Fate of arsenic-bearing phases during the suspended transport in a gold mining district (Isle river Basin, France)

Abstract

Arsenic-rich (~140-1520 mg x kg(-1)) suspended particulate matter (SPM) was collected daily with an automatic sampler in the Upper Isle River (France) draining a former gold mining district in order to better understand the fate of arsenic during the suspended transport (particles smaller than 50 μm). Various techniques at a micrometric scale (EPMA, quantitative SEM-EDS with an automated particle counting including classification system and μXRD) were used to directly characterize As-bearing phases. The most frequent ones were aggregates of fine clay particles. Their mineralogy varied with particle sources involved. These aggregates were formed by chlorite-phlogopite-kaolinite assemblages during the high flow and chlorite-illite-montmorillonite during the low flow. Among all the observed As-carriers in SPM, these clay assemblages were the least As-rich (0.10 up to 1.58 wt.% As) and their median As concentrations suggested that they were less concentrated during the high flow than during the low flow. Iron oxyhydroxides were evidenced by μXRD in these clay aggregates, either as micro- to nano-sized particles and/or as coating. (Mn, Fe)oxyhydroxides were also present as discrete particles. Manganese oxides (0.14-1.26 wt.% As) transport significantly more arsenic during the low flow than during the high flow (0.16-0.79 wt.% As). The occurrence of Fe oxyhydroxide particles appeared more complex. During the low flow, observations on banks and in wetlands of freshly precipitated Fe hydroxides (ferrihydrite-type) presented the highest As concentrations (up to 6.5 wt.% As) but they were barely detected in SPM at a microscale. During the high flow, As-rich Fe-oxyhydroxides (0.10-2.80 wt.% As) were more frequent, reflecting mechanical erosion and transport when the surface water level increased. Arsenic transfers from SPM to corresponding aqueous fraction mostly depend on As-carrier stability. This study shows the temporal occurrence of each type of As-bearing phases in SPM, their As concentrations at a particle scale and abundance according to hydrological periods.

Iron oxide - clay composite vectors on long-distance transport of arsenic and toxic metals in mining-affected areas

“…This points out the potential role of composite Fe-oxyhydroxides and phyllosilicate mineral vectors as element carriers in riverine soil-water systems, acting as mineral assemblages as described by Grosbois et al (2011). The proposed mechanism would be for As being attached to Fe-oxyhydroxide phases, which in turn use clays as an effective physical transport media.…”

Geochemical Footprint of Megacities on River Sediments: A Case Study of the Fourth Most Populous Area in India, Chennai

“…Trace elements and organic compounds present in waters and sediments of urban rivers are one of the major quality issues in many fast-developing cities [11][12][13][14][15][16]. The presence of certain trace elements may highlight certain sources, for example, trace elements such as Ag, Cd, Cr, Cu, Hg, Ni, Pb and Zn from domestic and industrial effluents [17][18][19][20].…”

XMAS: A Versatile Tool for Analyzing Synchrotron X-ray Microdiffraction Data

“…It is used in a variety of scientific fields ranging from the reliability study of endovascular stents for medical applications (Mehta et al, 2007) to elucidating the growth mechanism of nacre in abalone shell (Gilbert et al, 2008), and from the study of metal-insulator transitions in strongly correlated electron materials (Cao et al, 2010) to following the fate of toxic elements leached out from mining districts (Grosbois et al, 2011). In the wake of the tremendous progress made in the design of efficient X-ray focusing optics and 2D area detectors during the last two decades, high spatial resolution data of the distribution of materials' crystalline phases, texture and deformation can now be rapidly and routinely collected for a variety of samples.…”