Complexation of arsenate to humic acid with different molecular weight fractions in aqueous solution

Abstract

Natural organic matter (NOM) has been considered a critical substance in the transport and transformation of arsenic. NOM is a complex mixture of multifunctional organic components with a wide molecular weight (MW) distribution, and it is necessary to understand the complexation of arsenic with MW-dependent NOM fractions. In this study, humic acid (HA) was chosen as the representative fraction of NOM to investigate the complexation mechanism with arsenic. The bulk HA sample was fractionated to five fractions by ultrafiltration technology, and the complexing property of HA fractions with arsenic was analyzed by the dialysis method. We observed that the acidic and neutral conditions favor the complexation of HA fractions with arsenate (As(V)). The HA fractions with molecular weight > 100 kDa, 1-10 kDa, and <1 kDa have the stronger complexing capacity of As(V) than the other HA fractions. The bound As(V) percentage was positively associated with carboxyl content, phenolic content, and especially total acidity. A two-site ligand-binding model can describe the complexing capacity of arsenic onto HA fractions. The results can provide some fundamental information about the complexation of arsenic with MW-dependent HA fractions quantitatively.

Keywords:

• Arsenic
• humic acid
• complexation
• molecular weight

Disclosure statement

The authors declare that they have no conflict of interest.

Data availability statement

The data that support the findings of this study are openly available in figshare at https://doi.org/10.6084/m9.figshare.16917331.v1.

Additional information

Funding

We thank the Scientific Research Fund of Liaoning Provincial Education Department (No. LQ2020027), China Postdoctoral Science Foundation (No. 2015M571343), and Science and Technology Program of Shenyang University of Chemical Technology (No. XXL2019003) for the financial support.