United States Patent: 5019360

We've now documented many instances wherein technology has been developed, by very credible people and organizations, that enables the extraction of valuable minerals and metals from Coal power plant ash.

Oddly, most such Coal Ash "mining" technologies have originated in the upper mid-west, where they don't mine a whole lot of Coal, but sure do burn a bunch of it to generate economical electricity.

One of our reports on technologies for the extraction of valuable metals from Coal Ash coming from that area of the country can be accessed via:

Iowa Mines Metals from Coal Ash for the USDOE | Research & Development; wherein we documented both:

"United States Patent 4,386,057 - Recovery of Iron Oxide from Coal Fly Ash; 1983; Assignee: The United States of America; The U.S. Government has rights in this invention pursuant to Contract No. W-7405-ENG-82 between the U.S. Department of Energy and Ames Laboratory (at Iowa State University); Abstract: A high quality iron oxide concentrate, suitable as a feed for blast and electric reduction furnaces is recovered from pulverized coal fly ash. This invention relates to a process for the recovery of iron from coal fly ash"; and:

"United States Patent 4,397,822 - Process for the Recovery of Alumina from Fly Ash; 1983; Government Interests: The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-82 between the U.S. Department of Energy and Ames Laboratory (at Iowa State University); Abstract: An improvement in the lime-sinter process for recovering alumina from pulverized coal fly ash is disclosed"

We submit that one initial processing step that Coal Ash could be subjected to, without affecting subsequent metals recovery, as via the above Iowa processes of United States Patents "4,386,057" and "4,397,822", would be that developed in Wisconsin, as we reported in:

Wisconsin Recovers "Cenospheres" from Coal Fly Ash | Research & Development; concerning: "United States Patent 8,074,804 - Separation of Cenospheres from Fly Ash; 2011; Assignee: Wisconsin Electric Power Company, Milwaukee (WI); 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";

wherein "cenospheres", tiny, hollow bubbles of silicate minerals, which have value as a density-reducing and insulating particle "filler" for both concrete and plastics, can be extracted from Coal Ash without affecting, at all, the basic chemical constituents of that Coal Ash, leaving it still-suitable for processing for metals extraction via the above Iowa-developed processes of United States Patents "4,386,057" and "4,397,822", or, via the process of our subject herein, as seen, with comment appended, in excerpts from the initial link in this dispatch to:

"United States Patent 5,019,360 - Processing of Fly Ash, Scrubber Sludge and the Like; and Product

Date: May, 1991

Inventor: John Lehto, MN

Assignee: Northern States Power Company, Minneapolis

Abstract: A method for the processing of fly ash scrubber sludge or the like is provided. The method yields unique products, including a usable calcium silicate material and a high purity alumina material. The process involves a plurality of stages including a first magnetic separation in an acid leach. During the acid leach, valuable mineral components are converted into soluble sulfates. The leach residue, containing calcium materials, is extracted with ammonia solution to yield a desirable calcium silicate product. The leach liquor is treated in a preferred manner to precipitate relatively acid free aluminum sulfate. The aluminum sulfate is then converted into a desirable alumina product.

(We have documented multiple times that Coal Ash can be a rich source of Aluminum. See, for instance:

USDOE Says Coal Ash Could End Aluminum Ore Imports | Research & Development; concerning both the:

"Economic Metal Recovery from Fly Ash; 1981; Oak Ridge National Laboratory, USDOE; Results show that (our described) methods can remove from fly ash all metals that would otherwise be available for release to the environment after disposal and that a major portion of the leached metals can be separated in saleable form. A capital investment of $38.2 million (to process a specified amount) of ash per year (will generate) a net yearly cash flow of $15.2 million"; and:

"Resource Recovery from Coal Residues; 73rd Annual Meeting of the American Institute of Chemical Engineers; 1980; G. Jones, et. al.; Oak Ridge National Laboratory; USDOE; Abstract: Several processes are being developed to recover metals from coal combustion and conversion residues. Methods to obtain substantial amounts of aluminum, iron, and titanium from these wastes are presented".

