Fate of Sb(v) and Sb(iii) species along a gradient of pH and oxygen concentration in the Carnoulès mine waters (Southern France)

Abstract

The speciation and behaviour of antimony were investigated in surface waters downstream from the abandoned Pb-Zn Carnoulès mine (Gard, France). These waters exhibit a permanent gradient of oxygen concentration and pH, ranging from acid suboxic in Reigous Creek at the outlet of sulfide tailings impoundment, to near neutral oxygenated at downstream sites along the rivers Amous and Gardon. The concentration of total dissolved (<0.22 μm) antimony, acquired through a seven-year monitoring, decreased from 7.7-409.9 μg L(-1) at the source of Reigous Creek to 0.22-0.45 μg L(-1) in the Gardon River, showing natural Sb attenuation. Speciation analysis carried out during three surveys indicated that Sb(III) represented up to 70% of the total dissolved Sb concentration at the source of Reigous Creek, while Sb(V) represented less than 50%. Field characterization showed that Sb(III) and Sb(V) species were attenuated through dilution and were also removed from the dissolved phase during downstream transport. Speciation analysis in suspended particulate matter extracts gave a distribution of particulate Sb into 70 to 100% of Sb(III) and less than 30% of Sb(V). The removal of Sb(III) and Sb(V) species from the dissolved phase was concordant with the oversaturation of Reigous Creek water relative to Sb(III)- and Sb(V)-oxides and Sb(III)- and Sb(V)-Fe oxides. Sb(III) was more efficiently removed than Sb(V) or As(III) and it was no more detectable in the dissolved phase at downstream sites in the rivers Amous and Gardon. Conversely, the concentration of Sb(V) in the rivers Amous and Gardon still denoted contamination arising from the Carnoulès mine. The range of log Kd values, from 2.4 L kg(-1) to 4.9 L kg(-1), indicated that Sb was mainly transported in the dissolved phase downstream the Reigous Creek input. Altogether, these results give a better understanding of the fate of Sb downstream from sulfide-rich mining wastes.

Antimony isotopic composition in river waters affected by ancient mining activity

“…Antimony(III) was the predominant species (up to 70%) in the acid mine drainage (AMD) at the outlet of the tailings impoundment. Antimony(III) oxidation occurred along the AMD flow, as well as removal of Sb(III) and Sb(V) species with Fe precipitates and there was no more Sb(III) in the alkaline Amous river that receives the AMD (Resongles et al 2013). …”

“…That may be related to the mineralogy of Sb-bearing phases in the exploited ore. At the Carnoulès mine, which impacts the Amous River (T4), Sb is mainly associated to pyrargyrite (Ag 3 SbS 3 ) and galena (PbS) (Alkaaby 1986). The fate of Sb at the outlet of the tailings impoundment has been investigated at this site (Resongles et al 2013). Antimony(III) was the predominant species (up to 70%) in the acid mine drainage (AMD) at the outlet of the tailings impoundment.…”

“…Casiot et al 2007Casiot et al , 2009Resongles et al 2014). Among these elements, Sb is of great concern in the area; Sb concentration reaches 32 µg.L -1 in the small river downstream from the Sb mine of Bournac (Casiot et al 2007), 410 µg.L -1 downstream from the Pb-Zn mine of Carnoulès (Resongles et al 2013) and 11 µg.L -1 along the upper Gardon of Alès River where both Sb and Pb-Zn have been mined (Resongles et al under review). In this last area, there are aquifers supplying small villages that occasionally exceed drinking water standards (5 µg.L -1 ) (ARS website).…”

“…Performance Liquid Chromatography coupled to Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS) as described in Resongles et al (2013).…”

“…However, it can reach hundreds µg.L -1 in polluted rivers, especially close to current or former mining sites and smelters (Filella et al 2002a(Filella et al , 2009Casiot et al 2007;Liu et al 2010;Wang et al 2011;Asaoka et al 2012;He et al 2012;Hiller et al 2012;Resongles et al 2013). In this context, Sb sources and behavior need to be fully understood to predict its potential mobility, bioavailability and toxicity in aquatic environments and to initiate relevant remediation plans in mining-affected hydrosystems.…”