Dissolving your phone
They say that silence is golden, but so, it turns out, are our mobile phones. In fact, they’re stuffed full of rare metals. And since we’re beginning to run low on our supplies of these materials, and demand for technology is rising, how can we get the precious metals back out once we don’t want the phone any more? One way might be to chuck it in a vat of acid! Eva Higginbotham spoke with Euan Doidge, from Imperial College London, who’s looking at how to do exactly that...
Euan - All the metals in the world mainly come from rocks. The problem is there's not a lot of metals in those rocks. It takes a lot of energy and effort and resources to get not a lot of metal out, for a lot of input in the first place. Our solution is to try and recycle as much metal as possible from secondary sources, such as mobile phones. So whereas you can only get up to a gram of gold out from a rock, you can get 300 grams out from a mobile phone.
Eva - I never realised that my phone contained so much gold. What is the gold doing in there in the first place?
Euan - The gold is present in your printed circuit boards as the contacts between components. So it's not exclusive to mobile phones, it's anything with a circuit board will have gold present. It's not there really doing anything but being an electrical contact. I should say there's not a lot of gold in any one person's phone - it's only 30 mg worth, 85p worth. It's when you start getting lots of phones together that's when it becomes much more viable and important.
Eva - So how are you trying to extract the gold from the phone?
Euan - The classic way of doing this, the kind of low-tech way is pyrometallurgy, essentially melting metals out of the source. That's not green, it's not sustainable and it's not really great just to have more emissions going into the atmosphere. Our solution is not green, it's greener, it's more sustainable. It's a technique called solvent extraction. It was first pioneered during the Manhattan project but we our using it now to recover metals in solution. So rather than using high energies we using just liquids. Essentially we're dissolving all your metals into one aqueous solution, designing something that's selected for one metal and extracting it into an oil. Once you do that you can separate off the oil, recover the metal that way and you've got selective and efficient recovery without using high temperatures.
Eva - Cool. And so how long does that process take?
Euan - It depends. Everything's got a rate determining step somewhere. The first step might be how long does it take to dissolve your phone in the acid, then the separation stage needs to be quick. We aim to do that in two minutes or less but this happens in a continuous flow. So that's from the very start to the very end that can take ten minutes but any one section should take no more than two. The reduction step again, dependent on time, how quickly do you want to do it? The quicker you do it the lower purity you get, so it's how long do you want it to be essentially for the quality of products you want.
Eva - So it goes from the phone, I guess you might strip away some of the screen and stuff, those sorts of parts first and then you just put the circuit board into the solution?
Euan - So this is the big question: what's the most efficient way to dismantle the phone? So our solution is to dissolve the whole circuit board in an acid solution, that gives you one big mixture of metals, then you selectively take out each metal. Now the choice is, do you pre-dismantle the phone. Do you separate as many components as you can to make it a simpler mixture or do you do selective leaching. So before you dissolve it do you say well I'm only going to try dissolving some of the metals and then separate those. My preferred option is to dissolve the whole phone.You've gone to the effort of dissolving it; then get the metals out; that's one step rather than multiple.
Eva - And about what sort of percentage of recovery are you getting?
Euan - That's an interesting point. So any one cycle will load a hundred percent. Now there's always going to be loss and you have to do things in sequence. So as something goes forward and then something goes back the other way, but together you can recover all of the gold. It's a remarkably efficient process.
Eva - You work on this in an academic context as well, is there a company that is trying to do this as well?
Euan - Lots of companies are now thinking about this. They've realised there's only thirty years left of copper, thirteen years left of indium and potentially we've already run out of lanthanides. We need to start recycling metals. So all the big mobile phone companies, tech companies are now thinking about how do we recover these metals.
Eva - And once the gold or whatever other metal you're taking out of the phone is extracted, can it just immediately be repurposed for something else?
Euan - So this is the big question about how you want to recover the gold? Everyone's going to want it in slightly different form, so our proposal is we give you a pure solution of gold and then you can choose to reduce it, to replace it or you can just precipitate it and get lumps of gold that you can melt down to make rings.