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Production of Iron and Steel

Brief History and Definition

Iron and steel production refers to the manufacture of iron with small amount of carbon. Generally steel is an alloy of carbon and iron which has mostly with the addition of other elements. Iron and steel have served an essential role in the growth of human civilization over several decades and have been used in the construction, the manufacturing of machinery and equipment, agriculture, the generation and distribution of power, in medicine and most commonly in the household. Iron and steel together with coal and cotton, were the main materials upon which the industrial revolution has been based. The developments from the early eighteenth century onwards allowed increases in output, for example by substituting relatively scarce charcoal with hard coal/lignite and coke respectively and by the development of the puddling process for changing pig iron to steel. The production of steel has grown exponentially in the second half of  twentieth century which resulted to the rising to a world total of 757 million tones in 1995 (Integrated 2001).

Sources of Pollutants in an Iron and Steel Production Industry

In metal industries like in an Iron and Steel production industry, steel mills produce waste water from the coking of coal,

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washing of blast furnace flue gasses, and the pickling of the steel (Hodges 1975). These wastes tend to be acidic and contain cyanogens, phenols, ore, coke, limestone, alkali, oils, mill scales, and fine suspended solids. Large mills may recover by-products but smaller mills do not find this economical and may simply neutralize the acidity with lime, which leads to large volume of sludge. Other metal industries have similar problems and their waste generally contain the metal produced or plated- chromium, lead, nickel, cadmium, zinc, copper, silver, as well as acids, alkaline cleaners, grease and oil.

There are a lot of pollutants which are produced from a metal fabricating industry like in an Iron and Steel Production Industry and some of this is Glycol ethers, trichloroethane, xylene, methyl ethyl ketone, sulfuric acid, toluene, trichloroethylene, hydrochloric acid, zinc compounds, acetone, dichloromethane, ntric acid, methyl isobutyl ketone, nickel, Freon 113, tetrachloroethylene, zinc fumes, chromium, copper, chromium compounds, and ethylene glycol (Freeman 1995). These compounds constitute or accounts for the 94 percent released. Most of these discharges go to ambient air. Forty percent of these pollutants are discharged from stacks, point air sources, and another 25 percent are released as fugitive air emissions. Eighty percent of the total emissions have been identified as candidates for regulation under various provisions of the Clean Air Act. The amounts sent to deep well injection, surface waters, land disposal and publicly owned water treatment facilities is small. Approximately 30 percent of the wastes are sent off site for treatment, disposal or recycle. Five common parts-processing operations were identified as major pollutant discharge sources and these are stripping, cleaning, painting, inorganic surface treatment and inorganic surface finishing.

Environmental Impacts of Pollutants in an Iron and Steel Production Industry

Exposure to pollutants such as from an Iron and Steel Production Industry via mechanism such as ingestion, inhalation, skin contact, direct uptake through gills, membrane uptake processes in micro-organism, foliar deposition, direct uptake through roots and leaves and the likes may have lethal and sub lethal effects on the health of flora and fauna (Petts 1994). These effects may include leaf damage, tissue damage, reduced productivity in plants, morbidity and mortality in fauna, reproductive effects, skin damage and irritation, and carcinogenic effects. For plants growing on contaminated soils, uptake may occur via the root system, or via dust blown onto leaves and stems. Migration of chemicals from roots to fruits and seeds is generally low, but on leafy crops such as lettuce, transport of the chemicals to the leaves in the transpiration stream may be important. For compounds with low vapor pressure and low water solubility, uptake through leaves, either via direct contact with material deposited from the atmosphere or via soil blown onto the plant, is a more significant exposure route than root uptake. Landfill gas migration to surface cover may result in soil temperature rise and the depletion of air in the root zone causing die-back of vegetation. The dominant exposure roots of terrestrial animals will normally be the food chain and will be more or less comparable with the routes of human exposure. All higher order animals can be directly exposed to pollutants before and after birth by transfer of contaminant in the mother’s tissue to progeny (Petts 1994).

Direct loss of aquatic flora and fauna can occur where dissolved oxygen levels are lowered in water by high organic strength effluents, or from settlement of suspended matter giving rise to putrefaction and blanketing of stream and river beads. Aquatic fauna may be exposed directly to pollutants dissolved in water or absorbed onto particles, sediments and biomass. Chemicals strongly bound to particles may pass into the food chain mainly by aquatic organisms feeding on sediments or by filter feeders such as mollusk. For more water-soluble compounds, skin and gills uptake play a more important role. Effects on invertebrates capable of sequestrating contaminants could lead to a loss of feeding resource or indirect effects, for example, upon wildfowl and wading birds from prolonged feeding (Petts 1994). Damage to plants can result from emissions of particulate matter, acid gases, ozone, metals, fluorides, etc and can be manifested as visible effects such as changes in leaf structure, pigmentation of tissue damage, and as more subtle effects such as retardation in growth. Particulate matter can obstruct the stomata pores and interfere with gas exchange. Gases such as sulfur dioxide may affect plant growth particularly when pollution levels are greatest in the winter and natural growth is slowest, and at sub-lethal can cause leaf damage. Some gaseous pollutants may be absorbed by the leaf cuticle and lead to enhanced water loss may predispose plants to attack by insects and fungi. Most air pollutants have been considered in terms of their individual effects rather than as combinations, although simultaneous exposure to the mixtures of sulphur dioxide and nitrogen dioxide have been found to cause greater damage than exposure to the same chemicals singularly(Petts 1994).

