*2.3. Methods*

The particle size analysis was performed using a Particle Size Analyzer (AntonPaar GmbH, Graz, Austria) for the milled mine tailings after the calcination process to confirm the size of obtained grain and its distribution.

The mechanical properties of the samples were investigated using the MATEST 3000 kN test machine (Matest, Treviolo, Italy), according to the following regulations.


The applied speed in both cases was 0.05 MPa/s. The flexural strength was investigated in prismatic samples having dimensions: 50 mm × 50 mm × 200 mm and the distance between the supports was 150 mm (three-point bending test). The compressive strength was investigated in the samples after the flexural strength test with the use of a metal plate with dimensions: 50 mm × 50 mm.

The mineralogical composition was determined using X-ray diffraction XRD analysis. This investigation was carried out on powdered mine tailing before calcination using PANalytical AERIS (PANalytical, Almelo, The Netherlands). This device applies the X-ray method (Debye–Scherrer) for phase analysis. It was carried out using Cu-Kα radiation and components such as a nickel filter on the lamp, mask 13, and Szlot 1◦. The following parameters were applied to this research—angle range: 9999–100◦2ʤ, measurement step: 0,0027166◦2ʤ, time of counts: 340,425 s, and total measurement time: 13 h 2 min 32 s. Next, the results were analyzed using HighScore Plus software, based on PDF4 + crystallographic database.

Microstructure investigation was performed on a JEOL JSM-IT200 scanning electron microscope (JEOL, Tokyo, Japan). This type of scanning electron microscope (SEM) has an energy-dispersive X-ray spectroscopy system (EDS), which allows for analyzing the chemical and oxygen composition of the investigated material. The research was provided on the material after mechanical properties tests. The samples were covered by gold plating for good conductivity. The cover layer was applied by a DII-29030SCTR Smart Coater (JEOL, Tokyo, Japan).
