EP0880467A1 - Traitement des boues rouges - Google Patents

Traitement des boues rouges

Info

Publication number
EP0880467A1
EP0880467A1 EP97902107A EP97902107A EP0880467A1 EP 0880467 A1 EP0880467 A1 EP 0880467A1 EP 97902107 A EP97902107 A EP 97902107A EP 97902107 A EP97902107 A EP 97902107A EP 0880467 A1 EP0880467 A1 EP 0880467A1
Authority
EP
European Patent Office
Prior art keywords
dsp
red mud
soda
alumina
alumina values
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Withdrawn
Application number
EP97902107A
Other languages
German (de)
English (en)
Other versions
EP0880467A4 (fr
Inventor
Tony Picaro
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.)
Queensland Alumina Ltd
Original Assignee
Queensland Alumina Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Queensland Alumina Ltd filed Critical Queensland Alumina Ltd
Publication of EP0880467A1 publication Critical patent/EP0880467A1/fr
Publication of EP0880467A4 publication Critical patent/EP0880467A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C01D1/28—Purification; Separation
    • 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
    • C01F7/066—Treatment of the separated residue

Definitions

  • the present invention relates to a method for recovering soda and/or alumina values from red mud produced in the Bayer process for extracting alumina from bauxite.
  • the Bayer process was first developed in 1888 and presently accounts for over 90% of the world's alumina production.
  • the process utilises a digestion solution at elevated temperature to digest alumina in bauxite.
  • the digestion solution is typically caustic soda but other solutions in which alumina can be dissolved may be used.
  • the digestion solution may be potassium hydroxide or ammonium hydroxide.
  • a Bayer process is to be understood to mean a process as described in the preceding paragraph.
  • the caustic soda solution is typically at a temperature in the range of 150-280°C, with the temperature used being largely dependent upon the nature of the bauxite.
  • the alumina rich liquor phase is separated from undissolved impurities by settling and alumina is recovered from the liquor phase by precipitation of aluminium hydrate crystals.
  • the aluminium hydrate crystals are calcined to produce anhydrous aluminium oxide.
  • the slurry of undissolved impurities resulting from digestion of the bauxite with caustic soda at elevated temperature is commonly referred to as red mud and typically comprises inert iron oxides, titanium oxides and silica compounds. Prior to discharge from the process, the red mud is typically washed with water to recover entrained caustic soda in solution.
  • the caustic soda During digestion, in addition to reacting with alumina in bauxite, the caustic soda also reacts with silica which is typically present in bauxite.
  • the consumption of caustic soda resulting from reaction with silica minerals is a world-wide problem in the alumina refining industry.
  • bauxite deposits which contain high concentrations of silica minerals, the caustic soda loss associated with reaction with silica can represent a significant fraction of overall alumina production costs.
  • Silica may be present in bauxite deposits in various forms including kaolinite (Al 2 ⁇ 3 .2Si0 2 .2H 2 0) and quartz. In general, kaolinite accounts for the majority of the reactive silica found in bauxite.
  • dissolved silica, alumina and sodium combine to precipitate out of solution as a sodium-aluminium-silicate desilication product (DSP) .
  • DSP sodium-aluminium-silicate desilication product
  • Each tonne of silica that dissolves from bauxite consumes approximately 1.18 tonnes of caustic soda in forming DSP.
  • the DSP is discharged from the process as a significant component (up to 40% by weight) of the red mud waste product and hence soda and alumina values are lost. It would therefore be desirable to recover soda and/or alumina values from red mud.
  • US patent no. 4044095 teaches a process in which red mud is treated with concentrated caustic soda at high temperatures (in the order of 300°C) in the presence of lime.
  • the DSP in the red mud is converted to a sodium- calcium-silicate and, in a second stage of the process, the sodium-calcium-silicate is converted to calcium- silicate releasing soda for recovery.
  • alumina is recovered from DSP in the process.
  • US patent no. 938270 also teaches the digestion of red mud with lime at elevated temperature to recover soda from DSP.
  • the processes of US patent nos. 4044095 and 938270 are elevated temperature processes in which the amount of lime consumed exceeds the amount of soda recovered.
  • US 2992893 teaches a process similar to that described above which uses finely divided slaked lime and employs vigorous stirring.
  • the thermal energy requirement of the process is demonstrated by the reaction conditions taught by the patent, namely 30 minutes at 255°C, 6 hours at 90°C and 8 hours at 75°C.
  • AU 88102/82 teaches a process similar to that described in relation to US 4044095 which utilises a single digestion stage at lower caustic concentrations but with a higher rate of lime addition.
  • DSP is converted to an iron substituted calcium-aluminium- silicate of the hydrogarnet type with high soda and alumina recovery.
  • lime is reacted with DSP under atmospheric conditions to liberate soda and form a hydrogarnet.
