Concentration Distribution of Molecules and Particles in a Chrome-Containing Model System: Fe–K2Cr2O7–NaCl–H2SO4–H2O at Different Temperatures of the Electrocoagulation Process
摘要
For the purpose of water purification from chromium (Cr6+), thermodynamic modeling of the electrocoagulation process has been carried out in the Fe–K2Cr2O7–NaCl–H2SO4–H2O system over a wide temperature range (278–300 K). The physicochemical (pH, I, Eh, Cp) and thermodynamic (H, S, U, G) parameters of the system have been calculated at established optimal ratios of the initial components. Based on the calculated data, an experimental study was performed and the influence on the electrocoagulation processes of pH, current strength, type, and concentration of electrolytes has been revealed. The concentration distribution of individual molecules and species (cations, anions) has been established, including: Cr2+, Cr3+, CrO+, CrOH2+, Fe+, FeOH+, FeOH2+ in the solution, thereby eliminating the need for ion chromatography for analytical purposes. An Eh–pH diagram has been constructed indicating the stability fields of various chromium forms, and a formula has been derived for calculating the redox potential depending on the solution pH. It is shown that Eh > 0, i.e., the medium is oxidative, and the formation of Cr3+ is noted in the concentrated solution (I > 0.8). During electrocoagulation, the binding of sulfur and iron in the form of FeS2 has been achieved, followed by the formation of Fe(OH)3 and coprecipitation of Cr(OH)3. The degree of water purification from chromium exceeded 97% (reduction of Cr6+ in water from 100 mg/L to 2.29–2.30 mg/L).