| It is significant for the environment protection and economic development to separate heavy metal ions from industrial wastewater. Polymeric chelate resins can adsorb selectively heavy metal ions as well as can release them under appropriate conditions. This characteristic makes chelate resins to be applied widely in the separation and extraction of heavy metal ions.Both salicylic acid (SA) and 8-hydroxyquinoline (HQ) are the organic compounds having chelate function. In this work, crosslinked polystyrene (CPS) microspheres were first chloromethylated by using 1,4-bis(chloromethoxy)butane as chloromethylation regeant which has not to carcinogenic toxicity, obtaining chloromethylated crosslinked polystyrene (CMCPS) microspheres. Subsequently, SA and HQ were bound onto the surface of CMCPS microspheres via polymer reactions and using 5-amino salicylic acid (ASA) and 5-chloromethyl-8-hydroxyquinoline chloride as small reactants, and the two chelate resins of salicylic acid-type and 8-hydroxyquinoline-type, ASA-CPS and HQ-CPS were prepared successfully. The chemical structures and bonding degrees of the chelate groups for two chelate resins were characterized with infrared spectra, chemical method and spectrophotography. The effects of the main factors on the preparation process of the chelate resins were examined to determine the fitting reaction conditions. The adsorption behaviors of the two chelate resins for heavy metal ions were mainly researched, and the adsorption mechanisms and thermodynamics were studied in depth.The experimental results show that in the preparation process of ASA-CPS via the reaction of CMCPS microspheres and ASA, the amino group of ASA was as the nucleophilic attack group, and the nucleophilic substitution reaction occurred between the amino group and the chloromethyl group of CMCPS microspheres. The result indicates that the nucleophilic substitution reaction has a mechanism of unimolecule substitution reaction, namely SN1 mechanism. The reaction rate is independent of ASA concentration. To enhance the reaction temperature and to adopt the solvent with strong polarity are advantageous to the reaction.The results also show that the ASA-CPS resin possesses strong adsorption ability by right of the synergism of electrostatic interaction and coordination chelation, and the adsorption capacity can reach 21g/100g. The adsorption ability of ASA-CPS resin towards heavy metal ions increases with pH value of the medium in the pH range in which the hydrolysis of the heavy metal ions does not occur. This adsorption is a chemical adsorption process driven by entropy, and to enhance temperature accelerate the adsorption process. For the different heavy metal ions, the adsorption capacity of ASA-CPS resin is in the order: Fe3+>Ni2+>Cu2+>Zn2+.The preparation process of HQ-CPS resin was composed of two polymer reaction steps. Hexane diamine (HDA) was first reacted with CMCPS microspheres, resulting in amination microspheres HDA-CPS, and then HDA-CPS microspheres were reacted with 5-chloromethyl-8-hydroxyquinoline chloride under alkality condition, obtaining the chelate resin HQ-CPS. During the amination process, HDA not only was as a reactant, but also was a capturing-acid reagent. Thus, increasing the used amount of HDA is be instrumental in the reaction.The results also show that the chelate resin HQ-CPS has stronger adsorption ability through chelation, and the adsorption capacity for Cu2+ ion gets up to 7g/100g. The adsorption ability of HQ-CPS resin is also increased with the increase of pH value of the medium. The adsorption is also a chemical adsorption process driven by entropy, and to enhance temperature accelerate the adsorption process. For the different heavy metal ions, the adsorption capacity of ASA-CPS resin is in the order: Cu2+>Fe3+>Ni2+. |
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