TG/DTA studies of the mixture of Korean monazite and sodium carbonate to get optimum condition for phosphate decomposition

Abstract

TG/DTA is one of the important thermal pre-treatment processes in which material sare heated at high temperature in a furnace to identify the change in the properties due to thermal decomposition of sample i.e, loss in weight, melting point, type of reaction, etc. as well as compounds emitted. Present paper reports the TG/DTA studies of Korean monazite when mixed with an hydrous sodium carbonate and its decomposition behavior particularly for phosphate. A weak peak of decalescence was observed on DTA curve between 750˚C to 850˚C indicating the reaction of monazite. The shape of the peak suggests a phase shift between the two temperatures. The peak indicated that the decomposition starts after 700˚C and it requires energy i.e. an endothermic reaction. The first depletion in the TG curve noticed around 100˚C shows the reaction of sodium carbonate with SiO2 present in the monazite to form metal silicate whch is followed by the formation of meta disilicate starting at ~700˚C with the evolution of CO2. An equivalent amount of CO2 would have been released during the reaction between sodium carbonate and Korean monazite i.e. a rare earth(RE) phosphate mineral(REPO4)at 850˚C, which melts and react with REPO4 to form RE oxide sand sodium phosphate. XRD analysis of the sample after TG-DTA test was performed to confirm the phases present after heat treatment. The optimum condition obtained by TG-DTA for dephosphorisation of monazite was validated in muffle furnace in laboratory scale and found the result similar and satisfactory. The roasted sample could be processed further to recover RE metals by hydrometallurgical processes.