We've previously reported on a high-value product that can be directly separated from the bulk of Coal Fly Ash; and, then used in a number of productive ways without much, if anything, in the way of chemical treatment or processing.
"Cenospheres", as seen in:
Cenosphere - Wikipedia, the free encyclopedia; "A cenosphere is a light weight, inert, hollow sphere made largely of silica and alumina and filled with air or inert gas, typically produced as a byproduct of coal combustion at thermal power plants. The color of cenospheres varies from gray to almost white and their density is about 0.4–0.8 grams per cubic centimeter, which gives them a great buoyancy. Cenospheres are hard and rigid, light, waterproof, innoxious, and insulative. This makes them highly useful in a variety of products, notably fillers. Cenospheres are now used as fillers in cement to produce low density concrete. Recently, some manufacturers have begun filling metals and polymers with cenospheres to make lightweight composite materials with higher strength than other types of foam materials. Such composite materials are called syntactic foam. Aluminum-based syntactic foams are finding applications in the automitive sector. Silver-coated cenospheres are used in conductive coatings, tiles and fabrics. Another use is in conductive paints for antistatic coatings and electromagnetic shielding. The word Cenosphere is derived from two Greek words "kenos" (hollow, void) and sphaera (sphere), literally meaning hollow spheres. The process of burning coal in thermal power plants produces fly ash containing ceramic particles made largely of alumina and silica. They are produced at temperatures of 1,500 to 1,750 Celsius through complicated chemical and physical transformation. Their chemical composition and structure varies considerably depending on the composition of coal that generated them. ... Due to the hollow structure cenospheres have low density";
are a known commodity, a recognized byproduct arising from our essential use of Coal in the generation of truly abundant and truly affordable electric power. And, as seen for only two examples in:
CenoStar and Cenospheres - CenoStar; "CenoStar's cenospheres are integrated into flight-control surfaces on the F-22 Raptor ... that reflect incoming radar waves internally rather than back to the radar. Radar-absorbing coatings can be applied to the surface of the body that effectively drains the energy of the radar signal"; and:
Sphere Services Inc. and https://www.sphereservices.
there are a number of commercial collectors and suppliers of them; and, they have a number of intriguing uses, especially in the metal and polymer "syntactic foam"s noted by the Wikipedia; and, as suggested for one example in our report of:
West Virginia Coal Association | Coal Ash and Aluminum Alloy Composites | Research & Development; concerning, in part: "United States Patent 5,899,256 - Metal-Fly Ash Composites and Low Pressure Infiltration Methods; 1999; Inventor: Pradeep Rohatgi, WI; Assignee: Electric Power Research Institute, CA;
Abstract: Metal matrix composites are made by infiltrating packed loose fly ash with molten metal or metal alloy under low pressure. In some embodiments the infiltration is driven by pressurized gas. Coating the fly ash prior to infiltration can lower the threshold of pressure required for satisfactory infiltration by the molten metal. ... The densities of the composites are relatively low, particularly in composites made using cenosphere fly ash".
