# Sintering with Sodium Carbonate and Leaching of Wolframite Cakes
## 3 Results and Discussion  
The decomposition of wolframite concentrate by sintering it with sodium carbonate in the presence of oxygen proceeds according to reactions [3; 7; 8; 14; 15]. \[2\mathrm{FeWO_{4}}+2\mathrm{Na_{2}CO_{3}}+0.5\mathrm{O_{2}}=2\mathrm{Na_{2}WO_{ 4}}+\mathrm{Fe_{2}O_{3}}+2\mathrm{CO_{2}} \tag{2}\]  
\[3\mathrm{MnWO_{4}}+3\mathrm{Na_{2}CO_{3}}+0.5\mathrm{O_{2}}=3\mathrm{Na_{2}WO_{ 4}}+\mathrm{Mn_{3}O_{4}}+3\mathrm{CO_{2}} \tag{3}\]  
\[\mathrm{WO_{3}}+\mathrm{Na_{2}CO_{3}}=\mathrm{Na_{2}WO_{4}}+\mathrm{CO_{2}} \tag{4}\]  
\[\mathrm{WO_{3}}\times\mathrm{H_{2}O}+\mathrm{Na_{2}CO_{3}}=\mathrm{Na_{2}WO_{ 4}}+\mathrm{CO_{2}}+\mathrm{H_{2}O} \tag{5}\]  
\[\mathrm{WO_{2}}+\mathrm{Na_{2}CO_{3}}+\mathrm{\SIUnitSymbolMicro O_{2}}=\mathrm{ Na_{2}WO_{4}}+\mathrm{CO_{2}} \tag{6}\]  
\[\mathrm{WO_{2}}\cdot\mathrm{H_{2}O}+\mathrm{Na_{2}CO_{3}}+\mathrm{\SIUnitSymbolMicro O _{2}}=\mathrm{Na_{2}WO_{4}}+\mathrm{CO_{2}}+\mathrm{H_{2}O} \tag{7}\]  
An increase in the coefficient of excess sodium carbonate during sintering of the charge in the range from 1.05 to 1.2 leads to a greater completion of the formation reactions of \(\mathrm{Na_{2}WO_{4}}\), and at the stage of sinter leaching, the extraction of sodium tungstate into the solution increases from 87.4 to 98.6% and is described by the dependence:  
\[\mathrm{y}=-0.5115\mathrm{x^{2}}+5.8247\mathrm{x}+82.914;\,\mathrm{R^{2}}=0.9707\]  
where \(\mathrm{y}\) is the degree of extraction of sodium tungstate into solution, %, x = 1, 2, 3, 4-coded values of the excess coefficient values (1.05, 1.10, 1.15, 1.20). An increase in the sintering temperature of the charge within 700-800 \({}^{\circ}\)C leads to an increase in the extraction of sodium tungstate into the solution from 83.1 to 97.8%:  
\[\mathrm{y}=-0.9244\mathrm{x^{2}}+9.1753\mathrm{x}+75.35;\,\mathrm{R^{2}}=0.9822\]  
where \(\mathrm{y}\) is the degree of extraction of sodium tungstate into solution, %, x = 1, 2, 3-coded values of sintering temperatures (700 \({}^{\circ}\)C, 750 \({}^{\circ}\)C, 800 \({}^{\circ}\)C). During leaching of the cake [3; 7; 8; 14], sodium tungstate and soluble impurities pass into the solution (\(\mathrm{Na_{2}SiO_{3}}\), \(\mathrm{Na_{2}HPO_{4}}\), \(\mathrm{Na_{2}HasO_{4}}\), \(\mathrm{Na_{2}MoO_{4}}\), \(\mathrm{Na_{2}SO_{4}}\)), as well as excess of \(\mathrm{Na_{2}CO_{3}}\). The density of the resulting sodium tungstate solutions was in the range of 1105-1128 g/L, and the content of the extracted component in terms of \(\mathrm{WO_{3}}\) was 93-110 g/L; the cake yield after leaching was 4.1-6.1 g. Composition of the cake obtained at 750 \({}^{\circ}\)C and sodium carbonate excess coefficient \(\mathrm{Kc}\) = 1.2, as well as the mass and composition of the cake obtained during leaching, are given in Table 5.  
Processing of experimental data made it possible to identify the dependences of tungsten trioxide leaching into solution and the trend equations presented for the sinter obtained at 750 \({}^{\circ}\)C in Figure 1a-e. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multirow{2}{*}{**Weight, g**} & \multicolumn{8}{c}{**Content of Chemical Elements, \%**} \\ \cline{3-10}  & & **WO\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **P\({}_{2}\)O\({}_{5}\)** & **S** & **CaO** & **MnO** & **MgO** \\ \hline
1. Sinter & 20 & 54.67 & 5.18 & 2.35 & 1.99 & 0.03 & 1.54 & 4.38 & 5.81 & 2.11 \\ \hline
2. Cake & 5.19 & 11.31 & 19.96 & 9.06 & 7.68 & 0.11 & 5.94 & 16.86 & 22.37 & 8.11 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Composition of cake obtained at 750 \({}^{\circ}\)C and water leaching cake. Figure 1: _Cont._  
Figure 1: Cont. Experimental data are described by polynomials of the 2 nd degree (the x-values correspond to the levels of factors in codes 1, 2, 3, 4 in the equations).