Залежність швидкості знекиснення води від концентрації метабісульфіту натрію в присутності іонів заліза

This study explores the kinetics of oxygen removal from water using sodium metabisulfite (Na₂S₂O₅) in the presence of iron(II) ions as a catalyst. The research addresses the urgent need for effective and environmentally safe deoxygenation methods, particularly in thermal energy systems where dissolved oxygen causes severe corrosion of metallic surfaces, especially in steam generation processes. Conventional corrosion inhibitors are often ineffective or unsafe for use in such systems. Therefore, deoxygenation remains the most viable approach for preventing oxygen-induced corrosion in industrial water systems. The paper provides a comprehensive analysis of existing water deoxygenation techniques, including physical methods (thermal, vacuum, barbotage), gas-based methods (air stripping, nitrogen or hydrogen saturation), and chemical methods. Among chemical reagents, hydrazine is recognized as highly effective; however, its high toxicity and handling complexity limit its industrial application. Sodium sulfite and its derivatives offer safer alternatives, though their effectiveness can be limited by slow reaction kinetics and the need for subsequent removal of oxidation by-products such as sodium sulfate. To enhance the efficiency of sulfite-based deoxygenation, the authors investigate the catalytic role of iron(II) ions in accelerating the oxidation of sodium metabisulfite by dissolved oxygen. The experimental work involves adding controlled concentrations of sodium metabisulfite and iron(II) sulfate to aerated distilled water and measuring the concentration of oxygen over time using a dissolved oxygen meter. Experiments were conducted under static conditions at room temperature, with variations in Na₂S₂O₅ concentration (50–300 mg/dm³) and Fe²⁺ concentration (0.1–0.5 mg/dm³). The results demonstrate a strong dependence of the oxygen removal rate on both the concentration of the reducing agent (sulfite) and the catalyst (iron ions). At low concentrations of both reagents, the oxygen binding process follows third-order reaction kinetics, with the rate depending simultaneously on the concentrations of oxygen, sulfite, and iron. As the concentrations increase, the reaction order decreases, transitioning to second-order and, eventually, first-order kinetics. At higher levels of sulfite (200–300 mg/dm³) and iron (≥0.5 mg/dm³), the rate-limiting step becomes the oxygen concentration alone, indicating that excess reductant and catalyst are present throughout the reaction duration. The authors calculated reaction rate constants for various concentration combinations and confirmed the reaction order using integrated rate equations. The findings highlight the significant catalytic effect of iron(II) on the rate of oxygen removal, even at low concentrations. The study also proposes a reaction mechanism involving the formation of iron hydroxide complexes and their subsequent oxidation–reduction cycles with sulfite and oxygen. The research contributes to the optimization of chemical deoxygenation processes in water treatment systems, especially for thermal power and heating applications. By understanding the kinetic dependencies and optimizing reagent dosages, industrial operators can achieve faster and more efficient deoxygenation while minimizing reagent consumption and environmental impact. The study emphasizes the potential of sodium metabisulfite as a practical and safer alternative to hydrazine in oxygen removal applications. Future work will focus on evaluating the influence of pH and temperature on the kinetics of oxygen removal by sodium sulfite and metabisulfite, with the goal of further refining deoxygenation technologies under varying operational conditions.