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Researchers Submit Patent Application, "Process for Magnesium Production", for Approval

March 6, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Short, Stephen A. (Mount Ousley, AU), filed on August 25, 2011, was made available online on February 20, 2014.

The patent's assignee is Magnesium Investments Pty Ltd.

News editors obtained the following quote from the background information supplied by the inventors: "Magnesium is a useful and valuable metal and is commonly used in aluminium alloys, in die-casting (alloyed with zinc), to remove sulfur in the production of iron and steel, and in the production of titanium. Magnesium is used in several high volume part manufacturing applications, including automotive and machine components. Because of its low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop computers, cameras, and other electronic components.

"Most of the world supply of magnesium comes from processing naturally occurring materials such as dolomite and magnesite. Another potential source of magnesium is waste ash material from coal fired power stations burning brown coals.

"There are several brown coal deposits around the world. Some of the larger deposits of brown coal, also referred to as lignite, are found in Russia, the United States Germany, Poland and Australia.

"The brown coal is typically prepared as a pulverized fine powder (PF) in which form it is delivered to vertical water wall boilers where it is combusted to release heat for steam generation by turbines. The majority of the combustion products are fine particles which are carried by the flue gases out of the boiler and are known as fly ash. The coarser ash particles, principally sand, settle to the bottom of the boiler from where they are collected. This fraction is known as bottom ash and generally constitutes about 20% of the total ash content of the combusted coal. The flue gases from the boiler are often treated with an electrostatic precipitator to remove the fine particles (>99%) and this fraction is known as electrostatic precipitator (EP) fly ash and comprises about 80% of the total ash content of the combusted coal. The fly ash typically contains about 5-20% char (unburnt or partially carbonised coal).

"The two ash types are typically mixed with recycled ash pond water and temporarily held in a large ash pit within the power station where some chemical reactions and hydrochemical alterations to the ash begin to occur. The mixed ash slurry, with a liquid to solid ratio typically ranging from about 100:1 down to 10:1, depending on the particular power station, is then pumped to an ash pond for disposal.

"Emplaced ash typically continues to 'age', i.e. undergoes further chemical alterations, including most notably hydration and decomposition of brownmillerite (calcium alumino-ferrite) Ca.sub.2(Al,Fe).sub.2O.sub.5 to a variety of products such as hydrated calcium alumino-ferrites, hematite, iron hydrotalcites, hematite and magnetite and absorption of carbon dioxide (CO.sub.2) from the atmosphere which may markedly increase the chemically fixed CO.sub.2 content of the emplaced mixed ash. The CO.sub.2 content of raw dry EP fly ash is relatively low, typically

"The ash from brown coals has a wide variety of applications including soil conditioning/fertilization, as an extender in cement and concrete production and as fillers in non-metallic minerals and building materials. The relatively high magnesium and calcium contents in brown coals results in the brown coal fly ash being classified as 'Class C' fly ash in the American classification system and this also raises the possibility of recovering magnesium (Mg) from the fly ash.

"One of the principal methods of manufacture of magnesium metal from suitable feedstock is the pyrometallurgical method known as the Pidgeon Process.

"Most raw materials collected from brown coal power generation ash pits or ponds do not have suitable compositional qualities for direct conversion to magnesium using the Pidgeon Process, Failure to treat such raw material, as well as other raw material having similar composition, to achieve compositional qualities suited to the Pidgeon Process or other suitable reductive pyrometallurgical process may inhibit or prevent magnesium formation. Furthermore, magnesium generated from the raw starting material may have multiple impurities rendering it unfit for commercial use or sale.

"Furthermore, the calcining stage typically used in the Pidgeon Process to convert dolomite-type feedstock into dame-type form for generation of magnesium requires significant temperatures, which can be energy and cost inefficient.

"The present inventor has developed a process particularly suitable for processing fly ash and other materials for reductive pyrometallurgical magnesium production by the Pidgeon Process or other suitable reductive pyrometallurgical processes."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "There are a number of potential sources of magnesium but many of these sources contain contaminating materials that prevent their use for reductive pyrometallurgical magnesium production. For example, numerous contaminants present in waste fly ash resultant from burning of brown coal to generate power prevent that material from being suitable feedstock to obtain magnesium from a reductive pyrometallurgical process such as the Pidgeon Process. If these contaminants could be removed or reduced, then it is possible to produce magnesium from these materials.

