EP1135332A1 - Procede d'epuration des liqueurs d'aluminate de sodium contenant de l'oxalate de sodium - Google Patents
Procede d'epuration des liqueurs d'aluminate de sodium contenant de l'oxalate de sodiumInfo
- Publication number
- EP1135332A1 EP1135332A1 EP99972192A EP99972192A EP1135332A1 EP 1135332 A1 EP1135332 A1 EP 1135332A1 EP 99972192 A EP99972192 A EP 99972192A EP 99972192 A EP99972192 A EP 99972192A EP 1135332 A1 EP1135332 A1 EP 1135332A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- series
- decomposition
- liquor
- oxalate
- suspension
- 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.)
- Withdrawn
Links
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
-
- 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
- C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
- C01F7/47—Purification of aluminium oxide, aluminium hydroxide or aluminates of aluminates, e.g. removal of compounds of Si, Fe, Ga or of organic compounds from Bayer process liquors
- C01F7/473—Removal of organic compounds, e.g. sodium oxalate
Definitions
- the invention relates to a process for purifying sodium aluminate liquors resulting from the alkaline attack of bauxites according to the Bayer process and containing sodium oxalate.
- the Bayer process makes it possible to produce alumina from bauxite ore, in particular alumina intended to be transformed into aluminum by igneous electrolysis.
- the bauxite ore is treated hot with an aqueous solution of sodium hydroxide, at an appropriate concentration, thus causing the solubilization of the alumina and obtaining a suspension containing supersaturated liquor sodium aluminate and insoluble residues.
- the supersaturated sodium aluminate liquor also called Bayer liquor
- aluminum trihydroxide alumina trihydrate
- hydroxide sodium hydroxide
- caustic soda aluminum trihydroxide
- the alumina-depleted sodium aluminate liquor is then recycled to the attack stage after being concentrated in sodium hydroxide, or caustic soda, to restore the concentration suitable for attacking the ore.
- the supersaturated sodium aluminate liquor resulting from the attack gradually takes charge of organic compounds produced by the more or less complete degradation of the organic materials contained in these ores. These organic compounds, degraded in the form of organic sodium salts and mainly in the form of sodium oxalate, prove to be very troublesome.
- the oxalates quickly reach their critical concentration threshold and precipitate in the form of fine needles on the aluminum hydroxide primer.
- These fine needles of sodium oxalate then act as true germs and cause an uncontrolled and undesirable increase in the number of fine particles of alumina hydrate formed during the decomposition of sodium aluminate.
- the precipitation of sodium oxalate affects the quality of the alumina trihydrate produced and leads in particular to large variations in the particle size of the alumina produced as well as to embrittlement of the grains which constitute major drawbacks even prohibitive for the use of this alumina in the production of aluminum by electrolysis.
- a destabilization of the concentration is carried out on at least a fraction of the sodium aluminate liquor resulting from decomposition, but already supersaturated with sodium oxalate, to precipitate and specifically separate the sodium oxalate from the liquor then desaturated.
- the organic matter content of bauxite is characterized by the quantity of oxalate ions generated during its attack, expressed in terms of mass of oxalic carbon generated per tonne of alumina produced.
- the field targeted by the present invention relates to the treatment of bauxites whose oxalic carbon content is less than 400 grams per tonne of alumina produced.
- the process developed by the applicant not only makes it possible to treat bauxites with low organic matter content under satisfactory economic conditions, but it also makes it possible to increase the amount of alumina produced. It consists in treating a relatively small proportion of the de-concentrated depleted aluminate liquor (typically 10 to 30%), by making it follow a circuit passing through a series of low temperature decomposition tanks, the oxalate precipitating on part of the hydrate which is then recovered after washing, in an amount slightly greater than the amount withdrawn.
- the deoxalation treatment is carried out on an aliquot of the decomposed aluminate liquor, preferably representing 10 to 30% thereof, taken before reconcentration.
