WO2005035445A2 - Procede pour reduire l'encrassement des echangeurs thermiques d'un circuit bayer - Google Patents
Procede pour reduire l'encrassement des echangeurs thermiques d'un circuit bayer Download PDFInfo
- Publication number
- WO2005035445A2 WO2005035445A2 PCT/FR2004/002538 FR2004002538W WO2005035445A2 WO 2005035445 A2 WO2005035445 A2 WO 2005035445A2 FR 2004002538 W FR2004002538 W FR 2004002538W WO 2005035445 A2 WO2005035445 A2 WO 2005035445A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- liquor
- calcium
- based compound
- sodium aluminate
- bauxite
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F7/00—Compounds of aluminium
- C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
- C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
- C01F7/06—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom by treating aluminous minerals or waste-like raw materials with alkali hydroxide, e.g. leaching of bauxite according to the Bayer process
- C01F7/0606—Making-up the alkali hydroxide solution from recycled spent liquor
Definitions
- the present invention relates to a method for reducing the fouling of the heat exchangers of the Bayer chain drive circuit. It relates more particularly to the reduction of the volume of siliceous deposits in the heat exchangers on the aluminate liquor before the latter is directed towards the attack of bauxite: evaporators and other heat exchangers treating the liquor alone, in particular before mixing with bauxite.
- the exchangers which allow the suspension resulting from mixing the ground bauxite with the aluminate liquor to heat up to the attack temperature (typically dry matter content greater than 50 g / l) are therefore not affected.
- the Bayer process is a well known process for the production of aluminum trihydrate. It comprises a stage of grinding - generally wet - of bauxite, possibly a stage of desilication, then a stage of attack of said bauxite by a sodium liquor with high caustic concentration, typically a sodium aluminate liquor, which we thereafter will be called attack liquor.
- attack liquor a sodium liquor with high caustic concentration
- the attack leads to the formation of a suspension which, after dilution, is decanted and filtered to separate the insoluble residues from the sodium aluminate liquor.
- the extraction yields of solubilizable alumina in the attack liquor expressed as a proportion of the alumina trihydrate contained in the ore, can exceed 95%, if the unfavorable influence of certain impurities, in particular silica, is indeed control.
- Silica can appear in bauxite in several mineralogical forms that are not equally soluble in the attack liquor. Some mineralogical forms, including kaolin (AI203, 2 Si02, 2 H20) is the most widespread species, dissolve during the attack of bauxite. The part of the silica present in bauxite in one of these forms is commonly called "reactive silica". The reactive silica is therefore dissolved in the attack liquor and the content of dissolved silica reaches a level of supersaturation such that the silica re-precipitates in the form of sparingly soluble sodium silico-aluminate. A good control of the precipitation of silica is therefore essential if one wants to produce alumina trihydrate free of siliceous impurities.
- kaolin AI203, 2 Si02, 2 H20
- the current desiccation treatments are primarily intended to prevent pollution of the trihydrate during decomposition. Most of these treatments, described for example in applications US 3 413 087 (Reynolds), US 4426363 (Sumitomo), US 5 1 18484 and US 6 086 834 (Alcan), EP 0203873, EP 0739 309 and EP 0765290 (Aluminum Pechiney), are carried out on the liquor before and / or after attack. They result in the formation of compounds, of the sodium silico-aluminate type, called DSP ("dessilication products"), which are then eliminated with the insoluble residues of the attack (red mud).
- DSP desilication products
- Patent application WO96 / 06043 (Comalco), more particularly dealing with the double attack of a bauxite rich in boehmite, incidentally indicates that, to reduce the risks of scaling, lime can be introduced into the liquor broken down into upstream of the heat exchangers intended to heat the liquor before the bohemian attack.
- the applicant therefore sought a complementary solution which makes it possible to further lower the level of the silica concentration in the liquor ⁇ v ⁇ nt attack, at least at the level of the heat exchangers which process the liquor in the attack circuit.
- the object of the invention is a Bayer process in which a calcium-based compound belonging to the group of tricalcium aluminates is introduced into the aluminate liquor, the introduction of the said calcium-based compound being carried out in the said liquor aluminate between its exit from the decomposition chain and its mixture with the crushed bauxite, upstream of a heat exchanger intended to increase the temperature of said aluminate liquor.
- calcium up to 10 atomic%) or aluminum (up to 20 atomic%) with another metal: calcium can be replaced by iron (ferrous ion), manganese or magnesium, aluminum can be replaced by chromium or iron (ferric ion);
- the point (s) of introduction of said calcium-based compound into the aluminate liquor is (are) located between the outlet of the chain of decomposition - in this place, the liquor, before being concentrated by evaporation, is called "decomposed liquor" - and the mixture with bauxite - upstream of the entry into the first attack tank.
