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.本研究采用外加热高压釜，在500~700 ℃、1.5 kbar的条件下，于含NaCl-HCl的水溶液（25 ℃时pH为2）中开展了一系列合成磷酸镝（DyPO₄）的溶解度实验。在本次测试的所有流体盐度（0~0.5 m NaCl）范围内，磷酸镝的溶解度均随温度呈现显著的正向递增趋势。500 ℃、600 ℃与700 ℃下的磷酸镝溶解度等温线与盐度呈现复杂关联：在0 m NaCl溶液中，磷酸镝溶解度最高（500~700 ℃下为39.2~1552 ppm）；在0.06 m NaCl溶液中，溶解度大幅降低（500~700 ℃下为21~331 ppm）；而在0.25 m NaCl（42.8~248 ppm）与0.5 m NaCl（40.2~124 ppm）溶液中，溶解度基本保持稳定。