EP2516331A1 - Procédé de préparation de dichromate d'ammonium - Google Patents

Procédé de préparation de dichromate d'ammonium

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Publication number
EP2516331A1
EP2516331A1 EP10787480A EP10787480A EP2516331A1 EP 2516331 A1 EP2516331 A1 EP 2516331A1 EP 10787480 A EP10787480 A EP 10787480A EP 10787480 A EP10787480 A EP 10787480A EP 2516331 A1 EP2516331 A1 EP 2516331A1
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EP
European Patent Office
Prior art keywords
ammonium
dichromate
sodium
double salt
alkali metal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP10787480A
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German (de)
English (en)
Inventor
Holger Friedrich
Rainer Ortmann
Matthias Stenger
Matthias Boll
Daniel Van Rooyen
Naveen Kalideen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lanxess Deutschland GmbH
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Lanxess Deutschland GmbH
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Filing date
Publication date
Application filed by Lanxess Deutschland GmbH filed Critical Lanxess Deutschland GmbH
Priority to EP10787480A priority Critical patent/EP2516331A1/fr
Publication of EP2516331A1 publication Critical patent/EP2516331A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G37/00—Compounds of chromium
    • C01G37/14—Chromates; Bichromates

Definitions

  • the invention relates to a process for the preparation of Ammoniumsdiehromat starting from alkali metal ammonium chromate Doppeisaizen.
  • Chromium (iH) oxide is a versatile product with a wide range of applications. Thus, it can be used as a pigment for coloring different application media, such as, for example, building materials, plastics, paints and varnishes, glasses or ceramics. For this application, the lowest possible content of water-soluble impurities is required.
  • chromium (III) oxide is also used in abrasives and high-temperature resistant materials.
  • chromium (III) oxide is also used in high-temperature resistant materials.
  • the lowest possible alkali metal content is desired in order to maximize the oxidation of Cr (IIl) to alkali metal chromate favored at high temperatures and the presence of alkali metal ions suppress.
  • chromium (IIi) oxide Another important industrial application for chromium (IIi) oxide is its use as starting material for the production of chromium eta and / or chromium-containing high-performance alloys.
  • chromium (II) oxides can be used here, which are characterized by a low sulfur content and a low carbon content.
  • the term "low-sulfur chromium (III) oxide” is therefore often used as a synonym for "chromium (III) oxide for metallurgical purposes”.
  • Chromium (III) oxide can be prepared according to the prior art by various methods. Usually, it is produced at higher temperatures from hexavalent chromium compounds, whereby different degrees of purity can be achieved.
  • chromic acid As starting compounds of the hexavalent chromium, chromic acid, ammonium chromates or alkali chromates are used.
  • the reaction can be carried out with or without the addition of a reducing agent.
  • Reducing agents are organic or inorganic reducing agents such as sawdust, molasses, cellulose acetate, acetylene, methane, sulfur and its compounds, phosphorus, carbon, hydrogen and the like.
  • reducing agents are organic or inorganic reducing agents such as sawdust, molasses, cellulose acetate, acetylene, methane, sulfur and its compounds, phosphorus, carbon, hydrogen and the like.
  • Such methods are described in numerous patents.
  • US Pat. No. 1,893,761 and DE-A-20 30 510 are mentioned.
  • US 1, 893, 761 discloses the preparation of chromium (HI) oxide by the reduction of alkali metal chromates with organic substances.
  • the process can be conducted so that sodium carbonate is finally obtained as a by-product, as already mentioned in US Pat. No. 1,893,761.
  • This may optionally be in the production process of Sodium dichromate can be recycled when the sodium dichromate is prepared via an oxidative alkaline digestion from chrome ore.
  • the chromium (III) oxide obtained in this way contains a high proportion of carbon which renders it unsuitable for metallurgical use.
  • DE-A-20 30 510 describes a process for the continuous production of very pure, low-sulfur chromium (III) oxide, by reduction of alkali chromates with hydrogen at higher temperatures and a device suitable for this purpose.
