A team of researchers from Rice University in Houston, Texas have identified a novel application for a method originally created to produce graphene – extracting valuable metals from electronic waste.
The electronic waste (or e-waste) industry poses a huge problem. Not only is the increasing digitisation of our world causing this to be our fastest growing area of waste, but many of the discarded materials contain hazardous components that cause contamination and damage to both our environment and food chain. While nations around the world are producing masses of this waste product, many offload the burden of recycling onto others, with the majority going to those in the developing world. Finding a means of recycling this waste (and doing so domestically) is crucial, and the team at Rice just may have found a way to do that.
Here, we spoke with study lead Dr James Tour to find out more about the process, and the role it could play in the circular economy.
Breaking down the method
The process– known as the flash Joule heating method – was developed in 2018 and places a carbon source between electrodes with high voltage and high current, breaking down the carbon bonds in the process and reconstructing the carbon atoms to make graphene, all in a matter of seconds. The process operates using high temperatures, heating to 3000 Kelvin (or 2800 degrees centigrade) in less than five milliseconds.
“We then scaled this system to become very large, it’s set to have a commercial line in the second quarter of 2022, doing a tonne of day of graphene, and 100 tonnes a day a year after that,” says Tour. “So we know there’s no issue with scale-up here. Once we knew we had this process, we said what other things can we do with these high voltages and high current systems?”
Next, the team took a printed circuit board and applied the same process to it. While at first it did not yield as effective results as the team hoped, adding other industrial waste products such as Teflon and PVC pipe to the mix allowed them to convert the metals into metal halides – thus allowing them to be extracted far more efficiently.
“It’s hard to extract precious metals from e-waste, because in the electronics industry these metal layers are coated with all sorts of casings that often can resist typical aqueous acid etching, plus aqueous acid actions are so messy for the environment,” Tour says. “This is why, at least in the US, most of our electronic waste is either landfill or shipped overseas to have it recycled. But in this case, we’re talking about a heating and cooling system that’s so rapid and so extreme that the plastic encasements crack open. It’s like if you take a really hot piece of glass and you stick it into cold water, it just shatters.”
Not only does the technology have no water needs, the energy input is far smaller than other extraction methods – meaning it is also far cheaper.
“The flash method is 80 times cheaper than what’s used industrially. This is a huge number for the amount of energy, and that then translates into the amount of greenhouse gas emissions that are used,” Tour says. “You can also do it all using renewable power. Even though we use very little electricity (only about $30 of electricity per tonne of graphene), we’re doing it all with hydroelectric power sources.”
Not only can the team extract precious metals such as rhodium, palladium, gold and silver, from the process, but also heavy, toxic elements such as chromium, arsenic, cadmium, mercury and lead. So effective is this method in removing metals, the resulting byproduct was found to be clean enough to be repurposed as soil on agricultural land – storing the carbon back into the ground and offering full cyclability.
Not only is the process useful for tackling our e-waste problem (which Tour says is increasing at a rate of 8% every year), but it also has potential applications in recycling waste from electric vehicles – including, potentially, even batteries.
“There’s another paper that’s going to be coming out where we use a similar process to recycle batteries,” Tour says. “Or we could capture the lithium and cobalt and nickel and manganese materials for solar. So that’s in a paper that will come out in the next few months.”
Given the scope of the problem, any technologies addressing e-waste would need to operate at scale, but Tour says this isn’t a problem.
“If you look at this process and you wonder if it can really scale, we’re already demonstrating this with flash graphene and we can do the same process on ores,” he says. “My opinion is, why mine? Why destroy the Earth? Why go to remote places in the world that are dangerous and expensive to strip the earth? We’ve already got all the elements, we’ve already mined them, we just need to learn how to recapture them through urban mining.”
Next, the team is set to build a demonstration plant in Toronto to trial the efficacy of this metal extraction process at scale, before hopefully seeing it progress to market.
“Scaling is never easy, never linear. There’s always a lot you have to learn,” Tour cautions. “This is just going to be small engineering steps that we’re going to have to learn along the way, in the scaling process. We’re currently using machine learning to do the optimisation of electrical policies to optimise the type of thing we want to make. We’ll do the same for e-waste, and let the computer decide and optimise the process.”