Classifications

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  • C04B33/00—Clay-wares
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  • C04B18/00—Use of agglomerated or waste materials or refuse as fillers for mortars, concrete or artificial stone; Treatment of agglomerated or waste materials or refuse, specially adapted to enhance their filling properties in mortars, concrete or artificial stone
  • C04B18/02—Agglomerated materials, e.g. artificial aggregates
  • C04B18/023—Fired or melted materials
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  • C04B33/00—Clay-wares
  • C04B33/02—Preparing or treating the raw materials individually or as batches
  • C04B33/13—Compounding ingredients
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  • C04B33/1321—Waste slurries, e.g. harbour sludge, industrial muds
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  • C04B33/00—Clay-wares
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  • C04B33/1324—Recycled material, e.g. tile dust, stone waste, spent refractory material
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  • C04B33/00—Clay-wares
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  • C04B33/1328—Waste materials; Refuse; Residues without additional clay
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  • C04B33/00—Clay-wares
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  • C04B33/00—Clay-wares
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  • C04B33/13—Compounding ingredients
  • C04B33/132—Waste materials; Refuse; Residues
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  • C04B33/00—Clay-wares
  • C04B33/02—Preparing or treating the raw materials individually or as batches
  • C04B33/13—Compounding ingredients
  • C04B33/132—Waste materials; Refuse; Residues
  • C04B33/135—Combustion residues, e.g. fly ash, incineration waste
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  • C04B33/00—Clay-wares
  • C04B33/02—Preparing or treating the raw materials individually or as batches
  • C04B33/13—Compounding ingredients
  • C04B33/132—Waste materials; Refuse; Residues
  • C04B33/138—Waste materials; Refuse; Residues from metallurgical processes, e.g. slag, furnace dust, galvanic waste
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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
  • C04B35/62605—Treating the starting powders individually or as mixtures
  • C04B35/62695—Granulation or pelletising
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  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/40—Porous or lightweight materials
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
  • C04B2235/3208—Calcium oxide or oxide-forming salts thereof, e.g. lime
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
  • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
  • C04B2235/327—Iron group oxides, their mixed metal oxides, or oxide-forming salts thereof
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
  • C04B2235/5427—Particle size related information expressed by the size of the particles or aggregates thereof millimeter or submillimeter sized, i.e. larger than 0,1 mm
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
  • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
  • C04B2235/96—Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/60—Production of ceramic materials or ceramic elements, e.g. substitution of clay or shale by alternative raw materials, e.g. ashes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Definitions

• Synthetic aggregates and, more particularly, synthetic aggregates comprising sewage sludge and silicoaluminous materials, and synthetic aggregates comprising combinations of low and high calcium containing silicoaluminous materials.
• Aggregates are essential ingredients of concrete, masonry, and cavity fill insulation. Other applications for aggregates include filler aid or horticultural aggregate. Aggregates may be derived from natural sources with minimal processing or from naturally occurring materials that are heat treated. Aggregates may also be synthetic. Aggregates from natural sources, such as quarries, pits in ground, and riverbeds, for example, are generally composed of rock fragments, gravel, stone, and sand, which may be crushed, washed, and sized for use, as needed. Aggregates from natural materials that may be used to form aggregates include clay, shale, and slate, which are pyroprocessed, causing expansion of the material. OPTIROC and LECA are examples of commercially available expanded clay aggregates, for example.
• Synthetic aggregates may comprise industrial byproducts, which may be waste materials.
• LYTAG for example, is a commercially available sintered aggregate comprising pulverized fuel ash (“PFA”), also known as fly ash. PFA is produced from the combustion of coal in power plants, for example.
• PFA pulverized fuel ash
• aggregate resources are finite and extracting and processing these materials is complicated by environmental issues, legal issues, availability, urban expansion, and transportation costs, for example.
• most generated waste is disposed of in landfills at a great expense. Due to the exhaustion of available landfill sites, the difficulties in acquiring new sites, the potential adverse environmental effects, and the cost of landfilling, disposal of waste materials has been a significant problem for many years.
• the processing and transformation of waste materials to produce viable synthetic aggregates for use in concrete and in other applications would alleviate both waste problems and the depletion of natural aggregate resources.
• Aggregates may be lightweight or normal weight.
• LWAs Lightweight aggregates
• High quality LWAs have a strong but low density porous sintered ceramic core of uniform structural strength and a dense, continuous, relatively impermeable surface layer to inhibit water absorption. They are physically stable, durable, and environmentally inert.
• LWAs For use in concrete, LWAs should have a sufficient crushing strength and resistance to fragmentation so that the resulting concrete has a strength of greater than 10 MPa and a dry density in a range of about 1.5 g/cm 3 to about 2.0 g/cm 3 . Lower density LWAs may also be produced. Concrete containing LWAs (“LWA concrete”) may also have a density as low as about 0.3 g/cm 3 .
• LWAs Synthetic lightweight aggregates
• Concrete containing LWAs (“LWA concrete”) may be 20-30% lighter than conventional concrete, but just as strong. Even when it is not as strong as conventional concrete, the LWA concrete may have reduced structural dead loads enabling the use of longer spans, narrower cross-sections, and reduced reinforcement in structures. The lower weight of the LWA concrete facilitates handling and reduces transport, equipment, and manpower costs. LWA concrete may also have improved insulating properties, freeze-thaw performance, fire resistance, and sound reduction.
• Sewage sludge which is produced by biological wastewater treatment plants, is a significant waste in terms of volume and heavy metal content.
• Sewage sludge comprises settled solids accumulated and subsequently separated from the liquid stream during various treatment stages in a plant, such as primary or secondary settling, aerobic or anaerobic digestion or other processes.
• the composition and characteristics of the sewage sludge may also vary depending upon the wastewater treatment process and the sewage sludge treatment process applied.
• Sewage sludge can be raw, digested, or de-watered.
• Sewage sludge contains significant amounts of organic materials and may also contain high concentrations of heavy metals and pathogens.
• Sewage sludge has been generally disposed of by incineration to form an inert ash that is disposed by lagooning, landfilling, spreading on land as fertilizer or soil conditioning, and ocean dumping, for example. If the sewage sludge has not been treated prior to being spread on land or disposed of in a landfill, undesirable contamination may occur.
• MSW Municipal solid waste
• IBA Incinerator bottom ash
• IBA is currently used in its raw form (without heat treatment) in the construction of embankments, pavement base and road sub-base courses, soil stabilization, in bricks, blocks, and paving stones, and as fillers in particular applications. Although considered a relatively inert waste, leaching of heavy metals in these applications is possible.
• MSW incineration also produces a particulate residue in the form of dust suspended in the combustion gases or collected in emission control devices, which is called air pollution control (“APC”) residue.
• APC air pollution control
• the incinerator filter dusts (“IFD”) are an APC residue collected in baghouse filters produced at a rate of 25-30 kg per 1000 kg of incinerated waste, while fly ash, which in some cases includes IFD, accounts for about 10% to 15% of the total combined ash stream.
• MSW incinerator fly ash (“IFA”) contains high concentrations of hazardous materials, such as heavy metals, dioxins, sulphur compounds, and chlorine compounds, and is therefore classified in most European countries as a toxic and dangerous residue. Therefore, it can only be disposed in special landfills, which is costly and environmentally unsafe.
• Electricity- generating power plants also produce large volumes of ash residues in the form of a fine-grained particulate, known as pulverized fuel ash (“PFA”) and a coarse fraction, known as furnace bottom ash (“FBA”).
• PFA pulverized fuel ash
• FBA furnace bottom ash
• the heavier ash material accounts for 20-30% of the total coal ash produced and is the fraction that falls through the bottom of the furnace.
