Hexavalent chromium Cr

Chromium Removal System. Chlorate manufacturers must remove chromium from the chlorate solution as a result of environmental regulations. During crystallization of sodium chlorate, essentially all of the sodium dichromate is recycled back to the electrolyzer. Alternatively, hexavalent chromium, Cr, can be reduced and coprecipitated in an agitated reactor using a choice of reducing agents, eg, sodium sulfide, sulfite, thiosulfate, hydrosulfite, hydrazine, etc. The product is chromium(III) oxide [1333-82-0] (98—106). Ion exchange and solvent extraction techniques have also... 

Hexavalent chromium (Cr+6) is the most biologically active chromium chemical species, although little is known about the properties of organochromium compounds, water-soluble species, or their interactions in complex mixtures... 

Impact on human health is a common theme used by authors to justify the importance of their research. This theme also appears in the Introduction section of the chromium article. As illustrated in P8, the authors first highlight the well-documented health risks of hexavalent chromium (Cr ) and then indicate why it is also Important to study trlvalent chromium (Cr ). 

While chromium metal or trivalent chromium is not very toxic, hexavalent chromium (Cr +) is carcinogenic and moderately toxic. Cr + is corrosive to skin and causes denaturation and precipitation of tissue proteins. Inhalation of Cr6+ dust or mist can cause perforation of the nasal septum, lung irritation, and congestion of the respiratory passsages. Chronic exposure may produce cancer of the respiratory tract. 

Elizabeth City, NC, electroplating Hexavalent chromium (Cr), TCE 1996 500,000 for design and installation... 

The popular movie Erin Brockovich, although focusing on the power industry, is an example of how the popular media can simplify the public s perception of chemical exposure. In Erin Brockovich the chemical of concern was hexavalent chromium, Cr +. Hexavalent chromium is listed as a carcinogen by EPA, but complicated questions dealing with exposure (drinking, inhalation, absorption through skin), toxicity levels, and specific health effects were lost in Hollywood s version. 

Not only the efficient removal of toxic heavy metals like hexavalent chromium (Cr(VI)), cadmium (Cd), zinc (Zn), nickel (Ni), etc., and other contaminants like phenol from industrial wastewaters [8-18] but also the recovery of valuable solutes from aqueous phases, for example, citric acid, carboxylic acids, amino acids, L-phenylalanine, etc. [19,20], are well-demonstrated applications of this technique. 

Chromium occurs in three basic forms metallic chromium (Cr(0)), trivalent chromium (Cr(III)), and hexavalent chromium (Cr(VI)). Hexavalent chromium can exist as chromium hexavalent ion and as part of a number of compounds including calcium chromate, chromic acid, chromium trioxide, lead chromate, strontium chromate, potassium dichromate, and zinc chromate. 

List the possible sources of highly toxic hexavalent chromium (Cr " ") and methods to remove it from a wastewater stream. 

Paustenbach (USA) 2003 Characterization of absorbed dose of Cr(VI) following contact with tap water via all routes of exposure Hexavalent chromium [Cr(VI)] Red blood cell upteike tmd sequestration of chromium along with total urinary excretion (mg/L)... 

The NIOSH REL (10-hour TWA) is 0.001 mg Cr(VI)/m for all hexavalent chromium [Cr(VI)] compounds. NIOSH considers all Cr(VI) compounds (including chromic acid, tert-butyl chromate, zine ehromate, and chromyl chloride) to be potential occupational carcinogens. The NIOSH REL (8-hour TWA) is 0.5 mg Cr/m for chromium metal and chromium(II) and chromium(III) compounds. 

TABLE 8.1. Total Chromium, Cr(T), and Hexavalent Chromium, Cr(VI), Data for the Three Experiments... 

The radical scavenging activity of resveratrol has also been shown in a number of in vitro studies. Leonard et al. reports that resveratrol is an efficient OH and 02 radical scavenger. By using hexavalent chromium (Cr IV]), they have shown the ability of resveratrol to scavenge radicals produced by the enzymatic reaction with... 

