| As the pollution problems become more and more serious,the research and development of heavy metal wastewater treatment methods and materials with low cost and good performance properties prove to be the most urgent thing.In the various wastewater treatment methods,the adsorption has become a widely used physical chemistry method in the industry due to its efficient,simple and economical advantages.Carboxymethyl cellulose?CMC?has many adsorptive carboxymethyl functional groups,thereby showing adsorption capacity for amount of heavy metal ions.However,it is complex to separate the CMC from water phase after the heavy metal adsorption due to the water-soluble property of CMC,which is not conducive to practical applications.Based on the synthesis fundamental of water-soluble CMC and took example by the research ideas of fibrous adsorbent,a carboxymethylated fiber?CMF?material with high carboxyl content and insoluble desirable fiber morphology was obtained.And the adsorption behavior and mechanism of heavy metal ions adsorbed onto CMF were investigated.This study aims to promote the research and development of heavy metal ions adsorbent materials and facilitate high value utilization of natural fiber materials.The main results were as follows:The laws of the various factors effecting on the yield and the carboxyl content of fibers were respectively studied in the CMF preparation process by solvent-medium method and water-medium method,the usability of these two methods for the preparation of CMF were compared,and the optimum condition for the CMF preparation was selected.The results showed that the modified water-medium method,which reduced the damage extent of fiber morphology caused by alkali swelling efficiently,was more suitable for the preparation of the CMF with high carboxyl content and desirable fiber morphology.In the CMF preparation process,the sodium chloroacetate amount was the most significant effect factor for both the yield and the carboxyl content of fibers,while the sodium hydroxide amount was a significant effect factor for the yield of fibers,and the etherification temperature was a significant effect factor for the carboxyl content of fibers.In consideration of the carboxyl content,the yield and the cost,the optimum condition for the CMF preparation was selected as follows.In the carboxymethylation process,the preimpregnation temperature was optimized to60?,the etherification temperature was optimized to 80?,the preimpregnation time was optimized to 2 h,the etherification time was optimized to 2 h,the sodium chloroacetate amount was optimized to 12.5 g,and the sodium hydroxide amount was optimized to 7.5 g.Accordingly,the carboxyl content of the resultant CMF obtained under the optimum conditions was 107.64 mmol/100g sample,and the yield was 102.77%.The adsorption behavior of heavy metal ions adsorbed onto CMF was studied.The results showed that the pH value of the heavy metal solution was an important affecting factor to the adsorption process of heavy metal ions.The competitive adsorption between hydrogen ions and heavy metal ions was the main reason affecting the adsorption performance of CMF.When the pH value in the range of 3.0 to 6.0,CMF showed good adsorption performance of heavy metal ions,whereas the best adsorption performance was arrived at the pH value of 6.0.According to adsorption kinetics analysis,it demonstrated that the adsorption of heavy metal ions onto CMF was a highly efficient process,which could reach the adsorption equilibrium in 10 min.Furthermore,the adsorption process mentioned above was fitted with pseudo-second-order kinetic adsorption model,thereby demonstrating that the chemical adsorption played the leading role in the adsorption process.According to adsorption isotherm analysis,it was found that the adsorption process of heavy metal ions onto CMF was fitted with Langmuir isotherm adsorption model,which proved to be monolayer adsorption.The regeneration performance as well as the optimized regeneration method of CMF were investigated.The results showed that the CMF had good regeneration performance.The optimized regeneration method was treating CMF with hydrochloric acid firstly to remove the heavy metal ions through the competitive adsorption between hydrogen ions and heavy metal ions in acidic environment,and then treating with sodium hydroxide to recover the exist form of–COONa group of CMF in alkaline environment.And the resultant CMF obtained with the optimized method above exhibited good adsorption properties.The adsorption mechanism of heavy metal ions adsorbed onto CMF was analyzed and explained.The results indicated that the adsorption of heavy metal ions onto CMF was mainly caused by electrostatic interaction and chemical complexation.After carboxymethylation,The swelling ability of fibers significantly increased,while the crystallinity of fibers decreased significantly,and the properties changes above resulted in that the adsorption of heavy metal ions occurred not only on the surface of fiber,but also in the fiber interior.At the meantime,the adsorption occurred in the fiber interior played a dominant role in the adsorption process of heavy metal ions due to that the carboxyl content in the fiber interior was higher than that on the fiber surface. |
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