TY - JOUR
T1 - Dissolution of arsenopyrite (FeAsS) and galena (PbS) in the presence of desferrioxamine-B at pH 5
AU - Cornejo-Garrido, Hilda
AU - Fernández-Lomelín, Pilar
AU - Guzmán, José
AU - Cervini-Silva, Javiera
N1 - Funding Information:
Hilda Cornejo-Garrido gratefully acknowledges the support of an undergraduate fellowship from The National Autonomous University of Mexico [DGAPA-UNAM, PAPITT (Grant No. IN116007-2)]. Javiera Cervini-Silva thanks the support of the Mexican Academy of Sciences (Academia Mexicana de Ciencias) and The United States-Mexico Foundation for Science (Fundación México-Estados Unidos para la Ciencia) through the 2006-Young Researcher Summer Program Fellowship (AMC-FUMEC). The authors are most grateful to Kent Ross (University of California Berkeley) for providing mineral samples, and to Elizabeth Chávira (Instituto de Investigación en Materiales, UNAM), Sergey Sedov (Instituto de Geología, UNAM), and Gretchen Lapidus Lavine (Universidad Autónoma Metropolitana, Itzapalapa) for technical assistance. This research was supported in part by The National Autonomous University of Mexico [DGAPA-UNAM, PAPITT (Grant No. IN116007-2)], CONACYT [SEP-CONACYT Ciencia Básica 2006, Grant No. 61670], and the UC MEXUS Program. The original form of this manuscript was improved significantly thanks to comments by one anonymous reviewer, Dave Craw (U. Otago, New Zealand), D. Kirk Nordstrom (U.S. Geological Survey, Boulder, CO) and Rebecca Sutton (Environmental Working Group, Oakland, CA).
PY - 2008/6/15
Y1 - 2008/6/15
N2 - Microorganisms and higher plants produce biogenic ligands, such as siderophores, to mobilize Fe that otherwise would be unavailable. In this paper, we study the stability of arsenopyrite (FeAsS), one of the most important natural sources of arsenic on Earth, in the presence of desferrioxamine (DFO-B), a common siderophore ligand, at pH 5. Arsenopyrite specimens from mines in Panasqueira, Portugal (100-149 μm) that contained incrustations of Pb, corresponding to elemental Pb as determined by scanning electron microscopy-electron diffraction spectroscopy (SEM-EDX), were used for this study. Batch dissolution experiments of arsenopyrite (1 g L-1) in the presence of 200 μM DFO-B at initial pH (pH0) 5 were conducted for 110 h. In the presence of DFO-B, release of Fe, As, and Pb showed positive trends with time; less dependency was observed for the release of Fe, As, and Pb in the presence of only water under similar experimental conditions. Detected concentrations of soluble Fe, As, and Pb in suspensions containing only water were found to be ca. 0.09 ± 0.004, 0.15 ± 0.003, and 0.01 ± 0.01 ppm, respectively. In contrast, concentrations of soluble Fe, As, and Pb in suspensions containing DFO-B were found to be 0.4 ± 0.006, 0.27 ± 0.009, and 0.14 ± 0.005 ppm, respectively. Notably, the effectiveness of DFO-B for releasing Pb was ca. 10 times higher than that for releasing Fe. These results cannot be accounted for by thermodynamic considerations, namely, by size-to-charge ratio considerations of metal complexation by DFO-B. As determined by SEM-EDX, elemental sample enrichment analysis supports the idea that the Fe-S subunit bond energy is limiting for Fe release. Likely, the mechanism(s) of dissolution for Pb incrustations is independent and occurs concurrently to that for Fe and As. Our results show that dissolution of arsenopyrite leads to precipitation of elemental sulfur, and is consistent with a non-enzymatic mineral dissolution pathway. Finally, speciation analyses for As indicate variability in the As(III)/As(V) ratio with time, regardless of the presence of DFO-B or water. At reaction times <30 h, As(V) concentrations were found to be 50-70%, regardless of the presence of DFO-B. These results are interpreted to indicate that transformations of As are not imposed by ligand-mediated mechanisms. Experiments were also conducted to study the dissolution behavior of galena (PbS) in the presence of 200 μM at pH0 5. Results show that, unlike arsenopyrite, the dissolution behavior of galena shows coupled increases in pH with decreases in metal solubility at t > 80 h. Oxidative dissolution mechanisms conveying sulfur oxidation bring about the production of {H+}. However, dissolution data trends for arsenopyrite and galena indicate {H+} consumption. It is plausible that the formation of Pb species is dependent on {H+} and {OH-}, namely, stable surface hydroxyl complexes of the form Pb4 (OH)4 4 + (pH50 5.8) and Pb6 (OH)8 4 + for pH values 5.8 or above.