And, since the Wiki article notes that "Cenospheres are now used as fillers in cement to produce low density concrete", we remind you of our report:
West Virginia Coal Association | Georgia Tech Recycles Coal Utilization Byproducts | Research & Development; concerning: "United States Patent 8,057,594 - High Strength Pozzolan Foam Materials and Methods of Making Same; 2011; Assignee: Georgia Tech Research Corporation, Atlanta, GA; Abstract: The various embodiments of the present invention relate generally to high strength foam materials and methods of making the same. More particularly, various embodiments of the present invention relate to high strength foam materials comprising pozzolans, such as cenospheres derived from fly ash. An embodiment of the present invention comprises, a pozzolan foam material comprising a pozzolan, an alkali, a silicate, and an organosilicon compound. Various embodiments of the present invention are directed to strong, lightweight materials that are environmentally-friendly and can be economically manufactured".Further, a number of technologies have been developed for the separation of valuable cenospheres from the bulk of Coal Ash, among them that disclosed in our report of:
West Virginia Coal Association | Wisconsin Recovers "Cenospheres" from Coal Fly Ash | Research & Development; concerning: "United States Patent 8,074,804 - Separation of Cenospheres from Fly Ash; 2011; Inventors: Bruce Ramme, et. al., WI; Assignee: Wisconsin Electric Power Company, Milwaukee; Abstract: Methods for increasing the amount of cenospheres in a fly ash sample are disclosed. The cenospheres are obtained in a dry state by using air as the "fluid" media for separation. In one version, the invention is a two step process, that is, screen by size followed by density separation such as in a fluidizing vertical column by density. In another version of the invention, the separation by density is followed by screening by size. Additional cycles can improve purity as defined by concentration of cenospheres. The method ... wherein: the fly ash is a byproduct of burning subbituminous or bituminous coal and fly ash recovered from a previous burning of coal".
Note, in the above, the statement that Cenosphere's can be extracted as well from "fly ash recovered from a previous burning of coal"; and, the implication, as we have previously suggested, that accumulations of Fly Ash already in some way disposed of could be "re-mined", as it were, for the recovery of valuable components.
The above "Wisconsin Electric Power Company", aka "We Energies", we note, as seen for two additional examples in our reports of:
West Virginia Coal Association | Wisconsin Coal Ash Utilization Guidebook Available | Research & Development; concerning: "Coal Combustion Products Utilization Handbook (2nd Edition); By Bruce Ramme & Mathew Tharaniyil (We Energies); 2004"; with chapters such as: "4.1. Concrete and Concrete Masonry Products Containing Fly Ash" and "7. Fly Ash Stabilized Cold In-Place Recycled Asphalt Pavements"; and:
West Virginia Coal Association | Coal Ash and Sewer Sludge to Lightweight Concrete Aggregate | Research & Development; concerning: "United States Patent 5,342,442 - Lightweight Aggregate from Flyash and Sewage Sludge; 1994; Inventors: Timothy Nechvatal and Glenn Heian, WI; Assignee: Wisconsin Electric Power Company, Milwaukee; Abstract: A method is shown for producing a lightweight aggregate by treating flyash and sewage sludge. The flyash and sewage sludge are mixed together and then agglomerated into pellets, with or without the use of a binder. The pellets may be coated and then are dried. The dried pellets are introduced into a rotary kiln in a direction that is co-current with the flow of fuel and air through the kiln. The pellets in the kiln will be indurated and will experience complete calcination as well as varying degrees of pyrolizing and sintering. The product of the kiln is a nodular material having a low density but with a hard and porous structure. The product of the kiln is feed to a cooler. The flyash sewage sludge mixture has a significant fuel value that is usable in the kiln. Furthermore, the fuel value available in the kiln off-gases may be used for drying the materials";
have established their commendable interest in, and defined a number of processes for, the productive consumption and use of "Coal Combustion Products", even in ways that also consume otherwise "waste" materials.
And, herein, we learn that they, in the persons especially of their employee, Bruce Ramme, lead named inventor of the above-cited "US Patent 8,074,804 - Separation of Cenospheres from Fly Ash"; and Pradeep Rohatgi, lead named inventor of the above-cited "US Patent 5,899,256 - Metal-Fly Ash Composites and Low Pressure Infiltration Methods", have just recently improved their methods, not just for extracting the uniquely valuable Cenospheres from Coal Ash; but, for first determining if a given Fly Ash sample contains enough Cenospheres to make recovery worthwhile; for determining the best method for that recovery; and, for sorting the recovered Cenospheres by size and density.
There are some analytical technicalities included, and the Disclosure can seem tedious because of them; but, it's interesting to note how sophisticated our understanding of Coal Combustion Byproducts, and their commercial utility, has become.