  • the reaction temperature is between 1000-1800 ° C., advantageously between 1100-1400 ° C., and the product obtained is separated from the exhaust gas with the aid of an alkaline dispersion.
  • a disadvantage of all these methods, which work with a reducing agent, however, is that inevitably a by-product is obtained by the use of the reducing agent, which must be worked up.
  • Metallurgical chromium (III) oxide was previously industrially produced by calcining in an oven a mixture of ammonium dichromate and sodium chloride obtained by in-situ reaction of sodium dichromate and ammonium chloride in virtually stoichiometric equivalent amounts.
  • the calcination temperature should be above 700 ° C to ensure that the reaction mixture has a high chromium (i) oxide content; however, if the temperature is too high, the risk of slag formation in the furnace increases, and the temperature is therefore generally kept below 850 ° C.
  • ammonium sulfate instead of ammonium chloride is often preferred because the ammonium chloride sublimated due to its low sublimation in the calcination as NH 3 and HCl and so can get into the exhaust air. For this reason, the use of ammonium chloride has no economic significance today.
  • the disadvantage of using ammonium sulfate, however, is that in this way sulfur is introduced into the production process, although a chromium (III) oxide with the lowest possible sulfur content is desired.
  • DE-A-26 35 086 discloses a process for producing a sulfurous chromium (IIl) oxide obtained by calcining a mixture of alkali metal dichromate and ammonium sulfate at a calcination temperature of 800 to 1100 ° C. and separation of the chromium (III) oxide formed from alkali metal salt formed, 0.7 to 0.89, preferably 0.7 to 0.84, moles of ammonium sulfate being used per mole of alkali metal chromate.
  • the workup of the chromium (lIi) oxide after the annealing is carried out in a conventional manner by washing out of water-soluble salts and drying.
  • Sulfur contents in chromium (III) oxide of 50 to 100 ppm can be achieved by this process.
  • a disadvantage of this method is that to obtain low sulfur contents, the starting materials must not be mixed in the stoichiometric ratio and ammonium sulfate is used in significant deficit. This results in low sales in the range of about 90%, and the maintenance of a high annealing temperature is required.
  • alkali metal sulfate for example sodium sulfate
  • the reaction always produces alkali metal chromate (for example sodium chromate) which, during later leaching, passes into the mother liquor or washing liquid and then has to be separated in order to possibly return it to the process.
  • alkali metal chromate for example sodium chromate
  • the mother liquor then also contains the inevitable accumulation of alkali metal sulfate, which must be lavishly purified, since it is always contaminated with alkali metal chromate.
  • US Pat. No. 4,296,076 discloses a process in which, inter alia, sodium dichromate and ammonium chloride or sodium dichromate and ammonium sulfate are used. In contrast to DE-A-26 35 086, essentially a stoichiometric ratio is selected or preferably an excess of the ammonium compound is used. In a first reaction step, the starting compounds are reacted to ammonium dichromate and sodium chloride or ammonium di chromate and sodium sulfate.
  • this reaction step takes place at 400 to 800 ° C, followed by the aqueous work-up and then a second annealing process at a temperature above 1100 ° C. Sulfur levels in chromium (II) oxide below 40 ppm are achieved by this process. In this method, however, large amounts of sodium chloride or sodium sulfate, which must be cleaned consuming. In addition, the use of said ammonium compounds, in particular of ammonium chloride, not without problems, because they sublimate very easily and thus can get into the exhaust air. Another method described in the prior art for producing high quality chromium (IIl) oxide is disclosed in RU 2 258 039.
  • ammonium dichromate - obtained by reaction of sodium dichromate with ammonium sulfate in an aqueous phase - for the production of chromium (IlI) oxide used, but the forcibly obtained in the reaction of sodium sulfate is separated from the reaction mixture, so that a relatively pure, the means low-sulfur, ammonium dichromate is thermally decomposed to chromium (III) oxide.
  • sodium sulphate is always by-produced as a by-product which must be laboriously purified since it is contaminated with Cr (VI).
  • the calcination starting from the ammonium dichromate is carried out in one stage at a temperature of 440-1400 ° C in a rotary kiln.