- the addition must be made upstream or at the entrance of this exchanger on the whole or on an aliquot having as high a proportion as possible of the flow of aluminate having to pass through said exchanger.
- heat exchangers acting on the aluminate liquor before it is directed towards the attack of bauxite are either evaporators used to increase the caustic concentration of the liquor decomposed and recycle it as attack liquor, i.e. heat exchangers which treat the liquor alone before mixing with bauxite, in particular to reheat it before attack.
- heat exchangers which treat the liquor alone before mixing with bauxite, in particular to reheat it before attack.
- Any other type of exchanger for example an exchanger used to cool the aluminate liquor alone, could also be concerned with the invention.
- the addition of compound is preferably carried out in a single location, for example upstream of the heat exchange device located most upstream of the part of the circuit between the outlet of the decomposition and the mixture with bauxite.
- the installations include series of exchangers and it is advantageous to locate the point of introduction of the calcium-based compound upstream of this series of exchangers, that is to say either upstream of the chain. evaporation, either upstream of the liquor preheating chain, if it exists. When it is planned to preheat the liquor alone to a temperature close to the attack temperature, it may prove advantageous to add only to the entry of this preheating chain.
- Said calcium-based compound is introduced into the decomposed liquor or the attack liquor in a proportion preferably comprised between 0.1 g C ⁇ O / liter of aluminate and 50 g CaO / liter of aluminate.
- a lower proportion would not reduce the risk of scaling.
- the upper limit is indicated mainly for economic reasons.
- Said calcium-based compound reacts with part of the silica contained in the liquor and the latter is transformed into a hydrogrenate with a higher silica content.
- a hydrogrenate introduced into the liquor with a k close to 0 becomes a hydrogrenate having a k close to 1.
- this addition leads to an increase in the overall consumption of lime in the Bayer circuit since the solid products of the reaction, which are in the attack liquor, are quickly mixed with bauxite and are discharged with the sludge. red.
- the hydrogrenates formed at safety filtration through which the supersaturated liquor passes before being directed to the decomposition chain. At this stage, the liquor has less than 200 mg / l of solid particles which are difficult to filter.
- lime or tricalcium aluminate is poured into the supersaturated liquor upstream of these filters. The adjuvant is transformed into a hydrogrenate which is gradually enriched with silica.
- the effect of the reaction of said calcium-based compound with part of the silica contained in the liquor has the consequence of reducing the equilibrium content of the dissolved silica at the level of the exchanger.
- the rate of scaling is substantially proportional to the square of the supersaturation in silica, that is to say the difference between the effective concentration of dissolved silica and the concentration at equilibrium.
- the speed of scaling is all the more important the higher the temperature prevailing within the liquor. The effect of the addition according to the invention of said calcium-based compound will therefore be more effective on the exchangers operating at high temperature.
- the heat exchanger can be an evaporation device making it possible to concentrate the liquor to transform it into attack liquor.
- the first example given below describes a Bayer process of European type intended to attack a bauxite with diaspore where the caustic concentration of the liquor passes by evaporation typically from 160 g Na20 / liter of aluminate to 240 g Na20 / liter of aluminate in evaporators operating at 145 ° C - 150 ° C.
- the heat exchanger can also be a preheating device, which allows the liquor to be brought to the appropriate temperature before attack, which varies according to the type of bauxite.
- the second example given below describes a Bayer process of the American type intended to attack a bauxite with trihydrates where the liquor is heated separately in exchangers.
- the hydrogrenates which come from the safety filtration cake are used.
- Safety filtration is carried out on the overflow of the decanters, that is to say on the supersaturated aluminate liquor which is directed towards the decomposition chain.
- Lime or tricalcium aluminate is commonly used in this safety filtration as a filter aid. The latter, facilitating the filterability of the residual sludge present on the overflow of the settling tanks, is found in the form of a hydrogenate with little silica content in the filter cake. Instead of discharging said cake with the sludge, it is advantageous to recycle it by introducing it into the aluminate liquor upstream of an exchanger.
- the aim is for the liquor intended to pass through said exchanger has a dry matter content of less than 100 g / l. More preferably still, for more security, one seeks not to exceed 3g / l.
- FIG. 1 schematically illustrates a method of treatment of bauxite in the Bayer cycle locating the preferred points for the introduction according to the invention of said calcium-based compound.