• FBA is currently used in its raw form as aggregate in lightweight concrete, in Portland cement production and other asphalt or road base applications.
• CKD cement kiln dusts
• blast furnace slag Other waste generated at high rates include cement kiln dusts ("CKD") and blast furnace slag.
• CKD is a fine-powdery by-product of cement manufacture operations captured in the air pollution control dust collection systems of the manufacturing plant.
• CKD is a fine-powdery by-product of cement manufacture operations captured in the air pollution control dust collection systems of the manufacturing plant.
• GGBS is a nonmetallic product of the production and processing of iron in blast furnaces. It is estimated that approximately 15.5 million tons of GGBS are produced annually in the United States, and the majority is used in cement production, as an aggregate or insulating material.
• a method for producing an aggregate comprising mixing sewage sludge from a waste water treatment facility with a non-coal combustion ash silicoaluminous waste material. The method further comprises agglomerating the mixture to form an agglomerate and pyroprocessing the agglomerate to form an aggregate.
• the waste material may comprise municipal solid waste incinerator residues, waste glass, blast furnace slag, kiln dusts, and/or mining waste.
• the municipal solid waste incinerator residues may comprise air pollution control residues and/or incinerator bottom ash.
• Air pollution control residues include incinerator fly ash and/or incinerator filter dusts.
• the kiln dusts comprise cement kiln dusts.
• the mining waste includes granite sawing residues.
• the waste material comprises more calcium than the sewage sludge.
• the waste material includes incinerator filter dusts, incinerator bottom ash, cement kiln dusts, waste glass, and/or blast furnace slag.
• the waste material may comprise more than 9% calcium and the sewage sludge may comprise less than 3% calcium.
• the resulting aggregate may comprise less than about 10% calcium by dry weight.
• the method may comprise mixing from about 99% to about 60% sewage sludge by dry weight of the mixture with from about 1% to about 40% of the waste material by dry weight of the mixture.
• the method comprises mixing from about 80% to about 90% sewage sludge by dry weight of the mixture with from about 10% to about 20% of the waste material.
• the waste material comprises less calcium than the sewage sludge.
• the waste material may comprises furnace bottom ash, granite sawing residues, and/or waste glass.
• the waste material may comprise less than about 10% calcium and the sewage sludge may comprise greater than about 10% calcium.
• the aggregate may comprise less than about 10% calcium.
• the method may comprise mixing from about 5% to about 95% sewage sludge by dry weight of the mixture with from about 95% to about 5% of the waste material by dry weight of the mixture.
• the method comprises mixing from about 30% to about 70% sewage sludge by dry weight of the mixture with from about 70% to about 30% of the waste material by dry weight of the mixture. More preferably, the method comprises mixing from about 30% to about 50% sewage sludge by dry weight of the mixture with from about 70% to about 50% of the waste material by dry weight of the mixture.
• the method may further comprise milling the waste material prior to mixing.
• the milling is wet milling.
• the mixture of the sewage sludge and the waste material is preferably milled prior to agglomerating.
• the agglomerating comprises pelletizing. At least some of the water may be removed from the wet milled waste material and at least some of that water may be used during pelletizing and/or quenching of the pyroprocessed agglomerate.
• the resulting aggregates may have a diameter of from about 3 mm to about 40 mm.
• the agglomerates may be coated with an inorganic powder.
• a plastic binder may be mixed with the sewage sludge and waste material prior to agglomerating.
• the plastic binder may comprise clay.
• the clay binder may comprise from about 5% to about 20% by dry weight of the mixture.
• Pyroprocessing of the agglomerate may take place in a rotary kiln.
• the resulting aggregate may be a lightweight aggregate or a normal weight aggregate, for example.
• the agglomerate may be vitrified.
• Selected properties of the aggregate may be controlled based, at least in part, on a proportion of the sewage sludge to the waste material and the pyroprocessing temperature. The selected properties may include the density, water absorption, and/or strength of the aggregate.
• a method for producing a sintered lightweight aggregate comprising preparing a mixture comprising sewage sludge from a waste water treatment facility and a non- coal combustion ash, silicoaluminous waste material, agglomerating the mixture to form an agglomerate, and sintering the agglomerate.
• the waste material may comprise incinerator fly ash, incinerator filter dust, incinerator bottom ash, furnace bottom ash, waste glass, blast furnace slag, cement kiln dusts, and/or granite sawing residues.
• a sintered lightweight aggregate comprising sewage sludge from a waste water treatment facility and a non-coal combustion ash, silicoaluminous waste material. A mixture of the sewage sludge and the waste material is sintered at a temperature to form the sintered lightweight aggregate.
• the waste material may comprise incinerator fly ash, incinerator filter dust, incinerator bottom ash, waste glass, blast furnace slag, cement kiln dust, and/or granite sawing residues, for example.
• the lightweight sintered aggregate may comprise from about 2% calcium to about 10% calcium. Preferably, the lightweight sintered aggregate comprises from about 3% to about 6% calcium.
• the lightweight sintered aggregate may be chemically inert.
• a pyroprocessed aggregate comprises sewage sludge from a waste water treatment facility and a non-coal combustion ash, silicoaluminous waste material.
• the aggregate may be sintered or vitrified.
• the aggregate may be a normal weight or lightweight aggregate.
• a pyroprocessed aggregate consists of sewage sludge.
• the sewage sludge may comprise less than 40% organic material, by weight.
• a method for producing an aggregate comprising mixing sewage sludge from a waste water treatment facility and furnace bottom ash ("FBA") from a coal-burning facility, agglomerating the mixture to form an agglomerate, and pyroprocessing the agglomerate to form an aggregate.
• a pyroprocessed aggregate is disclosed comprising sewage sludge from a waste water treatment facility and furnace bottom ash from a coal burning facility.
• a method for producing an aggregate comprising reducing a moisture content of sewage sludge from a wastewater treatment facility to a level to allow agglomeration, agglomerating the sewage sludge, and pyroprocessing the agglomerate to form an aggregate.
• a method for producing an aggregate comprising milling at least one of clay or shale, removing at least some of the water in sewage sludge from a wastewater treatment facility, and mixing the sewage sludge with the clay or shale.
• the mixture is pelletized and. the pellets are pyroprocessing to form an aggregate, in a rotary kiln.
• the mixture of the sewage sludge and the clay or shale may be wet milled.
• a process for producing aggregates comprising mixing sewage sludge from a waste water treatment facility with slate, lime, limestone, dolomite, and/or gypsum.
• the mixture is agglomerated to form an agglomerate.
• the agglomerate is then pyroprocessed to form an aggregate.
• One or more natural materials such as slate, lime, limestone, dolomite, or gypsum, may be processed prior to being mixed with the sewage sludge.
• a pyroprocessed aggregate is disclosed comprising sewage sludge from a waste water treatment facility and slate, lime, limestone, dolomite, and/or gypsum.
• a method for producing an aggregate comprising mixing a first material, which may comprise pulverized fuel ash from coal combustion, coal, clay, shale, slate, granite sawing residues, waste glass, and/or furnace bottom ash, with a second material, which may comprise incinerator fly ash, cement kiln dust, incinerator filter dust, blast furnace slag, limestone, gypsum, dolomite, and/or waste glass.
• the mixture is agglomerated the mixture to form an agglomerate and the agglomerate is pyroprocessed to form an aggregate.
• the first material may comprise less than about 3% by dry weight calcium and the second material may comprise more than about 9% calcium.
• a method for producing an aggregate comprising mixing sewage sludge from a waste water treatment facility and incinerator residues from a municipal solid waste incinerator, agglomerating the mixture to form an agglomerate, and pyroprocessing the agglomerate to form an aggregate.
