Abstract The growing volume of spent etching solutions generated by the metallurgical industry represents a significant environmental challenge due to their high acidity and high concentrations of dissolved iron. Developing efficient treatment methods that ensure both decontamination and resource recovery is a priority for sustainable industrial wastewater management. Ferritization is a process that converts dissolved iron into stable ferrite phases and thus offers an effective pathway for transforming hazardous waste into environmentally safe and technologically valuable materials. This study evaluates the ferritization of diluted sulfuric acid under three activation conditions: thermal, ultrasonic, and alternating magnetic field. Experiments were conducted with air oxygen bubbling rate of 0.02–0.06 dm³/s and reaction durations of 30–75 min. The resulting precipitates were characterized using X-ray diffraction to determine their phase composition, while leaching tests assessed the stability of the ferrite products in aqueous environments. The results show that thermal activation at 75 °C combined with the highest aeration rate significantly enhances the conversion of iron oxyhydroxides into magnetite (Fe₃O₄). Under optimal conditions, magnetite content approached 100%, iron removal reached 99.99%, and leaching of iron ions did not exceed 0.2 mg/dm³. Overall, the study demonstrates that ferritization is an efficient and environmentally viable method for treating spent pickling solutions while obtaining valuable iron-containing products.

This study presents a sustainable approach to recycling exhausted etching solutions through ferritization, using various activation methods and aeration rates. The process transforms industrial waste into valuable magnetic sorbents, supporting circular economy principles. Structural and chemical analysis of the ferritization products revealed the formation of ferromagnetic crystalline phases, including lepidocrocite (ɣ-FeOOH), ferrooxygite (δ-FeOOH), and magnetite (Fe3O4). Increasing the aeration rate and use of ultrasound treatment enhances Fe3O4 content and iron ion removal efficiency. The adsorption capacity of the recycled materials for Zn2+ removal was assessed under different pH conditions using mechanical mixing and ultrasound treatment. The highest level of Zn2+ removal (92.0%) was achieved at pH 8 with ultrasound-activated sorbents containing 61.3% δ-FeOOH and 38.7% Fe3O4. At pH 10, magnetite-based sorbents achieved over 98.9% Zn2+ removal, enabling the treated water’s reuse in industrial rinsing processes. Electron microscopy and X-ray fluorescence confirmed the presence of fine, spherical magnetite and zinc ferrite particles. These findings underscore the potential of ferritization-based recycling as an eco-friendly and efficient strategy for heavy metal removal from galvanic wastewater.

Currently, development of resource-saving technologies for industrial wastewater treatment with further utilization of residuals is highly relevant. In this work, for the first time, advanced ferritization method with energy-saving AC-magnetic field activation was applied for the treatment of concentrated chromium-containing wastewater-exhausted chromium electrolytes. An experimental setup has been created to test the basic parameters of the ferritization process. The best generation values of AC-magnetic field activation for ferritization process were determined: amplitude of magnetic induction of 0.14 T and pulse frequency of 1 Hz. The optimal concentration ratio of iron to chromium ions 10:1 in the reaction mixture of ferritization was also established. The degree of removal of chromium ions from exhausted electrolyte of 99.96

Every year, metallurgical enterprises generate a massive amount of toxic exhausted high-concentration etching solutions. Application of the ferritization process to recycle exhausted etching solutions can help to prevent environmental pollution. It enables a cost-efficient use of water at an industrial plant and allows the plant to obtain products from toxic industrial waste and utilize it. The aim of the study was to analyze the qualitative and quantitative composition of the formed sediment and its grain size composition. Variable study parameters were the initial pH values of the solutions, the initial concentrations of total iron, and the duration of the aeration process of the reaction mixture. Thermal activation and alternating magnetic fields were used to activate the ferritization. The XRD showed that the formed sediments contained phases of γ-FeOOH, δ-FeOOH, Fe3O4, and γ-Fe2O3. Granulometry analysis showed that these sediments were highly dispersed and heterogeneous. Chemically stable phases of magnetite were obtained in the composition of sediments, with an initial concentration of iron in the reaction mixture of 16.6 g/dm3, a pH of 11.5, and a process duration of 15 min. The study results demonstrated the feasibility of further study and possible use of such sediments with a high magnetite content for the production of materials with ferromagnetic and sorption properties.

