JP2010265455A - Method for producing treated coal and silica from fly ash-including coal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing clean treated coal and silicon dioxide by efficiently separating coal and fly ash comprising a metal oxide, silicon dioxide and a sulfur compound. <P>SOLUTION: The method for producing treated coal 38 and practically pure silicon dioxide 45 comprises the following processes: [1] a process for reacting a mixture 23 of coal and fly ash with an aqueous solution of hydrogen fluoride to generate a liquid flow 27 including silicon fluoride and a metal fluoride and a solid flow 29 including unreacted coal and a sulfur compound; [2] a process for reacting the sulfur compound with a metal nitrate dissolved in water to generate an aqueous solution of a nitrate ion, a metal ion and a sulfur ion; [3] a process for separating an aqueous solution of a nitrate ion, a sulfur ion and a metal ion from solid coal 38; [4] a process for cleansing the treated coal 38; and [5] a process for reacting silicon fluoride and the metal fluoride with a metal nitrate in an aqueous mixture to generate solid silicon dioxide 45 and then separating the solid silicon dioxide 45 from an aqueous mixture. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to inorganic impurities present in coal containing particulate fly ash containing metal oxides such as Al ₂ O ₃ , SiO ₂ , Fe ₂ O ₃ and sulfur, calcium and other oxides commonly found in coal ash. It is related with the removal method. This process allows for the production of clean treated coal and at the same time the separation and recovery of relatively pure (commercial grade) silicon dioxide (SiO ₂ ) as a valuable by-product.

  Industrial use of untreated coal, especially coal containing sulfur and fly ash as fuel, may result in unacceptable levels of air pollution and maintenance costs for industrial plants that rely on coal as the main hydrocarbon fuel source Has been known for a long time. The presence of contaminants such as nitrogen and sulfur compounds in coal fly ash causes two serious obstacles. First, the presence of fly ash reduces the potential heating value of the coal and tends to reduce the thermal efficiency of the coal in the plant process. Second, fly ash can cause serious environmental and / or operational problems in industrial applications such as direct coal-fired turbine plants used for power generation. As a result, it is necessary to reduce or eliminate pollutants in carbon-based fuels, resulting in higher manufacturing costs and stricter environmental considerations, reducing the use of coal containing fly ash in the United States year by year. is doing.

  Furthermore, the installation and operating costs of power plants that use coal containing fly ash are increasing, as pollution control equipment that cleans or eliminates exhaust gases is required to meet increasingly stringent government environmental regulations. Coal-fired power plants also have the problem of high maintenance costs associated with cleaning equipment that is usually contaminated by surface deposits exposed to coal combustion.

Over the years, progress has been made in increasing the efficiency of coal-fired thermal processes, but it is still possible to develop clean and highly efficient coal for use in combined cycle power systems to increase the amount of power generated per unit of CO ₂ emissions. There is a strong need. Unfortunately, coal suitable for turbine plants can contain only trace amounts of granular fly ash for operational efficiency. Numerous R & D programs have been implemented over the last decade to reduce fly ash content, with most programs focusing on chemical processing to produce ultra-low ash coal. In these methods, the coal raw material is usually subjected to some form of caustic treatment and / or acid treatment for the purpose of extracting the ash component as a soluble species and separating the dissolved ash component from the coal fuel. Such methods have only achieved some success, examples being a caustic treatment to produce soluble sodium aluminosilicate and a hydrofluoric acid based treatment to produce a fluoro complex.

  The disadvantages of these conventional systems are that they involve high operating temperatures, high acidity and a considerable amount of water, which contains a lot of soluble organic and inorganic substances that contaminate other natural resources. Therefore, it cannot be discharged into the environment without secondary treatment. The large amount of water required puts pressure on the means necessary to treat the water downstream of the production facility, making most processes impractical from a cost standpoint. Many of the pollution regulations in force require that these processes approach near-zero emissions of removed species from coal and the recovery of water used for coal processing.

Another obvious shortage of currently available coal treatment systems is the inability to recover potentially beneficial silicon dioxide present in fly ash. Currently, the world production of silica is about 40,000 tons / year, but the demand is steadily increasing and approaching 75,000 tons / year. Demand for alternative solar source is increased, also rose cost silica commercial grade because cost-prohibitive for current commercial SiO ₂ process.

