Slag recycling and reuse – GREENY approach

Material efficiency also means using the available resources better — using reduced amounts of primary raw materials and substituting them with secondary raw materials recycled from the original process. Increasing the use of recycled content of raw materials is an efficient way to reduce the total environmental impact resulting from the production processes.

GREENY (GRinding Energy EfficiencY) is a collaborative research project focused in developing the beneficiation route of difficult to process secondary raw materials, such as industrial slags. Target is to develop innovative processes involving selective, energy-efficient crushing and separation processes of slags. After the separation, the metallic fractions of the slag can be brought back to the production process and the mineral fractions can be processed into manufactured aggregates. The targeted cost- and resource-efficient beneficiation route will enhance the application of industrial slags so that these secondary raw material deposits can be brought back to circular economy.

The GREENY project partners form an interdisciplinary group with strong technology knowledge on crushing and beneficiation of raw materials, material physics and chemistry as well as simulation and modelling of industrial processes. Participants are Metso Outotec, ERAMET Ideas, Technical Research Centre of Finland (VTT), Technische Universität Bergacademie Freiberg (TUBAF) and Luleå University of Technology (LTU), supported by EIT RawMaterials. EiT RawMaterials is a community of the EIT, a body of European Union and largest consortium in the raw materials sector worldwide.

New simulation tool for planning and optimization

In addition to the beneficiation process development, a new simulation tool is developed which can be used for planning and optimization of the process for various secondary raw materials. The simulation tool covers the whole refining process starting from slag by introducing respective modelling capabilities as a customization of the workflow. The simulation tool can predict the size distribution and morphology of the end product after the crushing steps in the process sequence. Also, the energy need for the whole crushing process is evaluated, including the wear of the consumables. This provides the user with the capability to develop and optimize comminution processes and improve their efficiency for the beneficiation of difficult to process raw materials. 

Nowadays, landfilling is still used for large amount of the industrial slags globally. In many countries, costs for landfilling are constantly increasing and it is highly taxed, landfilling areas are limited and permissions for new areas are difficult to obtain. The reuse of slag should be organized at the site where the slag is stored, as any transport costs will increase the processing costs significantly. From the environmental point of view, the landfilling of slags is a significant source of pollution of air, water and soil. Slag landfills can emit heavy metals to the environment (soil and water) for very long time periods what represents a high environmental impact. Instead of storing slag as industrial waste, it is nowadays considered more as a valuable secondary raw material.

The value of the slag as a secondary raw material depends of the final application and the processing costs. The critical factor is the cost of the valorization process, consisting of total process energy need and cost of it, and cost of labour and equipment needed for processing. The end user value of the product greatly depends of the final product size, form and quality. A better knowledge of the secondary raw material properties, such as slag formation, composition and physical properties is fundamental for increasing slag application both internally back in industrial production and externally in different innovative reuse applications.