Physical properties measurements and leaching behavior of chromium compounds solidified in a cement matrix

Zamorani, E.; Sheikh, Irfan Ahmed; Serrini, G.

doi:10.1016/0191-815x(88)90031-9

Cited by 21 publications

(7 citation statements)

References 7 publications

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“…Leaching tests on cement mixtures containing CrCl3, CrO3, or Cr2O3 showed that cement was very good for immobilizing Cr"' as a result of the formation of Cr(OH)3. However, Crvy readily leached from the cement at relatively high concentrations (88). The release of the Crvy is similar to the release of Ca2+ and may be related to the formation of CaCrO4 within the cement mixture.…”

Section: Soil Solidification/stabilizationmentioning

confidence: 86%

Processes affecting the remediation of chromium-contaminated sites.

Palmer

Wittbrodt

1991

Environ Health Perspect

385

172

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The remediation of chromium-contaminated sites requires knowledge of the processes that control the migration and transformation of chromium. Advection, dispersion, and diffusion are physical processes affecting the rate at which contaminants can migrate in the subsurface. Heterogeneity is an important factor that affects the contribution of each of these mechanisms to the migration of chromium-laden waters. Redox reactions, chemical speciation, adsorption/desorption phenomena, and precipitation/dissolution reactions control the transformation and mobility of chromium. The reduction of CrVI to CrIII can occur in the presence of ferrous iron in solution or in mineral phases, reduced sulfur compounds, or soil organic matter. At neutral to alkaline pH, the CrIII precipitates as amorphous hydroxides or forms complexes with organic matter. CrIII is oxidized by manganese dioxide, a common mineral found in many soils. Solid-phase precipitates of hexavalent chromium such as barium chromate can serve either as sources or sinks for CrVI. Adsorption of CrVI in soils increases with decreasing chromium concentration, making it more difficult to remove the chromium as the concentration decreases during pump-and-treat remediation. Knowledge of these chemical and physical processes is important in developing and selecting effective, cost-efficient remediation designs for chromium-contaminated sites.

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Section: Soil Solidification/stabilizationmentioning

confidence: 86%

Processes affecting the remediation of chromium-contaminated sites.

Palmer

Wittbrodt

1991

Environ Health Perspect

385

172

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“…The ability of cement mixtures to bind chromium depends on the oxidation state of the chromium (6,9). Cr(III) is not readily removed from cement, however, as much as 95% of added Cr(VI) can be leached (9).…”

Section: Introductionmentioning

confidence: 99%

Precipitates in a Cr(VI)-Contaminated Concrete

Palmer

2000

Environ. Sci. Technol.

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Examination of Cr(VI)-contaminated concrete from a former hard-chrome plating shop revealed the presence of long, thin crystals varying from white to bright yellow. Many of the crystals examined by scanning electron microscopy (SEM) were acicular and 25-100 µm in length and 1-15 µm wide. The composition, determined by energydispersive X-ray spectroscopy, morphology, and d spacings, measured by electron diffraction, identifies these crystals as chromate enriched ettringite (Ca 6 Al 2 ((S,-Cr)O 4 ) 2 (OH) 12 ‚26H 2 O) with the mole fraction of CrO 4 2in the SO 4 2position being 0.41 and 0.72. A nearly pure CrO 4 2-hydrocalumite (3CaO‚Al 2 O 3 ‚CaCrO 4 ‚nH 2 O) is also observed. Some of these crystals appear to be pseudomorphs of ettringite. The CrO 4 2--hydrocalumite crystals are coated with smaller acicular crystals that are most likely solid solutions between Si-ettringite (Ca 6 Al 2 (SiO 3 ) 3 (OH) 12 ‚26H 2 O) and CrO 4 2--ettringite. These crystals are bound together by an amorphous appearing SiO 2 phase. Ca-silicate-hydrate gel (CSH) has precipitated around ettringite-group crystals containing chromium indicating that some CSH formation occurred after contamination of the concrete.

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“…Calcium silicate hydrate (C-S-H), which is the primary hydration and binding product in PC-based materials, contains most of the microporosity, resulting in a large specific surface area that provides physical sorption and co-precipitation sites for heavy metal ions like Cr(VI). It should also be noted that Zamorani et al [ 12 ] observed co-precipitated phase of CaCrO 4 when Cr(VI) reacted with C-S-H, suggesting that molecular-level surface reactions are important in determining the reaction rates and pathways when hydrated products of PC-based materials react with Cr(VI) [ 3 ]. Ettringite (3CaO·Al 2 O 3 ·3CaSO 4 ·32H 2 O) has also been identified as one of PC’s hydration products and, with its highly reactive and needle-like column structure, has been proposed as a surface site for Cr(VI) immobilization via anion substitution, where CrO 4 2− is exchanged for SO 4 2− [ 13 , 14 ].…”

Section: Introductionmentioning

confidence: 99%

Removal of Hexavalent Chromium in Portland Cement Using Ground Granulated Blast-Furnace Slag Powder

et al. 2017

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Using ground granulated blast-furnace slag (GGBS) under different alkaline conditions, we studied the mechanisms and extents of Cr(VI) reduction and sorption and compared them to reactions with Portland cement (PC). We also investigated the effects of mixing PC/GGBS ratios on Cr(VI) dissolution after carbonating the substrates. We observed a complete sorption and reduction of Cr(VI) to Cr(III) in a GGBS-in-Ca(OH)2 solution (pH > ~12.5) after 10 h, whereas in distilled water (pH = ~11.5) GGBS exhibited only marginal sorption and reduction (20%). Cr reactions with dissolved ions in supernatants derived from GGBS indicated that the anions dissolved from GGBS act as a reducing agent for Cr(VI) in a Ca(OH)2 solution. Soft X-ray absorption microscopy identified a partial reduction of Cr(VI) to Cr(III) on the GGBS surface. The carbonation of pure PC paste substantially increased the amount of dissolved Cr(VI) in a solution phase whereas a 5 wt % replacement of PC with GGBS significantly reduced the amount of dissolved Cr(VI). We concluded that in the mixed paste during the early curing stage GGBS reduced a significant fraction of Cr(VI) to Cr(III) and that the Cr(III) adsorbed in the GGBS-PC mixture’s hydration products does not readily dissolve, even under carbonation conditions.

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Physical properties measurements and leaching behavior of chromium compounds solidified in a cement matrix

Cited by 21 publications

References 7 publications

Processes affecting the remediation of chromium-contaminated sites.

Processes affecting the remediation of chromium-contaminated sites.

Precipitates in a Cr(VI)-Contaminated Concrete

Removal of Hexavalent Chromium in Portland Cement Using Ground Granulated Blast-Furnace Slag Powder

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