  The present invention produces two commercially valuable independent products from the same raw coal supply, ie, producing treated coal using the hydrofluoric acid / nitrate method described below, and a solar energy panel and Producing commercial grade silica (silicon dioxide) that can be used in the semiconductor industry brings significant progress to the industry. Treated coal produced by the method of the present invention is particularly beneficial for coal fired turbine plants that need to meet environmental control standards for power generation in combined cycle power plants. Similarly, recovering commercial grade silicon dioxide from the same feed provides additional cost effectiveness and commercial benefits compared to conventional coal processing methods.

  It is known to use treated coal itself as a potential energy source. However, currently, such coal is economically produced using raw materials containing troublesome components that are normally present in fly ash particles, especially sulfur or undesirable oxides (eg, aluminum, iron, calcium and silicon). At the same time, it is impossible to produce commercial grade (relatively pure) silica as a by-product. Typically, ash from coal is converted to slag / fly ash, then collected and sold as a low value product such as a product for another application, such as cement production, structural filler or asphalt paving components. The ash content of coal varies from region to region, but usually falls within the range of about 5-7% by weight in the United States. In 2001, the US electricity business produced more than 70 million tons of fly ash, of which about 25 million tons could be used as cement production and related industrial materials. Thus, large amounts of fly ash are not utilized and must eventually be disposed of as waste.

  Besides power generation, the potential uses of treated coal are well known, for example the production of heavy oil, graphite and carbon fibers. Coal itself has non-fuel applications, for example, as a raw material for producing high purity carbon-based products, specifically, electrodes for the aluminum industry. Similarly, pure silica can be used in the manufacture of various products such as silicon chips and solar cells.

US Pat. No. 4,442,062

  An exemplary method for treating a mixture of solid coal and fly ash containing metal oxide, silicon dioxide and sulfur compounds in accordance with the present invention to produce treated coal and substantially pure silicon dioxide includes the following: Process. (1) A mixture of coal and fly ash is reacted with an aqueous hydrogen fluoride solution to contain a liquid stream containing silicon fluoride and a metal fluoride and unreacted coal and a sulfur compound (eg, metal sulfide). A solid stream is produced. (2) The sulfur compound is reacted with a metal nitrate dissolved in water to produce an aqueous solution of nitrate ions, metal ions and sulfur ions. (3) Separate the aqueous solution of nitrate, sulfur and metal ions from the solid, ie the first treated coal. (4) Wash the treated coal with water. (5) Silicon fluoride and metal fluoride are reacted with metal nitrate in an aqueous mixture to produce silicon dioxide as a solid component. The silicon dioxide product is separated from the aqueous mixture.

The present invention also dissolves metal oxides (eg, Al ₂ O ₃ and Fe ₂ O ₃ ) present in the fly ash component of the treated coal, and then separates and almost any sulfur compound, eg, iron sulfide. And a step of treating and removing aluminum sulfide. In certain embodiments, the method is capable of significantly reducing the fly ash content of the resulting treated coal, preferably to a level of 0.01% or less. Furthermore, in the present invention, hydrogen fluoride used in the first fluoride reaction with the metal oxide in fly ash is recovered by using a high-temperature reaction of the metal fluoride component generated in the initial reaction step.

1 is a block flow diagram showing the steps of an exemplary method for producing treated coal and substantially pure silica in accordance with the present invention. FIG. 2 is a detailed process flow diagram showing the main process equipment, associated process flow and control parameters of an exemplary method of the present invention.

  As described above, the present invention efficiently separates the metallic and inorganic components of coal fly ash and recovers silica present in fly ash almost completely on a commercial grade. The method is particularly troublesome to fly ash components (eg, metal oxides, sulfur, etc.) to impurity levels that easily meet current environmental regulations without the need for complex and expensive emission control equipment, such as in coal-fired turbine plants and power plants. And silicon dioxide). At the same time, the process provides an economical way to recover essentially pure silica as a valuable by-product.

  In an exemplary method according to the present invention, metal “impurities” present in fly ash are separated by conversion into soluble inorganic oxides that can be removed from the system as waste. The method also removes the silica as a separate product by modifying the silica component and then separating it. As a result, little silica remains in the treated coal end product or residual fly ash. As noted above, the conventional method, even in small amounts of silica in coal fly ash, may be commercially disadvantageous due to the extreme abrasive properties of silica and the inherent thermal efficiency reduction caused by non-hydrocarbon components in coal used as fuel. There is. Therefore, this method is advantageous in that silica present in fly ash can be removed at a high rate. In addition, almost all of the hydrogen fluoride that reacts with silicon present in fly ash is later recovered and recycled for reuse in this process.

