Searching for non toxic e-waste processing alternatives VTT Technical Research Centre of Finland has developed a biological filter made of mushroom mycelium mats that could recover of as much as 80% of the gold in electronic scrap. The researchers are also looking at ways to extract copper from circuit board waste by flotating the crushed and sieved material rather than indiscriminate smelting.
In VTT experiments, cell phones were crushed and the particles sieved and separated magnetically and by eddy current into circuit board fractions.
Further crushing, sieving and flotation (a separation method that separates hydrophobic particles from hydrophilic particles by blowing air into the sludge) resulted in a fraction with high concentration of valuable metals for solution extraction experiments. The researchers say their flotation technique raised the copper content of circuit board fraction from 25% to 45%, while gold content increased by a factor of 1.5.
Close-up on the biosorben film: courtesy VTT Technical Research Centre of Finland.
“Because it is difficult to remove the components from the circuit boards, the first step in most recycling processes is to crush everything into particulates and that’s how we start too”, explained Jarno Mäkinen, Research Scientist at VTT Technical Research Centre of Finland.
“But then, using non-toxic water-based solutions, we have managed to engineer mycelium-based biomass that acts as a biosorbent specifically targeted at gold complexes”.
Using biosorbents such as fungal and algae biomass, the Finnish lab demonstrated that more than 80% of the gold in the solution adhered to the biomass, compared with only 10 to 20% of gold recovery when using most commonly used harmful chemical preparations.
Different filament structures can be formed, for example, into biological filters, which could make that specially engineered biomass useful to recycle precious metals on an industrial scale.
Mäkinen didn’t want to say more about the biomass engineering tricks used to make the biosorbents more effective for gold or other precious metals. But in principle, the idea would be to engineer various biosorbents targeted at different metals (including rare earth metals) and cascading the e-waste recycling process through different metal absorption steps.
At the end of each step, the collected biomass is burnt or chemically processed to recover the metal complexes inside.