CC BY
1
УДК 628.33 DOI https://doi.Org/10.35546/kntu2078-4481.2023.4.21
Ю. М. ФЕДЕНКО
кандидат техшчних наук, старший викладач кафедри технологи неоргашчних речовин, водоочищення та загально! хiмiчно! технологи Нацюнальний техшчний унiверситет Укра!ни «Ки!вський пол^ехшчний iнститут iменi 1горя Сшорського» ORCID: 0000-0002-8599-1717
В. В. СИН1ЦЬКА
бакалавр кафедри технологи неоргашчних речовин, водоочищення та загально! хiмiчно! технологи Нацюнальний техшчний ушверситет Укра!ни «Ки!вський пол^ехшчний iнститут iменi 1горя Сшорського» ORCID: 0009-0004-7272-0207
ОСОБЛИВОСТ1 ОЧИЩЕННЯ СТ1ЧНИХ ВОД ГАЛЬВАН1ЧНИХ ВИРОБНИЦТВ В1Д ВАЖКИХ МЕТАЛ1В НА ПРИКЛАД1 ШЕСТИВАЛЕНТНОГО ХРОМУ.
ЕКОЛОГ1ЧН1 АСПЕКТИ
Гальватка - галузь промисловостг, яка займаеться нанесенням захисних i декоративних покриттгв на мета-левi та неметалевi вироби. Гальватка - електрохiмiчний процес. Електричний ланцюг мiстить електролт, два аноди, пiдключенi до джерела струму, i заготовку, що обробляеться, яка виступае в ролi катода. Коли через ньо-го проходить електричний струм, юни металу вiдновлюються на катодi в електролiтi, утворюючи тонку плiвку при осадженн на поверхнi виробу.
Процес гальванки вiдбуваеться в спецiалiзованих ваннах (електролiзерах). У ванну завантажують електролт, до складу якого входять солi металу, що осiдае на поверхш катода. Для очищення промислових стiчних вод використовуються лужнi та rn^i промивнi води. Концентрованими стiчними водами, витрата яких визнача-еться об'емом ванни i складом розчину, е вiдпрацьований технологiчний розчин у ванн або промивнi води з iншоi технологiчноi операцп. 90-95% гальванiчноi води використовуеться на промивнi операцп. При цьому близько 80% маси вах шюдливих речовин у стiчних водах надходить зi стiчними водами i розчинами електролiтiв.
Р1зш процеси, пов'язанi з гальваткою, призводять до утворення стiчних вод ргзного складу. Загалом, для кож-но'1' групи забруднювачiв юнують сво'1' методи очищення.
Значно'1' шкоди довкшлю завдають виробництва, як продукують стiчнi води, що мютять хром. Якщо забруд-неш промисловi стiчнi води скидати у водойму без попереднього очищення, це може призвести до серйозних порушень бiологiчного режиму водойми. Сполуки хрому е канцерогенними i мають шюдливий вплив на живi орга-тзми. У гальватчнш промисловостi стiчнi води, забрудненi сполуками хрому, утворюються тд час хромування, травлення та очищення виробiв пюля пасивацп поверхонь деталей. Через використання шестивалентного хрому ц стiчнi води необхiдно вiдокремлювати i попередньо очищати в окремш системi.
Перевагою реагентного очищення стiчних вод е його економiчнiсть i простота. Однак цей метод вимагае споживання велико'1' кiлькостi реагентiв, громiздкого обладнання та утилгзацИ велико'1' кiлькостi шламу.
Ключовi слова: гальванiчний процес, електролiзер, юни важких металiв, хром, стiчнi води.
YU. M. FEDENKO
Candidate of Technical Sciences, Senior Lecturer at the Department of Technology of Inorganic Substances, Water Treatment and General Chemical Technology National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" ORCID: 0000-0002-8599-1717
V. V. SYNITSKA
Bachelor Student at the Department of Technology of Inorganic Substances, Water Treatment and General Chemical Technology National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute" ORCID: 0009-0004-7272-0207
PECULIARITIES OF WASTEWATER TREATMENT OF ELECTROPLATING INDUSTRIES FROM HEAVY METALS ON THE EXAMPLE OF HEXAVALENT CHROMIUM.
