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

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2002
A mortar-mixing mechanical apparatus, ASTM Vicat apparatus, steel specimen moulds (4x4x16 cm 3 ),
tamping-vibrating apparatus, and testing equipment for flexural and compressive strength tests were used
for following the solidification process and the mechanical strength of the final concrete blocks.
The textile dyes used for modeling textile wastes were analyzed by UV/visible spectrophotometry.
The adsorption isotherms conforming to Langmuir, Freundlich, B.E.T. and Frumkin isotherm equations
were evaluated by linear regression and non-linear curve fitting of experimental data.
5. RESULTS
The distribution coefficients of metals (as log KD) between the solid (red mud, fly ash, etc.) and solution
phases varied between 1-3 and showed a gradual decrease with increasing equilibrium concentration of
the metal remaining in solution.
The Langmuir saturation capacities of the sorbents (in the units of mg metal per g sorbent as red mud-fly
ash, in this order) for the metals averaged at approximately 50-200 mg Cd.g−1, 40-100 mg Cu.g−1, and
100-350 mg Pb.g−1.
The adsorption isotherms were somewhat S-shaped B.E.T. type isotherms showing layered sorption at the
natural pH of equilibration, but saturation of the sorbent was attained at a definite concentration enabling
an approximated Langmuir evaluation of equilibrium data in operational sense.
The order of hydrolysable divalent metal cation retention on the selected sorbents was as follows in terms
of molar saturation capacities: Cu > Pb > Cd for fly ashes and Cu > Cd > Pb for red muds. The degree of
insolubility of the metal hydroxides approximately followed the same order. The simulation of CO2injected
groundwater conditions were achieved by saturated aqueous CO2 (pH 4.8) and carbonic
acid/bicarbonate buffer (pH 7.0) solutions. The heavy metals (Cu, Pb, Cd) retained on the sorbents were
not leached out by these carbonated leachant solutions.
Heavy metal adsorption onto red muds, either as free metal ion or in chelated metal-EDTA forms, has
been effectively modeled for (M+M-EDTA) mixtures. The adsorption data could be theoretically
generated by using simple quadratic equations in terms of covalently- and ionically- adsorbed metal
concentrations in the sorbent phase, once the total metal concentration prior to equilibration and final
solution pH were known.
As for solidification of the metal-loaded solid wastes, when these loaded wastes were added up to 20% by
mass to Portland cement-based formulations, the fixed metals did not leach out from the solidified
concrete blocks over extended periods, with the exception of Cu(II), which reached a concentration of 0.4
ppm after 8 months in a water leachate of pH 8-9. 2% setting accelerator Ca3(PO4) 2- added improved
formulations could bear only 10% of lead-loaded fly ash, while this tolerance could be raised to 20% fly
ash by incorporating (3% Ca3(PO4)2+1% CaCl2) mixed additive.
The studied radionuclides did not show a significant temperature dependency in adsorption. Especially
radiostrontium retention increased with pH. These observations are in accord with ion exchange
mechanism of sorption. Radiocesium adsorption is maximal around neutral pH, which is specific for most
natural waters.
Of the textile dyes tested, acid blue and acid yellow showed 75-90% and 60-80% removal, respectively,
when passed through a granular iron bed at an initial concentration of 10-100 ppm dye containing 0.10 M
HCl in solution.
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