Study On The Regulation Of Phosphate Ion Adsorption By Red Mud Granular Adsorbent

Red mud is a kind of solid waste discharged from the aluminum industry during the extraction of alumina.Because of its unique physical and chemical properties,it is often used as an adsorbent to treat wastewater.The rational use of red mud is of great significance to the improvement of the ecological environment in China.In this paper,the Bayer red mud was used as the raw material to research of mechanical modification,specific surface area modification,surface wetting modification and porous filler control.The red mud was modified by adding high alumina cement and common silicon cement to improve the compressive strength of the adsorbent.The specific surface area of red mud was modified by adding hydrogen peroxide and ammonium carbonate to increase the specific surface area of the adsorbent.The anionic wetting agent sodium dodecylbenzene sulfonate(SDBS)and the non-ionic wetting agent alkylphenol polyoxyethylene ether(PE-100)were added to wetting modification to improve the wettability of the adsorbent.In addition,porous fillers such as zeolite and silica fume were added to improve the adsorption performance of the adsorbent.Then,the red mud particle adsorbent was made into a slurry with good fluidity,which was granulated and formed in a special silica gel mold to prepare a non-sintered red mud particle adsorbent with good adsorption performance for phosphate ion.Based on the density functional theory and Monte Carlo method of the quantum mechanics and the molecular dynamics,the crystal cell of each mineral component of red mud was calculated and optimized,and a suitable red mud unit cell was established with the simulation software(Materials Studio).the adsorption sites and adsorption capacity of the red mud granular adsorbent for H₂PO₄^-?HPO₄^2-?PO₄^3-ions were explained from the micro perspective.The conclusions are shown as follows:(1)Determine the addition of binders,other adsorbed minerals,pore-forming agents and wetting agents to control the adsorption of red mud to phosphate ions.First,computer simulations are used to prepare for the test,and the red mud is subjected to X-ray diffraction(XRD)Qualitative and quantitative analysis to determine that the main crystal minerals contained in it are:Katoite?Calcite?Hematite?Cancrinite?Diaspore?Anatase?Kaolinite?Clinochlore?Muscovite.(2)Through the orthogonal test of single factor and four factors and four levels,the best ratio of red mud granular adsorbent is finally obtained:water-cement ratio 1:4;among which,the binder is 18%of high-alumina cement,and the other adsorption The mineral selection zeolite accounted for 12%;the pore former selected ammonium carbonate accounted for 0.07%;the wetting agent selected sodium dodecylbenzene sulfonate accounted for 1.1%.(3)After the addition of wetting agent,the surface wettability of the adsorbent of red mud particles increased significantly,which showed that the contact Angle of the adsorbent surface decreased and the adsorption performance of the adsorbent improved.(4)The static adsorption test showed that when the red mud particle adsorbent adsorbed the phosphate ore flotation backwater,when the phosphorus concentration of the phosphate ore flotation backwater was 103.3 mg/L,the adsorbent dosage was 31.25g/L,the adsorption time was 24 h,the shape of the adsorbent was a ball with a diameter of 0.5 cm,and the adsorption temperature was 25?,the adsorption capacity of the red mud particle adsorbent was the maximum 35.59 mg/g,the removal rate was 82.50%.(5)Based on density functional theory and Monte Carlo method,the structure optimization and dynamic relaxation of the main crystalline minerals in red mud were carried out,and the surface wetting of the main crystalline minerals in red mud was obtained as follows:Katoite>Diaspore>Anatase>Kaolinite>Clinochlore>Muscovite>Hematite>Calcite>Cancrinite(H₂O clusters)Katoite>Diaspore>Kaolinite>Clinochlore>Muscovite>Anatase>Hematite>Calcite>Cancrinite(H₂O+PO₄^3-clusters)Katoite>Diaspore>Kaolinite>Clinochlore>Muscovite>Anatase>Hematite>Calcite>Cancrinite(H₂O+HPO₄^2-clusters)Katoite>Diaspore>Muscovite>Clinochlore>Kaolinite>Anatase>Hematite>Calcite>Cancrinite(H₂O+H₂PO₄^-clusters)(6)Based on molecular dynamics method,the adsorption calculation of the main crystalline minerals in red mud was carried out.The results show that there are differences in the adsorption sites of phosphoric acid and ions for each component.Among them,the monolayer adsorption of phosphoric acid and ions by each mineral is mainly composed of calcite,bauxite and anatase.Various components of the mineral adsorption phosphoric acid and ions in the multi-layer adsorption of substances mainly include gartenite?calcite?hematite?kaolinite?chlorite and mica.Chlorite is a monolayer adsorbent for H₂PO₄^-.Under the same conditions,the order of adsorption of phosphate ions by the same substance is:For PO₄^3-:Katoite>Hematite>Calcite>Clinochlore>Kaolinite>Diaspore>Muscovite>Anatase>Cancrinite.For HPO₄^2-:Katoite>Calcite>Muscovite>Anatase>Hematite>Diaspore>Kaolinite>Cancrinite>Clinochlore.For H₂PO₄^-:Katoite>Cancrinite>Calcite>Anatase>Diaspore>Kaolinite>Hematite>Clinochlore>Muscovite.(7)The adsorption of H₂PO₄^-and HPO₄^2-on the surface of kattenite and chlorite is accompanied by chemical adsorption,while the adsorption of PO₄^3-is only physical adsorption.The physical adsorption of H₂PO₄^-,HPO₄^2-and PO₄^3-on the surface of calcite?hematite?calcitine?bauxite?anatase?kaolinite and mica.Under the same pressure,the adsorption capacity of phosphate ions on the crystal structure of the same mineral varies from large to small:H₂PO₄^->HPO₄^2->PO₄^3-;Under the same conditions,the adsorption strength of the crystal structure of the same mineral to the phosphate-containing clusters is from strong to weak:H₂PO₄^->HPO₄^2->PO₄^3-;Under the same conditions,the adsorption heat of phosphate ions in the crystal structure of the same mineral varies from large to small:H₂PO₄^->HPO₄^2->PO₄^3-.