  • this procedure has proven to be disadvantageous because it leads to a high Cr (VI) -containing fines, which is partially incomplete decomposed and must be deposited separately and again the calcination must be supplied so that much material is in the recycling process.
  • a preferred method for producing chromium (IIl) oxide comprises the steps of a) thermal decomposition of ammonium dichromate at a temperature of 200 to 650 ° C, in particular 210 to 550 ° C, preferably from 210 to 430 ° C and b) subsequent calcination of the obtained from step a)
  • Step a) takes place in an indirectly heated reactor and step b) in a directly heated reactor.
  • the thermal decomposition of the ammonium dichromate according to step a) is carried out in the process preferably at a temperature of 200 to 650 ° C, more preferably 210 to 550 ° C, most preferably 210 to 430 ° C, in particular over a period of 5 to 300 minutes, more preferably from 30 to 240 minutes.
  • the thermal decomposition can, for example, in an indirectly heated rotary kiln, chamber furnace or in a fluidized bed.
  • An indirectly heated rotary kiln is particularly preferably used for the thermal decomposition of the ammonium dichromate.
  • the preferably used ammonium dichromate has a Na content of less than 2% by weight, in particular less than 1% by weight, more preferably less than 0.5% by weight, very preferably less than 0.2% by weight, calculated as Na metal.
  • the thermal decomposition according to step a) is carried out under normal pressure or under reduced pressure.
  • the decomposition product obtained after step a) can still be washed before it is fed to step b), but as a rule such a washing is not necessary.
  • the chromium (III) oxide obtained after step b) is first washed.
  • the thermal treatment at elevated temperature, so the Kaizinians, obtained from the step a) decomposition product according to step b) is carried out at a temperature of 700 to 1400 ° C., more preferably from 800 to 1300 ° C. This preferably takes place over a period of more than 20 minutes, particularly preferably for more than 30 minutes.
  • the expert knows a variety of directly heatable reactors. Preferably, only ring hearth furnaces, but in particular rotary kilns, are mentioned at this point.
  • the residence time of the material to be calcined is preferably from 30 minutes to 4 hours, depending on the design and length of the furnace.
  • the calcination is preferably carried out in air or in an atmosphere of pure oxygen or in an atmosphere of air, which is optionally enriched with oxygen.
  • one or more alkali metal halides or ammonium halides or alkaline earth metal halides are present before the thermal decomposition of the ammonium dichromate according to step a) and / or before the calcination according to step b) of sodium or potassium or ammonium, or alkali metal hydroxides, in particular sodium hydroxide, or potassium hydroxide, or chromic acid in an amount of 0.01 wt .-% to 3.0 wt .-%, particularly preferably from 0.02 wt .-% to 1.0 wt .-%, based added to the ammonium dichromate used or the resulting decomposition product.
  • the performance properties in particular the increase in the bulk density of the resulting chromium (III) oxide can be influenced.
  • the chromium (III) oxide obtained after the calcination according to step b) is preferably cooled and optionally ground.
  • the calcined product is leached with water after step b), whereby a mother liquor is formed, and washed, whereby wash water is formed and then dried again.
  • the washing can be carried out analogously to the procedure described below in step d).
  • chromium (III) oxide still existing water-soluble impurities (water-soluble salts) - essentially sodium, which is formed by oxidation of chromium (IIl) oxide at high temperatures - one or more stages with known methods with Washed out water or aqueous media and the solid are separated from the liquid.
  • the preferred embodiments for the solid / liquid separation and the washing as stated below under step d) apply.
  • the chromium (III) oxide obtained after step b) generally has good filtration and washing properties.
  • the wet chromium (III) oxide obtained after the Fes liquid separation is then preferably dried.
  • the optionally dried chromium (III) oxide is preferably subjected to a grinding.
  • the calcined and optionally washed and optionally dried product is still subjected to a grinding.
  • grinders of different types are suitable, such as roll mills, edge mills, pendulum mills, hammer mills, pin mills, turbo mills, ball mills or jet mills.
  • a milling dryer in which the drying and grinding are carried out in only one working step.
