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Chromate Ion Exchange
Published in Arup K. Sengupta, Ion Exchange Technology, 2021
Chromic acid and chromates are oxyacids and oxyanions of hexavalent chromium, Cr(VI), and used widely in anodizing, electroplating, corrosion control, oxidation, wood treatment, and several other industrial applications [1,2]. Unlike other toxic metals, however, oxyanions of Cr(VI) or chromates are quite soluble in the aqueous phase almost over the entire pH range and, thus, quite mobile in the natural environment. Toxicity, accompanied by widespread industrial applications and high mobility, has earned Cr(VI) an unusual notoriety in the area of environmental pollution. Contrary to Cr(VI) species or chromates, Cr(III) is less toxic and very insoluble at neutral to alkaline pH. As a result, chemical reduction of Cr(VI) to Cr(III), followed by precipitation as chromic hydroxide, Cr(OH)3(S), has been the traditional approach for treating Cr(IV)-laden wastewater [3,4]. Such an approach, however, does not allow recovery of Cr(VI) and is not efficient both thermodynamically and kinetically when Cr(VI) species are present at very low concentrations (from mg/L to μg/L). Furthermore, there is scientific evidence suggesting that chromic hydroxide sludges disposed of at landfills may be oxidized to mobile Cr(VI) in natural environments, thus threatening contamination of groundwater [5,6].
2 Nanotubes for Heavy Metal Ions Removal
Published in Zainovia Lockman, 1-Dimensional Metal Oxide Nanostructures, 2018
Nurulhuda Bashirom, Monna Rozana, Nurul Izza Soaid, Khairunisak Abdul Razak, Andrey Berenov, Syahriza Ismail, Tan Wai Kian, Go Kawamura, Atsunori Matsuda, Zainovia Lockman
There are several methods to remove Cr(VI) from wastewater including adsorption, membrane filtration, ion exchange, electrochemical treatment and, as mentioned, photocatalytic reduction (Owlad et al., 2009). Each of these methods has their own advantages and disadvantages as listed in Table 6.4. Among all of these methods, photocatalytic reduction appears to be the most promising as it can directly eliminate Cr(VI) by reducing it to Cr(III). Cr(III) can then be precipitated into chromium hydroxide, Cr(OH)3 in alkaline media and safely discharged into the environment or it can be recycled.
Precipitation Technology
Published in Jiaping Paul Chen, Decontamination of Heavy Metals, 2012
Trivalent chromium is typically precipitated through the addition of hydroxide, which forms chromium hydroxide (Cr(OH)3). Other precipitation treatment reagents such as carbonate and sulfide can also be used.
Reclamation of forward osmosis reject water containing hexavalent chromium via coupled electrochemical-physical processes
Published in Environmental Technology, 2022
Milad Mousazadeh, Zohreh Naghdali, Işık Kabdaşlı, Miguel A. Sandoval, Fatima Ezzahra Titchou, Farideh Malekdar, Mahmoud Nasr, Carlos A. Martínez-Huitle, Eric Lichtfouse, Mohammad Mahdi Emamjomeh
Trivalent chromium combines with hydroxyl ions to form chromium hydroxide (Cr(OH)3) which precipitate as amorphous solids. In addition, negative chromium species might adsorb on the positively charged metal hydroxide [21]. Moreover, trivalent chromium removal may occur through other means as well, such as adsorption onto ferric oxyhydroxide and goethite.