Synthesis of djerfisherite K6Fe24.5S26Cl by isobaric-isothermal holding method at T = 500 °C and P = 500 atm

Research subject. A series of experiments on the synthesis of ferrous djerfisherite by the isobaric-isothermal holding method were carried out. We used standard autoclaves made of alloy steel with a volume of 200 cm 3 as high-pressure vessels. The starting material for the synthesis was a mixture of FeS 2 (pyrite) + Fe 2 O 3 + K 2 CO 3 + KCl, ground into powder, metallic aluminum and fluid (water + ethanol) were used to maintain reducing conditions. Aim. To establish the optimal parameters for the synthesis of djerfisherite and to obtain a representative amount of djerfisherite for further studies of its stability under controlled conditions (T, P, fO 2 , etc.). Methods. In order to identify the obtained phases, we first carried out X-ray diffraction analysis and then Raman spectroscopy; scanning electron microscopy with energy-dispersive spectrometry were used to determine the chemical composition of all newly formed phases. Results. Djerfisherite of the composition K 6 Fe 24.5 S 26 Cl was synthesized together with troilite ± sylvite. Semi-quantitative ratios of newly formed phases indicate the presence of djerfisherite in amounts from 30 to 80 wt %. The Raman spectra of synthetic djerfisherite correspond to previous studies. Conclusions. Favorable parameters for the synthesis of djerfisherite are: T = 500°C, P = 500 atm, t = 168 hours. As a result of experiments we synthesized djerfisherite (72 wt %), together with troilite (21 wt %) and sylvite (7 wt %), with a total mass of about 15 g.