| Nitrogen and phosphorus remains still the most concerned pollutants in waters,and the excessive discharge of them will cause serious eutrophication.Therefore,it is of great significance to develop highly efficiency environmental functional materials to remove nitrogen and phosphorus simultaneously from water body.This study aimed at the simultaneous removal of ammonium and phosphate,nitrate and phosphate,and functionally regulated the internal structure and surface characteristics of natural zeolite.The preparation conditions of sodium hydroxide modified-lanthanum oxide regulated zeolite(Z-Na-La)and zeolite supported nano-zero-valent iron-nickel composites(Z-Fe/Ni),as well as the environmental factors on the influence of simultaneous removal of nitrogen and phosphorus were well investigated.The regulation and pollutants removal mechanism were systematically elucidated.The optimal preparation conditions,i.e.NaOH concentration 1.0 mol/L,LaCl3 solution pH 10,LaCl3 concentration 0.4%and heat treatment temperature 200℃,were obtained for Z-Na-La.SEM-EDS,FTIR and XPS results demonstrated that Na+ entered the zeolite framework through ion exchange,and La3+ was loaded on or into the zeolite through co-precipitation and exchanging with Ca2+.Z-Na-La exhibited better performance for ammonium and phosphate removal in the initial solution pH ranging 3.0-7.0 with their maximum removal efficiency of 82%and 98%,respectively.The presence of Na+ and K+ inhibited the ammonium removal,while the effect of Ca2+ and Mg2+ were negligible.Cl-,SO42-,NO3-could hardly affected the removal of phosphate,and HCO3-played an inhibitory role.The pseudo-second-order kinetic and Langmuir isotherm model could better describe the adsorption characteristic of ammonium and phosphate with their maximum adsorption capacity of 21.5 and 17.2 mg/g,respectively,which were higher than most of other materials for simultaneous removal of both.The internal-diffusion was determined as the main control step of adsorption rate,and the adsorption process was spontaneous and endothermic.ICP-MS,FTIR,Zeta and XPS tests indicated that ion exchange and inner-layer complexation were the main removal mechanism for ammonium and phosphate,respectively.The optimum preparation conditions of Z-Fe/Ni as follows:absolute ethanol concentration 70%,mass ratio of Fe and zeolite 1:4,molar ratio of Fe3+ and BH4-1:5,and Ni loading 1.0%.TEM results showed that nano-zero-valent iron particles uniformly dispersed on the surface of zeolite with the size less than 25 nm.XRD,FTIR and XPS demonstrated that the nano-zero-valent iron/nickel was successfully loaded on the surface,and the zeolite can prevent them from oxidation and improved the stability.At the same initial pH condition,Z-Fe/Ni performed higher removal efficiency of nitrate and phosphate than Nano-Fe/Ni,and Z-Fe/Ni exhibited much less dependence on the initial solution pH,which demonstrated the existence of synergistic effects between zeolite and Nano-Fe/Ni.The coexistence of Cl-promoted the removal of nitrate and phosphate,while HCO3-,SO42-and HA showed inhibitory effect.Nitrate can promote the removal of phosphate,while phosphate inhibited nitrate reduction by Z-Fe/Ni.The reaction pathway of Z-Fe/Ni with nitrate and phosphate were identified.SEM-EDS,XRD,FTIR and XPS results indicated that nitrate was removed by catalytic reduction and phosphate was removed by precipitation and complexation.This study will provide theoretical basis for the regulation and application of environmental functional mineral materials and provide a reference for the research on the synergistic mechanism of nano-zero-valent iron and carrier. |
