Thermogravimetric analysis of wheatleyite Na2Cu2+(C2O4)2.2H2O

Abstract

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC2O4as the natural copper (II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na2Cu2+(C2O4)2.2H2O.
High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255 degrees Celsius. Two higher temperature mass losses are observed at 324 and 349 degrees Celsius. Higher temperature mass losses are observed at 819, 833 and 857 degrees Celsius. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260 degrees Celsius. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper (II) oxalate as compared to the synthetic compound which is the dihydrate.