Thiocyanate Wet Oxidation

Abstract

Aqueous solutions of thiocyanate were oxidized in a semi-batch reactor at temperatures between 170 and 210 °C and system total pressures ranging from 70 to 100 atm. The initial pH of the solution was set at 12, while initial concentrations have ranged between 20 and 1000 ppm according to the typical concentrations of thiocyanate-containing wastewater. The kinetic data discussion was based on the establishment of a kinetic regime control that guaranteed the validity of the experimental data and that oxygen excess was assured for all the runs. An attempt to establish a thiocyanate wet oxidation pathway has been made on the basis of the reaction intermediates and final oxidation products identified during the experimental work. SO42- and CO3- have been pointed out as the main final reaction products whereas (SCN)2 and SCNO- are suggested as possible short-life oxidation intermediates. The oxidation reaction results were fitted to a first-order kinetic equation with respect to thiocyanate and to 0.81 with respect to oxygen, with an activation energy of 84.4 kJ mol-1.