• the incinerator residues may comprise incinerator bottom ash, incinerator fly ash, and/or incinerator filter dusts.
• a method for producing an aggregate comprising mixing a first material, which comprises first materials: pulverized fuel ash from coal combustion or clay, with one or more of the following second materials: slate, lime, limestone, dolomite, gypsum, blast furnace slag, incinerator fly ash, incinerator filter dust, or cement kiln dust.
• the mixture is agglomerated and the agglomerate are pyroprocessed to form an aggregate.
• a pyroprocessed aggregate comprising a first material, which may be pulverized fuel ash from coal combustion and/or clay, and a second material, which may be slate, lime, limestone, dolomite, gypsum, blast furnace slag, incinerator fly ash, incinerator filter dust, and/or cement kiln dust.
• Fig. 1 is a graph of density (g/cm 3 ) versus pyroprocessing temperature
• Fig. 2 is a graph of density (g/cm 3 ) versus pyroprocessing temperature
• FIG. 3 is a schematic cross-section of an example of an agglomerate produced in accordance with processes of the invention.
• Fig. 4 is a schematic cross-sectional view of an example of a sintered aggregate, in accordance with embodiments of the invention.
• FIG. 5 is a schematic cross-section of an example of a vitrified aggregate, in accordance with embodiments of the invention.
• Fig. 6 is an example of a method for producing aggregates, in accordance with an embodiment of the invention.
• Fig. 7 is a photograph of an example of sintered aggregates, in accordance with embodiments of the invention.
• Fig. 8 is an example of another method for producing aggregates, in accordance with another embodiment of the invention.
• Fig. 9 is a graph of density (g/cm 3 ) versus pyroprocessing temperature ( 0 C) for IBA and mixtures of sewage sludge and waste glass, in accordance with an embodiment of the invention
• Fig. 10 is a graph of density (g/cm 3 ) versus pyroprocessing temperature ( 0 C) for sewage sludge (Sample Y) and mixtures of sewage sludge and granite sawing residues, in accordance with an embodiment of the invention;
• Fig. 11 is a graph of density (g/cm 3 ) versus pyroprocessing temperature(°C) for sewage sludge and mixtures of sewage sludge and bentonite, in accordance with an embodiment of the invention
• Fig. 12 is a graph of density (g/cm 3 ) versus pyroprocessing temperature(°C) for sewage sludge and mixtures of sewage sludge and limestone, in accordance with an embodiment of the invention
• Fig. 13 is a graph of density (g/cm 3 ) versus pyroprocessing temperature(°C) for sewage sludge and mixtures of sewage sludge and incinerator fly ash, in accordance with an embodiment of the invention.
• Fig. 14 is a graph of density (g/cm 3 ) versus pyroprocessing temperature(°C) for sewage sludge and mixtures of sewage sludge and ground granulated blast furnace slag, in accordance with an embodiment of the invention.
• the behavior of a material when heated is primarily dependent on its composition, grain size, and mineral composition.
• a good ratio between fluxing materials and refractory minerals is required.
• Refractory minerals such as silica and alumina, generally have high melting points.
• the fluxing minerals promote sintering and melting at the temperature of the lowest eutectic point of the components in the mixture.
• the fluxing minerals which have low viscosity and high mobility, assist in the formation of a sintered or vitrified product, depending on the temperatures involved, by liquid phase sintering.
• Sewage sludge is a heterogeneous waste material whose composition is quite variable, depending principally on the characteristics of the wastewater influent entering a particular wastewater treatment plant and the treatment processes used for wastewater and sludge treatment processes. Sewage sludge is used in certain embodiments of the invention as the initial raw material for the production of pyroprocessed aggregates. Sewage sludge from two different treatment plants has been subjected to aggregate production processing in accordance with embodiments of the invention.
• Sewage sludge samples from one waste water treatment facility comprised, in part, about 16.02% silica (SiO 2 ), 6.83% alumina (Al 2 O 3 ), and 20.28% calcium oxide (CaO).
• Sample Y also discussed in Example 1, below, comprised, in part, about 31.24% silica (SiO 2 ), 6.22% alumina (Al 2 O 3 ), and 12.12% calcium oxide (CaO). These samples contained high amounts of the alkali earth metals calcium, which lower the melting point of the remaining compounds in the sludge.
• Densification therefore occurs at lower temperatures than the melting points of the refractory minerals silica and alumina, hi addition, the calcium components act as fluxes, assisting in the formation of a sintered or vitrified product by liquid phase sintering. Whether a mixture is sintered or vitrified depends on the pyroprocessing temperature and the composition of the mixture.
• the fluxing minerals melt to form a low viscosity, high mobility liquid that absorbs and dissolves the remaining refractory minerals very rapidly. Furthermore, the mobility of the silicate melt is increased by the presence of volatile components in the sludge. This liquid formation is responsible for an accelerated densification behavior of this type of sewage sludge with increasing pyroprocessing temperature.
• Sample Z is an example of a low calcium sewage sludge having a partial composition of 3.20% calcium oxide (CaO), 3.80% aluminum oxide (Al 2 O 3 ), and 39.50% silicon oxide (SiO 2 ). Densification took place at higher temperatures and over a wider temperature range, due to the higher concentrations of refractory minerals, such as silica.
• a pyroprocessed aggregate comprising 100% sewage sludge and a method for producing such an aggregate are disclosed.
• sewage sludge having a high calcium content such as a calcium content higher than 10%, for example
• LCSAMs low calcium silicoaluminous materials
• the high calcium content silicoaluminous sewage sludge may have a calcium content greater than 10%
• the LCSAM may have a calcium content of less than about 10%, for example.
• the LCSAMs are also referred to in this embodiment as Group A additives or materials.
• LCSAMs include waste materials, such as waste glass (“WG"), furnace bottom ash (“FBA”), and certain mining wastes, such as granite sawing residues ("GSR").
• LCSAMs also include the natural material slate.
• LCSAMs to high calcium sewage sludge has been found to 1) delay the densification of the material, and/or 2) increase the temperature range between the initial softening, sintering, and melting of the aggregates, by providing a lower mobility and higher viscosity melt from the LCSAMs. This has been found to provide better control of the aggregate production process as compared to the processing of the 100% high calcium sewage sludge.
• sewage sludge having a low calcium content is mixed with high calcium silicoaluminous materials (“HCSAMs”), which are referred to in this embodiment as Group B additives or materials.
• HCSAMs high calcium silicoaluminous materials
• Low calcium sewage sludge may have a calcium content of less than 3% and HCSAMs may have a calcium content of greater than 9%.
• HCSAMs in this embodiment include, for example: 1) the wastes: municipal solid waste (“MSW”) residues, cement kiln dust (“CKD”), and blast furnace slag; and 2) the natural materials: limestone, gypsum, and dolomite.
• Municipal solid waste (“MSW”) residues include air pollution control residues and incinerator bottom ash (“IBA").
• Air pollution control residues include incinerator fly ash and incinerator filter dust.
• HCSAMs to low calcium sewage sludge has been found to 1) reduce the temperature range over which the aggregates containing sewage sludge can be pyroprocessed; 2) provide a liquid melt that accelerates sintering and/or vitrification; and 3) enable production of aggregates with selected characteristics (such as density, for example), dependent upon temperature and composition.
• Waste glass comprises considerable amounts of fluxing components, such as calcium and sodium (9% and 12% by weight, respectively), and refractory minerals, such as silica (71.7% by weight). Waste glass may therefore be both a Group A and a Group B additive, depending on the composition of the sewage sludge. In other words, the waste glass can lower the calcium content of high calcium sewage sludge or raise the calcium content of low calcium sewage sludge.