- the reconcentration is generally carried out by heating and evaporation, it is advantageous to take the sample before this reheating, since there are fewer calories to be evacuated for cooling in step b).
- the liquor is at the end of decomposition and is at a temperature typically between 65 ° C and 50 ° C. Its cooling is carried out to a temperature between 40 ° C and 60 ° C, preferably at 40 ° C. Cooling to a lower temperature is possible but seems unnecessarily expensive. The deoxalation is not further and in this case it would be necessary to introduce more powerful cooling groups, the investment of which does not seem justified in the light of the expected gain in trihydrate production.
- the cooled aliquot is mixed in a priming tank with a destabilizing agent which comprises alumina trihydrate, originating in particular from the precipitated trihydrate and oxalate cake resulting from the filtration of the overflow of the last decomposer of the mini-series. cold described in d).
- a destabilizing agent which comprises alumina trihydrate, originating in particular from the precipitated trihydrate and oxalate cake resulting from the filtration of the overflow of the last decomposer of the mini-series. cold described in d).
- the suspension thus formed is mixed with alumina trihydrate taken at the end of the decomposition chain, that is to say with particle size characteristics corresponding to those targeted for the final product. In practice, it is advantageous to take the suspension from the underflow of the last decomposer.
- the mixture then passes through a series of decomposers, which we call "cold mini-series" of decomposition, in which the aluminate liquor continues to decompose.
- the number of bins in this cold mini-series depends on the quantity of additional trihydrate that one wants to obtain. This quantity is however limited since we are here in the presence of an already highly depleted liquor.
- the Applicant has noted, however, that under these particular decomposition conditions, the precipitated oxalate does not influence the alumina productivity: although oxalate needles are deposited on the hydrate grains, this has had no effect on the surface active primer.
- the suspension is divided into two parts at the outlet of the last decomposing tank, in order firstly to maintain in the cold mini-series a dry matter content of between 400 and 800 grams per liter of suspension and on the other hand to evacuate the hydrargiliite introduced and obtained during the decomposition of the cold miniseries.
- the overflow and the underflow for example, the regularly stirred suspension from the last tank is removed.
- the overflow of the last decomposer is filtered.
- the filtrate is returned to the decomposed aluminate liquor from the Bayer circuit, before concentration to form the attack liquor.
- the cake is a mixture of precipitated hydrate and oxalate particles which is reintroduced as a decomposition initiator at the start of the cold miniseries.
- Precipitation of the oxalate in the form of fine needles causes filtration problems. These difficulties are characterized by resistance specific of the filter cake, expressed in m / kg. Thus, during the priming filtration of step e), a specific resistance of the cake is observed of the order of 1.2 ⁇ 10.0 m / kg.
- the surfactant is an organic compound chosen from oleic and stearic acids, lauryl sulfates, alkylaminobutyric acids, sulfonates and polymers having an alkyl chain of at least ten atoms and comprising at least one of the following functions: carboxyl, ester (preferably sulfate esters), phenol, acrylate (preferably copolymers of methacrylic acid and stearyl methacr ⁇ late), acrylamide and hydroxamate.
- the "Crystal Growth Modifier” from the company NALCO CHEMICALS, product intended to promote the enlargement of the trihydrate grains during decomposition, described in patent US Pat. No. 4,737,352, greatly improves the filterability of the rich suspension in oxalates at the level of the primer filter when it is introduced at any point in the cold miniseries.
- the specific resistance of the filter cake was divided by 4 thanks to the addition of CGM.
- the improvement in the filterability of the suspension rich in oxalates makes it possible to significantly reduce the size of installations which implement the method according to the invention, in particular the size of the primer filtration device.
- the hydrate from the filtration of the underflow of the last decomposer is washed, preferably by performing a simple displacement of the impregnation in a band filter, with cold water, so as to reduce the soda content retained in the trihydrate.
