Oxidative destruction of anionite AV-17×8 using the Fenton reaction Chimica Techno Acta ARTICLE published by Ural Federal University 2021, vol. 8(4), № 20218406 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.4.06 1 of 5 Oxidative destruction of anionite AV-17×8 using the Fenton reaction M.M. Kozlova a*, V.F. Markov ab, L.N. Maskaeva ab a: Ural Federal University, 620002 Mira st., 19, Ekaterinburg, Russia b: Ural State Fire Service Institute of Emergency Ministry of Russia, 620022 Mira st., 22, Ekaterinburg, Russia * Corresponding author: marina.kozlova2014@mail.ru This article belongs to the MOSM2021 Special Issue. © 2021, The Authors. This article is published in open access form under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract The kinetic studies of AV-17×8 strongly basic anionite’s oxidative de- struction using the Fenton reaction have been carried out. The effect of the process’s temperature and the concentration of catalysts of iron(II) sulfate or copper(II) sulfate on the oxidation of anion - exchange resin with hydrogen peroxide is estimated. With an in- crease in temperature in the range of 323–348 K, a regular increase in the effective rate constant of oxidative anionite destruction is ob- served when using iron(II) sulfate by 1.5 times, and when using cop- per(II) sulfate – by 22 times. It was found that the obtained values of the activation energy of the anion exchanger’s oxidation with the ad- dition of copper(II) sulfate are 124.3–115.7 kJ/mol and are character- istic of the process proceeding in the kinetic region. The nature of the change in the surface morphology of the anionite granules in the process of oxidative decomposition has been revealed . Keywords anion exchanger AV-17×8 hydrogen peroxide Fenton process process rate constant activation energy Received: 02.11.2021 Revised: 22.11.2021 Accepted: 23.11.2021 Available online: 26.11.2021 1. Introduction The ion exchange resins are widely used in the field of waste and wash water treatment at the nuclear power plants. As a result, the spent ion-exchange resins are formed, which are low-activity heterogeneous waste in the form of spherical granules from a cross-linked organic polymer. Over the years, the significant amounts of waste resins have accumulated at nuclear power plants, which subsequently cannot be regenerated [1]. Thus, an effective technology is needed for the disposal of the spent ion- exchange resins in order to reduce their negative impact on the environment. At present, such technologies as immobilization (ce- mentation, bitumization, vitrification) or incineration, pyrolysis, thermal vacuum drying, and supercritical water oxidation are used to dispose of waste resins [1, 2]. How- ever, regular recycling technologies are characterized by significant economic costs, also there are difficulties with the transportation and storage of wastes that can be ac- companied by the formation of explosive products associ- ated with the radiolysis of organic substances and water. An effective way of the spent ion-exchange resins re- moval can be oxidative destruction, which significantly reduces the concentration of organic substances. A prom- ising method is the Fenton process, based on the oxidation of organic compounds under the action of hydrogen perox- ide. The catalytic additive can be ions of divalent transi- tion metals, for example, iron(II) sulfate or copper(II) sul- fate. The Fenton process is characterized by the formation of free hydroxyl radicals НО• in the system, which have minimal selectivity to various organic substances. НО• radicals are characterized by a high potential (2.80 V), and, therefore, have high oxidizing capacity [3]. The main mechanism of the classical Fenton process can be represented in the form of a redox reaction with the ferrous ions [3]: Fe2+ + H2O2 → Fe3+ + ОН•+ OH¯. (1) As a result of chain reactions and an increase in the concentration of chemically active particles, a complex organic compound RH decomposes into small frag- ments [3]: НО• + H2O2 → HOO• + Н2О, (2) Fe3+ + HOO• → Fe2+ + Н+ + O2, (3) Fe2+ + HOO• → Fe3+ + HOО¯, (4) Fe2+ + НО• → Fe3+ + OH¯, (5) НО• + RH → R• + H2O. (6) http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.4.06 