Fabrication of nano-layer-structure alumina powders from an alumina concentrate through an intensified Bayer process

An intensified Bayer process (high temperature, high pressure, and high alkalinity) was used to recover Al2O3 to prepare nano-layer-structure Al2O3 powders using Al2O3 concentrate separated from large-scale pyrite tailings as the raw material. This process consisted of four main steps: pretreatment of the concentrate, leaching of the Al2O3, decomposition of the sodium aluminate solution, and sintering of the decomposed product at a high temperature. The results of the orthogonal leaching experiment revealed that the relative leaching efficiency (eta R) of Al2O3 reached 98.28% under the optimum conditions: TL = 280 degrees C, tL = 90 min, cNaOH = 9 N, and L/S = 4. The results of the kinetic analysis indicated that the leaching reactions followed the unreacted-shrinkage-nuclearreaction model controlled by solid film diffusion. After decomposition and sintering under proper conditions, fine Al2O3 powders composed of many tiny clusters with a nano-layer structure were finally prepared. The purity of the Al2O3 products reached 99.23%, and all of the chemical compositions of the Al2O3 products nearly met the grade I quality standard requirement in China. Additionally, TiO2 was effectively enriched to 9.74% in the leaching residue. This study demonstrated that the concentrates with abundant reserves were an important Al2O3 resource.