- the displaced impregnation is taken back to the Bayer circuit, added to the decomposed aluminate liquor before reconcentration.
- the aqueous suspension obtained after cold washing is then washed with hot water in order to dissolve the oxalate precipitated on the trihydrate grains.
- the washing water is partially removed, carrying with it the dissolved oxalate, the other part being introduced at the start of the mini-series of decomposition, so as to increase the concentration of oxalate in the aluminate liquor .
- the trihydrate, once washed, is recovered, for example by scraping on a drum filter and added to the production trihydrate, since its particle size characteristics have not varied significantly. Thanks to the cold mini-series, an amount of trihydrate is thus obtained which is greater than the amount initially taken.
- This bauxite generates 220 grams of oxalic carbon per tonne of alumina produced.
- this aluminate liquor is characterized by a ratio of oxalic carbon to caustic soda, expressed by Cox (in g / 1) / Na20 cstq (in g / 1). Without a deoxalation device, this ratio can reach a critical value, from which sodium oxalate can precipitate at the same time as the hydrate during decomposition.
- This threshold is between 0.2 and 0.5% in the temperature range of decomposition. Thanks to the cold mini-series according to the invention described below, this ratio stabilizes at a significantly lower value, for example less than 0.15% if the precipitation threshold is 0.2%.
- the resulting decomposed liquor Ll whose ratio Rp of the concentrations AI203 sol (in g / 1) / Na20 cstq (in g / 1) is between 0.5 and 0.7 and the concentration of caustic soda is preferably between 130 and 165 g Na20 / I, is separated into two fractions: a main fraction L3 and a minor fraction L4 which is intended to undergo deoxalation according to the method of the invention.
- the size of the minor fraction L4 sampled is a function of the quantity of oxalate to be eliminated in each cycle so as to prevent the progressive enrichment of the Bayer liquor with sodium oxalate and therefore any risk of untimely precipitation of this oxalate. on alumina trihydrate grains during decomposition.
- the fraction L4 represents 20% of the total decomposed liquor L1.
- the minor fraction L4 of the liquor is cooled at C to 40 ° C, so that w the liquor is very close to its critical concentration threshold for sodium oxalate. It is then sent to a first stirred reactor D1, called a priming tank, where it is brought into contact with a recycled S7 suspension containing alumina trihydrate and precipitated sodium oxalate, at a rate of 400 to 800 grams. dry matter per liter of suspension.
- the suspension S1 thus formed is transferred to another stirred reactor where it is brought into contact with a fraction S8 of the suspension withdrawn under the last decomposer of the Bayer circuit to maintain the dry matter content.
- the suspension thus obtained passes through a series of tanks (D2 ... Dn), called the cold mini-series of decomposition, which aims to allow the further decomposition of the aluminate liquor.
- the suspension On leaving the last decomposing tank Dn, the suspension is divided into two parts S3 and S4.
- the fraction S3 of the suspension is filtered on a disc filter F (primer filter), the cake S7 obtained being recycled in the primer tank.
- the filtrate L6 is mixed with the fraction L3 not withdrawn from the decomposed liquor L1.
- the fraction S4 is placed in a band filter and washed with cold water L'8 (G and I), so that, by displacement of the impregnation, the filtrate L12 remains highly concentrated in soda which allows reintroduce it into the major fraction L3 of the decomposed liquor Ll.
- the insoluble residue S'4 which is less concentrated in sodium hydroxide following this washing with cold water, is subjected to washing with hot water H, preferably carried out by stirring.
- the wash water has a pH> 6. It consists of an external supply of pure L8 water.
- the wash-down temperature should not be less than 40 ° C to ensure sufficiently complete and rapid dissolution of the oxalate and the co-precipitated organic materials.
- the wash water L9 is partially discharged LU, thus carrying with it the dissolved oxalate.
- the other part L13 is introduced at the start of the mini-series of decomposition, in tank D2 and / or, optionally, in primer tank D1, so as to increase the concentration of oxalate in the aluminate liquor.
