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The photocatalytic degradation of humic acid (HA) in aqueous solution with titanium dioxide (TiO2) as catalyst has been studied. The effect of initial pH of the solution on the photocatalytic degradation has been examined. The photocatalytic process of humic acid has been followed by the determination of UV-VIS spectra and total organic carbon (TOC) of the reaction solution. The results showed that at low pH values, the degradation of HA was very favorable due to the adsorbent nature of the catalyst. The mineralization of the organic matter was observed with a reduction of the TOC of the order of 70 and 80% at pH = 7 and 3 respectively. Parameters such as absorbance ratio and Specific UV Absorbance (SUVA) were also calculated and the results revealed a reduction of the macromolecules of HA into compounds of smaller sizes. Moreover an aromaticity reduction of the treated HA was observed due to the action of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

Adsorption behaviours of humic acid on three natural clays from Ivory Coast were studied. In order to investigate the adsorption mechanism, characterization of clays and the humic acid–clay complex was conducted by using various analytical methods (attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), specific surface area analysis (BET) and chemical composition). As a result, adsorption process showed that the maximum adsorption capacity of humic acid was achieved at pH = 3 and was found to be to 115 mg/g obtained for the best sample. For all clays, the adsorption was found to be strongly dependent on pH and well fitted by the Langmuir model. In addition, it was shown that the adsorption capacity was linked to the kaolinite content of each sample. The results showed that humic acid adsorption onto clay was made via electrostatic interactions, ligand exchange and hydrophobic interactions. This study showed that clays are valuable adsorbents for the removal of humic acid. [ABSTRACT FROM AUTHOR]