4th EucheMs chemistry congress

tuesday, 28-Aug 2012
s642
chem. Listy 106, s587–s1425 (2012)
Environment and Green Chemistry
Mining and the Environment – Remediation of pollution
o - 1 4 9
ACid Mine drAinAGe in the iBeriAn Pyrite
BeLt: SourCeS And reMediAtion StrAteGieS
C. AyorA 1
1 Institute of Environmental Assessment and Water Research,
Geosciences, Barcelona, Spain
The Iberian Pyrite Belt (SW Spain and Portugal) contains
the highest reserves of pyrite in the world with mining activities
dating back to prehistoric times. About one hundred abandoned
mine wastes and galleries release a huge acidity and metal load
to the Tinto and Odiel rivers. Once the mining activity is over,
polluting discharges can remain for centuries with no specific
responsible entity. In-situ passive remediation technologies are
especially suitable for these orphan sites. The concept is to insert
a reactive porous material in the natural flowpath of surface and
ground waters, and it is implemented through infiltration ponds
and reactive barriers, respectively. Calcium carbonate pea-size
gravel is the common alkalinity supplier to neutralize acidity and
precipitate metals. These remediation systems have been
traditionally implemented in coal mines. However, the acid
drainages from the Iberian Pyrite Belt contain metal
concentrations one to two orders of magnitude higher than those
from coal mines and require special designs to avoid quick
clogging or passivation (coating) of the grains of reactive material.
To overcome these problems, a Dispersed Alkaline Substrate
(DAS) mixed from fine-grained calcite sand and a coarse inert
matrix (wood chips) was developed. The small grains provide a
large reactive surface and dissolve almost completely before the
growing layer of precipitates passivates the substrate. The high
porosity and dispersion of nuclei for precipitation retard clogging.
However, calcite dissolution only raises pH to values around 6.5,
which is sufficient to precipitate the hydroxides of trivalent metals
(Al, Fe), but it is not alkaline enough to remove divalent metals.
Magnesium oxide buffers the solution pH between 8.5 and 10. A
DAS system replacing calcite with caustic magnesium oxide was
tested to be very efficient to remove divalent metals (Zn, Cd, Mn,
Cu, Co, Ni, Pb) from the water previously treated with calcite.
Keywords: acid mine drainage; passive remediation; disperse
alkaline substrate; calcite; caustic magnesia;
4 th EucheMs chemistry congress
Mining and the Environment – Remediation of pollution
o - 1 5 0
PerforMAnCe of A BioLoGiCAL PerMeABLe
reACtive BArrier for in-Situ reMediAtion of
ACid Mine drAinAGe: SuCCeSSeS And
ShortCoMinGS
o. GiBert 1 , J. L. CortinA 1 , J. de PABLo 1 , C. AyorA 2
1 Universitat Politecnica de Catalunya, Chemical Engineering,
Barcelona, Spain
2 Consejo Superior de Investigaciones Científicas, Institut de
Diagnosi Ambiental i Estudis de l’Aigua, Barcelona, Spain
Goal, Scope and Background. Acid mine drainage (AMD)
is a major environmental concern at numerous mining sites
worldwide. AMD is characterised by a high acidity and elevated
concentrations of heavy metals and sulphate and, because of its
negative impact on the subsurface systems, much attention is
focused on rehabilitating AMD-contaminated groundwater.
Biological Permeable Reactive Barriers (bPRBs) have emerged
in the last decades as a promising technology for this purpose.
objectives. This work aims at reporting the 3-year
performance of a bPRB for the bioremediation of an
AMD-contaminated groundwater. From a broader perspective,
and given the scarce data on full-scale bPRBs within this field,
the ultimate goal is to provide insights into such systems and aid
design of other future bPRBs.
Methods. Following a throughout investigation of a site
seriously affected by AMD, a bPRB was installed at the
underlying aquifer. The bPRB was divided into three modules
containing different proportions of compost, limestone and
zero-valent iron. A network of piezometers upstream, inside and
downstream the bPRB was used to monitor changes in
groundwater quality by the passage through the bPRB.
results and discussion. Overall, the bPRB proved to be
effective at neutralizing pH and removing heavy metals from
groundwater (removals >95%). However, shortcomings were also
evident. Sulphate was far from being completely depleted,
probably due to the poor degradability of compost and to the too
short residence time within the bPRB. From a hydraulic
perspective, the low permeability of some modules prevented the
bPRB from properly intercepting the entire contaminated
groundwater plume.
Conclusions. The results demonstrated that bPRBs can
be an effective technology for in-situ bioremediation of
AMD-impacted aquifers. Considering the expansion of this
technology, more data will predictably be generated within the
coming years and will provide a good base for better identifying
benefits and limitations of this technology.
Keywords: acidity; biological activity; environmental
chemistry; transition metals;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc