Geoscience Reference
In-Depth Information
Fig. 12.14 Release of As during leaching of mine tailings with a solution containing 500 lMof
both oxalate and citrate. Error bars represent 95 % confidence intervals (±3.18r) calculated for
all measurements inherent to these data. The inset table summarizes the concentrations of As in
the colloid composites and analytical error is less than the significant figures reported (Slowey
et al.
2007
). Reprinted from Slowey et al. (
2007
). Copyright 2007 with permission from Elsevier
show that in the case of a calcareous soil and due to a limited concentration of Fe
and Al oxyhydroxide, the contribution of nonlinear sorption to the retardation of
arsenate is negligible.
Metal presence in geological deposits may sometimes be associated with As
presence (Smedley and Kinniburgh
2002
). In particular, abandoned mine tailings
are often an important source of arsenic contamination in soil-subsurface systems.
For example, transport of As(V) adsorbed on suspended particles, from mine
tailings, was investigated at a contaminated site at Clear Lake, California, USA
Slowey et al.
2007
). The mineralogy of the studied site includes the presence of
multiple particles of jarosite, a basic hydrous sulfate and iron, which may serve as
a potential host of As. It was determined that arsenic concentration increases as
particle size decreases in the following dry-sieved fractions: particle sizes of
500-2,000 lm, 250-500 lm, 150-250 lm, 75-150 lm, 45-75 lm, and \45 lm
yield arsenic concentrations of 78, 92, 110, 125, 150, and 152 lg/g, respectively.
As(V) transport was examined in columns packed with mine tailings and lea-
ched with an electrolyte solution, at a pH of 5.7. Almost all of the measurable
As(V) removed from the column was adsorbed on solid state, and only traces of
dissolved As(V) were observed (Fig.
12.14
). Chemical analysis of the column
effluent indicated that all of the mobilized As was particulate, representing 6 % of
the total As through 255 pore volumes of leaching. Slowey et al. (
2007
) conclude
that the main mode of arsenic transport from the mine tailings occurs as As-
bearing colloidal particles, including As(V) sorbed to Fe(III)-hydroxides and
