Hydrothermal Synthesis and Thermal Stability of Natural Mineral Lindgrenite1

A natural mineral, lindgrenite Cu3 (MoO4)2 (OH)2, was synthesized from a mixture of sodium molybdate, copper sulfate, and morpholine in water under autogenous pressure at 170 °C. The crystal structure of the mineral was determined and the final refinement for 791 observed reflections with I > 2σ (I) gave R1 = 0.0205 and wR2 = 0.0496. The thermal stability of the mineral was investigated by using TG-DTA and variable-temperature in situ X-ray diffraction (XRD) techniques. The crystalline Cu3Mo2O9 was obtained when the mineral underwent thermal dehydration at a temperature ranging from 300 to 400 °C, and the mixture of MoO3 and CuO was formed through decomposition of Cu3 Mo2 O9 at a temperature ranging from 650 to 700 °C. Therefore, the structure of the mineral was thermally unstable at above 300 °C, suggesting that Lindgrenite was likely formed via the hydrothermal route occurring in the nature.