Fe-, Cd-, and Sn-based alloys. Chromate solutions are also used to seal coatings formed by anodizing or hydrothermal treatment. CCCs are primarily used to improve adherence of subsequently applied organic coatings, or to impart corrosion resistance under atmospheric exposure conditions. Certain types of CCCs contain labile hexavalent chromium (Cr(VI)), which can be leached from the coating when it is contacted by an attacking solution. This Cr(VI) can be transported... 

The European Union has taken the lead in restricting the use of some hazardous materials in the manufacture of electrical and electronic hardware. The program, referred to as Restriction of Hazardous Substances (RoHS), applies to all electrical and electronic products produced in Europe and products imported from other countries, thus has very broad application. The regulations put into force on July 1, 2006, apply to lead, cadmium, mercury, hexavalent chromium (Cr ), poly-brominated biphenyl (PBB), and polybrominated diphenyl ether (PBDE). The RoHS guideline document specifies 0.1% or 1,000 ppm as the maximum amount permitted for lead, mercury, Cr" " , PBB, and PBDE and 0.01% or 100 ppm for cadmium. The document also describes guidelines for sample preparation and analyses of the restricted materials. 

The Restriction of Hazardous Substances Directive (RoHS) is the shortened form for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment. It was adopted by the European Union in February 2003 [9]. In July 2006, the RoHS 1 directive took effect and was required to be enforced in each member state [10]. Each member state used the directive as a guide to establish its own enforcement and implementatiOTi policies. This directive restricts (with some exceptions) the use of certain hazardous materials in the manufacturing of various types of electronic and electrical equipment The hazardous materials include lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (Cr polybrominated biphenyl (PBB), and polybrominated diphenyl ether (PBDE), [10]. 

The Restriction of Hazardous Substances Directive (RoHS) restricts (with some exceptions) the use of certain hazardous materials in the manufacturing of various types of electronic and electrical equipment. These hazardous materials include lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (Cr " ), polybrominated biphenyl (PBB), and polybrominated diphenyl ether (PBDE). 

Toxic metals in water include arsenic, barium, cadmium, hexavalent chromium (Cr+ ), lead, mercury, selenium, and silver. The most cormnon sources are natural mineral formations, and consequently, toxic metals are most cormnonly associated with groimdwater. Removal using ion exchange processes or by reverse osmosis is most common. 

Historically, various investigators in Europe have used hydrochloric acid-px>tassium dichromate solutions for testing the exfoliation susceptibility of all types of aluminum alloys. An example is the Russian Stanchtid GOST 9.904-82, Aluminium Alloys Methods of Accelerated Exfohation Corrosion Testing [22]. It should be noted, however, that hexavalent chromium (Cr ) solutions are considered undesirable for health and environmental considerations and have been prohibited in some countries. 

Because of the high temperature corrosion resistance and thermal stability exhibited by magnesium-chromium oxide refractories in copper smelting, converting and fire refining furnaces, little research has been conducted on other refractory families. However, the concern for hexavalent chromium (Cr ) as a potentially hazardous waste in spent refractories from copper production furnaces has prompted the recognition that a more environmentally acceptable material is needed for the copper industry. 

Hexavalent chromium Cr 0.1 Platings, especially for surface passivation of environmentally unstable metals, pigments, and plastics colorant as lead chromate hexavalent chromate finish for plated metal enclosures, fasteners, clips, and screws... 

Sharma P, Bihari V, Agarwal SK, Verma V, Kesavachandran CN, Pangtey BS, et al. Groundwater contaminated with hexavalent chromium [Cr (VI)] a health survey and clinical examination of community inhabitants (Kanpur, India). PLoS One 2012 7(10) e47877. 

Measurement of different oxidation states—For example, hexavalent chromium, Cr (VI), is a powerful oxidant and is extremely toxic, bnt in soil and water systems it reacts with organic matter to form trivalent chrominm,... 

Gu J-D, Cheung KH (2001) Phenotypic e3q>ression of Vogesella indigofera upon e3q)osure to hexavalent chromium, Cr ". World J Microbiol Biotechnol... 

Another interesting study is the determination of the distribution of Cr valence states in human cells after in vitro exposure to soluble or particulate chromium compounds. The chromium biological activity depends strongly upon its oxidation state and solubihty. Several hexavalent chromium, Cr(VI),... 

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