Environmental Assessment
Volume E-3.2
Tailings Facility
Geology and Geochemistry
Ambatovy Project
26
January 2006
•
the potential of these materials to impact surface water and groundwater
quality by leaching chemical constituents.
The tailings geochemical characterization program conducted by Dynatec
included the following:
•
chemical analysis of tailings solids;
•
acid-base accounting; and
•
chemical analysis of liquids:
entrained water from pilot plant test work;
supernatant;
drained seepage from settling test; and
three-stage sequential leaching.
The geochemical testing program resulted in the following findings.
The tailings samples included in Dynatec’s geochemical characterization
program are considered to be representative of expected operational processing
conditions. The QA/QC procedures and standards followed by SGS Lakefield
Research and Dynatec Technology Services are described in Volume I,
Section 2.1. However, it is not possible to determine the precision and accuracy
of the analytical results generated by these investigations.
The chemical compositions of the two tailings samples tested are consistent with
their mineralogical make-up, comprising principally hematite and gypsum
[CaSO
4
2H
2
O] with lesser amounts of hydronium alunite [(H
3
O)Al
3
(SO
4
)
2
(OH)
6
],
silica and unleached chromite [FeCr
2
O
4
]. The compositions are typical of
residues produced by pressure acid leaching of laterites.
Based on the acid-base accounting results, the two tailings samples tested are
classified as being non-acid-generating with Neutralization Potential Ratio (NPR)
values equal to or exceeding 4. Their lack of acid-generating potential is further
supported by the very low sulphide sulphur contents (i.e., below 0.3 wt%) and
the paste pH values greater than 5.5.
Despite having been generated by different methods, the chemical compositions of
the six entrained tailings solutions included in the geochemical characterization
program generally are similar. All solutions are circumneutral and have low trace
metal concentrations. Elevated concentrations are observed for calcium, magnesium,