http://creativecommons.org/licenses/by/4.0/ Chimica Techno Acta 2021, vol. 8(4), № 20218406 ARTICLE 2 of 5 The Fenton process is characterized by a high reactivi- ty, a deep oxidation state, and sufficiently mild operating conditions. The reaction efficiency is influenced by such factors as temperature, pH of the medium, concentration of hydrogen peroxide and catalyst. The oxidation of sulfonic acid cation exchangers with hydrogen peroxide, as well as strongly basic anion ex- changers with tertiary trimethylammonium groups in the presence of catalytic additions of transition metal salts, was described in [4–14]. Thus, in the study [4], the com- plete decomposition of domestic brand anionite AV-17×8 was achieved by the action of a 30% solution of hydrogen peroxide with the addition of an iron(II) salt in the tem- perature range 363–373 K. The works of the authors [5–14] are aimed at choosing the optimal conditions for the oxidative destruction of ion exchange resins of some foreign brands. The research [9] is devoted to the com- plete decomposition of a foreign brand of anion-exchange resin Amberlite INR78 by exposure to a 30% hydrogen peroxide solution with the addition of a copper (II) salt at a temperature of 368 K. In the above mentioned works the individual aspects of the influence such as the concentra- tion of the oxidizing agent, the temperature of the solu- tion, and the concentration of catalytic additives on the Fenton process were studied. However, there is currently no information on kinetic s of the ion-exchange resins oxidative destruction using the Fenton process. Previously, the studies were carried out on the oxidation of hydrogen peroxide using the Fenton reaction of the highly acidic universal cation exchanger KU-2-8 [15]. This works object is to the study of the kinet- ics of catalytic oxidative destruction of the domestic ani- onite AV-17×8 using the Fenton process. 2. Experimental The object of the study was the strongly basic anion ex- changer AV-17×8 (GOST 20301-74), the crosslinked copol- ymer of styrene and divinylbenzene. The diameters of spherical resin granules are in range of 315–1250 µm, the content of the working fraction is not less than 95%, the uniformity coefficient is 1.6, and the specific volume is 3.0±0.3 cm3/g. For the oxidation of the AV-17×8 anionite, we used an environmentally friendly oxidizing agent — hydrogen peroxide H2O2, the concentration of which was determined by permanganatometry [16]. The preparation of 0.1 M catalyst solutions was carried out using salts of iron(II) sulfate FeSO47H2O and copper(II) sulfate CuSO45H2O. In all experiments, the amount of anion-exchange resin was constant and was 0.5 g based on the weight of the air- dry mass. To study the catalytic oxidation, a weighed por- tion of the AV-17×8 anionite was introduced into the reac- tors, then 10 ml of a hydrogen peroxide solution with an H2O2 concentration of 20 vol.%, then 0.001–0.005 mol/L FeSO4 or CuSO4 was added. The reactors were placed in the thermostat of the brand LOIP LT-105a. The process was carried out in the tempera- ture range of 323–348 K. Each reactor was removed from the thermostat after a certain time. The remaining AV-17×8 ani- onite in the reactors was thoroughly washed, filtered, dried in air for a week at room conditions, then heated in a PM-1.0-7 electric furnace for 2.5 h at the temperature of 377±1 K. After that, it was weighed on an analytical balance VIBRA HTR-220CE with a readability of ±0.0001 g. The study of the surface morphology of the granules of the anionite AV-17×8 was carried out by scanning electron microscopy using a JEOL JSM-6390 LA microscope. 3. R esults and discussion To explain the physicochemical process of AV-17×8 ani- onite oxidation, it is necessary to consider the patterns of the process in time, depending on the mechanism of the chemical reaction and on thermodynamic factors - the temperature and concentration of the catalyst. Let us con- sider the effect of temperature as a parameter that has the most significant impact on the rate of anion exchanger oxidative destruction. The kinetic studies of the AV-17×8 anionite catalytic ox- idation with hydrogen peroxide were carried out with the addition of 0.001–0.005 mol/L iron(II) sulfate and cop- per(II) sulfate. The dependences of the relative weight loss of the anion exchange resin on the exposure time of 20 vol.