http://www.ucalgary.ca/files/
The title of this dispatch is a bit of an extrapolation, but not much of one. We'll explain, after we remind you, that, as seen in our report of:
West Virginia Coal Association | USDOE Says Coal Ash Could End Aluminum Ore Imports | Research & Development; concerning:
"Economic Metal Recovery from Fly Ash; 1981; Oak Ridge National Laboratory, USDOE; Abstract: Although most coal combustion ash produced in the United States is discarded as a waste, results are presented to show that fly ash can be an economical source of Al2O3, Fe2/O3, and possibly several other metals, many of which are presently being imported";
one of our prestigious US National Laboratories established the fact, more than three decades ago, that Coal Ash can serve as "an economical source of" Aluminum ore, "Al2O3"; all, or nearly all, of which we consume in the United States of America we now import.
And, as seen in our report of:
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. At an aluminium conference in (China) earlier this month, (it was stated that) "fly ash ... will probably become the important alternative resource for alumina production in China";
they are smart enough, in China, to put the information established by our United States tax dollars more than thirty years ago to work, even if we, in the United States of America, are not.
Further, as seen in our report of:
West Virginia Coal Association | Iowa Mines Metals from Coal Ash for the USDOE | Research & Development; concerning, in part: "Title: Mineral Recovery from Coal-conversion Solid Wastes; 1982; DOE Contract Number: W-7405-ENG-82; Report Number: IS-M-426; CONF-8210188-1; Ames Lab (Iowa State University), IA (USA); Bradford University (UK); Abstract: The utilization or disposal of coal conversion solid wastes is an important environmental problem of the future. Work is described on the development of two processes for the large scale extraction of Aluminum, Titanium, and Iron from these wastes. Such processes not only appreciably reduce the disposal problem but also provide an indigenous source of valuable metals. One process involves the production of soluble aluminates in the clinker resulting from a lime-fly ash sinter and the other is a high temperature chlorination process that converts the metal oxides in the ash to volatile metal chlorides. Work is proceeding from bench scale up to large scale feasibility studies";
our United States Department of Energy, at one time, was insightful enough to pay to have different processes developed for the extraction of valuable metals from "coal conversion", i.e. Coal Liquefaction and Coal Gasification, "solid wastes", i.e. Ash.
And, herein, we learn that our good neighbor to the north, Canada, as well, has recognized and acknowledged those potentials for recovering such naturally-occurring, valuable metals from all the solid residua resulting from all our uses of Coal.
As seen in excerpts from the initial link in this dispatch to:
"Metal Recovery from Coal Ash Via Chlorination - A Thermodynamic Study;
K. Mehrotra, et. al., Department of Chemical Engineering, The University of Calgary, Alberta
The Canadian Journal of Chemical Engineering, April, 1979
Coal ash can become an important mineral substitute for the recovery of several metals, especially aluminum and titanium.
A plausible route for the recovery could be via high temperature chlorination in the presence of a reducing agent.
(The "chlorination" would be as in our above-cited report concerning: "Mineral Recovery from Coal-conversion Solid Wastes", and the "high temperature chlorination process" that was examined by the Iowa State and Bradford universities.)
The results (of our work) indicate that the chlorination route is feasible over a wide temperature range.
Conventionally the coal ash produced by coal fired power plants is disposed by burial in either surface or deep mines, that is as landfill or backfill. Similarly the wet slurried ash is discharged into disposal ponds. The filled-ponds are allowed to dry completely or the partially dried sludge is periodically dredged from the pond for ultimate disposal.
In the recent years there has been an increasing number of attempts made to use ash in a more productive manner. These applications vary widely in nature, as diverse as road paving to waste water effluent treatment. Other suggested means of ash utilization include applications in cement manufacture, brick making, soil conditioning, and as rubber filler.
(See, variously, for examples of the above uses of Coal Ash, our reports of:
West Virginia Coal Association | Coal Ash Makes Better Bricks | Research & Development; and:
West Virginia Coal Association | Coal Ash Reinforced Recycled Plastic | Research & Development.)
But ... with large-scale utilization of ash for purposes such as metals recovery, the environmental impact would be (further) alleviated both qualitatively and quantitatively.
One distinct advantage in using ash for the recovery of metals is that as raw material, it is already in the “mined” and “crushed” form. The ready access of ash as a feed stock reduces significantly the fraction of costs incurred in the mining and size reduction step necessary for conventional ores. This should make the substitution of ores by ash commercially more attractive.
A single metal, which at the present time, appears most promising for the recovery is aluminum. The
concentration of aluminum in coal ash compares well with those found in several bauxite ores. However, attempts to recover or extract aluminum have not been made, perhaps because of insufficient quantities of ash available from any single source.
With the construction of large coal conversion facilities such as (a) coal gasification or liquefaction complex, the possibility of employing ash as a source of aluminum, in future, should become more attractive.
(Note: Coal "gasification or liquefaction" makes using the "ash as a source of aluminum ... more attractive". Now, admittedly, the advantage seems to be more a matter of scale, than anything else. A Coal conversion facility might process more Coal than a typical Coal-fired power plant, and, thus, make more ash for extracting aluminum and other metals from. But, don't we have "collections" of Coal-fired power plants located in fairly close proximity to each other in certain places, whose ash output could be consolidated? And, are there not accumulations of old Coal Ash, already disposed of, which could be mined?)
