In theory, urban mining—harvesting materials from used electronic devices—is a commonsense route toward reducing society’s reliance on traditional mining to source the dozens of metals the semiconductor industry relies on to make and package chips. In practice, it’s not so simple.
It is possible to harvest meaningful amounts of precious metals from e-waste. For example, leading up to the 2020 Tokyo Olympics (which happened in 2021, but that’s not relevant here), Japanese residents dropped off over five million old smartphones at specially marked kiosks. That was more than the amount needed to extract enough gold, silver, and copper (bronze is mostly copper) to produce all the medals for the Olympic athletes.
Fun fact: silver medals are made from solid sterling silver, but gold medals are mostly silver with gold plating. The alloy used for bronze medals contains 97 percent copper plus some tin and zinc.
While the Olympics are an attention-grabbing application, we need to increase e-waste collection rates worldwide on a consistent basis. E-waste regulations are spotty outside of Europe (see map in Figure 1). The solid teal color in North America is somewhat misleading. The U.S. is shaded, but regulations cover only half the states in the country, the most recent of which was enacted in 2011.
Even with regulations, collection rates are dismal. If more places made collection easy, that would help. For example, supermarkets in The Netherlands have boxes where people can drop off old electronics. Financial incentives will help as well.
What Can E-waste Processing Recover?
Most e-waste recycling efforts target gold because of its high value for jewelry and coins. That makes it more economical to recover compared to other metals.
Consumer electronics don’t contain a lot of gold. An iPhone 6 from 2017, for example, contained 129 grams of metals, including 31 grams of aluminum and only 0.014 grams of gold. The gold content in today’s phones might be even lower.
To put that in context, if the iPhone weighs 200 grams, that’s 70 ppm (parts per million) of gold. Even so, that’s a lot more than a typical gold mine.
The most efficient gold mines require around 7 metric tons of ore to extract one ounce (28 grams) of gold. That’s only 4 ppm. Less efficient mines require over ten times as much gold ore to extract the same amount of gold.
Beyond precious metals, electronics contain valuable rare earth metals like neodymium, lanthanum, and yttrium. Just like rare earth metals are expensive to mine because they occur with other ores and are present in small quantities, rare earths are hard to extract efficiently from electronics.
There are other perhaps surprising and more efficient ways to recover rare earths. A 2010 Toyota Prius holds one kg of neodymium and over five kg of lanthanum. The magnets in air conditioner units are made from rare earth metals as well.
A Better Way to Process E-waste?
The standard way to extract metals from e-waste is with smelters, high-temperature furnaces that incinerate the circuit boards. Chemical leaching is another method.
The rare earth metals inside various electronic devices are a precious commodity, especially if global politics threatens supplies of these necessary elements. However, common extraction methods require high temperatures or toxic chemicals and create hazardous waste. Without strong regulations protecting workers from exposure, e-waste processing is a dangerous job. The vision of child workers in Ghana surrounded by piles of burning phones is disturbing.
Fortunately, certified e-waste recyclers run much safer operations. Workers wear suitable personal protective equipment (PPE), and filters contain the toxic dust and fumes created during grinding and incineration.
This is also an application where robots can help. Robotic systems can disassemble electronics quickly and sort out components that contain valuable materials. That can improve recovery rates and make e-waste processing more efficient. It also means that humans don’t need to handle toxic elements such as lead and cadmium or be exposed to toxic fumes.
Bioleaching is a possible alternative to smelting or chemical leaching. Bacteria or fungi can produce acids that dissolve metals at ambient or slightly elevated temperatures. The mechanisms and details of the process are complex, and trials to date suggest that efficiency needs to improve to make bioleaching workable on an industrial scale.
Where 3D Integration Fits In
Companies throughout the semiconductor manufacturing supply chain should be aware of the issues surrounding e-waste. Our industry is the source of the problem, but we can also be part of the solution.
Increasing e-waste collection rates and improving e-waste processing is only one aspect to consider. In the hierarchy of the “re” words, recycle is at the bottom. For companies, “refuse” can mean refusing to collaborate with suppliers that don’t adhere to their code of conduct or refusing to design a new product without first considering the social and environmental impacts of all their choices.