As seen in excerpts from the initial link in this dispatch to:
"United States Patent 8,520,210 - Separation of Cenospheres from Fly Ash
Patent US8520210 - Separation of cenospheres from fly ash - Google Patents
Separation of cenospheres from fly ash - Wisconsin Electric Power Company
Date: August 27, 2013
Inventors: Bruce Ramme, John Noegel, and Pradeep Rohatgi, WI
Assignee: Wisconsin Electric Power Company, Milwaukee
Abstract: Methods for increasing the amount of cenospheres in a fly ash sample are disclosed. The cenospheres are obtained in a dry state by using air as the "fluid" media for separation. In one version, the invention is a two step process, that is, screen by size followed by density separation such as in a fluidizing vertical column by density. In another version of the invention, the separation by density is followed by screening by size. Additional cycles can improve purity as defined by concentration of cenospheres.
Claims: A method for identifying particles of different density in a sample of particles using a light microscope, the method comprising: providing a sample of particles having particles of at least two different densities; spreading the sample of particles on a film of liquid; creating an image of the sample of particles with the light microscope; and identifying imaged particles floating on the film of liquid, the imaged particles floating on the film of liquid having a lower density than particles not floating on the film of liquid.
The method ... further comprising: identifying imaged particles floating on the film of liquid that have a central darkened area, the imaged particles having a central darkened area being hollow particles (and) counting all imaged particles having a central darkened area to provide a number of hollow particles in the sample; counting all particles in the sample to provide a number of all particles in the sample; and calculating a ratio of the number of hollow particles to the number of all particles in the sample.
The method ... wherein: the sample comprises fly ash particles (and) wherein: the step of identifying imaged particles floating on the film of liquid comprises focusing light on a top layer of the film of liquid (and) wherein: the step of imaging the sample of particles with a light microscope comprises observing the sample of particles through transmitted light (and) wherein: the imaged particles floating on the film of liquid have densities above 1.0 gram per cubic centimeter.
The method ... wherein: the particles are fly ash particles, and the imaged particles floating on the film of liquid are cenospheres.
The method ... further comprising: determining diameters of the fly ash particles and the cenospheres, and calculating a volume percentage of cenospheres in the fly ash particles.
Background and Field: This invention relates to a method for increasing the amount of cenospheres in a fly ash sample.
Coal fired boilers are widely used to generate steam for producing electricity. A common form of boiler uses a pulverized coal that is injected into a furnace. The process of burning coal in a boiler produces fly ash.
Some of the recovered fly ash is commercially usable in concrete, concrete products, cement production, sewage sludge stabilization, pavement base materials, lightweight aggregate, reinforced plastics, and other miscellaneous purposes.
(Rather than cite any of our past reports documenting the above potentials, we refer you to We Energy's "Coal Combustion Products Utilization Handbook", noted in our introductory comments.)
The remaining fly ash must generally be disposed of by landfilling since it has no commercial value. It is well known that landfill space is rapidly dwindling in many regions and that the construction of new landfills is very costly. Therefore, much effort has been directed at finding uses for fly ash so that the fly ash does not need to be landfilled.
The composition of fly ash can vary depending on the composition of coal that generated the fly ash. Therefore, material specifications have been developed for fly ash that is to be used in specific applications. For example, fly ash that is used as a filler in concrete should meet the specifications described in American Society for Testing and Materials, "Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete", Designation: C 618.
(We've previously reported on the American Society for Testing and Materials Specification C 618 for Coal Ash for use in concrete. The full document must be purchased; but, for a description of it, see:
ASTM C618 - 12a Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete; "This specification covers coal fly ash and raw or calcined natural pozzolan for use in concrete where cementitious or pozzolanic action, or both, is desired, or where other properties normally attributed to fly ash or pozzolans may be desired, or where both objectives are to be achieved. Fly ash and natural pozzolans shall conform to the prescribed chemical composition requirements and physical requirements. The materials shall be tested for fineness, strength activity index, water requirement, soundness, and autoclave expansion or contraction."