"In a first aspect, the present invention provides a process for conditioning material containing magnesium for pyrometallurgical conversion to magnesium, the process comprising:

"carrying out de-sulfation of the material in a slurry to reduce sulfur content of the material; and

"carrying out de-ferration of the de-sulfated material in a slurry to reduce iron content of the material to produce a conditioned material suitable for pyrometallurgical conversion to magnesium.

"The material containing magnesium may be ashes derived from brown coal or lignite being in the form of raw dry fly ash, dry emplaced ash, stored or aged dry ash, wet emplaced ash, stored or aged wet ash, raw dry or aged dry or wet slags derived from metallurgical production of iron, steel or other ferrous metals, blast furnace slags and dusts, basic oxygen furnace slags and dusts, electric arc furnace slags, dusts and sludges, dolomite, dolime, limestone, any material having a realisable MgO and CaO content, and any and all mixtures thereof.

"Preferably, the material containing magnesium is a fly ash, preferably fly ash from a brown coal power station.

"Preferably, the material has a realisable magnesium oxide (MgO) and calcium oxide (CaO) content. In a preferred form, the raw material has a CaO:MgO mass ratio of greater than about 1.54.

"Preferably, the slurry of up to about 30% (w/v) material in water. In a preferred form, the slurry is at least 1% (w/v) and up to about 20% (w/v) material in water.

"In a preferred form, de-sulfation is carried out using a carbonation agent. Preferably, the carbonation agent is a combination of both a strong alkali cation and carbon dioxide. Preferably, the strong alkali cation is sodium, potassium or ammonium.

"The strong alkali drives the formation of ion pairs between the cation of an alkali such as sodium and ammonium and sulfate to optimize solubility of sulfate-containing species and therefore to maximize the leaching (removal) of sulfur from the material. The strong alkali also drives the solubility of silicon and aluminium-containing minerals to assist leaching (removal) of silicon and aluminium from the material.

"The strong alkali may be caustic soda (NaOH), caustic potash (KOH), soda ash (Na.sub.2CO.sub.3), potash (K.sub.2CO.sub.3) or ammonia (NH.sub.4OH) or any combination of these. In a preferred process, the alkali is soda ash (Na.sub.2CO.sub.3).

"The carbon dioxide drives the formation of calcium carbonate thereby reducing the available amount of calcium in solution therefore also maximizing the solubility of sulfate as salts of sodium, potassium and/or ammonium.

"Preferably, the process is carried on the site of a brown coal power station where the material can be directly sourced.

"The carbon dioxide is preferably sourced from the emission stack of a power station.

"The sulfur-containing species in the feed material containing magnesium can be anhydrite (CaSO.sub.4), bassanite (CaSO.sub.4:0.5H.sub.2O), ettringite (Ca.sub.6Al.sub.2(SO.sub.4).sub.3(OH).sub.12:26H.sub.2O), burkeite (Na.sub.6CO.sub.3(SO.sub.4).sub.2), pyrrhotite (FeS), etc.

"The carbonation also has the secondary purposes of accelerating the decomposition of the mineral brownmillerite (nominally Ca.sub.2AlFeO.sub.5) in the fly ash, thereby releasing more calcium for precipitation as calcium carbonate and releasing iron as hematite and amorphous iron hydroxide.

"De-sulfation can be carried at an elevated temperature. The present inventor has found that an elevated temperature of about 60.degree. C. to 75.degree. C. is suitable but other temperatures can be used such as ambient to about 100.degree. C. Depending on the material, temperatures above about 75.degree. C. can have the potential to produce iron hydrotalcite, which is amorphous or fine grained, of low density and resists physical separation on the basis of density.

"Preferably, the sulfur content is reduced to less than about 0.5% on a calcined basis. More preferably, the sulfur content is reduced to about 0.2% on a calcined basis.

