Scrap computers, cell phones and other electronic devices are good sources of gold, silver and other valuable metals. During recycling, components are dissolved in baths of acid or cyanide. An electrochemical process -- electrolysis -- extracts the gold by depositing it onto electrodes.
Soaking in nitric acid, hydrochloric acid or cyanide solution dissolves precious metals from electrical components. Gold is extracted from this solution -- known as the electrolyte -- using a pair of electrodes attached to a battery. The electrolyte conducts electricity between the electrodes. Gaining a positive charge, metal ions in the solution are attracted to the negative electrode (cathode) and deposited there. Gold deposited on the cathode can be scraped or melted off. Cathodes with larger surface area speed gold deposition.
Electrolyte solutions obtained from electronic scrap contain copper, silver, lead and other metals as well as gold. High silver or copper content can inhibit gold deposition. The gold deposited may be impure -- blended with these metals. As today's electronic devices get smaller, the amount of gold they contain is shrinking.
Lead, mercury, cadmium and other elements found in scrap electronics are toxic. Both dissolution in acid and dissolution with dilute cyanide carry health risks. Toxic gases may be given off during the extraction process. This should not be undertaken by amateurs. Safer methods are being developed.