ENVIRONMENTAL ASPECTS
Electroplating is an industrial sector that applies protective and decorative coatings to metal and non-metal products. Electroplating is an electrochemical process. An electrical circuit contains an electrolyte, two anodes connected to a current source, and the workpiece to be processed, which acts as a cathode. When an electric current is passed through, metal ions are reduced on the cathode in the electrolyte, forming a thin film when deposited on the surface of the product.
The electroplating process takes place in specialized baths (electrolyzers). An electrolyte is loaded into the bath, which includes salts of the metal deposited on the cathode surface. Alkaline and acidic wash water is used to treat industrial wastewater. Concentrated wastewater, the consumption of which is determined by the volume of the bath and the composition of the solution, is the spent process solution in the bath or rinsing water from another process operation. 90-95% of electroplating water is used for rinsing operations. At the same time, about 80% of the mass of all harmful substances in wastewater comes from wastewater and electrolyte solutions.
Various processes related to electroplating produce wastewater of different composition. In general, each group of pollutants has its own treatment methods.
Industries that produce chromium-containing wastewater cause significant environmental damage. If contaminated industrial wastewater is discharged into a water body without prior treatment, it can lead to serious disruption of the biological regime of the water body. Chromium compounds are carcinogenic and have a harmful effect on living organisms. In the electroplating industry, wastewater contaminated with chromium compounds is generated during chrome plating, pickling, and cleaning of products after passivation of component surfaces. Due to the use of hexavalent chromium, this wastewater must be separated andpretreated in a separate system.
The advantage of reagent wastewater treatment is its cost-effectiveness and simplicity. However, this method requires the consumption of large quantities of reagents, bulky equipment, and the disposal of large amounts of sludge.
Key words: electroplating process, electrolyzer, heavy metal ions, chromium, wastewater.
Introduction
Electroplating is an industrial sector that applies protective and decorative coatings to metal and non-metal products.
Electroplating is an electrochemical process. An electrical circuit contains an electrolyte, two anodes connected to a current source, and the workpiece to be processed, which acts as a cathode. When an electric current is passed through the electrolyte, metal ions are reduced at the cathode, forming a thin film when deposited on the surface of the product [1-3].
Electroplating is used to improve the protective properties and decorative characteristics of products. It is used if it is impossible to make a whole product from metal or if the cost of the product is too high. A good example is chrome. The production of parts and objects from chrome is impossible because this metal is hard, but also has a brittle property. Nevertheless, when chrome is applied to steel, it makes it harder and more resistant to corrosion. The most common processes are galvanizing, nickel plating, chrome plating, copper plating, silver plating, and gilding [4-7].
The electroplating process takes place in specialized baths (electrolyzers). An electrolyte is loaded into the bath, which includes salts of the metal that is deposited on the cathode surface. Electrodes are connected to the bath and the product to allow electric current to flow. The positive charge is connected to the anodes, and the negative charge is connected to the workpiece. When the galvanic system is started, an electric current pass through the electrolyte. The metal contained in the electrolyte is deposited on the workpiece in a uniform layer. Two anodes in the electrolysis tank are used to treat both surfaces simultaneously [8].
Each galvanic process consists of various operations that can be divided into three groups:
• Preparatory work. Before starting the main electroplating process, the components must be cleaned. At this stage, the parts are processed, degreased, etched, and polished.
• The main process is the application of a suitable metal coating using electroplating techniques.
• Finishing processes are necessary to maintain and improve the appearance of galvanic coatings. For this purpose, painting, polishing, and varnishing are commonly used [9-12].
The purpose of degreasing is to remove organic oils, mineral oils, and various solids retained in the oil film from the surface of the film components. Alkaline degreasing agents should contain substances that neutralize fatty acids and emulsifiers. They should also not cause corrosion of metals and should be easily removed with water. These conditions are best met by silicates and phosphates of alkali metals. Surfactants with good emulsifying properties are also added. After degreasing, the solution is sent for refining [13].
Before painting, metal surfaces must be cleaned of scale, rust, and oxide films by pickling. The pickling process usually follows the degreasing process, and the quality of cleaning directly depends on the quality of the previous degreasing process. Pickling is carried out with solutions based on sulfuric, nitric, chloric, and phosphoric acids. Chloric acid mainly dissolves and removes oxides on the surface of the part. When sulfuric acid is used, oxides are removed mainly by etching the metal and mechanically removing a loose oxide film with the help of hydrogen released. The solution after pickling should be aimed at removing harmful contaminants [14].