The "calcium silicate" byproduct might not sound too exciting, but it is a material, as can be learned via:

Calcium silicate - Wikipedia, the free encyclopedia; wherein we're told, in part, that: "Calcium silicate is commonly used as a safe alternative to asbestos for high temperature insulation materials. Industrial grade piping and equipment insulation is often fabricated from calcium silicate";

that does have a fairly significant "commodity"-type market in the fabrication of insulation and other specialty construction materials.)

Claims: A method of processing fly ash material having bulk silicates, magnesium, magnetic iron and aluminum components therein; said method including the steps of: 

(a) removing a magnetic component of said fly ash material by a magnetic separation to leave a non-magnetic component; said magnetic component including iron component therein;

(We haven't focused on the issue, since the results, to us, seem that they would be relatively minor; but, various processes and technologies we have reviewed relating to the recovery of various values from Coal Ash often do, as above, stipulate an initial "magnetic separation" of Iron from the Ash. We have yet to find documentation attesting as to just how much of the Iron bound in the Ash could be recovered in that fashion, but, we have encountered so many references indicating that it should be done that it might just be a worthwhile exercise.)

(b) extracting the non-magnetic component from step (a) with sulfuric acid leach under reflux at atmospheric pressure, to form a sludge residue and a hot sulfuric acid liquor; said hot sulfuric acid liquor having the magnesium and aluminum components dissolved therein;

(c) separating the sludge residue and the hot sulfuric acid liquor form step (b); 

(d) subjecting the sludge residue from step (c) to an aqueous ammonium carbonate extraction to form an aqueous solution having a white precipitate therein; (and) separating the white precipitate ... ; 

(f) cooling, without acid neutralization, the hot sulfuric acid liquor from step (b) to precipitate a crude solid including ammonium sulfate and magnesium sulfate from the resulting cooled acid liquor;

(Note, that, although Aluminum recovery is the primary focus, Magnesium, as well, can be recovered, and, which Magnesium finds its broadest commercial use, actually and coincidentally, as a component of Aluminum alloys, to which the Magnesium imparts some desirable properties.

The method ... including a step of calcining the aluminum hydroxide ... to form alumina.

(We've edited the Claims in the extreme. They do fully disclose the processing steps required to extract, from the above "white precipitate", the "aluminum hydroxide".)

A method of processing fly ash material having bulk silicates, magnesium, magnetic iron and aluminum components therein ... .

Background and Field: The present invention relates to the processing of fly ash, scrubber sludge and similar materials. The invention particularly concerns a method whereby many of the components of such materials can be isolated and/or converted into useful products. 

As used herein, the term "fly ash" refers to the ash produced by and from the the combustion of powdered or other particulate forms of coal, such as in power station boilers or the like, and includes entrained ash from a gassifier. The term "scrubber sludge" includes the solid materials recovered from the combustion gases of coal, through conventional means such as smoke stacks, scrubbers and the like. Chemically, fly ash and scrubber sludge comprise very similar materials, except that scrubber sludge generally has a considerable amount of calcium sulfate in it, as a result of the limestone slurry typically used to react with sulfur dioxide in the gases. For the descriptions herein, "fly ash" and "scrubber sludge" will be understood to be interchangeable terms.

(Note the above inclusion of "entrained ash from a gassifier", and, we remind you of our recent report of:

Exxon Improves Coal Conversion Ash Removal | Research & Development; concerning: "United States Patent 3,957,459 - Coal Gasification Ash Removal System; 1976; Exxon Research & Engineering Company; Abstract: In a fluidized bed process for the gasification of coal or similar carbonaceous solids wherein char particles are withdrawn from a fluidized bed reaction vessel, transported to a second vessel, and later returned to the initial vessel, char particles of high ash content are separated from particles to be returned to the fluidized bed reaction vessel by injecting a dense phase stream of char particles including particles of both high and low ash content into a vertically moving gas stream having a velocity sufficient to transport relatively light particles of low ash content upwardly into the fluidized bed reaction vessel but insufficient to suspend relatively dense particles of high ash content, collecting the high ash content particles which are not entrained by the gas stream, and periodically withdrawing the collected particles from the system";

wherein Exxon stipulate that they are removing Ash from, specifically, "hydrocarbon gases" and hydrocarbon "synthesis gas" generated from Coal and the Coal gasification's residual Char.)

