The Effect Of Degree Of Esterification And Molecular Weight Of Pectins On The Adsorption Of Pb²⁺

With our country the rapid development of industrialization and the acceleration of urbanization,more and more the wastewater riched in heavy metals was discharged,the heavy metals are harmful to health through the food chain.Lead is the one of the most commonly used heavy metals in industry.Numerous studies showed that biosorption was more effective for removal of Pb²⁺.One of the most promising and available biopolymers was pectins,it was meaning for removing the Pb²⁺pollution in the food chain.In this research,a new sampling method for determining the absorption capacity of pectin was established.The effect of pectin structures（different degree of esterification and different molecular weight）on the adsorption of Pb²⁺was investigated.In this paper,main conclusions are as follows:1.Conventional sampling methods before analysis of adsorption capacity are membrane filtration and centrifugal method.With the decrease of membrane pore size,more pectin-lead complexes were intercepted,the amount of Pb²⁺adsorbed increased.Moreover,with the decrease of centrifugal speed,the sedimentation of pectin-lead complexes was easier,the amount of Pb²⁺adsorbed increased.Form the adsorption mechanism of pectin on heavy metal,this study proposed a dialysis method to determine the amount of Pb²⁺adsorbed by pectin.The dialysis method can distinguish free Pb²⁺from the absorbed one.This amount almost remained constant after dialysis for different time periods,and the measured adsorption capacity was significantly higher than those of the other two sampling methods,it was more likely to close the true ones.Determination of galacturonic acid content and potentiometric titration proved its’advantages.This study showed that dialysis method could be used a new sampling method when the adsorption capacity of polysaccharide-like adsorbent is evaluated.2.The pectins with different degree of esterification（73.02%,65.31%,42.86%and 32.56%）were prepared,the intrinsic viscosity increased and the apparent viscosity decreased with the decrease of esterification degree.Pectins with different molecular weight（155700,70440,10600 and 6385 Da）were prepared.Both the intrinsic viscosity and apparent viscosity decreased with the decrease of the molecular weight.Moreover,the pectins with low esterification and low molecular weight were beneficial for adsorbing Pb²⁺.All the pectins showed good adsorption when the Pb²⁺solution temperature was 30℃and pH was 5.0.The more concentration of Pb²⁺solution,the more adsorption capacity.The pectins with different degree of esterification and different molecular weight could adsorb Pb²⁺at a fast rate,they almost achieved adsorption equilibrium after 40 minutes.3.The adsorption of pectin could be described by the pseudo-second-order kinetics model,which showed the chemisorption of the process.It was known that the carboxyl groups participated in the reaction during the adsorption process,according to the change of pH,Zeta potential and shift of the peaks on pectin before and after adsorption of Pb²⁺.It was speculated that the existing adsorption mechanism was ion exchange,when the pectins with different degree of esterification and different molecular weight absorbed Pb²⁺.