Preparation Of Activated Red Mud Adsorbent And Its Adsorption Mechanism Of Phosphate In Phosphate Ore Flotation Wastewater

Phosphate ore flotation wastewater?PW?discharge is large,high phosphorus content,complex composition,reuse difficulties and high treatment costs.Red mud?RM?is the red slime solid waste discharged in the process of aluminum production.In this study,bayer red mud was used as the main raw material to activate and prepare adsorbents.A non-thermal activated red mud particle adsorbent with high adsorption capacity,strong mechanical properties,good regeneration ability and good removal effect for phosphorus from phosphate ore flotation wastewater?PW?was prepared by two-step granulation?ARMFA?.In addition,the static and dynamic adsorption/desorption of phosphorus in the tailings water from the tailings dam of Guizhou Wengfu phosphate dressing plant was studied.Finally,the adsorption mechanism of the adsorbent on phosphorus was discussed by means of macroscopic adsorption kinetics,adsorption thermodynamics,microscopic test and molecular calculation test,the conclusions are as follows:?1?The adsorbent was activated by means of comprehensive regulation.By using single factor,orthogonal test and BP neural network to optimize and predict the index,the optimized formula was obtained:RM 95%+FA 5.2%+water-cement ratio 0.33+A2C 8.2%+HPMC 0.25%+Na₂SiO₄ 2%+KH-602 0.01%+H₂O₂1.64%+Mn O₂ 0.33%+HCl 0.75%+Cyan 0.05%+SDBS 0.21%.Under the optimized formulation,10%nucleating particle proppant was added to prepare ARMFA adsorbent with p H 10.16,specific surface area?BET?48.92 m²/g,pore volume?V?2.10 cm³/g,compressive strength?ST?1.12 KPa and 24 h immersion pulverization rate 3.72%.The adsorbent has a good adsorption effect on phosphorus in phosphate ore flotation wastewater.?2?Static adsorption/desorption tests were performed on the tail water of phosphate flotation with low concentration PW₁ and high concentration PW₂.In the static adsorption process,the adsorption parameters of the adsorbent to PW₁were as follows:the dosage of the adsorbent is 12.5 g/L,the adsorption time is 18 h,the maximum number of adsorption is 3 times,the adsorption concentration is 0.6?0.7 mg/L,the adsorption temperature is 25?,the maximum adsorption capacity of ARMFA is 0.96 mg/g,and the removal rate is99.25%.Adsorption parameters of the adsorbent on PW₂ were as follows:dosage of the adsorbent 25.0 g/L,adsorption time 14 h,maximum adsorption times 3 times,adsorption concentration 127.8 mg/L,adsorption temperature 25?,maximum adsorption capacity of ARMFA 48.63 mg/g,removal rate 96.13%.For the two kinds of water,with the increase of adsorption times,the pulverization rate of the adsorbent increased from3.72%to 11.56%,which decreased by 7.84%,and the compressive strength decreased from 1.12 KPa to 0.86KPa.The adsorption times increased,and the performance of the adsorbent decreased.In the static desorption process,the desorption effect of desorption agent Na OH>HCl>Na Cl>deionized washing.The higher the temperature is,the better the desorption effect is.The desorption time at low concentration is 15 min,and that at high concentration is 40 min.The higher the temperature is,the more obvious the desorption effect is.?3?A dynamic adsorption/desorption device was developed and a dynamic adsorption/desorption test was carried out on low concentration PW₁.The dynamic adsorption parameters are as follows:the initial concentration is 0.91 mg/L,the adsorption temperature is 25?,the height of the dynamic filler layer is 0.40 m,the flow velocity of the flotation wastewater is 0.15 L/min,the moving velocity of the adsorbent is 0.20 cm/min,the adsorption capacity is 0.90 mg/g,the removal rate is 98.12%,and the phosphorus concentration of the adsorbed tail water reaches below the standard limit;In the dynamic desorption process,when the desorption velocity is 0.90 L/min and the desorption time is 30 min,the concentration of phosphorus in the desorption solution reaches 18.72 mg/L and the desorption rate reaches 94.23%.?4?Through the comprehensive modification of the