  FIG. 1 shows a flow of basic process steps for producing treated coal and by-product silica in accordance with the present invention. The purpose of the three basic processes: the initial treatment of fly ash components containing silicon dioxide and metal oxides with hydrogen fluoride; followed by the production of treated coal products by removal of residual sulfur and nitrate compounds; and the liquid state FIG. 3 is a process flow for achieving regeneration to essentially pure solid state silica after separation of the silica component from the initial fly ash component remaining in FIG.

As shown in FIG. 1, the initial “dirty” coal feed 10 containing fly ash is typically silicon dioxide, metal oxides (such as aluminum oxide and iron oxide) and relatively small amounts, but environmentally Includes solid coal containing a significant amount of sulfur compounds. In one embodiment, an initial fly ash reaction is performed using a hydrogen fluoride feed 11 in a batch mixed reaction step 12 to produce SiF ₄ and metal fluorides (eg, aluminum fluoride and iron fluoride); These are soluble in the water present in the process. The resulting solid stream comprises an initially treated coal stream 13, which is then separated as a wet solid along with trace amounts of unreacted solid sulfur compounds and residual metal oxides. The pretreated clean coal is subjected to the second basic reaction step using nitric acid (addition indicated by nitric acid line 14). Nitric acid allows the removal and final separation of residual sulfur and nitrate compounds from coal and fly ash in the nitrate treatment and sulfur removal step 15. Finally, a treated coal product 16 is obtained.

Also, as shown in FIG. 1, the product of the initial reaction of the fly ash compound and hydrogen fluoride produces water soluble SiF ₄ and various metal fluorides present in the initial reaction mixture. The aqueous solution stream 17 containing the dissolved metal fluoride and silicon fluoride compound can be combined with the reaction product of the nitrate treatment and sulfur removal step 15 containing the metal nitrate described above. Silicon fluoride and nitrate react in SiO ₂ production step 19 to produce solid silicon oxide, which is separated and removed from the system in an essentially “pure” state as solid SiO ₂ (20a). Residual metal fluoride compounds and nitrate ions remaining in the solution are separated and processed in downstream operations to produce metal oxides as waste that can be finally disposed of, as well as recycled for use in recycling and initial reaction operations. Regenerate hydrogen fluoride (indicated by recycle and regeneration line 20b).

Referring to the more detailed process and equipment flow diagram illustrated in FIG. 2, the feedstock to the system (Step 1) has a relatively low moisture content and is a metal such as Al ₂ O ₃ and Fe ₂ O _3. The raw material coal containing the fly ash component which consists of an oxide is included. Fly ash usually contains small amounts but contains commercially significant amounts of SiO ₂ and residual amounts of FeS ₂ and CaO that should ultimately be removed to produce treated coal. A coal and fly ash mixed stream 23 is fed to an agitated reactor 21 along with an aqueous hydrogen fluoride stream 24 (nominally about 1 wt% HF aqueous solution) and is exemplified by the following general formula (typically a temperature of about 150 ° F.): The first reaction is performed at a reaction pressure of approximately atmospheric pressure.

反応器２１でのバッチ反応は反応成分を撹拌しながら約２〜３時間かけて起こり、撹拌反応器２１を包囲する水（又はスチーム）ジャケット２２を用いて反応を制御することができる。得られる「石炭スラリー」（二重線の石炭スラリープロセスライン２５で示す）は、水に溶解した反応生成物のフッ化物及び同伴固体を含有し、撹拌反応器２１から真空ドラムフィルター２６に移される（工程２）。ドラムフィルターがほとんどすべての液状成分を除去する。ドラムフィルターからの液状分は、溶解しているが未反応のフッ化水素、並びに最初の反応で生成し、水に溶解したフッ化物化合物、例えばフッ化ケイ素（ＳｉＦ_４）、フッ化アルミニウム及びフッ化鉄を含有し、その他に最初の石炭及びフライアッシュ供給物に存在する金属酸化物種に依存する少量の金属フッ化物を含有する可能性もある。

