Termične spremembe mineralov pri kalcinaciji rdečega blata in vpliv na njegovo reaktivnost : magistrsko delo

Štruc, Miha (author), Dolenec, Sabina (mentor), Dolenec, Matej (comentor)

Rdeče blato je trden ostanek, ki nastaja med proizvodnjo aluminija iz boksita pri Bayerjevem procesu. Vsako leto na novo proizvedemo 100 milijonov ton rdečega blata. Do danes se ga je na svetu proizvedlo že več kot tri milijarde ton. V večini je sestavljeno iz različnih aluminijevih oksidov in hidroksidov, kot so gibbsit, boehmit in diaspor ter železovih oksidov, kot je hematit, prisotni pa so lahko tudi kalcit, kremen, rutil in ilmenit. V manjših količinah vsebuje tudi elemente kot so vanadij (V), krom (Cr), mangan (Mn), baker (Cu), kadmij (Cd), nikelj (Ni), cink (Zn), svinec (Pb), magnezij (Mg), in kalij (K) ter elemente redkih zemelj. Njegovo shranjevanje predstavlja velik okoljski problem, zaradi česar se iščejo načini recikliranja in njegove ponovne uporabe. Glavni namen magistrske naloge je bila določitev termičnih sprememb mineralov v rdečem blatu pri različnih temperaturah kalcinacije ter vpliva na njegovo reaktivnost. Vzorce smo kalcinirali pri temperaturah 400, 500, 600, 700, 800, 900 in 1000 °C. Temu so sledile rentgenska praškovna difrakcijska analiza z Rietveldovo metodo, s katero smo določili mineralno sestavo vsakega vzorca, meritve specifične površine s plinsko sorpcijo (BET), meritve velikosti delcev z lasersko granulometrijo ter določanje reaktivnosti z izotermno kalorimetrijo. Ugotovili smo, da z naraščanjem temperature narajščajo količine perovskita, gehlenita in nefelina. Aluminijevi oksidi kot so gibbsit, boehmit in diaspor razpadejo pri 400 °C, kalcit pa do temperature 800 °C. Goetit z višanjem temperature razpade v hematit in vodo Meritve specifične površine so pokazale, da slednja narašča do temperature kalcinacije 500 °C, potem pa do temperature 1000 °C pada. Velikost delcev se z višanjem temperature veča. Najbolj reaktivni vzorci so vzorci kalcinirani pri temperaturah nad 700 °C. Bistveni parametri, ki vplivajo na reaktivnost vzorcev, so vsebnost amorfne faze, vsebnost kankrinita in velikost delcev.

• Language: Slovenian
• Keywords: rdeče blato, termične spremembe, reaktivnost, velikost delcev, specifična površina
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: Ljubljana
• Publisher: [M. Štruc]
• Year: 2022
• Number of pages: XIV, 53 f.
• PID: 20.500.12556/RUL-140375
• UDC: 55
• COBISS.SI-ID: 131620099
• Publication date in RUL: 14.09.2022

Secondary language

• Language: English
• Title: Thermal phase transformations during red mud calcination and influence on its reactivity : master's thesis

Abstract

Red mud is a solid residue produced during the production of aluminum from bauxite in the Bayer process. 100 million tons of red mud is produced every year. To date, more than three billion tons have been produced in the world. It mostly consists of various aluminum oxides and hydroxides, such as gibbsite, boehmite, and diaspore, and iron oxides, such as hematite, but calcite, quartz, rutile, and ilmenite may also be present. In smaller quantities, it also contains elements such as vanadium (V), chromium (Cr), manganese (Mn), copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), zinc (Zn), magnesium (Mg) and potassium (K), as well as rare earth elements. Its storage is a major environmental problem, which leads to the search for ways to recycle and reuse it. The main purpose of the master's thesis was to determine the thermal changes of minerals in red mud at different calcination temperatures and the effect on its reactivity. The samples were calcined at temperatures of 400, 500, 600, 700, 800, 900 and 1000 °C. This was followed by X-ray powder diffraction analysis using the Rietveld method, which was used to determine the mineral composition of each sample, specific surface area measurements by gas sorption (BET), particle size measurements by laser granulometry, and determination of reactivity by isothermal calorimetry. Results showed that the amount of perovskite, gehlenite and nepheline increases with increasing temperature. Aluminum oxides such as gibbsite, boehmite and diaspore decompose at 400 °C, and calcite up to a temperature of 800 °C. Goethite decomposes into hematite and water as the temperature increases. Measurements of the specific surface area showed that the specific surface area of the samples increases up to the calcination temperature of 500 °C, but then decreases until the temperature of 1000 °C. The particle size increases with increasing temperature. The most reactive samples were samples calcined at temperatures above 700 °C. The essential parameters that influenced the reactivity of the samples are the content of the amorphous phase, the content of cancrinite and particle size.

• Keywords: red mud, thermal transformations, reactivity, particle size, specific surface are