A comparative evaluation of hexavalent chromium treatment in contaminated soil by calcium polysulfide and green-tea nanoscale zero-valent iron. 2012

Maria Chrysochoou, and Chad P Johnston, and Geeta Dahal
University of Connecticut, Department of Civil and Environmental Engineering, Storrs, CT 06269, United States. mchrysoc@engr.uconn.edu

A column study for hexavalent chromium (Cr(VI)) removal from contaminated soil was performed using calcium polysulfide (CPS) and nanoscale zero-valent iron stabilized with green tea extract (GT-nZVI). Injection of CPS at 12 times the stoichiometric requirement (12×) resulted in quantitative Cr(VI) removal for up to 195 days of equivalent groundwater flow. Solid-bound Cr(VI) was reduced up to >99% (<2mg/kg). Treatment with CPS resulted in a short-term release of high sulfur concentrations. Injections of 12× and 24× stoichiometric GT-nZVI resulted in decrease in leachate pH from 6 to 2.5, which rebounded to 4.5 after the equivalent of 45 days and remained stable for the next equivalent 3 years. Metals concentrations in the effluent (Pb, Cr and Fe) increased following injection and quickly decreased, such that the mass flux was low with respect to the total amounts in the solid. Aqueous Cr(VI) was non-detect for the majority of the monitoring time, but concentrations eventually increased with respect to the control sample. Solid-bound Cr(VI) concentrations decreased by 30% and 66% in the 12× and 24× treatments, respectively. The low efficiency was attributed to increased sorption to iron surfaces at pH 2.5 and slow dissolution of PbCrO4, both of which were identified by micro-X-ray fluorescence and absorption analyses.

UI MeSH Term Description Entries
D007501 Iron A metallic element with atomic symbol Fe, atomic number 26, and atomic weight 55.85. It is an essential constituent of HEMOGLOBINS; CYTOCHROMES; and IRON-BINDING PROTEINS. It plays a role in cellular redox reactions and in the transport of OXYGEN. Iron-56,Iron 56
D002857 Chromium A trace element that plays a role in glucose metabolism. It has the atomic symbol Cr, atomic number 24, and atomic weight 52. According to the Fourth Annual Report on Carcinogens (NTP85-002,1985), chromium and some of its compounds have been listed as known carcinogens.
D006863 Hydrogen-Ion Concentration The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH pH,Concentration, Hydrogen-Ion,Concentrations, Hydrogen-Ion,Hydrogen Ion Concentration,Hydrogen-Ion Concentrations
D012987 Soil The unconsolidated mineral or organic matter on the surface of the earth that serves as a natural medium for the growth of land plants. Peat,Humus,Soils
D012989 Soil Pollutants Substances which pollute the soil. Use for soil pollutants in general or for which there is no specific heading. Soil Pollutant,Pollutant, Soil,Pollutants, Soil
D013440 Sulfides Chemical groups containing the covalent sulfur bonds -S-. The sulfur atom can be bound to inorganic or organic moieties. Sulfide,Thioether,Thioethers,Sulfur Ethers,Ethers, Sulfur
D013662 Tea The infusion of leaves of CAMELLIA SINENSIS (formerly Thea sinensis) as a beverage, the familiar Asian tea, which contains CATECHIN (especially epigallocatechin gallate) and CAFFEINE. Black Tea,Green Tea,Black Teas,Green Teas,Tea, Black,Tea, Green,Teas, Black,Teas, Green
D013885 Thiosulfates Inorganic salts of thiosulfuric acid possessing the general formula R2S2O3. Thiosulfate
D014874 Water Pollutants, Chemical Chemical compounds which pollute the water of rivers, streams, lakes, the sea, reservoirs, or other bodies of water. Chemical Water Pollutants,Landfill Leachate,Leachate, Landfill,Pollutants, Chemical Water
D014876 Water Pollution Contamination of bodies of water (such as LAKES; RIVERS; SEAS; and GROUNDWATER.) Thermal Water Pollution,Water Pollution, Thermal,Pollution, Thermal Water,Pollution, Water,Pollutions, Thermal Water,Pollutions, Water,Thermal Water Pollutions,Water Pollutions,Water Pollutions, Thermal

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