Carla Napoli Barbato

Synthesis and Characterization of Sodalite and Cancrinite from Kaolin

Cancrinite and sodalite are characterized by high capacity of adsorption due to its porous structure. The aim of this work was to use kaolin from Borborema-Serido/Brazil as a source of aluminium and silicon to hydrothermal synthesis of sodalite and cancrinite and to evaluate the best conditions to the formation of these phases. Therefore, kaolin was heated at 700 and 900 °C for 2 h in order to transform kaolinite in metakaolin. Thereafter, experiments with the calcined kaolin’s were carried out between 150 and 230 °C for 30–270 min on a stainless steel pressure vessel using NaOH, Na2CO3 and H2O. The samples were characterized by X-ray diffraction, nuclear magnetic resonance, scanning electronic microscopy, thermogravimetry, and Zeta potential. The most pure sodalite phase was obtained at 230 °C, with the kaolin/NaOH ratio of 1:1, low concentration of Na2CO3 and smaller time of synthesis (30 min). On the other hand, for the synthesis of cancrinite phase at 230 °C, it was necessary to use kaolin heated at 900 °C, a longer time of synthesis (270 min) and a higher concentration of Na2CO3.

Mechanochemical Activation of Bauxite

The crystallized layer that compounds the bauxite’s geological profile from NE Para was ore dressed through the processes of crushing, screening, washing and grinding, in order to reach the same size distribution of that in the alumina production industry. After the preparation process, the sample (90%, < 0.21 mm) containing 5.3% reactive silica and 47.2% available alumina was submitted to mechanochemical activation with different kinds of reagents (CaO, Ca(OH)2, CaCO3, CaO+HCl), in different concentrations, which resulted in the formation of a calcium aluminum hydrosilicate (hydrogarnet). This phase was formed in the first 30 min of grinding with the use of CaO and Ca(OH)2. However, chemical characterization showed that the principal phase obtained, katoite hydrogarnet, had high aluminum content in its chemical composition thus proving that its formation is not good for the Bayer process.

Characterization and Ore Dressing of Bauxite from Brazil

The Bauxite from North Brazil is characterized by a geological profile with different layers. The differences among these layers are percentage of bauxite constituents (gibbsite, kaolinite and hematite). Nowadays, only one layer is used for alumina production by Bayer process, the commercial or crystallized bauxite. This work intended to characterize and to ore dress crystallized bauxite (CB), amorphous crystallized (MB) and nodular bauxite (MNB) from Para to make them usable in the Bayer process. The ore dressing was developed by mechanochemical activation with an alkaline reagent in different concentrations and conditioning time. After ore dressing, the samples were submitted to characterization by X-ray diffraction (XRD), X-ray fluorescence (XFR) and rheological characterization. CB and MB ore dressing products were characterized by an increase of mass ratio Al2O3available/SiO2reactive and it was observed that the total silica of MNB, after ore dressing, decreased around 13%. These results were a strong indication that these bauxites could be used in the Bayer process.

Avaliação estatística das variáveis que influenciam a viscosidade da polpa de bauxita do pará com alto teor de SiO2 reativa

Bauxite from Para is constituted by the following layers: nodular (BN), nodular crystallized (BNC), crystal

Influence of Solids Concentration, Particle Size Distribution, pH and Temperature on Yield Stress of Bauxite Pulp

In Northern Brazil, bauxite pulp is transported through pipelines to the plant where alumina is produced. In slurry transportation through pipelines, knowing the yield stress value is essential for the pumps and pipeline design. Yield stress is the minimum shear stress and corresponds to the first evidence of flow. This rheological property is influenced by factors, such as: particle form, temperature, particle size distribution and interaction among the particles. Within the context above, the objective of this work is to verify the influence of solids concentration, particle size distribution produced by different grinding time, temperature and pH on the yield stress of bauxite pulp. It was verified that the yield stress of bauxite slurry increases as solids concentration and grinding time go up and decreases with temperature and pH.