Study On Phosphorus Absorption From Wastewater By Multi-wall Carbon Nanotube Modified With Mg

Phosphorus resources on the earth are facing exhaustion,while a large amount of phosphorus is discharged into the environment with wastewater emission every year,leading to water eutrophication.Phosphorus recovery from wastewater can solve the problem of environmental pollution and phosphorus shortage simultaneously.Adsorption technology for phosphate recovery has attracted more and more attention in recent decades since it is relatively lower consumption and easier operation compared with other approaches.In this study,a new Mg-modified multi-walled carbon nanotubes（MWCNTs）adsorbent was prepared to recover phosphate from wastewater.Firstly,Mg modified MWCNTs adsorbent（Mg@CNT）was prepared using blending-calcination method.The mass ratio of 0.48（Mg versus MWCNTs）was selected as the optimal preparation ratio of Mg@CNT.The Langmuir isothermal model and pseudo-second-order kinetic model fit the adsorption performance better.It is demonstrated that the adsorption of phosphate by Mg@CNT was mono-molecular layer chemisorption,and the experimental maximum adsorption capacity is 284 mg P/g.The adsorption capacity of phosphate decreased with the increase of the initial pH value of phosphate aqueous.Several common coexisting ions such as Cl^-,NO₃-and humic acid（HA）had no obvious effect on the phosphate adsorption capacity,while the existences of SO₄^2-and CO₃^2-in the solution only leaded to a 13.2%,39.2%decrease in the phosphate adsorption capacity.The results of characterization methods,FESEM,FT-IR,XRD,BET,showed that the specific surface area of Mg@CNT was 139 m²/g,and Mg O nanoflakes with a transverse diameter of 500 nm were deposited on the surface of MWCNTs,which played a major role in the phosphate adsorption process.Mg₃（PO₄）₂·10H₂O was formed as the final product of adsorption.Combined with the above experimental results,it can be concluded that the main mechanisms of phosphate adsorption were electrostatic attraction and ligand exchange.After three adsorption-desorption cycles,the adsorption capacity of Mg@CNT remained more than 90%of the initial adsorption capacity,and 84%of the adsorbed phosphate can be recovered.In the second stage,Mg@CNT-S was prepared using Mg（OH）₂ as the precursor by pre-adjusting the pH of MgCl₂ solution.The Langmuir isothermal adsorption model and the pseudo-second-order kinetic model fit the phosphate adsorption process better.It is proved that the adsorption of phosphate by Mg@CNT-S was still mono-molecular layer chemisorption,and the maximum experimental adsorption capacity was 212 mg P/g.The adsorption rate of Mg@CNT-S on phosphate was 2.2 times quicker than that the Mg@CNT,and the adsorption capacity and removal rate were also significantly improved than Mg@CNT.TEM,FESEM,and XRD results showed that there were Mg O nanoflakes with a diameter of less than 200 nm on the surface of Mg@CNT-S.The results of XPS and FT-IR characterization showed that the final product of adsorption was still Mg₃（PO₄）₂.After three cycles of adsorption-desorption,the adsorption capacity of Mg@CNT-S was 73%of the initial adsorption capacity,and 94%of the adsorbed phosphate can be recoveredThe experimental results showed that adsorbent prepared by Mg modified MWCNTs possessed high adsorption capacity for phosphate.The adsorbed phosphate can be greatly recycling,and regenerated adsorbent still maintained a high adsorption capacity after several regeneration,which proved that the adsorbents had great application potential in phosphate adsorption and recovery.