"Preferably de-ferration is a combination of a prior physical separation of bulk iron-containing minerals on the basis of density and/or magnetic susceptibility followed by a later chemical treatment step involving the use of a complexing agent for leaching iron, aluminium and silicon.

"Preferably the physical separation of bulk iron-containing minerals is based on a density separation using a cyclone multi-gravity separator such as a Mozley Multi-Gravity Separator (MGS) or similar device. Preferably the physical separation of bulk iron-containing minerals uses a slurry in the 10% (w/v) to 30% (w/v) range.

"Preferably, the complexing agent used in for chemical leaching of the de-ferration step is an alkanolamine, more preferably an alkanolamine selected from one or more of triethanolamine (C.sub.8H.sub.15NO.sub.3), monoethanolamine (C.sub.2H.sub.7NO), diethanolamine (C.sub.4H.sub.11NO.sub.2), methyldiethanolamine (C.sub.5H.sub.13NO.sub.2), tri-isopropanolamine (C.sub.9H.sub.21NO.sub.3), or any combination thereof.

"In a preferred process, the complexing agent is triethanolamine (abbreviated TEOA) typically either of 100% chemical quality or of 85% industrial quality with diethanolamine (abbreviated DEOA) and/or monoethanolamine (abbreviated MEOA) comprising the remaining 15%.

"Preferably, the triethanolamine is used at a concentration of about 1.0 molar to 3.0 molar, preferably about 2.0 molar.

"A secondary organic complexing agent may also be used in process. Preferably, the organic complexing agent is selected from one or more of the common glycols (diols) ethylene glycol (C.sub.2H.sub.6O.sub.4; abbreviated EG), propylene glycol (1,2-propanediol; 1,3-propanediol (C.sub.3H.sub.8O.sub.2) or 1,3-butanediol (C.sub.4H.sub.10O.sub.2), or from the common polyols (polyalcohols) especially having at least 2 adjacent OH groups with the middle two in the threo position, such as threitol (C.sub.4H.sub.10O.sub.4), mannitol, sorbitol and xylitol.

"In a preferred embodiment, the secondary organic complexing agent is ethylene glycol (EG). In a preferred process, the secondary organic complexing agent is ethylene glycol (EG) present at concentrations of 1.0 to 3.0 molar, preferably 2.0 molar.

"The complexing agent(s) reacts with iron, aluminium and silicon under alkaline conditions to form water-soluble complexes, such as organo-silicates, silatranes, ferratranes and alumatranes to enable the leaching of iron, aluminium and silicon from the material.

"The complexing agent(s) may be regenerated for reuse. The complexing agent maybe regenerated by neutralisation of the spent de-ferration leach liquor with carbon dioxide or hydrochloric acid and subsequent evaporation of bulk water to separate waste solids from the complexing agent. The complexing agent maybe regenerated for reuse by simultaneous neutralisation and evaporation of bulk water by treating spent de-ferration leach liquor with a hot source of carbon dioxide.

"Preferably, the iron content is reduced to less than about 12% on a calcined basis. More preferably, the iron content is reduced to about 4% on a calcined basis.

"Chemical de-ferration can be carried at an elevated temperature of up to about 100.degree. C. The present inventor has found that an elevated temperature of about 75.degree. C. is suitable but other lower temperatures can be used such as 40.degree. C.-75.degree. C. Depending on the material, temperatures above about 75.degree. C. can have the potential to produce iron hydrotalcite, which resists dissolution by complexation of iron in a chemical leach 'de-ferration' stage.

"In a second aspect, the present invention provides a process for producing magnesium comprising:

"carrying out the process according to the first aspect of the present invention to obtain a conditioned material containing magnesium; and

"carrying out a pyrometallurgical process on the cconditioned material to obtain magnesium metal.

"Preferably, the pyrometallurgical process is the Pidgeon Process. It will be appreciated that other reductive pyrometallurgical processes may be used for production of magnesium from the conditioned material.

"Throughout this specification, unless the context requires otherwise, the word 'comprise', or variations such as 'comprises' or 'comprising', will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

"Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention.

