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More critical metal by recovery

analyse critical raw metals in waste waters

The use of waste materials as resources for critical raw materials (CRMs) provides an opportunity to recycle waste and promote self-sufficiency across the EU. Researchers from the department of chemistry at Finland’s University of Jyväskylä have developed a modular approach for recycling heterogeneous waste electrical and electronic equipment (WEEE).

Researchers from the department of chemistry at Finland’s University of Jyväskylä have developed a modular approach for recycling heterogeneous waste electrical and electronic equipment (WEEE).

The recovery process is based on hydrometallurgy with modern metal scavenger technologies (a purification technique). Treated WEEE is leached in stages to separate metals into the leachates. Copper is recovered via electrowinning (a process used to remove metal ions from liquid solutions) while noble metals (those that resist oxidation and corrosion in moist air) are recovered using modern metal scavenger technologies, including recovery methods based on 3D-printed functional materials invented at the university. The recovery process is designed to produce high-purity metals with a minimum amount of waste fractions.

The first separation of CRMs is performed by using the specially designed dissolution process. Most of the copper, gold and platinum group metals are separated into fractions according to their dissolution properties. This enables the efficient recovery process of the metals.

Dissolution is performed with diluted acids or acid mixtures, and the procedure has been optimised – solid to liquid ratio, acid concentrations, time and temperature – at the laboratory scale. In addition, the recovery processes using metal scavengers have been optimised by determining optimal contact time of metal scavengers with the solutions. The method will be optimised at pilot scale to operate safely and have high output of pure fractions of metals.

Dissolved metals can be captured using commercially available granulated metal scavengers with the appropriate functionality. The disadvantages of granulated scavengers is the need for filtering and, usually, loaded scavengers need to be burned to recover captured metals.

In the Finnish process, the 3D-printed metal scavengers, capable of selectively capturing metals from solutions, can be used for the recovery of gold, palladium, platinum, silver and rare earth metals (REMs). Such 3D-printed scavengers operate as selective filters for metals, and are used by simply passing the liquid flow through the object.

The 3D-printed scavengers can operate on a wide pH range and low concentration level. This means the metal recovery process is performed without changes in pH, enabling the recirculation of acids after separation of metals. This allows huge cost savings and a significant decrease in emissions and the amount of wastes produced.

The captured metals can be leached easily from the 3D-printed scavenger, which is reusable. With this process, high selectivity and recovery rates for metals can be obtained: gold and copper with purity/recovery of 99%; palladium, platinum and silver with purity/recovery greater than 98% from printed circuit boards (PCBs); and REMs with a recovery of more than 90% from neodymium (NdFeB) magnets.

A consortium of partner companies (Jyväskylä Energy Group, Tapojärvi and Elker) have taken concrete steps to use the developed process and then design and build a circular economy R&D facility. The principal goal of the facility is to recover CRMs from various waste fractions and to provide an R&D environment for testing innovations. The facility is currently in its process design and simulation phase, and the final decision on the building of the facility will be done in August 2018.

The first waste materials to be processed are PCBs and NdFeB magnets. The facility is targeted to process one tonne a day of WEEE to produce approximately 250kg of copper and 0.6kg of gold, 50g of platinum, 200g of palladium and several grammes of REMs. In the case of NdFeB magnets, iron, boron and REMs are separated and a mixture of REM oxides with high purity is obtained. These yields are substantially higher when compared with those obtained from one tonne of ore/minerals: typically 6g of gold, 3g of platinum or 1.3g of palladium.

When the R&D platform and its technology is fully tested, it will be open to industrial operators for testing and developing their processes for the recovery of CRMs from WEEE and other waste materials in a sustainable and environmentally friendly way.

Ari Väisänen is an adjunct professor and Siiri Perämäki is a postdoctoral researcher, both at the University of Jyväskylä in Finland

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