Synthesis of djerfisherite K₆Fe_24.5S₂₆Cl 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 cm3 as high-pressure vessels. The starting material for the synthesis was a mixture of FeS2 (pyrite) + Fe2O3 + K2CO3 + 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, fO2, 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 K6Fe24.5S26Cl 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.

djerfisherite, synthesis, experiment, autoclave, temperature, pressure