Hydrothermal Synthesis and Thermal Stability of Natural Mineral Lindgrenite

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 ℃. The crystal structure of the mineral was determined and the final refinement for 791 observed reflections with I＞2σ(I) gave R 1 =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 ℃, and the mixture of MoO3 and CuO was formed through decomposition of Cu3Mo2O9 at a temperature ranging from 650 to 700 ℃. Therefore, the structure of the mineral was thermally unstable at above 300 ℃, suggesting that Lindgrenite was likely formed via the hydrothermal route occurring in the nature.