Effect of Silicate Matter on Pyrochlore Solubility in Fluoride Solutions at Т = 550–850°C, Р = 50–100 MPa (Experimental Studies)

Abstract

The experimental results of natural pyrochlore behavior in KF solutions in the presence of quartz at 550–850°C and 50–100 MPa are presented. It is shown that silicate matter (quartz) exerts a significant effect on pyrochlore solubility in aqueous solutions of fluorides of alkaline metals under hydrothermal conditions. This study of the fluid inclusions has revealed the occurrence of reactions of high-temperature hydrolysis of KF under the experimental conditions: KF + H₂O = KOH + HF; in which case, the interaction with quartz SiO₂ + 2KOH = K₂SiO₃ + H₂O is followed by the formation of a silicate glass phase (an aqueous solution–melt). This phase of alkaline glass is a Nb concentrator (Nb₂O₅ up to 16 wt %). The coefficient of Nb distribution between the glass and the fluid is ≈500 (in favor of the glass). It is determined that the phase of the silicate solution–melt can serve as an effective concentrator of the ore component (Nb) at the last lowtemperature stages of crystallization of rare-metal granites.