The batch reaction in the reactor 21 takes about 2 to 3 hours while stirring the reaction components, and the water (or steam) jacket 22 surrounding the stirred reactor 21 can be used to control the reaction. The resulting “coal slurry” (shown as a double line coal slurry process line 25) contains the reaction product fluoride dissolved in water and entrained solids and is transferred from the stirred reactor 21 to the vacuum drum filter 26. (Step 2). The drum filter removes almost all liquid components. The liquid content from the drum filter is dissolved but unreacted hydrogen fluoride, and fluoride compounds produced in the first reaction and dissolved in water, such as silicon fluoride (SiF ₄ ), aluminum fluoride and fluorine. It may also contain small amounts of metal fluorides that contain ferric oxide and otherwise depend on the metal oxide species present in the initial coal and fly ash feed.

  The drum filter 26 separates the initial “clean” coal product along with other solid compounds that remain in the mixture that are not soluble in water, such as iron sulfide, calcium oxide and similar solid compounds, and are illustrated using ordinary knife edges 28. Remove the solid as shown in The separated mixture 29 consisting of wet coal product and other trace solids is transferred to the nitrate reactor 30 (step 3). Reactor 30 functions to remove residual amounts of sulfur, calcium and inorganic compounds from the coal feed by reaction with a stream of metal nitrate and water (feed 32 to nitrate reactor 30). The reaction of the nitrate / water liquid stream fed to the nitrate reactor 30 with the metal sulfide component is illustrated by the following general formula:

真空ドラムフィルター２６（工程２）から排出される液体流２７は、少量の未反応のフッ化水素及び上記の金属フッ化物とフッ化ケイ素との混合物を含有し、以下に詳しく説明する下流混合反応器４０に供給される（工程６）。

The liquid stream 27 discharged from the vacuum drum filter 26 (step 2) contains a small amount of unreacted hydrogen fluoride and a mixture of the above metal fluoride and silicon fluoride, and will be described in detail below. Is supplied to the container 40 (step 6).

  On the other hand, the reaction product of the nitrate reactor 30 containing the original coal feed (solid component) and the product of the above reaction (solution at this stage) is discharged from the reactor 30 to the nitrate reactor discharge line 31. . The entire liquid / solid stream containing the reaction product of reactor 30 enters a second vacuum drum filter 33 (step 4), which removes the entrained liquid 34 containing various dissolved compounds and again normal A knife edge 35 is used to separate the wet coal product 36. The coal product 36 then enters a washing station 37 (step 5) where residual amounts of final waste compounds that are soluble in water are removed (denoted “washing water” 39) and dry ash is less than 0.1% by weight, A clean coal product 38, preferably less than 0.01% by weight, is produced.

  The reaction of the liquid component supplied to the mixing reactor 40 (step 6) is exemplified below.

上記の式が示すように、最初の反応（工程１）時に生成したフッ化ケイ素成分は、溶液中の金属硝酸塩と反応して主な反応生成物としての二酸化ケイ素並びに金属フッ化物（例えば、アルミニウム及び鉄）及び硝酸を生成し、後者はすべて水部分に溶解したままである。重要なことに、この時、二酸化ケイ素は固体状態である。ＳｉＯ_２を含有する液体／固体混合スラリーを混合反応器４０から底部排出ライン４１へ排出し、第３の真空ドラムフィルター４２に通し（工程７）、実質的に純粋な二酸化ケイ素製品４５を固形分として取り除く。ここでも、湿っているが、実質的に純粋なＳｉＯ_２固体製品を、図に示すように普通のナイフエッジ４４を用いて取り除くことができ、金属フッ化物水溶液及び硝酸を含有する分離後の液状分をドラムフィルター排出ライン４３に排出して、さらに処理し、最終的にリサイクルする。

As the above formula shows, the silicon fluoride component generated during the first reaction (step 1) reacts with the metal nitrate in the solution to form silicon dioxide as a main reaction product as well as metal fluoride (for example, aluminum And iron) and nitric acid, the latter all remaining dissolved in the water portion. Importantly, at this time, silicon dioxide is in a solid state. The liquid / solid mixed slurry containing SiO ₂ is discharged from the mixing reactor 40 to the bottom discharge line 41 and passed through a third vacuum drum filter 42 (step 7) to pass substantially pure silicon dioxide product 45 to a solid content. Remove as. Again, the wet but substantially pure SiO ₂ solid product can be removed using a normal knife edge 44 as shown, and the separated liquid containing aqueous metal fluoride and nitric acid. The portion is discharged to the drum filter discharge line 43 for further processing and finally recycling.