"In order that the present invention may be more clearly understood, preferred embodiments will be described with reference to the following drawings and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 shows the results of residual sulfur levels attained in some 30 laboratory bench trials.

"FIG. 2 of residual iron levels as Fe.sub.2O.sub.3 attained in some 30 laboratory bench trials.

"MODE(S) FOR CARRYING OUT THE INVENTION

"Material

"The material containing magnesium may be ashes derived from brown coal or lignite being in the form of raw dry fly ash, dry emplaced ash, stored or aged dry ash, wet emplaced ash, stored or aged wet ash, raw dry or aged dry or wet slags derived from metallurgical production of iron, steel or other ferrous metals, blast furnace slags and dusts, basic oxygen furnace slags and dusts, electric arc furnace slags, dusts and sludges, dolomite, dolime, limestone, any material having a realisable MgO and CaO content, and any and all mixtures thereof.

"In this invention fly ash is taken to generically mean the product, obtained by combustion in air or oxygen, in a furnace, of brown coal, also known as lignite. Fly ash is typically the ash having the finer particle size range which is exhausted from a furnace with the hot exhaust gases. Such ash is typically captured for disposal in electrostatic precipitators (EP) or fabric filter 'baghouses'.

"Fly ash from a brown coal power station contains up to about 14% sulfur and up to about 17% iron on a calcined basis. To recover magnesium from a source material using a pyrometallurgical conversion process such as the Pidgeon Proces, sulphur content needs to be less than about 0.5% and iron content less than about 8%. Thus, to use fly ash or orther similar materials as a source of magnesiyum for a pyrometallurgical conversion process, the material has to processed (termed conditioning or beneficiation) to significantly reduce the sulphur and iron content.

"In this invention the term fly ash is not intended to exclude the use or partial inclusion of other forms of ash from lignite in particular coarser forms of ash such as that known as 'bottom ash' which has a coarser particle size range and typically falls under gravity from the bottom of a furnace.

"Pidgeon Process

"Magnesium is produced from any suitable feedstock by a pyrometallurgical conversion process. The Pidgeon Process is the most commonly used pyrometallurgical conversion process and is typically carried-out is a batch-wise thermal reduction process using Ferrosilicon (FeSi) to reduce magnesium from Dolime (a mixture of calcium and magnesium oxides; CaO+MgO) at high temperature. It is a simple and well understood process throughout the global magnesium industry. The raw material source of magnesium ions for the process is usually dolomite (CaMg(CO.sub.3).sub.2), which is typically transported from a nearby mine to a Pigeon Process Plant where it is firstly crushed, cleaned and calcined at a temperature around 1300.degree. C. to produce Dolime via the following reaction:

"CaMg(CO.sub.3).sub.2(solid)+Heat?CaO+MgO+2CO.sub.2(gas)

"where CaMg(CO.sub.3).sub.2 is dolomite

"CaO is Calcium Oxide

"MgO is Magnesium Oxide

"CO.sub.2 is Carbon Dioxide

"Calcining typically takes place in either vertical (batch) retorts or rotary (continuous) furnaces depending on the scale of the operation, the quality of the dolomite and the source of the energy used e.g. coal or natural gas.

"Next, the two major feeds into the Pidgeon reduction process proper, Dolime and FeSi, are typically finely ground, mixed to a specific ratio, sometimes with inclusion of a calcium fluoride (CaF.sub.2) flux, pelletised and then fed into a steel, horizontal cylindrical reaction chamber, known as a retort. The feed end of the retort is typically eater cooled and protrudes from the reduction furnace. Typical dimensions for a retort are of the order of 250-300 m internal diameter and approximately 3000 mm in length.

"The retorts are heated in refractory brick furnaces, in banks, to a temperature of around 1200.degree. C. under a strong vacuum (approximately 10-15 mm Hg), whereby the following reduction reaction proceeds to produce magnesium vapour:

"2(CaO+MgO)(solid)+FeSi(solid)?2Mg(vapour)+((CaO).sub.2SiO.sub.2)Fe(s- olid)

"where (CaO).sub.2SiO.sub.2Fe is calcium ferrosilicate.