- FIG. 2 schematically illustrates a process for treating diaspore bauxite in the Bayer cycle in which the introduction, according to a preferred embodiment of the invention, of the safety filtration cake is carried out at the level of an evaporator.
- FIG. 3 schematically illustrates a method of bauxite treatment in the Bayer cycle in which the introduction, according to a preferred form of the invention, of the safety filtration cake is carried out in the preheating chain of the attack liquor.
- FIG. 1 schematically illustrates a typical Bayer cycle in which the bauxite 10 is ground by wet grinding (B), here in the presence of an aliquot L2 of the attack liquor L0.
- An L1 aliquot which accounts for most of the L0 attack liquor, typically more than 80%, is not directed to the wet grinding of bauxite.
- case 1 this aliquot is heated alone (L'1) in a preheating chain P "l.
- the aliquot thus preheated (L'10) is then mixed with the suspension S'1 resulting from wet grinding of bauxite and directed towards the attack chain A.
- case 2 this aliquot is added (L “l) to the suspension S" after the wet grinding and therefore very rich in dry matter - that is to say comprising a large number of solid particles - to obtain a suspension S "10 less viscous which is preheated in a chain P" 1.
- the suspension thus preheated (S "100) is introduced into the attack chain A.
- the attack is usually done under pressure.
- the attack chain then takes the form of a series of autoclaves in which the suspension must circulate.
- the suspension S2 is directed to a liquid / solid separation device (C), typically a decanter in which the insoluble residues are separated by gravitation from the liquor: the insoluble residues are removed in the form of red mud while the overflow L3, still charged with a few particles, is subjected to filtration F, known as "red filtration” or "safety filtration”.
- the filtrate L4 is the supersaturated aluminate liquor which is directed towards the decomposition chain D to precipitate the alumina trihydrate 30.
- the depleted liquor 15 is concentrated by evaporation (E ) to be redirected to the attack (attack liquor L0).
- a calcium-based compound belonging to the group grouping together lime and tricalcium aluminates in the depleted liquor or in the attack liquor, preferably at the point of introduction 11, that is to say that is to say in the depleted liquor 15, before it is concentrated by evaporation to be transformed into attack liquor or even at the point of introduction IV into the aliquot L'1 of the attack liquor, when it must be preheated alone (P'1).
- Example 1 deals with the recycling of the safety filter cake upstream of evaporation.
- FIG. 2 schematically illustrates a process for treating diaspore bauxite in the Bayer cycle.
- the various elements involved in the Bayer cycle are repeated with the same references as in FIG. 1.
- the suspension S "10 which results from the mixture of the main aliquot L is preheated before attack (A).
- the attack, intended to dissolve the diaspore (alumina monohydrate) contained in the bauxite is carried out at high temperature (257 ° C) in an autoclave with a liquor with a typical caustic concentration of 240 g Na20 / liter.
- the decomposed .liqueur L5 has only a caustic concentration of 160 g Na20 / liter and must be concentrated by evaporation to find the attack concentration (240 g Na20 / liter).
- the evaporator chain (E) used for this purpose operates at a temperature between 145 and 150 ° C.
- Tricalcium aluminate hexahydrate is used as filter aid 100 to safety filtration F.
- the supersaturated liquor indeed comes from the overflow of the decanters and still contains a certain amount of solid particles. These generally prove to be very sticky and, in order not to clog the screen of the filters, a filter aid is added which modifies the physicochemical behavior of these fine particles.
- Lime or tricalcium aluminate, in particular tricalcium hexahydrate is generally used.
- Safety filtration includes several filters operating under pressure in parallel, one or more of them being removed from the circuit for removal of the filter cake and cleaning.
- a particle of filter aid remains for approximately 4 hours in contact with the liquor oversaturated and becomes a hydrogrenate which is gradually enriched with silica.
- the filter cake 111 intended until the present invention to be removed with the insoluble residues, is recovered and introduced upstream of the evaporation chain E.
- the liquor has a caustic concentration of
- R _ concentration of dissolved alumina g A12O3 / l.
- p concentration of caustic soda g Na 2 0 / l
- % ctq expresses the content of dissolved silica by the concentration ratio of dissolved silica ( g SiO2 / l) 1 ⁇ chronological_ -, _ ⁇ resort,.,, •, - -: -_ -: / T ⁇ ,, x, ⁇ l00 - ⁇ 0.700% ctq, i.e. a drop in caustic soda concentration (g Na2O / l)
- the attack (A) is carried out at 257 ° C in an autoclave.
