Study On The Removal Performance Of Sulfur-modified Nano-zero Valent Iron Composites For Water Pollutants

Nanometer zero-valent iron（nZⅥ）has been widely used in the treatment of pollutants in water and soil because of its strong reducibility and low cost.However,due to the small size and high surface energy of nanosized zero-valent iron particles,it is easy to agglomerate,which reduces the reactivity and limits its application in practical environmental remediation to a certain extent.Surface chemical modification and supporting of nanometer zero-valent iron are effective methods to increase its reactivity.Research through the study of the sulfide of n ZⅥ surface modification,and selects environmentally friendly hydroxyapatite and natural mineral attapulgite support modified nano zero-valent iron,sulfur,respectively,the preparation of hydroxyapatite/sulfur modified nano zero-valent iron and concave-convex rod/sulfur modified nano zero-valent iron materials,applied to the heavy metal ions removal.In addition,based on the characteristics of nano zero-valent iron that can slowly release Fe²⁺in aqueous solution,the reduction of sulfurized nano zero-valent iron was combined with the fenton oxidation process of persulfate（Ps）and hydrogen peroxide（H₂O₂）,and the removal mechanism and performance of attapulgite/sulfur-modified nano zero-valent iron on p-nitrophenol organic pollutants were discussed.The main research contents are as following:（1）Hydroxyapatite supported sulfur-modified nano zero-valent iron（HAP/S-n ZⅥ）was synthesized by chemical liquid phase reduction method using ferrous sulfate as an iron source,sodium borohydride as reducing agent,sodium disulfite as curing agent and hydroxyapatite as carrier.The effects of different materials,molar ratio,solution p H,initial concentration of Ni（II）and amount of adsorbent on the removal performance of Ni（II）were investigated.The kinetics model and thermodynamic model were utilized to analyze the removal process of Ni（II）.The results show that sulfur surface modification of n ZⅥ and HAP can significantly improve the reaction activity and stability of n ZⅥ.The Ni（II）removal rate of HAP/S-n ZⅥ was 98.25%,which was much higher than that of HAP（79.83%）and n ZⅥ（84.52%）.Compared with n ZⅥ,S-n ZⅥ has a shorter adsorption equilibrium time and a wider p H range,and can still maintain a higher Ni（II）removal rate after 60days of storage.The adsorption process of Ni（II）satisfies the pseudo-second-order adsorption kinetics model and the Freundlich isothermal model.The theoretical maximum adsorption capacity of Ni（II）is 302.27 mg/g.The removal mechanism of Ni（II）includes electrostatic adsorption,reduction and surface complexation,and the results of dynamic adsorption experiments further illustrate its potential in practical applications.（2）Apulgapulgate supported sulfur-modified nanosized zero-valent iron（APT/S-n ZⅥ）was prepared by liquid phase reduction method with apulgapulgate supported sulfur-modified nanosized zero-valent iron（APT/S-n ZⅥ）with sodium disulfite as vulcanizing agent.The modified nanosized zero-valent iron（APT/S-n ZⅥ）was used to remove heavy metal ions such as Cr（Ⅵ）,Cu（Ⅱ）and Zn（Ⅱ）.The effects of different materials,S/Fe molar ratio,p H of solution,amount of adsorbent,initial concentration of heavy metal ions and coexistence of three heavy metal ions on the removal performance of heavy metal ions were investigated.The kinetic and thermodynamic models were used to study the activation energy changes in the reaction process,which provided a basis for the mechanism analysis of Cr（Ⅵ）,Cu（Ⅱ）and Zn（Ⅱ）removal by APT/S-n ZⅥ.The results show that the conductive Fe S_x and APT support dispersions on n ZⅥ surface can effectively improve the reaction activity of n ZⅥ,and achieve efficient removal of heavy metal ions such as Cr（Ⅵ）,Cu（Ⅱ）and Zn（Ⅱ）.Under the optimum experimental conditions,the removal efficiency of Cr（Ⅵ）,Cu（Ⅱ）and Zn（Ⅱ）by APT/S-n ZⅥ are 98.60%,99.97%and 99.72%,respectively.The removal mechanism of Cr（Ⅵ）,Cu（Ⅱ）and Zn（Ⅱ）by APT/S-n ZⅥ is closely related to the redox potential of heavy metal ions and the solubility product constant(K_sp)of metal sulfides.Among them,Cr（Ⅵ）is mainly removed by adsorption,reduction and co-precipitation,Cu（II）is removed by reduction and substitution precipitation,and Zn（II）is removed by surface adsorption and complexation.（3）In the presence of persulfate and hydrogen peroxide,the removal performance of APT/S-n ZⅥ composite for p-nitrophenol（PNP）was studied by using the synergistic action of zero-valent iron nanoparticles and Fenton oxidation to remove organic pollutants.The effects of different systems,S/Fe mole ratio,oxidant concentration,initial concentration of PNP,p H and temperature on the removal of PNP were investigated.The degradation mechanism and degradation products of PNP in different systems were analyzed by using UV-vis,gas chromatography-mass spectrometry（GC-MS）and the effects of different free radical scavengers on the removal performance of PNP.The results showed that APT/S-n ZⅥ could effectively remove PNP in the presence of persulfate and hydrogen peroxide,but the degradation mechanism and degradation products were different due to the different free radicals generated by Fe²⁺activation of Ps and H₂O₂,leading to different factors affecting the removal performance of PNP.The main degradation products of PNP in APT/S-n ZⅥ/Ps system are p-aminophenol,while the main degradation products in APT/S-n ZⅥ/H₂O₂ system are p-aminophenol and other inorganic small molecules.Under the same conditions,APT/S-n ZⅥ/H₂O₂ system has stronger removal efficiency and reaction rate of PNP than APT/S-n ZⅥ/Ps system.Among them,S/Fe mole ratio and initial PNP concentration have great influence on the PNP removal performance of APT/S-n ZⅥ/Ps system,while the dosage of oxidant,p H value and temperature have more obvious influence on the PNP removal performance of APT/S-nZⅥ/H₂O₂ system.