Modification Of Tara Gum And Its Adsorption Properties For Metal Ions

In this paper,Carboxymethyl tara gum（CMTG）was synthesized by tara gum（TG）and sodium chloroacetate（SMA）in the presence of sodium hydroxide.The best process parameters of CMTG were determined as follows:the mass ratio of TG to dispersant was0.2g/mL,m_NaOH:m_TG=0.4,alkalization time was 30 min,m_SMA:m_TG=0.45,etherification temperature was 60℃,etherification time was 3h.The degree of substitution of CMTG could reach 0.406.The viscosity of CMTG solution decreased by 28%when the mass fraction of NaCl was 15%.The viscosity of CMTG solution was the highest at pH=6-8.The speed of rotor increased from 10 RPM to 60 RPM,and the viscosity of CMTG solution with mass fraction of 2.5%decreased by 12.15%.This result proved that there existed shear thinning pseudoplastic behavior in CMTG solution.The viscosity of CMTG solution was smaller than TG.The viscosity of 1.5%TG solution was 182 times higher than that of 1.5%CMTG solution.FTIR showed that carboxymethyl was introduced successfully,TGA showed that the thermal stability of carboxymethyl modified tara gum decreased slightly.Cross-linked Tara Gum（CTG）was prepared by using tara gum as raw material,sodium hydroxide as catalyst,epichlorohydrin as crosslinking agent and 95%ethanol as solvent.Four factors and three levels orthogonal experiments were designed to optimize the experimental conditions for CTG preparation.The order of influence factors was:reaction time>reaction temperature>dosage of crosslinking agent>pH.The optimal combination of parameters was obtained as follows:m_ECH:m_TG=0.08,the reaction time was 5h,the reaction temperature was 45℃,and the pH was 10.FTIR analysis showed that TG did cross-linking with ECH,TGA analysis showed that CTG had better heat resistance than TG.Using CMTG as raw material,ECH as crosslinking agent and isopropanol as dispersing agent,two kinds of crosslinked carboxymethyl tarragonate（CCMTG）with substitution degree of 0.202 and 0.407 were prepared.The optimum adsorption conditions were determined as follows:the maximum adsorption capacity of Pb²⁺at pH=4 and Cd²⁺at pH=5;the adsorption capacity of CCMTG with high degree of substitution was 67 mg/g(Pd²⁺)and 62 mg/g(Cd²⁺)when the initial concentration of metal ions reached 300 mg/L and the mass fraction of adsorbent was 1%.The adsorption behavior of CCMTG for Pd²⁺and Cd²⁺was more in line with Freundlich isothermal adsorption model and the kinetic model of second-order reaction.After five times of CCMTG regeneration,the adsorption capacity did not decrease significantly,and the desorption rate was more than 90%,which indicated that CCMTG could be used as metal ion adsorbent.It is expected to be used as an effective adsorbent for Pd²⁺,Cd²⁺.FTIR showed that the cross-linking carboxymethyl modification of CCMTG was successful.TGA showed that the heat resistance of CCMTG was worse than TG.