Therefore, alkaline, and acidic wash water is used to treat industrial wastewater. Concentrated wastewater, the consumption of which is determined by the volume of the bath and the composition of the solution, is the spent process solution in the bath or rinsing water from another process operation. 90-95 % of electroplating water is used for rinsing operations. At the same time, about 80 % of the mass of all harmful substances in wastewater comes from wastewater and electrolyte solutions [15, 16].
The quantity, quantitative and qualitative composition of wastewater depends on the water consumption for washing, the cleaning method, and the composition of the technical solution.
For example, consider a galvanic line with a capacity of 26 m2/h of nickel and 2 m2/h of chromium with a decorative nickel-chromium coating and a stationary hand bath for one-stage purification (Fig. 1).
Fig. 1. Galvanic lines for applying decorative coatings (nickel and chrome) with a nickel-plating capacity of 26 m2/h and a chrome plating capacity of 2 m2/h: 1 - degreasing, 4 - nickel plating, 5 - metal recovery, 6 - chrome plating, 7 - drying of components, 8 - cold rinsing
In this method, the acid-base drainage consists of alkaline rinse water after degreasing 1, acid rinse water after nickel plating 4, and process fluids. Concentrate wastewater is represented by rinsing water and wastewater after chrome plating 6. The volume and composition of the wastewater of such a galvanic line are shown in Table 1 [17-19].
Table 1
Composition of wastewater from the electroplating line [19]
Component Max. concentration of the component in the bath, g/L Max. component outreach, g/h Maximum concentration of components in wastewater, mg/L
NaOH 36 263 15
Na3PO„-12H2O 35 263 15
Na2CO3 35 263 15
HCl 100 500 28
NiSO„-7H2O 320 1600 89
NiCl2-6H2O 60 300 17
H3BO4 40 200 11
Formalin 1.2 6 0.3
Chloramine B 2.5 13 0.7
CrO3 250 225 49
H2SO4 2.5 2.3 0.5
Chromoxane 0.2 0.2 0.04
The choice of equipment and flushing method determines the quantitative and qualitative composition of flushing and wastewater, which in turn determines the composition and efficiency of the treatment plant [20].
Methods of wastewater treatment of electroplating production
The various processes involved in electroplating produce wastewater of varying composition. Depending on the phase state of the substances in solution, all pollutants in wastewater can be divided into the following groups:
• Fine suspensions, emulsions.
• Polymeric compounds, colloids.
• Organic substances dissolved in water.
• Salts, acids, and alkalis dissolved in water.
In general, each of these groups of pollutants has its own treatment methods. For example, gravity, flotation, and adhesion are the most effective methods for treating water from fine suspensions and emulsions. For colloidal systems, coagulation methods are used. Dissolved organic substances are most effectively removed from water by adsorption methods
of purification, while salts, acids and alkalis dissolved in electrolytes are most effectively removed from water by reactive methods or desalination methods by converting ions into insoluble compounds [21].
If we classify purification methods by the dominant process (or main equipment), they can be divided into seven groups: mechanical, chemical, flocculation-suspension, electrochemical, sorption, membrane, and biological.
However, these methods alone cannot fully satisfy modern requirements, treatment in accordance with MPC standards (especially heavy metal ions), 90-95 % of water returns to the circulation cycle, lower treatment costs, and utilization of valuable resources (acids, alkalis, metals) [21].
Treatment of hexavalent chromium waste with reagents
Industries that produce chromium-containing wastewater cause significant environmental damage. If contaminated industrial wastewater is discharged into a water body without prior treatment, it can lead to serious disruption of the biological regime of the water body. Chromium compounds are carcinogenic and have a harmful effect on living organisms.
In the electroplating industry, wastewater contaminated with chromium compounds is generated during chrome plating, pickling, and cleaning of products after passivation of component surfaces. Due to the use of hexavalent chromium, this wastewater must be separated and pretreated in a separate system [22].
This wastewater is subjected to a two-stage hexavalent chromium recovery process:
• Conversion of hexavalent chromium to trivalent chromium.
• Precipitation as trivalent chromium hydroxide.
