Gold Recovery

When electronic products, such as computers, cell phones, televisions, VCRs, stereos, copiers, fax machines1, internal chips and other relating parts, reach the end of their lifetime, they become electronic waste, otherwise known as “e-waste.” E-waste can often comprise of several hazardous components which can include heavy metals like mercury and lead. Despite this reality, gold, as well as other precious metals, also make up a significant amount of e-waste, and its extraction could have advantageous properties for the gold industry.     E-Waste Statistics2 It is estimated that 20-50 million metric tons of e-waste is disposed in landfills around the world each year. Dumped e-waste is estimated to contain over $60 million in gold and silver every year. In the United States alone, e-waste accounts for 2% of all trash that is dumped in landfills. E-waste also accounts for 70% of all overall toxic waste in the United States. Approximately 12.5% of e-waste is currently being recycled. For every 1 million cell phones that are recycled, the following amounts of precious metals can be recovered: 16,000 kg of copper 350 kg of silver 34 kg of gold 15 kg of palladium Gold Extraction by Cyanide Since its introduction into the mining industry during the 1870s, the use of cyanide in gold leaching has been a useful, but dangerous technique of metal extraction. This extraction process involves the chemical reaction between the pulverized e-waste and sodium cyanide, which produces a soluble gold cyanide solution that allows for easier extraction of the precious metal3. While useful, gold cyanidation remains a controversial technique that is prohibited in several countries around the world. Several mining extraction procedures throughout history that have employed this technique have resulted in disastrous cyanide spills that have severely effected the environment. Other Traditional Methods of Gold Extraction from E-Waste Acid Treatment The combination of hydrochloric acid and nitric acid have been found to be useful chemicals in the extraction of gold from e-waste. Other mild acids have also been successful in their extraction of gold, as these acids can successfully dissolve gold while limiting their potential to cause adverse effects to the environment. Bioleaching Microbiological processes have been proposed over the last decade as possible alternatives to extracting precious metals such as copper, gold, palladium and silver from e-waste. Bacteria such as Thiobacillus ferrooxidans and T. thiooxidans, as well as fungi including Aspergillus niger and Penicillum simplicissimum have been documented to successfully extract copper, aluminum, lead and zinc from e-waste4. Aspergillus niger and Chromobacterium biolaceum are two microorganisms that have been found as suitable and sustainable methods of extracting gold from gold plated electronic devices5.