# Technological Aspects of Sintering Low-Quality Wolframite Concentrate with Potassium Carbonate
## 3 The Results and Discussion
### Thermodynamic Assessment of the Main Reactions
The following process parameters are accepted: temperature--1073 K, duration--120 min, the number of carbonates--110% according to stoichiometric requirements for the formation of K\({}_{2}\)WO\({}_{4}\), K\({}_{2}\)MoO\({}_{4}\), and K\({}_{2}\)SO\({}_{4}\), and 140%--for the formation of Na\({}_{2}\)WO\({}_{4}\), Na\({}_{2}\)MoO\({}_{4}\), Na\({}_{2}\)SO\({}_{4}\). The technological and hardware test diagrams are shown in Figures 5 and 6. The resulting sintering products (Figure 7) after sintering treatment at 1073 K for 2 h have a different structure. When sintering with Na\({}_{2}\)CO\({}_{3}\), a high proportion of the liquid phase was observed, making mixing difficult. Partial meltback is associated with the formation of tungstate and sodium molybdate--Na\({}_{2}\)WO\({}_{4}\) and Na\({}_{2}\)MoO\({}_{4}\), having melting temperatures below the process temperature--971 and 960 K, respectively. The partially melted sintering product with Na\({}_{2}\)CO\({}_{3}\) was dense and heterogeneous: Gray (area 1) and black areas (area 2) were visually distinguishable. The weight loss was 13.8%. When using K\({}_{2}\)CO\({}_{3}\), on the contrary, the sintered mass was porous, uniform in color, crumbling into powder under low loads. The weight loss was \(-\)8.96%. Figure 4: The degree of tungsten extraction into solution depends on the amount of carbonates and the duration of sintering at 1073 and 1123 K: **(a)**—sintering with Na\({}_{2}\)CO\({}_{3}\), **(b)**—sintering with K\({}_{2}\)CO\({}_{3}\). Figure 5: Process flow of integrated tests with indication of parameters based on the results of the probabilistic-deterministic method of experiment planning. Figure 6: Hardware diagram of the enlarged tests: 1—ball mill; 2—chamber furnace; 3—pallet for oxidative roasting; 4—scrubber; 5—stirrer; 6—sintering pallets; 7—jaw crusher; 8—agitator; 9—nutsche filter. The arrows in the figure illustrate the progression from one phase of the process to the subsequent phase. According to the X-ray phase analysis (Figure 8), the products of the thermal interaction of the cinder with Na\({}_{2}\)CO\({}_{3}\) are mainly represented by Na\({}_{2}\)WO\({}_{4}\), Na\({}_{2}\)MoO\({}_{4}\), and SiO\({}_{2}\) phases. Sodium compounds predominate in the composition of the sinter from region 1 (gray areas): in addition to Na\({}_{2}\)WO\({}_{4}\), unreacted Na\({}_{2}\)CO\({}_{3}\), Na\({}_{2}\)SO\({}_{4}\). In region 2 (dark areas), in addition to Na\({}_{2}\)WO\({}_{4}\), the oxide phases Fe\({}_{3}\)O\({}_{4}\), Mn\({}_{2}\)O\({}_{3}\), and Al\({}_{2}\)SiO\({}_{5}\) were revealed. The product of the interaction of the cinder with potassium carbonate is represented by the phases K\({}_{2}\)WO\({}_{4}\), K\({}_{2}\)MoO\({}_{4}\), Fe\({}_{2}\)MnO\({}_{4}\), and K\({}_{2}\)Fe\({}_{2}\)O\({}_{4}\). According to the chemical analysis data, during sintering, the product was diluted in terms of tungsten content and impurities. The analysis of the obtained results shows that the product obtained by sintering the burnt concentrate with potassium carbonate contains the following by weight. %: 22.4 W, 3.08 Mo, 8.20 Si, 8.36 Fe, 3.69 Mn, 4.32 Cu, 0.78 Al, 0.13 P, 0.61 S, 16.3 K. The sintering product of the burnt concentrate with sodium carbonate contains by weight. % 23.7 W, 3.25 Mo, 8.66 Si, 14.2 Fe, 3.90 Mn, 4.57 Cu, 0.82 Al, 0.14 P, 0.65 S, 13.1 Na. The amount of cake from the leaching of the sintering products of the burnt concentrate with Na\({}_{2}\)CO\({}_{3}\) was 59.36%, and with K\({}_{2}\)CO\({}_{3}\)--46.05%. According to the data on the compositions of the obtained cakes (Table 5), the distribution of elements by leaching products was analyzed. The lower the residual content of target metals (W, Mo) in aqueous leaching cakes, the higher the transition of metals into solution is.