PLATIRUS has studied several direct recovery processes for obtaining PGMs that are either diluted in a liquid medium or deposited on a solid separator. The following methods have been considered as the most promising.
Gas-Diffusion Electrocrystallization (GDEx)
Recovery of PGMs from leachate or extractant solutions, to their oxide or elemental forms, can be carried out through GDEx, a novel electrochemical technology developed at VITO. GDEx consists of a rapid one-pot process occurring at the three-phase junction between a porous electroactive material, an aqueous electrolyte, and an oxidant gas (i.e. air, O2, CO2)—in a so-called gas-diffusion electrode. In this embodiment, reaction precipitation of PGMs takes place at the electrochemical interface.
The composition of the PGM-products formed can be tailored by changing the supplied gas (i.e., O2 to form oxides, or CO2 to obtain elemental PGMs). In addition, other properties can be controlled (e.g., crystallite and unit cell size, particle size, etc.), by manipulating other operational variables (e.g., PGM-precursor concentration, electrochemical potential).
PGM recovery from PGM-containing wastes
One of the most interesting applications of “molten-salt” extractive metallurgy is the selective chemical reaction with the ores, metal oxide mixtures, or waste material. The molten mixtures can be fed to industrial electrolytic cells (electrometallurgy) where the reactions can take place. One example of this type of reactions is the selective chlorination using gaseous mixtures in a molten chloride salt mixture.
In the frame of PLATIRUS project, SINTEF has demonstrated the selective chlorination of the PGM elements contained in the spent catalyst samples, without pre-treatment of the catalyst raw material, and the subsequent electrolytic reduction of the PGM-chloro-complexes in metals, all this from a molten salt reaction media. In this way, many steps can be avoided, and the PGM can be separated from the matrix and converted to metals in a single and simple step.
This innovation has reached the final of the Innovation Radar Prize from the EU Commission. The 4 finalists will meet 5-6 December 2018 at the ICT 2018 Conference in Vienna. Read more about it here.
The biggest advantage of this technology lies in the process simplicity and low cost.
An electrodeposition process was developed at TECNALIA as a PGM recovery step, using different starting electrolytes and in which the PGMs are selectively electrodeposited in their metallic form in good to high recovery yield.