% hydrogen peroxide with the addition of 0.002 mol/L FeSO4 at temperatures from 323 to 343 K are shown in Fig. 1a. It is observed that the process of the ani- onite destruction by hydrogen peroxide with iron(II) sulfate proceeds relatively slowly, and with a decrease in the reac- tion temperature, the longer induction period occurs. So, at 343 K in 360 min, only 36% of the anion exchanger was dissolved. The lowering of the temperature to 333 K leads to the decomposition of 17% of resin within 210 min. At 323 K, 10% of the anion exchanger is oxidized in 270 min. With the use of copper(II) sulfate as a catalytic addi- tive at the temperatures in range of 323–348 K, the com- plete oxidation of the AV-17×8 anionite was achieved (Fig. 1b). The graph shows how the duration of the induc- tion period decreases with increasing temperature. At 348 K the intense oxidation of the anion exchange resin is observed during the first 24 min. The decrease in the working temperature of the solution to 343 and 333 K leads to the complete decomposition of the resin after 35 and 110 min, respectively. At 323 K after 270 min, the res- in mass loss was ~92%. Thus, an increase in the process temperature from 323 K to 348 K significantly influences the rate of anion exchange resin decomposition. It should be noted that in- creasing the catalyst concentration that is iron(II) sulfate or copper(II) sulfate at a given temperature does not sig- nificantly accelerate the decomposition of the AV-17×8 anionite. Chimica Techno Acta 2021, vol. 8(4), № 20218406 ARTICLE 3 of 5 Fi g. 1 Kinetic curves of the AV-17×8 anionite relative weight loss in 20% H2O2 with the addition of 0.002 mol/L FeSO4 (a) and 0.003 CuSO4 mol/L (b) at a temperature, K: 348 (1), 343 (2), 333 (3), 323 (4) The effect of catalytic additions of copper and iron salts, according to studies [6–9, 11, 14], is based on an increase in the concentration of active oxygen during the decomposition of hydrogen peroxide, which promotes more active resin oxidative destruction. In the works [6, 9], the activities of catalytic additives in the Fe2+/H2O2 and Cu2+/H2O2 solutions have been compared and it is concluded that copper(II) ions have a stronger catalytic effect in the process of the anion exchanger oxi- dation compared to iron(II) ions. To determine the rate of the heterogeneous process in the "anionite-solution" system, it is necessary to take into account the interfacial area that changes during oxidative destruction, as well as the geometry of the spherical parti- cles of the anion-exchange resin. The reaction rate, that is, the loss of anionite’s mass, can be determined according to the equation: − 𝑑𝑚 𝑑𝜏 = 𝑘𝐹𝐶 (7) where m is the mass of the anionite AV-17×8 granule at the time τ, F is its surface area, C is the concentration of Н2О2, k is the rate constant of the oxidation reaction. By transforming Eq. (7), it is possible to obtain the dependence of the change in the mass of the anion resin granule on the duration of the process of its oxidation "m1/3 – τ" [17]. The processing of the experimental re- sults, carried out in coordinates "m1/3 – τ", allows taking into account the heterogeneous nature of the oxidation reaction and the spherical shape of the anionite AV-17×8 granules. The effective rate constant of the process k was de- termined from the slope of the obtained straight line in the coordinates "m1/3 – τ". Table 1 shows the calculated values of the effective rate constants of the anion ex- changer oxidative destruction process depending on the temperature and the concentration of catalytic additives . From the calculated values with the addition of 0.002 mol/L FeSO4 catalyst, it shows that an increase in the process temperature from 323 to 343 K leads to an in- crease in the rate constant by a factor of 1.5. With an increase in the content of the cataly tic additive from 0.001 to 0.005 mol/L, the rate constant of the process increases by a factor of 1.2. According to the obtained values of the process effec- tive rate constant with the addition of 0.002 mol/L CuSO4, and with increase in the process temperature from 323 to 348 K