Opposite effects of dissolved oxygen on the removal of As(III) and As(V) by carbonate structural Fe(II)

Abstract

Freshly prepared carbonate structural Fe(II) (CSF) was used to immobilize As(III) and As(V) in wastewater under oxic and anoxic conditions. Dissolved oxygen was found to exert opposite effects on these two arsenic species. The sorption density of As(III) was higher under oxic conditions, whereas that of As(V) was higher under anoxic conditions. X-ray diffraction and infrared spectroscopic analyses indicated that crystalline parasymplesite (Fe(II)3(AsO4)2·8H2O) was formed when As(V) was removed under anoxic conditions, while an amorphous Fe-As-containing precipitate was formed when As(III) was removed under oxic conditions. The distribution of arsenic and iron between the solution and sediments suggested that the oxidation of structural Fe(II) promoted coprecipitation process and inhibited surface complexation. X-ray photoelectron spectroscopic analyses revealed that more As(III) was oxidized under oxic condition, which contributed to a higher sorption capacity for As(III). The formation of parasymplesite through surface complexation/precipitation was proposed to be more effective for the removal of As(V) by CSF, while As(III) was more efficiently removed through coprecipitation. Together, the results suggest that CSF may be an effective material for sequestering both As(III) and As(V). In addition, attention should be paid to the dissolved oxygen content when remediating different arsenic species.

Enhanced Arsenic (III and V) Removal in Anoxic Environments by Hierarchically Structured Citrate/FeCO3 Nanocomposites

“…The position of the sharp intense absorption peaks “white line” (dashed line) for the arsenic-sorbed samples in the normalized arsenic K-edge XANES showed no changes with respect to the peaks of As(III) reference sample, NaAsO 2 (11.868 KeV), and As(V) reference sample, Na 2 HAsO 4 ·7H 2 O (11.874 KeV) ( Figure 10 A), indicating no oxidation changes in the sorbed arsenic species. These observations are consistent with previous studies reporting no evidence of oxidation of sorbed arsenic on siderite, green rust, and a Fe(II)-carbonate sorbent under anoxic conditions [ 23 , 28 , 60 ]. Therefore, we note that both As(III) and As(V) are sorbed on CF-NCs without any oxidation changes.…”

“…Recently, siderite (FeCO 3 ) has received considerable attention as a promising arsenic sorbent which is both cost-effective and environmentally harmless. In particular, it features high surface reactivity [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ] and remains stable in anoxic-reducing systems where ferrous iron, carbonate, and organics are abundant [ 30 , 31 , 32 ]. For these reasons, it has been deemed a suitable material for attenuating As(III) in subsurface environments.…”

“…For these reasons, it has been deemed a suitable material for attenuating As(III) in subsurface environments. However, according to earlier studies on As(III) sorption on siderite in anoxic conditions, the sorption performance of siderite for As(III) is very low compared to that for As(V) [ 24 , 28 ]. Therefore, it is necessary to improve the sorption capacity of siderite for practical use as an effective sorbent in anoxic environments.…”

Biological Fe(II) and As(III) oxidation immobilizes arsenic in micro-oxic environments

“…This might facilitate arsenic adsorption and/or co-precipitation. During Fe(II) oxidation, arsenic can also be co-precipitated with Fe(III), resulting in the formation of amorphous ferric arsenate (Fernandez-Rojo et al, 2017;Tian et al, 2017). In this study, although a large proportion of arsenic was co-precipitated during Fe(III) precipitation (Fig.…”

“…Generally, the ferrihydrite formed by FeOB has a large surface area, which facilitates the adsorption of arsenic (Fuller et al, 1993;Sowers et al, 2017). A previous study concluded that the incorporation of arsenic into Fe(III) oxyhydroxides can produce amorphous ferric arsenate (or amorphous scorodite), which further accelerated arsenic immobilization (Tian et al, 2017).…”