Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Prasanna, S.; Kamath, P. Vishnu; Shivakumara, C.

doi:10.1016/j.materresbull.2006.09.021

Cited by 58 publications

(33 citation statements)

References 29 publications

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“…In GB, the amount of CAC was estimated at approximately 3 wt.%, accounting for 2360 mg/kg Cr(VI) or 35% of the total Cr(VI). Ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 · 26H 2 O) is a cementitious mineral that can, theoretically, act as a Cr(VI) host. Chrysochoou and Dermatas (9) reported the presence of ettringite in SA7 COPR as pure sulfate species, with negligible chromate substitution.…”

Section: Resultsmentioning

confidence: 99%

“…Chrysochoou and Dermatas (9) reported the presence of calcium aluminum chromium oxides hydrates (CAC) in COPR with the chemical formula Ca 4 Al 2 (CrO 4 )(OH) 12 · nH 2 O (n ) 3,6,8). CACs accounted for 50% on average (25-75% range) of the total Cr(VI).…”

Section: Introductionmentioning

confidence: 99%

“…Hillier et al (10,11) reported that hydrogarnet (Ca 3 Al 2 (OH) 12 ) was also an important host phase for chromate in COPR from Glasgow, Scotland. Hillier et al (10) reported Cr(VI)-hydrocalumite as Cr(VI) host instead of CAC to account for the X-ray diffraction (XRD) peak at 7.9 Å. Hydrocalumite (Ca 4 Al 2 Cl 2 (OH) 12 · 6H 2 O) is isostructural with the CACs, with chloride instead of chromate. This phase shares several peaks with the hydrotalcite group (Mg 6 Al 2 (CO 3 )(OH) 16 · 4H 2 O), which was reported instead of hydrocalumite in SA7 COPR.…”

Section: Introductionmentioning

confidence: 99%

“…LDH have the same layered structure ( Figure S1), consisting of brucite-like sheets, held together by anions and water molecules. LDH are capable of multiple cationic and anionic substitutions (12). Goswamee et al (13) showed that a variety of LDH phases (Mg-Al, Ni-Al) could incorporate chromate in their structure.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the chemical composition of an LDH structure that produces an XRD peak at 7.9 Å in COPR can vary (with Ca, Mg, Al, and Fe in the octahedral sheet and chloride, carbonate, or chromate in the interlayer). Ca-Al phases tend to be stable at higher pH values (>11), while Mg-Al phases are stable down to pH 8 or lower (12). The original pH of COPR is in the range 11.5-12.5, so that pH reduction is necessary to dissolve Cr(VI)-bearing phases.…”

Section: Introductionmentioning

confidence: 99%

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Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Chrysochoou

Fakra

Marcus

et al. 2009

Environ. Sci. Technol.

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The speciation and distribution of Cr(VI) in the solid phase was investigated for two types of chromite ore processing residue (COPR) found at two deposition sites in the United States: gray-black (GB) granular and hard brown (HB) cemented COPR. COPR chemistry and mineralogy were investigated using micro-X-ray absorption spectroscopy and micro-X-ray diffraction, complemented by laboratory analyses. GB COPR contained 30% of its total Cr(VI) (6000 mg/kg) as large crystals (>20 µm diameter) of a previously unreported Na-rich analog of calcium aluminum chromate hydrates. These Cr(VI)-rich phases are thought to be vulnerable to reductive and pH treatments. More than 50% of the Cr(VI) was located within nodules, not easily accessible to dissolved reductants, and bound to Fe-rich hydrogarnet, hydrotalcite, and possibly brucite. These phases are stable over a large pH range, thus harder to dissolve. Brownmillerite was also likely associated with physical entrapment of Cr(VI) in the interior of nodules. HB COPR contained no Cr(VI)-rich phases; all Cr(VI) was diffuse within the nodules and absent from the cementing matrix, with hydrogarnet and hydrotalcite being the main Cr(VI) binding phases. Treatment of HB COPR is challenging in terms of dissolving the acidity-resistant, inaccessible Cr(VI) compounds; the same applies to ∼50% of Cr(VI) in GB COPR.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Chrysochoou

Fakra

Marcus

et al. 2009

Environ. Sci. Technol.

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Layered Double Hydroxides for Anion Capture and Storage

Phillips¹,

Vandeperre²

2011

Ceramic Materials for Energy Applications

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CuAl Hydrotalcite Formed CuAl‐Mixed Metal Oxides for Photocatalytic Removal of Rhodamine B and Cr(VI)

Mao

Jiao

2018

ChemistrySelect

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Mixed metal oxides (MMOs) are important semiconductor photocatalysts for water treatment, such as removal of organic dyes and metal ions. In this paper, CuAl hydrotalcite-like compounds (CuAl-HTLcs) were synthesized by the coprecipitation method using Al(NO 3 ) 3 ⋅9H 2 O and Cu (NO 3 ) 2 ⋅3H 2 O as raw materials. Cu 2 O/Cu 2 Al 2 O 4 mixed metal oxides (MMO) were prepared by calcining CuAl-HTLcs at 900°C. The obtained composites were characterized by various methods, including X-ray diffraction (XRD), Scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (DRS), among others. Their photocatalytic activities towards removal of Rhodamine B (RhB) and Cr(VI) were evaluated by spectrophotometry, XRD revealed that CuAl-MMO composites were composed of high crystallinity Cu 2 O and Cu 2 Al 2 O 4 grains. DRS showed the strong ultraviolet absorption ability of the composites. The electrochemical testing demonstrated CuAl-MMO composites with good photocatalytic activities towards the removal of Rhodamine B (RhB) and Cr(VI) under ultraviolet light, with reaction rate constants determined as 0.41 h À 1 and 0.49 h À 1 , respectively. The relevant photocatalytic activities of CuAl-MMO composites were attributed to the synergy between the two components. Overall, these data look promising for future use of CuAl-MMO as an important photocatalyst for water remediation.

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Synthesis and characterization of layered double hydroxides (LDHs) with intercalated chromate ions

Cited by 58 publications

References 29 publications

Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Microstructural Analyses of Cr(VI) Speciation in Chromite Ore Processing Residue (COPR)

Layered Double Hydroxides for Anion Capture and Storage

CuAl Hydrotalcite Formed CuAl‐Mixed Metal Oxides for Photocatalytic Removal of Rhodamine B and Cr(VI)

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