Study On The Preparation Of Lignin-based Adsorbent With Purified And Fractionized Magnesium Ignosulfonate And Its Adsorption Performance

As lignosulfonate was main byproduct of the pulp and paper industry using acid method, only a small part was widely used in the polymeric surfactant, while most was simple heat utilization or discharged directly into the environment causing serious environmental pollution. Industrial lignosulfonates, owning low purity and high degree of dispersion of the molecular weight, severely limit their commercial application value. Constituted by a variety of active hydrophilic group of phenylpropane skeleton, therefore lignosulfonates can be prepared as a multi-functional and high performance lignin-based polymeric adsorption material for industrial wastewater treatment by appropriate graft-modified polymerization, which also enables the efficient use of resources. In this paper, several MWCO of ultrafiltration membrane was used to purify and classify the RMLS into different molecular weight fractions. Then these fractions as raw material and formaldehyde as the crosslinking agent were used to prepared lignin-based polymeric adsorption material, furthermore adsorption performance of simulated lead wastewater w7as investigated.Ultrafiltration technology was employed to purify and classify the RMLS, then the available MLS content of various fractions, content of total sugar and three main functional groups. It has shown that MWCO was reduced, the available MLS content of various fractions was in a trend of decrease. Meanwhile, available MLS content and its total sugar content were positively correlated. The fraction of total sugar content of<5K and3K were the lowest,9.27%,7.79%respectively. After ultrafiltration and classification, content of phenolic hydroxyl group and sulfonic acid group were significantly increased. As MWCO increases, the content of the phenolic hydroxyl group, a carboxyl group and a sulfonic acid group were reduced simultaneously. In high MWCO fractions, etherification and condensation lead to strong reduction of phenolic hydroxyl group content. While available MLS content was small in the low MWCO fractions, containing large amount of carbohydrates, low molecular weight sugar acids, sugar sulfonic acid and other organic matter, thus the content of sulfonic acid group and carboxyl group were relatively high.The polycondensation reaction showed that the poly condensation products of>10K,5K-10K,>5K and RMLS could be prepared by the polycondensation reaction, among which the polycondensation products yield of>10K was maximum, up to51.0%, while polycondensation products yield of5K-10K was minimum, only3.1%. It was consistent with the results reported in the literature that available MLS of herbaceous bagasse mainly concentrated in the10K Da fraction, this fraction of MLS is mainly composed of guaiacyl and syringyl.Adsorption performance of simulated lead wastewater onto PM10K (polycondensation products of>10K). PM5K,(polycondensation products of>5K) and PRMLS(polycondensation products of RMLS) were studied. Various factors affecting adsorption properties such as contact time, initial concentration adsorption temperature and adsorbent dose were investigated. It has shown that adsorption capacity of40mg/L Pb2+onto this three adsorbent(PM10K,PM5K, PRMLS) were25.45mg/g,24.8mg/g and23.12mg/g. respectively. The best adsorption performance of PM10K was selected as adsorbent, and then effects of temperature, pH, and dosage were investigated. Adsorption of200mg/L Pb2+onto PM10K reached equilibrium after90min, and the equilibrium adsorption capacity was69.75mg/g. The equilibrium data of Pb2+adsorption on PM10K were well fitted to the Langmuir isotherm, Langmuir monolayer maximum adsorption capacity (Qm) was108.70mg/g. The equilibrium adsorption capacity slightly reduced as the temperature increased from308K to318K. Value of pH played the most important role in adsorption of Pb2+on PM10K.When pH was2.25, the equilibrium adsorption capacity was highest, up to113.15mg/g. The kinetics of adsorption followed pseudo-second-order model and the adsorption of Pb2+was found to be spontaneous and endothermic process.