  • the choice of suitable grinding unit depends, inter alia, on the particular field of application for the chromium (IIi) oxide produced.
  • the mother liquors and the respective washing waters in both cases essentially contain alkali metal chromate, in particular sodium chromate or alkali metal dichromate, especially sodium dichromate.
  • the mother liquors and the respective washwaters from the preparation according to the invention of ammonium dichromate, containing steps c) and d), may additionally also contain ammonium dichromate.
  • These recyclables can be recycled back into the production process, for example, for the preparation of sodium dichromate or, most preferably, for the production of a sodium dichromate.
  • Ammoniumchromat double Sizes are used, in particular as described below.
  • mother liquors and washings which are obtained in the solid / liquid separation and washing of the ammonium dichromate and / or calcined product are again used for the preparation of sodium dichromate or an alkali metal ammonium chromate double salt, in particular sodium ammonium chromate double salt. With very particular preference they are used for the preparation of an alkali metal ammonium chromate double salt.
  • the chromium (IIl) oxide produced by the process is highly pure. It is therefore eminently suitable for metallurgical purposes such as the production of chromium metal or chromium-containing high performance alloys, in particular by reduction in the presence of aluminum metal via the aluminothermic process, and for the production of high temperature resistant materials, but it can also be used as a color pigment for pigmentary applications It also has a very low content of water-soluble salts.
  • the chromium (II) oxide obtained by the process is highly pure and in particular very sulfuric.
  • low-sulfur is understood to mean chromium (II) oxides which have a sulfur content of less than 200 ppm, preferably less than 50 ppm, very particularly preferably less than 40 ppm Chromium (III) oxides which have a sodium metal content, calculated as sodium metal, of less than 1500 ppm, preferably less than 500 ppm.
  • the advantage of the method compared to that of RU 2 258 039 C l is in particular the fact that the amount of dust is reduced and must not be driven in a circle.
  • the chromium (III) oxide produced by the process can, as a color pigment, abrasive and as a starting material for the production of high-temperature resistant materials, Chromnietal! or chromium-containing high performance alloys, especially by reduction in the presence of aluminum metal via the aluminothermic process.
  • the invention therefore relates to a process for the preparation of ammonium dichromate, comprising the steps c) thennish decomposition of a Doppelimetalf-Ammoniumchrornat double salt, in particular a sodium ammonium chromate double salt or their
  • M is Na or K, with Na being particularly preferred;
  • x is a number from 0.1 to 0.9, preferably from 0.4 to 0.7, y, for a number from 1.1 to 1.9, preferably from 1, 3 to 1, 6 and the sum of x and y is 2.
  • the alkali metal ammonium chromate double salt in particular the sodium ammonium sulfate double salt, have a molar ammonium: alkali metal, in particular ammonium: sodium ratio> 2.
  • the optimum temperature range depends, among other things, on whether the thermal decomposition is carried out, for example, in the solid state or in aqueous solution.
  • the thermal decomposition of the alkali metal ammonium chromate Doppeisalz, especially sodium ammonium chloride double salt takes place at a temperature of 75 to 190 ° C.
  • the preferred reaction time is 15 to 240 minutes.
  • the thermal decomposition according to step c) is carried out under atmospheric pressure or under reduced pressure.
  • the thermal decomposition according to step c), in particular of the sodium ammonium double chromosome takes place in the solid state, in particular at a temperature of 120 to 1 0 ° C, particularly preferably from 120 to 170 ° C.
  • the thermal decomposition of the sodium ammonium chromate double salt to ammonium dichromate and sodium dichromate or ammonium dichromate and sodium chromate in the solid state need not necessarily be completed.
  • the thermal decomposition preferably takes place until less than 98%, but more than 50%, in particular more than 75%, of the originally present monochromate has been converted from the alkali metal ammonium chromate double salt into dichromate.
  • degree of acidification can be determined to be 0%, provided that 100% of monochromate is present and 100%, provided that 100% has been converted to dichromate, the degree of acidification is preferably determined by titration.