"The magnesium vapour typically condenses in crystalline form at the water-cooled end of the retort, on a recyclable steel sleeve. The condensate is known as a 'crown' and, typically, the crown produced in each retort weighs between 18 and 22 kg per processed batch charge, depending on the charge size and the particular reaction conditions.

"A wide range of furnace designs exist, with the number of retorts per furnace typically ranging from 10 to 30. Around 9 hours are required for the basic reaction to occur plus an additional 2-3 hours for retort emptying, cleaning and refilling. Most retorts are therefore typically operated on 12-hour cycle.

"Once cooled, the crowns are typically collected and transported to a nearby casting plant, remelted and cast as pure ingots. There is a growing tendency for the metal to be alloyed during the melting and casting process.

"The Pidgeon Process typically requires the following composition qualities: MgO content is preferably >20% for a Dolomite-type feedstock (i.e. CaMg(CO.sub.3).sub.2) to the calcining stage or preferably >38% for a Dolime-type feedstock (i.e. CaO+MgO) to the final retorting stage. CaO content is preferably >30% for a Dolomite-type feedstock to the calcining stage or preferably >57% for a Dolime-type feedstock to the final retorting stage. The mass ratio of CaO/MgO for both stages is preferably >1.54 (unless supplementary additions of pure MgO or CaO are made just before the retorting stage). The sum of the alkali metal oxides, potassium and sodium oxide i.e. K.sub.2O+Na.sub.2O is preferably

"The above compositional qualities for the feedstock to the final retorting stage of the Pidgeon Process represent preferable compositional qualities for a dolomite (CaMg(CO.sub.3).sub.2) feedstock to the calcining stage and/or for a dolime feedstock to the final retorting stage.

"While some raw material collected from brown coal power generation ash pits or ponds already has suitable compositional qualities for conversion to magnesium using the Pidgeon Process, this is very uncommon. Failure to treat such raw material, as well as any other raw material having similar composition, to achieve compositional qualities suited to the Pidgeon Process may inhibit or prevent magnesium formation or magnesium generated from the raw material starting material may have multiple impurities rendering it unfit for commercial use or sale.

"Results

"Research and development for this process was conducted with raw dry electrostatic precipitator (EP) fly ash sourced from Victorian brown coal combusted at the Hazelwood Power Station in the Latrobe Valley, Victoria, Australia.

"The coal being combusted at the time of generation of this fly ash would have been sourced from the West Field coalfield. Well-mixed, this raw EP fly ash was found to contain about 5.5% organic carbon (char).

"Table 1 compares the analysis of this fly ash used for the research and development of this process, corrected to be on a residual combustibles-free basis not including any chloride (Cl) or carbon dioxide (CO.sub.2) content, compared with published typical total ash analyses for other open cut brown coals mined for power generation in the Latrobe Valley.

"TABLE-US-00001 TABLE 1 Yallourn Loy Loy Hazel- Ash Morwell North Yang Yang wood Composition Yallourn Seam Extension Seam Seam EP Analyses Seam Y M1 Seam M2 M1B M2 fly ash SiO.sub.2 26.9 16.4 8.6 17.2 45.5 9.5 Al.sub.2O.sub.3 8.6 3.4 5.0 12.4 8.5 2.7 Fe.sub.2O.sub.3 20.0 9.3 19.8 11.5 17.4 11.5 TiO.sub.2 0.5 0.3 0.6 0.0 0.0 0.2 CaO 6.0 24.7 25.1 3.0 4.8 27.0 MgO 14.3 14.2 8.6 11.6 6.6 16.7 Na.sub.2O 6.5 4.9 3.5 17.4 4.6 7.8 K.sub.2O 0.3 0.3 0.2 0.0 0.0 0.7 SO.sub.3 17.1 26.6 28.6 26.9 12.7 23.7

"The composition of Hazelwood EP fly ash is, in some senses, similar to that of fly ash obtained from other Latrobe valley power stations. For example, the MgO and CaO contents of Hazelwood EP fly ash are not significantly superior to the Morwell Seam M1 and Yalloum North Extension Seam M2 mixed coal ash.

