A promising green process for synthesis of high purity activated-alumina nanopowder from secondary aluminum dross

Abstract

Abstract More than one million tons of secondary aluminum dross as a hazardous waste are produced by aluminum manufacturers per year throughout the world, which imposes high disposal costs and serious environmental problems. As secondary aluminum dross is considered as an alumina-rich inorganic waste, this study aims to propose a promising approach for clean production of activated-alumina as a widely-used adsorbent, catalyst and catalyst support. In this paper, synthesis and characterization of high crystalline activated-alumina nanopowder from secondary aluminum dross using a novel five-step leaching-based process are presented. To optimize the process, various parameters of dross particle size, leaching time, leaching temperature, acid concentration, and liquid-to-solid ratio were studied using One-Factor-At-a Time approach (OFAT). For the following optimum leaching conditions: particle sizes between 38 and 75 μm, leaching time of 120 min, leaching temperature of 85 °C, acid concentration of 5 M, and the liquid-to-solid ratio of 20 ml/g, the extraction efficiency of alumina was around 83%. The leach liquor was purified by adding 2 N NaOH resulting in sodium aluminate-rich solution. The purified liquor was treated by adding HCl to precipitate Al(OH)3, and the Al(OH)3 was then washed and calcined at 700 °C for 2 h to obtain alumina. Chemical composition, mineralogical phases, chemical bonds, morphology, and particle size distribution of the as-synthesized activated-alumina were determined using X-ray fluorescence (XRF), X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and dynamic light scattering (DLS), respectively. The as-synthesized activated-alumina exhibited 97.61% purity. Its XRD pattern showed mainly characteristic peaks of gamma phase of alumina. Morphological study by FESEM revealed that the as-synthesized alumina particles have rounded-corner shape. The crystal and average particle size values were about 18.47 and 513 nm, respectively.