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Corrosion Inhibitors and Rust Preventatives
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Chromates are another inhibitor that is part of the class of anodic passivators, which appear to inhibit corrosion through the formation of an oxide coating [18,26]. Historically, chromates have been used in steel plating and finishing, aqueous corrosion inhibition, and leather tanning, and although there have been attempts to make oil-soluble chromate derivatives [27], they have not been widely used in lubricants due to their instability in the presence of organics. In water treatment, these products were applied as chromic acid, sodium chromate (Na2CrO4), or sodium dichromate (Na2Cr2O7), all of which contain hexavalent chromium. Subsequently, the hexavalent chromium (Cr6+) was found to be a powerful respiratory carcinogen and possessed high aquatic toxicity. As a result, the use of chromates in aqueous water treatment was banned in 1990, and interest in using them in lubricants has disappeared [28].
Kinetics of formation of sodium chromate from El-Baramiya chromite ore concentrate with soda ash pellets
Published in Gülhan Özbayoğlu, Çetin Hoşten, M. Ümit Atalay, Cahit Hiçyılmaz, A. İhsan Arol, Mineral Processing on the Verge of the 21st Century, 2017
M.E.H. Shalabi, N.A. El-Hussiny, S. Y. El-Afifi, N. N. El-Ebiary, F. M. S. Zaher
Sodium chromate and dichromate are manufactured by roasting chrome ore with soda ash (Kirk 1964) as follows: The chrome ore is crushed, dried and ground in ball mill to a fineness of 90–98 % through 200 mesh. The pulverized ore is mixed with soda ash and with a diluent. The proportion of soda ash is such as to obtain the optimum economy in recovery of chromium values from the ore. The chemical reaction of sodium chromate production is as follows: 2Cr2O3 + 4 Na2CO3 + 3O2 → 4 Na2CrO4+ 4C02
Remediation of lime-free roasting chromite ore processing residue (COPR) by water leaching and pyrolysis process
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Cunfang Lu, Wenchang Xi, Xuejun Quan, Zhien Zhang
Chromium salt is one of the most critical materials widely used in pigments, ceramics, electronics, anticorrosion, metallurgy, etc. (Kleynhans et al. 2016; Li, Zhang, and Liu 2017; Matern et al. 2017; Zhang et al. 2018; Zhao et al. 2017). Chromite ore processing residue (COPR) is a byproduct of the chromium salt manufacturing process. In the process, chromite ore is roasted at high temperatures with fusion agent, oxidizing Cr(III) to Cr(VI), and then formed the sodium chromate chemically (Wu, Li, and Yang 2015). The manufacturing process can be classified into high calcium roasting, low lime roasting, and lime-free roasting process according to the used fusion agent (Jagupilla et al. 2015). The lime-based roasting process has been eliminated gradually because of some shortcomings, especially the carcinogenic CaCrO4 formation (Wang and Li 2004), the large amount of COPR production. The chromium contents in COPR can be as high as 46000 mg/kg, about 30% of which in the form of Cr(VI) (Liao et al. 2017). Thus, the chromium salt industry has become a major concern in recent decades from health and environment perspectives.