This work is focused on the study of the properties of powder paint coatings modified with fillers, which are obtained from ferritization waste processing of spent technological solutions of galvanic industries. The physical, mechanical and shielding properties of powder systems with iron-containing products introduced into their composition were investigated in the work. It is shown that the use of iron-containing waste in general contributes to the increase of both mechanical characteristics and corrosion resistance of coatings. It was determined that the introduction of Ni0.5Cu0.5Fe2O4 and Zn0.5Cu0.5Fe2O4 into the composition allows to significantly increase their mechanical and shielding properties

Given the relevance of the problem of wastewater treatment from heavy metal ions, and in particular from zinc ions, it is necessary to study the regularities of the process. One of the key aspects is the kinetics of the process and the dependence of the ion extraction efficiency on the duration of the purification process. Reducing the time of the process makes it possible to reduce the cost of electrical energy for technological processes, in particular for the activation of the reaction mixture by heating or electromagnetic pulses. Based on the obtained results of the experiment, a mathematical model of the kinetics of the process of extracting zinc ions from wastewater by ferritization with thermal and electromagnetic pulse activation was built. A regression model was used for data processing and an algorithm for calculating the dependence of the degree of purification on the time of the process was proposed. Determined the degree of purification of wastewater from heavy metal ions at different values ​​of the process duration. The expediency of carrying out the process of ferritization cleaning with a duration of 10-15 minutes has been substantiated.

Показано, що в умовах підвищення амплітуд та розширення частотного спектра техногенних електромагнітних полів найбільш прийнятними екрануючими матеріалами є композити з потрібними властивостями. Особливістю композиційних матеріалів усіх класів є відсутність стандартних довідкових даних щодо їх ефективності та електрофізичних і магнітних властивостей, які визначають коефіцієнти екранування. Для спрощення процесів проектування екрануючих сумішей доцільне попереднє розрахункове оцінювання значень діелектричної і магнітної проникностей та питомої провідності кінцевого матеріалу. Проаналізовано можливість використання для цих розрахунків співвідношень Лорентца, Максвела-Гарнета, Оделевського та Ліхтенеккера. Показано пов'язані з цим труднощі і межі застосування та необхідність врахування морфології екрануючих частинок у матриці. Наголошено, що у процесі проектування слід враховувати залежність електрофізичних властивостей компонентів від частоти поля, яке потребує екранування. Такий підхід дозволяє отримати рідкі матеріали з різними властивостями для формування багатошарової структури: верхній шар може мати мінімальні коефіцієнт відбиття, а нижній – максимальні поглинальні властивості. Надано послідовність дій при проектуванні захисних композицій для раціоналізації проєктних робіт.

Aspects for increasing the corrosion resistance of powder coating materials as a result of the involvement of the latest technologies for cleaning electroplating production waste are considered. The results of the effect of ferritization waste on the formation of corrosion resistance of coatings based on powder coating are shown. The introduction of the obtained ferritization waste into the composition of powder coating systems has a different effect on the formation of corrosion resistance of coatings was found. Thus, the control composition of the powder coating using a filler in the form of barium sulfate during 480 hours of exposure in the salt fog chamber is characterized by peeling of the coating at the level of 7.5 mm. The average width of metal corrosion is 5.5 mm. The category of corrosion resistance of the coating corresponds to class C3 (average) with the provision of an average durability class (M) from 7 to 15 years. Examples of typical environments (according to DSTU ISO 12944-2:2019) where the resulting coatings can be used are urban and industrial atmospheres, moderate sulfur dioxide pollution, coastal areas with low salinity. The use of galvanic waste sediments in general contributes to increasing the corrosion resistance of the powder coating. The efficiency of their use depends on the chemical composition of ferritization waste. Among the studied samples, the most effective is the introduction of waste in the form of Ni0.5Cu0.5Fe2O4 and Zn0.5Cu0.5Fe2O4 into the composition of powder systems, which helps to reduce the width of coating peeling by 65...79 %, as well as the width of metal corrosion by 75...80 % compared to the control composition. The least effective among the studied samples is the use of waste in the form of Ni0.5Zn0.5Al0.15Fe1.85O4 and CrFe2O4 due to a significant decrease in the corrosion resistance of the powder coating Powder coating systems were obtained using ferritization waste, the category of corrosion resistance of which corresponds to class C4 (high) with a high durability class (H) from 15 to 25 years. In general, the use of ferritization waste provides better corrosion resistance of coatings compared to traditional systems based on barium sulfate, which in turn gives reason to consider such systems as an alternative for corrosion protection of construction metal products and structures.

