Mobile phone scrap can contain precious metals, such as gold and copper. VTT
Technical Research Centre of Finland has developed a biological filter
made of mushroom mycelium mats enabling recovery of as much as 80% of
the gold in electronic scrap. Extraction
of copper from circuit board waste, on the other hand, can be enhanced
significantly by flotation the crushed and sieved material.
Although
research into the biological methods is active, these are still rarely
used in metal recovery chains. In a European “Value from Waste” project,
VTT developed both biological and mechanical pre-treatment methods for
more efficient recovery of precious metals from electronic waste. Other
methods developed by researchers included recovery of gold from
dissolved materials by biosorption and extraction, using as few harmful
chemicals as possible.
Fungi catch gold and filter out impurities
VTT has developed a
method that harnesses biosorbents, such as fungal and algae biomass, for
the recovery of precious metals converted to a solution. In VTT tests,
more than 80% of the gold in the solution adhered to the biomass,
compared with only 10–20% of the harmful process chemicals.
The uniqueness of the
method lies in the structure of the biomass. Different filament
structures can be formed, for example, into biological filters, which
makes further industrial processing of precious metals easier.
Gold also separates well in liquid-liquid extraction
The project developed a
method with high extraction capacity for gold recovery, using the
newest environmentally-friendly extraction reagents. In VTT experiments,
it was possible to recover more than 90% of the metal solution
dissolved from a circuit board with the help of functional ionic liquid.
The method facilitates extraction of desired components from
impurities.
Recovering copper from circuit boards by flotation
The new pre-treatment
methods developed by VTT allow separation of most plastics and ceramics
from waste. In VTT experiments, cell phones were crushed and the
particles sieved and separated magnetically and by eddy current into
circuit board fraction. Treating once more by crushing, sieving and
flotation, resulted in a fraction with high concentration of valuable
metals for solution extraction experiments. Flotation raised the copper
content of circuit board fraction from 25% to 45%, while gold content
increased by a factor of 1.5.
“Value from Waste” project
The growth of
cleantech industry, the rise in the world market prices of metals, and
concentration of metal production in China have resulted in a situation
in which extraction of several metals from waste streams has become
advisable even in Finland. Ever stricter recycling and utilisation rates
for electronic waste are also pushing the development of recycling
technologies. The purpose of the EU project “Value from Waste” was to
develop recovery processes on a more sustainable basis, to clean
materials of impurities that reduce opportunities for further use, and
to increase the amount of recovered materials.
The methods developed in the project included mechanical pre-treatment, solution extraction, use of biological methods, and optimisation of treatment chains. The new treatment methods will enable the metal refining industry to use cleaner electronic waste in larger amounts.
The methods developed in the project included mechanical pre-treatment, solution extraction, use of biological methods, and optimisation of treatment chains. The new treatment methods will enable the metal refining industry to use cleaner electronic waste in larger amounts.
In the two-year “Value
from Waste” project of the research consortium AERTO (Associated
European Research and Technology Organizations), VTT participated in
joint technology R&D with the following six European research
institutes: Fraunhofer ICT and Umsicht (Germany), CEA (France), TNO (the
Netherlands), SINTEF (Norway), Tecnalia (Spain) and SP (Sweden). The
project was co-ordinated by SINTEF from Norway.
Flotation
Flotation is a
separation method that separates hydrophobic particles from hydrophilic
particles by blowing air into sludge containing both types of particles. Hydrophobic
particles are picked up by air bubbles and float to the top of the
sludge as froth that can be skimmed off mechanically.
Liquid-liquid extraction
Liquid-liquid
extraction is a method that extracts metals at aqueous interface
selectively into another organic interface immiscible with water. This method, widely used in industrial processes, enables selective extraction of precious and heavy metals from water. The metal solution concentrated into an organic interface is thus extracted in purer form for further processing.
