Type
Text
Type
Thesis
Advisor
Reeder, Richard J | Phillips, Brian | Hanson, Gilbert.
Date
2014-12-01
Keywords
Behavior, Hydroxapatite, Isotherm, Sb(V), Sorption | Geochemistry
Department
Department of Geosciences.
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/77667
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
Antimony (Sb) is regarded as an emerging environmental contaminant, reflecting its previously unrecognized presence in aquatic and soil systems. Oxidative dissolution releases Sb into surface environments primarily in the form of oxyanions. A primary control on the mobility of Sb species is sorption onto mineral surfaces. Although recent studies have reported Sb sorption onto various mineral surfaces, no studies have been performed on the sorption behavior of Sb with hydroxyapatite, which is an effective sorbent. The objective of this study is to understand the sorption behavior of Sb(V) on the surface of hydroxyapatite, Ca5(PO4)3OH. The oxidized form of antimony, Sb(V), occurs mainly as Sb(OH)6- in aqueous systems above pH 3.0. In the present study, batch sorption experiments were conducted over a range of conditions, including pH, ionic strength, and initial concentration of Sb(V). All sorption experiments were conducted in solution that was pre-equilibrated with hydroxyapatite, using a particle loading of 1.0 gL-1. The range of solution conditions encompassed pH 5.5-8.0, ionic strength 0.005 and 0.01 M, and initial Sb(V) concentration from 50-2000 µM. The isotherm experiments (determined at 24 hr) showed that Sb(V) sorption decreases as pH increases at I = 0.005 M. However, a sharp increase in uptake in the isotherm suggests that precipitation occurred in the solution at [Sb(V)] > 1000 µM. The type of background electrolyte has an effect on the sorption behavior of Sb(V). Using NaCl as the background electrolyte, evidence for the onset of precipitation was found at a lower Sb(V) concentration at I = 0.01 M (compared to I = 0.005 M), and was more pronounced at pH 7.0 and 8.0. To confirm formation of a solid precipitate in the solution, the filtered, dried samples were analyzed with powder X-ray diffraction. Sodium hexahydroantimonate (NaSb(OH)6), with the mineral name mopungite, was observed as the only secondary phase. Above the initial Sb(V) concentration 1000 µM, mopungite formed over the entire pH range at I = 0.005 M, and was observed to form at lower Sb(V) concentration at I = 0.01 M. This precipitation dominates sorption behavior of Sb(V) on hydroxyapatite at higher Sb concentrations. This study suggests that lower concentrations of Sb(V) could be effectively removed by sorption on hydroxyapatite at I = 0.005 M, consistent with previous work showing that metal oxides are effective sorbents of Sb(V). However, the sorption behavior of Sb(V) is critically affected by the existence of Na+ in the solution, which may promote precipitation. In nature, Na+ is one of the most abundant ions in aquatic systems, especially freshwater and seawater. Therefore, a comprehensive understanding of actual conditions, including properties of the aqueous and solid phases, is necessary for predicting the transport and fate of Sb in the environment. | Antimony (Sb) is regarded as an emerging environmental contaminant, reflecting its previously unrecognized presence in aquatic and soil systems. Oxidative dissolution releases Sb into surface environments primarily in the form of oxyanions. A primary control on the mobility of Sb species is sorption onto mineral surfaces. Although recent studies have reported Sb sorption onto various mineral surfaces, no studies have been performed on the sorption behavior of Sb with hydroxyapatite, which is an effective sorbent. The objective of this study is to understand the sorption behavior of Sb(V) on the surface of hydroxyapatite, Ca5(PO4)3OH. The oxidized form of antimony, Sb(V), occurs mainly as Sb(OH)6- in aqueous systems above pH 3.0. In the present study, batch sorption experiments were conducted over a range of conditions, including pH, ionic strength, and initial concentration of Sb(V). All sorption experiments were conducted in solution that was pre-equilibrated with hydroxyapatite, using a particle loading of 1.0 gL-1. The range of solution conditions encompassed pH 5.5-8.0, ionic strength 0.005 and 0.01 M, and initial Sb(V) concentration from 50-2000 µM. The isotherm experiments (determined at 24 hr) showed that Sb(V) sorption decreases as pH increases at I = 0.005 M. However, a sharp increase in uptake in the isotherm suggests that precipitation occurred in the solution at [Sb(V)] > 1000 µM. The type of background electrolyte has an effect on the sorption behavior of Sb(V). Using NaCl as the background electrolyte, evidence for the onset of precipitation was found at a lower Sb(V) concentration at I = 0.01 M (compared to I = 0.005 M), and was more pronounced at pH 7.0 and 8.0. To confirm formation of a solid precipitate in the solution, the filtered, dried samples were analyzed with powder X-ray diffraction. Sodium hexahydroantimonate (NaSb(OH)6), with the mineral name mopungite, was observed as the only secondary phase. Above the initial Sb(V) concentration 1000 µM, mopungite formed over the entire pH range at I = 0.005 M, and was observed to form at lower Sb(V) concentration at I = 0.01 M. This precipitation dominates sorption behavior of Sb(V) on hydroxyapatite at higher Sb concentrations. This study suggests that lower concentrations of Sb(V) could be effectively removed by sorption on hydroxyapatite at I = 0.005 M, consistent with previous work showing that metal oxides are effective sorbents of Sb(V). However, the sorption behavior of Sb(V) is critically affected by the existence of Na+ in the solution, which may promote precipitation. In nature, Na+ is one of the most abundant ions in aquatic systems, especially freshwater and seawater. Therefore, a comprehensive understanding of actual conditions, including properties of the aqueous and solid phases, is necessary for predicting the transport and fate of Sb in the environment. | 48 pages
Recommended Citation
Song, Boyoung, "Sorption Behavior of Antimony(V) on Hydroxyapatite" (2014). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 3459.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/3459