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Wastewater Treatment with Green Chemical Ferrate: An Eco-Sustainable Option
Published in Prabhat Kumar Rai, Phytoremediation of Emerging Contaminants in Wetlands, 2018
The ferrate(VI) ion, with the molecular formula, FeO42−, is a very strong oxidant. Under acidic conditions, the redox potential of ferrate(VI) ions (2.2 V) is the strongest of all the oxidants/disinfectants practically used for water and wastewater treatment (Table 8.1); note that it is greater than that of ozone (2.0 V). Moreover, during the oxidation/disinfection process, ferrate(VI) ions will be reduced to Fe(III) ions or ferric hydroxide. As such, this simultaneously generates a coagulant in a single dosing and mixing unit process (Jiang and Lloyd, 2002). The FeO42− ion has a tetrahedral structure similar to its geometry in the solid state; these four Fe–O bonds are equivalent with covalent characteristics (Jiang and Lloyd, 2002; Hoppe et al., 1982). The thermodynamic constants of potassium ferrate were first measured/calculated by Wood (1958). There are two major methods for characterizing ferrate(VI) salts in practice, such as the volumetric titration method and spectroscopy method (Jiang and Lloyd, 2002).
A review of technologies for bromide and iodide removal from water
Published in Environmental Technology Reviews, 2023
Ferrate is considered an environmentally friendly oxidant [122]. It could oxidize iodide to iodate at sufficient ferrate concentrations, and active iodine (I2, I3- and HOI) at low ferrate concentrations according to Equations (17) and (18) [123]. Simultaneously, hydrogen peroxide was generated by ferrate decomposing. It could reduce hypoiodous acid to iodide at pH 7.5, while the reduction could be ignored at pH 6. The oxidation ability of ferrate increased as pH decreased. Previous studies showed that ferrate pre-oxidation before disinfection reduced I-THMs formation. This was because ferrate could react with NOM and oxidize iodide to iodate quickly [123,124]. Huang et al. [125] investigated the reaction between ferrate and bromide, and found that the toxic bromate was generated under non-phosphate and acidic conditions. Phosphate could increase hydrogen peroxide intermediate thereby reducing the toxic bromate formation.
Treatment of bypass wastewater using potassium ferrate(VI): assessing the role of mixing
Published in Environmental Technology, 2020
Ferrate(VI) is considered one of the promising multi-purpose chemical enhancement alternatives for primary wastewater treatment [7] as it has shown the versatility to act as an oxidant, disinfectant and coagulant [7–11]. The standard half-cell reduction potential of ferrate(VI) ions () at E° = 2.20 ± 0.03 V under acidic pH conditions is among the highest of all oxidants and disinfectants (Reaction 1), whereas under alkaline conditions, ferrate(VI) is a mild oxidant with E° = 0.72 ± 0.03 V (Reaction 2) [12].The speciation and decomposition of ferrate(VI) have been studied previously using phosphate/acetate buffer, and the pKa values are shown in Reactions 3–5 [13]. The reaction rates of different pollutants with ferrate(VI) increase with decreasing pH due to the faster reaction rates of the protonated form of ferrate(VI) () as compared to the unprotonated form () [9,14]. Pre-acidification or alkalisation of the flow to be treated followed by pH adjustment may be effective for the removal of certain contaminants [10,15,16]. However, such change in the pH of the wastewater adds extra cost to the treatment.
Removal of sulfapyridine by ferrate(VI): efficiency, influencing factors and oxidation pathway
Published in Environmental Technology, 2018
Jing Deng, Huadan Wu, Sujuan Wang, Yibing Liu, Hongyu Wang
Ferrate(VI) has been demonstrated to be a promising multipurpose treatment agent, which can be employed for oxidation, coagulation and disinfection simultaneously [11,12]. It is a simple and cheap to use for treating microorganisms, suspended particles and natural organic matter (NOM). Moreover, ferrate(VI) was also reported to control the formation of chlorinated by-products and the probable carcinogenic bromate (BrO3−), which can be generated during chlorination and ozonation [13]. Under acidic conditions, the redox potential of ferrate(VI) (2.2 eV) is the strongest of all the water purifiers practically used for water and wastewater treatment [14]. Therefore, the application of ferrate(VI) can be counted as an alternative method for the elimination of emerging pollutants in water [15,16]. So far, the removal of SPY has been reported by irradiation under simulated solar [17], UV/H2O2 system [18], heat-activated persulfate system [19], the white rot fungus [20], Electrochemistry [21], Flocculation [22] and the adsorption onto carbon nanotubes in fixed-bed columns [23]. Compared with adsorption and advanced oxidation, ferrate(VI) has the advantages of being cost-effective and convenient to use and so on. However, to the best of our knowledge, very limited information is available on SPY removal using ferrate(VI), despite its common occurrence.