Investigating the binding properties between antimony(V) and dissolved organic matter (DOM) under different pH conditions during the soil sorption process using fluorescence and FTIR spectroscopy

Abstract

Antimony (Sb) is listed as a priority pollutant by European Union and U.S. Environmental Protection Agency. However, reports on its environmental behavior, particularly the sorption process in soil are still limited. In this paper, Sb(V) was selected as the sorbate and the black soil as the sorbent. The initial sorption rate (k₂q_e,cal²) was calculated to be 0.1254 mg g^-1∙min^-1 and the maximum sorption amount (q_m) 57.33 mg g^-1. Once the dissolved organic matter (DOM) was removed from the soil, the values of k₂q_e,cal² and q_m went down to 0.1066 mg g^-1∙min^-1 and 19.01 mg g^-1, respectively. These results suggested that the existence of DOM significantly influenced the mass transfer rate and sorption amount of Sb(V) in soil. In order to find out the reason why DOM exerted such an influence, the binding interaction mechanism between Sb(V) and DOM was investigated under different pH values. The protein-like and humic-like substances as well as the functional groups of CO, phenol hydroxyl, C-O, C-H, C-X and sulfur/phosphorus contributed to the formation of DOM-Sb(V)-complexes under pH of 7.0, in which the humic-like substance and the functional groups containing oxygen showed higher binding affinity for Sb(V) than protein-like substance and other functional groups, respectively. The protein-like substance and some functional groups disappeared under pH of 4.0 and 10.0. Alkaline condition resulted in a bigger impact on reducing the number of functional groups than acid condition. It can be concluded that the strongest binding interaction occurred at pH of 7.0 then followed by 4.0 and 10.0. This paper might be helpful to further studying the environmental behavior of Sb(V) in soil.

Keywords: Antimony(V); Binding interaction; Dissolved organic matter; Sorption.