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

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2001
6. HEALTH AND SAFETY
The primary components of the unconventional sorbent suspensions, i.e., red muds and fly ashes
containing Fe2O3, Al2O3, SiO2, TiO2 and some aluminosilicates, to be used as barrier material are
essentially non-toxic. The tested heavy metals, either as free ions or in chelated forms, i.e., Cd 2+ , Pb 2+
(and partly Cu 2+ ) and Cd-EDTA 2− , Pb-EDTA 2− , Cu-EDTA 2− , were toxic, so care should be exercised
especially in solidification/ stabilization processes using the heavy metal-loaded sorbents in dry form
where small particles could be inhaled by workers. Also working with radionuclide solutions, even in
very dilute forms, needs special pipettes and glassware to be used under a hood on a stainless steel
workbench, and special laboratory practice with workers wearing radiation dosimeters. All waste
solutions, even at very low-level activity, should be properly collected and submitted to the nuclear
energy authority for waste storage and stabilization.
7. ENVIRONMENTAL IMPACTS
Prior acid or water leaching of the sorbents before adsorption experiments did not effectively increase the
specific surface area or chemical adsorption power of these sorbents, but rather these sorbents were
stabilized so as not to leach out any micropollutants to water at the time of heavy metal adsorption. It is
also indicated in literature that iron oxyhydroxide based grouts as barrier material can be made from low
cost industrial by-products, which should be tested for safety and effectiveness on a case-by-case basis
(Hapka et al., 1995). Thus these criteria should be judged for red muds and fly ashes.
Stabilization/solidification of the metal-loaded solid wastes puts these wastes and incorporated toxic
metals into environmentally safe (mechanically strong, durable and unleachable) forms. The matrix
disrupting effect of Pb was eliminated by using relatively small amounts of sodium aluminate or calcium
phosphate to improve the setting, hardening and mechanical properties of the final concrete blocks. It was
environmentally safe to observe that the matrix-held metals (either as a result of irreversible adsorption or
solidification) did not leach out by carbonate or carbonic acid solutions ensuring the chemical stability of
these solid wastes under changing groundwater conditions.
8. COSTS
Because iron-based grouts (without relatively expensive additives such as citric acid, urea, and urease)
can be prepared from inexpensive by-products, the primary costs involved come from transportation and
additives (Jet grouted, 25% grout) roughly around 50 USD per m 2 for 1m thick wall, i.e., or 50 USD for 1
cubic meter. The overall cost data have not yet been obtained.
9. CONCLUSIONS
In investigation of the possibility of usage of metallurgical solid wastes as cost-effective sorbents in
heavy metal (Pb, Cu, Cd) and radionuclide (Cs-137 and Sr-90) removal from contaminated water, red
muds and especially fly ashes have been shown to exhibit a high capacity. Extensive modeling of heavy
metal sorption—either as free metal ions or in the form of EDTA-chelates—has been performed by
simple quadratic equations in terms of the retained metal concentration in the sorbent phase. These
modeling efforts enable the prediction of heavy metal adsorption in different media over a wide pH and
concentration range. The developed iron- and aluminum-oxide based sorbents may be used as barrier
material as cost-effective grout for the prevention of expansion of a heavy metal contaminant plume.
Heavy metal-loaded solid wastes have been effectively solidified by adding cement, sand, and water. The
setting and mechanical properties of concrete specimens obtained by optimal dosage of waste addition
were satisfactory. The fixed heavy metals did not leach out appreciably into water over extended periods.
The usage of iron fillings as potential barrier material has been successfully tested for the management of
textile dyeing wastes, i.e., acid blue and acid yellow.
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