Degradation of xanthate in waters by hydrogen peroxide, fenton and simulated solar photo-fenton processes

This work reports the findings of a preliminary study of oxidative degradation of ethyl xanthate (EX) in aqueous solutions comparing hydrogen peroxide, the Fenton process, and photo-Fenton process driven by simulated solar radiation. Kinetic runs were carried out following a factorial design using a synthetic effluent with initial [EX] = 100 mg/L. H2O2 was dosed at the stoichiometric amount required for complete mineralization of EX. The variables studied were: initial pH: 5 and 9; [Fe2+]:[H2O2] molar ratio: 0:0 and 1:40; and irradiance: 0 and 30 mW/cm2. An initial fast step breaks down more than 90% of the xanthate, forming intermediates that still contain unoxidized carbon and sulphur. Additional steps occur in which organic carbon and reduced sulphur from the intermediates may ultimately be converted into bicarbonate and sulphate. The progress of the reaction is indicated by reduction in TOC, gain in sulphate (SO4), and H2O2 consumption. Overall the optimum conditions for the breakdown of EX were those using the photo-Fenton process: initial pH = 5; [Fe2+]:[H2O2] molar ratio = 1:40; and irradiance = 30 mW/cm2. After 2 h the best results were: xanthate breakdown = 98.6%; TOC reduction = 39.2%; SO4 generation = 43.1%. The experiments were conducted batchwise and this led to partial mineralization of the xanthate's organic and sulphur contents. The statistical design using simulated solar radiation enabled us to conclude that tailings ponds could be used as treatment reactors, where their efficiency is enhanced by sunlight.