Chapter 24 SYNTHESIS, METAL-BINDING PROPERTIES AND DETOXIFYING ABILITY OF SULPHONATED HUMIC ACIDS

The complexing properties of humic substances are of primary importance for their application as detoxifying agents and microfertilizers. The promising approach for enhancing solubility of metal-humics complexes is incorporation of SO3H-groups into the structure of humics. The water soluble sulphonated humic materials can be used as flushing agents for heavy metal polluted sites and as chelating agents for production of microfertilizers. The objectives of this study were: 1) to synthesize sulphonated humic materials; 2) to evaluate solubility and stability of their complexes with Fe(III) and Hg(II); 3) to assess potential toxicity and detoxifying properties of the sulphoderivatives with respect to Hg(II) and Cu(II). Humic acids (HA) from leonardite and peat were used for modification. Concentrated sulphuric acid and chlorosulphonic acid were used as sulphonating agents. Chlorosulphonic acid was found to be much more efficient sulphonating agent causing introduction of 1.6 and 0.4 mmol SO3H per g of humic material from leonardite and peat, respectively. The binding properties of the sulphonated HA were studied in relation to Hg(II) and Fe(III). The solubility of metal