The efficiency of the AC-magnetic field usage for resource-saving activation of the reaction mixture in the ferritization process with the extraction of heavy metals ions from galvanic waste has been confirmed. The one of the key parameters of the ferritization process—the ratio of the concentration of iron ions to the total concentration of other metal ions on the quality of galvanic waste processing has been investigated. It is determined that under the optimal processing conditions (ratio of concentrations of iron ions to other heavy metal ions 3.5 ÷ 4/1) the residual concentrations of heavy metal ions decrease to the values: Fe2+;3+—0,1; Ni2 +—0.26; Cu2 +—0.2; Zn2 +—0.19 mg/dm3. It is established that the AC-magnetic field activation provides the metal ions extraction degree of 99.96%, and also has undeniable energy advantages in comparison with thermal technique: the energy consumption is reduced by more than 60%. This indicates the suitability of purified water for reuse in galvanic production due to the requirements for the heavy metal ions content. Also, the structural studies of ferritic sediments shown that samples obtained at the ratio of heavy metal ions concentrations 4/1 phases characterized by the maximum content of crystalline ferromagnetic ferrite (Ni0.53Cu0.3 Zn0.17Fe2O4) ≥ 76% were detected.

Exhausted etching solutions are the waste of industrial enterprises and contain toxic pollutants that have a detrimental effect on the environment. Currently, the processing of these solutions to obtain marketable products is important. The paper presents the results of research on the application of the ferritization method for processing of exhausted etching solutions of steel surfaces. Energy-saving activation of the process by alternating magnetic fields was used, which has undeniable advantages compared to traditional thermal activation. The influence of the initial concentration of iron ions in the reaction mixture of ferritization process and the methods of its activation on the treatment quality of exhausted etching solutions was studied. It was established that the best degree of extraction of heavy metal ions from exhausted etching solutions by ferritization is achieved when the reaction mixture is activated by alternating magnetic fields at an initial concentration of iron ions of 6.6 g/dm3 . At the same time, the residual concentration of iron ions in purified solutions does not exceed 0.03 mg/dm3 , that corresponds to degree of purification of solutions of 99.999%. Those solutions can be reused in situ. The qualitative and quantitative composition of ferritization sediments was studied. Phases of ferroxygite δ-FeOОН, magnetite Fe3O4 and maghemite ɣ-Fe2O3 were detected by X-ray phase analysis in the sediments. It was established that at the initial concentration of iron ions of 26.6 g/dm3 with thermal activation of the reaction mixture and 16.6 g/dm3 with alternating magnetic fields activation, the sediment exclusively contains the magnetite phase. The results of the study indicate the possibility of further use of sediments for the production of important industrial products and materials containing ferromagnetic compounds. The implamitation of improved ferritization process in industrial enterprises will allow to achieve decrease of energy consumption compared to known technologies of exhausted etching solutions processing.

