Dehydroxylation Kinetics of Alunite

Abstract

In this study, dehydroxylation of alunite was studied. On the basis of thermogravimetric results and sulfur loss, dehydroxylation of alunite occurs from 508 to 577 °C. In this temperature range, temperature and time, as well as their interaction, have the greatest effect on alunite conversion (dehydroxylation) with 99.85% contribution, while the contribution of particle size was only 0.11%. Dehydroxylation increased with time up to a maximum and reached a plateau beyond that time. The time required (t max) for maximum dehydroxylation (i.e., maximum conversion) for various temperatures was different and showed decreasing trend with increasing temperature. Kinetic studies below t max showed that dehydroxylation of alunite follows Avrami–Erofeev models with different reaction indexes. In the temperature range of 508–534 °C, dehydroxylation occurs according to the model α = e((−1.77×1011e–23314/T )(t–0.9r 1/3))1.5 , while in the 534–575 °C temperature range, the α = e((−11065.64e–9924/T )(t–0.213r 1/3) is applicable.

Study of the dehydroxylation of kaolinite and alunite from a Mexican clay with DRIFTS-MS

“…This transformation is followed by change in the coordination of the octahedral Al from Al VI to a combination of Al IV and Al V (Liu and Zhao, 2010;Sperinck et al, 2011;White et al, 2011). The dehydroxylation temperatures of kaolinite and alunite are comparable to reports from other authors (Kavak, 2009;Ilićet al, 2010;Sahnoune et al, 2011;Tong et al, 2012;Ece et al, 2013;Mohammadi & Salarirad, 2013;Ptáček et al, 2013), considering that the weight losses of 450 to 610°C of the TG/DTA results (Fig. 4) include the released -OH{16 } groups of kaolinite and alunite.…”

“…The raw clay identified as KN was fractionated to sizes between 180 and 246 μm and was characterized chemically, mineralogically and thermogravimetrically. Particle size was maintained because it does not contribute significantly to the dehydroxylation process (Mohammadi & Salarirad, 2013). In addition, the clay was analysed, by infrared (IR) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM), in its natural state and after heating at 550°C and 1000°C for 2 h in a muffle furnace (NOVATECH, Mexico) to obtain the K550 and K1000 samples, respectively.…”

Optimizing Seed‐Induced Nucleation for Enhanced Al(OH)3 Crystal Precipitation from Supersaturated Potassium Aluminate Solution

“…This innovative approach offers advantages such as reduced energy consumption and environmental pollution when compared to conventional methods. [ 4,5 ] In this process, at the low leaching temperature of 343.15 K and 50 wt.% KOH solution (sub‐molten salt), most potassium alunite resources from alunite tailings could be extracted into the alkaline solution efficiently while the kaolinite and quartz impurities are still kept in the leaching residues. The alumina‐rich potassium aluminate liquor is separated from the leaching solution, and then the Al(OH) 3 product could be obtained by using a seeded precipitation process from the supersaturated potassium aluminate solution.…”