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

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 H₂O₂ 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 H₂O₂. 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