Waste metallic iron (iron powder) or iron (II) sulfate can be used as reducing agents. In the first case, the wastewater is acidified to pH 2 and filtered through a foam layer of iron powder with a continuous supply of air. In the second case, a solution of ferrous (II) sulfate (in the form of a 10 % aqueous solution) is added to the reactor receiving the wastewater. The reduction of Cr®+ to Cr3+ by iron salts occurs at a very high rate.
The advantage of this method is its cost-effectiveness: only a small amount of ferrous (II) sulfate is required to reduce Cr®+ to Cr3+, regardless of the initial Cr®+ concentration and pH value in the wastewater. The disadvantage of using ferrous (II) sulfate and ferrous metal as reducing agents is that a large amount of precipitate is generated during the neutralization process. In addition, when stored in unfavorable conditions, iron (II) is easily oxidized to iron (III), which makes it difficult to properly dose the salt solution into the wastewater [23].
The salts are added to the wastewater in the form of a 10% aqueous solution; the speed and completeness of the Cr®+ to Cr3+ reduction reaction strongly depends on the pH of the reaction mixture. The highest rate of the reduction reaction is achieved in an acidic environment with a pH of 2-2.5 and usually requires further acidification of the wastewater with a 10-15% sulfuric acid solution (solutions of other mineral acids can also be used). An overdose of the reagent, even at the level of 10%, is unacceptable, as complex salts of chromium (III) and sulfuric acid are formed, which are destroyed during further neutralization of the wastewater.
After the reduction of Cr®+ in an acidic environment is completed, the wastewater is sent for neutralization, and the reaction results in the precipitation of Cr3+ in the form of hydroxides.
The wastewater containing Cr3+ is pre-mixed with acidic and basic wastewater from electroplating production and neutralized.
Table 2 shows the theoretical reagent consumption required to remove 1 kg of C1O3 from wastewater. [23].
Thus, it can be concluded that the usage of NaHSO3 as a reducing agent is the most suitable method for removing harmful Cr®+. The amount of precipitate formed after neutralization is almost the same in all cases, but the consumption of reagents is the lowest for the chosen method.
Table 2
Stoichiometric flow rate of the reagent and mass of the precipitate formed during the neutralization of 1 kg of CrO3
Reductant Consumption of the reductant, kg Consumption of H2SO4, kg Consumption of NaOH, kg Mass of sludge, kg
FeSO4 8.340 2.940 4.800 4.230
NaHSO3 1.561 0.735 1.200 4.414
N2SO3 1.891 1.470 1.200 5.576
The strong point of reagent wastewater treatment is its cost-effectiveness and simplicity. However, this method requires the consumption of large amounts of reagents, bulky equipment, and the disposal of large amounts of sludge. In addition, after the reactive removal of heavy metals in the form of hydroxides, small residual concentrations of these metals remain in the wastewater. The final treatment can be carried out by various methods, such as ion exchange, electrolocation, elec-trodialysis, reverse osmosis, and ultrafiltration [24].
Bibliography
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2. Favero B.M., Favero A.C., Da Silva D.C. Treatment of galvanic effluent through electrocoagulation process: Cr, Cu, Mn, Ni removal and reuse of sludge generated as inorganic pigment. Environmental Technology (UnitedKingdom). 2022. Vol. 43, № 20. P. 3107-3120.
3. Kozodaev A.S., Shulzhenko A.D., Korpusova Y.V. Representation of the galvanic coagulation process using a mathematical model. IOP Conference Series: Earth and Environmental Science. 2021. Vol. 815. № 1. P. 271-274.
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5. Petrichenko S.V. Tsolin P.L., Yushchishina A.N. Electrospark Purification of Galvanic Effluents from Heavy Metal Ions in the Flow Reactor. Surface Engineering and Applied Electrochemistry. 2021. Vol. 57. № 1. P. 148-153.
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10. Luz G., Sales V. Evaluation of technology potential of Aloe arborescens biopolymer in galvanic effluent treatment. Water Science and Technology. 2018. Vol. 2017. № 1. P. 48-57.
11. Wysokowsky M., Bartczak P., Chudzinska A. Adhesive Stalks of Diatom Didymosphenia geminata as a Novel Biological Adsorbent for Hazardous Metals Removal. Clean - Soil, Air, Water. 2017. Vol. 45. № 11. P. 28-43.
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13. Kvartenko A., Orlov V., Pletuk O. Research into the biosorption process of heavy metal ions by the sediments from stations of biological iron removal. Eastern-European Journal of Enterprise Technologies. 2017. Vol. 4. № 10. P. 37-43.
