engleski

Efficiency of separation of raw and used emulsions of mineral oil in water by electrocoagulation method

Oil in water type emulsions provide a good combination of cooling and lubrication and are therefore widely applied in the metal processing industry for various processes. They contain a high concentration of substances, which make them harmful for the environment after usage and should be handled appropriately. For this purpose, many processing techniques have been developed and used, including electrocoagulation as an increasingly used method. This paper examines the effectiveness of the separation of fresh and used mineral oil / water emulsion type by electrochemical coagulation, i.e. electrocoagulation (EC). EC combines three key processes: electrolysis, coagulation and flotation. It is known as a fast and efficient method that requires minimal or no addition of chemicals. EC is widely used to remove metals, colloidal particles, textile dyes, and for breaking the stable emulsions. Processes are performed in a batch reactor with aluminum electrodes and with the addition of NaCl in order to increase the electrical conductivity of the solution. Interdependence of salt concentration and conductivity of the emulsion was determined by separate experiments. The influence of current density and reaction time on the efficiency of the emulsion separation was examined by measuring the total organic carbon, the filtrate volume, mass of separated impurities and changes in weight of aluminum electrodes. The results obtained for fresh emulsion showed high efficiency of electrocoagulation regarding separation of hydrocarbons from emulsions (> 97%), expressed with the content of total organic hydrocarbons in water. Thereat, lower current density (0.5 A) during longer procedure proved as slightly more effective in comparison with higher current density (1.0 A) of electrocoagulation process in a shorter time. Also, a fresh mineral emulsion turns into a transparent aqueous solution, from initially milky white. Minimum efficiency of separating hydrocarbons from the used emulsion (79.9%) was achieved at the lowest current (0.1 A), while the maximum current (1.0 A) achieved an efficiency of 90.5%. By acidification of emulsion and at the current strength of 0.1 A the efficiency of hydrocarbons separation of 91.0% is achieved. U industriji obrade metala široko se primjenjuju emulzije tipa ulja u vodi koje osiguravaju dobru kombinaciju hlađenja i podmazivanja za brojne procese. Nakon upotrebe u njihovom sastavu se nalazi visoka koncentracija tvari koje ih čine štetnima za okoliš, te ih je potrebno primjereno zbrinuti. U tu svrhu su razvijene i upotrebljavaju se brojne tehnike obrade, a među njima, sve više se koristi metoda elektrokoagulacije. U radu je ispitana učinkovitost razdvajanja svježih i rabljenih emulzija na osnovi mineralnog ulja i vode, metodom elektrokemijske koagulacije, odnosno elektro-koagulacije (EC). EC objedinjava djelovanje triju osnovnih procesa: elektrolize, koagulacije i flotacije. Poznata je kao brza i učinkovita metoda koja zahtijeva minimalni ili nikakav dodatak kemikalija. EC se široko koristi za uklanjanje metala, koloidnih čestica, tekstilnih bojila, te za razbijanje stabilnih emulzija. Procesi su provođeni šaržno, u reaktoru s aluminijevim elektrodama i uz dodatak NaCl radi povećanja električne provodnosti otopine. Međuovisnost koncentracije soli i provodnosti emulzije utvrđena je zasebnim eksperimentima. Istražen je utjecaj jakosti struje i vremena reakcije na učinkovitost razdvajanja emulzija mjerenjem ukupnog organskog ugljika, volumena filtrata, mase izdvojenih nečistoća i promjene mase aluminijevih elektroda. Rezultati dobiveni za svježu emulziju pokazali su visoku učinkovitost elektrokoagulacije za odvajanje ugljikovodika iz emulzije (> 97 %), izraženo prema sadržaju ukupnih organskih ugljikovodika u vodi. Pri tome se manja jakost struje (0, 5 A) uz dulje trajanje postupka pokazala neznatno učinkovitijom u usporedbi s većom jakosti struje (1, 0 A) u kraćem vremenu procesa elektro-koagulacije. Također, svježa mineralna emulzija od početne mliječno bijele boje s vremenom prelazi u prozirnu vodenu otopinu. Kod rabljene emulzije najmanja učinkovitost odvajanja ugljikovodika iz emulzije (79, 9 %) postignuta je pri najmanjoj jakosti struje (0, 1 A), dok je pri najvećoj jakosti struje (1, 0 A) postignuta učinkovitost od 90, 5 %. Zakiseljavanjem emulzije i pri jakosti struje od 0, 1 A postiže se učinkovitost odvajanja ugljikovodika od 91, 0 %.

electrocoagulation; separation; used mineral oil in water emulsions

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