Study On Preparation And Phosphorus Removal Characteristics Of Steel Slag Ceramsite Modified By Lanthanum Iron Oxide And Lanthanum Oxide

The eutrophication of water bodies is an unnegligible environmental pollution issue in the construction of urban ecological civilization.Phosphorus is the main factor leading to eutrophication and eutrophication may occur when the phosphorus content in the water exceeds 20μg/L.For the removal of low concentration phosphorus in water,the adsorption method has the advantages of low cost,high phosphorus removal efficiency,simple operation and no secondary pollution.Steel slag is a typical industrial waste.Because of its adsorption capacity,it is often used as adsorbent for phosphorus removal in water.However,there are some problems such as low removal rate and difficult to recycle.In this paper,modified steel slag ceramsite was prepared as a new type of adsorbent,and its adsorption characteristics and mechanism of phosphorus removal in water were studied,and its regeneration performance was investigated in order to provide a scientific basis for the comprehensive utilization of steel slag.In this study,two kinds of modified steel slag ceramics with high phosphorus removal efficiency were prepared by calcination at high temperature using lanthanum-iron oxide and lanthanum oxide as modifiers,montmorillonite as binder and soluble starch as pore-forming agent.Optimizing the raw material composition and roasting conditions of modified steel slag ceramsite.The chemical composition and micro-morphology of modified steel slag ceramics were characterized by scanning electron microscopy-X-ray energy dispersive spectrometer（SEM-EDS）,X-ray powder diffraction（XRD）and specific surface area and pore size distribution tester（BET）.The effects of dosage,initial concentration of phosphorus solution,p H value and coexisting ions on phosphorus removal efficiency of modified steel slag ceramsite were studied through adsorption experiments.The adsorption kinetics and isotherm model were fitted,and the mechanism of phosphorus removal was discussed.The saturated modified steel slag ceramsite was regenerated by the solvent regeneration method,and the phosphorus removal ability of the modified steel slag ceramsite after one regeneration was investigated.The results showed that when the mass ratio of steel slag,modifier,binder and pore former in the raw material was 50:10:25:15,the modified steel slag ceramsite prepared by calcination at 1000℃for 30 min had good phosphorus removal performance and was not easy to break.Compared with unmodified steel slag ceramsite,lanthanum-iron complex oxide modified steel slag ceramsite（LFSC）and lanthanum oxide modified steel slag ceramsite（LOSC）had coarser surface after modification and evacuated porous structure,which provided favorable pore and channel for improving the adsorption of phosphate in aqueous solution by steel slag ceramsite.La element was added to the surface of LFSC and LOSC,and the content of Fe element on the surface of LFSC increased.Most of the metal elements in the modified steel slag ceramsite exist in the form of metal oxides or hydroxides.The specific surface areas of LFSC and LOSC were 5.677 m²/g and 6.148 m²/g,respectively.Compared with unmodified steel slag ceramsite,the specific surface areas of LFSC and LOSC were obviously increased,which was conducive to phosphorus adsorption.LFSC and LOSC were used to treat water samples with phosphorus concentration of 1.0 mg/L,when the dosage was 5 g/L,and after four hours of reaction,the removal rates reached 99.07%and 98.29%,respectively.The removal rates of phosphorus by LFSC and LOSC were above 90%in the range of p H 3～11.Anions inhibited the phosphorus removal of modified steel slag ceramsite in varying degrees.HCO₃^-inhibited the phosphorus removal more strongly,while Mg²⁺and Ca²⁺promoted the phosphorus removal.Quasi-second-order kinetic model could well describe the adsorption process of phosphorus by LFSC and LOSC in aqueous solution.The adsorption isotherms of phosphorus by LFSC and LOSC were consistent with the Langmuir isotherm adsorption model and after phosphorus removal by modified steel slag ceramsite,the energy spectrum peaks of P element appeared on the surface of the material,and phosphorus precipitation such as La PO₄and Fe PO₄was formed,which indicated that LFSC and LOSC mainly achieved phosphorus removal by single molecular layer chemical adsorption and precipitation.Soaking with 1.5 mol/L Na OH for 60 min could effectively regenerate the saturated steel slag ceramsite.Regenerated LFSC and LOSC treated water samples with phosphorus concentration of 1.0 mg/L.When the dosage was 5 g/L,the phosphorus removal rates were 98.51%and 95.62%,respectively.