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15. He Y., Wei Y., Wang H. Notice of retraction: study on disposal of groundwater containing Cr (VI) - the case of waste iron chippings-fly ash and Fe-fly ash. 5th International Conference on Bioinformatics and Biomedical Engineering, iCBBE 2011. 2011. Vol. 1. P. 12-17.
16. Marquinez R., Pourcelly G., Bauer B. Chromic acid recycling from rinse water in galvanic plants by electro-electrodialysis (recy-chrom). REWAS'04 - Global Symposium on Recycling, Waste Treatment and Clean Technology. 2005. Vol. 2005. P. 1039-1048.
17. Ковальчук 1.А., Тобшко В.Ю., Бондарева A.I. Очищення вод ввд юнш важких металiв i3 використанням нано-розмiрних Fe0/каолiнiт композита. Reports of the National Academy of Sciences of Ukraine. 2020. № 11. P. 96-103.
18. Grebenyuk V.D., Verbich V.D., Sorokin G.V. Regeneration of heavy metals from galvanic rinsing water. Khimiya i Tekhnologiya Vody. 1996. Vol. 18. № 4. P. 379-383.
19. Zoria O., Ternovtsev O., Kapanytsia Y. Resource-saving technology of industrial wastewater treatment from nickel compounds. AIP Conference Proceedings. 2021. Vol. 2534. P. 176-184.
20. Naser H. Assessment and management of heavy metal pollution in the marine environment of the Arabian Gulf: A review. Marine Pollution Bulletin. 2013. Vol. 72. № 1. P. 6-13.
21. Su R., Zolotarev A. Novel mixed matrix membranes based on polyelectrolyte complex modified with fullerene derivatives for enhanced pervaporation and nanofiltration. Separation and purification technology. 2022. Vol. 298. P. 124-132.
22. Yeh L., Yeh C., Kao Yu. Inactivation of Escherichia coli by dual-functional zerovalent Fe/Al composites in water. Chemosphere. 2022. Vol 299. P. 378-392.
23. Lupascu T., Sandu M. The road to environmental chemistry in republic of Moldova paved by the illustrious scientist and renowned ecologist Valeriu Ropot. Chemistry Journal of Moldova. 2022. Vol 17. № 2. P. 7-18.
24. Li M., Shang H., Li H. Kirkendall effect boosts phosphorylated nZVI for efficient heavy metal wastewater treatment. Angewandte Chemie - International Edition. 2021. Vol. 60. № 31. P. 17115-17122.
References
1. Tatarintseva E. A., Arefieva O. A., Olshanskaya L. N. (2023) Extraction of copper and zinc ions from wastewater by a sorbent based on chitosan. Theoretical and Applied Technology, vol. 1, pp. 148-153.
2. Favero B. M., Favero A. C., Da Silva D. C. (2022) Treatment of galvanic effluent through electrocoagulation process: Cr, Cu, Mn, Ni removal and reuse of sludge generated as inorganic pigment. Environmental Technology (United Kingdom), vol. 43, no. 20, pp. 3107-3120.
3. Kozodaev A. S., Shulzhenko A. D., Korpusova Y. V. (2021) Representation of the galvanic coagulation process using a mathematical model. IOP Conference Series: Earth and Environmental Science, vol. 815, no. 1, pp. 271-274.
4. Youssef M., Moukhtar N., Hassan I. (2021) Recovery of Heavy Metals from Liquid Effluent by Galvanic Cementation. Mining, Metallurgy and Exploration, vol. 38, no. 1, pp. 177-186.
5. Petrichenko S. V Tsolin P. L., Yushchishina A. N. (2021) Electrospark Purification of Galvanic Effluents from Heavy Metal Ions in the Flow Reactor. Surface Engineering and Applied Electrochemistry, vol. 57, no. 1, pp. 148-153.
6. Petrov O., Petrichenko S., Yushchishina A. (2020) Electrospark method in galvanic wastewater treatment for heavy metal removal. Applied Sciences (Switzerland), vol. 10, no. 15, pp. 284-295.
7. Trus I., Gomelya M., Vorobyova V. (2021) Effectiveness of complexation-nanofiltration during water purification from copper ions. Journal of Chemical Technology and Metallurgy, vol. 56, no. 5, pp. 1008-1015.
