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2011, vol. 65, br. 3, str. 271-277
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Dobijanje prelaznih faza aluminijum-oksida polazeći od natrijum-aluminata primenom Bajerovog postupka
Obtaining of transition phases of alumina starting from sodium aluminate in Bayer process
aFabrika glinice 'Birač' AD, Zvornik, Republika Srpska, Bosna i Hercegovina + Univerzitet u Istočnom Sarajevu, Tehnološki fakultet, Zvornik, Republika Srpska, BiH bUniverzitet u Novom Sadu, Tehnološki fakultet
e-adresa: ljunik@uns.ac.rs
Projekat: Projekat Ministarstva nauke Republike Srbije, br. 142059 i III45021
Keywords: Bayer liquor; Bayerite; η-Al2O3; γ-Al2O3; Surface area
Sažetak
Polazni aluminijum-hidroksidni i aluminijum-oksihidroksidni prahovi za dobijanje prelaznih faza Al2O3 su dobijeni u postupku neutralizacije natrijum-aluminata, dobijenog u klasičnom Bajerovom postupku, 1 M rastvorom sumporne kiseline. U zavisnosti od koncentracije polazog rastvora, trajanja reakcije neutralizacije i pH rastvora, sintetisani su prahovi različitog faznog sastava, uglavnom višefazni, ali sa dominantnom fazom gibsita, bajerita ili bemita. Pored toga, različiti uslovi sinteze uticali su na dobijanje prahova različite morfologije i specifične površine. Posle termičke obrade prahova na 500ºC u trajanju od 30 min, u zavisnosti od njihovog polaznog sastava i morfoloških karakteristika dobijene su prelazne faze aluminijum-oksida i to η - i γ-Al2O3, specifične površine od 264 do 373 m2/g. Pri tome je pokazano da se zagrevanjem bajerit i pseudobemit transformišu u η-fazu, a gibsit u γ-fazu, zadržavajući morfologiju polaznog praha.
Abstract
Transition (active) phases of alumina were synthesized starting from sodium aluminate solution prepared out of Bayer liquor. The neutralisation of sodium aluminate solution was performed by sulphuric acid. Powder X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and low-temperature nitrogen absorption studies were employed to trace the formation of the transition phases of alumina. The results show that the properties of the powders (phase composition, morphology and specific surface area) are strongly influenced by the initial pH value of the system, as well as by the duration of neutralisation step. It is possible to obtain powders with heterogeneous structure with dominant phase of bayerite, gibbsite or boehmit by tuning the pH and concentration of the starting sodium aluminate solution. The transition (active) phases of alumina (η- and γ-alumina) with high specific surface area (264-373m2/g) are formed through the thermal dehydratation of aluminium hydroxide (bayerite and gibbsite) and aluminium oxyhydroxide (boehmite or pseudoboehmite) at the temperature of 500°C. Namely, bayerite and pseudoboehmite transforms to η-phase of alumina upon heating, while gibbsite transforms to γ-phase, maintaining the parent morphology.
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