Päivi Kivikytö-Reponen, Tarja Laitinen ja Marjaana Karhu
VTT Technical Research Centre of Finland
Long known earlier generations’ ideas and habits can be utilized during circular economy transition from the times of shortage of materials and products. New circular economy business models cover profitable longer life products, more efficient use of resources and product loop closure, i.e. looping (maintain, remanufacture, reuse, and recycle). Responsible material design, production and use are highlighted to be one of the core competences in the circular transition. Latest research and technology up-scaling are enablers for current residue and waste challenge.
Material production and recovery generates various currently unutilized residues. Residue related material design and enables and barriers of utilization differ from primary or recycled materials, e.g. in terms of cost, environmental aspects and indicators, locality, traceability, chemical composition, possible hazardous substances, processing technology and potential utilization sector. Taking into consideration the framework (enables and barriers) of residue and specific secondary raw materials, the potential design strategies have been mapped, and demonstrated with three case examples. The set of case examples are selected based on the secondary raw materials origin: primary production residues and tailings (case 1), industrial secondary sources such as by-products, side-streams and residues (case 2) and end-of-life product recycling residues (case 3).
Mining waste is a worldwide challenge, especially due to the large volumes and potential environmental issues. Case 1 presents design strategy to utilize mining residues as raw materials for ceramic materials that are developed at VTT e.g. in CeraTail and SECO-MIN projects. In Ceratail project, funded by Academy of Finland, robust energy efficient processes for utilizing mine tailings as raw material for porous ceramics are developed. In SECO-MIM project, funded by Tekes, mine tailings has been used to demonstrate the possibility to produce ceramic materials by powder injection moulding *. As a result, sintered compacts of ground mine tailing powder have been produced.
* Powder injection moulding, PIM, is a method to produce small pieces with complicated shape. Powder base material is mixed with polymer mixture. The powder load is high in order to keep dimensions of the pieces exact. The polymer part of the mass mixture is melted in injection moulding making the mass mouldable. After solidification the polymer is removed and the remaining part, which is composed of the powder material, is sintered.
Industrial residues form a group of various streams starting from metal fabrication towards manufacturing. Case 2 proposes alumina industry side stream utilization in high temperature alumina based composite for potential substituting e.g. high temperature metal alloys.
** For example aluminium is a widely used in modern life, and it is incorporated into many products, from cans, cell phones and window frames to aeroplanes on the other hand alumina is one of the most common ceramic materials.
End-of-life recycling residues are important, due to the growing material flows, e.g. Waste Electrical and Electronic Equipment (WEEE) belongs to the fastest growing waste stream in the world. WEEE contains in average about 2.2 % (by weight) of Printed Circuit Boards (PCBs). Case 3 proposes direct material processing instead of longer recovery of separate elements is a potential way of reducing energy consumption and time needed in reutilization of the recycled materials. Recovering Cu in electroless plating *** in developed in CloseLoop project funded by Academy of Finland. This method can also be utilized in conductive solutions e.g. with wear resistance requirements, and can offer potential substitute. Furthermore, the recovery residues have been analysed and further processed.
*** In this process, Cu dissolved by an acid treatment from waste PCB is deposited on a powder substrate to form a pure copper layer on the particle surfaces. Potential technology applicable for various substrates, e.g. alumina, carbon nanofibers and plastics.
Presented design and development strategies are only examples of countless of possibilities. The straight residue valorization often do not offer several possibilities but through chemical, mechanical and thermal treatments and synthesizing to added value material creates new opportunities for utilization. It is also important to remember the possible hazardous substances and their processing to harmless form in final product. It is possible to reach this all with relatively profitable processing techniques, also scalable, by tuning the material design, material synthesis and chemistry. Unfortunately, piloting is not enough but research, concept development and laboratory experiments will be needed.