HOW IS THE POTENTIAL RISK OF RELEASE OF ARSENIC AND ANTIMONY IN WATER DRAINING MINING RESIDUES ASSESSED?
Mining activities produce residues that contain high levels of Arsenic sulphides and Antimony sulphides and hence release and Arsenic(As) and Antimony(Sb) into the aquatic ecosystem. Both metalloids are highly toxic for biota and humans, and a possible synergistic effect in cancer development has been suggested for Sb and As in drinking water (Gebel,1997, 1999). The two elements are present in the form of oxy anions with +V and +III redox states in natural waters. Arsenic mobility in oxic water is limited by its ability to bind to Fe-oxy hydroxides (Bowell, 1994;Sadiq, 1997) and hence As(V) adsorbs more strongly on Fe-oxyhydroxides than As(III).
This study tends to assess the potential risk of the release of Sb and As as a function of redox conditions and microbial activity in water draining mining residues. For this purpose, variations in the concentrations of Sb and As were measured as a function of pH, dissolved O2 in Bournac Creek which drains a former Sb mine. Complex sulphide mineralization occurs in this mine with Stibnite (Sb2S3) as the most abundant mineral . The mine site is drained by a small creek which flows through a mineralized area and drains a tailings heap before entering a settling pool. In the pool, the particulate matter gets settled . Water samples for As, Sb and Fe measurements were taken from the the pool and pH, temperature and dissolved O2 concentrations were measured.
Leaching experiments of sediments were performed in the laboratory in oxic and anoxic conditions with and without bacteria.
The field experiments indicated that there was a significant increase in the dissolved As, Sb and Fe concentrations and these concentrations exceed the European drinking water limits.In the suspended particulate matter of Bournac Creek, the good correlation between particulate As, Sb, and Fe concentrations suggests that Fe oxy-hydroxides containing pyrite grains are the major carrier phases for As and Sb. (Pierce and Moore (1982); Ambe et al. (1986); Raven et al. (1998); Lintschinger et al. (1998); Dixit and Hering (2003), and Wilson et al.(2004). The mobilization of As and Sb was also observed in the laboratory experiments performed in oxic conditions and involves the oxidation of pyrite by reductive dissolution of Fe oxides . Field experiments conﬁrmed that the process is more efficient in the presence of bacteria, which generally catalyse the oxidation of pyrite (Stumm and Morgan, 1981). In anaerobic sterile conditions, most of the As was released in the oxidized form. In contrast, in anaerobic, non-sterile conditions, the vast majority of the As was released into solution in the form of As(III). These observations suggest a bacterially mediated reduction of As adsorbed on Fe-oxy hydroxides as also reported by Zobrist et al. (2000).
This study conﬁrms that Fe-oxides are the main carrier phases of As and Sb. Both elements may be released into solution in aerobic and anaerobic conditions. In aerobic conditions, the process involves pyrite oxidation . The presence of bacteria increases the release of both elements in aerobic conditions. In anaerobic conditions, the bacteria only favour the release of As.
1.Ambe, F., Ambe, S., Okada, T., Sekizawa, H., 1986. In situ Mossbauer studies of metal-oxide-aqueous solution interfaces with adsorbed cobalt-57 and antimony-118 ions. In:Davis, J.A., Hayes, K.F. (Eds.).Geochemical Processes at Mineral Surfaces, ACS Symp. Series, vol. 323. American Chemical Society, Washington, DC, pp. 403 –424.
2..Bowell, R.J., 1994. Sorption of arsenic by iron oxides and oxyhydroxides in soils.
Appl. Geochem. 9, 279 –288
3.Dixit, S., Hering, J.G., 2003. Comparison of arsenic(V) and arsenic(III) sorption onto iron oxide minerals: Implications for arsenic mobility. Environ. Sci. Technol. 37,4182-4189.
4.Gebel, T., 1997. Arsenic and antimony: comparative approach on mechanistic toxicology. Chemico-Biological Interactions 107,131 – 144.
5.Gebel, T.W., 1999. Arsenic in drinking water contamination. Science 283 (5407), 1455.
6.Lintschinger, J., Michalke, B., Schulte-Hostede, S., Schramel, P.,1998. Studies on speciation of antimony in soils contaminated by industrial activity. Internat. J. Environ. Anal. Chem. 72,11 –25.
7.Pierce, M.L., Moore, C.B., 1982. Adsorption of arsenite and arsenate on amorphous
iron hydroxide. Water. Res. 16, 1247 –1253.
8.Raven, K.P., Jain, A., Loeppert, R.H., 1998. Arsenite and arsenate adsorption on
ferrihydrite: kinetics, equilibrium, and adsorption envelopes. Environ. Sci. Technol. 32,
9.Sadiq, M., 1997. Arsenic chemistry in soils: an overview of thermodynamic predictions
and ﬁeld observations. Water Air Soil Pollut. 93, 117 –136.
10.Stumm, W., Morgan, J.J., 1981. Aquatic Chemistry: An Introduction Emphasizing
Chemical Equilibria in Natural Waters.Wiley, New York.
11.Wilson, N.J., Craw, D., Hunter, K., 2004. Antimony distribution and environmental
mobility at an historic antimony smelter site, New Zealand. Environ. Pollut. 129, 257 –
12.Zobrist, J., Dowdle, P.R., Davis, J.A., Oremland, R.S., 2000. Mobilisation of arsenite
by dissimilatory reduction of adsorbed arsenate. Environ. Sci. Technol. 34, 4747 –4753.
This is a summary of a Geology paper entitled “Antimony and arsenic mobility in a creek
draining an antimony mine abandoned 85 years ago (upper Orb basin, France)”
by C.Casiot, M. Ujevic , M. Munoz , J.L. Seidel , F. Elbaz-Poulichet