"Furthermore the Hazelwood EP fly ash contains a comparable amount to other Latrobe Valley fly ashes of the most critical contaminant with respect to any process for preparing a viable feedstock for reductive pyrometallurgical production of magnesium namely, the sulfur (as SO.sub.3) content.

"It has been observed in the field of reactive chemical hydrometallurgy using solids that the rate of reactions and optimization of their approach to equilibrium chemothermodynamics is achieved by reactions between chemicals in solution and solid particles of the smallest achievable particle size. Mineral species retained in larger particle sizes are less reactive due to reduced surface area and, in some cases, greater hardness.

"It is known from optical microscopy and particle sizing studies conducted during development of this process that the coarser particles in brown coal ashes are dominated by coarse silica (sand) and unburnt 'char'.

"These physical tests and associated calculations showed that it was likely that the major part of the silica (SiO.sub.2) content, which is generally required to be removed for pyrometallurgical production of magnesium by the Pidgeon Process, could be removed by wet screening to exclude all coarse particles from subsequent hydrometallurgical process steps.

"The other reason why this hydrometallurgical process is based on an alkali such as soda ash, caustic soda or ammonia in the presence of dissolved carbon dioxide and/or bicarbonate and/or carbonate species in the first chemical stage is that this maximises the leaching of the most critical contaminant in the ash, being sulfur (S) from the material, preferably through maximisation of the dissolution of the minerals gypsum (CaSO.sub.4:2H.sub.2O) and anhydrite (CaSO.sub.4) which are the principal loci of sulfur, and of thenardite (Na.sub.2SO.sub.4), ettringite (Ca.sub.6Al.sub.2(SO.sub.4).sub.3(OH).sub.12:26H.sub.2O), ettringite-Fe (Ca.sub.6Fe.sub.2(SO.sub.4).sub.3(OH).sub.12:26H.sub.2O) and pyrrhotite (FeS) which are the minor loci of sulfur. This was achieved through maximising the solution concentration of sulfate (SO.sub.4) by Minimising the solution concentration of calcium and maximisation of the concentration in the solution of negatively charged sodium, potassium or ammonium ion pairs with sulfate, which ion pairing increases the net solubility of sulfate in the presence of low levels of calcium.

"It is common in hydrometallurgical science to attempt to derive a thermodynamic model of the individual unit processes which comprise the overall hydrometallurgical process. In the first instance, such models usually assume that each unit process is operated in such a way that full chemical equilibrium is attained. In practice this may not occur for a variety of chemical and physical reasons but close attainment of equilibrium in each unit process is generally aimed for on the basis that it optimizes its reliability and predictability.

"The primary basis for guiding further research and development of this process was therefore the writing of a comprehensive equilibrium chemothermodynamic model of the hydrometallurgical sequence of the process. Two thermodynamic databases which are suitable for the weakly to strongly alkaline, siliceous, ferruginous and aluminous systems of fly ashes, slags, dolomites and magnesites are; THERMODDEM released 26 Feb. 2008, originating from BRGM, the French Geological Survey, and CEMDATA.7.2 released 14 Aug. 2008, originating from ETH, the Swiss Institute of Technology. These databases are available in forms which are compatible with the United States Geological Survey open source chemothermodynamic model PHREEQC version 2.15 used in the conception and design of this process."

For additional information on this patent application, see: Short, Stephen A. Process for Magnesium Production. Filed August 25, 2011 and posted February 20, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=6127&p=123&f=G&l=50&d=PG01&S1=20140213.PD.&OS=PD/20140213&RS=PD/20140213

Keywords for this news article include: Anions, Sulfur, Alkenes, Silicon, Alkalies, Minerals, Chemistry, Chalcogens, Light Metals, Carbonic Acid, Carbon Dioxide, Magnesium Oxide, Ethylene Glycols, Calcium Carbonate, Calcium Compounds, Inorganic Chemicals, Inorganic Carbon Compounds, Magnesium Investments Pty Ltd.

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