the rate constant is increasing by a factor of 23. At 0.003, 0.004, and 0.005 mol/L CuSO 4, the effective rate constant of the process increases by a factor of 22. With a decrease in the concentration of the catalytic additive to 0.001 mol/L CuSO4, an increase in the rate constant by a factor of 18 is observed. An increase in the concentration of the CuSO4 catalyst from 0.001 to 0.005 mol/L slows down the increase in the process rate constant, increasing it by no more than 1.3–2.2 times. T a ble 1 Effective process rate constant (k×103, g1/3 min–1) oxidative destruction of the anionite AV-17×8, depending on the temperature and concentration of catalytic additives when using 20 vol.% hydrogen peroxide Т, К [FeSO4], mol/L [CuSO4], mol/L 0.001 0.002 0.003 0.004 0.005 0.001 0.002 0.003 0.004 0.005 323 – 0.23 0.25 0.34 0.35 2.15 2.71 2.93 3.20 3.25 333 0.20 0.24 0.25 – – 5.82 7.88 9.13 10.29 12.67 343 0.27 0.34 – – – 32.07 33.49 35.99 42.13 41.83 348 – – – – – 38.41 63.73 65.96 70.67 72.75 Chimica Techno Acta 2021, vol. 8(4), № 20218406 ARTICLE 4 of 5 Using the calculated values of the effective rate con- stants, the activation energy Eа of the process of the ani- onite oxidative destruction was determined by the graph- ical solution of the Arrhenius equation in the coordinates "lnk – 103/T". According to the data presented in Table 2, the activation energies of the anionite oxidation process with the addition of the CuSO 4 catalyst are in the range from 124.3 to 115.7 kJ/mol, which indicates that the pro- cess is of the kinetic type. T a ble 2 Activation energy of the process of oxidative destruction of the AV-17×8 anionite in 20% hydrogen peroxide at various concentrations of the CuSO4 catalyst [CuSO4], mol/L 0.001 0.002 0.003 0.004 0.005 Eа, kJ/mol 124.3 118.1 116.4 115.7 116.2 The surface of the anionite AV-17×8 granules in the process of catalytic oxidative destruction has been investi- gated. For comparison, Fig. 2a shows a relatively smooth and practically undeformed surface of granules before oxidation. Fig. 2b shows an electron microscopic image of a surface of granules after 2.5 h of contact at the tempera- ture of 343 K with a 20 vol.% aqueous solution of hydro- gen peroxide containing 0.002 mol/L FeSO 4, which corre- sponds to a loss of 20% of granule’s mass. Fig. 2c shows a surface of anionite granules after exposure to a 20 vol.% aqueous solution of H2O2 containing 0.005 mol/L CuSO 4. As a result of contact for 10 min at the temperature of 343 K, the weight loss of the anionite was 85%. In Fig. 2(b, c), the local changes can be observed on the resin surface. At the same time, the sorbent granule changed its shape, volume, and its surface was covered with cracks, which may indicate the destruction of the crosslinks of the AV-17×8 anionite in the process of oxidative destruction and a decrease in its mechanical strength. 4. Conclusions Thus, the kinetic studies of the AV-17×8 anionite cata- lytic oxidative destruction by hydrogen peroxide showed that the introduction of 0.001–0.005 mol/L of the cop- per(II) sulfate catalyst significantly increases the intensity of the oxidation process as compared to the addition of 0.001–0.005 mol/L of iron(II) sulfate. It was found that in the presence of 0.002 mol/L catalytic additives in a 20% aqueous solution of hydrogen peroxide in the temperature range 323–348 K the rate constant of the oxidative decom- position of the anion exchanger increases by a factor of 1. 5 when using iron(II) sulfate at an operating temperature of 343 K, and with the introduction of copper(II) sulfate at 348 K – by a factor of 23. The calculated activation ener- gies of the process of oxidative destruction of the AV -17×8 anionite by hydrogen peroxide with the addition of cop- per(II) sulfate are in the range 124.3–115.7 kJ/mol, which is typical for the kinetic type process. Fi g. 2 Electron microscopic images of the surface of the anionite AV-17×8 before oxidation (a), after exposure to 20% H2O2 with the addition of FeSO4 (b) and with the addition of CuSO4 (c) R eferences 1. Smolnikov MI, Markov VF, Maskaeva LN, Bobylev AE, Mokrousova OA. Utilization problems of spent ion-exchange resins of nuclear power plants. 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