Preparation Of Magnetic Solid Chelating Adsorption Materials And Their Removal Performances For Heavy Metal Ions

Heavy metal wastewater has become a major global environmental problem,because it is toxic to humans,animals,plants and microorganisms and cannot be degraded by microorganisms.The adsorption method has the characteristics of simple operation,high efficiency,low cost and well adaptability,and has been widely used in the treatment of heavy metal wastewater.omote the treatment of heavy metal wastewater.In recent years,chelating adsorption materials have been gradually paid attention to in the field of heavy metal wastewater treatment due to their strong chelating ability to heavy metal ions in wastewater and good chemical stability.The Fe₃O₄magnetic particles have strong magnetic properties and can be efficiently separated by an external magnetic field,simplifying the separation operation.However,they have poor adsorption capacity for heavy metals,and it is often necessary to modify the surface of the active group with good adsorption performance for heavy metal ions.Base on this,our study comprehensively considers the advantages of the two,designs and constructs two magnetic solid chelate adsorption materials,and studied their adsorption performance for heavy metal ions,related adsorption thermodynamics and kinetics,and preliminary discussed the mechanism of adsorption.Firstly,using epichlorohydrin and triethylenetetramine as raw materials for copolymerization to obtain poly（epichlorohydrin-co-triethylenetetramine）（[ECH-co-TETA]_n）,then it was coated on the surface of Fe₃O₄microspheres by adhesion and crosslinking,and then reacted with CS₂under strong alkaline conditions to graft dithiocarbamate（-CSS^-）onto it.A new magnetic solid chelate adsorption material（Fe₃O₄@[ECH-TETA]_n-g-CSSNa）was successfully prepared.The structure,morphology,magnetism and composition of Fe₃O₄@[ECH-TETA]_n-g-CSSNa were characterized,and its adsorption characteristics and mechanism for Pb²⁺,Cd²⁺,Cu²⁺and Zn²⁺were systematically studied.The results showed that the prepared Fe₃O₄@[ECH-TETA]_n-g-CSSNa microspheres had a uniform core-shell structure with a particle size of about 600 nm and a coating of 50 nm.The-CSS^-content of Fe₃O₄@[ECH-TETA]_n-g-CSSNa was 1.9257 mmol/g and the magnetization saturation value was 50.513 emu/g.Fe₃O₄@[ECH-TETA]_n-g-CSSNa had a high adsorption capacity for Pb²⁺,Cd²⁺,Cu²⁺and Zn²⁺in the p H range of 5.00-8.00 at 293K and initial concentration of 200mg/g,reaching 174.31,148.25,149.83 and 128.59 mg/g,respectively.And its adsorption experiment data was in accordance with Lanmuir and pseudo second-order models.The adsorption rate of Fe₃O₄@[ECH-TETA]_n-g-CSSNa to Pb²⁺,Cd²⁺,Cu²⁺and Zn²⁺was extremely fast,and equilibrium is reached within 10 minutes.Its adsorption of these heavy metal ions was a spontaneous endothermic entropy increasing process,including electrostatic attraction,physical adsorption and chemical adsorption（especially surface complex adsorption）.In chemical adsorption,S,N and O in the active layer of Fe₃O₄@[ECH-TETA]_n-g-CSSNa were involved in the formation of coordination bonds,especially the symmetrical S-coordinated four-membered ring（-CSS^-）₂M²⁺.Among them,Cu（II）was reduced to Cu（I）,and part of-CSS^-was oxidized to-SO₃^-.And Fe₃O₄@[ECH-TETA]_n-g-CSSNa can be effectively regenerated by 0.1 mol/L HCl and recycled 5 times,and its removal rates dropped by 18.23%,17.64%,24.79%and 14.85%,respectively.Using glyceryl methacrylate as raw material to prepare polyglyceryl methacrylate（PGMA）by free radical polymerization,and then reacted with triethylenetetramine（TETA）to connect TETA to the PGMA molecular chain to obtain polyglyceryl methacrylate（PGMA-TETA）.Then PGMA-TETA was coated on the surface of Fe₃O₄microspheres by adhesion and crosslinking,and then reacted with carbon disulfide under strong alkaline conditions to attach-CSS^-to it.The adsorption material Fe₃O₄@PGMA-TETA-g-CSSNa was successfully prepared.The morphology,structure,magnetism and composition of Fe₃O₄@PGMA-TETA-g-CSSNa were characterized,the adsorption characteristics of Fe₃O₄@PGMA-TETA-g-CSSNa for Pb²⁺and Cd²⁺were investigated and the mechanism of adsorption was preliminary discussed.The results showed that the prepared Fe₃O₄@PGMA-TETA-g-CSSNa microspheres had a uniform core-shell structure,the particle size was about 700 nm,the coating layer was about 70 nm,and the magnetization saturation value was 48.917 emu/g.Fe₃O₄@PGMA-TETA-g-CSSNa had a high adsorption capacity for Pb²⁺and Cd²⁺in the p H range of 5.00-8.00 at 293K and initial concentration of 200 mg/g,reaching 153.17 and 158.92 mg/g,respectively.The adsorption experiment data was in accordance with Langmuir and quasi-second-order kinetic model.The adsorption rate of Fe₃O₄@PGMA-TETA-g-CSSNa on Pb²⁺and Cd²⁺was also very fast,reaching equilibrium within 10 minutes.Similar to Fe₃O₄@PGMA-TETA-g-CSSNa,the adsorption of Pb²⁺and Cd²⁺by this adsorption material was also a spontaneous endothermic entropy increasing process,including electrostatic attraction,physical adsorption and chemical adsorption.S,N and O in the active layer of Fe₃O₄@PGMA-TETA-g-CSSNa were involved in the formation of coordination bonds and formed（-CSS^-）₂M²⁺.Fe₃O₄@PMA-TETA-g-CSSNa can also be effectively regenerated with 0.1 mol/L HCl and recycled 5 times,the removal rates of Pb²⁺and Cd²⁺were reduced by 15.95%and 16.42%respectively.In short,the prepared magnetic solid chelate adsorption materials（Fe₃O₄@[ECH-TETA]_n-g-CSSNa and Fe₃O₄@PGMA-TETA-g-CSSNa）had excellent adsorption performance,regeneration performance and magnetic separation performance.It is easy to realize continuous automation of wastewater treatment,So they have a wide range of applications in the treatment of heavy metal wastewater prospect.