  • the Mud Caustication Process also requires high levels of lime consumption and relatively long reaction times. As much as 2-3 tonnes of CaO can be consumed per tonne of soda recovered. No alumina is recovered in the Mud Caustication Process and the degree of soda recovery is adversely affected where soluble caustic levels in the red mud slurry exceed about 30 grams per litre.
  • Mechanical activation is a process in which mechanical energy is utilised to increase the chemical reactivity of a system. Mechanochemical reactions are induced which result in changes in chemical composition and structure as a consequence of the input of mechanical energy.
  • US patent no. 5328501 teaches a mechanical activation process in which chemical reduction of reducible metal compounds with a reductant is mechanically activated during milling in a high energy ball mill to refine and manufacture metals and alloys. During milling, the energy imparted to the reactants through ball-reactant collision events enables the starting materials to react resulting in the reduction reaction proceeding without the need for high temperatures or melting to increase reaction rates.
  • the present invention provides a method for recovering soda and/or alumina values from DSP formed in a Bayer process, the method comprising mechanically activating the DSP to induce a mechanochemical reaction whereby soda and/or alumina values are solubilised.
  • the present invention provides a method for recovering alumina values from red mud formed in a Bayer process wherein the alumina values are alumina values other than alumina values derivable from DSP, the method comprising mechanically activating the red mud and recovering the alumina values.
  • the method according to the first aspect of the present invention is applicable to either the mechanical activation treatment of red mud or a DSP concentrate of red mud.
  • a DSP concentrate may be formed by subjecting red mud to a separation technique, for example, a gravity separation technique or a hydrocycloning technique.
  • red mud During the caustic digestion of bauxite in a Bayer process it is not uncommon for red mud to contain alumina values that have neither been dissolved and separated in the liquor phase nor have been reacted in the formation of DSP.
  • alumina values are derived from boehmite and, where red mud is mechanically activated in accordance with the second aspect of the present invention, such alumina values are believed to be recoverable.
  • Red mud may also contain alumina values derived from alumina which was dissolved during digestion but which precipitated from the alumina rich liquor phase prior to separation of the alumina rich liquor phase. Again, such alumina values are believed to be recoverable in accordance with the second aspect of the present invention.
  • the particle size of the red mud/DSP may be reduced by grinding or the like prior to mechanical activation.
  • the methods of the present invention are suitable for either batch processing or continuous processing of red mud/DSP concentrate.
  • DSP/red mud can be mechanically activated without any externally applied heat with soda and/or alumina values recoverable by conventional washing techniques following conversion into soluble or partially soluble forms.
  • the solubilisation of soda and/or alumina values from DSP is believed to be thermodynamically favoured at ambient temperature but in prior art processes input of thermal energy is believed to have been required due to kinetic limitations. In the absence of mechanical activation it is believed not to be possible to solubilise soda and/or alumina values from DSP at ambient temperature within a commercially feasible period of time.
  • the mechanical activation of DSP is believed to increase the reaction kinetics or increase the chemical reactivity of the DSP with the result that a chemical reaction or phase change occurs which produces a new compound or phase that can be more readily processed for extraction of soda and/or alumina values.
  • the mechanical activation of ambient temperature DSP is believed to generate localised regions of high temperature and pressure. Localised temperatures are believed to be as high as 400°C even though average temperature may only be 40°C- 60°C.
  • the recovery of soda and/or alumina values can be enhanced by mechanically activating the DSP in the presence of a reagent.
  • a reagent which is thermodynamically capable of reacting with DSP to solubilise soda and/or alumina values may be used.
  • Suitable reagents include oxides and hydroxides such as CaO, NaOH and Ca(OH) 2 .
  • one class of reagents are believed to undergo a cation exchange mechanism with DSP in which sodium is released and replaced with a reagent cation.
  • the reagent cation may be selected from Ca 2+ , K + , Ba 2+ and Mg 2+ .
  • the red mud/DSP concentrate is mechanically activated in a mechanical mill.
  • the expression mechanical mill is to be understood to include ball mills, nutating mills, tower mills, planetary mills, vibratory mills, attritor mills, gravity-dependent-type ball mills, jet mills, rod mills, high pressure roller mills and the like.
  • a ball mill is a vessel which contains grinding media which is kept in a state of continuous relative motion by input of mechanical energy.
  • the grinding media is typically steel or ceramic balls.
  • Energy is imparted to the DSP within a ball mill by ball-DSP-ball and ball-DSP-mill collisions with the energy being sufficient to cause mechanical activation of the DSP.