This paper reports the results of studying the application of a ferritization method for the integrated purification of used etching solutions. A feature of this work is the use of energy-saving activation of the process by alternating magnetic fields. Its advantages are shown in comparison with traditional thermal activation. The influence of magnetic induction amplitude and key technological parameters of ferritization on the quality of cleaning an etching solution has been studied. The qualitative and quantitative composition of sediments obtained after the ferritization of etching solutions was investigated. Used etching solutions are large-tonnage waste of industrial enterprises. They contain harmful pollutants that have a detrimental effect on the environment. It is promising to treat these solutions in order to obtain valuable commodity products. It is established that with an optimal value of magnetic induction amplitude of 0.1 Tl, the degree of extraction of iron ions from the solution reaches a value of 99.99 %. The best values for the main technological parameters of the process have been determined: the concentration of iron ions in the reaction mixture is 6.6 g/dm3; pH, 11.5; the duration of ferritization is 15 min. The residual concentration of iron ions in purified solutions does not exceed 0.3 mg/dm3. Thus, according to the norms of current standards, they can be reused in production. Comparative analysis indicates the advantages of electromagnetic activation of the reaction mixture. The phases of magnetite Fe3O4 and iron monohydrate δ ‒ FeOОН were detected by the method of X-ray phase analysis in ferritization sediments. It is established that with an amplitude of 0.1 Tl, the sediment contains only magnetite. The study's results indicate the possibility of further use of sediments for the manufacture of important ferromagnetic substances. The application of the improved ferritization process in production will achieve less energy consumption compared to well-known processing technologies

The prospects of increasing the level of environmental safety of industrial enterprises as a result of the implementation of the latest sorption technologies for wastewater treatment are considered. An analysis of the effectiveness of the existing methods of sorption water purification, which contain compounds of heavy metals, was carried out. Highly effective magnetic sorbents were obtained by electroerosion dispersion, which contains polyvalent iron oxides. The effect of the method of introducing the sorbent into wastewater on the degree of its purification was investigated. The most effective results in water purification were achieved with the use of freshly obtained powder of electroerosion dispersion of iron in water in the form of a suspension, which allows to achieve a high degree of water purification from zinc ions - more than 99%. Such water meets the standards for washing parts in galvanic production with regard to the content of nickel ions. The expediency of recycling spent nano-sorbents in the composition of powder paint and varnish materials is shown. When a coating chemically stable in water treatment waste, which has ferromagnetic properties, is included in the composition, in quantity15% by weight high corrosion resistance of the coating is ensured and shielding of electromagnetic radiation increases approximately 3 times compared to the standard sample. The use of research results at enterprises will prevent environmental pollution with toxic substances, change outdated production technologies, ensure efficient and rational use of water, raw materials and energy in the industrial production system.

Influence of the key parameter for the ferritization process - initial total concentration of heavy metal ions (СƩ) on the quality of galvanic sludge processing has been experimentally studied. It was determined, that at СƩ = 5.33 g/dm3 and electromagnetic pulse activation of the ferritization process, the lowest values ​​of residual concentrations of heavy metal ions in the purified solution were obtained: for iron – 0,10; nickel – 0,19; copper – 0,12; zinc – 0,10 mg/dm3. The obtained values ​​correspond to the average degree of extraction of these ions of 99,97%. The purified solution is suitable for reuse in electroplating facilities. As a result of structural studies of sediment samples, it was found that at total heavy metal concentration of 5,33 g/dm3 in the ferritization reaction mixture, regardless of the method of activating the process, phases containing crystalline ferromagnetic phases of ferrites (Ni, Cu, Zn) Fe2O4 exceeds 92%. The efficiency of resource-saving electromagnetic pulse activation of the reaction mixture in the ferritization process is confirmed. Using this method of activation, energy consumption is reduced by 1,5 times compared to thermal one. The proposed resource-saving ferritization technology prevents environmental pollution, ensures the rational use of raw materials and energy, as well as allows to obtain marketable products from industrial waste.

