With Apple rolling out a new iPhone every year and planned obsolescence encouraging consumers to buy and throw out more and more electronics, electronic waste is piling up in landfills globally. Over 40 million tons of e-waste are produced annually, making it the fastest growing category of solid waste globally. E-waste often includes heavy toxic metals that can leach into the surrounding environment, contaminating soil, water, and food sources. Workers who dispose of e-waste have been found to have higher lead content in their blood because of exposure to dangerous dust and smoke when working with the waste and in the recycling process. Intensive mining practices to recover precious metals found in e-waste further harm the environment by releasing toxic fumes.
Urban mining is a process by which precious metals like gold, silver, rhodium, and palladium are recovered from urban waste. Researchers have been working to develop new urban mining techniques that are more sustainable and efficient in an effort to reclaim precious metals from old electronics and minimize the need for further intensive mining. However, current techniques primarily involve smelting and leaching. Smelting involves melting down metals and can release toxic air pollutants that contaminate much of the surrounding environment. Leaching is the process of treating e-waste with chemicals that turn precious metals into salts that can later be extracted, but this process isn’t efficient and often leaves behind large quantities of acidic and toxic residue.
In an article published in early October 2021 in Nature Communications, Ding et al. at Rice University propose flash Joule heating (FJH) as a method to better recover precious metals from e-waste by reducing the energy, time, and money involved in urban mining. FJH was originally used to produce graphene, a usable form of carbon in a honeycomb structure, from food waste and plastics, and applying this technique to e-waste could be a breakthrough in dealing with what is now piling up in landfills. In around one second, electricity raises the temperature of the e-waste to 5,660 ℉, vaporizing the precious metals and leaving behind heavy toxic metals. The precious metal vapors are then moved into a cold trap, where they are condensed back into solid, refined and purified, and later reused.
Over ten times more silver is able to be recovered compared to traditional urban mining methods.
FJH as applied to urban mining has proven to have both higher recovery rates of precious metals and lower removal rates of hazardous heavy metals. Over ten times more silver is able to be recovered compared to traditional urban mining methods, and the recovery of other precious metals has also shown significant increase. With FJH, soil once polluted with toxic heavy metals such as mercury, lead, arsenic, and cadmium has returned to safe limits, and some agricultural land can now be reclaimed.
As our world becomes increasingly digitized, e-waste will continue to be a problem that we need to seek solutions for. Finding ways to reduce and reuse waste may be a vital method of combating the climate crisis and preventing further harm to the environment.
This article was edited by Kate Braverman and Emily Almgren.