FeS-coated sand for removal of arsenic(III) under anaerobic conditions in permeable reactive barriers.
Iron sulfide (as mackinawite, FeS) has shown considerable promise as a material for the removal of As(III) under anoxic conditions. However, as a nanoparticulate material, synthetic FeS is not suitable for use in conventional permeable reactive barriers (PRBs). This study developed a methodology for coating a natural silica sand to produce a material of an appropriate diameter for a PRB. Aging time, pH, rinse time, and volume ratios were varied, with a maximum coating of 4.0 mg FeS/g sand achieved using a pH 5.5 solution at a 1:4 volume ratio (sand: 2 g/L FeS suspension), three days of aging and no rinsing. Comparing the mass deposited on the sand, which had a natural iron-oxide coating, with and without chemical washing showed that the iron-oxide coating was essential to the formation of a stable FeS coating. Scanning electron microscopy images of the FeS-coated sand showed a patchwise FeS surface coating. X-ray photoelectron spectroscopy showed a partial oxidation of the Fe(II) to Fe(III) during the coating process, and some oxidation of S to polysulfides. Removal of As(III) by FeS-coated sand was 30% of that by nanoparticulate FeS at pH 5 and 7. At pH 9, the relative removal was 400%, perhaps due to the natural oxide coating of the sand or a secondary mineral phase from mackinawite oxidation. Although many studies have investigated the coating of sands with iron oxides, little prior work reports coating with iron sulfides. The results suggest that a suitable PRB material for the removal of As(III) under anoxic conditions can be produced through the deposition of a coating of FeS onto natural silica sand with an iron-oxide coating.
Han
Young-Soo
YS
Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109-2125, USA.
Gallegos
Tanya J
TJ
Demond
Avery H
AH
Hayes
Kim F
KF
D000693:Anaerobiosis; D001151:Arsenic / Q000737:chemistry / Q000302:isolation & purification*; D005296:Ferrous Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D012822:Silicon Dioxide
D005296:Ferrous Compounds; D012822:Silicon Dioxide; D001151:Arsenic; C022597:ferrous sulfide