Other trace metals of increasing commercial importance, which can in addition be recovered from ash are titanium, gallium, germanium . . . .
(See, for one example, our report of:
West Virginia Coal Association | Coal Ash a Superior Source of High-Tech Metal | Research & Development; concerning, only in part: "United States Patent 4,643,110 - The Recovery of Gallium and Germanium from Coal Fly Ash; 1987; Assignee: Enron, Inc., Houston, TX; Abstract: A furnace arrangement ... for the recovery of gallium and germanium from pelletized fly ash";
as confirmation that valuable metals like "gallium and germanium" can also be extracted, on a practical basis, from Coal Ash. Note, though, that extraction processes disclosed by Enron in "United States Patent 4,643,110" and by the University of Calgary herein are based on very different technologies.)
The work described herein forms a vital part of the research in progress on the recovery of metals from fly ash. The purpose of the outlined free energy calculations is to explore the following important features:
(i) possibility of recovery of aluminum and other important metals as chlorides from fly ash from a themodynamic view-point,
(ii) selective recovery of aluminum from chiefly a mixture consisting oxides of silicon, aluminum, iron and calcium,
(iii) ratio of fly ash and chlorine and/or other reactants necessary for a reasonable recovery of aluminum,
(iv) the effect of temperature in altering the equilibrium composition of products, and:
(v) the effect of variation in feed composition on redistribution of reaction products.
(The University of Calgary devotes the bulk of the article to detailed descriptions of their experimental work and presentation of the formulas illustrating the thermodynamics of the processes. All would be beyond the understanding or interest of all but the most technically-minded among our readers, who are invited to explore those minutiae in the full discourse, as accessible via the link. Should that link fail to function, we have downloaded a file of the full report, and can, if needed, transmit that file it to the West Virginia Coal Association.)
Conclusions: Coal ash has the potential of becoming an important raw material for the recovery of metals, especially aluminum.The complex silicate compounds in ash are found to be unstable at the chlorination conditions described in this work. The metal constituents can be treated as their simple oxides.
From the free energy calculations, there does not appear a pathway for selective chlorination of aluminum oxide from a mixture such as ash. The use of chlorine alone will not result in the chlorination of aluminum and silicon in ash.
Either carbon or carbon monoxide could provide a suitable reducing atmosphere for the chlorination reactions.
From a thermodynamic view-point, a chlorination process employing reducing agents such as carbon or carbon monoxide will yield aluminum and other metals as their chlorides.
(And, if we want to use "carbon monoxide" as a "reducing agent" in the University of Calgary's scheme for the recovery of Aluminum ores from Coal Ash, we remind you, that, as seen for only one example in:
West Virginia Coal Association | Carbon Dioxide Recycled in the Manufacture of Plastics | Research & Development; concerning, in part: "United States Patent 4,564,513 - Process for the Production of Carbon Monoxide; 1986; Bayer Aktiengesellschaft (AG), Germany; Abstract: Carbon monoxide is produced in an improved process in a carbon-filled, water-cooled generator in the configuration of a truncated cone in the longitudinal section, by the gasification of said carbon with a mixed gas of oxygen and carbon dioxide ... . Claims: In a process for the production of carbon monoxide in a carbon-filled, water-cooled generator in the configuration of a truncated cone in the longitudinal section, by the gasification of said carbon with a mixed gas of oxygen and carbon dioxide";
there are some intriguing options available to us for the manufacture of Carbon Monoxide.)
Aluminum trichloride being vapor above 200C, it can be fractionally condensed from the reaction gas mixture.
Aluminum appears to be the last metal constituent to be chlorinated. It implies that there will be a loss of reactants in chlorinating other metals of low commercial significance.
Thus to improve the economics of the chlorination process, attention should be given to recover and recycle chlorine from Silicon Chloride, in particular.
The separation of chlorides of value, such as Titanium Chloride, may make the chlorination process even more attractive.
For almost complete recovery of aluminum from ash, stoichiometric quantities of chlorine and carbon/carbon monoxide are required. The variation in system temperature has a dominant effect on the redistribution of aluminum and iron compounds. In the temperature range of interest for the present study, almost total chlorination of aluminum in ash is predicted at the equilibrium."
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The United States of America currently imports all of the raw Aluminum ore, primarily from Jamaica, Guinea, and Brazil, and a few others, which we refine into Aluminum. Our domestic sources of Aluminum ore which can be economically refined have always been limited; and, as can be learned via:
Full text of "Strategic Minerals"; ";Strategic Minerals; A Summary Of Uses, World Output, Stockpiles Procurement'; The Reconstruction Finance Corporation; 1947";
plans were first laid to stockpile the metal in the United States as a strategic resource as early as 1941; and, formal allocations of available Aluminum and Aluminum ore, between the defense establishment and commercial industry, were made by the United States government throughout most of the 1940's.
For well more than half a century, in other words, we have had to concern ourselves with ensuring, for our national security, an adequate supply of Aluminum.
As herein confirmed by Canada's University of Calgary, Coal Ash, whether resulting from the combustion of Coal for the generation of electrical power or, maybe even preferably, from the conversion of Coal into gaseous and liquid hydrocarbon fuels, could lay that concern over our supply of Aluminum to rest.