  • the decomposition product obtained from step c) generally contains! in addition to sodium, ammonium and dichromate ions also monochromate ions. If the thermal decomposition of the alkali metal ammonium chromate double zeolite takes place at too high temperatures and / or for long reaction times, then a part of the ammonium dichromate formed can continue to react.
  • the ammonium dichromate can decompose into an X-ray amorphous product, which does not dissolve when dissolved in water. It remains as a brown, flaky, unresolved residue. However, this does not disturb the production process, which will be explained in more detail below.
  • the thermal decomposition according to step c), in particular the alkali metal ammonium chromate double salt takes place in aqueous solution at a temperature of 75 to 1 10 ° C.
  • This type of decomposition has the significant advantage over the already described thermal decomposition of the alkali metal ammonium chromate double salt in the solid state that the thermal decomposition in aqueous solution proceeds at lower temperatures and, secondly, the further thermal decomposition is inhibited to undesired by-products.
  • the thermal decomposition is operated until less than 98%, but more than 50%, in particular more than 75% of the original monochromate have converted into dichromate.
  • the decomposition product obtained from step c) can generally also contain monochromate ions in addition to sodium, ammonium and dichromate ions.
  • monochromate ions in addition to sodium, ammonium and dichromate ions.
  • chromic anhydride CrOj be added, whereby the conversion of monochromate can be influenced in dichromate.
  • the thermal decomposition of the sodium ammonium chromate double salts takes place in a solid state, it is preferable that when the resulting solid decomposition product is dissolved in water, before it can be fed to step d).
  • warm water is used, in particular at a temperature of 30 to 100 ° C. If the thermal decomposition of the sodium ammonium double chromosome takes place in an aqueous solution, then in most cases a warm aqueous solution is already present, which can be fed to step d).
  • the aqueous solution of the decomposition product is particularly preferably concentrated after step c) before it is fed to step d).
  • This is particularly preferably by evaporation.
  • the evaporation can be carried out under normal pressure, but usually it is carried out under reduced pressure.
  • the skilled person knows this for a variety of technical apparatuses in which water can be evaporated from a solution by heat and removed, so that the remaining solution has a higher concentration of dissolved ions. It should be mentioned at this point only bubbles evaporator, tube evaporator or thin film evaporator. Preference is given to Verdampferan layers with mixture preheating, used with vapor compression or multi-body evaporation systems.
  • step c) The thermal decomposition of the sodium ammonium chromate double salt according to step c) is associated with the liberation of ammonia, as illustrated by the reaction equations (7) using the example of the 1: 1 double salt.
  • the process according to the invention is particularly preferably operated in such a way that the thermal decomposition of the alkali metal -Ammoniumchrornat double salt, in particular the sodium ammonium chromate double salt released ammonia as a gas or aqueous solution wins back and used again for the preparation of Natriurn-Ammoniumchromat- double salt.
  • the liberated ammonia gas is preferably condensed in the form of an aqueous ammonia solution and then either directly as ammonia solution or optionally after renewed splitting into gaseous ammonia and water again for the preparation of the alkali metal ammonium chromate double salt, in particular sodium ammonium chromium double salt starts.
  • Step d) Ammonium dichromate is then crystallized from the decomposition product obtained from step c), preferably in the form of an aqueous solution of the decomposition product, which may have been concentrated, and the resulting solid is preferably separated from the mother liquor.
  • Crystallization in the sense of this invention is understood to mean the precipitation of a crystalline solid from a solution.
  • the crystallization of the ammonium dichromate can be carried out by evaporation crystallization, cooling crystallization or vacuum crystallization. The person skilled in the art knows a large number of crystallization apparatuses which work according to these principles.
  • ammonium dichromate is deposited from an aqueous solution of the decomposition product after step c) by cystallization, which is preferably separated from the mother liquor by solid-liquid separation and, if appropriate, also washed.
  • the warm aqueous solution of the decomposition product is preferably cooled to a temperature of from 50 to -10 ° C., in particular from 40 to -5 ° C., according to step c).
  • the solid ammonium dichromate is preferably separated from the mother liquor.
  • the skilled person knows a variety of suitable units and methods. It does not matter if the Fes liquid separation is continuous or discontinuous. It is also irrelevant whether it is carried out under pressure or under vacuum.
