Preparation Of Threonine And Tyrosine Modified Montmorillonite And Its Capturing Effect On Lead And Copper Ions

Metal ion pollution transmitted through water body is the most common form of heavy metal pollution,and the use of water is involved in all aspects of production and life,so the treatment of heavy metal ion pollution in water is particularly important.Natural montmorillonite not only adsorbs organic molecules,but also metal cations due to its special2:1 interlayer structure.Through amino acid modification of montmorillonite,the interlayer distance and adsorption stability of montmorillonite were further increased,which made it possible to be used in the field of industrial wastewater treatment.The main contents are as follows:（1）A series of Thr-Mt and Tyr-Mt were prepared by using R-based threonine and tyrosine with hydroxyl groups were used as chelate modifiers under different preparation conditions.The optimum preparation conditions were determined by comparing the adsorption capacity of metal ions and structure characterization:the pH of the modified solution was 5,the dosage of threonine and tyrosine reached 214.43 mg（1.0 CEC）and 195.68 mg（0.6 CEC）,respectively.Thr-Mt-1.0 and Tyr-Mt-0.6 have the best performance at these two conditions.（2）XRD,FTIR and Zeta potential characterization analysis of various series of modified montmorillonites confirmed that L-threonine and L-tyrosine had successfully entered the interlayer structure as modifiers,and the modification process did not destroy the basic structure of montmorillonite.The order of interlayer spacing was Thr-Mt-1.0（1.54 nm）>Tyr-Mt-0.6（1.52 nm）>Na-Mt（1.23 nm）.The specific surface area of montmorillonite modified by different amino acids was increased to a certain extent.SEM also confirmed the change of the morphology of montmorillonite.Zeta potential results of Thr-Mt and Tyr-Mt showed that introduction of amino acids changed the charge properties of montmorillonite surface.（3）With Na-Mt as a reference,single-ion adsorption experiments were carried out with Thr-Mt-1.0 and Tyr-Mt-0.6 for Pb²⁺or Cu²⁺in aqueous solution.The effects of solution pH,initial concentration,contact time and solution temperature on the adsorption efficiency were investigated.The results showed that the shortest adsorption equilibrium time was 20 min.In addition,solution pH and C₀ had significant effects on the adsorption capacity.The maximum adsorption capacity of Thr-Mt-1.0 and Tyr-Mt-0.6 on Pb²⁺(Cu²⁺)could reach 120.44（30.1）mg L^-1 and 115.65（30.5）mg L^-1,Thr-Mt has better adsorption ability than Tyr-Mt due to its stronger alcoholic hydroxyl group.respectively.The adsorption process of three adsorbents for Pb²⁺(Cu²⁺)is spontaneous endothermic process,which conforms to pseudo-second-order kinetic model.The adsorption isotherm is fitted to Langmuir adsorption model,It shows that the adsorption model of adsorbent is determined by the modified raw material（Na-Mt）to some extent..（4）The desorption experiments of different amino acid modified montmorillonite in various acidic environments proved that the interlayer amino acid could effectively increase the adsorption stability of the adsorbent.In the co-adsorption experiment of two-ion system consisting of Pb²⁺and Cu²⁺,we found that there was competitive adsorption between different metal ions.Finally,the practical electroplating wastewater was used as ion source,and Thr-Mt-1.0 was used to adsorb the wastewater.The more economical and practical dosage was determined to be 8.6 g L^-1 through experiments.