  • mechanical activation and thermal treatment can be combined by the use of a thermally insulated high energy mill such as an attritor.
  • a thermally insulated high energy mill such as an attritor.
  • power inputs of the order of 100kW/m 3 can be achieved.
  • the thermal energy generated during milling can result in temperature elevation.
  • utilisation of the generated heat during milling is believed to substantially increase reaction kinetics through the combined effects of mechanical and thermal activation with the result that milling time and cost may be reduced. Accordingly, process efficiency is increased by utilising the generated thermal energy which would otherwise tend to be lost.
  • At least preferred embodiments of the first aspect of the present invention are advantageous when compared with prior art processes because
  • DSP can be mechanically activated at ambient temperature; (2) where lime is utilised as a reagent, the level of lime consumption is low;
  • Example 1 is set forth for the purposes of illustration only and are not to be construed as limiting the scope of the present invention in any way.
  • Example 1 is set forth for the purposes of illustration only and are not to be construed as limiting the scope of the present invention in any way.
  • Example 1 is set forth for the purposes of illustration only and are not to be construed as limiting the scope of the present invention in any way.
  • Example 1 is set forth for the purposes of illustration only and are not to be construed as limiting the scope of the present invention in any way.
  • a red mud slurry containing 470 grams of solids per litre was loaded together with 3kg of 6mm grinding balls into a 1 litre capacity horizontal attritor mill operated with a rotor speed of 600rpm.
  • the red mud was mechanically activated in the presence of either CaO or NaOH with the mass ratio of red mud:reagent being varied in different tests.
  • the charge ratio (grinding balls:red mud solids g/g) and milling time were varied in different tests. Following milling the slurry was washed from the mill in a manner to ensure 100% recovery of the slurry and the solids were separated from the initial wash liquor by centrifuging.
  • the separated solids were dried in an oven at 100°C, ground with a mortar and pestle and washed with a cold 10% ammonia solution for 10 minutes followed by vacuum filtering and drying at 100°C. The washing procedure was repeated. The milled, washed and dried solids were analysed by X-ray diffraction (XRD) to identify crystalline phases present and by X-ray fluorescence (XRF) to provide a standard chemical analysis to determine the chemical composition of the solids. Chemical analyses of the initial wash liquor were carried out on selected samples.
  • XRD X-ray diffraction
  • XRF X-ray fluorescence
  • Soda recovery was calculated from the total soda content of the feed and product (milled) samples. Soda values in the product were normalised to the feed sample by the Tie element method using Ti0 2 which is unaffected by the milling process and remains constant in the red mud. The corrected soda value was calculated from:
  • the soda removed was then expressed as a percentage of the soda in the feed sample:
  • Table l sets out the results of a series of ten tests which were carrie ⁇ out on two samples of red mud.
  • the first tample was 1 mud obtained from Queensland Alumina Li m ited's p ;essing plant at Gladstone, Australia and the second sample was a portion of the first sample which had been washed with a 10% ammonia solution and dried to remove any entrained liquor from the Bayer process.
  • the dried second sample was mixed with distilled water to form a 470 grams per litre slurry. The following observations can be made from the results of the ten tests.
  • Alumina recovery was also enhanced when red mud was milled with CaO.
  • Typical XRD measurements of (a) the second sample (ie. ammonia washed and dried slurry) and (b) a sample of the milled washed and dried solids from Test No. 7 are illustrated in Figure 1.
  • the XRD patterns show a reduction in peak intensity and a broadening of the diffraction peaks for the milled, washed and dried solids from Test No. 7. Without wishing to be bound by theory, this is believed to be a consequence of extreme reduction in crystal size and the introduction of disorder and crystal defects during milling.
  • the intensities of the DSP peaks relative to the Fe 2 0 3 peaks are substantially reduced during milling.
  • the initial wash liquor contains only sodium and aluminium, with the soda recovered as NaOH and Na 2 C0 3 .
  • the red mud was mechanically activated in the presence of CaO with the mass ratio of red mud:CaO being varied in different tests.
  • the charge ratio (grinding balls:red mud solids g/g) and milling time were varied in different tests.
  • Example 2 An identical procedure to that used in Example 1 was used for washing and drying the slurry recovered from the mill. Soda recovery and alumina recovery were calculated in the same manner as used in Example 1 and Table 3 sets out the results of a series of 10 tests. The results of Example 2 indicate that different mechanical mills can be used in the present invention.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Analytical Chemistry (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Geology (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Treatment Of Sludge (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

