Treatment Of Hexavalent Chromium In Aqueous Solution With Modified Macroporous Ion Exchange Resin Loaded With Nano-zero-valent Iron

With the rapid development of industry and economy,hexavalent chromium(Cr(?))is widely used in electroplating,dyeing and leather processing industries.However,Cr(?)is potentially toxic and may cause cancer in long-term or short-term exposure or inhalation.Therefore,solving the Cr(?)pollution problem has become the focus of environmental workers.Among them,nano-zero-valent iron(n Z?)particles have become a hot spot in the treatment of Cr(?)pollution due to their small particle size,large specific surface area,high reaction activity and environmental friendliness.However,n Z? is easy to agglomerate and oxidize,which reduces the activity of n Z?,so it needs to be modified to improve its dispersibility and stability.In view of the above problems,this paper successfully prepared n Z? by liquid-phase reduction method,and modified it to prepare three composite adsorption materials for the treatment of simulated Cr(?)wastewater.The processing performance of the composite adsorption material was evaluated,and the factors affecting the removal of Cr(?)and the reaction mechanism were investigated.The main research contents and conclusions are as follows:1.D201@n Z? adsorbent was prepared by liquid phase reduction method and used to treat simulated Cr(?)wastewater.The study found that the best mass ratio for preparing D201@n Z? is 2:1,and resin D201 improves the dispersibility of n Z?,thereby increasing the reactivity of n Z?.The efficiency of D201@n Z? to remove Cr(?)increases with the increase of the dosage of D201@n Z? and then remains stable.It decreases with the increase of the initial concentration of Cr(?),and is less affected by the initial p H.It is available in a wide p H range.Higher removal rate,the coexisting ion PO₄^3-promotes the removal of Cr(?),CO₃^2-,Ca²⁺and Mg²⁺have an inhibitory effect,while Cl^-has almost no effect.The adsorption of Cr(?)by D201@n Z? conforms to the Langmuir model and the quasi-second-order kinetic model.The maximum adsorption capacity of D201@n Z? for Cr(?)is 123.14 mg/g.Its excellent adsorption performance is due to the electrostatic attraction of D201 and the reduction of n Z? Due to the synergistic effect.2.The D201-Fe/Ni adsorbent with nano-bimetallic system was successfully prepared by the liquid-phase reduction method and used to treat simulated Cr(?)wastewater.The best mass ratio for preparing D201-Fe/Ni is 20:10:3.The hydrogen storage metal Ni can form nickel hydride and accelerate the reduction of Cr(?).At the same time,it can form a galvanic cell with Fe to reduce the formation of passivation layer.Resin D201 improves the dispersibility of nano bimetal.The efficiency of D201-Fe/Ni to remove Cr(?)increased with the increase of the dosage of D201-Fe/Ni,and then remained stable,and decreased with the increase of the initial p H value and initial concentration of the Cr(?)solution.The adsorption of Cr(?)on D201-Fe/Ni conforms to the Langmuir model and the quasi-second-order kinetic model.The maximum adsorption capacity of D201-Fe/Ni for Cr(?)is 155.16mg/g.The reaction mechanism is mainly electrostatic attraction,Ni catalysis,n Z? reduction and co-precipitation.3.The PDA/n Z?/D201 adsorbent was successfully prepared by liquid phase reduction method and in-situ growth method.The resin D201 was selected as the carrier and modified by polydopamine(PDA),which also solved the shortcomings of n Z? that it is easy to agglomerate and easy to oxidize.Compared with n Z?,the removal efficiency of PDA/n Z?/D201 for 100 mg/L Cr(?)is increased by 61.1%.The efficiency of PDA/n Z?/D201 to remove Cr(?)increases with the increase of the dosage of PDA/n Z?/D201 and then remains stable.It decreases with the increase of the initial p H value and initial concentration of the Cr(?)solution,and is affected by coexisting ions.Very small.The adsorption of Cr(?)on PDA/n Z?/D201 follows the Langmuir adsorption isotherm model,and the maximum adsorption capacity reaches 184.9 mg/g.During the reaction,Cr(?)is attracted to the surface of the material by electrostatic attraction,and reduced to Cr(III)by n Z?.Part of Cr(III)and Fe(III)form a co-precipitation and adhere to the resin,part of Cr(III))Chelate with PDA which is hydrophilic and rich in amino and hydroxyl groups,that is,the mechanism of PDA/n Z?/D201 to remove Cr(?)is mainly electrostatic attraction,redox,chelation and co-precipitation.4.In this paper,a total of three n Z?-based composite materials were prepared for the adsorption of Cr(?).Three kinds of adsorbents,D201@n Z?,D201-Fe/Ni and PDA/n Z?/D201,were prepared by liquid phase reduction method and in-situ growth method.The maximum adsorption capacity for Cr(?)is 123.14,155.16 and 184.9 mg/g,respectively.The adsorption capacity of PDA/n Z?/D201 is higher than most of the reported n Z?-based composite adsorbents.