Assessment of catalytic activities of selected iron hydroxysulphates biosynthesized using Acidithiobacillus ferrooxidans for the degradation of phenol in heterogeneous Fenton-like reactions

Abstract

Schwertmannite and jarosite, two secondary Fe(III)-hydroxysulfate minerals abundant in acid-mine drainage, can be biosynthesized by an Fe-oxidizing bacterium Acidithiobacillus ferrooxidans, but the differences of their catalytic activities in heterogeneous Fenton-like reactions are still unclear to date. In the present study, the catalytic activities of biosynthesized schwertmannite and jarosite were compared through investigating the heterogeneous Fenton-like degradation of a target organic pollutant phenol. Results showed that these two catalysts efficiently catalyzed heterogeneous Fenton-like degradation of phenol, and the degradation in both systems consisted of an induction period (first-stage) and a followed rapid degradation stage (second-stage). Schwertmannite exhibited a much higher catalytic capacity than jarosite, because of its shorter induction period and higher kinetic rate (k) of the second-stage, but jarosite catalytically degraded phenol in a much wider pH range (pH 3.0–7.5) over schwertmannite (pH 3.0–4.5). Based on the results of radical scavenger effect, H2O2 decomposition, Fe leaching and X-ray photoelectron spectroscopic (XPS) analysis, similar catalytic mechanisms were proposed in schwertmannite/H2O2 and jarosite/H2O2 systems, in which the induction period can be ascribed to the activation of catalysts by H2O2 and the second-stage was mainly attributed to the homogeneous Fenton reaction in bulk solution. During the catalytic degradation of phenol, catechol was firstly accumulated and was then further decomposed into smaller molecular organic acids. The repeated uses of schwertmannite and jarosite for phenol degradation manifested their stability and reusability as Fenton-like catalysts for the degradation of organic pollutants.