Red Mud To Prepare Multi-stage Porous Aluminum / Iron Functional Oxide Process, Performance And Application

Red mud,a reddish-brown strongly alkaline solid waste,is the by-product of alumina production following extraction of the metal from bauxite ore via the Bayer process.With the increasing demand for alumina worldwide,the generation of red mud has also been dramatically increased every year.Up to date,however,the red mud produced from these industries is generally stacked in open yard,leading to much cultivated land occupied.It is thus extremely urgent to cope with the increasingly environmental problems brought about by red mud both in academia and industry.Presently,red mud has been applied preliminarily in catalysis,building materials,fillers,sorbents and valuable metals recovery.As known,red mud still contains more or less of aluminum and a large amount of iron.So this thesis has thus been focused on the novel and high value utilization of aluminum and iron leached from red mud.The three-dimensional(3D)metal oxide nanostructures were successfully synthesized via a mild hydrothermal route,which was further evaluated for application in adsorption.The work mainly includes the flowing two aspects.Firstly,we report for the first time to the best of our knowledge,a facile hydrothermal conversion of the red mud into the hierarchical porous y-AlOOH microspheres,followed by a thermal conversion which led to the ?-Al2O3 microspheres.The NaAlO2 leached from the red mud is hydrothermally treated at 150 ? for 6.0 h in the presence of urea,resulting in the hierarchical porous y-AlOOH microspheres,with a specific surface area of 76.8 m2 g-1,and ca.93%of which have a diameter within the range of 3.5-7.5 ?m.The subsequent mild thermal conversion at 600 0C for 2.0 h brings about the hierarchical porous ?-Al2O3 microspheres with a specific surface area of 158.6 m2 g-1,and ca.92%of which bear a size of 3.0-7.0 ?m.Both the porous y-AlOOH and ?-Al2O3 microspheres exhibit satisfactory adsorption for Methy Blue(MB)from the mimetic wastewater,with the maximum adsorption capabilities of 953.0 mg g-1 and 1587.6 mg g-1,respectively,better than most of the reported results.The possible formation mechanism,i.e.bubble induced self-assembly for the hierarchical porous ?-AlOOH microspheres is proposed,and the adsorption mechanism of MB is also discussed in detail.In addition,the porous ?-Al2O3 microspheres also indicated satisfactory adsorption for Congo red(CR)from corresponding mimetic wastewater.Secondly,with the target on the possible utilization of the relatively high quantity of iron from red mud,preliminary study has also been performed.The Fe2O3·xH2O microspheres were obtained via a facile hydrothermal route by using the iron leached from the red mud in the presence of urea.Then the hydrothermal product was calcined to obtain Fe2O3 microspheres.The preliminary results proved the feasibility for the synthesis of functional iron oxides from the red mud.In brief,the present work provides a new insight into the comprehensive utilization of the red mud as great potential adsorbents for removal of anionic dyes from the mimetic waste water,and also is helpful for the future potential applications of the unique hierarchical porous metal oxide nanostructures in catalysis and other related fields.