Preparation And Application Of Cation Exchange Cellulose Fiber Adsorption Material

With the rapid development of industrialization,a large number of pollutants are discharged into water,causing serious damage to the environment.The wastewater containing heavy metal ions and organic dye was one of the most serious and harmful industrial wastewater.Therefore,it has become a hot topic to develop techniques to solve the problem.Among the related wastewater treatment technologies,the adsorption is regarded as an efficient one to remove the heavy metal ions and organic dye due to its simple operation,mature method,high removal efficiency and environmental friendliness.Adsorption material was the core of adsorption technology.Therefore,it was of great significance to develop adsorption materials with simple preparation,low price,and high repeatability.In this work,we prepared a novel adsorbent with the structure of“core-shell" by simply modifying the chemi-mechanical pulp fibers via a slight etherification,namely cation exchange cellulose fibers.The preparation process of cation exchange cellulose fibers was studied,and the chemical structure of the as-prepared fibers was characterized.Meanwhile,the adsorption properties of heavy metal ions and dyes were also investigated.The main findings are as follows:(1)The yield of water-insoluble cation exchange cellulose fibers and its carboxylate content are a contradiction.The higher the carboxyl content,the lower the yield of the fibers.In order to solve the contradiction between the yield and the carboxylate content,the etherification process was optimized to balance the yield and the carboxylate content.The preparation of the cation exchange cellulose fibers was carried out as follows:chemical pulp of 10 g,sodium hydroxide of 8 g,sodium chloroacetate of 14 g,etherification temperature of 60?,and etherification time of 8 h.The carboxylate content of the water-insoluble cation exchange cellulose fibers was 175.4 mmol/100g,and the yield of the fibers was 84.55%.(2)The lignin on the surface of the chemi-mechanical pulp acts as the shell of the inner carboxymethyl cellulose forming cation exchange cellulose fibers with a core-shell structure.This core-shell structure renders the cation exchange cellulose fibers higher carboxyl ate content than those counterparts prepared with chemical pulp.Polyelectrolyte titration was used to test the charge distribution of the water-insoluble cation exchange fibers.The results showed that the total charge was 175.4 mmol/100g,the surface charge was 56.21 mmol/100g,and the charge ratio was 32.05%.XRD was used to analyze its crystal structure,FT-IR was used to test its chemical structure and SEM was used to analyze its microstructure of the cationic exchange cellulose fibers.And the cationic exchange cellulose fibers were proved to have a core-shell structure with a laser scanning confocal microscope,that is,lignin was used to as a "shell",carboxymethylcellulose was used to as a"core".(3)The adsorption properties of Cu(?)and Pb(?)with cation exchange cellulose fibers were studied,in terms of the adsorption kinetics and thermodynamics.The results showed that pH was the most important factor affecting the process of adsorption.The pH value affects the valence state of heavy metal ions in wastewater and the presence state of adsorbent surface charge.When the pH is in the range of 2?6,the cation exchange cellulose fibers showed excellent adsorption capacity.At pH-value of 5,the adsorption capacity of cation exchange cellulose fibers to Cu(?)reached a maximum of 43.23 mg/g,and at pH value of 6,the adsorption capacity of cation exchange cellulose fibers to Pb(?)reached a maximum of 47.96 mg/g.According to the adsorption kinetics analysis,it indicated that the adsorption of Cu(?)and Pb(?)by cation exchange cellulose fibers is a rapid adsorption process,reaching the adsorption equilibrium within about 20 min,and the adsorption process was simulated with pseudo secondary kinetics.According to the analysis of isotherms and thermodynamics,the adsorption process of cation exchange cellulose fibers on Cu(?)and Pb(?)was simulated with Langmuir model,and the sorption of Cu(?)and Pb(?)was endothermic and spontaneous process.The cation exchange cellulose fibers were desorbed and regenerated by 0.1 mol/L HCl,the results showed that the adsorbent can be reused at least 4 times and the adsorption rate can maintain 80%of the original adsorption capacity.The adsorption mechanism of Cu(?)and Pb(?)by cation exchange cellulose fibers was ion exchange and coordination chelation.(4)The adsorption property of MB with cation exchange cellulose fibers was studied,in terms of the adsorption kinetics and thermodynamics.The results showed that pH was an important factor affecting the adsorption MB with cation exchange cellulose fibers.The cation exchange cellulose fibers have excellent adsorption capacity to MB when the value of pH is in the range of 3?10.At pH value of 8,the maximum adsorption capacity of MB was 741.3 mg/g.According to the adsorption kinetics analysis,the adsorption of cation exchange cellulose fibers to MB is a fast adsorption process,reaching the adsorption equilibrium within about 10 min,and the adsorption processes could be well described with pseudo-second-order kinetics.According to the isotherm and thermodynamic analysis,the process of adsorption for MB was simulated with Langmuir model,and the adsorption process was a spontaneous endothermic reaction.1 mol/L of HCl was used to desorb MB from cation exchange cellulose fibers.The results showed that the adsorbent had good chemical stability and regenerability,and could be reused for at least 3 times.The adsorption mechanism of cation exchange cellulose fibers to MB was ion exchange,van der Waals force and hydrogen bonding.