# Technological Aspects of Sintering Low-Quality Wolframite Concentrate with Potassium Carbonate
## 3 The Results and Discussion  
### Thermodynamic Assessment of the Main Reactions  
According to the results of TDM (Figure 1), the interaction of the concentrate phase components with alkali metal carbonates in an oxidizing medium is accompanied by the formation of Na\({}_{2}\)WO\({}_{4}\), Na\({}_{2}\)MoO\({}_{4}\) and K\({}_{2}\)WO\({}_{4}\), K\({}_{2}\)MoO\({}_{4}\) for the systems containing Na\({}_{2}\)CO\({}_{3}\) and K\({}_{2}\)CO\({}_{3}\), respectively, as well as manganese oxides and iron of various degrees of oxidation. The number of phases formed depends on the temperature and flow rate of Na\({}_{2}\)CO\({}_{3}\) and K\({}_{2}\)CO\({}_{3}\). The degree of transition of tungsten (Figure 2) to water-soluble compounds, close to 100%, corresponds to an excess of K\({}_{2}\)CO\({}_{3}\)--110% of the stoichiometric, unlike Na\({}_{2}\)CO\({}_{3}\), where an excess of 170% is required to achieve such indicators. Figure 1: Change in the proportion of equilibrium phases with temperature during the interaction of the cinder containing Na\({}_{2}\)CO\({}_{3}\) (**a**,**b**) and K\({}_{2}\)CO\({}_{3}\) (**c**,**d**). Dotted lines indicate gaps in the ordinate axes for the purpose of space reduction. The replacement of Na\({}_{2}\)CO\({}_{3}\) by K\({}_{2}\)CO\({}_{3}\) for almost all reactions leads to a decrease in Gibbs energy values (\(\Delta\)G). However, an inverse relationship is observed for reactions with SiO\({}_{2}\). \(\Delta\)G values of the reactions of the interaction of SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) with alkali metal carbonates determine the sequence of transformations with both temperature changes and the number of reagents introduced. Under conditions of a limited number of carbonates, reactions will occur with the formation of alkali metal tungstate. An excess of carbonate against the stoichiometric requirements for the formation of tungstates will lead to the formation of a large amount of sodium silicate, while when using potassium carbonate, only 0.1% of potassium silicate is formed. Such differences in the phase equilibrium composition should be considered a disadvantage of using Na\({}_{2}\)CO\({}_{3}\) in the processing of low-quality concentrates. Therefore, according to the simulation results, the use of K\({}_{2}\)CO\({}_{3}\) in heat treatment with low-quality wolframite concentrate is preferable, especially in case of increased content of silicon dioxide (quartz) in the feedstock. With an increase in the quality of concentrates, the effect of using K\({}_{2}\)CO\({}_{3}\) decreases. Optimization of Sintering Treatment Parameters Using the Method of Probabilistically Deterministic Planning of the Experiment  
Table 3 contains experimental data on the influence of various factors during the sintering of burnt concentrate with sodium and potassium carbonates, and Figure 3 shows the partial dependences of the degree of conversion of tungsten into a water-soluble compound on the studied factors. The composition of the thermally treated concentrate is presented in Table 1.  
Figure 2: Change in the degree of transition of elements (\(\alpha\)) into the products of the interaction of the cinder containing Na\({}_{2}\)CO\({}_{3}\) (**a**,**c**) and K\({}_{2}\)CO\({}_{3}\) (**b**,**d**). Figure 3: Partial dependences of tungsten extraction degree into solution on the sintering temperature, duration, and consumption of Na\({}_{2}\)CO\({}_{3}\) (**a**) and K\({}_{2}\)CO\({}_{3}\) (**b**). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Experience Number**} & \multirow{2}{*}{**T, K**} & \multirow{2}{*}{**\(\tau\), min**} & \multirow{2}{*}{**Q, \%**} & \multicolumn{3}{c}{\(\gamma_{\alpha}\) for Various Systems} \\ \cline{5-6}  & & & & **Na\({}_{2}\)CO\({}_{3}\) System** & \multicolumn{2}{c}{**K\({}_{2}\)CO\({}_{3}\) System**} \\ \hline  
& \multicolumn{3}{c}{Average} & & 62.55 & 56.54 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The three-coefficient experiment matrix.