  • vacuum drum filters or vacuum belt filters are particularly preferred in the continuous filtration units.
  • discontinuous filtration units filter presses are particularly preferred. The preferred further use of the mother liquor and washings obtained from the solid / liquid separation has already been described above.
  • step c) If the thermal decomposition of the sodium ammonium chromate double salt in step c) leads to X-ray amorphous product which remains on dissolution of the decomposition product in water as undissolved residue, this can be filtered from the solution before the crystallization of ammonium dichromate or the evaporation of the aqueous solution the decomposition product takes place. In practice, however, this separate separation step is not necessary, since this undissolved residue can also be separated off after the crystallization of the ammonium dichromate in the context of the preferably carried out and already described above FesWlüssig separation together with the ammonium dichromate.
  • the separated insoluble residue may preferably also be fed together with the ammonium dichromate to step a) or separately to step b). He is finally converted to chromium (iII) oxide.
  • the moist ammonium dichromate obtained after the Fes liquid separation is either fed directly to the thermal decomposition according to step a) or is previously washed and / or dried.
  • the wet ammonium dichromate obtained after the solid / liquid separation is washed before it is optionally dried and then supplied to the thermal decomposition in step a).
  • washing the still adhering mother liquor can be largely displaced and so the alkali metal content of the resulting ammonium dichromate can be significantly lowered, whereby the degree of purity increases significantly.
  • the washing is preferably carried out on the same aggregate which was also used for the solid / liquid separation.
  • the wet filter cake is fed directly to the calcination, the handling of which in the dry state is much more difficult and more demanding than in the wet state. It is therefore advantageous in a technical process to dispense with the drying of the moist ammonium dichromate and to supply the moist filter cake directly to the thermal decomposition in step a).
  • the inventive method for the production of ammonium dichromate characterized in that the employed alkali metal ammonium chromate double salt is prepared by reacting NH 3, preferably in a 1 .0 to S.Ofachen, particularly preferably in a 1.4 to 4.5fachen, is preferred molar excess, based on Alkalidichromat, in particular M 2 Cr 2 0 7 , wherein M is Na or K, in particular Na, in a
  • step c) alkali metal ammonium chromate double salt
  • M is Na or, especially Na
  • x is a number from 0, 1 to 0.9, preferably from 0.4 to 0.7 y for a number from 1.1 to 1.9, preferably from 1.3 to 1.6
  • the sum of x and y is 2, characterized in that NHj is preferably in a 1 .0 to 5.0 times, more preferably in a 1.4 to 4.5 times, molar excess, based on alkali metal dichromate, in particular Na 2 Cr 2 0 7 , preferably at one temperature from 55 to 95 ° C to an aqueous solution of alkali metal dichromate, in particular Na 2 Cr 2 0 7 or Na 2 Cr 2 0 7 * 2H 2 0 admits.
  • the ammonium dichromate used is prepared by the process according to the invention comprising at least steps c) and d), as described above in its general or preferred embodiment.
  • This combination of process steps to produce high purity, low sulfur chromium (III) oxide has numerous advantages over the processes described in the prior art.
  • a significant advantage is that form as by-products sodium chromate and / or sodium dichromate and ammonium dichromate, which can be easily recycled back into the manufacturing process. Thus, no by-product is produced, which has to be removed from the process and thoroughly cleaned because it is contaminated with Cr (VI).
  • Natriumdichromai dihydrate Na 2 Cr 2 07 * 2H 2 0
  • a 2.7-fold molar excess of ammonia with respect to Natriumdichromai Na 2 Cr 2 0 7
  • the warm suspension was filtered, the filter cake washed with 99% ethanol and dried at 100 ° C to constant weight.
  • Example 3 The sodium ammonium chromate double salt described above was decomposed as a solid at 130 ° C over a period of 165 minutes.
