The method developed at Aalto University enables the recovery of trace platinum from industrial hydrometallurgy solutions. In the photo platinum has replaced the less noble metal on the surface of pyrolyzed carbon. Photo by Petteri Halli
The requirement for platinum is growing particularly because of its catalytic properties and corrosion resistance. The growing numbers of electric cars will further increase the need for platinum and other critical metals.
Platinum and other precious metals can be found in copper-, nickel- and zinc-based minerals, and consequently also in solutions resulting from the base metal industry. Typically, the concentrations of solutions resulting from base metal processing are so small that their utilisation is very difficult. In accordance with the principles of the circular economy and because of the growing demand for precious metals, their high price and the depletion of supplies, it is, however, very important to recover even trace quantities of these metals.
Researchers at Aalto University have, under the leadership of Professor Mari Lundström and University Lecturer Kirsi Yliniemi, developed a selective method for platinum recovery from industrial hydrometallurgy solutions.
"We used the so-called electrodeposition-redox replacement, EDRR, method for the recovery of precious metals from industrial process solutions", Kirsi Yliniemi says.
"The solutions contained large amounts of nickel and other base metals, and very small amounts (ppb, meaning parts per billion) of platinum, palladium and silver. Because of this ratio, it is very difficult to recover precious metals from such solutions, and without the currently developed method, they could not be fully exploited."
In addition, the process used a completely new type of electrode material, pyrolyzed carbon, PyC, developed by Professor Sami Franssila’s research group at Aalto University. Its porous surface pattern provides a surface area several hundred times larger than conventional electrodes. This carbon structure considerably improves the efficiency of the method.
An environmentally friendly, energy efficient and diverse method
The EDRR method is based on spontaneous oxidation-reduction reactions of metals, in which the more noble metal, such as platinum, oxidises the less noble metal, such as nickel or copper, already concentrated on the surface of the electrode; in the end, platinum replaces the nickel or copper on the surface, which in turn dissolves back to the solution.
Because these industrial process solutions contain only small amounts of precious metals, very little energy is required in the process. In the EDRR method, energy is supplied in short pulses rather than a continuous stream, and the replacement reaction takes place in between these pulses, for instance, between platinum and nickel. The replacement reaction of the EDDR method does not require an external energy supply, but it takes place spontaneously, specifically as a result of the metals’ purity. This method is also easy to customise and it enables the creation of a very clean platinum coating starting from the atomic level.