer effective.

  3. Rinse acid-soaked boards with water in another bucket. Any brown particles are likely to be gold and should be recovered and put into a future refining bath. If you believe that some solid bits have fallen into the solution during dissolving, then (after the acid is no longer effective in dissolving any more metal), you should pour the solution into different container, leaving the solids behind.

Any solids left in the solution will contaminate the pure gold you are about to precipitate.

 

If you're using the Aqua Regia System:

  1. Connect the fluid transfer apparatus to the dissolution chamber and precipitation flask.

  2. Trigger the pump until the solution is transferred.

For a more detailed explanation, please see: Transferring Fluids to Precipitation Flask in the instruction guide.

 

Step 3: Decanting (or filtering)

After all of the metal is dissolved, it is common for some materials such as stones, ceramics, plastics sodium nitrate beads, etc. to be left behind, undissolved.

Since that would contaminate the pure gold that you will retrieve from the solution, you need to separate that before you precipitate the gold.

 

You can decant or you can filter.

If filtering, do not use a coffee funnel. Use a Buchner filter funnel. Most people find that decanting is just as effective as filtering, however.

Please note: The solution should be either decanted or filtered into a beaker or similar container that is made to be heated.

 

Stage 2: Precipitating Pure Gold

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