Humic substances act as a chelating agent for metal ion extraction. Soluble humic substances (HS) might be an alternative to use instead of synthetic chemicals such as mineral acid or EDTA. These natural extractants are less expensive, biodegradable, environment friendly, less destructive to soil structure and also improve soil properties. Two peat soils were collected one from Khulna University campus and another from Gopalganj basin. Humic substances were extracted from peat soils. The characterization of humic substances was done by determining various parameters to evaluate their maturity. The quantifications of functional groups of humic substances were also performed. The complexing capacities of humic substances with metal ions depend on its maturity, molecular dimension and presence of functional groups. The optical density, E4:E6 ratio and coagulation thresholds of humic substances of Khulna region indicated more maturity due to intense humification process than that of HS in Gopalganj region. Consequently the functional groups including carboxylic (-COOH), phenolic (-OH) and aliphatic (-OH) of humic substances of Khulna region were relatively higher (from FTIR spectroscopy and potentiometric titration) which increased its metal holding capacity over that of Gopanganj region. Furthermore, the yield of humic and fulvic acids from mature peat of Khulna region were 2.48 and 2.29 folds higher than that of Gopalganj peat, respectively These characteristics may be attributable to the climatic conditions of the peatland of two regions. Therefore the humic substances of Khulna region were selected for further investigation.
