Taking advantage of iron contained in natural volcanic ash for catalytic degradation of Rhodamine 6G

Using Fe‐containing silica‐alumina materials as heterogeneous catalyst for Fenton‐like degradation of organic pollutants has attracted a lot of attention during the last decades. In this work the catalytic activity of an iron‐rich natural silica‐alumina material (namely volcanic ash) for the abatement of Rhodamine 6G (Rh6G) has been evaluated. The X‐ray diffraction (XRD) and Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM‐EDS) results showed that such material contains about 13wt% of iron mainly present in augite and ferroanforsterite crystalline phases. Such iron content was sufficient to activate hydrogen peroxide via Fenton process. Indeed, 78% of Rh6G was degraded after 120 min of reaction in the presence of volcanic ash ([VA] = 5 g/L; [Rh6G] = 25 mg/L and initial pH = 3). The dye abatement efficiency increased with decrease of initial dye concentration, and with increase of catalyst dosage. However, the process was efficient only in acid medium (pH = 2.5 – 3) in which the leaching of the catalyst could not be avoided. As a consequence, a drastic decrease in abatement efficiency was observed during the recyclability test. This suggests that the studied volcanic ash can be used as low cost material for wastewater treatment. However it needs to be pre‐treated for efficient use as heterogeneous catalyst