Application of Potassium Ferrate(Vi) in the Treatment of Selected Water and Wastewater Pollutants – Short Review

ARCHITECTURE CIVIL ENGINEERING E NVIRONMENT The Silesian University of Technology No. 1/2020 doi : 10.21307/ACEE-2020-011 APPLICATION OF POTASSIUM FERRATE(VI) IN THE TREATMENT OF SELECTED WATER AND WASTEWATER POLLUTANTS – SHORT REVIEW Simona KLIŚ a, Krzysztof BARBUSIŃSKI b, Maciej THOMAS c*, Anna MOCHNACKA d a PhD Eng.; Graduate of Silesian Environmental Doctoral Studies of the Central Mining Institute in Katowice, Plac Gwarków 1, 40-166, Katowice, Poland b Prof.; The Silesian University of Technology, Faculty of Energy and Environmental Engineering, Konarskiego Str. 18, 44-100 Gliwice, Poland c PhD Eng.; Chemiqua Water & Wastewater Company, Skawińska Str. 25/1, 31-066 Kraków, Poland *E-mail address: [email protected] d MSc; AHIS S.A., Oswobodzenia Str. 1, 40-403 Katowice, Poland Received: 3.09.2019; Revised: 19.10.2019; Accepted: 20.10.2019 Abstract The paper presents the application of potassium ferrate(VI) (K 2FeO 4) for the removal of selected pollutants from water and wastewater. The research results on the degradation of endocrine disrupting compounds (EDCs), decomposition of surfac - tants (SPCs), personal care products (PCPs), pharmaceuticals and their metabolites have been reviewed. Due to K 2FeO 4 strong oxidizing and coagulating properties, high stability, non–toxic by–products and non–selectivity it is sometimes called “environmentally friendly oxidant”. Due to this reasons K 2FeO 4 can be a multi–purpose water and wastewater treatment chemical and an alternative to advanced oxidation processes (AOPs). Keywords: Potassium ferrate(VI), K2FeO 4, EDCs, SPCs, PCPs, Pharmaceuticals. 1. INTRODUCTION accumulate in other components of the natural envi - ronment, e.g. in groundwater or soil. A huge progress Water is used as an indispensable component in in many fields of technology, entailing the production almost every area of economic life. The energy, min - of a large number of products, causes formation of ing, food, dye and other industries consume a signifi - new impurities. Despite the availability of a large cant amount of water for technological processes, at number of water and wastewater treatment methods, the same time contaminating it. These impurities can degradation of the aquatic environment still occurs in appear in dissolved form as well as in the form of sus - many parts of the world. Therefore, it is necessary to pensions. It is often thought that dissolved impurities develop new, effective methods degradation of pollu - are more dangerous than in the form of suspensions. tants and the use of Fe(VI) compounds for wastewater However, it has been proven that suspensions of both treatment is part of this trend. Fe(VI) salts, such as natural origin and discharged into wastewater, togeth - K2FeO 4 (potassium ferrate(VI)) [2] (Fig. 1) are strong er with the pollutants adsorbed on them, also adverse - oxidants, and their redox potential is even higher than ly affect the entire aquatic ecosystem. It is also impor - permanganates and dichromates. Table 1 shows redox tant, that in suspensions a higher content of toxic potentials of selected oxidants. Analysis of these val - impurities is generally observed compared to bottom ues indicates that K FeO is characterized by one of sediments [1]. Contaminants getting in the aquatic 2 4 environment, can have a negative impact on them and the highest values of the redox potential, which in con - sequence is associated with its very strong oxidizing 1/2020 ARCHITECTURE CIVIL ENGINEERING ENVIRONMENT 129 S. Kliś, K. Barbusiński, M. Thomas, A. Mochnacka flocs of iron(III) hydroxide. Potassium ferrate(VI) does not react with bromide ions, which avoids the formation of carcinogenic bromates. Among many methods of obtaining K 2FeO 4 it can distinguish three most common and proven methods of synthesis (wet, dry and electrochemical synthesis) [6]. • Wet synthesis consists of the preparation of sodi - um ferrate(VI) (Na 2FeO 4), in the reaction of FeCl 3 with NaClO 3 (at a concentration greater than 12%), in the presence of NaOH. Then KOH Figure 1. is added to the solution until precipitation of Structural formula of K 2FeO 4 [2] K2FeO 4 [7]. However, this method requires many subsequent purification operations, such as: crys - properties. Only the fluorine and the •OH (hydroxyl tallization with 3 mol/L KOH, washing with anhy - radical) have a higher value of the redox potential. drous CH 3OH to obtain a solid K 2FeO 4, with puri - Under appropriate conditions, Fe(VI) ions are even ty > 90%. The above method, without using men - able to oxidize water and the reaction products are tioned purification processes of the synthesis prod - hydrogen protons and oxygen [4]. They are also char - ucts, makes it possible to obtain a technical acterized by the ability to oxidize compounds contain - K2FeO 4, containing only 10–15% pure