Kiln Dusts

Kiln dusts (KD) are fine by-products of Portland cement and lime high-tem-perature rotary kiln production operations [88-98] that are captured in the air pollution control dust collection systems (cyclones, electrostatic precipitators, and baghouses). Different types of KD are discussed in Table 4. 

In addition to fresh cement kiln dust (CKD) and hme kiln dust (LKD) production, it is estimated that the total amount of KD currently stockpiled throughout the country exceeds close to 90 milhon metric tons (100 million tons). These stockpiles are usually located relatively close to the cement and Hme manufac-tining plants, and vary in age and composition, with exposure to the elements reducing the chemical reactivity of the dusts. 

Cement kiln - CKD is a fine powdery material similar in appearance to Portland dust (CKD) cement- Fresh CKD can be classified as belonging to one of four 

9 million metric tons (14.2 million tons) of CKD are produced annually 

Limekiln LKD is physically similar to CKD, but chemically quite different 

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Cement plants in the United States are now carehiUy monitored for compliance with Environmental Protection Agency (EPA) standards for emissions of particulates, SO, NO, and hydrocarbons. AH plants incorporate particulate collection devices such as baghouses and electrostatic precipitators (see Air POLLUTION CONTROL methods). The particulates removed from stack emissions are called cement kiln dust (CKD). It has been shown that CKD is characterized by low concentrations of metals which leach from the CKD at levels far below regulatory limits (63,64). Environmental issues continue to be of concern as the use of waste fuel in cement kilns becomes more widespread. 

An Analysis of Selected Trace Metals in Cement and Kiln Dust, SP109, Pordand Cement Association, Skokie, Dl., 1992. 

Lime kilns dust emissions are controlled by baghouse systems. Kiln fuels can be selected to reduce SO, emissions however, this is not normally a problem, since most of the sulfur dioxide that is formed is absorbed in the kiln. 

We only briefly mentioned alkaline stabilization, but in reality this is a variation of sludge pasteurization. The basic process uses elevated pH and temperature to produce a stabilized, disinfected product. The two alkaline stabilization systems most common in the U.S. are a lime pasteurization system and a cement kiln dust pasteurization system. The lime pasteurization product has a wet-cake consistency, while the kiln dust pasteurization has a moist solid like consistency. Both products can be transported to agricultural areas for ultimate use. Literature studies show that the kiln dust product can capture a marketable value of 6.60/Mg ( 6.00/ton) to offset hauling costs, while the lime product does not appear to be able to capture financial credits for product revenues at this point in time. The reasons for this are not entirely clear. 

It is assumed that the moisture content of the soil has been determined to be approximately 50% under worst-case conditions. Using this information and the results from vendor tests, it has been determined that a minimum dose of one part solidification reagent to two parts soil is required for the migration control of lead. Testing has shown that the optimum solidification reagent mixture would comprise ca. 50% fly ash and ca. 50% kiln dust. Thus, ca. 7000 t (6364 T) each of fly ash and cement kiln dust would be required. The reagents would be added in situ with a backhoe. As one area of the soil is fixed, the equipment could be moved onto the fixed soil to blend the next section. It may be anticipated that the soil volume would expand by ca. 20% as a result of the fixation process. This additional volume would be used to achieve the required slope for the cap. An RCRA soil/clay cap placed over the solidified material is necessary to prevent infiltration and additional hydraulic stress on the fixed soil. It is estimated that the fixation would reduce lead migration by 40% and that the fixed soil may pass the U.S. EPA levels for lead. 

Massicotte, R. et al., Immunological response of the earthworm Lumbircus terrestris following exposure to cement kiln dusts, Ecotox. Environ. Safety, 59, 10, 2004. 

Cementite, 4 647 23 272, 274, 275 Cement kiln dust, 5 492, 495 Cement kilns, 13 178 scrap tire fuel in, 21 464 Cement-matrix composites, 26 751 Cement plants, sulfuric acid and, 23 787 Cement rock, raw material for cement,... 

Electrostatic precipitators and baghouses are used to catch dust particles containing metals. Electrostatic precipitators use an electrical field to remove the particles. Baghouses use fiberglass filters, similar to vacuum cleaner bags, to catch them. The majority of theses particles, called cement kiln dust (CKD), are trapped by this equipment and returned to the kiln for incorporation into the cement clinker. Under USEPA s BIF rule. Southdown tests its cement kiln dust to judge whether it is hazardous. If the CKD does not meet the standards set under the BIF rule, it must be disposed of in accordance with USEPA s strict hazardous waste regulations. For that reason. Southdown does not accept fuels that would cause the waste CKD to fail this test. 

