Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-07-19
2001-06-05
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C106S405000, C106S461000, C106S466000, C106S481000, C106S483000, C106S484000, C106SDIG001, C209S002000, C209S011000, C428S403000
Reexamination Certificate
active
06242098
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of making an industrial mineral filler and a pozzolan product from fly ash, and more particularly, to a method in which raw fly ash is dry processed into fine and coarse fractions which can be utilized as mineral filler and pozzolan products.
Fly ash is a by-product derived from the combustion of coal and comprises finely divided inorganic products. Enormous amounts of fly ash are produced annually nationwide, primarily from burning coal in electric power plants. Disposal of fly ash has posed an increasingly difficult problem because the volume, the particulate nature, and the varied chemical composition of fly ash limit the number of acceptable disposal sites.
Accordingly, efforts have been made to find alternative, economic uses for fly ash. For example, fly ash has been used as a pozzolan material in concrete applications. However, the direct use of fly ash as a pozzolan product has been limited as the high carbon content in the fly ash prevents entrainment of the concrete, causing non-uniform hardening. In order for larger amounts of fly ash to be suitable for use as a pozzolan product, the fly ash should have a low carbon content.
Another potential use for fly ash is as an industrial mineral filler. Mineral fillers are widely used in plastic products to improve performance and reduce costs. Mineral fillers commonly used for applications such as plastics, compounding, injection molding, paper products and the like include calcium carbonate, kaolin, aluminum hydrate, mica, talc and ground silica. The chemistry and characteristics of fly ash are close to those of such commercial fillers and would be a desirable substitute. However, the particle size of fly ash is much larger than that of typical commercial fillers. Wet processing such as wet milling, froth flotation, attrition grinding, and wet magnetic iron removal have been used in the past to reduce and control the particle size of fly ash. However, such methods are complicated, expensive, and require a multi-step process as the wet fly ash must be oven dried. In addition, methods such as froth flotation utilize reagents such as turpentine which must be safely disposed of.
Accordingly, there is still a need in the art for a method for producing useful products from fly ash such as mineral filler and pozzolan which method is economical and easy to implement.
SUMMARY OF THE INVENTION
The present invention meets that need by providing a method of processing fly ash into mineral filler and pozzolan products which utilizes fly ash having a low carbon content and which utilizes a dry method of processing, i.e., the method does not require or involve wetting, drying, or rewetting of the fly ash during processing. The resulting filler has an average particle size of from about 0.1 to 5 microns and may be used in a number of filler applications including plastics, paint, rubber, putty insecticides, textile coatings, putty, sealants, paper, calking, rubber, asphalt, and tiles. The enhanced pozzolan has an average particle size of less than about 10-20 microns and may be used in the manufacture and replacement of cement, as well as in soil stabilization.
In accordance with one aspect of the invention, a method for producing mineral filler from fly ash is provided comprising the steps of providing a quantity of raw fly ash having a carbon content of about 0.1 to 40% by weight, and passing the fly ash through an air classifier to obtain from about 0.1% to about 65% by weight of a fine fraction having an average particle size of from about 0.1 to about 5 microns. The method preferably includes the step of passing the fine fraction obtained through a magnetic separator to remove from about 0.1 to 99% by weight ferrous iron oxide from the fine fraction.
Preferably, the method further includes the step of treating or coating the filler with a surface modifier such as a surfactant, coupling agent, lubricant, or acid scavenger. The surface modifier is preferably selected from the group consisting of silanes, stearates, aluminate, titanate, and zirconate. A preferred silane is vinyl-amino methoxyl siloxane. A preferred stearate is calcium stearate. A preferred titanate is amino titanate. The surface modifier is preferably applied at a dry coating weight of between about 0.1 to 5% by weight.
The resulting filler may be used in a number of filler or extender applications as well as in composites. Specific uses for the fillers include thermoplastic compounding of polypropylene, low and high density polyethylene molds and extrusions, and in thermosetting bulk molding, compounding and reinforced injection molding of unsaturated polyesters and polystyrenes. The filler may also be used in the thermoforming compounding of rigid or flexible polyvinyl chloride.
A method for producing an improved pozzolan product from fly ash is also provided which comprises the steps of providing a quantity of raw fly ash having a carbon content of about 0.1 to 40% by weight, and passing the fly ash through an air classifier to obtain from about 35 to 95% by weight of a coarse fraction. The method preferably further includes the step of passing the coarse fraction through a 100 mesh screen. The resulting pozzolan product exhibits a compressive strength of at least 3000 psi for 28 days and provides provides uniform hydration when used in cement manufacture or replacement applications.
While the methods for forming a mineral filler and pozzolan product have been described herein as separate methods, it should be appreciated that both the mineral filler and pozzolan product may be produced from fly ash in a single process. Such a process comprises the steps of providing a quantity of fly ash having a carbon content of about 0.1 to 40% by weight; and passing the fly ash through an air classifier to obtain from about 35 to 95% by weight of a coarse fraction and from about 5 to 65% by weight of a fine fraction. The fine fraction obtained is then preferably passed through a magnetic separator to obtain the mineral filler, and the coarse fraction is preferably passed through a 100 mesh screen obtain the pozzolan product.
Accordingly, it is a feature of the present invention to provide a method for forming mineral filler and pozzolan products from fly ash. Other features and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.
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Jarvela et al., “Multicomponent compounding of polypropylene”, Article from publication © 1996 Chappman & Hall, pp. 3853-3860.
Wong & Truss, “Effect of Flyash Content and Coupling Agent on the Mechanical Properties of Flyash-Filled Polypropylene”,Composites Science&Technology,1994, pp. 361-368.
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Abstract: Khytsnar, Y., et al.; “Fly Ash: A Fi
Abiodun Kamal Seyi
Styron Robert William
Killworth, Gottman Hagan & Schaeff, L.L.P.
Le Hoa T.
Mineral Resources Technologies, LLC
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