- the substitution of silica increases to a content of 8% by mass. This corresponds to an additional capture of silica by hydrogrenate of 1.25 kg Si02 / t AI203.
- the silica captured by the hydrogrenate is not used for the formation of DSPs, which translates into a gain on soda consumption of 0.86 kg Na20 / 1 AI203.
- the suspension S2 is cooled and directed to a decanter under atmospheric pressure (C).
- the insoluble residues are removed in the form of red mud 20 while the overflow L3, still charged with a few particles, is subjected to safety filtration F.
- the saturation index Rp of the supersaturated liquor is equal to 1.22.
- Tricalcium aluminate hexahydrate 100 is introduced upstream of the filter at a rate of 0.95 g CaO per liter of liquor.
- the filter cake 111 thus formed is recycled in the form of sludge at 1000 g / l in dry matter, directed towards the point of introduction upstream of the evaporation chain (E).
- Example 2 deals with the recycling of the safety filter cake upstream of the preheating chain.
- the suspension S'I resulting from the wet grinding of bauxite 310 in the presence of an aliquot L2 of the attack liquor L0 is subjected to a predessilication treatment G before being injected (S'10) into the attack chain A.
- the main aliquot L'1 of the attack liquor L0 is preheated individually in the preheating chain P'1.
- the 11V calcium-based compound is, as in the previous example, the cake of the safety filtration F. It is introduced upstream of the preheating chain (P'1) of the liquor.
- Tricalcium aluminate hexahydrate is used as filter aid 100 for safety filtration F.
- the filter cake ll l ', intended up to the present invention to be removed with the insoluble residues, is recovered and introduced upstream of the preheating chain P'1.
- the liquor has a caustic concentration of 155 g / L, a silica content (expressed as a percentage of caustic soda) equal to 0.583% ctq and a saturation index Rp equal to 0.70 .
- Preheating P'1 is carried out at 220 ° C. At this temperature, the substitution of silica goes from 0.2% by mass to 6% by mass.
- the recycling of the filter cake upstream of the preheating chain results in a drop in the level of silica in the liquor from 0.583% ctq to 0.543% ctq, ie a decrease of 0.04% ctq.
- the square of the silica supersaturation is then divided by 1.45, which results in a reduction in the rate of fouling by siliceous deposits (proportional to the square of the silica supersaturation).
- the advantage of introducing a hydrogrenate is more significant than in the case of evaporators, operating at a lower temperature.
- the reaction (A) is carried out at 253 ° C in an autoclave.
- the substitution of silica increases to a content of 8% by mass. This corresponds to an additional capture of silica by the hydrogrenate of 0.24 kg Si02 / 1 AI203.
- the silica captured by the hydrogrenate is not used for the formation of DSPs, which results in a gain on the soda consumption of 0.16 kg Na2O / t AI2O3.
- the suspension S2 is cooled and directed to a decanter under atmospheric pressure (C).
- the insoluble residues are removed in the form of red mud 20 while the overflow L3, still charged with a few particles, is subjected to safety filtration F.
- the saturation index Rp of the supersaturated liquor is equal to 1.22.
- Tricalcium aluminate hexahydrate 100 is introduced upstream of the filter at a rate of 0.46 g CaO per liter of liquor.
- the 11 V filter cake thus formed is recycled in the form of sludge at 1000 g / l in dry matter, directed to the point of introduction upstream of the preheating chain (P'1).