  The liquid content of the drum filter 42 containing metal fluoride and dissolved nitric acid is transferred from the drum filter 42 to a plurality of separation chambers 46, 46a, 46b and 46c in series, and passed therethrough, for example using reverse osmosis. Remove a significant portion of the accompanying water. The separated liquid stream 47 is further processed using a distillation column 48 (step 8) to separate the metal fluoride component and nitric acid / water. The distillation column includes a conventional reboiler 53 using steam 55 and returns steam 54 from the reboiler to the distillation column 48. As shown, the system also includes a condenser 51 having an overhead vapor line 50 and a condensate recycle line 52. Nitric acid and water recovered from the distillation column 48 become a liquid feed 56 to the mixing reactor 57 (described later).

  The metal fluoride compound remaining in the feed to the distillation column is removed from the bottom of the distillation column (step 8), resulting in a bottom feed 49 to the high temperature hydrolysis apparatus 60 at about 750 ° (step 9). In order to maintain proper temperature control of the reaction components, the hydrolysis apparatus 60 has a steam jacket 61. The reaction in the hydrolysis apparatus 60 follows the following general formula.

上記の一般式に示すように、加水分解装置６０は、塔頂蒸気ライン６３で示すように補給フッ化水素を塔頂に生成し、次いでこのフッ化水素を急冷ステーション６４で水を用いて急冷し（工程１０）、上記の最初の金属酸化物撹拌反応器２１に供給する。ＨＦライン６５で示すように補給ＨＦを添加することもできる。加水分解装置６０の底部の固体生成物は残留金属酸化物化合物を含有し、金属酸化物化合物の一部を残留供給物５９として反応器５７に戻し（工程１１）、リサイクル硝酸と反応させて、前述したように反応器３０中で起こる反応に使用する金属硝酸塩を生成することができる。加水分解装置６０の残りの金属酸化物成分を廃棄物６２として廃棄することができる。

As shown in the general formula above, the hydrolyzer 60 produces make-up hydrogen fluoride at the top of the tower as indicated by the overhead vapor line 63 and then quenches this hydrogen fluoride with water at the quenching station 64. (Step 10) and fed to the first metal oxide stirred reactor 21 described above. Replenishment HF can also be added as indicated by HF line 65. The solid product at the bottom of the hydrolyzer 60 contains residual metal oxide compound, a portion of the metal oxide compound is returned to reactor 57 as residual feed 59 (step 11), reacted with recycled nitric acid, As described above, the metal nitrate used for the reaction occurring in the reactor 30 can be produced. The remaining metal oxide component of the hydrolysis device 60 can be discarded as waste 62.

  The substantially pure silicon dioxide product 45 removed in step 7 of FIG. 2 is used to produce various end products such as semiconductor parts, soda lime glass (typically used for drinking glass), white ceramics such as ceramics, Can be manufactured using a container, a food additive (mainly as a fluidizing agent in powdered foods), a high-temperature heat protection cloth, and irregular reflection characteristics. Since the final product 45 is in a relatively pure state, various basic metal oxides such as sodium oxide, potassium oxide, lead (II) oxide, zinc oxide or silicate and glass, specifically It can also be used as a starting material for reactions involving oxide mixtures that form borosilicate glass, lead glass, and the like.

The SiO ₂ product 45 can also be a raw material for the production of polydimethylsiloxane (PDMS) of the following general formula.

ＰＤＭＳは、高分子有機ケイ素化合物類に属し、通常「シリコーン」と呼ばれ、並はずれたレオロジー（流動）特性で知られている。ＰＤＭＳの用途はコンタクトレンズ及び医療機器からシャンプー中のエラストマー、コーキング、潤滑油及び耐熱タイルと多岐にわたる。

PDMS belongs to polymeric organosilicon compounds and is commonly referred to as “silicone” and is known for its exceptional rheological properties. PDMS applications range from contact lenses and medical devices to elastomers in shampoos, caulks, lubricants and heat-resistant tiles.

