Photolysis of ferric ions in the presence of sulfate or chloride ions: implications for the photo-Fenton process

Abstract

The photo-Fenton process (Fe(2+)/Fe(3+), H(2)O(2), UV light) is one of the most efficient and advanced oxidation processes for the mineralization of the organic pollutants of industrial effluents and wastewater. The overall rate of the photo-Fenton process is controlled by the rate of the photolytic step that converts Fe(3+) back to Fe(2+). In this paper, the effect of sulfate or chloride ions on the net yield of Fe(2+) during the photolysis of Fe(3+) has been investigated in aqueous solution at pH 3.0 and 1.0 in the absence of hydrogen peroxide. A kinetic model based on the principal reactions that occur in the system fits the data for formation of Fe(2+) satisfactorily. Both experimental data and model prediction show that the availability of Fe(2+) produced by photolysis of Fe(3+) is inhibited much more in the presence of sulfate ion than in the presence of chloride ion as a function of the irradiation time at pH 3.0.

Fundamental Mechanistic Studies of the Photo-Fenton Reaction for the Degradation of Organic Pollutants

“…For this purpose, one must include additional kinetic steps that are too slow to be relevant on the time scale of the laser flash photolysis experiments. Experimentally (Machulek et al, 2009b) it is found that the concentration of Fe 2+ eventually reaches a plateau value at long times, more quickly in the presence of chloride ion than in its absence ( Figure 6). Simulation of this behavior required the inclusion of additional kinetic steps, in particular for the back reactions that result in reoxidation of Fe 2+ .…”

“…Table 2. Set of additional ground state reactions required to fit the accumulation of Fe 2+ during the steady-state irradiation of Fe 3+ in the presence and absence of chloride ion (Machulek et al, 2009b) …”

“…Thus, for example, in a municipal water treatment system, Kim & Vogelpohl (1998) found that, with UV irradiation, the photo-Fenton process was at least 30% more energy efficient in the presence of oxalate than in its absence. Clearly, the sensitivity of the ferrioxalate-catalyzed photo-Fenton process to both UV and visible light makes it particularly attractive for applications in which the sun is employed as the radiation source (Silva et al, 2010;Trovó & Nogueira, 2011 (Machulek et al, 2009b). (Puigdomenech, 2010), employing the equilibrium constants for complexation supplied with the program (excluding the insoluble iron species).…”

Effect of chloride and sulfate ions on the advanced photo Fenton and modified photo Fenton degradation process of Alizarin Red S

“…Further the generated ferrous ions reacts with hydrogen peroxide forming ferric ions and hydroxyl radicals as discussed previously (Eqs. (7) and (10)) [24,25]. The various possible reactions that can take place between chloride and Fe 3+ ions are shown below:…”

“…At pH 3.0, FeSO 4 + and Fe (OH) 2+ are the major predominant ferric species present. On irradiation with UV light FeSO 4 + produces ferrous ions and sulfate anions whose quantum yield is quite low [23,24].…”