The solution is made up of 3% Hydrochloric Acid and distilled water. Lysol toilet bowl cleaner has an HCL percentage of 9% which can be diluted in a 1:3 ratio to make the 3% concentration. The PCB parts are then submerged into this solution and left there to dissolve the copper laminate layer of the board.

After 2 weeks the pieces of the PCB are removed from the solution and placed in a 10mm or less mesh filter to separate the fiberglass layer of the PCB and isolate the precious metals in the solution. At this point, the copper and laminate from the board are completely dissolved into the solution.

The solution is then poured through a coffee filter to capture the gold floating inside. This collects all the gold, but the solution dissolves the copper.

There are 2 processes in this step; one for gold, and one for copper.

The gold is purified through a process called aqua regia. This process is extremely dangerous because it involves nitric acid, a very corrosive chemical. We did not perform this part of the process due to a lack of proper safety equipment.

The copper in the solution is not pure. It’s bonded with the hydrochloric acid to form Copper (II) Chloride (CuCl2). Then, baking soda (NaHCO3) is poured into the solution, which removes the carbon dioxide from the hydrochloric acid as a gas and leaves the Copper (II) Chloride and salt water. This Copper (II) Chloride is also known as malachite, a green powder often used in paint.