We've also previously reported on the "pozzolanic" properties, as frequently referred to herein, of some Coal Ash. For a fuller exposition of what a "pozzolan" is, and why "pozzolanic" properties can be of importance, see:
Pozzolan - Wikipedia, the free encyclopedia; "A pozzolan is a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties (ASTM C618).")
(ASTM specification 618) indicates that fly ash particles are made largely of silicon dioxide, aluminum oxide and iron oxide. The particles in fly ash have different types of structures. Some particles in fly ash are solid. Other particles in fly ash are hollow and are called cenospheres. A cenosphere is a lightweight, inert, hollow sphere filled with inert air or gas. Cenospheres are hard and rigid, light, waterproof and insulative. Due to the hollow structure, cenospheres have lower density (e.g., some cenospheres have a density below 1 gram per cubic centimeter) as compared to solid fly ash particles. Cenospheres have traditionally been reported to represent about 1-3% by weight of the total fly ash produced.
In the composite materials field, there is increasing interest in ultra light energy-absorbing materials and structures which incorporate hollow particles. Accordingly, cenospheres have been added to polymers and there is growing interest in incorporating them in metals. Fine and sized cenospheres can be sold at attractive prices to this segment of industry providing syntactic foams and cellular solids. In addition, there is a growing market for fine solid microspheres to produce reinforced polymers, metals and ceramics.
Methods are known for recovering cenospheres from fly ash (but, typically) these methods only collect cenospheres (with densities low enough so that they) float on water. Also, the fly ash that is produced from burning subbituminous western coal includes significant amounts of calcium compounds. For example, this fly ash may include 10% or more lime. These high calcium fly ashes (such as ASTM C 618 Class C fly ash) have cementitious properties and therefore, when mixed with water these fly ashes rapidly harden and the remainder cannot then be used for other purposes such as a cementitious material in the production of concrete. In the case of Class F fly ash, a dry method also provides the advantage of not expending energy to dry the remainder after separation of cenospheres for other uses. Another disadvantage is that, many cenospheres are entrapped in agglomerated and/or hardened masses before flotation occurs. Furthermore, the known methods for recovering cenospheres from fly ash do not allow for recovery of cenospheres of controlled sizes and densities. As a result, the properties of polymeric composites including cenospheres have not been optimized due to lack of availability of cenospheres of controlled sizes and densities.
Thus, there is a need for a method for recovering cenospheres from fly ash that has cementitious properties. There is also a need for a method for recovering cenospheres of narrow size ranges and densities from fly ash.
Summary: The need for an improved method for recovering cenospheres from fly ash is met by a method according to the invention. In the method, the weight or volume percentage of cenospheres in a fly ash sample is increased preferably providing a material of greater than 90% cenospheres.
In one aspect, the method includes the step of separating an amount of fly ash having an initial weight or volume percentage of cenospheres into a first fraction having particle sizes greater than a first particle size and a second fraction having particle sizes less than or equal to a second particle size smaller than the first particle size. Preferably, in this step, the fly ash is separated into the first fraction and the second fraction by dry screening of the fly ash. This is advantageous as it avoids any agglomeration of fly ash having calcium compounds such as the cementitious fly ash that is a byproduct of burning subbituminous or lignite coal.
The first fraction (which has fly ash of larger particle sizes) and/or the second fraction (which has fly ash of smaller particle sizes) is then separated into a third fraction having particle densities greater than a predetermined particle density and a fourth fraction having particle densities less than the predetermined particle density. Because cenospheres have a lower density than solid (non-hollow) particles, the resulting fourth fraction has a percentage of cenospheres greater than the initial percentage in the fly ash. The first fraction or the second fraction may be separated by density using fluidization or air classification, preferably in the absence of water. A fluidized column of air is suitable for separation by fluidization. The first fraction would be separated when it is desired to obtain larger particle size cenospheres, and the second fraction would be separated when it is desired to obtain smaller particle size cenospheres. Optionally, the fourth fraction may be separated by screening into a fifth fraction having larger particle sizes and a sixth fraction having smaller particle sizes. Further separation by screening is also possible.
