In Pictures: Tom's Hardware Recovers Gold And Silver From CPUs

Meet Our Mountain Of CPUs

A while back, we did a little do-it-yourself salvaging of gold from motherboards (Can You Mine Gold From Old Motherboards?). But that’s not the only part of a computer where the rustless, unalterable metal is used. It’s also in CPUs. Specifically, the element is used on the pins and on the mounting pads of the processor dies. Also, the small wires that connect the pads and the pins are made of gold.

Here's the hard part, though: recovering the precious metal through do-it-yourself techniques. In this piece, we're also going to recover another precious metal: silver.

Please note that the chemicals used in this demonstration are extremely dangerous, especially in the concentrations used. Therefore, we strongly discourage you from attempting to reproduce this experiment at home.

Nitric Acid

In our first step, the processors are dropped into a bath of concentrated nitric acid. They’re going to spend a while there, as we'll see. And the experience won't be particularly pleasant for them, either.

Splish Splash!

During this stage, the strong acid reacts with certain metals, particularly copper and silver. Nitric acid has no effect on gold, however.

Interestingly, our K5 doesn’t seem to react to the forced bath...yet.

Bath Time For Our CPUs

Let’s throw in a few more processors. On the left, our CPUs have just been tossed into a concentrated nitric acid solution. On the right, after a few minutes, the solution is already taking on a bluish color, characteristic of the presence of copper(II) nitrate, and thus of the Cu²⁺ ion. It's also important to note that the bath is now giving off a brown gas (nitrogen dioxide, or NO₂).

Cu + 4 HNO₃ -> Cu(NO₃)₂ + 2 NO₂ + 2 H₂O

Attention: This Is Dangerous

The reaction can be more rapid (and violent) at times, but it’s always dangerous.

The Bath, A Few Weeks Later

After a few weeks, the solution is very blue, due to the strong presence of Cu²⁺ ions. The copper and silver (among other things) are dissolved, but not the gold.

CPUs: No Longer Functional

Now we remove the processors from the bath.Needless to say, they wouldn’t perform quite as well now...

Filtering

The next step is to filter. Silver is in the solution as silver nitrate (AgNO₃), whereas the gold and a few other metals that weren't attacked by the nitric acid, plus the impurities, remain in the filter. We’ll set the filter aside for later and concentrate on the solution.

A Pinch Of Salt

We add a little sodium chloride (ordinary table salt) to the solution.

Silver Precipitates

It’s magic (well, almost)! The silver in the silver nitrate precipitates and forms silver chloride.

AgNO₃(aq) + NaCl(Aq) -> AgCl(s) + NaNO₃(aq)

A Little Zinc

Now we add a little hydrochloric acid. Then, we immerse a piece of zinc in the same solution. Attention: This is an exothermic reaction!