## 4 Conclusions  
The production of refractories from the mining wastes by-products of the magnesite mine \"Grecian Magnesites SA\" (Gerakini, Chalkidiki, N. Greece) with hematite addition and the application of different thermal treatments was examined. In all products, both the apparent porosity (AP%) and the water absorption (WA%), are favored by the addition of hematite nanoparticles at 1300 \({}^{\circ}\)C for 30 min and are suitable for producing refractory bricks. At the same time, the property of bulk density is increased, indicating the improvement of the products' refractoriness. The mechanical strength of the examined products was found to reach maximum values after the application of thermal treatment at 1300 \({}^{\circ}\)C for 120 min. According to the respective XRD patterns from the products, it was revealed that the samples consisted mainly of olivine, pyroxenes and magnesiofferrite, therefore resulting in the decrease of olivine and the pyroxenes' presence in the final product, alongside with a simultaneous increase of magnesiofferrite content. Regarding the addition of hematite, it is clear that the addition of 10 wt.% hematite in all samples shows a deterioration of refractory properties when compared with the 5 wt.% addition. In general, the 5 wt.% addition of hematite nanoparticles improves the main refractory parameters of examined samples when the applied thermal treatment is 1300 \({}^{\circ}\)C.  
The obtained results showed that the application of simple/preliminary thermal pre-treatment at 850 \({}^{\circ}\)C is not recommended, as it reduces the refractory properties. Regarding the examined higher firing temperature at 1600 \({}^{\circ}\)C, the results showed a significant increase of the firing shrinkage parameters, while the mechanical strength was diminished to almost zero. In terms of heating time, when the thermal treatment was performed at 1300 \({}^{\circ}\)C for 120 min, the products showed an increase of firing shrinkage of up to 3.0%, while the mechanical strength parameter even doubled for some samples, when compared to the thermal treatment at 1300 \({}^{\circ}\)C for 30 min. The obtained results reveal that the initial specific mineralogical content is an important factor that affects the refractory properties of obtained products after the hematite addition, with the sample W8 showing the highest improvement of refractory properties as compared with the other examined samples. The collaborating magnesite mine company (Grecian Magnesite SA) is already applying the dunite products in numerous industrial uses such as the application of blast furnaces in slag conditioning, as EBT (eccentric bottom tapping) filler, and also in other refractory products such as in foundry sand, for sandblasting purposes, and mineral wool in fluidized bed combustion and CO2 sequestration. Overall, the scale-up potential with the addition of 5% hematite gives the specific advantage of improved mechanical strength to the products. Most notably, the addition of hematite nanoparticles causes the serpentinized samples to form bricks for application at \(\leq\)1300 \({}^{\circ}\)C, turning them into value- added product suitable for application in a circular economy framework. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12042094/s1](https://www.mdpi.com/article/10.3390/app12042094/s1)]([https://www.mdpi.com/article/10.3390/app12042094/s1](https://www.mdpi.com/article/10.3390/app12042094/s1)), Table S1. Mineralogical content (wt.%) of examined samples; the numbering of samples follows the same numbering as presented in the previous publication of [PERSON] et al., 2020 [1]; Table S2. Chemical composition of the four examined samples [1]; Figure S1. Satellite photo of the Gerakini mining district with the sites marked are presented; Figure S2. TG-DTA curves of samples W5, W6, W7 and W8 [1]; Figure S3. XRD diagram for the fired Bayoxide at 850 \({}^{\circ}\)C; Figure S4.