Gibbsite to Boehmite Transformation in Strongly Caustic and Nitrate Environments

Abstract

The transformation of gibbsite to boehmite in strongly caustic solutions was studied using quantitative X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy techniques. Under hydrothermal conditions, we identified two transformation mechanisms: (1) dehydration and in situ nucleation and (2) dissolution and nucleation. If the reaction container was not completely sealed, dehydration of gibbsite followed by in situ nucleation of boehmite was the preferred mechanism. Boehmite produced fibrous boehmite particles within the amorphous matrix of the decomposed gibbsite particles, which exhibited a poorly crystalline structure and a smaller size than the initial gibbsite particles. In a closed environment, the preferred mechanism was the dissolution of gibbsite along (001) planes. The final boehmite particles were not morphologically related to the initial gibbsite particles and could be many times larger than the gibbsite particles.

Experimental Simulation of Long Term Weathering in Alkaline Bauxite Residue Tailings

“…This conclusion is consistent with the conversion mechanisms described elsewhere [23,46,47]. Calcite and sodalite precipitation were not observed in the fused silica capillary experiments; changes in calcite:anatase ratio in Table 2 indicate that this is a slower reaction and smaller in magnitude than the boehmite precipitation reaction.…”

“…The n values of 0.8-1.2 observed for gibbsite dissolution (Table 4) are consistent with first-order reaction kinetics (n = 1). Contracting area kinetics, with an n value of 1.04, and contracting volume kinetics, with an n value of 1.08, would also be feasible explanations for the observed n values and are consistent with the transformation of gibbsite to boehmite as a dissolution-precipitation mechanism [46,47]. Table 3.…”

“…Gibbsite and boehmite dynamics reflect a dissolution-precipitation mechanism based on observed rates of transformation in Figures 3-6, and previous studies of hydrothermal conversion [46,47]. This would aid in lowering pH, EC, and TA by diluting the supernatant (Equation (7)).…”

Surface morphology control of thin films prepared by solution processes and its application

“…It is known that gibbsite readily dissolves at moderate hydroxide concentrations and moderate temperatures, while boehmite dissolution requires more rigorous conditions and generally is kinetically slow. Gong et al 22) found that gibbsite [¡-Al(OH) 3 ] dissolved into a basic solution with sodium hydroxide and then crystallized as boehmite. Consequently, in the pseudoboehmite nanocrystal formation process of the present study, alumina constituents in the precursor amorphous gel film first dissolve in water.…”

Effect of Cations on Aluminum Speciation Under Alkaline Conditions

“…Fresh HLW slurries can self-heat due to radioactive decay, frequently reaching temperature of 100 -150 °C. 4 We performed a series of experiments designed to examine the effect of other common cations present in the HLW on the phase of aluminum formed.…”