Concentration Distribution of Molecules and Other Species in the Model System Fe–NaCl–Na2S–H2SO4–H2O at Various Temperatures of the Electrocoagulation Process

Under practical conditions, one of the possible solutions to the problem of treatment of hydrogen-sulfide-containing industrial wastewater is the electrochemical oxidation of sulfides. In this work, the model system Fe–NaCl–Na2S–H2SO4–H2O is considered, an experimental setup is constructed, and the electrocoagulation process is studied in a wide (288–308 K) range of temperatures of an aqueous solution of hydrogen sulfide. The optimal ratios between the initial components in the system are determined. The experimental and calculated pH of the solution are found. The system is thermodynamically modeled by minimizing the Gibbs energy, and the concentration distribution of individual molecules and other species (cations, anions) in the solution is characterized. Possible chemical reactions in the system Fe–NaCl–Na2S–H2SO4–H2O during the electrocoagulation of hydrogen-sulfide-containing wastewater are identified. Eh–pH diagrams are constructed to compare the redox potentials of the systems Fe–H2O, Fe–H2O–S, and Fe–NaCl–Na2S–H2SO4–H2O based on the determined concentrations of iron- and sulfur-containing particles in the solution. A calculation formula for the redox potential Eh of the system is obtained.