SEM, AES, WDS i korozijsko testiranje oksidnih i nitridnih zaštitnih slojeva oblikovanih toplinskom obradom nerđajućeg čelika

Protective oxide and/or nitride layers on AISI 321 stainless steel were prepared by thermal treatment in air and two controlled atmospheres in a laboratory simulation of an actual technological procedure. Samples’ surface was imaged by Scanning Electron Microscopy (SEM), elemental composition of the substrates was checked by Wavelength Dispersive Spectroscopy (WDS) and depth profiles of the samples were measured by Auger Electron Spectroscopy (AES). Since protective layer thicknesses were found to be of the order of hundreds of nanometers an attempt was made to obtain some fast averaged information about layers composition by Wavelength Dispersive Spectroscopy (WDS) with appropriately adjusted primary beam energy. Electrochemical corrosion testing was also performed on samples.Zaštitne oksidne i/ili nitridne slojeve na AISI 321 nerđajućem čeliku pripremljen toplinskom obradom materijala na zraku i u 2 kontrolirana tipa atmosfera kao laboratorijsku simulaciju stvarnog tehnološkog procesa. Slike površine uzoraka dobijene tehnikom SEM, sastav substrata metodom WDS a za profilnu analizu upotrijebljena je spektroskopija Augerovih elektrona (AES). Kako je ustanovljeno da su debljine formiranih zaštitnih slojeva reda veličine nekoliko stotina nanometara pokušalo se doći do ocjene o prosječnom sastavu unutar sloja upotrijebom tehnike WDS uz odgovarajuće odabranu energiju primarnog elektronskog snopa. Na uzorcima je provjereno i korozijsko testiranje

Heavy Metals in Steel Mill Electric Arc Furnace Dust

U okviru gospodarenja otpadom, koje obuhvaća i odabir rješenja za njegovo zbrinjavanje, bilo uporabom u vlastitim tehnološkim procesima, bilo prerađen u drugim industrijskim granama ili odgovarajućom obradom prije eventualnog odlaganja na propisanim odlagalištima, u Željezari Sisak se pristupilo sustavnom istraživanju fizikalno-kemijskih karakteristika metalurškog otpada kao i njegovog ponašanja u interakciji sa okolišem. Elektropećna prašina, kao metalurški otpad, razvrstana je prema US EPA klasifikaciji iz 1980. godine u opasni tehnološki otpad oznake K061. Elektropećna prašina Željezare Sisak svrstana je u opasni otpad na temelju ispitivanja fizikalno-kemijskih karakteristika od strane za to ovlaštenog laboratorija i dodijeljen joj je ključni broj *10 02 03, sukladno pravnim propisima Republike Hrvatske. Kako zbrinjavanje opasnog otpada nije moguće izravnim odlaganjem na tlo, ukazala se potreba pronalaženja rješenja za zbrinjavanje elektropećne prašine na ekološki prihvatljiv i ekonomski opravdan način. Naime, elektropećna prašina iz procesa proizvodnje čelika u čeličani Željezare Sisak, svojedobno je služila kao dodatak pri izradi sinter-mješavine za potrebe proizvodnje sirovog željeza visokopećnim postupkom. Zbrinjavanje elektropećne prašine na taj način bilo je jedino ekonomski opravdano radi iskorištavanja njezinog željezonosnog dijela, dok ekološka prihvatljivost tog načina zbrinjavanja opasnog otpada nije bila zadovoljena. Naime, teške kovine od elektropećne prašine kao toksični sastojci samo su mijenjali svoju matičnu osnovu tj. iz elektropećne prašine bivali preseljeni i ukoncentrirani u mulj ispirača visokopećnih otpadnih plinova. Zatvaranjem proizvodnje sirovog željeza u visokim pećima, napušten je i taj, ionako nepotpun način zbrinjavanja elektropećne prašine, a novonastale količine se otada privremeno odlažu u krugu tvornice i svakim su danom sve veća opasnost za okoliš. Radi pronalaženja mogućnosti i odabira optimalnog postupka zbrinjavanja nagomilanih količina opasnog metalurškog otpada provode se sustavna istraživanja od kojih je ovdje prikazan samo dio koji se odnosi na ispitivanje sadržaja teških kovina u elektropećnoj prašini, kao i međusobne povezanosti udjela teških kovina Zn, Pb, Cd s masenim udjelom željeza čiji oksidi čine osnovu tog otpada. Ostale kovine poput bakra, kroma i nikla nisu istraživane na isti način kao Zn, Pb i Cd s obzirom da je ispitivana prašina nastala u postupcima proizvodnje ugljičnih čelika te su u njoj koncentracije tih kovina vrlo niske.Within the scope of corporate waste management, Sisak Steelworks initiated a thorough and systematic examination of physical and chemical properties of metallurgical waste and of its behaviour in interaction with the environment. Electric arc furnace (EAF) dust has been categorized as hazardous technological waste and it can not be directly disposed of to the ground / in a land fill. Therefore, it is necessary to find a way to dispose of it in an environmentally friendly and economically acceptable manner. In order to elaborate different options and chose the optimal practice for the disposal of the accumulated volumes of hazardous metallurgical waste, comprehensive and systematic research has been conducted. This paper provides only a partial survey of the research of the heavy metal Zn, Pb, Cd content in electric arc furnace dust as well. Qualitative chemical analysis of samples of electric arc furnace dust was conducted on all observed samples and the presence of Fe, Zn, Pb, Mn, Cu, Al, Ca, Mg, K, S, P, C, O and Cl was established. The results of qualitative chemical analysis of monthly average samples of electric arc furnace dust obtained by other methods established that the mass fraction of iron was between 41.08 and 48.58 %, zinc between 3.75 and 8.10 %, lead between 0.94 and 2.07 %, and cadmium between 0.010 and 0.027 %. The results of the Zn, Pb, Cd fraction analysis in the observed samples of electric arc furnace dust are considerably lower, than the content of those metals in EAF dusts presented in the available references, where the mass fraction of zinc varies between 0.14 and 50 %, lead between 0.03 and 6.8 %, and cadmium between < 0.01 and 1.8 %. Quantitative analysis of Fe, Zn, Pb and Cd fraction was carried out in grain-metrical fractions of individual samples of EAF dust as well. The results have shown that the concentrations of Fe tend to increase with smaller fraction grains compared to an average sample, whereas concentrations of Zn, Pb and Cd in the same proportion display a descending tendency. Results of the Zn, Pb and Cd fraction analysis in the EAF dust samples from Sisak Steelworks compared to the mass fraction of those metals in EAF dust from other steel mills imply that the measured concentrations of zinc, lead, and cadmium are much higher. Therefore, it is not economically viable to recycle this dust for the lead, zinc or cadmium recovery. Consequently, the disposal of this kind of hazardous metallurgical waste must first be handled in another, environmentally acceptable and economically justifiable way. Additional investigations must be carried out before the final decision is made

