United States Patent: 8795429

Herein we report more confirmation by our United States Government that the solid mineral residua, the Ash, left behind by our economically essential use of Coal in the generation of truly abundant and genuinely affordable electric power, can be seen and treated as a valuable mineral resource. 

For example, Coal Ash can be used and consumed as a component of various construction materials, in which applications the Ash serves to replace virgin mineral materials that would otherwise have to be quarried or mined.

As seen in our reports of:

Coal Fly Ash Makes Wallboard Stronger | Research & Development | News; concerning: "United States Patent 4,403,006 - Sag-resistant Gypsum Board Containing Fly Ash; 1983; Assignee: United States Gypsum Company, Chicago; Abstract: A gypsum board consisting essentially of a monolithic cellular core of set gypsum and a fiberous cover sheet encasement provided with improved properties by the gypsum core having incorporated therein coal fly ash in an amount of about 1-20% by weight of stucco in the gypsum slurry used in forming the board"; and:

Synthetic Gypsum from Coal Power Plant Flue Gas | Research & Development | News; concerning, in part: "'FGD Gypsum in Wallboard and Other Products; United States Gypsum Company'; 2007; Gypsum Key Commercial Properties: Safe and non-toxic mineral; Common by-product from sulfur processing (i.e.,) FGD Gypsum - Can be calcined at low temperatures (and) Provides fire resistance (and) Produces a low cost inorganic binder. FGD Gypsum in Wallboard: 63% of all FGD Gypsum produced is recovered into wallboard (and over) 27% of wallboard (is) produced from FGD Gypsum";

both Coal Fly Ash and synthetic Gypsum made from Coal Flue Gas De-sulfurization (FGD) precipitates can be used and consumed in the manufacture of gypsum wallboard, aka "drywall".

And, as seen in our reports of: 

EPA Okays Use of Coal Ash in Concrete and Wallboard | Research & Development | News; concerning the US EPA news release: "'EPA Evaluation Finds Use of Coal Ash in Concrete and Wallboard Appropriate'; 02/07/2014; Using a newly developed methodology, the U.S. Environmental Protection Agency (EPA) today released its evaluation of the two largest beneficial uses of encapsulated coal combustion residuals (CCR or coal ash): use in concrete as a substitute for portland cement, and the use of flue gas desulfurization gypsum as a substitute for mined gypsum in wallboard. EPA’s evaluation concluded that the beneficial use of encapsulated CCRs in concrete and wallboard is appropriate because they are comparable to virgin materials or below the agency’s health and environmental benchmarks"; and:

EPA Concludes FGD Gypsum in Gypsum Board Contributes Significant Environmental and Economic Benefits; Affirms Environmental, H; concerning:  "'EPA Concludes FGD Gypsum in Gypsum Board Contributes Significant Environmental and Economic Benefits'; Affirms Environmental, Health and Safety Studies; March 2014; For more than 20 years, Gypsum Association members have successfully and safely developed and deployed technologies to use flue gas desulfurization (FGD) gypsum as a key ingredient in the manufacture of gypsum board (AKA wallboard or drywall). The gypsum industry purchases FGD gypsum from electric utilities who employ a washing and purification process to make FGD materials into an FGD gypsum product. Natural gypsum and FGD gypsum have the same chemical composition; they are each calcium sulfate dihydrate (CaSO4·2H2O). Today, almost half of all gypsum used in the manufacture of gypsum board in the United States is FGD gypsum, also known as byproduct or synthetic gypsum";

even such a seemingly-entrenched foe of our economically essential Coal-based industries as the United States Environmental Protection Agency finds that such uses of Coal Ash and FGD wastes can lead to "Significant Environmental and Economic Benefits".

Another, closely related use for Coal Ash, also developed by the above-cited United States Gypsum Company, is that seen in our report of: 

US Gypsum Improves Coal Ash Wallboard | Research & Development | News; concerning: "US Patent Application 20120167804 - In-Situ Manufacture of a Lightweight Fly Ash Based Aggregate; 2012; Inventor: Marianela Perez-Pena, IL; Assignee: United States Gypsum Company, Chicago; Abstract: A method of making a rapid setting lightweight homogeneous foamed fly ash based cementitious aggregate composition with improved compressive strength for products such as panels is disclosed. The method mixes fly ash, alkali metal salt of citric acid, foaming agent for entraining air, optional foam stabilizing agent, a calcium sulfate such as stucco or gypsum, and water. Compositions are also disclosed which include mixtures of fly ash, particularly Class C fly ash alone or in mixtures with Class F fly ash, alkali metal salts of citric acid, foaming agents, a calcium sulfate such as calcium sulfate dihydrate or hemihydrate and an optional portland cement";

wherein they disclosed a technical process for using both Class F Fly Ash, as we obtain as a byproduct from the combustion of our high-Btu content eastern bituminous Coal, and Class C Fly Ash, as co-produced by the combustion of, mostly western state, lower-Btu lignite Coal, and which exhibits cement-like properties as-is, in the making of an aggregate composition for other construction materials like gypsum wallboard, but with somewhat different, and desirable, properties. 