This paper considers prospects for increasing the level of environmental safety of industrial enterprises as a result of the implementation of resource-saving technology of processing galvanic sludge using the ferritization method. The effectiveness of the use of electromagnetic pulse discharges for resource-saving activation of the ferritization process with the extraction of heavy metal ions from sludge (Fe, Ni, Cu, Zn) has been confirmed. The influence of key parameters of the process such as the pH value of the reaction mixture and the initial concentrations of metals in the solution on the quality of processing galvanic sludge by ferritization has been experimentally investigated. It was determined that with an increase in the pH value from 8.5 to 10.5 the residual concentrations of metal ions decrease to the values of 0.1÷0.25 mg/dm3 regardless of the total initial concentrations. It has been established that the technique of electromagnetic pulse activation ensures an adequate degree of extraction of metal ions of 99.9 %; it also has indisputable energy advantages compared to the thermal method: energy costs are reduced by more than 60 %. That indicates the suitability of purified water for reuse in galvanic production in terms of the requirements for the content of heavy metal ions in it. In addition, the structural studies of ferritization sediment samples have been carried out. The sediment is characterized by the maximum content of crystalline ferromagnetic phases of ferrite. It was established that an increase in the pH of the initial reaction mixture leads to an increase in the ferrite phase in sedimentation: at pH=10.5, phases were detected, which are characterized by a maximum ferrite content (exceeding 76 %). The proposed resource-saving ferritization process prevents environmental pollution, ensures efficient and rational utilization of raw materials and energy in the industry; it also makes it possible to obtain commodity products from industrial waste.

Possibility of environmental safety increasing for industrial enterprises as a result of resource-saving technology implementation for processing galvanic sludge is considered. An experimental study of stability for sediments after ferritization processing of galvanic sludge and exhausted technological solutions was carried out. As a result of dynamic leaching of heavy metal ions, the immobilization properties of sediments were determined, which were obtained at different technological parameters of the ferritization process. It is shown that the level of immobilization of heavy metals in ferritic sediments has significantly higher values in comparison with sediments of traditional wastewater neutralization. It was found, that the precipitate obtained at following key parameters of reaction mixture for the ferritization process: the total concentration of heavy metal ions 10.41 g/dm3; ratio of concentrations of iron ions to total concentration of other heavy metals ions 4/1 and pH value of 10.5, is characterized by the highest degree of immobilization of heavy metals in the sediments of 99.96% mass. Using the results of a complete factorial experiment, regression equation for the leaching of heavy metal ions (iron, nickel, copper and zinc) from ferrite sediments was obtained: ratio of iron concentrations to the total concentration of other heavy metals and the pH value of reaction mixture. The adequacy of coefficients of regression equations was evaluated according to the criteria of Student and Fisher, which with 95% reliability correspond to the experimental results of the study. The proposed calculation algorithm provides an opportunity to increase efficiency and automation of ferritization process. Subsequent use of the research results will allow to implement reliable utilization of ferritized galvanic waste by application them into the row materials for obtaining alkaline cements for special purposes.

The aeration rate for the degree of purification of highly concentrated galvanic wastewater from zinc and ferrum ions was investigated using various activation methods. It is shown that the intensity of aeration has a significant effect on the quality of wastewater treatment and the characteristics of water treatment sludge. The efficiency of the use of an energy-saving method for activating the ferritization process with the use of electromagnetic pulses for the extraction of zinc ions from wastewater has been confirmed. It was determined that with an increase in the aeration rate to 3.5 dm3/min per 1 dm3 of the reaction mixture and the use of thermal activation of the process, the residual concentration of zinc ions remains within the range of 0.12÷0.2 mg/dm3. In this case, the concentration of ferrum ions decreases to values of 0.08÷0.14 mg/dm3. It was found that at an aeration rate of 2.5 dm3/min and the use of pulsed electromagnetic (EMP) activation, the residual concentrations of heavy metal ions decrease to values of 0.08÷0.16 mg/dm3. Comparison of the results indicates the advisability of using low rates of aeration of the reaction mixture. This, together with the use of resource-saving EMR process activation, allows to achieve a significant reduction in energy costs. The quantitative phase composition of ferritization precipitates was determined, in which the crystalline phases of zinc ferrite Zn2Fe2O4 and magnetite Fe3O4, as well as ferrum oxyhydroxide FeO (OH) and sodium sulfate Na2SO4, prevail. It is found that with an increase in the volumetric aeration rate, the proportion of the ferrite phase increases. At an aeration rate of 2.0 dm3/min, more than 85 % of the zinc ferrite phase was found in the sediments. Taking into account the qualitative and quantitative composition of precipitates, it is recommended to use them in the production of building materials. The experimental results obtained make it possible to provide a comprehensive processing of liquid galvanic waste.

