Chromium removal from wastewater

Chromium compounds are widely used in many industries metal finishing and electroplating, leather tanning, pigments manufacturing, photography and catalysts production [1]. The presence of chromium species in wastewater of all of these industries is a problem because of the affect onto die human physiolo. Chromium removal from wastewaters by adsorption onto activated charcoals is an important process in the environmental protection [2]. On the other hand the chromium species adsorption from aqueous solution is one of the processes for chromium catalysts supported on activated c ons production [3],... 

Concentrations of hexavalent chromium from metal finishing raw wastes are shown in Table 9.8. Hexavalent chromium enters wastewater as a result of many unit operations and can be very concentrated. Because of its high toxicity, it requires separate treatment so that it can be efficiently removed from wastewater. 

Gao, P., Chen, X.M, Shen, F. and Chen, G. (2005) Removal of chromium (VI) from wastewater by combined electrocoagulation-electro flotation without a filter. Separ. Purif. Technol. 43, 117-123. 

Removal of chromium (VI) from wastewater at the part-per-million level (Experiment 11)... 

Ferric chromium hydroxide adsorbent, cosmetic powders Polymethyl methacrylate adsorbent, Cr(VI) removal Ferric chromium hydroxide adsorbent, dye removal from wastewater Silica... 

Campbell, H.J.. Jr N.C. Scrivner, K. Batzar, R.F. White, "Evaluation of Chromium Removal from a Highly Variable Wastewater Stream", Proceedings of the 32nd Purdue Industrial Waste Conference, Purdue University, Ann Arbor Science (1977)... 

Qehk A, Dost K, Sezer H. An investigation of chromium(VI) ion removal from wastewaters by adsorption on residual lignin. Eresenius Environ Bull 2004 13 124-127. 

In removing excess free chlorine from municipal or industrial water and from wastewater, sodium sulfite competes with bisulfite or sulfur dioxide. Other commercial appHcations of sodium sulfite in wastewater treatment include the reduction of hexavalent chromium to the less toxic Cr " salts as well as the precipitation of silver and mercury. 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

Strong reducing agents such as sulfur dioxide, sodium bisulfite, sodium metabisulfite, and ferrous sulfate are used in the iron and steel finishing sites to reduce hexavalent chromium to the triva-lent form, which allows the metal to be removed from solution by chemical precipitation.21 23 Metal-containing wastewaters may also be treated by chemical precipitation or ion-exchange. 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

Chromate, dichromate, permanganate, chlorate and hypochlorite and other oxidants are readily reduced hy hydrazine for example, removal of chromate from wastewater may he achieved fuUy hy converting water-soluhle chromate to insoluble precipitate of chromium hydroxide, Cr(OH)3 ... 

Electrochemical treatment has been used for many years in the mining and utility industries and is a proven technology for removing hexavalent chromium from wastewater. 

Boddu, V.M., Abburi, K., Talbott, J., and Smith, E.D. 2003. Removal of hexavalent chromium from wastewater using a new composite Chitosan biosorbent. Environmental Science and Technology, 37 4449-56. 

After the toxic hexavalent chromium(VI) is reduced to less toxic trivalent chromium(III) ion, lime or another base chemical is added to convert soluble chromium(III) to insoluble chromium hydroxide in accordance with Eq. (7). A water-solid separation process unit is needed to remove the insoluble chromium hydroxide from the pretreatment wastewater. What are the feasible water-solid separation processes available ... 

Anirudhan. T.S. and Radhakrishnan, P.G., Chromium(III) removal from water and wastewater using a carboxylate-functionalized cation exchanger prepared from a lignocellusic residue, J. Colloid Intetf. Sci., 316, 268, 2007. 

LEMs have been applied for the separation and recovery of a host of different compounds. Previous efforts have been primarily focused on the recovery of metal ions from aqueous solutions (including copper, zinc, chromium, mercury, uranium, nickel, and iron (3)) and the removal of organic compounds from wastewater (14-17). 

The majority of laboratory experiments have dealt with the removal of metals. The nine most important metals from wastewater treatment considerations are addressed in this section. These are cadmium, chromium, copper, iron, leed, maxigenese, merosty, nickel and zinc. In consideration of space constraints only the studies producing tbe most efficient aod potentially applicable results ate summarized. 

Wastewaters coming from tannery, besides impurities removed from leather (hair, blood, epidermis, fat tissue) contain significant amounts of chemicals sulfuric acid and hydrogen chloride, lime, soda, sodium sulfide, chromium (El) compounds, detergents and organic solvents [14]. Water consumption in tanneries and furriery plants is from 30 to 81 m and from... 

Certain plants grown on serpentine soils containing 1000-50,000 mg Cr/kg dry weight (DW) may contain 10.0-100.0 mg Cr g DW -levels that may be toxic to wildlife, although no reports of this phenomenon are known. Most plant and invertebrate species die before accumulating amounts of chromium that are toxic to predators. Some species of terrestrial plants have been proposed for the removal of chromate from wastewaters. Terrestrial plants, such as wheat (Triticum aestivum), accumulate the greatest amount of chromium under conditions of sulfate deficiency or deprivation. Because... 

Ho W.S.W. and Poddar T.K., New membrane technology for removal and recovery of chromium from wastewaters. Environ. Prog. 20,44, 2001. 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of NOx Uses Nutrient, dietary supplement, iron source in foods for special dietary use Regulatory FDA21CFR 172.370, 573.580 Manuf./Distrib. Lohmann http //www.lohmann-chemikalien.de Sigma Ferric chromium hydroxide Synonyms Fe (lll)/Cr (III) hydroxide Uses Adsorbent for removal of Cr(VI) from aq. sol n. and chromium plating industry wastewater Ferric citrate... 

Namasivayam, C. and Ranganathan, K. 1993. Waste Fe(III)/Cr(ni) sludge as adsorbent for the removal of Cr(VI) from aqueous solution and chromium plating industry wastewater. Environ. Pollut. 82 255-261. Namasivayam, C. and Arasi, D. 1997. Removal of Congo red from wastewater by adsorption onto waste red mud. Chemosphere 34 401-417. 

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