Teške kovine u čeličanskoj elektropećnoj prašini

Within the scope of corporate waste management, Sisak Steelworks initiated a thorough and systematic examination of physical and chemical properties of metallurgical waste and of its behaviour in interaction with the environment. Electric arc furnace (EAF) dust has been categorized as hazardous technological waste and it can not be directly disposed of to the ground / in a land fill. Therefore, it is necessary to find a way to dispose of it in an environmentally friendly and economically acceptable manner. In order to elaborate different options and chose the optimal practice for the disposal of the accumulated volumes of hazardous metallurgical waste, comprehensive and systematic research has been conducted. This paper provides only a partial survey of the research of the heavy metal Zn, Pb, Cd content in electric arc furnace dust as well. Qualitative chemical analysis of samples of electric arc furnace dust was conducted on all observed samples and the presence of Fe, Zn, Pb, Mn, Cu, Al, Ca, Mg, K, S, P, C, O and Cl was established. The results of qualitative chemical analysis of monthly average samples of electric arc furnace dust obtained by other methods established that the mass fraction of iron was between 41.08 and 48.58 %, zinc between 3.75 and 8.10 %, lead between 0.94 and 2.07 %, and cadmium between 0.010 and 0.027 %. The results of the Zn, Pb, Cd fraction analysis in the observed samples of electric arc furnace dust are considerably lower, than the content of those metals in EAF dusts presented in the available references, where the mass fraction of zinc varies between 0.14 and 50 %, lead between 0.03 and 6.8 %, and cadmium between < 0.01 and 1.8 %. Quantitative analysis of Fe, Zn, Pb and Cd fraction was carried out in grain-metrical fractions of individual samples of EAF dust as well. The results have shown that the concentrations of Fe tend to increase with smaller fraction grains compared to an average sample, whereas concentrations of Zn, Pb and Cd in the same proportion display a descending tendency. Results of the Zn, Pb and Cd fraction analysis in the EAF dust samples from Sisak Steelworks compared to the mass fraction of those metals in EAF dust from other steel mills imply that the measured concentrations of zinc, lead, and cadmium are much higher. Therefore, it is not economically viable to recycle this dust for the lead, zinc or cadmium recovery. Consequently, the disposal of this kind of hazardous metallurgical waste must first be handled in another, environmentally acceptable and economically justifiable way. Additional investigations must be carried out before the final decision is made

Oxide and nitride protective layers formed on stainless steel by thermal treatment: SEM, AES, WDS and corrosion measurements

Protective oxide and/or nitride layers on AISI 321 stainless steel were prepared by thermal treatment in air and two controlled atmospheres in a laboratory simulation of an actual technological procedure. Samples’ surface was imaged by Scanning Electron Microscopy (SEM), elemental composition of the substrates was checked by Wavelength Dispersive Spectroscopy (WDS) and depth profiles of the samples were measured by Auger Electron Spectroscopy (AES). Since protective layer thicknesses were found to be of the order of hundreds of nanometers an attempt was made to obtain some fast averaged information about layers composition by Wavelength Dispersive Spectroscopy (WDS) with appropriately adjusted primary beam energy. Electrochemical corrosion testing was also performed on samples