Fenton-like process evaluation of textile effluent discolouration using pyrite tailings: Influence of dissolved iron

This study investigated the discoloration of real textile effluents using raw pyritic waste (RPW) as a Fenton-like process catalyst, as well as the influence of particle size and pre-treatment with distilled water only. The RPW was collected from a waste pile, following the ABNT NBR 10007:2004 standard, and ground to obtain particles with an average diameter of 0.75 and 1.5 mm. RPW and Washed Pyritic Waste (WPW) samples were characterized by XRF, FTIR and XRD. The operational conditions were assessed from an experimental design, varying the catalyst concentrations, H2O2 and the reaction time. XRD results showed the majority presence of FeS2 in the samples and the pre-treatment removed impurities, such as quartz and soluble compounds, from the catalyst surface. The experimental design determined that the 0.75 mm size was more efficient in removing colour from the effluent. The optimal condition was defined as 2 g/L of catalyst, 2 g/L of H2O2 and 2 h. The effluent colour degradation capacity was greater than 90% for RPW and WPW samples. However, WPW released less iron into the resulting solution (10.51 mg/L). The catalyst proved to be stable for sequential use and after five cycles, the discoloration rate was greater than 80%. Root growth was verified for the Allium cepa test using the post-treatment and neutralized effluent. The results indicate a potential use of pyritic wastes from coal mining as catalysts for the Fenton process for real textile effluents discoloration, adding environmentally friendly value to a material considered an environmental liability.