Study On The Regeneration Mechanism Of Activated Red Mud Granular Adsorben

Red mud is an industrial solid waste produced in the aluminium industry,with fine particles,large specific surface area and containing active oxides is a common phosphate adsorbent.However,there are few studies on the regeneration characteristics of red mud adsorbent for phosphate desorption.This paper summarizes the phosphorus adsorption and regeneration methods of red mud at home and abroad,on the basis of which the activated red mud particles adsorbent was prepared by sintering activation method using red mud as the main raw material,and the static adsorption/desorption study of phosphorus in the tailing water of the flotation tailing of the tailing dam of the phosphate beneficiation plant in Wengfu,Guizhou was carried out to optimize the preparation method and adsorption/desorption conditions,and the regeneration mechanism of the adsorbent was explored by macroscopic kinetics and thermodynamics,microscopic tests,molecular dynamics and Monte Carlo method simulations,and the following conclusions were obtained:（1）The adsorbent of activated red mud particles was sintered,and single-factor and orthogonal static adsorption tests on the wastewater yielded the best adsorption effect of the activated red mud particles prepared under the conditions of 92:5:3 mass ratio of red mud,charcoal powder and silica sol,sintering time of 30 min and sintering temperature of 700℃,reaction temperature of 35℃,reaction time of 18 h,initial phosphorus concentration of 300mg/L,and The adsorption rate was 99.26%.The orthogonal test showed that time was the main influencing factor in the reaction process.The adsorption process was entropically increasing and matched well with the Langmuir isothermal model and the pseudo-second-order kinetic linear model,indicating that phosphate adsorption by activated red mud particle adsorbents was mainly single-molecule layer adsorption and chemisorption/chemical interaction was the main rate-limiting factor for phosphate adsorption.Microscopic tests yielded three main adsorption pathways:ligand exchange between phosphate generated by electrostatic adsorption and-OH groups on the surface of the activated red mud particle adsorbent,chemical precipitation including precipitation of metal ions such as Ca²⁺ions with phosphate,and diffusion between structures on the adsorbent surface.（2）The adsorption of activated red mud adsorbent was regenerated and desorbed.It was found that the desorption effect of HCl>Na OH>Na Cl>deionized water,the higher the concentration of desorbent,the better the desorption effect.Different concentrations of Na OH,Na Cl and low concentrations of HCl were used to select a concentration of 0.2 mol/L HCl desorbent,and the combined particle mass loss and adsorption rate of the adsorbent could be regenerated three times.The average free energy for chemical desorption and the high temperature facilitate desorption.The desorption process matches well with the Langmuir model and the pseudo-second order kinetic linear model,indicating that the desorption is dominated by single molecule layer surface desorption and chemical desorption limits the rate.Microscopic tests showed that phosphorus was effectively removed by surface elemental analysis,in which the most metallic elements were dissolved in Ca,followed by Al and Fe,which indicated the HCl desorbent reacted with the active elements in the red mud,the corrosion caused the elements to dissolve in water from the surface of the activated red mud particle adsorbent and accompanied the desorption of phosphorus,the mineral composition was similar before and after desorption,which resulted in a low impact on the reuse of the adsorbent.The vibration of the[SiO₄]^4-group of calcium and iron garnets in the functional group basically disappears,The intensity of the wave peak of the PO₄^3-group decreases significantly,which indicated that the process of phosphorus desorption by the HCl desorbent was accompanied by a chemical reaction.（3）Molecular dynamics and Monte Carlo simulations to study the regeneration mechanism concluded that the adsorption process activates the red mud particle adsorbent to effectively adsorb phosphorus mainly by ionic bonding and to a lesser extent by hydrogen bonding,The HCl desorption process mainly involved the breaking of ionic bonds and hydrogen bonds between H₂PO₄^-and activated red mud particles adsorbent surface,which caused the reduction of van der Waals forces,the mean square displacement of HCl desorption system was greater than that of deionized water system,the interaction between HCl desorption system and phosphorus accelerated the diffusion leading to the decrease of adsorption capacity,the diffusion coefficient of HCl desorption agent system was greater than that of deionized water system and the higher the temperature the greater the diffusion coefficient.The HCl desorbent system adsorbed less than the deionized water system,the higher the temperature the stronger the desorbent desorption capacity,the HCl desorbent mainly desorbed phosphorus adsorbed by Ca and Al atoms in the activated red mud particle adsorbent,while the deionized water could only desorb the surface layer of phosphorus,The HCl desorbent accelerated the adsorption of the first characteristic peak energy drop and the backward shift of the wave peak during the desorption process.