Chromium-containing wastes

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. 

An intere.sting example in the context of waste minimization is the manufacture of the vitamin K intermediate, menadione. Traditionally it was produced by stoichiometric oxidation of 2-methylnaphthalene with chromium trioxide (Eqn. (8)), which generates 18 kg of solid, chromium containing waste per kg of menadione. Catalytic alternatives have been reported, but selectivities tend to be rather low owing to competing oxidation of the second aromatic ring (the. selectivity in the classical process is only 50-60%). The best results were obtained with a heteropolyanion as catalyst and O2 as the oxidant (Kozhevnikov, 1993). 

Stoichiometric hexavalent chromium oxidants have been used for a variety of oxidation reactions but, due to environmental problems of chromium-containing waste, catalytic versions with soluble chromium catalysts have been developed, for example by Muzart ° using mainly TBHP as oxygen source. For instance, Muzart and coworkers... 

Landfill sites with chromium-containing wastes... 

Electrodialysis and electrolytic treatments are providing an important contribution to the recycling and safe disposal of chromium containing wastes. A wide range of process strategies and celt designs have been considered at the laboratory and pilot-plam level. In this section, we will consider a number of industrial-scale processes and devices to illustrate some of the possibilities. 

Jacobs, J. H. 1992. Treatment and stabilisation of hexavalent chromium containing waste material. Environmental Progress, 11(2), 123-126. 

Biomarkers that demonstrate chromium exposure under field conditions is under active investigation. Laboratory studies with Prussian carp (Carassius auratus gibelio) exposed for 3 to 9 days to 25 to 100 pg Cr /L or 50 to 200 pg Cr+3/L show a dose-dependent increase in the frequency of micronuclei in erythrocytes, and this increase is considered indicative of increasing DNA damage (Al-Sabti et al. 1994). Similar increases in micronuclei were observed in Prussian carp from the River Ljubjanica near chromium-containing outfalls from leather waste products in the Republic of Slovenia (Al-Sabti et al. 1994). 

In some cases the methods may be combined. Examples would include the biotechnological precipitation of chromium from Cr(VI)-containing wastes from electroplating factories by sulfate reduction to precipitate chromium sulfide. Sulfate reduction can use fatty acids as organic substrates with no accumulation of sulfide. In the absence of fatty acids but with straw as organic substrate, the direct reduction of chromium has been observed without sulfate reduction [43]. 

In addition the walls of the combustion chamber must also be shielded from corrosive slag. Chemical waste is mostly incinerated in a rotating tubular oven coated with chromium-containing corundum stone or phosphate-bound corundum stone. 

Okrent and Xing (1993) analyzed the cancer risk resulting from inadvertent intrusion into a RCRA facility for hazardous chemical waste. The facility was assumed to contain waste from production of veterinary pharmaceuticals and other wastes that resulted in concentrations of 1,000 mg kg-1 of arsenic and 100 mg kg 1 of beryllium, cadmium, chromium, and nickel. A scenario for inadvertent intrusion involving permanent site occupancy similar to the scenario used by NRC to develop the Class-A, -B, and -C limits for near-surface disposal of radioactive waste (NRC, 1982b) was used to estimate the human health consequences of the postulated intrusion. 

Gasification of Leather Offal. Chrome-leather tanning scraps or offal are a waste product of the tanning and leather industries. These wastes are usually the result of trimming operations and contain 3.5 wt % chromium and about 50 wt % water. The wastes cannot be incinerated because malodorous substances and carcinogenic chromium-containing particulates are formed. Landfill disposal is presently used. 

River Ljubjanica near chromium-containing outfalls from leather waste products in the Republic of Slovenia. 

Chromium is an element with the symbol Cr and atomic number 24. This metal is highly valued because of its hardness and corrosion resistance. See Fig. 4 [20]. This metal is added to steel to form stainless steel. It is also electroplated onto other materials to protect them from corrosion. Chromium compounds are found in the enviromnent as a result of erosion of chromium-containing rocks, volcanic eruptions, and the dumping of chromium wastes from facihty production (in landfills). Chromium is mined as chromite (FeCr204) in places like South Africa, India, Russia, and Turkey [21]. 

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