compound. ing, e.g. sulfur, nitrogen, in particular phenols, • Dry synthesis is the process of oxidation of iron amines, aniline and alcohols [5, 6]. Generally, all pol - compounds at high temperatures and involves the lutants are degraded to water and carbon dioxide or heating of iron oxides, for examples Fe 2O3, with intermediates, which are less toxic than initial sub - potassium and sodium hydroxides or oxides and strates, which makes Fe(VI) salts environmentally potassium nitrate and sodium nitrate at a temper - friendly and therefore potassium ferrate(VI) is often ature of 420–600°C. Depending on the molar called “environmentally friendly oxidant” [7]. High ratios of the mixture components and tempera - oxidation capacity and non-toxic decomposition prod - ture, the process proceeds in different efficiency ucts allow to use K 2FeO 4 for the degradation of vari - and enables to obtain the final product with a puri - ous organic and inorganic compounds. During the ty of up to 99.9%. reduction of Fe(VI) to Fe(III) emerge a coagulation • Electrochemical synthesis consists in dissolving an and adsorption of contaminants on the formation of anode made of metallic iron in an aqueous solu - Table 1. Redox potentials of selected oxidants [3, modified] Element/Compound Chemical reaction E0, V - - Cl 2(g) + 2e 2Cl 1.358 Chlorine - - - - ClO + H 2O + 2e Cl + 2OH 0.841 + - - Chlorate(I) HClO + H + 2e Cl + H 2O 1.482 - - Chlorine(IV) oxide ClO 2(aq) + 2e ⇆ ClO 2 0.954 - + - - Chlorate(VII) ClO 4 + 8H + 8e ⇆ Cl + 4H 2O 1.389 - - Fluorine F2(g) + 2e ⇆2F 2.87 • • Hydroxyl radical OH + H 2O2 H2⇆O + HO 2 2.76 + - Ozone O3 + 2H + 2e ⇆O2 + 2H 2O 2.076 + - Hydrogen peroxide H2O2 +2H + 2⇆e 2H 2O 1.776 + - Oxygen O2(g) + 4H ⇆+ 4e 2H 2O 1.229 - + -⇆ MnO 4 + 4H + 3e MnO 2 + 2H 2O 1.679 Permanganate - + - 2+ MnO 4 + 8H + 5e M⇆n + 4H 2O 1.507 2- + - 3+ Dichromate Cr 2O7 + 14H + 6e ⇆2Cr + 7H 2O 1.33 2- + - 3+ FeO 4 + 8H + 3e ⇆ Fe + 4H 2O 2.2 Ferrate(VI) 2- - FeO 4 + 8H 2O + 3e ⇆ Fe(OH) 3 +8H 2O 0.7 ⇆ ⇆ 130 ARCHITECTURE CIVIL ENGINEERING EN⇆VIRONMENT 1/2020 APPLICATION OF POTASSIUM FERRATE(VI) IN THE TREATMENT OF SELECTED WATER AND WASTEWATER POLLUTANTS – SHORT REVIEW e T tion, which is associated with very low efficiency of try is located, several generations of animals inhabit - N the process and obtaining a low purity of the prod - ing this area were examined. As a result of research, E M uct. Only the use of a solution of concentrated it was found that the next generations are physically N hydroxides (KOH, NaOH) instead of water results weaker and thus the incidence of various types of dis - O R in K 2FeO 4 of high purity [8, 9]. eases, increases with subsequent generations. I V Various research investigations have been carried out Colbrom et al. [12] determined that substances escap - N ing from industrial plants into the environment are E on the application of K 2FeO 4 as an oxidizer in indus - permanently accumulated in animal organisms and trial wastewater treatment, because this method is destabilize their hormonal system. She also proved characterized by high efficiency of pollutant degrada - that these substances cause changes in the embryon - tion. Selected applications of K FeO for the degra - 2 4 ic phase of animals and on this basis, the conclusion dation of various pollutants in water and wastewater, is that these substances also threaten people [12]. such as EDCs, PCPs, SPCs, pharmaceuticals are pre - Therefore, the search for methods allowing effective sented below. removal of EDCs from the natural environment was started. However, the applied physical processes, 1.1. Degradation of Endocrine Disrupting Chemicals such as membrane methods, were characterized by (EDCs) different effectiveness of removal of individual com - pounds, as shown in Table 3. The very strong oxidiz - EDCs (Endocrine Disrupting Chemicals) are chemi - ing properties of potassium ferrate(VI) cause, that cal compounds that disrupt the hormonal balance of this compound is a place of interest to many scientists the body. They are common in everyday life, because around the world, including endocrine disrupting they are used for the production of plastic packaging, compounds (EDCs). Conventional methods of purifi - they are found in cleaning agents and detergents and cation are not effective, due to the huge amount and also a part of medicines or plant protection products. variety of pollutants. Most of the chemical com - EDCs also include natural origin compounds that, pounds used in wastewater treatment processes have despite their origin, also destabilize the functioning a low or selective effect, and the use of K FeO under of the endocrine system. In this group, hormonal 2 4 compounds can also be distinguished, which after appropriate process conditions (pH, temperature, entering the body may negatively affect its homeosta - time, dose) allows for complete degradation or sig - sis [10].

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