Hazardous chromium

All of the chromium reagents produce by-products and washings that contain hazardous chromium salts and must be collected as hazardous waste. In many cases, simple oxidants such as household bleach (sodium hypochlorite, NaOCl) can accomplish the same oxidations as chromic acid without using heavy metals, and without generating hazardous waste. Oxidations using sodium hypochlorite involve mildly acidic or basic conditions that may be better than chromic acid for acid-sensitive compounds. 

Biological interest in chromium has been traditionally focused upon its toxic properties as an industrial hazard to man (LangSrd and Norseth. 1979 Norseth, 1986). It was about half a century ago that scientific and public concern arose over the dangers of increased incidence of bronchial cancer in workers in the chromate industry. Hazardous chromium exposure is also reported in metallurgical, refractory and chemical industries, which are... 

Dye substances for example, lead chromate. They are usually in an insoluble hexavalent form and, thus, not relevant as a skin hazard. Chromium oxide, a trivalent form, is used in artists paints and ceramics. 

The bacterial reduction of Cr(VI) to Cr(III) discussed above is also being used to reduce the hazards of chromium in soils and water (104). 

Sodium Bisulfite, CHRIS Hazardous Chemical Data, Coast Guard, U.S. Dept, of Transportation, Washington, D.C., data sheet revised 1978. Treatment of Chromium Waste Eiquors, General Chemical Corp., Claymont, Del., 1989. 

The only components in a coating powder which might cause the waste to be classified as hazardous are certain heavy-metal pigments sometimes used as colorants. Lead- (qv) and cadmium-based pigments (qv) are seldom used, however, and other potentially hazardous elements such as barium, nickel, and chromium are usually in the form of highly insoluble materials that seldom cause of the spent powder to be characterized as a hazardous waste (86). 

The primary hazardous components of EAF dust are zinc, lead, and cadmium nickel and chromium are present when stainless steels are manufactured. 

Fire Hazards - Flash Point Not flammable Flammable limits in Air (%) Not flammable Fire Extinguishing Agents Not pertinent Fire Extinguishing Agents Not To Be Used Not pertinent Special Hazards cf Combustion Products Toxic chromium oxide fiunes may fom in fires Behavior in Fire Can increase the intensity of fires when in contact with combustible materials Ignition Temperature Not pertinent Electrical Hazard Not pertinent Burning Rate Not pertinent. 

Concern over the health hazards of the hexavalent chromium solutions used to form the top coat of conventional nickel plus chromium coatings have encouraged research into trivalent chromium plating solutions. A process with better throwing power and improved covering power than those of hexavalent chromium has been described by Smart etal". A process for depositing a chromium-iron, or chromium-nickel-iron alloy, has been outlined by Law. ... 

The ideal disposal method is a chemical treatment that can convert hazardous waste into environmentally benign materials. For example, trichloroethylene (CI2 C I CHCl) is highly toxic to aquatic life, but this compound can be made nontoxic by chemical treatment that converts its chlorine atoms into chloride anions. Similarly, the chromium-containing waste from electroplating operations contains highly toxic CrOq anions, but a chemical treatment that converts CrOq into Cr causes the chromium to precipitate from the solution as insoluble Cr (OH). This removal of chromium detoxifies the water. 

Although Cr(VI) oxidants are very versatile and efficient, they have one drawback, which becomes especially serious in larger-scale work the toxicity and environmental hazards associated with chromium compounds. The reagents are used in stoichiometric or excess amount and the Cr(III) by-products must be disposed of safely. 

The primary leachable hazardous constituents of EAF emission control dust/sludge are lead, cadmium, and hexavalent chromium. Generally, 20 to 40 lb of EAF dust per ton of steel are generated, depending on the mill s specific operating practices, with an average of about 35 lb/t of steel melted.1 Table 2.11 shows the typical ranges of concentration of each of these elements in EAF dust. 

Reuse minimal K062, Spent pickle liquor Hazardous components lead, nickel, chromium Total generation about 6 million t/yr Reuse some recycled... 

Pickling done before coating may use a mildly acidic bath such spent liquor is not considered hazardous. Waste pickle liquor flows typically range between 10 and 20 gal/t of pickled product. Rinsewater flows may range from less than 70 gal/t for bar products to more than 1000 gal/t for certain flat-rolled products. The principal pollutants in rinsewater include TSS, dissolved iron, and metals. For carbon steel operations, the principal metals are lead and zinc for specialty and stainless steels the metals include chromium and nickel.15... 

Spent pickle liquor in the acid pickling wastewaters is listed as hazardous waste K062, regulated under RCRA, as it contains considerable residual acidity and high concentrations of dissolved iron salts.2 Exhausted pickling baths are mainly composed of nitrate (150 to 180 g/L), fluoride (60 to 80 g/L), iron (III) (30 to 45 g/L), chromium (III) (5 to 10 g/L), and nickel (II) (3 to 5 g/L). 

Spent pickle liquor is considered a hazardous waste (K062) because it contains considerable residual acidity and high concentrations of dissolved iron salts. For example, spent pickle liquor and waste acid from the production of stainless steel is considered hazardous. The hazardous constituents in K062 are lead, nickel, and hexavalent chromium. Waste pickle liquor sludge generated by lime stabilization of spent pickle liquor is not considered hazardous unless it exhibits one or more of the characteristics of hazardous waste. An estimated 6 million tons of spent pickle liquor are generated annually in the U.S.1... 

FIGURE 9.7 Hexavalent chromium reduction. (Adapted from U.S. EPA, Meeting Hazardous Waste Requirements for Metal Finishers, Report EPA/625/4-87/018, U.S. Environmental Protection Agency, Cincinnati, OH, 1987.)... 

Elangovan, R., Philip, L., and Chandraraj, K., Biosorption of chromium species by aquatic weeds Kinetics and mechanism studies, Journal of Hazardous Materials, 152 (1), 100-112, 2008. 

Hazardous waste burning incinerators, cement kilns, and LWAKs do not follow a tiered approach to regulate the release of toxic metals into the atmosphere. The MACT rule finalized numerical emission standards for three categories of metals mercury, low-volatile metals (arsenic, beryllium, and chromium), and semivolatile metals (lead and cadmium). Units must meet emission standards for the amount of metals emitted. For example, a new cement kiln must meet an emission limit of 120pg/m3 of mercury, 54pg/m3 of low-volatile metals, and 180 pg/m3 of semivolatile metals. 

Ehrlich, H.L., Biological treatment of chromium, Annual Hazardous Waste Management Conference, Lake George, Rensselaer Polytechnic Institute, Troy, NY, 1991. 

A waste is toxic under 40 CFR Part 261 if the extract from a sample of the waste exceeds specified limits for any one of eight elements and five pesticides (arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, endrin, methoxychlor, toxaphene, 2,4-D and 2,4,5-TP Silvex using extraction procedure (EP) toxicity test methods. Note that this narrow definition of toxicity relates to whether a waste is defined as hazardous for regulatory purposes in the context of this chapter, toxicity has a broader meaning because most deep-well-injected wastes have properties that can be toxic to living organisms. 

Inorganic elements can be broadly classified as metals and nonmetals. Most metallic elements become toxic at some concentration. Nine elements (arsenic, barium, cadmium, chromium, lead, mercury, nickel, selenium, and thallium) and cyanide are defined as hazardous inorganics for the purposes of deep-well injection. 

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