• synthetic aggregates from mixes of at least one LCSAM with at least one HCSAM are produced. In one example, the LCSAMs comprise less than 3% calcium while the HCSAMs comprise of more than 10% calcium.
• LCSAMs in this embodiment include, for example, the wastes: pulverized fuel ash from a coal burning facility ("PFA"), and the other LCSAMs discussed above, as well as clay, shale, and slate.
• the clay may be bentonite and/or kaolin, for example.
• the HCSAMs in this embodiment are the same as those discussed above, except that MSW incinerator bottom ash is not included.
• the addition of HCSAMs to LCSAMs aims to provide a mixture with the desirable composition of the appropriate proportion of the fluxing to the refractory minerals, in order to achieve a better control of the production process to manufacture aggregates of the desired properties.
• Fig. 1 is a graph of density (g/cm 3 ) versus sintering temperature ( 0 C) for aggregates comprising sewage sludge (sample X in Example 2, below) and aggregates comprising mixtures of sewage sludge and granite sawing residues, over a range of about 92O 0 C to about 1,150 0 C.
• Curve A corresponding to aggregates comprising 100% SS, shows that as temperature increases from about 920 0 C to about 960 0 C, density increases from a low of about 1.2 g/cm 3 to a maximum density of about 2.5 g/cm 3 .
• the low calcium silicoaluminous materials (LCSAMs) used in embodiments of the invention comprise more silica and less calcium than sewage sludge.
• the sewage sludge sample (Sample X) used in Examples 1 and 2, below comprised about 16.02% silica (SiO 2 ), 6.83% alumina (Al 2 O 3 ), and 20.28% calcium oxide (CaO).
• the natural LCSAM clays (bentonite and kaolin, for example), shale, and slate comprise from about 48% to 58% silica (SiO 2 ), from about 18% to about 29% aluminum (Al 2 O 3 ), and less than about 3% calcium oxide (CaO).
• Granite sawing residues which is an example of a mining waste that may be used in certain embodiments of the invention, comprise about 65% silica (SiO 2 ), about 15% alumina (Al 2 O 3 ), and about 2.6% calcium oxide (CaO).
• Waste glass comprises about 72% silica (SiO 2 ), about 2% alumina (Al 2 O 3 ), and about 9% calcium oxide (CaO).
• Waste glass also comprises about 12% sodium oxide (Na 2 O), which is also a fluxing compound, so it may be used either to increase or decrease the amount of fluxing agents in sewage sludge.
• Furnace bottom ash which has the same composition as pulverized fuel ash from coal combustion (“PFA”), comprises about 52% silica (SiO 2 ), about 26% alumina (Al 2 O 3 ), and about 2% calcium oxide (CaO).
• silica SiO 2
• Al 2 O 3 alumina
• CaO calcium oxide
• the sintering temperature may be within a range of about 30° (from about l,010°C to about 1,040 0 C).
• similar densities may be achieved at a temperature within a 65 0 C range of from about 1,010 0 C to about 1,075 0 C.
• Fig. 2 is a graph of density (g/cm 3 ) versus sintering temperature ( 0 C) for aggregates comprising sewage sludge (Sample Z in Example 4, below) and aggregates comprising mixtures of sewage sludge and cement kiln dust, over a range of about 98O 0 C to about 1,11O 0 C.
• Curve B corresponding to 100% sewage sludge, shows that as temperature increases from about 980 0 C to about 1060 0 C, density increases from a low of about 1.9 g/cm 3 to a maximum density of about 2.4 g/cm 3 .
• density decreases from the maximum density of 2.4 g/cm to 2.0 g/cm .
• the aggregates having densities above 2.0 g/cm are normal weight aggregates.
• sewage sludge exhibits a delayed densification and a broad temperature interval between the initial material softening, sintering and melting, due to the high amounts of refractory components in the sewage sludge.
• the temperatures investigated produced normal weight aggregates having densities between 2.0 g/cm 3 and 2.4 g/cm 3 over a wide temperature range of 110 0 C (1000-1HO 0 C).
• a high calcium silicoaluminous, Group B material (“HCSAM”) is added to the sewage sludge.
• the HCSAM is cement kiln dust ("CKD"). Since CKD comprises a significant amount of CaO (63% by weight), only a small amount of CKD is needed to have an accelerating effect.
• An addition of 5% CKD in the sewage sludge results in the production of lightweight aggregates having densities of from about 1.7 g/cm 3 to about 2.4 g/cm 3 , when pyroprocessed in the same temperature range of the 100% sewage sludge mixture.
• CKD 10% CKD in the sewage sludge results in the production of lightweight aggregates having densities as low as 1.4 g/cm 3 and normal weight aggregates having densities of up to about 2.4 g/cm 3 , between the pyroprocessing temperatures of 940°C to 1060°C. Further additions of CKD are not preferred because it may further accelerate the densification of the mixture, which may be an obstacle in controlling the production process in a predictable manner in large scale aggregate production.
• an aggregate is formed by mixing predetermined amounts of sewage sludge and a second material, which may be an LCSAM or a HCSAM, depending on the composition of the sewage sludge, agglomerating the mixture, and pyroprocessing the agglomerate at a selected temperature.
• a second material which may be an LCSAM or a HCSAM, depending on the composition of the sewage sludge, agglomerating the mixture, and pyroprocessing the agglomerate at a selected temperature.
• the LCSAM has less calcium-containing components than the original sewage sludge
• the HCSAM has more calcium than the sewage sludge.
• the temperature may be selected based, at least in part, on the proportion of sewage sludge to the silicoaluminous material ("SAM"), and the desired density and other properties of the aggregate, such as water absorption and/or strength, based on data such as that graphically represented in Figs. 1 and 2.
• SAM silicoaluminous material
• a temperature that will cause sintering is preferred.
• the mixture is preferably agglomerated prior to sintering, to create agglomerates having a desired size and shape to form the sintered aggregate.
• Pelletization is a preferred agglomeration method.
• the sewage sludge may be dried prior to mixing with the second material. Alternatively, the sewage sludge may be added in wet form having the desirable moisture content to allow agglomeration.
• Fig. 3 is an example of an agglomerate 10 comprising LCSAM particles 12, such as clay, shale, slate, granite sawing residue, waste glass, and furnace bottom ash, or HCSAM particles 12, such as cement kiln dust, blast furnace slag, limestone, gypsum and dolomite, and sewage sludge particles 14. Pores 16 are also shown.
• the agglomerate 10 may be pyroprocessed, for example sintered, to form an aggregate in accordance with an embodiment of the present invention.
• fluxing compounds such as calcium, sodium, potassium, and magnesium oxide, and other compounds with melting points below the processing temperature in the original grain particles of sewage sludge 14 and high or low silicoaluminous materials (“SAM”) particles 12, melt and flow into the pores 16.
• SAM particles 12 are waste glass, which is a non-crystalline solid, densification occurs by fusing of softened glass particles by viscous sintering at temperatures that are generally much lower than the melting temperatures of other, crystalline SAM particles.
• Fig. 4 is a schematic cross-sectional view of an example of an aggregate 20 resulting from sintering the agglomerate 10, in accordance with an embodiment of the invention.
• the aggregate 20 comprises a mixture of sewage sludge and SAM.
• the agglomerate is sintered at a temperature that depends on the proportion of sewage sludge to SAM and the desired density and/or other characteristics.
• the sintered aggregate 20 comprises a plurality of grains 22 bonded to each other through a partly glassy and partly crystallized matrix 24, resulting from the melting and/or the crystallization of the components.
• the grains 22 may comprise silica, alumina, and other minerals with melting points above the processing temperature.
