The interaction between natural organic matter and antimony can alter the properties and behaviour of the metal in the environment. However, there is limited research on how the molecular weight of organic matter influences its binding to antimony. In this work, fulvic acid was used as a representative model of natural organic matter to investigate its complexation reaction with antimony. The physical and chemical properties of fulvic acid before and after complexation were thoroughly investigated using infrared and three-dimensional fluorescence spectroscopy. In addition, ultrafiltration was used to separate different molecular weight components within the fulvic acid solution for a comprehensive analysis of their complexation behaviour with antimony. The results showed that at pH 7, the dissolved organic carbon (DOC) concentration increased from 5 to 200 mg/L, and the proportion of Sb-HA (humic acid) increased from 8.86 to 15.18%. Conversely, at a DOC concentration of 30 mg/L and varying pH values (2, 7, and 10), the Sb ratio within the HA complexes decreased from 14.01 to 9.06%. In particular, when the Sb(V) concentration was 100 μg/L and fraction with molecular weight <10 kDa (UF4), the complexation ratio between fulvic acid and Sb reached 20.81%. It was found that the molecular weight of HA significantly influenced its complexation with Sb(V), especially those below 10 kDa showed superior performance compared to other fractions.
Yao et al. (Wed,) studied this question.