TY - JOUR
T1 - Chromium occurrence in a nickel laterite profile and its implications to surrounding surface waters
AU - Delina, Ruth Esther
AU - Arcilla, Carlo
AU - Otake, Tsubasa
AU - Garcia, Jhonard John
AU - Tan, Mark
AU - Ito, Akane
N1 - Funding Information:
The authors thank the Nickel Asia Corporation (NAC) and the Rio Tuba Nickel Mining Corporation (RTNMC) for generously supporting this research project and providing assistance throughout fieldworks. We also acknowledge the support given by the Japan International Cooperation Agency (JICA) through their Short-term Innovative Asia Program. We express our gratitude to C. Casalme, D. Rabang, R. Samosa, and the numerous students of the Earth Materials Science Laboratories, National Institute of Geological Sciences, University of the Philippines (UP-NIGS), for their field and laboratory aid. We also acknowledge colleagues in the Environmental Geology Laboratory, Hokkaido University, for their laboratory assistance and technical input: Prof. T. Sato, D. Yamauchi, K. Kinoshita, K. Toda, F. Dinala, K. Zay Ya, Y. Nishiki, and S. Higashino. We thank the Environmental Monitoring Laboratory and Nannoworks Laboratory in UP-NIGS for access to their laboratory equipment. The authors also appreciate Prof. C.P. David and Dr. J.P. Perez for their constructive comments. We also thank Dr. K. Johannesson for the editorial handling and the anonymous reviewers for their help in improving this manuscript.
Funding Information:
The authors thank the Nickel Asia Corporation (NAC) and the Rio Tuba Nickel Mining Corporation (RTNMC) for generously supporting this research project and providing assistance throughout fieldworks. We also acknowledge the support given by the Japan International Cooperation Agency (JICA) through their Short-term Innovative Asia Program. We express our gratitude to C. Casalme, D. Rabang, R. Samosa, and the numerous students of the Earth Materials Science Laboratories, National Institute of Geological Sciences, University of the Philippines (UP-NIGS), for their field and laboratory aid. We also acknowledge colleagues in the Environmental Geology Laboratory, Hokkaido University, for their laboratory assistance and technical input: Prof. T. Sato, D. Yamauchi, K. Kinoshita, K. Toda, F. Dinala, K. Zay Ya, Y. Nishiki, and S. Higashino. We thank the Environmental Monitoring Laboratory and Nannoworks Laboratory in UP-NIGS for access to their laboratory equipment. The authors also appreciate Prof. C.P. David and Dr. J.P. Perez for their constructive comments. We also thank Dr. K. Johannesson for the editorial handling and the anonymous reviewers for their help in improving this manuscript.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/12/30
Y1 - 2020/12/30
N2 - Ultramafic rocks are considered as the most important geogenic sources of Cr whose hexavalent species is of environmental concern. In tropical to subtropical areas (e.g. New Caledonia, Brazil, Philippines), prolonged and pervasive weathering of ultramafic rocks produces Ni laterite ores which are further enriched in Cr. While elevated levels of Cr have been identified in Ni laterites, Cr availability and export from these deposits and its contribution to natural waters remain poorly understood. Therefore, this study examined the speciation and flux of Cr in a Ni laterite profile through sequential extraction and leaching experiments coupled with physical, mineralogical, and geochemical characterization. These were correlated to the behavior and export of Cr in surrounding surface waters studied through hydrochemical investigation. This work demonstrates, through the example of the Rio Tuba Ni laterite deposit, that pervasive weathering of ultramafic rocks in tropical areas generate very important reservoirs of Cr(VI). Although Cr is primarily fixed in insoluble fractions (>89%) and least in bioavailable and easily mobilizable phases (<1%), due to the inherent elevated Cr content (up to 2.9 wt%) of the Ni laterites, the latter still provided water-extractable Cr(VI) contents surpassing drinking water and freshwater standards. By comparison with the silicate-rich saprolite unit, the overlying Fe-(oxyhydr)oxide dominated laterite layer yielded lower Cr(VI) contents due to its acidic nature and higher amounts of organic matter and Fe-(oxyhydr)oxides which promote reduction and readsorption of Cr(VI). During water infiltration, Cr(VI) migrates downward along the profile at a rate of 62 to 3446 t/km2/yr. While the alkaline and oxidizing conditions of the surrounding surface waters favor Cr(VI) mobilization, only a fraction of Cr(VI) from the Ni laterites reaches these water bodies. Cr(VI) concentrations (≤213 μg/L) and fluxes (mostly ≤50 kg/km2/yr) in the surface waters being significantly lower than that of the Ni laterites reflect the action of processes (e.g. dilution, reduction, adsorption) that attenuate the release of this species along water flow paths.
AB - Ultramafic rocks are considered as the most important geogenic sources of Cr whose hexavalent species is of environmental concern. In tropical to subtropical areas (e.g. New Caledonia, Brazil, Philippines), prolonged and pervasive weathering of ultramafic rocks produces Ni laterite ores which are further enriched in Cr. While elevated levels of Cr have been identified in Ni laterites, Cr availability and export from these deposits and its contribution to natural waters remain poorly understood. Therefore, this study examined the speciation and flux of Cr in a Ni laterite profile through sequential extraction and leaching experiments coupled with physical, mineralogical, and geochemical characterization. These were correlated to the behavior and export of Cr in surrounding surface waters studied through hydrochemical investigation. This work demonstrates, through the example of the Rio Tuba Ni laterite deposit, that pervasive weathering of ultramafic rocks in tropical areas generate very important reservoirs of Cr(VI). Although Cr is primarily fixed in insoluble fractions (>89%) and least in bioavailable and easily mobilizable phases (<1%), due to the inherent elevated Cr content (up to 2.9 wt%) of the Ni laterites, the latter still provided water-extractable Cr(VI) contents surpassing drinking water and freshwater standards. By comparison with the silicate-rich saprolite unit, the overlying Fe-(oxyhydr)oxide dominated laterite layer yielded lower Cr(VI) contents due to its acidic nature and higher amounts of organic matter and Fe-(oxyhydr)oxides which promote reduction and readsorption of Cr(VI). During water infiltration, Cr(VI) migrates downward along the profile at a rate of 62 to 3446 t/km2/yr. While the alkaline and oxidizing conditions of the surrounding surface waters favor Cr(VI) mobilization, only a fraction of Cr(VI) from the Ni laterites reaches these water bodies. Cr(VI) concentrations (≤213 μg/L) and fluxes (mostly ≤50 kg/km2/yr) in the surface waters being significantly lower than that of the Ni laterites reflect the action of processes (e.g. dilution, reduction, adsorption) that attenuate the release of this species along water flow paths.
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U2 - 10.1016/j.chemgeo.2020.119863
DO - 10.1016/j.chemgeo.2020.119863
M3 - Article
AN - SCOPUS:85091341297
VL - 558
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 119863
ER -