Fly ash and scrubber sludge are produced in great amounts almost any time coal is burned as a fuel, for example in thermoelectric power plants. Disposal of this material has been a considerable problem, and promises to be an ever increasing problem as a result of environmental restrictions, increasing costs of transport, the need for dumping sites and similar concerns

It has long been recognized that fly ash and scrubber sludge contain many potentially valuable mineral values. For example, typical fly ash includes a considerable amount of aluminum, iron, manganese, calcium, magnesium, titanium and potassium oxides therein. Further, small amounts of barium, cobalt, chromium, copper, gallium, nickel, lead, rubidium, strontium, zinc, zirconium, and other compounds have been found in fly ash. Typically, the most prevalent of these minerals is the aluminum value, which is sufficiently high to encourage the development of fly ash processing.

What has been needed ... (is) a method of fly ash and scrubber sludge processing which accomplishes and/or provides the following: 

1. Effective and efficient recovery of valuable mineral values, especially iron and aluminum values, in useful and desirable forms, and with desired purity. 

2. A process which substantially reduces the volume of waste material to be dumped. 

3. A process whereby the bulk, in terms of volume and weight, of the fly ash material is isolated as a useful product; and one potentially having reasonable market value and sufficient utility so as to not completely glut the market in that product, if produced in the very large scale quantities possible as a result of large scale fly ash processing. 

4. A process that uses relatively high temperature kiln or calcining operations to a lesser extent than conventional processes, to avoid excessive energy demands. And, 

5. A process which produces relatively little waste or product disposal or contamination problem.

Summary: According to the present invention, large amounts of fly ash or scrubber sludge, from the burning of coal, are fully processed and utilized. The overall process may be viewed as involving numerous stages, each of which provides significant steps of importance to overall efficient and effective processing. A general summation of the various stages is as follows: 

In a first stage (Stage 1), the fly ash and scrubber sludge is collected, classified, and is treated for the removal of magnetic components, typically magnetite (Fe3O4). The early removal of magnetite provides several important functions. First, the iron recovered has some commercial value. Secondly, its removal reduces contamination of other fractions, increasing their value. 

In Stage 2, the remaining fly ash/scrubber sludge material is extracted to obtain the important mineral values, particularly aluminum, in solution and to separate from them the bulk silicates. 

Stage 3 involves a unique processing of the sludge material, or bulk silicates, produced in Stage 2. As a result of the overall processing, and the particular Stage 3 processing described in detail (in the full Disclosure), the bulk silicates may be isolated as a unique, bright white, product. This product has many potential market uses, even in very high volume, including as a paper filler. As a result of the unique Stage 3 processing, a high volume of waste product is generally avoided. That is, a particular, specific, fault of previous methods is avoided, in that the silicate material is obtained in a form having significant and substantial use."

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We submit, that, the "very high volume" markets for the "bulk silicates", and, perhaps, any remaining mineral residue, could include incorporation, as simple aggregate materials, into various concrete mixtures, such as seen in:

US EPA Headquarters Housed in Coal Ash | Research & Development; wherein we're told, that: "In addition to its beneficial reuse in ...fiber cement products, fly ash has been used in concrete since the 1930’s.  Most notably, it has been used in several construction projects and prominent buildings, including the Ronald Reagan Government Office building, home to the Environmental Protection Agency (EPA)".

The end result might well be, that, after most of the valuable metals have been extracted, via the process of our subject herein, "United States Patent 5,019,360 - Processing of Fly Ash, Scrubber Sludge and the Like"; and, the resultant "bright white" and "calcium silicate" byproducts, and remaining residual minerals, directed into their various suitable markets, there just might not be much, if any, of our Coal Ash remaining to worry about disposing of.

Thus, a combined and coordinated Coal Ash processing system, if widely adopted, could, conceivably, not only prevent any Ash disposal costs from being generated, and being added to our electric bills, but, instead, generate a significant stream of income flowing into those areas where circumstances have led to accumulations, and ongoing production, of what must now be seen as a valuable raw material resource, i.e.:

Coal Power Plant Fly Ash.