Supercritical water oxidation of sulfide

Supercritical water oxidation (SCWO) of sulfide wastewater with oxygen as the oxidant was investigated using ammonium sulfide solution as the model waste. The experiments, which were conducted in a bench-scale continuous SCWO installation, indicated that S^2- could be completely oxidized to SO₄^2- within the residence time of less than 10 s under the supercritical water conditions at 698.2-773.2 K and 22.0 MPa-30.0 MPa. The reaction pathway of S^2- in SCWO was determined to be S^2- → S₂O₃^2- → SO₃^2- → SO₄^2-. The effects of temperature, pressure, and oxygen content on SCWO of S^2- were also studied. The kinetic model based on this pathway was established with the reaction rate constants and orders found by fitting the experimental data. The dependence of the rate constants on the temperature can be described with Arrhenius' law. The rate constants are dependent on the density of SCW, and the dependence is logarithmically linear.