• the grains 22 fully or partially crystallize during sintering, providing an additional bond between the grains 22.
• the aggregate 20 preferably has a dense, continuous, relatively impermeable surface layer 26, resulting from coating of the agglomerates 10 with an inorganic material, as discussed further below.
• Internal pores 28, which may be channel-like, and small surface pores 28a, which may be microscopic, are also present. The surface pores may connect with the internal pores, enabling the aggregate 20 to absorb water. The degree of water absorption is indicative of the volume and connectivity of the pores.
• Fig. 5 is a schematic cross-sectional view of an example of a vitrified aggregate 30, in accordance with another embodiment of the invention.
• the vitrified aggregate 30 comprises fewer grains 22 and a larger matrix 24 than the sintered aggregate of Fig. 4.
• Vitrification results from pyroprocessing of the agglomerate 10 at or above the temperature of maximum densification for the particular proportions of sewage sludge to SAM, where most of the components of the agglomerate melt.
• Fig. 6 is an example of a method 100 of manufacturing aggregates in accordance with an embodiment of the invention.
• the sewage sludge is first dried, in Step 105.
• Sludge may be dried in an oven at 110°C for 24 hours, for example. If the water content of the raw sludge is very high, the excess water is removed by filtering, gravity settling, flocculation, or precipitation, for example, before being dried in the oven. Lumps of dried sewage sludge are typically formed. The size of the lumps may then need to be reduced.
• a fine powder suitable for subsequent processing is preferably produced by dry milling or grinding, or by using a pestle and mortar, for example, in Step 110.
• the dry solid cake may be ground to a powder by a hammer mill, for example.
• the ground sewage sludge powder is separated to remove large particles through a sieve, for example, in Step 115.
• Coarse particles, such as stones, rocks, or metals present in the sewage sludge are preferably removed for further processing, as well. Separation may take place by mechanically shaking the sewage sludge powder onto ASTM standard stainless steel mesh screens having openings of 150 microns or 80 microns, for example.
• the sewage sludge having particle sizes less than 150 microns is further processed.
• Powders with fine particle size distributions have advantageous characteristics because the high surface area to volume ratio increases diffusion of small particles through the liquid phase to the larger particles, and because the powders are better distributed throughout the aggregate, with good packing densities.
• Sewage sludge may also be used in its raw wet form, as long as the material has suitable moisture content to be directly mixed with the SAM, allowing further processing according to Steps 125-150 of Fig. 6, for example. Excess water content may again be removed by drying, filtering, and/or other processes, to reach a suitable moisture content before mixing with the additives. In this case, Steps 105- 120 are not provided.
• the ground sewage sludge powder from Step 120 is then mixed with the appropriate SAM in the form of powder having a fine particle distribution, in Step 125.
• Mixing may be batch or continuous. If the SAM has a coarse particle size distribution, it may be pre-ground in a hammermill or a ball mill, for example, using dry or wet milling techniques, before being added to the mixer with the sludge powder. Any amount of high or low calcium SAM may be added to the low or high calcium sewage sludge, respectively, for improved pyroprocessing performance.
• sewage sludge to SAM depend on whether the sewage sludge is high or low calcium sewage sludge, hi accordance with an embodiment of the invention, clay, such as bentonite and kaolin, and/or shale are wet milled in Step 125.
• clay such as bentonite and kaolin, and/or shale are wet milled in Step 125.
• BDWM high calcium sewage sludge by dry weight of the mixture
• LCSAM low calcium sewage sludge
• the resulting aggregate has a calcuum content by dry weight, of from about 6% to about 15%. More preferably, from about 30% to about 50% high calcium sewage sludge BDWM is mixed with from about 70% to about 50% of the LCSAM, BDWM. In this range, the resulting aggregate has a calcium content by dry weight, of from about 6% to about 10%. It has been found that the densification behavior of the mixture may be better controlled, enabling the production of aggregates with desired characteristics, when the calcium content of the aggregate is from about 2% to about 10%, and even better control may be obtained when the calcium content is from about 3% to about 6%.
• BDWM is mixed with from about 1% to about 30% HCSAM, BDWM. More preferably, from about 80% to about 90% low calcium sewage sludge BDWM is mixed with from about 20% to about 10% HCSAM, BDWM. These ranges provide aggregate calcium content similar to that discussed above.
• a plastic binder such as clay
• the term "plastic binder” refers to a binder material having a high plasticity index. A plasticity index of at least 10 is preferred.
• the clay binder may comprise from about 5% to about 20% by dry weight of the mixture of IBA, the SAM, and the clay binder. The amount of binder used may depend on the type and characteristics of the sewage sludge and the SAM, such as the plasticity of individual components in the mix.
• the mixture preferably has a clay-like mixture, for example.
• the amount of water to be added is related to the amount and type of additive in the mixture. For example, if the proportion of sewage sludge to clay is about 80% sewage sludge ("SS") to 20% clay, the amount of water required has been found to be about 25% by weight of the total dry weight of the SS/clay mixture. If the proportion is 60%/40%, then the amount of water required has been found to be about 28% by weight. If the proportion is 20%/80%, then the amount of water required has been found to be about 32%.
• SS sewage sludge
• the resulting mixture is agglomerated, in Step 135.
• Agglomeration is a particle size enlargement technique in which small, fine particles, such as dusts or powders, are gathered into larger masses, such as pellets.
• the mixture is agglomerated by pelletization, wherein fine particles dispersed in either gas or liquid are enlarged by tumbling, without other external compacting forces.
• a pelletizing rotating drum or disc may be used, for example.
• the strength of the resulting pellets depends on the properties of the particles, the amount of moisture in the medium, and mechanical process parameters, such as the speed of rotation and angle of tilt of the rotating drum, as is known in the art.
• An example of the use of a rotating drum is described in the examples, below.
• the resulting pellets are nearly spherical or slightly angular, and vary in color from light to dark brown, depending on the carbon and iron content in the mixes. They may range in size from about 3 mm to about 40 mm, for example.
• Fig. 3 is an example of a pellet 10.
• Extrusion may be used instead of pelletization. Extrusion results in a brick-like material that can be crushed into smaller particles after hardening.
• compaction may be used to produce cylindrical agglomerates, such as tablets or other shapes.
• the agglomerated mixture is optionally surface coated and then dried, in Step 140.
• the amount of inorganic material used may be small.
• the pellets may be coated with an inorganic material that will not melt at the sintering temperature.
• the pellets may be coated by sprinkling the dust on them or by rolling the pellets in the dust. The use of a coating material depends on the characteristics of the sewage sludge and the selected additive.
• the inorganic material may comprise a LCSAM from Group A, such as granite sawing residues or furnace bottom ash in the form of dust, clay, ground shale, and slate, could also be used, for example.
• the inorganic material may comprise an HCSAM from Group B, such as cement kiln dust, incinerator fly ash, incinerator filter dust, limestone, gypsum, and ground granulated blast furnace slag, for example.
• Covering the pellet surface with a thin layer of non-sticking material results in formation of a skin on the pellet surface that decreases clustering of the pellets, enhances the pellet strength, and creates a thin dense outer skin on the aggregate, as shown in Fig. 4, for example.
• a clay binder is added to the mixture, coating of the pellet surface is not needed to enhance pellet integrity or to form a coating, since the clay provides improved internal bonding. Coating is an option, however. Drying may take place at about HO 0 C in an oven, for example. Drying is preferably provided because pyroprocessing wet pellets in a kiln may result in cracking and exploding of the pellets due to rapid temperature changes.
• the coated and dried pellets are pyroprocessed, in Step 145.
• the pyroprocessing takes place at a temperature of from about 1000 0 C to about 135O 0 C, for example, depending on the composition of the mixture and the desired properties of the aggregate, as discussed in more detail, below.
