Assessing the use of zero-valent iron microspheres to catalyze Fenton treatment processes

Abstract

The application of Fenton processes is limited by the production of iron sludge and its pH-dependence efficiency. UV-light assistance and the use of alternative catalysts as zero-valent iron (ZVI) may avoid both drawbacks favoring its potential industrial application. The use of ZVI microspheres as the catalyst of Fenton processes is herein assessed and optimized in terms of reagents dosage, particle size and surface area. Microspheres providing a surface area of 0.8m2/g showed the best performance and the lowest tendency to be dissolved under acidic conditions, resulting a concentration ratio of [H2O2]/[Fe0]=60 under optimal reaction conditions. The optimized 450W UV-radiation photo-Fenton treatment addressed the almost complete mineralization of phenol (COD and TOC removal≈98–99%) at both acidic and neutral initial pH values; whereas good mineralization results of oxalic acid were only achieved under acidic conditions (COD removal≈100%; TOC removal≈83%). Only initial neutral pH conditions enabled the recovery of the catalyst. Although a more powerful oxidation treatment was performed under acidic conditions, it also implied a higher dissolution of the microspheres. The application of less powerful radiation (100W) limited catalyst losses under acidic conditions, but longer treatment time is required aiming to address similar degradation results.