Release of arsenic and molybdenum by reductive dissolution of iron oxides in a soil with enriched levels of native arsenic

Abstract

This study examined the release of arsenic (As), molybdenum (Mo), and iron (Fe) into the aqueous phase during reductive dissolution of iron oxides in an amended acid sulfate soil naturally enriched in arsenic. These acid sulfate soils occur worldwide and have a significant distribution in parts of Alberta and British Columbia. Reactions were studied in incubation vessels under controlled laboratory conditions. Soils were driven anaerobic by stimulation of indigenous bacteria using a glucose addition and then periodically analyzed for redox potential (Eh), pH, electrical conductivity, and aqueous concentrations of Fe, As, Mo, and other chemical species. Dissolution of iron oxides was pronounced when Eh values dropped to below +100 mV. With dissolution, concentrations of Fe, As, and Mo increased in the solution phase. Aqueous As concentrations increased from 0.87 to 119 µg L −1 during a reduction period of 48 d. Molybdate (MoO 2− 4 ), an oxyanion similar to arsenate, also closely followed the release of Fe and As into solution during the incubation.The results indicate both As and Mo behave similarly in response to the dissolution of soil iron oxides under reducing conditions and that their aqueous phase concentrations are largely controlled by dissolution and desorption from the iron oxide host.Résumé : Cette étude examine la libération d'arsenic (As), de molybdène (Mo) et de fer (Fe) dans la phase aqueuse lors de la dissolution des oxydes de fer dans un sol sulfaté acide amendé naturellement riche en arsenic. Ces sols sulfatés acides se retrouvent partout dans le monde et sont aussi très répandus dans certaines parties de l'Alberta et de la Colombie-Britannique. Les réactions ont été étudiées dans des vaisseaux d'incubation sous des conditions contrôlées en laboratoire. Les sols ont été rendus anaérobies par la stimulation des bactéries indigènes par l'ajout de glucose; l'Eh, le pH, la conductivité électrique et les concentrations aqueuses de Fe, As, Mo et d'autres éléments chimiques ont ensuite été analysés périodiquement. La dissolution des oxydes de fer était prononcée lorsque les valeurs d'Eh chutaient sous +100 mV. Avec cette dissolution, les concentrations de Fe, As et Mo augmentaient dans la phase aqueuse. Les concentrations aqueuses d'As ont augmenté de 0, 87µg L −1 à 119µg L −1 durant la période de réduction de 48 jours. Le molybdate (MoO 2− 4 ), un anion polyatomique contenant de l'oxygène et similaire à l'arséniate, suivait également de très près la libération de Fe et de As en solution durant l'incubation. Les résultats indiquent que l'As et le Mo se comportent de même manière en réponse à la dissolution des oxydes de fer dans le sol sous des conditions de réduction et que leurs concentrations en phase aqueuse sont grandement contrôlées par la dissolution et la désorption de l'hôte d'oxyde de fer.

Sulfur Species as Redox Partners and Electron Shuttles for Ferrihydrite Reduction by Sulfurospirillum deleyianum

“…Stock solutions were either autoclaved or sterilely filtered and stored in serum bottles under N 2 . Solutions of sodium thiosulfate pentahydrate (Na 2 O 3 S 2 · 5H 2 O), sodium sulfite (Na 2 SO 3 [anhydrous]; Fluka), potassium tetrathionate (K 2 S 4 O 6 ; Sigma-Aldrich), sodium sulfide nonahydrate (Na 2 S · 9H 2 O; Sigma-Aldrich), and potassium polysulfide (K 2 S x ; Sigma-Aldrich) were prepared in ultrapure water. The latter two were prepared inside a Coy anoxic glove box (N 2 -H 2 [95/5, vol/vol]).…”

“…Potentially toxic trace metalloids and metals such as arsenic, lead, and cadmium sorb to the surface of iron(III) (oxyhydr)oxides and are removed from the aqueous phase (1)(2)(3)(4)(5). Also, the availability of nutrients such as phosphate can be limited by adsorption (6,7).…”

Liberation of Adsorbed and Co-Precipitated Arsenic from Jarosite, Schwertmannite, Ferrihydrite, and Goethite in Seawater

“…Weaker Fe(II) bonds enhance reductive dissolution and release of species from oxides surfaces. For example, in Alberta (Canada) microbial activity in acid sulphate soils released significant amounts of As when the Eh was below +100 mV [23]. Mine tailings at the former Delnite gold mine in Northern Ontario showed that As(V) reduction and mobilization occurred due to reductive dissolution of goethite, influenced by a biosolid-cover [24].…”

Groundwater Arsenic Contamination in Semi-Urban Areas of Tando Muhammad Khan District: A Case Study from Deltaic Flood Plain of Sindh, Pakistan

“…Although the study area is semi urban but surroundings are agricultural sites hence the nutrients leaching from fertilizer input in groundwater of study area is obvious. The strong loading of As and Fe is clear evidence of reductive dissolution of iron oxyhydroxide (FeOOH) which is widely believed mechanism of arsenic release in Holocene alluvial aquifers of the world (Smedley & Kinniburgh, 2002;Chatain et al, 2005;Bennett & Dudas, 2003). Due to high affinity of As for iron oxides, arsenic concentrations in natural ferrihydrite samples have been documented with values up to 14 wt% As (Rancourt et al, 2001).…”