Iron mining wastes collected from Mariana disaster: Reuse and application as catalyst in a heterogeneous electro-Fenton process

Abstract

A simple and environmental friendly strategy for recycling iron mining wastes from the Mariana disaster, one of the biggest environmental disasters in Brazil, involved the synthesis of a magnetic hybrid (HbLM) material at ambient temperature. XRD analysis revealed formation of the cobalt ferrite phase, while FTIR and TGA confirmed the presence of NOM in the structures. The HbLM showed high surface area of about 167.9 m2 g−1. Heterogeneous electro-Fenton (EF)-HbLM process achieved the total decolorization of a model pollutant, the Acid blue 29 diazo dye, after 20 min of electrolysis; while the electrochemical oxidation with hydrogen peroxide generation (EO-H2O2) only led to 62% of color removal. The limit current density was 33.3 mA cm−2, above this value the parasitic reactions overlapped, consequently the efficiency of the process decreased. At pH 3.0, complete color removal was achieved after 20 min of treatment while 60 min were necessary at pH 7.0 (natural pH). This means that, at neutral pH, the process is feasible and the acidification of the medium is not necessary to promote the main reactions. This work provides an example of a system to remove toxic contaminants from wastewater following the principles of green chemistry and industrial symbiosis, with sequential reuse of wastes and the generation of new raw materials with added commercial and technological values.