Investigation of NaF Solubility in Chloride Solutions at 400-500℃ and 200-1000 bar

摘要

The soluble fluorine compounds (HF, KF, and NaF) are the most important dissolving agents of ore components in natural processes. The ore elements form strong complex compounds with F and their content in hydrothermal solutions strongly depends on F concentration. The study of fluid inclusion composition in minerals provides grounds for assuming that the total F concentration in solutions did not exceed 0.n mol/kg H_2O and was much lower than the total Cl concentration. Calcium that forms up a low-soluble compound with F (fluorite) and can pretend to be an indicator and limiter of F concentration in hydrothermal solution. Fluorite solubility was studied in various solutions within a wide range of physicochemical parameters. In natural Ca-depleted systems, such as strongly altered metasomatic rocks, veins, and ore lodes, F content is controlled by the solubility of vil-liaumite (NaF), which is much less soluble than KF. At temperatures above 250℃, villiaumite is characterized by retrograde solubility in water at > 125℃ and belongs to salt of the second type with two critical points (P and Q). The solubility of villiaumite virtually equals zero at critical point P and may exceed 10 wt % at point Q. At T > T_Q (700-750℃) and P > P_Q (> 2000 bar), the solubility of villiaumite in two-phase fluid of the NaF-H_2O system may be considerable.