Thermally Activated Al(OH)3 Part II—Effect of Different Thermal Treatments

Abstract

In this paper, the thermal decomposition of crystalline Al(OH)3 was studied over the temperature range of 260–400 °C for particles with a size between 10 and 150 µm. The weight losses and thermal effects occurring in each of the dehydration process were assessed using thermogravimetry (TG) and differential scanning calorimetry (DSC) thermal analysis. X-ray diffraction (XRD) patterns, refined by the Rietveld method, were used for mineral phase identification, phase composition analysis, and crystallinity degree determination. Moreover, the particle size distributions and their corresponding D10, D50, and D90 numeric values were determined with a laser analyzer. We observed a strong relationship between the calcination temperature, the initial gibbsite grade particle size, and the crystallinity of the resulting powders. Hence, for all endothermic effects identified by DSC, the associated temperature values significantly decreased insofar as the particle dimensions decreased. When the gibbsite was calcined at a low temperature, we identified small amounts of boehmite phase along with amorphous new phases and unconverted gibbsite, while the powders calcined at 400 °C gradually yielded a mixture of boehmite and crystalized γ-Al2O3. The crystallinity % of all phase transition products declined with the increase in particle size or temperature for all the samples.

Scandium Recovery from Aqueous Solution by Adsorption Processes in Low-Temperature-Activated Alumina Products

“…The most important characteristic properties of low-temperature-activated alumina products are BET specific surface, Langmuir specific surface, average pore width, mineralogical phases: Gibbsite, Bayerite, Boehmite, Gamma-Al2O3 and their crystallinity (or amorphous phase content) and the particle size distribution (naming each product). Previous studies [ 54 , 58 ] show that all of these characteristics are controlled by two parameters (calcination temperature and particle size), which act throughout the thermal program of each group of samples. All these characteristic properties are given in Table 1 and Table 2 .…”

“…Sample GDAH-04-300 (fraction 0–10 µm), highlighted for the increased thermal stability and good adsorption capacity of the low-temperature-activated alumina products, was selected as a working model for all measurements included in previous papers concerning adsorption [ 60 ]. Actually, the absorption capacities of these samples represent the maximum capacities for all the low-temperature-activated alumina products saturated with Sc(III) from a Sc(III) solution with a concentration of 10 mg/L at 298 K. Moreover, the higher adsorbent capacity, assumed for samples GDAH-03-300 and GDAH-04-300, is a direct effect of both mechanical activation (milling and classification) and thermal activation as driving factors in the conversion process of the aluminium hydroxide into low-temperature-activated alumina products [ 54 , 58 , 59 , 60 , 64 , 65 ].…”

“…The dependence is so evident that the data for samples GDAH-03 (under 20 µm) and GDAH-04 (under 10 µm) are completely different from the same parameters for samples GDAH-01 and GDAH-02. The particular properties of these low-temperature-activated alumina products have been studied in our previous papers [ 54 , 58 , 59 , 60 , 65 ]. Therefore, all the scandium adsorption data can be analysed on the basis of rigorous knowledge about the sample mineralogy and chemistry, as well as about all other sample properties.…”

“…Data procurement in all categories of measurements required by this work is similar to the one used in our previous papers, including the analysis equipment [ 54 , 58 , 59 , 60 ].…”

“…The present paper studies scandium adsorption from pure scandium nitrate solutions in low-temperature-activated alumina products, whose properties have been largely presented in our previous papers [ 54 , 58 , 59 ]. The precursor of the low-temperature-activated alumina product is the aluminium hydroxide dried, milled and classified, and manufactured at Vimetco Alum SA Tulcea, Romania, after the implementation of the project “Endow the Research and Development Department of SC ALUM SA Tulcea with independent, efficient research facilities to support the economic competitiveness and business development”, a project co-funded by the European Regional Development Fund through the Competitiveness Operational Program 2014–2020.…”