And, herein we learn that technical experts in the employ of our United States Government recently confirmed the practicability of "US Patent Application 20120167804", through their allowance and issuance of, as excerpted from the initial link in this dispatch:

"United States Patent 8,795,429 - Method for In-situ Manufacture of a Lightweight Fly Ash Based Aggregate

Method for in-situ manufacture of a lightweight fly ash based aggregate - United States Gypsum Company

Date: August 5, 2014

Inventor: Marianela Perez-Pena, Illinois

Assignee: United States Gypsum Company, Chicago

Abstract:: A method of making a rapid setting lightweight homogeneous foamed fly ash based cementitious aggregate composition with improved compressive strength for products such as panels is disclosed. The method mixes fly ash, alkali metal salt of citric acid, foaming agent for entraining air, optional foam stabilizing agent, a calcium sulfate such as stucco or gypsum, and water. Compositions are also disclosed which include mixtures of fly ash, particularly Class C fly ash alone or in mixtures with Class F fly ash, alkali metal salts of citric acid, foaming agents, a calcium sulfate such as calcium sulfate dihydrate or hemihydrate and an optional portland cement.

(Keep in mind, that, if it is desirable to, as an "option", use "portland cement" as a component of this composition, then, as seen in;

Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development | News; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Dravo Lime Company, Pittsburgh; Abstract: Cement is produced (from) flue gas desulfurization process waste product (and) aluminum, iron, silica and carbon ... wherein said source of aluminum and iron comprises fly ash";

we can make that, too, out of Coal Ash and FGD residues.)

Claims:  A method of making loose aggregate particles consisting of the steps of: forming a mixture by mixing ingredients consisting essentially of: water, cementitious reactive powder consisting essentially of fly ash and a calcium sulfate selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof, and optional silica fume, an alkali metal salt of citric acid selected from the group consisting of sodium citrate, potassium citrate and mixtures thereof, a foaming agent, and optionally at least one or more member selected from the group consisting of secondary aggregate other than said loose aggregate, superplasticizer, set accelerating agents other than said alkali metal salt of citric acid, set retarding agents, shrinkage control agents, thickening agents, coloring agents, and internal curing agents, and reacting the mixture in situ at a temperature of about 20 to 41 C by mixing for about 3 to 6 minutes to form aggregate particles comprising hydration products of the fly ash and calcium sulfate in the mixture and crystalline hydration products of the fly ash and calcium sulfate which are also formed in situ and are interspersed within and between the aggregate particles to bind the aggregate particles, and separating the aggregate particles as loose aggregate particles from the mixture.

(Note, in the above, that the specified "calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof" could well be, are actually no doubt intended to be, as derived from Flue Gas De-sulfurization residues, as in the above-cited ""United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste".) ,  

The method ...  wherein the wet density of the resulting mixture is about 40 to 65 pounds per cubic foot, wherein the mixture has no hydraulic cement, and said ingredients consisting essentially of said water, said cementitious reactive powder, said alkali metal salt of citric acid, and said foaming agent. 

The method ...  wherein the cementitious reactive powder is selected from the group consisting of class C fly ash and calcium sulfate hemihydrate or ... mixtures of class C and class F fly ash ... or stucco and/or Portland cement and mixtures of class F fly ash .... . 

The method ... wherein the wet density of the resulting mixture is about 46 to 51 pounds per cubic foot; wherein the mixture has no hydraulic cement, wherein the ingredients consist of said water, said cementitious reactive powder, said alkali metal salt, said foaming agent, and optional superplasticizer (and) wherein the cementitious reactive powder comprises 60 to 95 wt. % fly ash and 5 to 40 wt. % calcium sulfate selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof. 

The method ...  further including setting the cementitious mixture comprising the aggregate particles in situ and recovering the aggregate particles from the set cementitious mixture by a suitable recovery process to separate the aggregate particles from the set mixture. 

The method ... for forming a lightweight cementitious aggregate: wherein the cementitious reactive powder consists of 60 to 95 wt. % fly ash, and wherein the ratio of water to cementitious reactive powder solids in the mixture is about 0.17 to 0.35:1(and) wherein the cementitious reactive powder consists of fly ash which is 88.5 to 100 wt. % Class C fly ash, calcium sulfate, optional silica fume and no Portland cement and no other hydraulic cement (or) wherein the cementitious reactive powder is selected from the group consisting of class C fly ash and calcium sulfate hemihydrate or stucco, mixtures of class C and class F fly ash and calcium sulfate hemihydrate or stucco; and mixtures of class F fly ash with class C fly ash and/or Portland cement and calcium sulfate hemihydrate stucco. 

The method ...  wherein the fly ash of the cementitious reactive powder consists of 30-46 wt % class F fly ash and 54-70 wt % class C fly ash and the mixture has no portland cement and no other hydraulic cement

The method ... wherein the cementitious reactive powder consists of 46 to 60 wt. % Class F fly ash, 10 to 32 wt. % Class C fly ash, and 10-29 wt % calcium sulfate hemihydrate or stucco ... . 

