Structure and thermal stability of toxic chromium(VI) species doped onto TiO2 powders through heat treatment

Lin, Su‐Hsia; Chen, Chia-Nan; Juang, Ruey‐Shin

doi:10.1016/j.jenvman.2008.12.013

Cited by 13 publications

(4 citation statements)

References 21 publications

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“…For the Cr 2 O 3 -containing refractory linings, since the operating conditions and service atmosphere in a given furnace can hardly be changed in practical production, most related work has focused on Cr(VI) minimization using some additives at high temperatures. The acidic components such as SiO 2 , TiO 2 , Fe 2 O 3 , and P 2 O 5 can effectively suppress the Cr(III) oxidation during thermal treatment of Cr 2 O 3 -containing refractories [ 19 , 20 , 21 , 22 ]. However, these oxide additives usually result in low melting point phases in the matrix, deteriorating either the thermo-mechanical properties or the slag corrosion resistance [ 23 , 24 ].…”

Section: Introductionmentioning

confidence: 99%

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

Liao

et al. 2021

Materials

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Al2O3-CaO-Cr2O3 castables are used in various furnaces due to excellent corrosion resistance and sufficient early strength, but toxic Cr(VI) generation during service remains a concern. Here, we investigated the relative reactivity of analogous Cr(III) phases such as Cr2O3, (Al1−xCrx)2O3 and in situ Cr(III) solid solution with the calcium aluminate cement under an oxidizing atmosphere at various temperatures. The aim is to comprehend the relative Cr(VI) generation in the low-cement castables (Al2O3-CaO-Cr2O3-O2 system) and achieve an environment-friendly application. The solid-state reactions and Cr(VI) formation were investigated using powder XRD, SEM, and leaching tests. Compared to Cr2O3, the stability of (Al1−xCrx)2O3 against CAC was much higher, which improved gradually with the concentration of Al2O3 in (Al1−xCrx)2O3. The substitution of Cr2O3 with (Al1−xCrx)2O3 in the Al2O3-CaO-Cr2O3 castables could completely inhibit the formation of Cr(VI) compound CaCrO4 at 500–1100 °C and could drastically suppress Ca4Al6CrO16 generation at 900 to 1300 °C. The Cr(VI) reduction amounting up to 98.1% could be achieved by replacing Cr2O3 with (Al1−xCrx)2O3 solid solution. However, in situ stabilized Cr(III) phases as a mixture of (Al1−xCrx)2O3 and Ca(Al12−xCrx)O19 solid solution hardly reveal any reoxidation. Moreover, the CA6 was much more stable than CA and CA2, and it did not participate in any chemical reaction with (Al1−xCrx)2O3 solid solution.

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Section: Introductionmentioning

confidence: 99%

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

Liao

et al. 2021

Materials

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“…For the Cr 2 O 3 containing refractory linings, since the operation conditions and service atmosphere in a given furnace can hardly be changed in practical production, most of the related work have focused on Cr(VI) minimization using some additives at high temperatures. And the results suggested that acidic components such as SiO 2 , TiO 2 , Fe 2 O 3 and P 2 O 5 can effectively suppress the Cr(III) oxidation during thermal treatment of Cr 2 O 3 containing refractories [4,[23][24][25][26][27][28][29]. However, these oxide additives usually result in formation of low melting point phases in the matrix, which would obviously deteriorate the thermo-mechanical properties or slag corrosion resistance of the refractories [30][31][32].…”

Section: Introductionmentioning

confidence: 99%

Inhibition of Cr(VI) in the Al2O3-CaO-Cr2O3 castables by using (Al1-x,Crx)2O3 solid solution

Xu¹,

Xu²,

Li³

et al. 2020

Preprint

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Al2O3-CaO-Cr2O3 castables are required for various furnaces due to excellent corrosion resistance and sufficient early strength. However, generation of toxic Cr(VI) caused subsequent problems with disposal. The present work aimed at achieving Cr(VI) reduction by replacing Cr2O3 with (Al1 − x,Crx)2O3 solid solution. The phase evolutions and Cr(VI) formation in castables were systemically investigated. Compared with Cr2O3, stability of (Al1 − x,Crx)2O3 in CAC was much higher and improved gradually with Al3+ proportion. The substitution of Cr2O3 with (Al1 − x,Crx)2O3 completely inhibited CaCrO4 formation at 300–1100 oC, and drastically suppressed Ca4Al6CrO16 generation at 900–1300 °C. Thus, a remarkable Cr(VI) reduction of 98.1% could be achieved. Moreover, In comparison with CA and CA2, CA6 was much more stable, which would not take chemical reaction with (Al1 − x,Crx)2O3. Thus, incorporating some Al2O3 powders in Al2O3-CaO-Cr2O3 castables to form CA6 at temperature above 1300 oC was also essential for inhibiting Cr(VI) formation when using (Al1 − x,Crx)2O3 as substitute for Cr2O3.

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“…Cr(VI) have extremely different environmental and chemical properties 6,7 . Cr(VI) is toxic for human beings, animals, plants and microorganisms 8 .…”

Section: Introductionmentioning

confidence: 99%

Specification of the Operational Parameters Contribution in the Efficiency of TiO2-P25 Nanoparticles in the Photocatalytic Removal of Cr(VI) by Taguchi Method

Sabonian¹,

Behnajady²

2014

Orient J Chem

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Chromium exists in environment both as trivalent [Cr(III)] and hexavalent [Cr(VI)] forms. However, hexavalent form is five hundred times more toxic than the trivalent form. Heterogeneous photocatalysis processes, using aqueous suspensions of semiconductors, have received considerable attention in the removal of toxic metals from aqueous media. In this work the nanoparticles of TiO 2 -P25 in the form of slurry were used for photoreduction of Cr(VI) to the less harmful Cr(III). The process has been conducted in different operational conditions such as different initial concentrations of Cr(VI), dosage of photocatalyst, irradiation times, irradiation intensities of light and pH. For the optimization of the process Taguchi experimental design was used. The results of optimization using the Taguchi method, indicated that the pH with 28%, initial concentration of Cr(VI) with 26.99% and dosage of TiO 2 nanocatalyst with 20.53% have the most effects among the selected factors. The intensity of UV light irradiation has the least effect on the efficiency of the process.

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Structure and thermal stability of toxic chromium(VI) species doped onto TiO2 powders through heat treatment

Cited by 13 publications

References 21 publications

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

Inhibition of Cr(VI) in the Al2O3-CaO-Cr2O3 castables by using (Al1-x,Crx)2O3 solid solution

Specification of the Operational Parameters Contribution in the Efficiency of TiO2-P25 Nanoparticles in the Photocatalytic Removal of Cr(VI) by Taguchi Method

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