AB - Microorganisms and higher plants produce biogenic ligands, such as siderophores, to mobilize Fe that otherwise would be unavailable. In this paper, we study the stability of arsenopyrite (FeAsS), one of the most important natural sources of arsenic on Earth, in the presence of desferrioxamine (DFO-B), a common siderophore ligand, at pH 5. Arsenopyrite specimens from mines in Panasqueira, Portugal (100-149 μm) that contained incrustations of Pb, corresponding to elemental Pb as determined by scanning electron microscopy-electron diffraction spectroscopy (SEM-EDX), were used for this study. Batch dissolution experiments of arsenopyrite (1 g L-1) in the presence of 200 μM DFO-B at initial pH (pH0) 5 were conducted for 110 h. In the presence of DFO-B, release of Fe, As, and Pb showed positive trends with time; less dependency was observed for the release of Fe, As, and Pb in the presence of only water under similar experimental conditions. Detected concentrations of soluble Fe, As, and Pb in suspensions containing only water were found to be ca. 0.09 ± 0.004, 0.15 ± 0.003, and 0.01 ± 0.01 ppm, respectively. In contrast, concentrations of soluble Fe, As, and Pb in suspensions containing DFO-B were found to be 0.4 ± 0.006, 0.27 ± 0.009, and 0.14 ± 0.005 ppm, respectively. Notably, the effectiveness of DFO-B for releasing Pb was ca. 10 times higher than that for releasing Fe. These results cannot be accounted for by thermodynamic considerations, namely, by size-to-charge ratio considerations of metal complexation by DFO-B. As determined by SEM-EDX, elemental sample enrichment analysis supports the idea that the Fe-S subunit bond energy is limiting for Fe release. Likely, the mechanism(s) of dissolution for Pb incrustations is independent and occurs concurrently to that for Fe and As. Our results show that dissolution of arsenopyrite leads to precipitation of elemental sulfur, and is consistent with a non-enzymatic mineral dissolution pathway. Finally, speciation analyses for As indicate variability in the As(III)/As(V) ratio with time, regardless of the presence of DFO-B or water. At reaction times <30 h, As(V) concentrations were found to be 50-70%, regardless of the presence of DFO-B. These results are interpreted to indicate that transformations of As are not imposed by ligand-mediated mechanisms. Experiments were also conducted to study the dissolution behavior of galena (PbS) in the presence of 200 μM at pH0 5. Results show that, unlike arsenopyrite, the dissolution behavior of galena shows coupled increases in pH with decreases in metal solubility at t > 80 h. Oxidative dissolution mechanisms conveying sulfur oxidation bring about the production of {H+}. However, dissolution data trends for arsenopyrite and galena indicate {H+} consumption. It is plausible that the formation of Pb species is dependent on {H+} and {OH-}, namely, stable surface hydroxyl complexes of the form Pb4 (OH)4 4 + (pH50 5.8) and Pb6 (OH)8 4 + for pH values 5.8 or above.
UR - http://www.scopus.com/inward/record.url?scp=44449165416&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2008.02.008
DO - 10.1016/j.gca.2008.02.008
M3 - Artículo
SN - 0016-7037
VL - 72
SP - 2754
EP - 2766
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 12
ER -