# Sintering with Sodium Carbonate and Leaching of Wolframite Cakes
## 2 Materials and Methods  
The interaction reactions of tungsten minerals with Na\({}_{2}\)CO\({}_{3}\) for concentrates from Akchatau ores begin at temperatures above 520-550 \({}^{\circ}\)C and proceed intensively in the range of 750-850 \({}^{\circ}\)C, as we have found. To study the temperature conditions of sintering concentrates with sodium carbonate and the influence of leaching factors on the extraction of sodium tungstate into aqueous solutions, the batch was sintered in a muffle furnace using carborundum crucibles at temperatures of 750, 800, and 850 \({}^{\circ}\)C, with an excess of sodium carbonate ranging from 1.05 to 1.2. The chemical and phase composition of the wolframite concentrate was analyzed using an SPM-35 X-ray spectrometer (CJSC \"Nauchpribor\", Orel, Russia) and an Empyrean multichannel diffractometer (Malvern Panalytical Company, Almelo, The Netherlands) at the \"Research Center KSP Steel\" LLP. The data obtained are presented in Tables 1 and 2 [3]. As a result of structural analysis, the minerals FeWO\({}_{4}\) (Ferberite), MnWO\({}_{4}\) (Manganese Wolframate), and tungsten oxides WO\({}_{2}\), WO\({}_{3}\), WO\({}_{2}\)-H\({}_{2}\)O were identified. As a result of sintering, black-colored cakes were obtained. The cakes were crushed and ground in a laboratory rod vibrating mill, followed by classification on sieves and allocation into classes with average particle size in microns: 815, 635, 365, 100. Cakes were leached with distilled water in laboratory thermostats at temperatures from 65 to 95 \({}^{\circ}\)C and stirred with a paddle-type stirrer at a rotation speed of 240 to 420 rpm. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & & & & & & & & & & & & \\ \hline WO\({}_{3}\) & FeWO\({}_{4}\) & MnWO\({}_{4}\) & SiO\({}_{2}\) & CaO & Al\({}_{2}\)O\({}_{3}\) & MgO & MoO\({}_{3}\) & S & C & Fe\({}_{2}\)O\({}_{3}\) & MoO\({}_{3}\) \\ \hline
25 & 27 & 31 & 3 & 6 & 3 & 3 & - & 14 & - & - & - \\ \hline \end{tabular}
\end{table} 
Table 2: Phase (structural) analysis of wolframite concentrate, % (wt. ). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & & & & & & & & & & & \\ \hline \multicolumn{1}{c}{**Content, wt.\%**} & & & & & & & & & & \\ \hline WO\({}_{3}\) & Fe\({}_{2}\)O\({}_{3}\) & SiO\({}_{2}\) & Al\({}_{2}\)O\({}_{3}\) & P\({}_{2}\)O\({}_{5}\) & S & CaO & MnO & MgO & MoO\({}_{3}\) & Re & C \\ \hline
68.8 & 6.52 & 2.96 & 2.51 & 0.037 & 1.94 & 5.51 & 7.31 & 2.65 & 0.35 & 0.06 & 0.73 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of wolframite concentrate, % (wt.). According to the data in Table 3, a linear dependence of the content of sodium tungstate in the solution was obtained in terms of WO\({}_{3}\), g/L. \[\text{Y}=0.88\times\text{X}-875.87;\,\text{R}^{2}=1.00, \tag{1}\]  
where Y is the content of sodium tungstate and metal in the solution in terms of WO\({}_{3}\), g/L; X is the density of the sodium tungstate solution, g/L. The density of the resulting solutions was measured at 20 \({}^{\circ}\)C with the use of a standard set of hydrometers and the pycnometric method [18] to calculate the extraction of sodium tungstate into solution, and optical and adsorption density measurements were also used by the photocalorimetric method with a Jenway 6300 spectrophotometer (Jenway Company, Stone, UK). The content of WO\({}_{3}\) in solutions was calculated based on the measured density of the solution. Leaching was carried out at a ratio of LS = 5:1 with 20 g of cake. Filtration of the pulp was carried out on paper filters; the pulp settles and filters relatively easily. Experiments with cakes obtained at temperatures of 750-850 \({}^{\circ}\)C were performed, taking into account 5 factors at 4 levels according to probabilistic design of experiments [19]. The conditions for leaching experiments of cakes obtained at different firing temperatures and the extraction of WO\({}_{3}\) into solution are specified in Table 4.