Ozonation and peroxone oxidation of ethylenethiourea in water: operational parameter optimization and by-product identification.

The objective of this work was to study the degradation and mineralization of ethylenethiourea (ETU) in water by ozonation at different pH values and in the presence of hydrogen peroxide. Degradation experiments were performed using an initial ETU concentration of 50 ppm for 180 min with a gas flux of 0.25 dm(3) min(-1) and an O3 production rate of 12.1 mg min(-1). Degradation of by-products was monitored by direct injection electrospray ionization mass spectrometry (ESI-MS), ETU concentration was determined by HPLC-UV, and its mineralization was detected by total organic carbon (TOC) analysis. Optimum degradation of ETU in water was observed at pH = 11, whereas at pH = 3, the degradation of ETU was slowest, indicating that the reaction occurred through different mechanisms. The additional effects of hydroxyl radicals formed at the highest pH can be used to explain the results obtained in this study. Peroxone experiments were carried out in the presence of 400 and 800 mg L(-1) H2O2; the degradation of ETU was faster at 400 mg L(-1) H2O2. This was attributed to the scavenging effect of the excess H2O2. ETU treatment by ozonation produced several by-products of degradation such as ethylene urea and 2-imidazoline.

Novel highly reactive and regenerable carbon/iron composites prepared from tar and hematite for the reduction of Cr(VI) contaminant.

Highly reactive carbon/Fe composites were prepared from tar used as a carbon source, and hematite (alpha-Fe(2)O(3)), a widespread naturally available iron oxide. Tar was impregnated on hematite and thermally treated under N(2) atmosphere. Mössbauer, powder X-ray diffraction and magnetization data suggested that treatment at 400 and 600 degrees C produced only magnetite (Fe(3)O(4)) whereas at 800 degrees C mainly metallic iron (Fe(0)) was produced. Raman, TG and XRD analyses of the different composites revealed the presence of amorphous and graphitic carbon highly dispersed on the iron oxide surface. The composites obtained at 800 degrees C were very efficient in reducing aqueous Cr(VI), as CrO(4)(2-), even compared to finely ground commercial Fe(0). XPS and Mössbauer data showed that after five consecutive reuses, the composites deactivated, due to the surface oxidation of Fe(0). A simple treatment at 800 degrees C completely regenerated the composite by reducing Fe(3+) species allowing several reuses.