• the pyroprocessing may be sintering, which takes place at temperatures below the temperature of maximum densification, or vitrification, which takes place at the temperature of the maximum densification and above.
• the pyroprocessing preferably takes place in a rotary kim. Sintering results in increased strength and density of formerly loosely bound particles, through the formation of interparticle bonds. Vitrification results in increased strength at the temperature of maximum densification. As vitrification progresses at higher temperatures, however, density and strength decrease due to bloating of the glassy amorphous matrix, as discussed above.
• the pyroprocessed aggregate may be quenched in water, in Step 150.
• the water may be at room temperature (about 30°C), for example.
• the pellets may be crushed and graded to the desired aggregate size, in Step 155.
• the coarse aggregates range from about 4.75 to about 19 mm. Smaller aggregates may also be used as fine aggregates in concrete, for example.
• the pyroprocessed aggregates may range in size from about 2 mm to about 30 mm, for example.
• Appropriate size ranges for the graded aggregates may be about 4 mm to about 8 mm, which may be used in filtration applications, and about 12 mm to about 19 mm, which may be used in concrete.
• Smaller aggregates may also be used as fine aggregates in concrete, for example.
• Fig. 7 is an example of plurality of sintered aggregates made in accordance with embodiments of the invention, from mixes containing 80%/20% of
• Fig. 8 is an example of a method 200 of manufacturing aggregates in accordance with an embodiment of the invention, in which specific SAMs having coarse particle distributions, are wet milled before mixing with the sewage sludge.
• Additives used in the present invention that have such distributions include EBA,
• IBA is added to a barrel of a ball mill in Step 205 and is milled with water, in Step 210.
• Milling is used to reduce the particle size distribution of the IBA to a distribution that is fine, to improve pyroprocessing.
• Powders with fine particle size distributions have advantageous characteristics because the high surface area to volume ratio increases diffusion of small particles through the liquid phase to the larger particles and because the powders are better distributed throughout the aggregate, with good packing densities.
• the resulting particles preferably have a mean particle size of about 45 microns and less, for example.
• Wet milling is preferred because it has been found to provide more uniform particle size distribution.
• the liquids used in the wet milling process tend to break up agglomerates and reduce welding of powder particles.
• the IBA may be dry milled in a hammer mill, for example. While the method 200 of Fig. 8 will be described with respect to the use of IBA, it is understood that if FBA or waste glass are used, they are preferably milled, as well.
• the IBA may be wet milled in a closed cylindrical container, for example, wherein grinding spherical media such as wet mill balls, in a liquid medium, such as water or alcohol, apply sufficient force to break particles suspended in the medium. Motion may be imparted to wet ball mills by tumbling, vibration, planetary rotation, and/or agitation.
• the most important variables controlling the powder particle size distribution is the speed of milling (rpm), the milling time, the amount of grinding media, the initial particle size of the raw material, and the desired product size. For most efficient results, the mill should be at least half filled with grinding media.
• the milling media may be high density, aluminum spheres, for example, with a total weight of about four times that of the solids.
• the wet milled IBA is separated to remove large particles through a sieve, for example, in Step 215. If the particles are too big, they will not form homogenous pellets. Separation may take place in multiple steps. For example, the IBA may be mechanically shaken over ASTM standard stainless steel mesh screens having openings of 355 microns or 150 microns, for example. The IBA having particle sizes less than 150 microns is further processed. The greater than 150 micron fraction may be separated into different types of materials that may be reused as a SAM additive, as waste glass.
• the resulting milled slurry of the finer fraction from Step 220 is dewatered in Step 225.
• the water removed is referred to as effluent, which may be used in Step 265, as discussed further below.
• Water may be removed in a filter press or other filtration apparatus, for example. Dewatering results in formation of a solid moist cake residue, in Step 230.
• the cake is dried and ground in Step 235. This step converts the cake into a powder.
• the cake may be dried in an oven at 110°C, for example.
• the powder may be ground by a mortar and pestle, for example.
• the dry solid cake may be ground to a powder in a mixer with blades or a dry hammer mill, for example, so that the dry milled IBA solid cake may be simultaneously ground to powder and consistently mixed with the raw additives which are also in the form of a powder.
• Step 240 Before mixing the milled IBA, with the sewage sludge, the sludge is dried, in Step 240. Sludge may be dried in an oven at 110°C for 24 hours, for example. The solid cake produced is ground into a powder, in Step 245. The powder may be produced by dry milling or grinding, or by using a pestle and mortar, for example. The sludge powder is passed through 150 micron or 80 micron sieves to remove coarse particles, in Step 250. The less than 150 micron fraction of Step 255 is thoroughly mixed with the milled IBA powder in, Step 260. Water is added to the mixture before the wet clay-like mixture is pelletized, in Step 265.
• the water may be some or all of the effluent produced from the dewatering Step 225, discussed above.
• Steps 265-285 correspond to Steps 130-155 in Fig. 6.
• sewage sludge may be mixed in its wet form with the IBA.
• the appropriate moisture content is required to avoid further addition of water for granulation of the mixture, hi this case, Steps 240-255 are not preferred.
• IBA are wet milled together in a ball mill, to produce a slurry. Then the milled slurry is sieved through a series of sieves and dewatered in a filtration apparatus to form a clay-like solid cake. The solid cake is then dried at 110°C and ground to a fine powder, which is further pelletized in the presence of water and pyroprocessed to form aggregates.
• the milled slurry formed from wet milling both materials may also be dewatered to the required moisture content to allow direct pelletization of the mixture. Formed pellets are dried at about 110°C before entering the pyroprocessing stage in the kiln.
• the WG was made from soda-lime glass, which accounts for about 90% of the glass produced in the United States. It consists mainly of silicon dioxide (71.7% by weight), sodium oxide (12.1% by weight), and calcium oxide (9.4% by weight) with other minor components, such as aluminum and magnesium oxides.
• the composition of the glass causes the material to densify by liquid phase sintering at lower temperatures than other glasses currently used to produce ceramics, therefore reducing energy production costs.
• WG can be used as both a LCSAM to increase the densification temperature range and also as a HCSAM that will act as a fluxing agent to accelerate densification.
• WG may be used with sewage sludge samples X, Y, and Z to produce synthetic aggregates.
• WG was added to dried SS powder before pelletization.
• Sample X was oven dried at 110°C for 24 hours.
• the resulting dry cake was added to a ball mill for grinding to powder.
• the mill was a Pascal Engineering Co., Ltd., Model No. 21589, containing about 2.172 kg of 3/4 inch (19.05 mm), high density, alumina sphere grinding media.
• the ground powder was sieved through a 150 microns sieve to remove coarse particles.
• the WG used was derived in part from bottles and window glass separated from raw IBA. This WG was washed and oven-dried overnight at 110°C.
• the WG was then crushed in a jaw crusher and separated to reduce the particle sizes to between 2 mm to 6 mm and then ground in a tungsten carbide Tema mill, available from Gy-Ro, Glen Creston Ltd., Brownfields, England by the use of vibrating rings, so that ninety five percent of the volume (dg 5 ) had a particle size less 710 microns. It was again dry milled in a carbide mill for an additional 4 minutes to further reduce the particle size distribution. This fine WG fraction was used in this Example. The d 50 value of the particle size of the crushed WG was 197.6 microns, which was reduced to 19.8 microns after 4 minutes of dry milling.
• the ground WG was added to the sludge powder in selected proportions of 100%/0%, 40%/60%, 60%/40% and 0%/100% (SS/WG).
