NATO/CCMS Pilot Study Evaluation of Demonstrated and ... - CLU-IN

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2002
Site Description Material tested
Redundant polymetallic sulfide mine Sulfidic and oxidic
Lavrion, GR
(argentiferous, galena, sphalerite, pyrite) tailings, soils
Active polymetallic sulfide mines (galena- Waste rock
Stratoni, GR
sphalerite-pyrite) with a mining history of
more than 2.500 years.
Montevecchio,
Extensive Pb-Zn historic mining area. Sulfidic tailings,
Monteponi, Sardinia, IT Currently, there is one operating and many calamina red mud,
redundant mines.
soils
Chemical industrial site. Production of Pyrite cinders
Estarreja, PT
sulfuric acid by roasting of pyrites in the
period 1952-1991.
3. DESCRIPTION OF THE PROCESSES-RESEARCH ACTIVITY
3.1 Preventive Technologies to Inhibit the Spread of Pollution from the Active Sources
Processes for the prevention of pollutant migration, which were investigated in laboratory scale and are
being evaluated in field scale, include:
A. Limestone or Fly Ash Addition to Prevent Acid Generation from Sulfidic Wastes
The technical objective is the development of a process for the inhibition of acid generation from sulfidic
wastes by making beneficial use of the oxidation-dissolution-neutralization-precipitation reactions so as
to achieve: on a microscale, precipitation of reaction products around the pyrite grains, inhibiting further
oxidation and/or on a macroscale, formation of a hard pan that will drastically reduce the permeability of
wastes to water and oxygen. By achieving these goals, the required limestone or other alkaline additive
will be only a fraction of the stoichiometric requirements; therefore, the cost of application will be
significantly lower compared to the current practice of adding near-stoichiometric quantities.
An extensive laboratory kinetic testwork was carried out using limestone, a low cost and commonly found
at mine sites alkaline material, and fly ash, a by product of Greek-lignite powered electricity plants with
significant neutralization potential and cementitious properties. Kinetic tests using columns or humidity
cells were carried out for a period of 270-600 days. After 270 days of operation a selected number of
columns as well the humidity cells were dismantled and a detailed geotechnical and geochemical
characterization of the solid residues was performed.
Based on the laboratory test results, field tests were constructed in Lavrion and Stratoni, for the
remediation of sulfidic tailings and waste rock respectively, which have been run for a period of sixteen
months.
B. Formation of Surface Barriers for the Pyrite Cinders and Calamina Residues
The technical objective is to develop an innovative, cost-effective process for the inhibition of the toxic
leachate generation from these wastes by modification of the top surface layer with bentonite or
bentonite-zeolite additives. The aim is to achieve very low permeability of the surface layer in order to
inhibit water infiltration and subsequent leaching of contaminants.
The laboratory work performed include: a) selection of the stabilizing agents (bentonites and/ or zeolites
and/ or other materials) having certain properties (proper sediment volume, swelling index, yield, filtrate
loss and high cation exchange capacity), b) short term leaching tests to preliminarily determine
parameters including mode of application and addition rates of the stabilizing agents and c) lysimeter
kinetic tests. Following laboratory testing, field scale tests were conducted to evaluate the performance of
low permeability layers including: a) a sand-bentonite mixture to cover pyrite cinders at the Estarreja site,
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