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Chromate conversion coating

About: Chromate conversion coating is a(n) research topic. Over the lifetime, 7087 publication(s) have been published within this topic receiving 118904 citation(s). The topic is also known as: chromatation.
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Journal ArticleDOI
Jianxin Pan1, Liangliang Liu1, Hanping Pan2, Li-Hui Yang1  +2 moreInstitutions (3)
Abstract: Metal sulfide-based biological process is considered as a promising biotechnology for next-generation wastewater treatment. However, it is not clear if simultaneous bio-reduction of nitrate and chromate was achievable in this process. This study aimed to evaluate the feasibility of metal sulfides (FeS and MnS) on simultaneous denitrification and chromate reduction in autotrophic denitrifying column bioreactors. Results showed that simultaneous reduction of nitrate and chromate was achieved using metal sulfides (FeS and MnS) as electron donors, in which sulfate was the sole soluble end-product. Apart from the sulfur element in the metal sulfides, Fe(II) and Mn(II) were also involved in nitrate and chromate reduction as indicative by the formation of their oxidative states compounds. In microbial communities, SHD-231 and Thiobacillus were the most predominant bacteria, which might have played important roles in simultaneous denitrification and chromate reduction. Compared to FeS, MnS showed a higher performance on nitrate and chromate removal, which could also reduce the toxic inhibition of chromate on nitrate reduction. According to results of XRD and XPS, as well as a lower sulfate production in the FeS system, FeS might have been covered easily to hydroxides due to its bio-oxidation, which limited mass transfer efficiency and bio-availability of FeS. The findings in this study offered insights in the development of promising approaches for the treatment of toxic and hazardous compounds using metal sulfide.

01 Feb 2022
Abstract: In this study, the organic coating of epoxy zinc-chromate (E) and the two-layer coating of epoxy zinc-chromate-polyurethane (PU-E) was coated on the steel substrate using the spraying method. Then, their corrosion resistance was compared using electrochemical impedance spectroscopy (EIS) and dynamic polarization tests. Comparison of corrosion properties using parameters of, phase angle at a maximum frequency (100kHz), and breakpoint frequency (fb) were performed during 2, 4, and 8 weeks. A comparison of these three parameters showed that the corrosion resistance of the PU-E coating was higher than the E coating due to the behavior of the polyurethane coating barrier as well as the active protective behavior induced by the chromate pigments which was distributed on the epoxy coating. According to the test results, E and PU-E coatings had good hardness and scratch resistance and were resistant to pencil scratches with H and F hardness, respectively. The salt spray test for the two-layer coating showed no qualitative change, damaged area, blistering/delamination, or corrosion products on the coated sample. The results showed that both coatings were suitable candidates for use in various industries, including marine and power industries, and other industries that suffered from corrosion problems.

Journal ArticleDOI
Abstract: Textile and tannery industries are highly contaminating with discharge of high Cr concentrations. Developing bio-based sorbents with strong affinity for chromate, fast kinetics, and high recyclability is strategic for better reuse of industrial wastewater. Magnetic chitosan micro-particles (MC, for enhancing mass transfer) may constitute a solution for chromate removal from acidic solutions. The functionalization of this support with aminothiazole groups (ATA@MC) or imidazole carboxamide (AIC@MC) significantly improves chromate removal, with sorption capacities close to 6 mmol Cr g−1, at pH 2. The Langmuir and the Sips equations finely fit sorption isotherms, while the pseudo-first order rate equation fits well uptake kinetics (equilibrium within 60 min). Sorption and desorption properties are remarkably stable: sorption efficiency decreases by less than 6% at the fifth cycle (while the desorption efficiency maintains above 99%). The sorbents are highly selective for chromate removal from acidic tannery wastewater (against base metals). FTIR and XPS analyses are used for characterizing the materials and for identifying the binding mechanisms (including chromate reduction into Cr(III)). The sorbents are both showing promising performances for Cr(VI) removal in acidic solutions, including in very complex solutions such as tannery wastewater. AIC@MC is more selective for Cr(VI) removal, while ATA@MC has a broader reactivity for a wider family of metal ions. The antimicrobial properties of the functionalized sorbents are characterized by the determination of the zone of inhibition (ZOI) against Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Candida albicans: the inhibition is slightly improved compared with magnetite chitosan microparticles. More generally, the Gram- bacteria are slightly more sensitive to the functionalized sorbents than Gram+ bacteria and Candida fungus.

5 citations

Journal ArticleDOI
Minji Park1, Sookyung Kim1, Seoha Kim1, Jungho Ryu  +2 moreInstitutions (1)
Abstract: We investigated the feasibility of using FeS-coated alumina and silica for permeable reactive barrier (PRB) applications. By both coated materials, Cr(VI) was reduced to Cr(III), which was immobilized via surface complexation/precipitation at acidic pH, and bulk precipitation at neutral to basic pH. Both pH and surface coating density (the amount of FeS deposits per unit surface area of a supporting matrix) controlled Cr(VI) reduction capacity and [Cr,Fe](OH)3 composition. The reduction was higher at acidic pH due to lower passivation, as evidenced by the increased production of Fe(III) (oxyhydr)oxides over Fe(II)-Fe(III) phases. The coated alumina, despite the lower amount of FeS deposits than the coated silica, showed greater reduction capacities due to its higher surface coating density, which made Fe(III) closer together to favor Fe(III) (oxyhydr)oxide formation. Since Cr(III) was preferentially substituted for Fe(III) in Fe(III) (oxyhydr)oxides, lower pH and higher surface coating density led to lower Cr fractions in [Cr,Fe](OH)3 because of the increased production of Fe(III) (oxyhydr)oxides. Given that Cr-poor [Cr,Fe](OH)3 is more resistant to re-oxidation, FeS-coated alumina is better for PRB applications. This study reveals the significance of the surface coating density when evaluating the effectiveness of coated materials in redox-based treatments.

2 citations

Journal ArticleDOI
A. Nehdi, N. Frini-Srasra, G. de Miguel1, I. Pavlovic1  +2 moreInstitutions (1)
Abstract: This work deals with the use of layered double hydroxides for a double environmental remediation. The residue obtained in the use of these materials as a chromate sorbent in water, was subsequently studied as a photocatalyst for the removal of NOx gases. With this aim, MgAl–CO3 layered double hydroxides were synthesized by the coprecipitation method with a divalent/trivalent metal ratio of 3. After its calcination at 500 °C, the mixed oxide was obtained and MgAl–CrO4 were synthesized by the reconstruction method. A complete chemical, morphological and photochemical study of the samples was carried out with techniques such as XRD, FT-IR, TGA, XRF, PL, DRIFTS and UV–Vis spectroscopy. Results showed that LDH materials presented no significant changes in their structure after their use as a sorbent. Photocatalytic tests of the samples showed a very good NO removal efficiency, as well as a high selectivity (low NO2 emissions) through complete oxidation of these oxides to nitrate. The incorporation of chromate into the LDH structure improved the absorption of light in the visible region of the spectra, producing an improvement of 20% in the NO elimination compared with the LDH without chromate.

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