The impact of release to atmosphere can be of two types and these are direct and indirect, direct impacts, those in which direct contact with the chemical in the air results in an adverse effect which includes health effects caused by inhalation, nuisance effects from odors and the effect of acid deposition on vegetation, while indirect are the higher order effect in which the receptor is in contact with the environmental media or materials which has been contaminated by chemicals in the air which includes the ingestion of foods affected by the atmospheric deposition. Indirect and direct impacts can be discussed under five headings such as human health, loss of amenity, flora and fauna, climate and materials. The manifestations of air pollutions in humans extend from lowering the amenity value of the environment to a more severe health effects such as respiratory illness or cancer. Short-term, acute exposures can arise during emergency situations on site such as in the case of spillage or fire involving chemicals, during periods of mal operation or during adverse weather conditions when pollutants emitted in the atmosphere accumulate rather than disperse. Long-term chronic effects includes respiratory diseases such as asthma that are exacerbated by pollution episodes involving the traditional pollutants such as suspended particulate matter, sulfur and nitrogen oxides, toxic effects cause by the intake of harmful levels of chemicals, and cancer. Loss of amenity can take the form of effects on the visibility like through the formation of mist or smog, causing nuisance, and emissions of dust and odors. Also, a wide range of chemicals affect fauna. Metals such as selenium, molybdenum and nickel are also released from certain manufacturing processes like in an iron and steel production, causing metabolic disturbances, malformation, growth and reproductive disorders and skin lesions when ingested in sufficient quantities (Petts 1994).

Air pollution can affect a range of materials and structure. Acid gases such as sulfur dioxide attack buildings, monuments, etc, by converting the insoluble calcium carbonate to sulfate, causing crumbling of the structure. Electrochemical corrosion and both direct and indirect chemical attack can occur when the pollutants acts in combination with moisture. Other potential impacts relate to damage to metals, paints, textiles, rubbers, leather and paper. The pollutants of concern are the acid gases, ozone, ammonia, hydrogen particulates and grit. Paint soiling weathering and loss in durability is affected by exposure to ammonia, ozone, sulfur dioxide, etc.

Monitoring and Control of Pollutants in an Iron and Steel Production Industry

Discharge of metals to the aquatic environment has been a major cause of concern and the treatment of these water has consequently attracted considerable attention Waste containing metals may arise from a variety of industrial operations like in the iron and steel production industry. Waste from metal processing may be as followed: mining, ore processing, machining, degreasing, pickling, dipping, polishing, electrochemical or chemical brightening or smoothing, cleaning, plating and anodizing (Harrison 1990). The sources of waste in metal processing are numerous and also extremely variable both in Quantity and quality. Metals in the waste occur in the form ranging from large particles of pure metal in suspension to metallic ions and complexes in solution. The most appropriate method of treatment depends upon the form of the metal, its concentration, pH, and other constituents of the waste. The technique most commonly employed in treating metal processing waste is precipitation using pH adjustment. The optimum pH for precipitation varies depending on the particular metal and where several metals are involved a compromise pH is used. Atypical value is in the range 8.0 – 9.0. With amphoteric metals, notably zinc, were must be taken to avoid too high pH to prevent the formation of zincates. It should also be appreciated that other constituents of waste like ammonia can significantly affect the solubility of the metal hydroxides and it is theredore not possible to predict accurately the level of residual metal in the treated effluent. While the hydroxide precipitation method is satisfactory for most metals encountered in effluents both hexa-valent chromium and lead are not precipitated in this way. Flotation may be used as an alternative to settlement. This process, which is gaining in popularity, consists in the carrying of the metal hydroxides and other particles in suspension to the surface of the liquid in the flotation vessel by increasing particle buoyancy using the gas bubbles and separated, is skimmed off (Harrison 1990). Where the metal is substantially in solution there are various techniques for separation or concentration of the metal so that a high quality treated may be obtained.

Ion Exchange resins are in general two types, insoluble organic acids, used for cation exchange. Cat ion exchangers may be either sulfunic or carboxylic acids, while anion exchangers may be either quaternary or tertiary amines.  An ion exchange system consists of pair of colums or pressure vessels, one containing an anion exchange resin, the other cation exchange resin. The effluent is continuously pumped through the two columns in series to yield the treated effluent. Where an exceptionally high quality effluent is required a third mixed bed exchanage column can be replaced after the cation exchange column.

Evaporation is one of the most common methods used in industry for the concentration of aqueous solutions. Nevertheless, use of this process as a means for effluent treatment is rare and occurs only under special circumstances where the effluent contains a high concentration of a valuable material.

Reverse osmosis, is a process which is still in its infancy. This process is used in the treatment of brackish water to yield potable water. In particular the process requires high pressures up to 100 atmospheres and is thus costly in terms of energy.

Solvent Extraction is a process in by which the components of a liquid mixture are separated by treatment with a solvent in which one or more of the desired components is preferentially soluble. It is a process which is widely used in the chemical and the petrochemical industries but which has only recently adopted for the recovery of metals from aqueous solutions.

Electrodialysis is also used in the treatment of metals. This is a process which is very dependent on dissolved solid concentration. It does not find common use in the effluent treatment but maybe appropriate in certain circumstances where concentrate is of value.

List of References

Freeman,H.(1995) Industrial Pollution Prevention Handbook:McGraw Hill, Inc

Harrison, R. (1990) Pollution Causes, Effect, and Control : The Royal Society of Chemistry

Hodges,L. (1973) Environmental Pollution: Holt, Rhinehart and Winston

Holmes, G. et al, (1993) Handbook of Environmental Management and Technology : John Wiley and Sons Inc.

Integrated Pollution Prevention and Control (2001) Best Available Techniques Reference       Document on the Production of Iron and Steel [online] available from <http://ec.europa.eu/environment/ippc/brefs/isp_bref_1201.pdf> [26 November 2007]

Petts,J, et al. (1994) Environmental Impact Assessment for Waste Treatment and Disposal Facilities: John Wiley and Sons

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