• the ground powder mixes of SS and WG were mixed with water (up to about 40% by total dry weight of the resulting mixture) in a batch mixer and then fed to a rotary drum pelletizer having a 40 cm diameter and a 1 meter length rotating at about 17 rpm at an angle of 30° to the horizontal.
• the resulting "green" pellets were generally spherical or slightly angular. They had an average of from about 4 mm to about 9.5 mm in diameter. The pellets less than 4 mm were returned to the drum for pelletizing again. The pellets greater than 9.5 mm were broken down into smaller pellets by hand and also returned to the pelletizer.
• the pellets were then dried at about HO 0 C and fed to a rotary kiln having a 77 mm internal diameter by 1,500 mm length, in which the heated zone was 900 mm long.
• the kiln was set to run at temperatures between 92O 0 C and 1,220 0 C for the different SSAVG mixes.
• the pellets traveled and rotated along a tube
• the rotary kiln was an electric fired rotary furnace available from Carbolite Hope Valley, England, Model No. GTF Rl 95.
• the pyroprocessed pellets were discharged from the kiln and were allowed to cool at room temperature.
• the temperature versus density curves may vary in each kiln.
• the curves corresponding to particular proportions of SS and WG or other SAMs may have a temperature of maximum densification slightly lower or higher than those using the specific kiln identified above.
• the curve shifting may be attributed to a number of factors related to the operational efficiency of the particular kiln, such as the stability of the temperature profile, energy losses, etc. It may therefore be necessary to prepare several samples in a particular kiln being used to identify the temperature range over which aggregates will have desired characteristics.
• Tables C-D summarize the physical and mechanical properties of aggregates formed in this Example. It is noted that the aggregates showed substantial changes in their properties with increasing concentrations of WG in the SS.
• Table C summarizes test results for aggregates comprising different proportions of SS and WG, pyroprocessed in different temperatures (10 centigrade degree increments).
• the data is an average of 4 values for the 100% sewage sludge and an average of 2 values for all WG containing samples.
• the data is plotted on the graph of Fig. 9.
• the relative dry density of pyroprocessed aggregates was calculated using Archimedes' method and the water absorption was determined from the increase in weight of "surface dry" samples after being submerged for 24 hours.
• temperature may be used to determine the density and other characteristics of the sintered product, for a given combination of SS and WG.
• sintering at 1000 0 C will yield a LWA with a density of about 1.4 g/cm 3
• sintering the same mixture at 1060°C will yield a normal weight aggregate with a density of about 2.6 g/cm 3 .
• Table C also shows the effect of WG addition on the water absorption of the different aggregates.
• LWAs which are produced at lower temperatures than the temperature of maximum densification, typically have some porosity. As maximum densification is approached, the size and number of the pores gradually decrease to zero, as the pores are filled with melted material. Aggregates containing high amounts of SS exhibit a rapid reduction in water absorption capacities with temperature, while high WG aggregates show a more gradual water absorption reduction with temperature. The 100% WG aggregates have substantially less water absorption than all other mixes at all temperatures examined, due to the melted glass filling the pores produced by volatization.
• Table D summarizes Aggregate Crushing Values ("ACVs"), as a percentage, for selected mixes of SS and WG, at specific pyroprocessing temperatures.
• the ACVs are provided at three different temperatures for the different proportions of WG to SS.
• ACV is inversely proportional to aggregate strength. The selected temperatures were those causing different product characteristics and different microstructures, for comparison.
• a sintered LWA was produced in accordance with a preferred embodiment of the invention.
• a well-sintered or vitrified, normal weight aggregate with small amounts of residual pores was produced, in accordance with an embodiment of the invention.
• a vitrified LWA was produced, also in accordance with an embodiment of the invention.
• ACVs were lower and the strengths of the aggregates were higher at the temperature of maximum densification (middle temperature). Below that temperature, the densities were lower, the ACVs were higher, and the strengths of individual or bulk aggregates were lower. Above that temperature (middle), the ACVs started to increase as the density and aggregate strength decreased, due to increasing sample melting.
• the aggregate strengths show the same trend of aggregate densities with increasing temperature, increasing to a maximum value and then decreasing, as expected.
• the LWAs comprising 40% SS and 60% WG at the temperatures shown in Table D in accordance with embodiments of the invention, also have lower ACVs and higher strengths than the commercially available lightweight aggregate LYTAG, which has an ACV of about 34%, as noted below.
• Table E summarizes certain physical properties (relative dry densities and water absorptions from Table C, and bulk densities) and mechanical properties (ACV from Table D) of aggregates from 40% SS/60% WG mix at three selected temperatures.
• the corresponding properties of the commercial aggregates LYTAG (sintered PFA) and OPTIROC (expanded clay) are also given in Table E.
• the individual aggregate properties are average values of 20 measurements and the bulk aggregate properties are averages of 2 measurements.
• OPTIROC has very low density, relatively low water absorption, and very low strength. This is to be expected since OPTIROC has a honeycombed microstructure having a high volume of isolated spherical porosity.
• the mix was fed to a revolving drum and the pellets collected at the end of the drum were sieved through 4 and 9.5 mm sieves.
• the pellets were coated with PFA (by sprinkling), and were then dried in an oven at about HO 0 C, overnight.
• the resulting green pellets were then sintered in a rotary kiln for about 10 to about 12 minutes.
• the pellets formed from SS Sample X and GSR dusts were fired at temperatures between 92O 0 C to 1150°C, while the pellets formed from SS Sample Y and GSR were fired at temperatures between 990 0 C to 1190 0 C.
• IACS Individual Aggregate Crushing Strength
• d sphere diameter (mm)
• P fracture load (N).
• Table G summarizes test results for aggregates comprising different proportions of SS and GSR at different temperatures, for the two Samples X and Y. The data is plotted on the graph of Fig. 1 and Fig. 10 for Samples X and Y respectively. Table G also summarizes IACS results for specific mixes of SS and GSR, at specific sintering temperatures. As discussed above, increasing the LCSAM concentration in the mixes (GSR in this example) resulted in a broader temperature interval between the initial softening, maximum densification, and complete or near complete melting of the samples, due to the modification of the chemical composition and mineralogy of the sewage sludge with the GSR dust.
• i nn/C/nc ⁇ ro r ⁇ r*n show a more gradual water absorption reduction with temperature.
• the IACS show similar trends to densities, as expected, increasing to the temperature of maximum densification and decreasing at greater temperatures.
• the increase in aggregate strength with increasing temperature is rapid for aggregates from 100% SS mixes and becomes more gradual with increasing amounts of GSR.
• a preferred SS/GSR mix to produce sintered products that can be used in a range of applications including LWA in concrete, is the 40%/60% SS/GSR mix for both Samples X and Y. Aggregates produced from mixes of SS containing GSR sinter over a wider temperature range than SS alone, so the behavior during sintering and the final properties of aggregates may, therefore, be more easily controlled.
• Table H summarizes the physical (relative dry and bulk densities, water absorptions) and mechanical properties (ACV) of sintered aggregates from 40%/60% mixes of Sample Y SS/GSR at four different temperatures, along with the corresponding properties of LYTAG aggregates. Aggregates produced at the temperatures below the temperature of maximum densification had densities less than 2.0 g/cm 3 , relatively low water absorptions, and high strengths. They were therefore well suited for use in lightweight concrete. LYTAG had a lower relative density and aggregate strength than these aggregates.
• the average chemical analyses of Sample Y SS, and slate, which were used in these experiments, are shown in Table I, below. Sewage sludge Sample Y was used in these experiments. The same equipment used in Example 1 is used here.
• Sewage sludge was dried at 110°C for 24 hours before the solid cake being ground to fine powder. Slate was added to the sewage sludge powder in selected proportions of 100%/0%, 80%/20%, 60%/40% and 40%/60% (SS/slate).
