The Phosphorylation Modification And Dialysis Of Alkali Lignin And Its Absorption Performance Of Lead

Compared with the traditional way of removing the metal ion from aqueous solution,such as chemical precipitation,membrane separation and ion exchange,lignin and its derivatives as adsorption material have the irreplaceable advantages.Lignin is a kind of biomass resource in nature,and it is also an industrial by-product of pulp and paper industry.Lignin is abundant in source,low in price,non-toxic,easy to be degraded and it contains many oxygen-containing functional groups in the structure,which is of great significance for the treatment of heavy metal pollution.Lignin is easy to aggregate due to the ?-? interaction of the aromatic groups and intramolecular hydrogen bonding between hydroxy,carboxyl and ether linkage.The adsorption capacity on metal ions was limited due to little activity group and small specific surface area.In this paper,the functional group of phosphoric acid,amino group,which can interact with lead,were introduced into the alkali lignin by phosphoric modification.After chemical modification,the solubility,content of activity group and surface area of lignin were improved,and the adsorption performance was enhanced.To understand the adsorption behavior,three kinds of modified lignin with different functional group were synthesized.In addition,the effects of alkali-acid treatment and alkali-dialysis treatment on the physical and chemical properties of lignin,furthermore,on the adsorption performance were studied.Results indicated that the surface area and solubility were enhanced,and the maximum adsorption performance of Pb²⁺on lignin can reach 174.80 mg/g after modification.The pH value has a great influence on the adsorption performance,it can up to 90% when pH =5.5,and its adsorption rate was quite fast,which can reach the saturated adsorption within 20 minutes.The adsorption mechanism mainly depended on the electrostatic interaction between the Pb²⁺ and negative functional groups such as phosphate,phenolic hydroxyl and carboxyl,as well as the ion exchange between H+ and Pb²⁺.In additional,alkali-acid treatment had little influence on purity,molecular weight,structure and content of lignin.When pH<10,serious aggregation,insoluble,less negatively charged,the adsorption capacity of lignin on lead is just 33.15 mg/g when pH =5.5.With the increase of pH,the degree of ionization of the functional groups of lignin increased,the adsorption capacity enhanced.After dialysis treatment,the water solubility was increased while active functional group on surface and the degree of ionization of the functional groups of lignin were enhanced,its adsorption capacity had little change with the increase of solution pH value,the adsorption capacity can reach 136.27 mg/g under the same conditions,its performance was better than amination lignin while slightly below carboxymethylation and sulfomethylation lignin.Alkali-dialysis treatment was proved to be a good way to improve the adsorption performance of lignin on lead,and it mainly because the molecular chain became loose and the aggregation of lignin was reduced in the process of alkali-dialysis,the removal rate for lead can reach over 90%.