8. Kardasz E., Kardasz P., Pohrebennyk V (2019) Evaluation of the influence of machine-building plant on the state of environment. International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM, vol. 19, no. 4.1, pp. 193-201.
9. Sofinska-Chmiel W., Kolodynska D. (2018) Application of ion exchangers for the purification of galvanic wastewater from heavy metals. Separation Science and Technology (Philadelphia), vol 53, no. 7, pp. 1097-1106.
10. Luz G., Sales V (2018) Evaluation of technology potential of Aloe arborescens biopolymer in galvanic effluent treatment. Water Science and Technology, vol. 2017, no. 1, pp. 48-57.
11. Wysokowsky M., Bartczak P., Chudzinska A. (2017) Adhesive Stalks of Diatom Didymosphenia geminata as a Novel Biological Adsorbent for Hazardous Metals Removal. Clean - Soil, Air, Water, vol. 45, no. 11, pp. 28-43.
12. Abbas A., Hussain M., Sher M. (2017) Design, characterization, and evaluation of hydroxyethylcellulose based novel regenerable supersorbent for heavy metal ions uptake and competitive adsorption. International Journal of BiologicalMacromolecules, vol. 102, pp. 170-180.
13. Kvartenko A., Orlov V, Pletuk O. (2017) Research into the biosorption process of heavy metal ions by the sediments from stations of biological iron removal. Eastern-European Journal of Enterprise Technologies, vol. 4, no. 10, pp. 37-43.
14. Fu F., Cheng Z. (2015) Fe/Al bimetallic particles for the fast and highly efficient removal of Cr (VI) over a wide pH range: performance and mechanism. Journal of Hazardous Materials, vol. 298, pp. 261-269.
15. He Y., Wei Y., Wang H. (2011) Notice of retraction: study on disposal of groundwater containing Cr (VI) - the case of waste iron chippings-fly ash and Fe-fly ash. 5th International Conference on Bioinformatics and Biomedical Engineering, iCBBE 2011, vol. 1, pp. 12-17.
16. Marquinez R., Pourcelly G., Bauer B. (2005) Chromic acid recycling from rinse water in galvanic plants by electro-electrodialysis (recy-chrom). REWAS'04 - Global Symposium on Recycling, Waste Treatment and Clean Technology, vol. 2005, pp. 1039-1048.
17. Kovalchuk I. A., Tobilko V. IU., Bondarieva A. I. (2020) Ochyshchennia vod vid ioniv vazhkykh metaliv iz vykorystanniam nanorozmirnykh Fe0/kaolinit kompozytiv. [Water purification from heavy metal ions using nanoscale Fe0/kaolinite composites]. Reports of the National Academy of Sciences of Ukraine, no. 11, pp. 96-103.
18. Grebenyuk V. D., Verbich V. D., Sorokin G. V. (1996) Regeneration of heavy metals from galvanic rinsing water. Khimiya i Tekhnologiya Vody, vol. 18, no. 4, pp. 379-383.
19. Zoria O., Ternovtsev O., Kapanytsia Y. (2021) Resource-saving technology of industrial wastewater treatment from nickel compounds. AIP Conference Proceedings, vol. 2534, pp. 176-184.
20. Naser H. (2013) Assessment and management of heavy metal pollution in the marine environment of the Arabian Gulf: A review. Marine Pollution Bulletin, vol. 72, no. 1, pp. 6-13.
21. Su R., Zolotarev A. (2022) Novel mixed matrix membranes based on polyelectrolyte complex modified with fullerene derivatives for enhanced pervaporation and nanofiltration. Separation and purification technology, vol. 298, pp. 124-132.
22. Yeh L., Yeh C., Kao Yu. (2022) Inactivation of Escherichia coli by dual-functional zerovalent Fe/Al composites in water. Chemosphere, vol. 299, pp. 378-392.
23. Lupascu T., Sandu M. (2022) The road to environmental chemistry in republic of Moldova paved by the illustrious scientist and renowned ecologist Valeriu Ropot. Chemistry Journal of Moldova, vol 17, no. 2, pp. 7-18.
24. Li M., Shang H., Li H. (2021) Kirkendall effect boosts phosphorylated nZVI for efficient heavy metal wastewater treatment. Angewandte Chemie - International Edition, vol. 60, no. 31, pp. 17115-17122.