The method ...  wherein the aggregate particles consist of a homogeneous mixture of spherical shaped particles of the reaction of the fly ash and calcium sulfate having a diameter of less than about 1 mm formed in situ and the crystalline hydration product of said fly ash and calcium sulfate, which is also formed in situ and interspersed in and between the particles and binding said particles together in the aggregate. 

A method of making loose aggregate particles consisting of: forming a mixture by mixing ingredients consisting of: water, cementitious reactive powder consisting of fly ash, optional hydraulic cement, optional non-fly ash mineral additive, optional added lime, a calcium sulfate selected from the group consisting of calcium sulfate hemihydrate, calcium sulfate dihydrate, and mixtures thereof.

Background and Field: This invention relates generally to fast setting cementitious compositions that can be used for a variety of applications in which rapid hardening and attainment of early strength is desirable. In particular, the invention relates to a method of making a homogenous lightweight fly ash based cementitious aggregate composition which has properties similar to expanded clay aggregates and lightweight fillers that can be used to make boards with excellent moisture durability for use in wet and dry locations in buildings... .

(At this point in the full Disclosure, even additional prior art is cited, including US Gypsum's and Perez-Pena's own:

(United States Patent: 6869474 - Very Fast Setting Cementitious Composition; 2005; United States Gypsum; Abstract: Extremely fast setting of cementitious compositions for producing cement-based products such as cement boards ... reactive materials may be included such as ... fly ash. The extremely fast rapid set permits rapid production of cementitious products.)

There is a need to find a method to reduce the weight of fly ash based binder mixes so these formulations can be used to manufacture of lightweight cementitious concrete products for applications such as backer board and other wall or ceiling applications with improved strength. The present method has developed formulations with enhanced compressive strength at reduced weight and with reduced cost. 

When lightweight concrete is made, a lightweight aggregate like expanded clay or perlite is generally used rather than sandy gravel or crushed stone. The expanded clay/perlie particles (nodules) are produced by a sophisticated pyrogenic process whereby geochemically specific clay or perlite is expanded in a rotary kiln at high temperatures. The expanded clay or perlite particles are extremely lightweight granular aggregate with a hard vitrified outer shell and an air filled honeycombed inner core. The expansion of the combined water in the crude clay or perlite (rock), results from the rapid heating of the crude rock to temperatures above 1600 F. (871 C), when the rock cracks and combined water vaporizes like popped corn. 

The present invention provides a method of making fast setting cementitious slurry used to manufacture lightweight aggregate particles (nodules) at a relatively low temperature. The lightweight aggregate particles (nodules) can form in situ in a cementitious mixture. Setting the mixture results in a solid product comprising particles (nodules) formed in situ in the matrix of cementitious material. This product can be used as is or crushed to form loose lightweight aggregate particles. 

The particles are extremely lightweight with a hard outer cementitious shell with an air filled crystalline inner core. The lightweight particles provide a low energy, low cost lightweight filler which is ideal for manufacturing lightweight cement panels, block or other lightweight concrete articles. 

The lightweight cementitious compositions of the present invention can be used to make precast concrete building products such as cementitious boards with excellent moisture durability for use in wet and dry locations in buildings. The precast concrete products such as cement boards are made under conditions which provide a rapid setting of the cementitious mixture so that the boards can be handled soon after the cementitious mixture is poured into a stationary or moving form or over a continuously moving belt. 

The lightweight cementitious compositions can be used in any concrete product application including concrete panels, flooring, overlays, finishes, capping, as well as patching mixes for concrete roads.

The concrete products made with the lightweight compositions of this invention have particular advantages for use which require water durability compared to compositions which contain gypsum and applications which require higher compressive strength than cement containing compositions which have a higher carbon foot print. 

Fly ash material is mostly aluminosilicates. Thus, it is theorized the lightweight aggregate of the invention may be similar to that of the most expensive perlite or expanded clay aggregate". 

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We'll close there, although there is much more of a highly-technical nature in the full Disclosure related to the chemistry of cement, and etc., which is likely of little interest.

We note in passing that this is one of many similar, or at least conceptually-related, technologies directed towards the processing of Coal Ash to make aggregate-type materials for use as property-modifiers in cement and concrete mixtures about which we've reported. A review of some of them can be found in our report of: 

Consol Converts More Coal Ash into More Construction Aggregate | Research & Development | News; which concerns, primarily: "United States Patent 6,054,074 - Manufactured Aggregates from Coal Combustion Byproducts; 2000; Assignee: Consol, Inc., Pittsburgh (PA)".

The point is that a lightweight aggregate, one that can reduce the weight of concrete items and structures when used as a component of the concrete mix,  and thus, in a number of ways, conserve energy, can be made, as herein, almost entirely from Coal Ash.

There are, as noted, many uses for such weight-reducing aggregate; and. the lightweight aggregate made herein from, primarily, Coal Ash can be used in all those applications where the "most expensive"  of such aggregates, made from mined and quarried minerals, are currently employed.  

And, it all serves to further confirm that even the Ash resulting from our economically essential use of Coal in the generation of reliable and affordable electrical power can be seen and treated more as a valuable mineral resource than a problematic waste - - a mineral resource the use of which could conserve both natural resources and energy, while creating more industries and more jobs in US Coal Country.


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