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Corrosion Resistance of Cast Duplex Steels

Müller Peter, Pernica V., Kaňa V.

Archives of Foundry Engineering

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2022

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Vol. 22, iss. 3

5--10

EN

The aim of this work is to investigate the resistance of cast duplex (austenitic-ferritic) steels to pitting corrosion with respect to the value of PREN (Pitting Resistance Equivalent Number). Pitting corrosion is one of the most common types of corrosion of stainless steels. In most cases, it is caused by the penetration of aggressive anions through the protective passive layer of the steel, and after its disruption, it leads to subsurface propagation of corrosion. The motivation for the research was a severe pitting corrosion attack on the blades of the gypsum-calcium water mixer in a thermal power plant operation. In order to examine the corrosion resistance, 4 samples of 1.4517 steel with different concentrations of alloying elements (within the interval indicated by the steel grade) and thus with a different PREN value were cast. The corrosion resistance of the samples was evaluated by the ASTM G48 – 11 corrosion test in a 6% aqueous FeCl3 solution at room and elevated solution temperatures. To verify the possible effect of different alloying element concentrations on the mechanical properties, the research was supplemented by tensile and Charpy impact tests. Based on the results, it was found that a significant factor in the resistance of duplex steels to pitting corrosion is the temperature of the solution. For the components in operation, it is therefore necessary to take this effect into account and thoroughly control and manage the temperature of the environment in which the components operate.

2

Elimination of organic matter by optimising coagulation treatment: Case of water from the Sidi Yacoub dam, Algeria

Hadbi Taieb, Saaed Hamoudi Abdelamir

Journal of Water and Land Development

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2021

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no. 51

72--77

EN

The presence of natural organic matter (NOM) in water has a significant influence on water treatment processes. Water industries around the world consider coagulation/flocculation to be one of the main water treatment methods. The chief objective of conventional coagulation-based processes is to reduce the turbidity of the water and to remove natural organic matter (NOM) present in solutions. The aim of this paper is to present some developments in terms of improved coagulation for the drinking water of Sidi Yacoub treatment plant located in the Northwest of Algeria. The experiments involved studying the effects of the application of two coagulants (ferric chloride and aluminium sulphate) on the removal of turbidity and natural organic matter from water by measuring the chemical oxygen demand (COD) and the UV absorbance at 254 nm. The results showed that the rate of turbidity removal increased from 81.3% to 88% when ferric chloride was applied and from 89.91% to 94% when aluminium sulphate was applied. For NOM removal, the maximum removal rates of COD and UV254 were 48% and 52%, respectively, in the case of ferric chloride. These rates increased to 59% and 65% after optimised coagulation. When aluminium sulphate was used, the rate of removal in water increased from 43% to 55% for COD and from 47% to 59% for UV254 after optimised coagulation. The combination of the two coagulants at equal dosage shows a slight improvement in the values obtained after optimisation, both in terms of turbidity and the NOM.

3

Improved Reduction of COD, BOD, TSS and Oil & Grease from Sugarcane Industry Effluent by Ferric Chloride and Polyaluminum Chloride Coupled with Polyvinyl Alcohol

Panhwar Aijaz, Bhutto Shahid

Ecological Engineering & Environmental Technology

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2021

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Vol. 22, iss. 2

8--14

EN

Rapid industrialization and urbanization severely affect our environment and water resources. Disposal of untreated wastewater to environment is a great threat to water bodies and environment. Sugarcane industry is an important industrial sector; globally it is also largest source of pollution of surface water and groundwater resources. It comprises a huge amount of chemicals and inorganic pollutants. Many treatment methods have been employed for the treatment of the sugarcane industry wastewater, such as chemical treatment, physical treatment, ion exchange, electrocoagulation and biological treatment. It is a fact that not a single treatment technique is effective for industrial effluent treatment. In this study, the physicochemical technique was used to remove the major pollutants as per Sindh Environmental Protection Agency (SEPA) effluent standards that include Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Total Suspended Solid (TSS) and Oil & Grease content. In these techniques e.g. chemical coagulation ferric chloride (FC) and poly aluminum chloride (PAC) coupled with polyvinyl alcohol (PVA), with different doses were used for achieving the optimum results. The best results were observed for COD, BOD, TSS and Oil & Grease reduction by FC and PAC dosing 180 mg/300 ml coupled with 45 mg/300 ml PVA. Further, it was also observed that the FC removal efficiency in slightly acidic to neutral medium (pH = 6–7) for COD (97.5%) and BOD (97.5%) is higher than PAC. However, PAC does perform well in slightly neutral to basic medium (pH = 7.5–8) than FC for the removal of Oil & Grease (95.3%) and TSS (97.4%) from the sugarcane effluent.

4

Utilization of Sodium Chloride Solutions to Obtain Ferrous Chlorides

Gomelya Mykola, Kryzhanovska Yana, Shabliy Tetyana, Levytska Olena

Journal of Ecological Engineering

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2020

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Vol. 21, nr 8

177--184

EN

In this work, the processes of electrochemical processing of sodium chloride solutions with the production of iron (III) chloride and alkali in a three-chamber electrolyzer with MA-41 anion-exchange membrane and MK-40 cation-exchange membrane were investigated. The conditions for the removal of sodium chloride from water in a three-chamber electrolyzer using an iron anode were determined depending on the anode current density and the reaction of the medium in the anode region. The parameters of the process of concentrating iron chloride in the anode region were established at relatively low concentrations of sodium chloride solution. It was shown that during the electrolysis of a sodium chloride solution with a concentration of 370 mg-eq/dm3 at a current of 0.2 A in a three-chamber electrolyzer with an iron anode, an iron chloride solution is formed in the anolyte at pH < 4.9. The rate of concentration of NaOH to catholyte and FeCl3 to anolyte increased along with the current density. It was found that in order to increase the concentration of iron (III) chloride in the anolyte at relatively low concentrations of sodium chloride solution, it is advisable to gradually renew the demineralized solutions in the working chamber.

