Preparation Of Self-supporting Steel Slag-based Porous Adsorption Material And Its Denitrification And Dephosphorization Effect

The water eutrophication caused by ammonia nitrogen and phosphorus is the hot and difficult point of water environment treatment.Adsorption of nitrogen and phosphorus polluted water has the advantages of high efficiency,low energy consumption and simple operation,and the adsorption material is the key.Zeolite has regular pore structure,large specific surface area,rich active sites,as a water treatment adsorption material has a wide application prospect,but there are low mass transfer capacity,low capacity of ion adsorption exchange performance defects.Geopolymers are considered as precursors of zeolite synthesis because their preparation process is similar to that of zeolite formation.It is not only theoretically feasible,but also has important scientific significance and environmental benefits to use geopolymer in situ converted zeolite as an adsorbent for ammonia-nitrogen and phosphorus treatment of polluted water bodies.In this study,using steel slag and high alumina coal ash as precursors,the porous geopolymer framework was prepared by chemical activation and chemical foaming technology,and further transformed into a self-supported steel slag-based multi-pore adsorption material rich in zeolite by hydrothermal principle.Based on orthogonal experiment,the process conditions of in situ conversion of PGSF-Z were optimized.The effects of precursor composition and foaming agent content on the basic properties and ammonia nitrogen adsorption capacity of PGSF-Z were studied under the optimum in-situ conversion conditions.Using PGSF-Z as adsorption material,the influence of adsorption environment on its nitrogen and phosphorus removal efficiency was studied.The mineral composition,microstructure and pore structure of PGSF-Z adsorption material were characterized by XRD,SEM and BET.The main research conclusions are as follows:(1)The optimum process conditions for in situ conversion of PGSF to PGSF-Z were as follows:alkali concentration of 2.5mol·L^-1,hydrothermal temperature of 180?,and time of 16h.When the ratio of steel slag to high alumina coal ash is 1?1,the zeolite phases in PGSF-Z are NAP and Na₆(Al Si O₄)₆·4H₂O zeolite under the optimum in-situ conversion conditions.When the ratio of steel slag to high alumina coal ash is 7?3,the zeolite phases in PGSF-Z are NAP,Na₆(Al Si O₄)₆·4H₂O,fibrous zeolite and rod zeolite.When the foaming agent(H₂O₂)content is 2.0%,the compressive strength of PGSF-Z material is 2.2MPa,the open porosity is 65.9%,the average mesopore diameter is 17.4nm,and the specific surface area is 49.3m²/g.(2)When the initial concentration of ammonia nitrogen was between 10mg·L^-1?100mg·L^-1,the adsorption capacity of PGSF-Z for ammonia nitrogen increased with the increase of the initial concentration.When the concentration was 100mg·L^-1,the adsorption capacity was 0.610mg·g^-1.When the p H of ammonia nitrogen solution was between 4?11,the adsorption capacity firstly increased and then decreased with the increase of p H.When the p H was 7,the adsorption effect was the best,and the cation exchange capacity was 0.181mg·g^-1.When the initial phosphate concentration was between 5mg·L^-1?75mg·L^-1,the adsorption capacity of PGSF-Z increased with the increase of the initial concentration.When the initial phosphate concentration was75mg·L^-1,the adsorption capacity was 0.678mg·g^-1.And it has better adsorption effect under acidic and neutral conditions.The adsorption of nitrogen and phosphorus by PGSF-Z showed the characteristics of rapid adsorption in the early stage and slow equilibrium in the later stage,and the quasi-second-order kinetics was more suitable to describe the kinetic characteristics of the adsorption of nitrogen and phosphorus by PGSF-Z.Freundlich isothermal adsorption model can more accurately describe the adsorption behavior of material belongs to multi-molecular layer adsorption.(3)By comparing the adsorption effect of PGSF-Z adsorption material in the complex solution of ammonium chloride and phosphate with that in the single solution of ammonia nitrogen and phosphate respectively,The adsorption equilibrium time of the two is correspondingly extended,and the adsorption capacity of phosphate is increased,the presence of ammonia nitrogen promoted the adsorption effect of PGSF-Z on phosphorus.