Details

Autor(en) / Beteiligte

• Gao, Zhipeng
• Guo, Huaming
• Zhao, Bo
• Wang, Ao
• Han, Shuangbao
• Dong, Hailiang

Titel

Experiment-based geochemical modeling of Arsenic(V) and Arsenic(III) adsorption onto aquifer sediments from an inland basin

Ist Teil von

• Journal of hydrology (Amsterdam), 2020-09, Vol.588, p.125094, Article 125094

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2020

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• •Experimental data were approximated well by the developed geochemical models.•Arsenic(V) sorption decreased at high PO4 concentration, while As(III) at high HCO3.•Kinetic As(III) oxidation was limited by available oxidation sites in oxic sediment.•Arsenic sorption capacities were related to content and phase of Fe(III) oxides. Natural occurrence of groundwater arsenic (As) exists in many aquifers and threatens the health of hundreds of millions of people. Adsorption of As is critical to its distribution in aquifer groundwater, as it can lower dissolved As concentrations and provide a source for As mobilization. However, little is known about As adsorption onto aquifer sediments in inland basins. To fill this gap, we investigated As(V) and As(III) adsorption onto a brown sediment hosting low-As groundwater and two gray sediments hosting high-As groundwater sampled from an approximate flow path of the Hetao Basin, China. Those three sediments had total Fe contents of around 1.3% and As contents of around 9.0 μg/g. Arsenic(III) adsorption were kinetically faster than As(V) adsorption on the sediments. The characteristics of As(V) and As(III) adsorption both exhibited nonlinear isotherms, with adsorption decreasing with increases in pH from around 7 to 9 (typical ambient groundwater pH of inland basins). Generally, As(V) adsorption was greater than As(III) adsorption at pH < 7.5, whereas the opposite was true at pH > 7.5. Phosphate competed more strongly with As(V) adsorption than As(III) adsorption, while HCO3 competed more strongly with As(III) adsorption. Aqueous As(III) was oxidized to As(V) by interaction with the brown sediment, mainly due to its high content of extractable Mn(IV) oxides. Arsenic adsorption onto the sediments was primarily controlled by the content and crystallinity of their Fe(III) oxides. The brown sediment showed weaker affinity for As(V) and As(III) than the gray sediments, possibly due to the better crystallinity of the Fe(III) oxides in the brown sediment. In the two gray sediments containing Fe(III) oxides with similar crystallinities, the As adsorption capacity was related to the content of Fe(III) oxides. Geochemical models were developed to quantitatively simulate As(V) and As(III) adsorption onto aquifer sediments. Experimental data were approximated well by these models, indicating that As(V) adsorption decreases at elevated pH and PO4 concentration, while As(III) desorption is favored at high pH and concentrations of HCO3 and PO4. According to the models, the extent and kinetics of As(III) oxidation are controlled by the number of free oxidation sites in Mn(IV) oxides, pH, and As(III) concentration. This study suggests that the characteristics of As adsorption are highly dependent on the mineral phases existing in the sediments, which must be fully understood to quantify the reactive transport of groundwater As in aquifer systems.