Valorization of Aluminum Chips into gamma-Al2O3 and eta-Al2O3 with High Surface Areas via the Precipitation Route

In this study, pseudo-boehmite and bayerite precursors have been prepared from aluminum chips collected from metal manufacturing industry in the region of Sfax, Tunisia for the production of gamma-Al2O3 and eta-Al2O3, respectively. The alkaline attack of the scraps with 2 M NaOH solution provides the sodium aluminate solution which was neutralize with 2 M HNO3 acid solution at room temperature to different pH values of 6-10. The neutralization pH is an important parameter that controls the nature of the precipitated phase. At pH 6, the XRD pattern of the as-dried sample showed the characteristic peaks of well crystallized bayerite. The increase of the neutralization pH to 7-9, there is precipitation of pseudo-boehmite. At pH 10, we obtained a mixture of bayerite and pseudo-boehmite. Through the calcination of bayerite at 400 degrees C, eta-Al2O3 was obtained with specific surface area of 455 m(2)/g, whereas the calcination of pseudo-boehmite leads to globular aggregate made by fibrous crystals of gamma-Al2O3. During the structural transformation of pseudo-boehmite into gamma-Al2O3 and bayerite into eta-Al2O3 a portion of the aluminum atoms migrate from octahedral sites to tetrahedral sites in the alumina lattice. The tetrahedral to octahedral Al ratios are about 1-3 and 1-4 for gamma-Al2O3 and eta-Al2O3, respectively.