In another aspect, the method includes the steps of separating an amount of fly ash into a first fraction of fly ash having particle densities greater than a predetermined particle density and a second fraction of fly ash having particle densities less than or equal to the predetermined particle density; and separating the first fraction of fly ash or the second fraction of fly ash into a third fraction of fly ash having particle sizes less than or equal to a predetermined particle size and a fourth fraction of fly ash having particle sizes greater than the predetermined particle size such that the fourth fraction of fly ash has a percentage of cenospheres greater than the initial percentage in the fly ash sample.
Thus, it is an advantage of the present invention to provide a method for increasing the amount of cenospheres in a fly ash sample. It is another advantage to provide a method for increasing the amount of cenospheres in a fly ash sample having cementitious (e.g., calcium) compounds. It is yet another advantage to provide a method for increasing the amount of cenospheres in a fly ash sample wherein the method can be undertaken in the absence of water. It is still another advantage to provide a method for increasing the amount of cenospheres in a fly ash sample wherein the method classifies cenospheres into different particle size ranges.
This invention relates to a method in which the weight or volume percentage of cenospheres in a fly ash sample is increased preferably providing a material of nearly 100% cenospheres. The recovered cenospheres may be used to produce reinforced polymers, metals, ceramics, and other products."
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It is, in sum, an air, or density, separation method conducted in conjunction with sieving or screening for size; with the various steps undertaken in a sequence dependent upon an initial microscopic assay.
And, the point of it all is to extract, from the bulk of Coal Ash, microscopic glassy spheres; and, to sort those spheres by size, so that they can be better and more effectively marketed to, and utilized in, various end-use applications, such as "reinforced polymers, metals (and) ceramics".
That would, of course, leave the bulk of the Coal Ash still available for various other uses, such as, as seen variously in:
West Virginia Coal Association | China Extracts Aluminum Ore from Coal Ash | Research & Development; concerning: "China's Shenua to Produce Alumina from Coal Ash; 2011; China's Shenhua Group began construction Sunday of a coal ash-based alumina refinery in the Inner Mongolia autonomous region, the official Xinhua news agency said. Shenhua plans to invest Yuan 135.8 billion ($21.4 billion) in the project, deputy manager Ling Wen is quoted as having said. Located in the Jungar coal mining area in Ordos city, the project will include a 6.6 GW power plant, an alumina plant and a gallium plant"; and:
West Virginia Coal Association | Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Assignee: Dravo Lime Company, Pittsburgh; Abstract: Cement is produced by forming a moist mixture of a flue gas desulfurization process waste product (and) aluminum, iron, silica and carbon (and) wherein said source of aluminum and iron comprises fly ash"; and:
West Virginia Coal Association | Ohio State Says Coal Ash Extends Service Life of Concrete | Research & Development; concerning: "'Prevention of Corrosion in Concrete Using Fly Ash Concrete Mixes'; ISG Resources, Inc. (and) The Ohio State University; This paper reviews the benefits of using high-volume fly ash in resisting corrosion damage in concrete structures. ... Reduced permeability, lower water/cement ratio, decreased drying shrinkage/cracking, and increased durability are all benefits of fly ash concrete. Results (of studies show that) high volume fly ash mixes could improve the concrete strength and permeability while providing workability superior to that of (non-fly ash mixes, and, that) high-volume fly ash mixes would be the most durable concrete mixes for preventing corrosion in reinforced concrete structures";
an ore of strategically critical metals, such as Aluminum; an environmentally-superior source of raw materials for making Portland-type Cement; and, as a property-enhancing fine aggregate for Cement, to make a superior Concrete.