non-thermal activation adsorbent,the pores belong to the narrow slot hole,the size of the hole is not uniform,formed by flake particles accumulation.The main phase types remain unchanged before and after adsorption,and the phosphorus after adsorption belongs to an amorphous structure.The main adsorptive components include Fe₂O₃,CaCO₃,Ca₂Fe₂O₅,Ca?Si₆Al₂?O₁₆,Ca₃Al₂O₆,Al₂O₃,SiO₂,etc.The adsorption of phosphorus from phosphate ore flotation wastewater by the adsorbent conforms to the pseudo-first-order Langmuir kinetic model.The adsorption forms are mainly monolayer adsorption and physical adsorption,accompanied by certain chemical adsorption.The adsorption process satisfies the Langmuir isothermal equation,and the adsorption process is an endothermic reaction process.During the process of adsorption,the adsorbant system successfully adsorbed phosphorus.When p H is8-9,phosphorus mainly exists in the form of HPO₄^2-and PO₄^3-.These ions and positively charged Ca²⁺/Na⁺/Al³⁺/Mg²⁺form strong chemical bonds through precipitation,surface deposition and ion exchange coordination,and are distributed on the inner surface of ARMFA channel.While removing phosphorus,the adsorbent also adsorbs compounds of As and F.The adsorbent has flocculation,surface deposition and ligand exchange effect on phosphorus adsorption.Al,Mg,Fe,Ca and Si in ARMFA will dissolve into solution.There were a lot of alkaline substances in RM.Due to the action of HPMC and A2C,the granular adsorbent was packaged and its p H decreased.When immersed in PW,the alkaline substance hydrolysed to produce OH^-and H⁺,realizing acid-base migration and synthesis.?5?Molecular mechanics and Monte Carlo methods were used to study the surface adsorption and pore adsorption of the adsorbent.For surface adsorption,the order of phosphate ions adsorption by the same substances are:PO₄^3-:ARMFA>Ca₃Al₂O₆>Al₂O₃>Ca?Si₆Al₂?O₁₆>CaCO₃>SiO₂>Ca₂Fe₂O₅>Fe₂O₃HPO₄^2-:ARMFA>Ca₃Al₂O₆>Ca?Si₆Al₂?O₁₆>Al₂O₃>CaCO₃>SiO₂>Ca₂Fe₂O₅>Fe₂O₃H₂PO₄^-:ARMFA>Ca₃Al₂O₆>Ca?Si₆Al₂?O₁₆>Al₂O₃>CaCO₃>SiO₂>Ca₂Fe₂O₅>Fe₂O₃For pore adsorption,the order of phosphate ions adsorption by the same substance are:PO₄^3-:ARMFA>Al₂O₃>Ca₃Al₂O₆>SiO₂>CaCO₃>Ca₂Fe₂O₅>Ca?Si₆Al₂?O₁₆>Fe₂O₃HPO₄^2-:ARMFA>Al₂O₃>Ca₃Al₂O₆>SiO₂>CaCO₃>Ca₂Fe₂O₅>Ca?Si₆Al₂?O₁₆>Fe₂O₃H₂PO₄^-:ARMFA>Al₂O₃>Ca₃Al₂O₆>CaCO₃>SiO₂>Fe₂O₃>Ca₂Fe₂O₅>Ca?Si₆Al₂?O₁₆There is a big difference between surface adsorption and pore adsorption.Whether surface adsorption or pore adsorption,the adsorption effect of adsorbent on phosphorus is better than that of a single component.?6?Among the adsorption components,the chemical bond energy?Ebond,Eangle?of CaCO₃,SiO₂,Al₂O₃and Fe₂O₃ did not change before and after adsorption,and the adsorption was mainly based on exchange adsorption and physical adsorption.Al₂O₃ has the lowest van der Waals force between phosphate and water and the highest intermolecular attraction.The intermolecular attraction between Fe₂O₃ and adsorptive mass is the smallest,and the ntermolecular attraction between other mineral molecules are similar.Adsorption accords with the characteristics of physical adsorption,such as low heat,fast adsorption rate,no selectivity and reversible adsorption process.The chemical bond energy of Ca₃Al₂O₆ and ARMFA changed before and after adsorption,indicating that certain chemical adsorption occurred during the adsorption process.?7?Based on the idea of"waste control by waste",this paper adopted the non-thermal activation method to improve the adsorption activity of RM and prepared particle adsorbent to adsorb the phosphorus in phosphate ore flotation wastewater,and carried out basic research on the adsorption process to improve the adsorption performance.After adsorption,the total phosphorus,F ions and arsenic ions in the wastewater reached the discharge standard,and the RM was used as concrete filler due to the decrease of p H value.In this study,the standard discharge of phosphate rock wastewater and the environmental hazard caused by RM stockpiling have been solved,and significant social,environmental and economic benefits have been generated.