Effects of roasting and NH 4 Cl catalysis on the direct electrotransformation products from an AlCl 3 solution

• Published in: Materials research express Vol. 8; no. 3; p. 35508
• Main Authors: Han, Xiuxiu, Zhang, Ting-an, Lv, Guozhi, Pan, Xijuan, Fu, Daxue
• Format: Journal Article
• Language: English
• Published: 01.03.2021
• ISSN: 2053-1591; 2053-1591
• DOI: 10.1088/2053-1591/abeecb

Abstract Contemporary processes for extracting alumina from fly ash involve various disadvantages, including high-energy consumption, heavy slag discharge, and severe equipment corrosion, so a new method for extracting alumina via electrotransformation was developed in this work. This novel method reduced slag discharge, enabled recycling, and produced no acid or alkali waste. The theoretical solution pH associated with Al(OH) 3 precipitation and the actual solution pH during electrotransformation were also compared herein. Differential thermogravimetric analysis was performed for the direct electrotransformation products generated with and without NH 4 Cl as a catalyst; the activation energy and reaction order of these reactions revealed large fluctuations. The effects of the roasting temperature on the phase, morphology, D(50), and D(90) of the roasting products were also studied. The results indicated that the solution reached the theoretical pH (4.7) of complete Al(OH) 3 precipitation in a short time when NH 4 Cl was implemented as a catalyst. Additionally, the D(50) and D(90) of the roasting products were nearly ten times higher when NH 4 Cl was used, relative to when it was not, reaching 227.1 and 519.6 μ m, respectively. The activation energies of each reaction in the electrotransformation and roasting process were also reduced in the presence of the NH 4 Cl catalyst. Between 100 °C–250 °C, the physical adsorption of water occurred, and some of the structural water of the electrotransformation products generated with NH 4 Cl were removed in an endothermic reaction (reaction order, n1 = 0.43; activation energy, E1 = 2.13J mol −1 ). At temperatures between 250 °C–500 °C, the nitrogen-containing substances were removed in another endothermic reaction (reaction order, n2 = 0.4697; activation energy, E2 = 5.316J mol −1 ). Increasing the roasting temperature was beneficial for improving the crystal form of the roasting products, and the reduced electrotransformation products appeared more compact after roasting.