Refractory breakouts: Comminution technology validation for MgO-C refractories

Zixuan Zhang

Research output: ThesisMaster's Thesis


Recycling has grown increasingly popular in the refractory industry. The recycling of used refractory bricks into high-quality, secondary raw materials can help to reduce the consumption of primary raw materials and thus conserve deposit reserves as well as significantly reduce the CO2 footprint resulting from extraction, preparation and further processing. However, because of their complex compositions and combinations, spent refractory materials are not sorted automated and manually instead. The investigations carried out in the course of this master's thesis focussed on MgO-C, which is frequently used as a refractory material. During the relining of ovens, a not inconsiderable amount of these used refractory bricks accumulate as waste, which is currently mainly sent to landfill. Since dumpingbring up costs, recycling the MgO-C refractory breakouts is also significant from an economic point of view. In this thesis, the focus is on recycling of MgO-C in order to create sufficient liberation conditions for subsequent sorting by applying five different comminution technologies, including electrodynamic fragmentation on lab-scale, electrodynamic fragmentation on semi-industrial scale, impact crusher, cone crusher and jaw crusher. In order to detect apparent colour differences, the samples were examined separately under a microscope before and after the density tests. Preliminary investigations showed that the first completely free phases of MgO-C could already be present from a size of less than 4 mm. The final particle fractions used in the course of raw material characterisation and for separation tests are 4 - 3.15 mm and 3.15 - 1 mm respectively. Float/sink analyses were performed by using the density differences of the phases contained in MgO-C. In order to detect apparent colour differences, the samples were examined separately under a microscope before and after the float/sink analyses. The samples were then investigated for Magnesia and Carbon enrichment using XRF and LECO. Finally, it was determined which is the most suitable for comminuting this refractory bricks. It also defines the particle sizes and density ranges that are best for generating enriched MgO and Carbon. As it was to be expected, the Henry-Reinhardt diagrams show that Carbon is enriched in < 3.0 g/cm³ while MgO is enriched in > 3.0 g/cm³. Extensive fractional class analyses were applied to some of the produced fractions of the comminution products in order to determine the comminution technology that best favours the liberation of the contained phases and the subsequent separation. The results suggest that both jaw crushers and cone crushers are suitable aggregates for this essential process step.
Translated title of the contributionFeuerfestausbruchmaterial: Validierung von Zerkleinerungsmethoden für MgO-C Feuerfeststeine
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Friedrich, Karl, Co-Supervisor (internal)
  • Flachberger, Helmut, Supervisor (internal)
Award date28 Jun 2024
Publication statusPublished - 2024

Bibliographical note

no embargo


  • MgO-C
  • Refractory
  • Recycling Comminution
  • Density

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