## 1 Introduction  
Currently, all industrial processes should be oriented towards the improvement of sustainability. Therefore, the reuse and/or recycling of by-products and wastes alongside economic interests are commonly required by applying circular economy principles. The mining waste is considered to be of particular interest due to the produced high mineral volumes. In this research, the upgrading of mineral wastes, produced in a magnesite mine (\"Grecian Magnesite SA\", Chalkidiki, N. Greece), due to the enrichment process of magnesite ore, are examined in order to improve the respective refractory properties and to recycle/reuse them for the production of useful products with economic value (e.g., bricks, metallurgical masses, etc. [1, 2]). The main point is to properly apply the so-called \"reverse mineralogy\", i.e., to produce from the serpentized wastes the useful forsterite mineral phase (Mg\({}_{2}\)SiO\({}_{4}\)), which is considered as a competitive refractory material [3]. The presence of other impurities, such as aluminum, calcium, and alkaline oxides in the initial serpentine/pyroxenes by-products, is generally unwanted because these constituents cannot efficiently be removed during the subsequently applied calcination process, and negatively affect the desirable refractory properties [4].  
The detailed characterization of these wastes/by-products currently stocked in the magnesite mine area contain several impurities [1] and present rather low refractoriness; hence, the addition of another environmentally friendly and low-cost mineral/materialthat can enhance the refractory properties is required. It is also worth noting that several researchers utilized these serpentinized wastes for the re-formation of a (useful) forsterite mineral phase and the subsequent production of forsterite-based refractories (e.g., [4; 5]). Thus, different additives, such as chromite [4], zirconia [6], aluminum titanate [3], magnesia [7], magnesium chloride hexahydrate [8], and iron oxides [9], etc., have been examined for this purpose. In present times, nanomaterials are considered as a specific material category, intensively investigated for the production of certain refractory materials due to their high surface to volume ratio which also increases the chemical reactivity and finally results in improved refractory products [10].  
According to current trends, considering that the lifecycle of any product should potentially result in zero-waste production, in the present study the exploitation of mining wastes/by-products from a magnesite mine with the addition of the examined hematite nanoparticles, aimed to create improved refractory characteristics of the products. The role of hematite (Fe\({}_{2}\)O\({}_{3}\)) is examined as a potential additive for the preparation of upgraded refractory materials after the application of appropriate thermal treatment processes. Iron oxide can promote the sintering of mineral grains with cation vacancies and, in the temperature range of 900 \({}^{\circ}\)C to 1200 \({}^{\circ}\)C, reacts with the MgO content to form MgFe\({}_{2}\)O\({}_{4}\), which is a high melting spinel phase [11]. During our previous studies [1; 2], the detailed qualitative and quantitative characterization of magnesite mine solid wastes was performed, whereas in this study the effects of hematite addition on the main refractory properties of products are examined. Different thermal treatments were applied, i.e., 1300 \({}^{\circ}\)C for 30 and 120 min and 1600 \({}^{\circ}\)C for 60 min, attempting to examine the heating temperature and time in the main physicochemical properties improvement of products. Moreover, the by-products/samples were also examined after the application of a simple pre-treatment thermal procedure, i.e., the samples were thermally treated at 850 \({}^{\circ}\)C for 30 min to achieve the optimum forsterite formation prior to pelletization.