Some of the most common stabilizing agents used in hazardous waste disposal are Portland cement, lime, fly ash, and cement kiln dust. Small quantities of hazardous wastes are disposed of by incineration, energy conversion, manufacture of fuels, or other practical applications. 

The DustMASTER system is designed to limit dust from fly ash and other dust generating waste streams such as fly and bottom ash from waste-to-energy and utility plants, cement kiln dust, baghouse residue, iron-oxide, and other powder-type materials. 

Products resulting from the decay of organic matter—e.g. Indian nitre and South African nitre. The value of saltpetre for the manufacture of gunpowder and in the chemical industries is greatly in excess of its value as a fertilizer and consequently nitre is not usually regarded as a source of potash supply. (6) Blast furnace and cement-kiln dust. (7) The insoluble potash minerals—e.g. felspar, alunite, leucite, etc. 

Full-scale separation/washing and bioslurry reactor operations have been used to treat creosote-contaminated soil at the former Southeastern Wood Preserving Site at Canton, Mississippi (Jerger et al., 1994 Woodhull Jerger, 1994). Here, an estimated 10 500 yd3 of soil and sludge were excavated from various process areas, stabilized with kiln dust and stockpiled for subsequent treatment. Based on the results of preliminary bench studies, four 680 000 liter reactors were eventually established to handle 7050 yd3 of the screened (200-mesh) soil fraction at a solids content of 20-25%. Other oil fractions and waters were handled separately (data and costs not reported). 

Carbon Black Iron Powder Carbon, Synthetic Graphite Cement, Raw Mix Cement Kiln Dust Alcohol-Carbowax Sodium Silicait Water Water TUrbulator TurbulatorVDisc Disc Pelletizer Turbulator /Disc... 

Dolomite Kiln Dust Dye Pigment Electric Furnace Dust Fertilizer Water Lignosulfonate Water Ammonia TurbulatorVDisc TurbulatorVDisc TurbulatorVDisc Drum... 

Refractories Bauxite, Alumina, Kiln Dust, Blends... 

Cement industry Waste cement cement kiln dust... 

Solidification/stabilization Refers to reducing the mobility of a contaminant in soils, other solids, or even liquid wastes by mixing them with Portland cement, lime, cement kiln dust, clays, slags, polymers, water treatment sludges, iron-rich gypsum, fly ash, and/or other binders. The process decreases the mobility of contaminants through physical encapsulation (solidification) and chemical bonding between the contaminants and the binders (stabilization). 

Fly ash, as it is a large-volume industrial waste, is both cheap and abundant, so that there is an economic incentive to use fly-ash-modified cements. In addition, C02 is also produced as a waste by-product of industrial processes (power generation, cement manufacture, etc.), and its permanent sequestration into cement is an added environmental benefit. A fully carbonated Portland cement permanently sequesters about 130 L of C02 per kilogram of cement. Figure 15.8 shows the structural and chemical modifications produced in cemented fly ash microspheres as a result of the supercritical C02 treatment. As is the case with fly ash, kiln dusts are primarily siliceous, so that the same benefits can be derived from their use as modifiers in immobilization and S/S matrices. 

US Environmental Protection Agency, Report to Congress on Cement Kiln Dust, Office of Solid... 

Lime/fly ash pozzolanic processes combine the properties of lime and fly ash to produce low-strength cementation. Kiln dust processes involve the addition of kiln dust to eliminate free liquids and usually form a low-strength solid. Lime-based processes for solidification use reactions of lime with water and pozzolanic (siliceous) materials, such as fly ash or dust from cement kilns, to form concrete, called a pozzolanic concrete. Wastes of desulfurization of gases and other inorganic wastes can be immobilized by this method. 

Ashes and residues. These are the materials remaining from the burning of wood, coal, coke, and other combustible wastes. Residues from power plants normally are composed of fine powdery materials, cinders, clinkers, and small amounts of burned and partially burned materials. Fly ash from coal boilers and CKD (cement kiln dust) are frequently sold for stabilization of waste, waste bulking operations, and incorporation into building products such as gypsum from sulfur dioxide scrubbing. 

Bulking of liquid wastes. Liquid wastes are prohibited from landfills. Wastes with free liquids are mixed with a bulking agent such as dry sawdust, cement kiln dust, or fly ash. 

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