Spectroscopic investigation of the uptake of arsenite from solution by synthetic mackinawite.
As(III) uptake from solution by synthetic mackinawite is examined as a function of pH and initial As(III) concentration using X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD). XAS data indicate that when mackinawite is reacted at pH 5, 7, and 9 with 5 x 10(-4) M As(III), arsenic is reduced from its original +3 valence state and is primarily coordinated as As-S (approximately 2.26 angstroms) and As-As (approximately 2.54 angstroms), which is consistent with the formation of a realgar-like phase in agreement with XRD data. At 5 x 10(-5) M As(III), samples are markedly different from those collected at an order of magnitude higher concentration and differ at each pH value. The XAS analysis of mackinawite samples reacted with 5 x 10(-5) M As(III) shows a transition from As-O coordination to As-S coordination as pH decreases, with the sample reacted at pH 5 resembling realgar. Under alkaline conditions, arsenic retains its original valence state of +3 and is primarily coordinated to oxygen at a distance of 1.75 angstroms. This may be attributed to uptake by adsorption as an As(III) oxyanion. These results provide the basis for selecting the reactions needed for modeling and are beneficial in understanding the mechanisms of arsenite uptake by mackinawite under anoxic sulfidic conditions.
Gallegos
Tanya J
TJ
Department of Civil and Environmental Engineering, University of Michigan, 181 EWRE, 1351 Beal Avenue, Ann Arbor, Michigan 48109, USA.
Hyun
Sung Pil
SP
Hayes
Kim F
KF
D015502:Absorptiometry, Photon / Q000379:methods*; D000693:Anaerobiosis; D000838:Anions; D001151:Arsenic / Q000737:chemistry*; D018053:Arsenites / Q000493:pharmacokinetics*; D005296:Ferrous Compounds / Q000032:analysis / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010100:Oxygen / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*; D013440:Sulfides / Q000737:chemistry; D013447:Sulfites / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D014961:X-Ray Diffraction
D000838:Anions; D018053:Arsenites; D005296:Ferrous Compounds; D013440:Sulfides; D013447:Sulfites; D013455:Sulfur; D007501:Iron; C015001:arsenite; D001151:Arsenic; D010100:Oxygen; C022597:ferrous sulfide