Trace Element Retention and Release on Minerals and Soil in a Constructed Wetland

Abstract

Constructed wetlands are one method under investigation for the remediation of trace element-contaminated agricultural drainwater. A greater understanding of the retention of trace elements by the bulk soil and soil constituents is necessary for their safe and effective use. To determine the capacity of soil, calcite, and goethite-coated quartz sand for retention of As, Mo, and V under field conditions, an in situ method was used whereby permeable bags containing those minerals were placed near the sediment surface of a flow-through constructed wetland for 3 or 12 mo. Accumulations of As, Mo, and V occurred on goethite-coated sand. Concentrations of Mo on goethite-coated sand were much higher in samples from a wetland cell with a water depth of 15 cm (38.23 +/- 7.27 mg kg(-1)) compared with those from a cell with a water depth of 3 cm (8.30 +/- 1.45 mg kg(-1)). Calcite sorbed no As and low amounts of Mo and V, indicating that it is not an important sink for those elements under these conditions. In soil bags, total As and V concentrations showed little change over 12 mo. Molybdenum accumulated in the soil bags, resulting in total concentrations (12 mo) of 27.22 +/- 2.69 mg kg(-1) and 11.42 +/- 1.35 mg kg(-1) at water depths of 15 and 3 cm, respectively. Nearly half of the Mo accumulation on soil became water soluble after air-drying. This has important implications for systems that may undergo changes in redox status, possibly resulting in large fluxes of water-soluble Mo.

Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

“…Molybdenum is generally found in two oxidation states in nature, Mo(IV) and Mo(VI) (Fox and Doner 2002). It may exist as MoS 2 in reducing environments although the formation may be kinetically limited (Helz et al 1996).…”

“…It may exist as MoS 2 in reducing environments although the formation may be kinetically limited (Helz et al 1996). Mo(VI) dominates under oxidizing conditions and is commonly present as MoO 2À 4 (Fox and Doner 2002). Therefore, the removal of MoO 2À 4 from wastewaters is of significant importance from an environmental point of view.…”

Evaluation of Electrokinetic Remediation of Arsenic-contaminated Soils

“…On the other hand, arsenic may be retained by its adsorption onto clays and metal oxides, particularly those of Fe, Al and Mn (Smedley and Kinniburgh 2002). Generally, there is a good correlation between extractable iron and arsenic in soils and sediments around arsenic-enriched areas (Fox and Doner 2002). However, the adsorbed arsenic is released from clays and oxides by reductive desorption, or reductive dissolution, under reducing conditions (Smedley and Kinniburgh 2002).…”

Behavior of redox-sensitive elements during weathering of granite in subtropical area using X-ray absorption fine structure spectroscopy

“…Specially, V displays inverted trend with Mn, Ce and Co. Fox and Doner (2002) reported that V was found in +3, +4, and +5 oxidation states in nature. Vanadyl is strongly adsorbed by solid phases, including organic and oxide-oxyhydroxide phases, whereas adsorption of the V anions is much lower than the cations (Wehrli and Stumm, 1989;Wanty and Goldhaber, 1992).…”

“…Previous studies on the chemical speciation of redox-sensitive elements were performed for seasonally saturated soils (Flessa and Fischer, 1992;Fox and Doner, 2002;Weber et al, 2009), bioturbated sediments (Aller, 1994;Collins and Kinsela, 2010), and forest soils (Clark et al, 1998;Silver et al, 1999). Comparatively, less information is available concerning redox transformation of trace metals during weathering of granitic rocks (Middelburg et al, 1988;van der Weijden and van der Weijden, 1995).…”