L'invention concerne la récupération, sous une forme réultilisable, de la soude et/ou de l'alumine, à partir du produit de désilicification (silicate de sodium et d'aluminium) présent dans les boues rouges produites par le procédé Bayer. Ce produit est activé mécaniquement pour induire une réaction chimico-mécanique au cours de laquelle la soude et/ou l'alumine sont solubilisées.
EP97902107A 1996-02-15 1997-02-11 Traitement des boues rouges Withdrawn EP0880467A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
AUPN8081/96 1996-02-15
AUPN8081A AUPN808196A0 (en) 1996-02-15 1996-02-15 Red mud processing
PCT/AU1997/000073 WO1997029992A1 (fr) 1996-02-15 1997-02-11 Traitement des boues rouges

Publications (2)

Publication Number Publication Date
EP0880467A1 true EP0880467A1 (fr) 1998-12-02
EP0880467A4 EP0880467A4 (fr) 1999-05-19

Family

ID=3792396

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97902107A Withdrawn EP0880467A4 (fr) 1996-02-15 1997-02-11 Traitement des boues rouges

Country Status (4)

Country Link
EP (1) EP0880467A4 (fr)
AU (1) AUPN808196A0 (fr)
BR (1) BR9707549A (fr)
WO (1) WO1997029992A1 (fr)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GR20090100008A (el) 2009-01-12 2010-09-09 Νικολαος Παπαδοπουλος Μεθοδος αποκτησης εκμεταλλευσιμων προϊοντων απο το στερεο αποβλητο της ερυθρας ιλυος
AU2010333699B2 (en) * 2009-12-14 2013-11-21 Xstrata Technology Pty Ltd Process for treating red mud
HUE024530T2 (en) * 2012-06-20 2016-01-28 Pleason Ventures Ltd A method for the hydrochemical decomposition of sodium hydrogen alumino-silicate
RU2585648C2 (ru) * 2014-10-06 2016-05-27 Общество с ограниченной ответственностью "АЛЮМПРОЕКТ" Способ гидрохимической переработки алюмосиликатного сырья
AU2014280962B2 (en) * 2014-12-24 2020-10-22 Pleason Ventures Ltd Process For The Cold Hydrochemical Decomposition Of Sodium Hydrogen Aluminosilicate
US9725785B2 (en) 2014-12-24 2017-08-08 Pleason Ventures Ltd Process for cold hydrochemical decomposition of sodium hydrogen aluminosilicate
CN113441519A (zh) * 2021-06-28 2021-09-28 广西田东锦鑫化工有限公司 一种拜耳法赤泥脱碱及碱回收工艺
GR1010484B (el) * 2022-06-22 2023-06-12 Σωκρατης Ιωαννη Αργυροπουλος Μεθοδος χημικης επεξεργασιας σοδουχας λασπης καθιζητηρων, προερχομενη απο την παραγωγικη διαδικασια αλουμινας απο βωξιτη

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT314473B (de) * 1972-07-28 1974-04-10 Tatabanyai Szenbanyak Verfahren zur Aufarbeitung von Rotschlamm

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3574537A (en) * 1967-12-18 1971-04-13 Jui Hsiung Tsai Process for the separation of useful compounds from waste of the aluminum industry
US4045537A (en) * 1975-07-03 1977-08-30 Reynolds Metals Company Process for recovering soda and alumina values from red mud
US4044095A (en) * 1975-10-20 1977-08-23 Aluminum Company Of America Process for recovery of alumina from high-silica ore
AU563304B2 (en) * 1984-12-21 1987-07-02 Comalco Aluminium Limited Soz leach to recover soda and alumina from red mud with recycle to bayer process

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT314473B (de) * 1972-07-28 1974-04-10 Tatabanyai Szenbanyak Verfahren zur Aufarbeitung von Rotschlamm

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CHEMICAL ABSTRACTS, vol. 101, no. 14, 1 October 1984 Columbus, Ohio, US; abstract no. 113170, KUNAEV, A. ET AL: "Hydroalkaline processing of high-silicon bauxites" XP002097276 & BAUXITE, PROC. BAUXITE SYMP. (1984), 831-41. EDITOR(S): JACOB, LEONARD, JR. PUBLISHER: SOC. MIN. ENG. AIME, NEW YORK, N. Y. CODEN: 52FYA6, *
R.S. THAKUR ET AL.: "Utilization of red mud: Part II." JOURNAL OF SCIENTIFIC AND INDUSTRIAL RESEARCH, vol. 42, August 1983, pages 456-468, XP002097275 *
See also references of WO9729992A1 *

Also Published As

Publication number Publication date
AUPN808196A0 (en) 1996-03-07
BR9707549A (pt) 2000-01-04
WO1997029992A1 (fr) 1997-08-21
EP0880467A4 (fr) 1999-05-19

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