  • the decomposition product had a degree of acidification of 88%. 50.1 g of this decomposition product were dissolved in 55 ml of water while warm. The solution was then heated to boiling and evaporated until 81.1 g of solution remained. The 81.1 g of solution had a pH of 6.2 at the boiling point and were slowly cooled to room temperature, during which time ammonium dichromate crystallized out. After about 16 hours, the ammonium dichromate crystals were filtered off from the mother liquor and washed with 15 ml of water.
  • the sodium ammonium chromate double salt described above was decomposed as a solid at 140 ° C over a period of 95 minutes.
  • the decomposition product had a degree of acidification of 81%.
  • 50.0 g of this decomposition product were dissolved in 40 ml of water at 75 ° C.
  • the solution was slowly cooled to + 8 ° C without further evaporation, during which time ammonium dichromate crystallized out.
  • the ammonium dichromate crystals were filtered off from the mother liquor and washed with 15 ml of water. After drying, 15.72 g of ammonium dichromate were obtained, which had a sodium content of 0.037 wt .-%.
  • the mother liquor obtained in the filtration had a sodium content of 86.1 g / l and an ammonium content of 31.0 g / l.
  • shee had a pH of 6.6.
  • the ammonium dichromate obtained from the above examples was decomposed slowly and gently under normal pressure in an indirectly heated oven in the temperature range of 235-260 ° C.
  • the resulting decomposition product still had a Cr (VI) content of 1.54%.
  • This decomposition product was then calcined at a temperature of 820 ° C for one hour in a directly heated oven.
  • the resulting chromium (III) oxide was leached with water, separated from the mother liquor, washed with water and separated from the washing water. Finally it was dried and ground. A low-sulfur and low-sodium chromium (III) oxide was obtained, which is suitable for a variety of applications.
  • Example 5 The decomposition product described in Example 5 was calcined at a temperature of 1250 ° C for one hour in a directly heated oven. The resulting chromium (III) oxide was leached with water, separated from the mother liquor, washed with water and separated from the wash water. Finally it was dried and ground. A low-sulfur and low-sodium chromium (II) oxide was obtained, which is suitable for metallurgical applications.
  • Example 3 of the present invention a 1: 1 double salt of the formula Na (NH) Cr0 4 * 2H 2 0 was decomposed at 130 ° C over a period of 165 minutes. 50 g of the obtained decomposition product was dissolved in 55 ml of water under heat. The solution was heated to boiling and evaporated until 78.8 g solution was left. The solution was slowly cooled to room temperature. After 16 hours, the resulting crystals were filtered off and washed with 15 ml of water. The crystals were analyzed after drying. Following this procedure (VI) and a further procedure (V2), the following results, in particular Na contents, were obtained:

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Abstract

La présente invention concerne un procédé de préparation de dichromate d'ammonium, comprenant les étapes suivantes : c) décomposition thermique d'un sel double de chromate d'ammonium-métal alcalin, notamment d'un sel double de chromate d'ammonium-sodium ou ses hydrates à une température allant jusqu'à 200°C, en particulier de 75 à 190°C avec formation de dichromate d'ammonium; et d) séparation du chromate d'ammonium du produit de décomposition obtenu en c), par cristallisation. L'invention se caractérise en ce que le sel double de chromate d'ammonium-métal alcalin correspond à la formule Mx (NH4)y CrO4 ou ses hydrates, M étant Na ou K, de préférence Na, x valant 0,1 à 0,9, de préférence de 0,4 à 0,7, y valant de 1,1 à 1,9, de préférence de 1,3 à 1,6 et la somme de x et y valant 2.
EP10787480A 2009-12-22 2010-12-08 Procédé de préparation de dichromate d'ammonium Withdrawn EP2516331A1 (fr)

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EP09180375 2009-12-22
EP10787480A EP2516331A1 (fr) 2009-12-22 2010-12-08 Procédé de préparation de dichromate d'ammonium
PCT/EP2010/069219 WO2011076574A1 (fr) 2009-12-22 2010-12-08 Procédé de préparation de dichromate d'ammonium

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AR (1) AR079534A1 (fr)
RU (1) RU2012131059A (fr)
WO (1) WO2011076574A1 (fr)
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AR079534A1 (es) 2012-02-01
US20130129604A1 (en) 2013-05-23

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