Testiranje možnosti vezave ogljikovega dioksida v rdečem mulju, preostalem po ekstrakciji glinice iz boksita

Borštnar, Petruša (author), Dolenec, Matej (mentor), Tavčar, Gašper (comentor), Herlec, Uroš (comentor)

Rdeči mulj, ki nastaja kot odpadni produkt pri predelavi boksitne rude za pridobivanje glinice, t. j. Bayerjevem procesu, predstavlja možnost za industrijsko mineralizacijo CO2 (vezavo v industrijsko proizvedene minerale). V magistrski nalogi smo želeli proučiti vezavo CO2 na Fe2+, pridobljenem iz hematita v rdečem mulju. Vzorce rdečega mulja iz deponije v Podgorici v Črni gori z zrnavostjo pod 63 µm smo analizirali z metodami rentgenske praškovne difrakcije, rentgenske fluorescenčne spektroskopije, vrstične elektronske mikroskopije in z masno spektrometrijo z induktivno sklopljeno plazmo z namenom določitve mineralne in kemične sestave. Za ugotovitev porazdelitve velikosti zrn smo izvedli lasersko granulometrično analizo. Ekonomsko ugodno metodo za redukcijo železa iz hematita v rdečem mulju predstavlja redukcija s pomočjo mikroorganizmov, zato smo izvedli poskus z uporabo bakterij Bacillus spp. in Pseudomonas spp. Pri metabolizmu bakterij nastanejo različne organske kisline, ki s kovinskimi ioni tvorijo topne komplekse. Ena izmed njih je mlečna kislina, zato smo testne poskuse mineralizacije izvedli z železovim laktatom. Opravili smo tri reakcije z laktatom, in sicer pri atmosferskih pogojih, pri povišanem tlaku v deionizirani vodi in v deionizirani razplinjeni vodi. Nastale produkte smo okarakterizirali z rentgensko praškovno difrakcijo, ramansko spektroskopijo in Mössbauerjevo spektroskopijo. Ugotovili smo, da je za reakcijo laktata s CO2 v raztopini nujno potrebno okolje brez kisika, tako v zraku kot tudi v vodi, saj v vodi raztopljen kisik takoj oksidira dvovalentno železo in onemogoči vezavo CO2 in posledično tvorbo železovega karbonata. V nadaljevanju raziskav bi bilo smiselno poskusiti vezavo CO2 na kisline, kot sta npr. glukonat in acetat, ki nastanejo pri pretvorbi drugih sladkorjev v bakterijskem presnovnem procesu. Preliminarni rezultati redukcije železa z bakterijami so pokazali, da proces bioizluževanja železa v rdečem mulju poteka, kar predstavlja obetavno in ekonomsko ugodno metodo, ki je primerna za nadaljnje raziskave na tem področju. Glede na visoko vsebnost hematita in ob ustrezno nizki ceni redukcije Fe3+ v Fe2+ v hematitu ima rdeči mulj izjemno velik potencial za uporabo v industrijski mineralizaciji CO2, vendar bi bile potrebne nadaljnje raziskave tudi drugih ekonomsko upravičenih metod za redukcijo železa.

• Language: Slovenian
• Keywords: skladiščenje CO2, rdeči mulj, hematit, laktat
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-120043
• COBISS.SI-ID: 31510787
• Publication date in RUL: 15.09.2020

Secondary language

• Language: English
• Title: Examining possibility of carbon dioxide sequestration with the red mud residue from alumina extraction from bauxite

Abstract

Red mud, a highly alkaline waste generated in the production of alumina from bauxite, ie. the Bayer process, can be used as a valuable feedstock for industrial CO2 capture. In the presented master's thesis, we wanted to examine the potential of red mud for carbon sequestration to Fe2+ from hematite, which is the main component of red mud. In order to determine the mineral and chemical composition, samples of red mud from a landfill in Podgorica, Montenegro, with fractions below 63 μm were analyzed with X-ray powder diffraction, X-ray fluorescence spectroscopy, scanning electron microscopy and inductively coupled plasma mass spectrometry. The laser granulometric analysis was performed to determine the grain size distribution. An economically feasible method for the reduction of iron from hematite in red mud is bioleaching with bacteria, thus we conducted an experiment using Bacillus spp. and Pseudomonas spp. During bacterial metabolism, various organic acids are produced that form complexes with metal ions. One of those is lactic acid, therefore mineralization experiments were performed on iron lactate. We performed 3 reactions with lactate: under atmospheric conditions, under pressure conditions in deionized water, and under pressure conditions in deionized degassed water. The resulting products were characterized by X-ray powder diffraction, Raman spectroscopy, and Mössbauer spectroscopy. It was found that an oxygen-free environment is essential for the reaction of lactate with CO2 in solution. Furthermore, it is important to remove oxygen from the water, as dissolved oxygen can cause iron oxidation and thus prevent the binding of CO2. For future work, reaction of CO2 with acids, such as e.g. gluconate and acetate, which are formed during the conversion of other sugars during bacterial metabolism, may be considered. Preliminary results of the iron reduction by bacteria have shown that bioleaching is taking place, which is a promising and cost-effective method, suitable for further research in this area. Due to the high content of hematite in red mud and together with a correspondingly low cost of reducing Fe3+ to Fe2+ in hematite, red mud has a huge potential for industrial CO2 mineralization. Further research into economically viable methods for iron reduction is needed.

• Keywords: CO2 storage, red mud, hematite, lactate