Modification Of Alkali Lignin And Its Absorption Of Pb²⁺ And Cu²⁺

Lignin is the only biomass resources with benzene ring structure and its amount is only second to cellulose in nature. Industrial lignin is widely used and low cost. As the waste of paper industry, most of the industrial lignin is burned directly, which is a great waste of resource. To explore the application of lignin is a necessary and urgent task. This work focuses on the development and application of industrial lignin, exploring the performance and influencing factors of industrial lignin as heavy metal adsorbent. The main research progress is as follows:First, the structure of different kinds of lignins and their effects on the adsorption of heavy metal ions were studied. The results showed that different lignin have big differences in function groups content, the content of methoxy is the highest; In AL alcohol hydroxyl content is higher than phenolic hydroxyl and carboxyl groups; In EHL, the contents of phenolic and alcoholic hydroxyl are higher than carboxyl. The heavy metal adsorption capacity of different lignin are as follows, straw AL> wood AL > EHL.Industrial lignins were purified and fractionated by base-dissolving acidification. The results showed that the higher the molecular weight of lignin, the easier it is to precipitate at high pH, conversely, when the lignin molecular weight is lower, it will precipitate at low p H. Lower molecular weight and larger particle size are better for the metal ions adsorption property of lignin fractions.In addition, Pb²⁺,Cu²⁺, Cr2O72- adsorption capacities of metal ions is proportional to the contents of phenolic hydroxyl group, alcohol hydroxyl group and methyl group.Three different sources of industrial lignin（Shuntai AL, Nanyang EHL, Shandong WAL） were carboxymethylated, of which Shuntai AL has the highest reaction activity. The adsorption amount of three different kinds of carboxymethylated products to Pb²⁺, Zn²⁺,, Fe²⁺ were all increased, among which the maximum increase was Fe²⁺ adsorption capacity.This work optimized the parameters of carboxymethylation reaction and found that with the increase of the concentration of chloride, the adsorption performance of the modified product on Cu²⁺ first increased and then decreased. Higher concentration of sodium hydroxide, longer reaction time made the carboxymethylated degree of the products higher. But reaction time and temperature make little difference to the adsorption performance of Cu²⁺.Xiangjiang AL was aminatied and the products with positively charged surface are obtained. With the increase of pH, the amount of positive charge on the surface will be reduced. In mannich reaction, amine aldehyde ratio, aminating agent consumption and aminating agent types will influence the adsorption properties of products on Pb²⁺, Cu²⁺. The optimal ratio of aldehyde amine was 3.5 and the optimal amination agent consumption was equal to AL. By ethylenediamine andsodium glutamate as amination agent, the products have larger differences in the adsorption properties of Pb²⁺. Diethylene triamine modified aminatied AL has the biggest adsorption ability of Cu²⁺ adsorption capacity, that is 39.59 mg/g. Carboxymethylated-aminated alkali lignin contain both amino and carboxyl functional group, the adsorption of Pb²⁺, Cu²⁺ is higher than carboxymethylated AL and aminated AL.Adsorption kinetics and thermodynamic curve showed that the adsorption of aminated lignin on Pb²⁺ and Cu²⁺ is endothermic and the adsorption rate is rapid first and then slow down.The adsorption of aminated lignin on Pb²⁺ and Cu²⁺ conformed to the pseudo second order reaction mechanism.