| Eutrophication of water body makes algae and other autotrophic organisms multiply rapidly,consuming oxygen,reducing dissolved oxygen in water,making water quality worse,destroying the ecological system,making aquatic animals and plants unable to survive,and even endangering human health.Phosphorus is one of the main factors of eutrophication,the natural water bodies of phosphorus pollution comes mainly from human life and production,and sewage wastewater treatment technology is to prevent the main method of phosphorus pollution in water,and limited to the current conditions of water treatment technology,the human life and is still in the production of waste water after processing the tail water containing low concentration of phosphate,which cause the phosphorus pollution of water body,therefore,sewage treatment plant tail low concentration of phosphorus in water treatment technology is one of the hot spot of the current water treatment technologies.The commonly used phosphorus removal methods include the traditional activated sludge method,chemical precipitation method and physical adsorption method.Physical adsorption method can be used for phosphorus removal alone or in combination with other processes due to its advantages of resource recovery,low pollution,high efficiency and renewable,etc.It is one of the hot technologies in wastewater phosphorus removal that have been studied a lot.The performance of adsorbent is the key factor that determines the phosphorus removal effect of adsorption method.Pure sepiolite has kind of fibrous crystal structure,and genesis contains a lot of impurities in natural sepiolite,making it both beam and on the structure transition properties of layered,the crystal of single-layer magnesia octahedron,caught in the middle of the continuous double oxygen-silicon tetrahedron,arranged alternately to form 2:1 layered structure,the whole structure by zeolite channel and pore water,the theoretical surface area of900 m2/g,and have a very strong ability of ion exchange,adsorption range is very wide,can effective adsorption materials such as water,high and low polarity polarity.Hydrotalcite is a kind of bimetallic hydroxide,which is generally composed of bivalent and trivalent metal ions.Its structure contains a large amount of net positive charge.By changing the proportion of metal ions in hydrotalcite laminates,the number of interlaminar anions can be adjusted to change the distance between laminates.At the same time,hydrotalcite compounds with good ion exchange ability and memory effect have been widely used in the study of phosphate adsorption.In this study,Mg-Al ions were introduced into commercial grade sepiolite for composite modification,and a mixture of fibrous structure of sepiolite and hydrotalc-like structure was formed in sepiolite,so as to enhance the adsorption characteristics of sepiolite to low-concentration phosphate in water.The phosphorus removal mechanism of modified sepiolite was investigated through different kinetic models and adsorption isotherm models by combining static and dynamic experiments,and the physical and chemical properties of modified sepiolite were further analyzed by SEM,FT-IR,XRD and other instrumental analysis methods.In the static adsorption experiment,the adsorption performance of mg-al composite modified sepiolite was studied by changing reaction time,dosage,p H value,initial total phosphorus concentration,coexisting ions and other experimental conditions.The experimental results showed that the removal efficiency of total phosphorus in water by modified sepiolite with an addition of 0.3g/L was up to more than 97%after reaction at 298K temperature for 30min in phosphorus solution with a p H of 6,P of 0.5mg/L.SO42-,CO32-water coexisting anions on its adsorption performance is larger,SO42-in 0～6mmol/L concentration range,the removal rate of phosphorus can still above 66%,and when the concentration of CO32-in 6mmol/L,phosphorus removal rate is only 40%,therefore,limit the water CO32-ions concentration can effectively improve the Mg-Al composite modified sepiolite removal of low concentration of phosphorus in water.The physical and chemical properties of Mg-Al composite modified sepiolite before and after phosphate adsorption in water were characterized by FT-IR and XRD.FT-IR results showed that after absorbing phosphate in water,Mg-Al composite modified sepiolite generated a new absorption peak at 1371cm-1,which corresponds to the stretching vibration peak of P-O,indicating that phosphate in water was successfully transferred from liquid phase to solid Mg-Al modified sepiolite,thus achieving the purpose of adsorption and removal.XRD analysis shows that the Mg-Al composite modified sepiolite into phosphate solution,the root and chloride ions quickly produce phosphate ion exchange,composite modified sepiolite in 2 theta=11.6°a species appeared hydrotalcite compound,weak diffraction peak,mean that sepiolite structure is the primary phase,the compound is the genesis of load in the hydrothermal modification of sepiolite magnesium,aluminum and hydroxyl medium such as precipitation,adsorption after the peak still exists.Langmuir,Freundlich and other isothermal adsorption models were used to fit the adsorption process.Under the condition of 298K,the theoretical maximum adsorption capacity of modified sepiolite is 10.25mg/g.The adsorption of trace phosphorus in water by composite modified sepiolite is more consistent with the pseudo-second-order kinetic model,which indicates that the adsorption activity site and phosphate are multilayer adsorption with physical and chemical interaction.The dynamic adsorption experiment of phosphate in water by Mg-Al composite modified sepiolite shows that the penetration time of adsorption column increases with the height of packing layer and decreases with the increase of initial concentration.The Thomas and Yoon-Nelson models can be used to fit the dynamic adsorption process.In conclusion,Mg-Al composite modified sepiolite prepared in this study has a good adsorption performance for trace phosphorus in wastewater treatment plant tailwater and is an ideal adsorption material. |
