Studies On Preparation And Adsorption Performance Of Red-Mud Based Porous Granular Materials

Red mud(RM)is a solid waste generated in the alumina industry,and its large accumulation not only occupies land resources but also leads to a series of environmental problems.Simultaneously,the pollution caused by printing and dyeing wastewater discharge is becoming increasingly severe.Congo red(CR),as a typical organic dye,is extremely difficult to remove from wastewater due to its stable molecular structure and strong water solubility.In order to achieve the goal of "waste treatment by waste",based on summarizing the research on the adsorption of organic dye CR in wastewater by using RM at home and abroad,this thesis takes RM as the main raw material,adds pore-forming agents and binders to prepare RM-based porous granular materials(GRM),and loads the zinc aluminum silicate(ZAS)nanomaterials on its surface by impregnation technology to enhance its removal ability for CR.This thesis focuses on the experimental removal of CR by GRM and ZAS/GRM porous granular composite materials,as well as the characterization of their physical and chemical properties.Furthermore,the CR removal performance and removal mechanism of the selected samples are studied.In addition,the stability of the material’s CR removal effect is evaluated through adsorption-regeneration cycle experiments,which is of great significance for the development and utilization of RM.The main research content and conclusions of the thesis are as follows:(1)In order to address the difficulty in recovering RM powder adsorbents,the GRM granular adsorbent was prepared using manual granulation and calcination processes with RM and other additives,and the effect of RM content on the compressive strength and CR adsorption performance of GRM was investigated.The research results show that by mixing RM,fly ash,sodium bicarbonate,and carboxymethyl cellulose in a certain mass ratio(75:10:5:10)with water,and then pre-calcining at 500℃ for 30 min followed by calcination at 900℃ for 20 min,the resulting GRM75 sample exhibits good adsorption performance for CR dye with a CR adsorption amount of 0.8199 mg g-1 within 3 h.The GRM porous granular material possesses abundant pore structure and excellent adsorption performance,which can effectively solve the problem of difficult recovery and utilization of RM powder adsorbents in practical applications for dye wastewater treatment.(2)In order to enhance the adsorption capacity of GRM75 towards CR dyes and achieve high value-added utilization of RM,surface modification of the preferred GRM75 sample was carried out using impregnation and calcination processes.ZAS/GRM75 composite material was obtained by loading ZAS nanomaterials onto the surface of GRM75 and the effect of different types and concentrations of zinc salts on the adsorption performance of ZAS/GRM75 was investigated.The research results showed that loading ZAS nanomaterials onto the surface of GRM75 could significantly increase the specific surface area of GRM75 porous granular material,thereby improving its adsorption capacity for CR dyes.Specifically,ZAS/GRM75 prepared by immersing GRM75 in a 0.15 mol L-1 ZnCl2 solution for 24 h,followed by drying and calcination at 500℃ for 2 h at a ratio of GRM75 mass to ZnCl2 solution volume of 1:20,exhibited high adsorption performance towards CR dyes,with a CR adsorption capacity of 3.5085 mg g-1 within 3 h,which was 4.28 times higher than that of unmodified GRM75 granular material.Therefore,it can be concluded that the porous granular adsorbent of GRM has more excellent adsorption performance after modification treatment,which can efficiently remove organic dyes in wastewater and improve the utilization value and environmental remediation effect of RM.(3)In order to investigate the adsorption mechanism of CR dye molecules by ZAS/GRM75,multiple characterization techniques were employed to analyze the effects of ZAS loading on the phase composition,microstructure,specific surface area,and dye adsorption properties of GRM75 granular material.The results indicated that the specific surface area and pore volume of ZAS/GRM75 were significantly higher than those of GRM75.Furthermore,the loading of ZAS nanoparticles increased the surface positive charge of GRM75,enhancing the electrostatic adsorption between the sample and CR,and thereby improving its adsorption capacity for CR dyes.Inductively coupled plasma(ICP)analysis results showed that the concentration of leached heavy metal ions in ZAS/GRM75 during the impregnation and CR adsorption experiments conformed to the national sewage discharge standard(GB8978-1996),and would not cause secondary pollution to the environment.The adsorption process follows the pseudo-secondorder kinetic model and Langmuir isotherm model,and the maximum monolayer adsorption capacity of CR on the surface of ZAS/GRM75 is as high as 6.5065 mg g-1.Under the same experimental conditions,after five continuous adsorptionregeneration cycles,the adsorption capacity of ZAS/GRM75 for CR could still be maintained at over 85%,indicating its good reusability performance.In summary,as an adsorbent with excellent adsorption performance,low cost,and environmentally friendly properties,ZAS/GRM75 has significant application value for the removal of organic dyes from wastewater.