• the resulting pellets were fired at temperatures between 990 to 116O 0 C for about 10 to 12 minutes before being discharged from the kiln and allowed to cool at room temperature.
• Tables J to K summarize the physical and mechanical properties of pyroprocessed aggregates from selected SS/slate mixes and pyroprocessing temperatures.
• Table J summarizes physical properties results (relative dry densities, water absorptions) and mechanical properties (IACS and ASMI). The data is plotted on the graph of Fig. 11. As discussed above, increasing the clay concentration in the mixes resulted in a broader temperature interval between the initial softening, maximum densification, and melting of the samples, due to the modification of the chemical composition and mineralogy of the SS with clay. TABLE J: PHYSICAL PROPERTIES OF SS/SHALE AGGREGATES
• Table K summarizes certain physical and mechanical properties of aggregates from 40%/60% mix of SS/slate at three selected temperatures, along with the corresponding properties of LYTAG aggregates.
• Aggregates may be produced with predetermined density and other characteristics, for a given combination of SS and slate, by controlling the temperature, as shown by Table K and Fig. 11. Lightweight aggregates having comparable or superior properties to LYTAG may be produced from this combination, according to the required aggregate properties.
• Table L summarizes the behaviour of the pyroprocessed aggregates resulting from the mixes of SS and slate.
• Sample Z SS and CKD were subjected to processing as described above and shown in Figure 6.
• the SS was dried at HO 0 C for 24 hours and then ground to fine powder.
• CKD having a fine particle size distribution (95% (dg 5 ) of the volume of the particles finer than 45 microns) was added to the dried SS powder before the mix was pelletized and pyroprocessed.
• the powders were mixed with water (up to 35% by total dry weight of the resulting mixture) in a batch mixer until the consistency of the mix allowed pelletization.
• the mix was fed to a revolving drum and the pellets were collected at the end of the drum were sieved through 4 and 9.5 mm sieves.
• the pellets were coated with CKD and then dried in an oven at about 110 0 C, overnight.
• the resulting green pellets were then pyroprocessed in a rotary kiln for about 10 to about 12 minutes at temperatures between 94O 0 C to 1110 0 C.
• the Individual Aggregate Crushing Strengths (“IACS”) were determined as described in Example 2.
• the compressive strength of individual aggregates was also defined as an Aggregate Strength Mass Index (“ASMI”) as follows:
• Tables N to O summarize the physical and mechanical properties of the aggregates formed by the process described above. The relative dry density, water absorption and ASMI of the aggregates were determined, as described in the Examples above.
• Table N summarizes test results for aggregates comprising different proportions of SS and CKD sintered at different temperatures. The data is plotted on the graph of Fig. 2.
• Table O summarizes physical properties results (relative dry densities, and water absorptions from Table N) and mechanical properties (ASMI from Table N).
• Increasing the CKD concentration in the mixes resulted in a slightly narrower pyroprocessing temperature range due to modifying the composition of the initial mixture. Since CKD has such a high calcium content, only a small amount was required to increase the mobility of the melts and accelerate the densification of the pellets of the mixture.
• Aggregates having lower densities and higher water absorptions may be manufactured when the aggregates from the SS/CKD mix are fired at lower temperatures than those used in this Example.
• the presence of fluxes in the material is believed to provide a more improved particle packing and densification, producing aggregates with superior properties to pyroprocessed aggregates from material which do not contain fluxes.
• Table O summarizes certain physical and mechanical properties of aggregates from 90%/10% mix of SS/CKD at three selected temperatures.
• controlling the pyroprocessing temperature enabled production of an aggregate with a predetermined density and other characteristics, for a given combination of SS and CKD.
• SS Sample Z
• limestone powder were subjected to processing described above and shown in Figure 6.
• SS was dried at 110°C for 24 hours before the solid cake being ground to fine powder.
• Limestone was added to dried sludge powder before the mix being pelletized and pyroprocessed.
• the powders were mixed with water (up to 32% by total dry weight of the resulting mixture) in a batch mixer until the consistency of the mix allowed pelletization.
• the mix was fed to a revolving drum and the pellets collected at the end of the drum were sieved through 4 and 9.5 mm sieves.
• the pellets were coated with limestone, and were then dried in an oven at about HO 0 C, overnight.
• the resulting green pellets were then pyroprocessed in a rotary kiln for about 10 to about 12 minutes at temperatures between 94O 0 C to H lO 0 C.
• Tables Q to R summarize the physical and mechanical properties of aggregates formed by the process described above. The relative dry density, water absorption and ASMI of aggregates were determined as described in the previous examples.
• Table Q summarizes test results for sintered aggregates comprising different proportions of SS and limestone sintered at different temperatures. The data is plotted on the graph of Fig. 12. Table R summarizes physical properties results and mechanical properties of selected aggregates. Increasing the limestone concentration in the mixes resulted in a slightly narrower temperature range over which the aggregates are pyroprocessed.
• Table R summarizes certain physical and mechanical properties of aggregates from 90%/10% mix of SS/limestone at three selected temperatures.
• Example Z MSW incinerator fly ash
• IFA MSW incinerator fly ash
• SS (Sampel Z) and IFA were subjected to processing described above and shown in Figure 6.
• SS was dried at HO 0 C for 24 hours before the solid cake being ground to fine powder.
• IFA was added to dried SS powder before the mix being pelletized and pyroprocessed.
• the IFA was added to SS powder in selected proportions of 100%/0%,
• the powders were mixed with water (up to 37% by total dry weight of the resulting mixture) in a batch mixer until the consistency of the mix allowed pelletization.
• the mix was fed to a revolving drum and the pellets were collected at the end of the drum were sieved through 4 and 9.5 mm sieves.
• the pellets were coated with fly ash, and were then dried in an oven at about HO 0 C, overnight.
• the resulting pellets were then pyroprocessed in a rotary kiln for about 10 to about 12 minutes at temperatures between 98O 0 C to HlO 0 C.
• Tables T to U summarize the physical and mechanical properties of aggregates formed by the process described above. The data is plotted on the graph of Fig. 13. Increasing the IFA concentration in the mixes resulted in a slightly narrower temperature interval between the initial softening, maximum densification, and melting of the samples, due to the modification of the chemical composition and mineralogy of the SS.
• the powders were mixed with water (up to 35% by total dry weight of the resulting mixture) in a batch mixer until the consistency of the mix allowed pelletization.
• the mix was pelletized and the pellets were sieved through 4 and 9.5 mm sieves.
• the pellets were coated with GBS, and were then dried in an oven at about HO 0 C, overnight.
• the resulting pellets were pyroprocessed in a rotary kiln for about 10 to about 12 minutes at temperatures between 97O 0 C to H lO 0 C.
• Tables W to X summarize the physical and mechanical properties of aggregates formed by the process described above.
• Table W summarizes test results for aggregates comprising different proportions of SS and GBS fired at different temperatures. The data is plotted on the graph of Fig. 14. A 0272
• Table X summarizes certain physical properties of aggregates from
• the materials were mixed in the above proportions and pelletized with the addition of water using the equipment described in the Examples above.
• the pellets were then dried in an oven at about HO 0 C, overnight.
• the resulting pellets were then pyroprocessed in a trefoil rotary kiln shaped like a three leaf clover using fuel propane for about 15 to about 20 minutes at temperatures between about 1000 0 C to about 1250 0 C.
• the aggregates were air-cooled.
• aggregates comprising high amounts of GBS appeared whitish, while aggregates containing high amounts of PFA appeared to be dark brown.
• the aggregates had a hard smooth surface and were lightweight. They had a relatively hard structure when randomly crushed.

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