Synthesis Of Modified Chitosan And Their Chelating Properties For Heavy Metals

With the development of industry,the quantity of the heavy-metal wastewater produced by the manufacture world is increasing.Traditional chemical precipitation method can not meet the emission regulation to treat the ever increasing wastewater.Finding new efficient measures to decrease the heavy metal concentration and precenting secondary pollution have become the top priority in the environment protection field.For well environment compatibility,reproducing property,resourceful and low cost,the researches of chitosan modification to improve its performance and enlarge its applied field,have received much more attention in recent years.In this paper, kinds of methods of removing heavy metal from solution,the development of chitosan modification and the applied status are summarized.In this dissertation,chitosan is modified and applied for the removal of heavy metal from aqueous solutions.Starting form chitosan,amidogen protecting,cross linking,etheration,amination,amidogen release and addition reaction with CS₂,and chitosan derivative containing dithiocarbamate group was firstly prepared.The structures of intermediate compounds and final product are confirmed by FTIR spectra analysis,element analysis,SEM and X-ray diffraction.Some factors affecting metal removal are investigated in this dissertation including pH,temperature,time and initial concentration.The best saturation for heavey metals,the performance for factual waste water,the stability of the chelating product and the situation of second-pollution are investigated,too.And some useful constants for application are obtained.Experimental results show that in simgle solution whose concentration is 1mmol/L,the removal efficiencies of modified chitsoan are all to 98%and the saturated adsorption are Cu²⁺1.94,Pb²⁺1.53,Zn²⁺1.67,Cd²⁺1.07,Ni²⁺0.81 mmol/g, while in the same solution the saturated adsorption of chitosan are Cu²⁺1.65,Pb²⁺0.83, Zn²⁺0.77,Cd²⁺0.35,Ni²⁺0.33 mmol/g.In the solutiong with complexing agent EDTA whose concentration is 0.1mmol/L,the removal efficiencies of modified chitosan are Cu²⁺97.9%,Pb²⁺94.0%,Zn²⁺+94.4%,Cd²⁺99.7%,Ni²⁺97.4%,while chitosan are Cu²⁺70.7%,Pb²⁺51.9%,Zn²⁺14.9%,Cd²⁺28.6%,Ni²⁺43.8%.In the plating waste water whose concentration of Cu²⁺is 133.68mg/L,the removal efficiency is to 99.9%. FTIR spectra analysis,SEM and X-ray diffraction of the compounds indicate that the chelating bonds are formed between this chelating reagent and metals,and the principium is dicussed originally.The experimental results show that this new kind of chitosan derivative has the characters of both chitosan and dithiocarbamate.This compound has much better selectivity and capability for heavy metals.Meanwhile,it is convenient,safe and more jarless in acid solution.All results above show that this chitosan derivative has a good application foreground.