Study On The Adsorption Of Modified Ramie To Water Heavy Metal Cd²⁺

The metal ions contained in industrial wastewater will have a certain impact on the environment.Among a variety of metal ion treatment methods,cellulose-based adsorbents have the advantages of low cost and wide sources,and exhibit excellent adsorption performance for metal ions in water.As a traditional economic crop in China,ramie has the advantages of fast growth and large yield,and is a good material for the preparation of heavy metal adsorbents.In this paper,ramie fiber is used as the matrix,and three high-efficiency and environmentally friendly heavy metal ion adsorbents are prepared by citric acid and acrylamide modification:citrate esterified ramie（RF-CA）,acrylamide grafted ramie（RF-AM）,citrate-acrylamide modified ramie（RF-CA-AM）.Through single-factor experiments and orthogonal experiments,we explored the optimal modification conditions of the materials,and analyzed the effects of adsorption time,adsorption temperature,adsorbent dosage,and solution p H on the material’s Cd²⁺adsorption performance.The main research situations include:（1）The optimal preparation conditions of RF-CA are:140℃,1.5h,m（ramie）:m（catalyst）=1:0.1,m（ramie）:m（citric acid）=1:5.Under these conditions,the adsorption capacity of RF-CA for Cd²⁺reached 44.84mg/g,which was 8.3 times higher than that before modification;The optimal preparation conditions of RF-AM are:modification reaction temperature is 70℃,modification reaction time is 3h,m（ramie）:m（catalyst）=1:0.1,acrylamide concentration 3mol/L.Under these conditions the adsorption capacity of RF-AM for Cd²⁺reaches 19.95mg/g;After modification,the adsorption performance of ramie is greatly improved,and the two modifiers work together to improve the adsorption performance of the adsorbent.（2）The adsorbent RF-CA-AM was used for the adsorption experiment,and the best adsorption conditions were obtained:the time was 1.5h,the p H was 7,the dosage was 3g/L,and the temperature was 20℃.Taking the concentration of Cd²⁺in the tailings wastewater as a reference,the adsorption rate of the adsorbent to the Cd²⁺solution with a concentration of 50 mg/L can reach 99.16%.（3）Langmuir isotherm adsorption model and Freundlich isotherm adsorption model were used to study RF-CA-AM isotherm adsorption,and pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to fit the adsorption kinetic curve.The results showed that the Cd²⁺adsorption process of the modified ramie was consistent with the Langmuir isothermal adsorption model and the quasi-second-order kinetic model,which means that the modified ramie mainly adsorbs the metal Cd2+through single-layer chemical adsorption.（4）Research the regeneration performance of the material.The results show that among the four desorbents（H₂O,HNO₃,EDTA,Na Cl）,HNO₃has better desorption performance.After five cycles,the adsorption performance of the material remained at 84%,indicating that the adsorbent has good recycling performance.（5）The competitive adsorption results showed that the adsorbent RF-CA-AM showed a trend of Cu>Cd>Mg>Zn for heavy metals.The material has good selective adsorption to Cd and Cu,and has selective adsorption performance,which can realize the separation and enrichment of heavy metals.