Composition And Structure Design Of Foamed Aggregate Based On Adsorption Kinetics And Evaluation Of Phosphorus Removal Performance Of Concrete

Water eutrophication is a serious water pollution problem caused by the enrichment of nutrient elements such as phosphorus in water.It can lead to the rapid proliferation of algae in water,water quality deterioration.Although the traditional single phosphorus removal method can alleviate the phenomenon to a certain extent,it also contains the disadvantages of slow phosphorus removal rate,high cost,secondary pollution and so on.To solve the above problems,based on the ecological floating bed,which is a water environment remediation technology,this study combined cement-based materials with phosphorus removal agents to prepare a kind of light porous foaming lightweight aggregate with high phosphorus removal ability,and then prepared it into lightweight aggregate concrete.The influencing factors of physical properties and phosphorus removal of lightweight aggregate and lightweight aggregate concrete were investigated respectively,and adsorption isotherm and kinetic fitting were carried out to explore the phosphorus removal mechanism of their respective phosphorus adsorption processes.Finally,the overall phosphorus removal performance of lightweight aggregate planted concrete planted with aquatic plants was evaluated.The results are as follows:(1)The loose bulk density,cylinder compression strength and softening coefficient of foamed lightweight aggregate all showed a downward trend with the increase of foam content,but showed an upward trend with the increase of phosphorus removal agent content,and the water absorption was opposite.When the content of dephosphorizer and foam are 40wt.%and6wt.%,respectively,the loose bulk density and barrel compressive strength of light aggregate reach the highest values of 533kg/m~3 and 0.67MPa,respectively.The experimental results of P adsorption of lightweight aggregate show that the P adsorption equilibrium can be reached in about 7 days,and the maximum P removal rate and P adsorption capacity can reach 96%and 0.057mg/g,respectively.The increase of phosphorus removal agent content reduces the phosphorus removal rate in the early stage but improves the phosphorus removal capacity to a certain extent.The better fitting of Langmuir adsorption isotherm means that phosphorus adsorption of light aggregate is mainly monolayer.The pseudo-first-order adsorption kinetics fit the phosphorus adsorption process of light aggregate well,indicating that the diffusion step is the main limiting step in the phosphorus adsorption process of light aggregate.(2)The changing trend of compressive strength and dry density of foamed lightweight aggregate concrete mainly depends on the changing trend of cylinder compressive strength and loose bulk density of lightweight aggregate concrete.The increase of HPMC(cellulose ether)content increases the compressive strength and dry density of concrete,and decreases the permeability coefficient.When 0.06wt.%HPMC is added,the compressive strength and dry density of concrete reach the maximum of 0.25MPa and 790kg/m~3,respectively,and the permeability coefficient decreases to 5.4cm/s.The concrete reaches phosphorus adsorption equilibrium in about 20 days.The adsorption isotherm and adsorption kinetics fitting results of concrete are basically consistent with the aggregate itself,indicating that concrete coating has little effect on the phosphorus removal performance of lightweight aggregate.In the early stage of the foamable lightweight aggregate planted with aquatic plants,the aggregate mainly carries out physical and chemical adsorption of phosphorus elements,and the total phosphorus concentration of the wastewater containing phosphorus decreases from 10mg/L to7.64mg/L in the first 5 days.In the later stage,it is mainly due to the absorption of plants.(3)When the content of shell foam and core dephosphorizer were 8wt.%and 70wt.%,respectively,the loose bulk density and softening coefficient of core-shell lightweight aggregate reached the highest values of 673kg/m~3 and 94.4%,respectively.And it decreased with the decrease of phosphorus removal agent content,and decreased with the increase of shell foam content.On the contrary,the water absorption rate,the compressive strength of the cylinder showed a trend of increasing first and then decreasing.The core-shell lightweight aggregate reached the phosphorus adsorption equilibrium in about 21 days,and the highest phosphorus removal rate reached 93%.The phosphorus removal capacity increased with the increase of phosphorus removal agent content in the core,but the phosphorus removal rate decreased in the early stage.Freundlich described the phosphorus adsorption process of core-shell lightweight aggregate better than Langmuir isothermal formula,indicating that the process includes both physical adsorption and chemical adsorption,but mainly chemical adsorption.Both pseudo-first-order and pseudo-second-order adsorption kinetics can well describe the phosphorus adsorption process of core-shell lightweight aggregate,indicating that diffusion and chemisorption play important roles in controlling the adsorption rate.(4)core-shell lightweight aggregate concrete can reach the phosphorus adsorption equilibrium in about 30 days,the highest phosphorus removal rate can reach 98.6%,and the phosphorus removal capacity can reach 0.029mg/g.With the increase of CE content,the early phosphorus removal rate of concrete decreases,but the final phosphorus removal capacity has little difference.The results of adsorption isotherm and adsorption kinetics are basically consistent with those of core-shell lightweight aggregate itself,including physical and chemical adsorption,among which chemical adsorption is the main adsorption mechanism.The phosphorus removal capacity of core-shell lightweight aggregate planted concrete is also significant.Especially in the early stage,the release of phosphorus removal components in the aggregate will carry out better chemical adsorption of phosphorus element,and combined with the biological absorption of plants in the middle and late stage,core-shell lightweight aggregate planted concrete will have better phosphorus removal performance.