Gas treatment of Cr(VI)-contaminated sediment samples from the North 60`s pits of the chemical waste landfill

Kinetic study of hexavalent Cr(VI) reduction by hydrogen sulfide through goethite surface catalytic reaction

“…Recently, Pacific Northwest National Laboratory has developed a technology for Cr(VI) reduction in the vadoze zone using hydrogen sulfide (H 2 S) as a reductant (Thornton and Amonette, 1997). Facile reduction of Cr(VI) by sulfide in the aqueous phase has been demonstrated by a number of studies (Schroeder and Lee, 1975;Smillie et al, 1981;Saleh et al, 1989).…”

In Situ Gaseous Reduction Pilot Demonstration - Final Report

“…A quantitative assessment of treatment effectiveness can be obtained by comparing the mass recovery of Cr(VI) in the leachate samples of the treated columns versus the untreated control (Thornton and Amonette 1997). For the untreated control (test GP5-14-1), 1.3192 mg of Cr(VI) were leached from 194.94 g of sediment, indicating a concentration of 6.8 m@g of Cr(V1) in the untreated sediment.…”

“…Greater than 99% immobilization was achieved in the two laboratory tests, but these tests were continued to high-breakthrough concentrations (C/CO>0.8). It is expected, however, that at least 900/0immobilization could be achieved if gas treatment were terminated at a C/COvalue of 0.7 (Thornton and Amonette 1997). In test GP5-14-2, which involved treatment of the soil with 100 ppm, HzS in Nz at a flow rate of 2.5 L/rein, it took -22 min to achieve 70'%0 breakthrough of H2S.…”

“…Mixtures of 100 ppmv HZSwere prepared (as described in Thornton and Amonette 1997) and directed through two of the columns at a flow rate of 2.5 L/rein for the duration of each test. In test GP5-14-2, the gas mixture consisted of 100 ppmv H2S in N2, while in test GP5-14-3, a mixture of 100 ppmv H2S in air was utilized.…”

Interfacial Reduction-Oxidation Mechanisms Governing Fate and Transport of Contaminants in the Vadose Zone

“…immobilization in the vadose zone , in which hydrogen sulfide is used as a reductant for Cr(VI) and other contaminant metals. Laboratory investigations have shown that 90% of Cr(VI) in soil samples can be immobilized by treatment with diluted H 2 S (Thornton and Amonette, 1997). A field test at White Sand Missile Range, New Mexico, has resulted in 70% immobilization of Cr(VI) (Thornton and Amonette, 1997).…”