Kinetics of the Natural Wolframite Interaction with Sodium and Potassium Carbonates

Abstract

The kinetics and mechanism of the natural wolframite interaction with sodium and potassium carbonate, when they are heated in the air, are studied. Using X-ray phase and X-ray structure microanalysis, it was established that the initial single crystal wolfram consists of Fe0.5Mn0.5WO4 and Fe0.3Mn0.7WO4. The method of differential thermal and subsequent phase analysis of products has shown that the interaction of wolframite with sodium and potassium carbonates begins above 450-470 °C with the formation of tungstate and ferrites of sodium and potassium, iron and manganese oxides. Conducting the model experiments on sintering with the subsequent removal of water-soluble compounds (alkalization) made it possible to follow the change in the structure of wolframite. Unit cells parameters of wolframites in solid products (cakes) of leaching do not change if sintering is carried out in the range up to 600 °С. In samples, the preparation of which is coupled with heating to 700–800 °C, the atomic ratio of Fe/Mn in wolframite decreases to 0.2. This allows to specify the mechanism of the process and judge the greater reactivity of wolframites with an increased proportion of iron. Thermal analysis with data processing using the methods of non-isothermal kinetics has established that the studied interactions proceed according to a two-stage mechanism, which in the first stage is limited by diffusion. The appearance of a low-melting eutectic Na2WO4 – Na2CO3 и K2WO4 – K2CO3 in the system contributes to the process transition to the autocatalytic mode.