Mobility of heavy rare earth elements in magmatic-hydrothermal systems: Experimental determination of DyPO4 solubility in supercritical fluids

We conducted a series of synthetic DyPO4 solubility experiments in NaCl-HCl-bearing aqueous solutions (pH of 2 at 25 °C) from 500 to 700 °C and 1.5 kbar using externally heated pressure vessels. DyPO4 displays a strong prograde solubility with temperature across all studied fluid salinities (0-0.5 m NaCl). The DyPO₄ solubility isotherms at 500 °C, 600 °C, and 700 °C show a complex relationship with salinity where DyPO₄ solubility is highest (39.2-1552 ppm at 500-700 ℃) in 0 m NaCl solutions, decreases strongly (21-331 ppm at 500-700 ℃) in the 0.06 m NaCl solutions and remains relatively constant in the 0.25 m (42.8-248 ppm) and 0.5 m NaCl (40.2-124 ppm) solutions.