A BSTRACT . Currently, much attention is paid to the treatment of industrial wastewater, which would provide the necessary degree of decontamination for organizing a recycled water supply and further disposal of the treatment-generated by-product. The paper presents an advanced technology using a new nanomaterial that decreases initial concentrations of heavy metal ions in electroplating production wastewater from 25 g/L to less than 0.6 mg/L. An integrated process of wastewater treatment consists of two stages: energy- and resource-efficient ferritization followed by sorption onto suspensions of nanopowders of polyvalent iron oxides. The advantages of an electromagnetic pulse method for achieving ferritization at frequencies up to 0.9 kHz in comparison with expensive thermal treatment at temperatures up to 75 °C are demonstrated. The polyvalent iron oxide nanosorbents were obtained by electroerosion dispersion. The result of the integrated treatment is that the purified water meets the requirements for water reuse in electroplating production. The treatment-generated by-product has high chemical stability and a significant content of magnetic ferrite phases, thus having a high potential for further utilization. In contrast to the widely used reagent-based treatment of concentrated wastewater contaminated by heavy metals (> 25 g/L), the integrated method developed here prevents environmental contamination by toxic effluents and ensures the rational use of water and energy inputs in the system of industrial production.

Currently, a major attention is paid to the development of integrated industrial wastewater treatment methods that ensure sufficient treatment efficiency for use of recycled water supply arrangements and further utilization of the treatment-generated waste. This paper dealt with the ferritization-based treatment of zinc-containing electroplating wastewater. Dependence of efficiency of heavy metal ions (HMIs) removal on aeration rates was determined. The highest efficiency of wastewater treatment was reached at low aeration rates. The influence of oxidant consumption on structure of ferritization treatment sediments was also studied. The sediments are chemically stable, have a dense crystalline structure and ferromagnetic properties. On the basis of experimental research, the optimal aeration rate for the ferritization treatment process was found to reach 0.5–1.5 dm3/min, allowing the reuse of the wastewater treatment effluent for on-site water supply.

Issues related to the prospects of implementing the latest technologies aimed at achieving energy efficiency in the field of water supply, resource conservation in material-intensive processes at industrial enterprises and prevention of environmental pollution are considered. A study of ferritative wastewater treatment from chromium compounds, which belong to the first class of danger. The efficiency of thermal and electromagnetic pulse activation of the process is compared. Appropriate experimental setups were developed and the main parameters of the purification process were studied and determined: the ratio of iron (II) and chromium (VI) ions, magnetic field strength, frequency of electromagnetic pulses, ferritization process duration, temperature and pH of the reaction mixture. The expediency of using electromagnetic pulse activation of the reaction mixture by passing electromagnetic pulses through the reaction mixture has been studied and scientifically substantiated. Rational values ​​of the strength and frequency of the electromagnetic field when using this method of activation, which are 0.01 - 0.14 Tl and 1 Hz, respectively, as well as the ratio of concentrations of heavy metal ions Fe2 + / Cr6 + = 10/1 for washing water chrome plating line . It is shown that purified water meets the requirements of category 1 when reused in production. The results of X-ray diffraction analysis of ferritization sediments showed that stable crystalline phases, such as chromium ferrites and magnetite, are formed with increasing magnetic field strength. The chemical resistance of sludge allows them to be safely disposed of. It is established that this method of electromagnetic pulse activation is not inferior to thermal, and the technical and economic calculations confirmed a significant reduction in industrial costs in its application

Сurrent state and efficiency of existing sorbtion methods of industrial wastewater treatment are considered. The influence of important parameters for sorbtion process - ratio of metal ion and nanosorbent concentrations in solution, as well as the method of sorbent addition into wastewater on degree of its purification was studied. The most effective results of water purification were achieved with usage of freshly obtained powder of electroerosive dispersion (EED) of iron in water in the form of a suspension at ratio of the concentration of Zn2+ ions and nanosorbent powder 1:10. It Under such conditions a high degree of removing as 98% is determined, and obtained purified solution meets the standards of rising water at galvanic facilities, regarding of Zn2+ content.