Raman spectra of pyromorphite, vanadinite and mimetite at high pressures and high temperatures

High-pressure and high-temperature Raman spectra of natural pyromorphite, vanadinite and mimetite were measured up to 11 GPa and 973 K, respectively. No phase transition was observed within the temperature and pressure ranges in this study. Raman modes for pyromorphite, vanadinite and mimetite vary with temperature or pressure linearly. The temperature and pressure dependence of the force constants for P-O, V-O and As-O stretching vibrations were determined. The isobaric and isothermal mode Grüneisen parameters of pyromorphite, vanadinite and mimetite were calculated. The intrinsic anharmonic mode parameters were estimated and nonzero, indicating the existence of intrinsic anharmonicity for pyromorphite, vanadinite and mimetite. Based on the Kieffer model, the thermodynamic parameters, including isochoric heat capacity, entropy and Gibbs free energy, were calculated. The thermal stability was determined with the Gibbs free energy of formation, and pyromorphite may be the most thermally stable mineral among pyromorphite, vanadinite and mimetite. The thermal stability is an important factor for the three lead-apatite minerals in immobilizing Pb, V and As, and the formation of lead-apatite minerals in contaminated areas contributes to environmental remediation.