Binding Characteristics Of Heavy Metals To Natural Humic Acid Fractions Sequentially Extracted From The Lake Sediments

Humic acid (HA) includes tons of functional groups, which has a strong adsorption and complexation to heavy metals, as well as a strong influence on landmark geochemical behaviors. There are significant differences on elementary composition, molecular weight, functional group content, and structures of aliphatic and aromatic among HA fractions, therefore, it determined that a significant difference of mechanism of mutual effect between HA fractions and heavy metals must be defined. This work was based on the separation, extraction and purification of HA fractions from lake sediments of Wuliangsuhai, which follows the core experimental direction of the study on mechanism of adsorption of heavy metals among HA fractions, and also bring in the methods of spectroscopy and topography in order to discuss the sorption characteristics among HA fractions to heavy metals. It is important for help understanding the environmental geochemistry behaviors of heavy metals in lakes. All the findings are listed below:1. The functional groups were similar among HA fractions, however, along the extracted times, the HA fractions were shown a series characteristics include difference in humification degree, increase in molecular weight and aliphatic, and decrease in sorption, content of oxygen functional groups. The adsorption among HA fractions followed the order of Pb2+>Cd2+>Cu2+2. Along the increase of pH and the decrease of ionic strength, the adsorption of HA fractions to heavy metals has all been improved. The results also indicate that the earlier extracted fractions were more pH incentive than the later fractions, however, ionic strength were evenly effective along the fractions.3. The sorption of HA fractions to Cu2+, Pb2+ and Cd2+ were affected by both strong (N, S functional groups) and weak (carboxyl and hydroxyl) adsorption points, which weak adsorption points were played a leader role. This work has applied the bi-Langmuir model in fitting the amount of sorption to various factors, and the results showed a positive correlation to oxygen functional group and polarity, and a negative correlation to humification degree, molecular weight, aliphatic. The results indicates that the HA fraction with high polarity, rich oxygen functional group, low humification degree, low molecular weight, and low aliphatic has a stronger sorption ability to Cu2+, Pb2+and Cd2+.4. The result of SEM indicates that Cu2+, Pb2+ and Cd2+ were adsorbed onto the surface of HA and aggregated. The result of FTIR indicates that, hydroxyl and amidogen of HA had a significant influence on the adsorption to Cu2+, Pb2+ and Cd2+ which Cu2+ was more sensitive to the effect than the rest.