SiO ₂ can also be used to produce oil-resistant silicone rubber compounds of the general formula:

以上、本発明を現時点で最も実用的で好ましいと考えられる実施形態について説明したが、本発明は開示した実施形態に限定されるものではなく、特許請求の範囲内での種々の変更や均等物の組合せを包含する。

While the present invention has been described above in terms of the most practical and preferred embodiments, the present invention is not limited to the disclosed embodiments, and various modifications and equivalents within the scope of the claims. A combination of

10 “Dirty” Coal Feed 11 Hydrogen Fluoride Feed 12 Batch Mixing Reaction Process 13 Initially Treated Coal Stream 14 Nitric Acid Line 15 Nitrate Treatment and Sulfur Removal Process 16 Treated Coal Products 17 Metal Fluoride and Silicon Fluoride Compound 18 dissolved sulfur compounds and metal nitrate 19 SiO ₂ forming step 20a solid SiO ₂
20b Recycling and regeneration line 21 Stirred reactor 22 Water (or steam) jacket 23 Coal and fly ash mixture 24 Hydrogen fluoride aqueous solution 25 Coal slurry process line
26 Vacuum drum filter 27 Liquid flow 28 Knife edge 29 Solid flow 30 Nitrate reactor 31 Nitrate reactor discharge line 32 Nitrate reactor feed 33 Second vacuum drum filter 34 Entrained liquid 35 Knife edge 36 Coal product 37 Cleaning station 38 Clean Coal product 39 Flushing liquid 40 Downstream mixing reactor 41 Bottom discharge line 42 Third vacuum drum filter 43 Drum filter discharge line 44 Knife edge 45 Silicon dioxide products 46a, 46b and 46c Separation chamber 47 Liquid stream after separation 48 Distillation tower 49 Bottom feed 50 Top steam line 51 Condenser 52 Condensate recycle line 53 Reboiler 54 Steam 55 Steam 56 Liquid feed 57 Mixing reactor 58 Make-up water 59 Residual feed 60 Hydrolysis unit 61 Over arm jacket 62 Waste 63 overhead vapor line 64 quench station 65 HF line

Claims (11)

A mixture of solid coal and fly ash (23) containing metal oxide, silicon dioxide and sulfur compounds is processed to produce reacted or treated coal (38) and substantially pure silicon dioxide (45). A method,
A mixture of coal and fly ash (23) is reacted with an aqueous hydrogen fluoride solution (24) to contain a liquid stream (27) containing silicon fluoride and metal fluoride and unreacted coal and sulfur compounds. Producing a solid stream (29);
Reacting the sulfur compound with metal nitrate dissolved in water to produce an aqueous solution of nitrate ion, metal ion and sulfur ion (31);
Separating an aqueous solution of nitrate ion, sulfur ion and metal ion (31) from solid coal (38);
Washing the solid coal (38) with water;
Reacting silicon fluoride and metal fluoride with metal nitrate in an aqueous mixture to produce solid silicon dioxide (45);
A process for producing reacted or treated coal (38) and substantially pure silicon dioxide (45) comprising the step of separating solid silicon dioxide (45) from an aqueous mixture. The method of claim 1, wherein the metal oxide comprises Al ₂ O ₃ and Fe ₂ O ₃ .   The method of claim 1, wherein the sulfur compound comprises iron sulfide and aluminum sulfide.   The method of claim 1, wherein the residual amount of fly ash (23) in the treated coal (38) is less than about 0.01 wt%. The process of claim 1 wherein the reaction of silicon fluoride and metal nitrate to form silicon dioxide (45) occurs according to the general formula:

The process of claim 1, wherein the reaction of silicon dioxide with hydrogen fluoride (24) to produce silicon fluoride occurs according to the following general formula:

4. A process according to claim 3, wherein the iron sulfide reacts with iron nitrate according to the general formula:

  The process of claim 1, wherein the reaction of fly ash (23) containing silicon dioxide (45) occurs at a temperature of about 150 ° F and a pressure of about atmospheric pressure. The method further includes the step of reacting nitric acid (HNO ₃ ) with a metal fluoride compound of the general formula (Al, Fe) F ₂ OH in water to produce a metal nitrate used in the reaction with the sulfur compound. The method according to 1. The method of claim 1, further comprising recovering the metal fluoride of aluminum and iron using a high temperature reaction according to the following general formula to regenerate hydrogen fluoride (24).

  The method of claim 10, wherein the reaction occurs at a temperature of about 750 ° F.

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