5

Ultradźwiękowe wspomaganie chlorku żelazowego w koagulacji domieszek wody

Bień J., Stępniak L., Szparkowska I.

Inżynieria i Ochrona Środowiska

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2001

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T. 4, nr 3-4

393-402

PL

Skuteczność ultradźwięków we wspomaganiu koagulacji domieszek badanej wody naturalnej analizowano na podstawie zmiany trzech wskaźników fizyczno-chemicznych, tj.: mętności, barwy i dodatkowo utlenialności. Oznaczenia te wykonywano przed i po procesie koagulacji, w układach z nadźwiękawianiem i dla porównania bez udziału ultradźwięków. W badaniach wykorzystano naturalną wodę rzeczną, co dało możliwość prowadzenia doświadczeń przy zróżnicowanej mętności (M0 = 34-49 mgSiO2/dm3) oraz barwie (B0 = 32-38 mgPt/dm3). Przed każdym badaniem wodę poddawano odstaniu w celu sedymentacji cząstek łatwo opadających. W procesie koagulacji stosowano techniczny chlorek żelazowy w postaci uwodnionej FeCl3 * 6H2O. Do uzdatnianej wody dodawane były zróżnicowane dawki koagulantu. Dawki te były zmniejszane w stosunku do optymalnych dla badanej wody, tak aby możliwa była ocena działania ultradźwięków. Proces koagulacji odbywał się przy dobranych na podstawie wstępnych badań wartościach pH. Badania te obejmowały optymalny zakres wskaźnika pH dla koagulacji chlorkiem żelazowym. Eksperymenty związane z badaną skojarzoną metodą koagulacji, tj. ultradźwięki w połączeniu z chlorkiem żelazowym, realizowano według wybranego układu technologicznego. Zgodnie z nim, po zastosowaniu ultradźwięków do próbek wody dodawano koagulantu, po czym następowały operacje szybkiego i wolnego mieszania (1 i 30 minut) oraz sedymentacja (60 minut). Nadźwiękawianie prowadzono w czasie t = 5 min i przy amplitudzie A = 8 žm (stała częstotliwość drgań f = 22 kHz). Przedstawione w pracy wyniki badań wskazują, iż istnieje możliwość ultradźwiękowego wspomagania procesu koagulacji prowadzonego chlorkiem żelazowym. Najlepsze efekty uzyskano dla dawki 40 mg/dm3 i przy pH = 6,0, kiedy wzrost skuteczności zmniejszania mętności wody wynosił 33,4%, a barwy 13,1%, w stosunku do układu bez ultradźwięków. Wiązało się to z jednoczesnym obniżeniem utlenialności o 11,9%. Zbadano również, że niezależnie od wartości wskaźnika pH, przy którym prowadzono proces koagulacji, ultradźwięki z chlorkiem żelazowym zasadniczo lepiej współdziałały w obniżaniu mętności niż barwy wody.

EN

The subject of the paper is evaluation of possibility of application of ultrasonic field to support the classical coagulation process conducted with selected coagulant - ferric chloride. Up to now this effect was investigated for aluminium sulfate and for modified (polimerized) coagulant WAC HB. In the both cases the intensive influence of ultrasounds was confirmed. Beneficial action of this agent is connected with decrease of investigated coagulants doses, which are used in the water treatment. However, it was observed that ultrasound effect on chemical coagulation could be various. For example, ultrasounds didn't aid aluminium sulfate action in the water colour decrease. To the further investigations the ferric chloride was chosen as the one of ferric coagulant quite often applied in the water treatment technology. In the experiments the natural river water was used. The tests were led for different turbidity (M0 = 34-49 mgSiO2/dm3) and colour (B0 = 32-38 mgPt/dm3). Before each experiment the samples of water were clarified for the sedimentation of free settling particles. In the coagulation process the technical ferric chloride in the hydrated form FeCl3 * 6H2O was used. To the treated water different doses of coagulant were added. These doses were reduced in comparison to the optimal doses for tested water, so the evaluation of ultrasound action was possible. Coagulation process was conducted for the values of pH exactly determined, after preliminary investigations. The experimental part connected with associated coagulation method (that means ultrasounds with ferric chloride) was realized by using selected technological system. In this system, after sonification of water samples, the coagulant was dosed and the next operations of fast and slow mixing (1 and 30 minutes) and sedimentation (60 minutes) for clarification were followed. Sonification was conducted for 5-minutes' exposure time, with vibration amplitude 8 žm and the constant frequency of acoustic vibration 22 kHz. Efficiency of ultrasounds in aided coagulation of water additions in the samples of natural water was analysed on the base of three physico-chemical indicators changes: turbidity, colour and additionally chemical oxygen demand. These determinations before and after coagulation were carried out in the both systems with sonification and without sonification for comparison. Results presented in the paper indicate that ultrasounds may aid coagulation process conducted with ferric chloride. The best results were obtained for the dose of 40 mg/dm3 and pH equal 6.0, when the increase of efficiency of turbidity removal was 33.4% and for water colour 13.1%, in relation to the system without sonification. It was connected with simultaneous oxygen consumption decrease of 11.9%. It was also stated that ultrasounds better co-operated with ferric chloride in turbidity elimination from water than colour. Considering the theoretical basis of ultrasounds action, the coagulation efficiency increase may result from both ultrasonic field coagulation and sonochemical reactions. Water oxygen consumption decrease after coagulation indicates that sonochemical reactions of oxydation predominate in the observed effect.