Synthesis Of Magnesium Aluminate Spinel From Waste Activated Alumina

Magnesium aluminate spinel is a unique stable compound in MgO-Al2O3systemand well-known material due to its excellent properties. It has been widely used invarious applications. In this research, waste activated alumina and basic magnesiumcarbonate were used as raw materials to synthesize magnesium aluminate spinel bydouble step firing process. Effects of different ratio of Al2O3to MgO, sinteringtemperature, soaking time and mineralizers on the formation and properties of spinelwere investigated to determinate the optimal one. Owing to the recycle of wasteactivated alumina, our research can be considered as a great significant project ofenvironmental protection and has economic benefit.XRD, SEM were used to characterize the crystalline phases and microstructures ofsintered samples. Rietveld quantification analysis was performed to calculate thecontent of crystalline phases. Moreover, the properties of all sintered samples werecharacterized in terms of bending strength, bulk density, apparent porosity and waterabsorption.The research results show that γ-Al2O3, which is the main crystalline phase ofwaste activated alumina, has high activity and thus can promote the formation ofmagnesium aluminate spinel, lower sintering temperature and soaking time andoptimize the performance of the sintered samples by solid-state reaction. XRD resultsshow that MgAl2O4and MgO are formed in different formula samples, and MgAl2O4which belongs to cubic crystal system and has a space group of Fd3m with octahedral orirregular shape is the main crystalline phase with its content of between89.0wt%and100wt%.The content of spinel reaches to a peak amount of100wt%when the mass ratioof Al2O3to MgO is2.9. The prescription H consisting of57wt%waste activated aluminaand43wt%basic magnesium carbonate, is determined to be the optimal one. MgAl2O4is the unique formed in samples with different sintering temperature and soaking time. The best processing condition is to be sintered at1560℃for3h to obtain spinel with thecorresponding spinel bulk density of2.93g/cm3, bending strength of117.67MPa,apparent porosity of17.58%. Mineralizer such as TiO2,Cr2O3and ZrO2with properamount, have a beneficial effect on the formation of magnesium aluminate spinel solidsolution and the densification of samples, and decrease of porosity. The optimal amountof TiO2,Cr2O3and ZrO2is determined to be2wt%,1.5wt%,2wt%separately.