- the hydrate obtained S10 can be recovered in an amount greater than that of the hydrate introduced S8 in the cold mini-series.
- CGM crystal growth modifier
- this process allows the production of an increased amount of trihydrate.
- the primer recycled not only is the primer recycled, but it is "over-regenerated” in the form of a trihydrate similar to that resulting from decomposition and therefore perfectly recoverable.
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR9814507A FR2785895B1 (fr) | 1998-11-16 | 1998-11-16 | Procede d'epuration des liqueurs d'aluminate de sodium contenant de l'oxalate de sodium permettant d'augmenter la quantite d'hydrate d'alumine produit |
FR9814507 | 1998-11-16 | ||
PCT/FR1999/002743 WO2000029328A1 (fr) | 1998-11-16 | 1999-11-09 | Procede d'epuration des liqueurs d'aluminate de sodium contenant de l'oxalate de sodium |
Publications (1)
Publication Number | Publication Date |
---|---|
EP1135332A1 true EP1135332A1 (fr) | 2001-09-26 |
Family
ID=9532886
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99972192A Withdrawn EP1135332A1 (fr) | 1998-11-16 | 1999-11-09 | Procede d'epuration des liqueurs d'aluminate de sodium contenant de l'oxalate de sodium |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP1135332A1 (fr) |
AU (1) | AU760072B2 (fr) |
BR (1) | BR9915405A (fr) |
CA (1) | CA2350686A1 (fr) |
FR (1) | FR2785895B1 (fr) |
WO (1) | WO2000029328A1 (fr) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN1730417A (zh) * | 2005-07-18 | 2006-02-08 | 贵阳铝镁设计研究院 | 粗赤泥过滤洗涤新方法 |
KR20200123152A (ko) * | 2018-02-23 | 2020-10-28 | 리오 틴토 알칸 인터내셔널 리미티드 | 바이어 공정 |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4263261A (en) * | 1978-12-21 | 1981-04-21 | Sumitomo Aluminium Smelting Company, Limited | Method for the removal of impurities from sodium aluminate solution |
AU613758B2 (en) * | 1988-06-03 | 1991-08-08 | Vereinigte Aluminium-Werke Aktiengesellschaft | Method for removing sodium oxalate from caustic aluminate liquors |
FR2686872B1 (fr) * | 1992-02-05 | 1994-06-03 | Pechiney Aluminium | Procede d'elimination de l'oxalate de sodium des solutions d'aluminate de sodium du cycle bayer. |
FR2736908B1 (fr) * | 1995-07-20 | 1997-08-29 | Pechiney Aluminium | Procede d'epuration des solutions d'aluminate de sodium contenant de l'oxalate de sodium |
-
1998
- 1998-11-16 FR FR9814507A patent/FR2785895B1/fr not_active Expired - Fee Related
-
1999
- 1999-11-09 CA CA002350686A patent/CA2350686A1/fr not_active Abandoned
- 1999-11-09 BR BR9915405-6A patent/BR9915405A/pt not_active Application Discontinuation
- 1999-11-09 EP EP99972192A patent/EP1135332A1/fr not_active Withdrawn
- 1999-11-09 WO PCT/FR1999/002743 patent/WO2000029328A1/fr active IP Right Grant
- 1999-11-09 AU AU11648/00A patent/AU760072B2/en not_active Ceased
Non-Patent Citations (1)
Title |
---|
See references of WO0029328A1 * |
Also Published As
Publication number | Publication date |
---|---|
BR9915405A (pt) | 2001-07-24 |
AU760072B2 (en) | 2003-05-08 |
AU1164800A (en) | 2000-06-05 |
FR2785895B1 (fr) | 2001-01-19 |
WO2000029328A1 (fr) | 2000-05-25 |
CA2350686A1 (fr) | 2000-05-25 |
FR2785895A1 (fr) | 2000-05-19 |
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