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ABIOTIC TRANSFORMATION OF CARBON TETRACHLORIDE AT MINERAL SURFACES
Citation:
Kriegman-King, M. AND M. Reinhard. ABIOTIC TRANSFORMATION OF CARBON TETRACHLORIDE AT MINERAL SURFACES. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-94/018.
Description:
Transformation of carbon tetrachloride (CCl4) by biotite, vermiculite, and pyrite in the presence of hydrogen sulfide (HS-) was studied under different environmental conditions. n systems containing biotite and vermiculite, the rate of CC4 transformation was dependent on the temperature, HS concentration, surface concentration, and Fe(II) content in the minerals. t 25 degrees C, the half-life of CCl4 with 1 mM HS- was calculated to be 2600, 160, and 50 days for the homogeneous, vermiculite (114 m2/L) and biotite (55.8 m2/L) systems, respectively. he transformation rate with biotite and vermiculite was nearly independent of pH in the range 6 - 10 at constant HS- concentration. he rate dependence on FE(II) content of the sheet silicates suggested that the transformation occurs at surface sites where HS- is associated with Fe(II). CCl4 reacted relatively rapidly in 1.2-1.4 m2/L pyrite with >90% of the Cl4 transformed within 12-36 days at 25 degrees C. he observed rate law supports a heterogeneous reaction mechanism. he reactivity of Cl4 with pyrite increased in the order: air-exposed pyrite/aerobic, air-exposed pyrite/HS-, air-exposed pyrite/anaerobic, and acid-treated pyrite/anaerobic but overall varied only by a factor of 2.5. he CCl4 transformation products were observed to vary under different reaction conditions. pproximately 80-85% of the CCl4 was transformed to CS2 which hydrolyzed to CO2-. nly 5-15% of the CCl4 was reduced to CHCl3. n the pyrite systems, CO2 was the major transformation product formed under aerobic conditions whereas CHCl3, was largely formed under anaerobic conditions. ormation of some CS2 was observed in all pyrite systems.