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- General Life Sciences & Earth Sciences (AREA)
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- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
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Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2004280272A AU2004280272B2 (en) | 2003-10-10 | 2004-10-08 | Method for reducing fouling of heat exchangers in a Bayer circuit |
BRPI0415197-6A BRPI0415197A (pt) | 2003-10-10 | 2004-10-08 | processo para reduzir a obstrução dos trocadores térmicos de um circuito bayer |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR0311909A FR2860782B1 (fr) | 2003-10-10 | 2003-10-10 | Procede pour reduire l'encrassement des echangeurs thermiques d'un circuit bayer |
FR0311909 | 2003-10-10 |
Publications (2)
Publication Number | Publication Date |
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WO2005035445A2 true WO2005035445A2 (fr) | 2005-04-21 |
WO2005035445A3 WO2005035445A3 (fr) | 2006-06-22 |
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Family Applications (1)
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PCT/FR2004/002538 WO2005035445A2 (fr) | 2003-10-10 | 2004-10-08 | Procede pour reduire l'encrassement des echangeurs thermiques d'un circuit bayer |
Country Status (6)
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CN (1) | CN1960945A (fr) |
AU (1) | AU2004280272B2 (fr) |
BR (1) | BRPI0415197A (fr) |
FR (1) | FR2860782B1 (fr) |
OA (1) | OA13269A (fr) |
WO (1) | WO2005035445A2 (fr) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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FR2934852B1 (fr) * | 2008-08-06 | 2011-06-24 | Alcan Int Ltd | Perfectionnement au procede bayer de production de trihydrate d'alumine, ledit procede comprenant une etape dans laquelle la liqueur sursaturee est filtree a haute temperature avant decomposition |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3499793A (en) * | 1966-02-07 | 1970-03-10 | Ugine Kuhlmann | Process for descaling devices used in concentrating sodium aluminate solutions |
WO1992003381A1 (fr) * | 1990-08-17 | 1992-03-05 | Alcan International Limited | Desiliciage de solutions obtenues par procede bayer |
EP0555163A1 (fr) * | 1992-02-05 | 1993-08-11 | Aluminium Pechiney | Procédé d'élimination de l'oxalate de sodium des solutions d'aluminate de sodium du cycle bayer |
WO1996006043A1 (fr) * | 1994-08-23 | 1996-02-29 | Comalco Aluminium Limited | Procede ameliore concernant l'extraction d'alumine a partir de la bauxite |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH0975498A (ja) * | 1995-09-07 | 1997-03-25 | Nishizawa:Kk | スキー |
-
2003
- 2003-10-10 FR FR0311909A patent/FR2860782B1/fr not_active Expired - Fee Related
-
2004
- 2004-10-08 AU AU2004280272A patent/AU2004280272B2/en not_active Ceased
- 2004-10-08 BR BRPI0415197-6A patent/BRPI0415197A/pt not_active IP Right Cessation
- 2004-10-08 OA OA1200600117A patent/OA13269A/fr unknown
- 2004-10-08 CN CNA200480033571XA patent/CN1960945A/zh active Pending
- 2004-10-08 WO PCT/FR2004/002538 patent/WO2005035445A2/fr active Application Filing
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3499793A (en) * | 1966-02-07 | 1970-03-10 | Ugine Kuhlmann | Process for descaling devices used in concentrating sodium aluminate solutions |
WO1992003381A1 (fr) * | 1990-08-17 | 1992-03-05 | Alcan International Limited | Desiliciage de solutions obtenues par procede bayer |
EP0555163A1 (fr) * | 1992-02-05 | 1993-08-11 | Aluminium Pechiney | Procédé d'élimination de l'oxalate de sodium des solutions d'aluminate de sodium du cycle bayer |
WO1996006043A1 (fr) * | 1994-08-23 | 1996-02-29 | Comalco Aluminium Limited | Procede ameliore concernant l'extraction d'alumine a partir de la bauxite |
Non-Patent Citations (2)
Title |
---|
BARNES M C ET AL: "THE KINETICS OF DESILICATION OF SYNTHETIC SPENT BAYER LIQUOR SEEDEDWITH PURE SODALITE, PURE CANCRINITE AND THEIR DIMORPHIC PHASE MIXTURES" LIGHT METALS 1999. PROCEEDINGS OF THE TECHNICAL SESSIONS PRESENTED BY THE TMS ALUMINUM COMMITTEE AT HTE 128TH. TMS ANNUAL MEETING, SAN DIEGO, CA FEB. 28 - MARCH 4, 1999, PROCEEDINGS OF THE TMS ANNUAL MEETING, WARRENDALE, PA : TMS, US, vol. MEETING 128, 28 février 1999 (1999-02-28), pages 121-129, XP000895483 ISBN: 0-87339-425-9 * |
DATABASE CA [Online] CHEMICAL ABSTRACTS SERVICE, COLUMBUS, OHIO, US; SHINOHARA, YUKIO ET AL: "Caustification of Bayer solution" XP002285556 extrait de STN Database accession no. 82:61381 & JP 49 075498 A2 (MITSUI MINING AND SMELTING CO., LTD.) 22 juillet 1974 (1974-07-22) * |
Also Published As
Publication number | Publication date |
---|---|
AU2004280272A1 (en) | 2005-04-21 |
AU2004280272B2 (en) | 2009-08-06 |
CN1960945A (zh) | 2007-05-09 |
WO2005035445A3 (fr) | 2006-06-22 |
FR2860782B1 (fr) | 2006-09-29 |
OA13269A (fr) | 2007-01-31 |
BRPI0415197A (pt) | 2006-12-05 |
FR2860782A1 (fr) | 2005-04-15 |
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