Catalytic wet peroxide oxidation of formic acid in wastewater with naturally-occurring iron ore

E Erasmus,Wa Van Der Westhuizen,Jo Claassen

doi:10.4314/wsa.v42i3.09

Abstract

The catalytic wet oxidation of formic acid, using hydrogen peroxide as the oxidizing agent over naturally-occurring iron ore, was explored. Firstly, the decomposition of hydrogen peroxide to its hydroxyl radicals (HO• and HOO•) over naturally-occurring iron ore was investigated. The reaction was monitored by ATR FTIR by following the disappearance of the O-H peak of H 2 O 2 at 2 860 cm -1 . Decomposition occurred according to the Fenton mechanism and resulted in observed first-order rate constants one order of magnitude faster than that without the catalyst. Turnover frequencies (TOF) of 1.97–8.85 x 10 -9 s -1 were obtained for the decomposition of H 2 O 2 . The wet oxidation of formic acid using hydrogen peroxide as the oxidizing agent over naturally-occurring iron ore reaction was also monitored by ATR FTIR, following the disappearance of the carbonyl stretching frequency of formic acid at 1 727 cm -1 . Experiments were performed at different hydrogen peroxide (2, 4, 6 and 8M) and formic acid (1.26, 2.52, 6.3 and 12.6 M) concentrations as well as with varying amounts of naturally-occurring iron ore catalyst, at pH = 2. Elevated hydrogen peroxide and formic acid concentrations led to increased observed first-order kinetics, as high as k obs = 21.75 x 10 -4 min -1 with a TOF = 1.73 x 10 -8 – 1.12 x 10 -6 s -1 . Keywords : iron ore, catalytic wet oxidation, formic acid, Fenton, hydrogen peroxide

Highlights

Apart from the large-scale exploitation of iron containing ore as raw material feed for iron extraction, it is one of the few naturally-occurring minerals that have been exploited for alternative applications
Chemical analysis of the iron ore X-ray diffraction (XRD) analysis of the iron ore revealed that the sample contains 98.13% Fe2O3, 0.45% Al2O3 and 1.12% SiO2
It has been confirmed that formic acid can be effectively wet oxidized by the decomposed products of hydrogen peroxide over a naturally-occurring iron ore catalyst

Summary

Introduction

Apart from the large-scale exploitation of iron containing ore as raw material feed for iron extraction, it is one of the few naturally-occurring minerals that have been exploited for alternative applications. Formic acid is a pollutant in wastewater from the effluents of some industries (Claudel et al, 1984) It is a stable intermediate from the decomposition of many organic pollutants (Chou et al, 1998; Davis et al, 1999; Hwang et al, 1999; Dinsdale et al, 2000), which is difficult to oxidize further (Ogata et al, 1981; Harmsen et al, 1997). For this reason, formic acid is often used as a model organic pollutant in wastewater treatment studies (Kawaguchi et al, 1993; Kim et al, 1996; Butterfield et al, 1997; Candal et al, 1997; Miller et al, 1999). These compounds are active even at room temperature and decompose to environmentally friendly O2 and H2O

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