Red Mud Preparation Of Multi-stage Porous Functional Oxide Technology And Performance

Known as bauxite residue,red mud is an industrial solid waste originated from bauxite refining for alumina by the Bayer process.Due to the as-contained alkaline chemicals,iron,aluminum as well as other impurities,it brings about severe pollution to the environment especially to the underground and surface water.It is considered that transforming residual valuable metal ions within red mud into functional materials is an important way to solve these problems.In this work,using waste red mud as raw material,using acid/base reflux and pH adjustment to separate Fe,Al,Si and other elements,functional oxides were prepared as adsorbents and catalysts for water pollution control.Three main areas of work are as follows:Using the red mud reasonably,some non-metallic elements such as Si contained in red mud were separated in solid by acid leaching,and a clarification solution containing metal ions was obtained.The Fe³⁺was separated in sediment form by adding NaOH and converted into functional hierarchical porous?-Fe₂O₃ microspheres comprising nanosheets(S_BET:78.75 m² g^-1,pore volume:0.35 cm³ g^-1,mean pore diameter:15.92 nm)via a facile hydrothermal route?180oC,12.0 h?,with the presence of urea and CTAB.When employed as the adsorbents for Congo red?CR?in simulated wastewater,the adsorption isotherm is well fitted with Langmuir isotherm model,and the corresponding maximum adsorption capacity is determined as 342.57 mg g^-1,superior to that of most referred adsorbents in literatures.Meanwhile,the adsorption kinetic data can be well interpretated via the pseudo-second-order and intra-particle diffusion models.Moreover,the red mud derived hierarchical porous?-Fe₂O₃ microspheres can be easily regenerated and reused with satisfactory chemical,morphological and structural stability.Recovery of valuable metal?Al?in the form of NaAlO₂ solution from red mud by adding NaOH,and synthesize functional flower-like hierarchical porous?-AlOOH microspheres(mean diameter:1.65mm,S_BET:77.81 m² g^-1,pore volume:0.38 cm³ g^-1,mean pore diameter:19.44 nm)as catalyst support via a facile and green one-pot hydrothermal method?150oC,12.0 h?without the aid of any organic additives or templates.Then the thermal conversion results in the?-Al₂O₃microspheres(S_BET:189.58 m² g^-1,pore volume:0.77 cm³ g^-1,mean pore diameter:16.32 nm) as catalyst support.The average size of Pd nanoparticles?NPs?supported on RM?-AlOOH and RM?-Al₂O₃ are 4.74 nm and 7.17 nm,respectively.The small size Pd NPs are highly dispersed on the surface of supports with less agglomeration due to the in-situ impregnation-reduction,large specific surface area and pore size.The turnover frequency?TOF?of RM Pd/?-AlOOH and RM Pd/?-Al₂O₃ catalysts are 1064.7 h^-1 and 710.5 h^-1 within 120 s and 180 s,respectively,which performed excellent catalytic property for reduction of 4-nitrophenol?4-NP?at room temperature.This part of the work is to use the red mud solid residue obtained after the above extraction of Fe,Al and other metal elements as raw materials,adding NaOH to separate the solid containing Si in the form of Na₂SiO₃ solution for the preparation of silica?SiO₂? through oil bath.The effects of ultrasonic dispersion and surfactants such as ethanol and lauryl glucoside on the morphology and composition of SiO₂ were investigated.Furthermore,the synthesis process was optimized to produce SiO₂ microspheres with uniform morphology and narrow size distribution.