That pile of old computer cases and circuit boards is a goldmine waiting to be excavated. With the technique known as aqua regia, you can extract and separate the gold on circuit board pins and connections. The process is not easy, but it can be completed if the steps are followed closely. Harvesting gold from boards can be good extra income for anyone with access to a large number of free electronics.
Remove all the metal from the circuit board using tweezers and a metal pick. Put all of the metal into the steel crucible. Heat the crucible until all of the metal becomes liquid. Pour the liquid in to a metal plate mould and allow it to cool.
Fill your glass tank to just below the top edge with distilled water. Place your metal plate in to a plate holder and submerge in to the water bath. Submerge a copper plate two inches from the plate you created.
Attach an alligator clip running from the positive terminal on the power supply to the created plate and a clip from the negative terminal to the copper plate. All of the copper on the created plate will be attracted to the copper plate. Remove the plates and allow them to dry. Repeat the process with a steel plate to remove all of the silver as crystals. The only thing left on your created plate is gold.
Mix your hydrochloric acid and nitric acid in the glass beaker at a ratio of 3:1. Make enough of the mixture to completely submerge the plate.
Submerge the plate in to the acid mixture and leave it until the mixture is no longer cloudy.
Pour slight amounts of the mixture in to a glass dish and let it dissolve. Repeat until there is no more of the mixture left. The flaky remains are pure gold that you worked so hard to extract.
Wear protective gloves and safety goggles while handling nitric acid and hydrochloric acid, both substances are harmful. Perform the procedure in a well ventilated area with proper lab safety equipment. Make sure to have a sprinkler system or a fire extinguisher available for the procedure.