Study On The Kraft Lignin As Soil Conditioning Agent

It is well known that Al ions eluted into soil solution under acidic conditions have a serious toxic effect to plant and forest. The problem of draining black liquor of middle and small-scaled Papermaking Company, not only polluted the environment seriously, but also endangered their existence and development. In this study, new soil conditioning agents were developed from Kraft lignin. We modified Kraft lignin by radical sulfonation and alkaline -oxygen treatment .T'he effect of the reaction factor on the sulfonation were studied. The chemical structure feature of modified lignin by alkaline-oxygen treatment was analyzed. Interaction between Al 3+ and modified lignin was examined by FTIR> GC, K^ GFC, NMR etc. The ability of modified lignin to retard the A13+ toxicity and improve the soil condition was evaluated by planting experiment.Conductometric titration of modified lignin indicate that acidic groups in the modified lignin can be classed into three groups, the strongly acidic group (A), intermediately acidic group (B) and weakly acidic group (C). Sulfonic acid group was introduced to or/Ao-position of phonlic hydroxyl group during radical sulfonation treatment. Introduction of sulfonic acid group to Kraft lignin by radical sulfonation could be confirmed also by the increased intensities of band at 1217 cm"1 and 1142 cm'1 in its FTIR spectrum.The chemical analysis result of modified lignin by alkaline-oxygen treatment is as following:The chemical analysis result of modified lignin by alkaline-oxygen treatment showed that the carboxyl group of modified lignin increased, since muconic acid type structure were generated from phenolic structure by ring-open reaction during alkaline-oxygen treatment. The analysis result of alkaline nitrobenzene oxidation and 'H NMR proved that amount of high molecular weight composition of KL still retention in the modified lignin. These characteristics of modified lignin are good for the formation of complex between A13+ and modified lignin under acid condition. Meanwhile these modified lignin also have properties of absorption and buffering in soil system.The GFC experiment of the mixture of Al3+and modified lignin showed that Al/S-1 changed under different pH condition. Al/S-1 stand for the amount of Al3+absorbed by each mol. of modified lignin. When pH5.8, the Al/S-1 reached maximum, about 0.358 mol.. The formation of complex between modified lignin and A13+ were further confirmed by potentionmetric titration.The planting experiment of modified lignin showed that both sulfonated lignin and alkaline -oxygen treatment lignin could retard the toxicity of aluminum to the growth of root elongation, although their efficiencies were different and depended on the chemical structure of modified lignin, namely the type and content of function group in the modified lignin. This was also proved by hematoxylin staining experiment.