Abstract
Assessing the potential uses as industrial mineral, bauxite from Débélé, Guinea, has been characterised by chemical and mineralogical analyses, the determination of the amorphous content, the rate of portlandite consumption in an aqueous solution, the strength activity index, and the thermal behaviour up to 1200°C. It was evidenced that the raw sample is gibbsite-rich type bauxite with about 45.06 wt% of alumina, 23.80 wt% of iron oxide, and 1.74 wt% of silica. It meets the chemical composition required for bauxites used for refractory cement. During heating, the raw bauxite undergoes high densification with low linear shrinkage, motivating a potential use in dense ceramic compositions with high thermal stability. Also, the heating at only 600°C gives a significant pozzolanic activity in combination with Portland cement. The correlation between the pozzolanicity, the amorphous phase content, and the specific surface area indicated that the raw and the calcined materials present an interesting reactivity for using them in alternative cement formulations.
Highlights
Bauxite is a source of diverse aluminum ores, with a high content of hydrated aluminum oxides such as gibbsite, boehmite, and diaspore
As for the pozzolanic degree, the bauxite powder sample exhibit a value of 748 mg of calcium hydroxide (CH) fixed per gram of sample, which is close to the lower limiting value of 700 mg reported in the ASTM C618-94 standard for pozzolanic material
The characterisations of bauxite from Débélé show the presence of mostly alumina hydroxide, and iron oxide, and silica and titanium oxide are in small quantities
Summary
Bauxite is a source of diverse aluminum ores, with a high content of hydrated aluminum oxides such as gibbsite, boehmite, and diaspore. Gibbsite is mostly found in the clayed fraction of bauxite, as a secondary phase It has many valuable effects on ceramic and cement applications due to the unique properties provided by alumina. It was found that the replacement of Portland cement by gibbsite up to 12.5 wt% contributes to the significant reduction of the setting time of pastes, the two times increase of the mechanical strength, and the reduction of porosity They are related to the high amount of ettringite crystals in the matrix that is favoured by the presence of gibbsite [5]. Bauxite and bauxite derivatives have been used in valuable refractory ceramics, ceramic, and glass products It is from the unique properties induced by the different forms of alumina obtained during the thermal process. Bauxite found further application in water treatment, satisfactory elimination of certain toxic elements such as fluorides was obtained thanks to the improvement of adsorbent properties through the chemical and heat activation [6]
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