This study demonstrates the possibility of vanadium extraction from coal ash and slag waste of thermal power plants in combination with experimental design by means of sulfuric acid dissolution with the addition of sodium chloride. The conditions of acid dissolution were optimized using the method of five-factor probabilistic-deterministic experimental design at five levels. The following factors were simultaneously varied: the concentration of sulfuric acid was changed in the range of (0.5-2.5) mol/dm3; the temperature of the acid dissolution process was maintained in the range of (25-70) °C; the process duration was (15-90) min; the concentration of sodium chloride was varied in the range of (0.5-15.0) g/dm3; the volume of sodium chloride was changed in the range of (0.05-0.25) cm3. Based on the results of the experiment, the regression and correlation analysis, a significant effect of all five factors on the degree of vanadium extraction from coal ash and slag waste of thermal power plants was established. The optimal conditions for vanadium extraction, allowing for its quantitative extraction (96% by weight or more), are a sulfuric acid concentration of 1.5 mol/dm3, a temperature of 60 ºC, a process duration of 60 min, a sodium chloride concentration in the solution of 0.5-15.0 g/dm3, and a sodium chloride solution addition volume of 0.20 cm3. Based on the established partial regression dependencies, a generalized Protodyakonov equation was derived; its adequacy and high predictive ability were proven using correlation analysis and the Student's coefficient. The obtained results can be applied in the development of a methodology for measuring the mass fraction of vanadium in samples of ash and slag waste from thermal power plants using the ICP-MS method and a technology for extracting vanadium from secondary raw materials of thermal power plants.

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