In this work, wet oxidative decomposition of (NH₄)₂SO₄ in an air and Ar atmosphere was conducted in a lab-scale airtight glass vessel reactor by adding Na₂S₂O₈ and H₂O₂ as oxidative agents to (NH₄)₂SO₄ solution. The initial concentration of NH₄⁺ in (NH₄)₂SO₄ aqueous solution was set to 1,000 mg-NH₄⁺/dm³. The experiments were conducted at temperatures of 343–363 K, keeping the initial pH at a prescribed value between 5.5 and 13.5. The mixing molar ratio of (NH₄)₂SO₄/oxidant was set to 1/1 – 1/10.
Results show that the decomposition of (NH₄)₂SO₄ by Na₂S₂O₈ in an alkaline region was more significant than that by H₂O₂ because most H₂O₂ disappeared by self-decomposition under the present conditions. Results further showed that (NH₄)₂SO₄ was almost decomposed completely in about 150 min reaction time by adding Na₂S₂O₈ at a molar ratio of (NH₄)₂SO₄/Na₂S₂O₈=1/3 at 363 K in an alkaline condition of pH=13.5. The rates of decomposition of Na₂S₂O₈ and (NH₄)₂SO₄ were expressed by the first-order kinetics with respect to the concentrations of Na₂S₂O₈ and (NH₄)₂SO₄ with constant initial concentrations of (NH₄)₂SO₄ and Na₂S₂O₈, respectively.
When Na₂S₂O₈ was added to (NH₄)₂SO₄ solution, NH_3(aq) was decomposed by reactive oxygen species such as • SO₄⁻, • OH⁻, • O⁻, • O₃⁻, etc. in an alkaline condition, producing the main reaction product of N₂ and small amounts of NO₂⁻ and NO₃⁻ by-products. In this oxidative decomposition of (NH₄)₂SO₄, O₂ formation was suppressed by the consumption of these reactive oxygen species.