WO1998051616A1 - Process for the production of gypsum from sulphuric acid containing waste streams - Google Patents

Process for the production of gypsum from sulphuric acid containing waste streams Download PDF

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Publication number
WO1998051616A1
WO1998051616A1 PCT/AU1998/000347 AU9800347W WO9851616A1 WO 1998051616 A1 WO1998051616 A1 WO 1998051616A1 AU 9800347 W AU9800347 W AU 9800347W WO 9851616 A1 WO9851616 A1 WO 9851616A1
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WO
WIPO (PCT)
Prior art keywords
gypsum
waste stream
process according
basic material
waste
Prior art date
Application number
PCT/AU1998/000347
Other languages
French (fr)
Inventor
Robert Hose
Gavan J. Stray
Franc Omahen
Original Assignee
Robert Hose
Stray Gavan J
Franc Omahen
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 Robert Hose, Stray Gavan J, Franc Omahen filed Critical Robert Hose
Priority to AU73253/98A priority Critical patent/AU7325398A/en
Publication of WO1998051616A1 publication Critical patent/WO1998051616A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
    • 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
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • This invention relates to the production of gypsum from waste streams containing sulphuric acid, in particular a process for the production of high purity gypsum from industrial waste streams containing sulphuric acid.
  • the production of gypsum from acidic waste streams containing sulphuric acid is normally carried out using a one or two step process, the key difference between the two processes being the pH at which the precipitation of the gypsum occurs.
  • the pH of the acid stream is raised, typically to the range of 4 to 6, and the gypsum recovered by a range of separation and/or filtration processes.
  • Resultant gypsum has a low gypsum content, typically less than 90%, and not uncommonly less than 80% .
  • the gypsum produced also has a small crystal size. Both of these factors make it unsuitable for use in the manufacture of plaster or other higher value products.
  • the gypsum from this process is commonly used for soil rehabilitation or as a setting control agent for cement.
  • gypsum is recovered from the sulphuric acid waste stream via precipitation at two different pH levels.
  • the gypsum is initially recovered by the addition of lime to the acid stream, increasing the pH to the range 2 to 2.4.
  • the precipitated gypsum is generally of high purity, typically greater than 90% , and has an acceptable particle size distribution for use in manufacturing processes. This method is presently being used to recover gypsum from waste acid streams generated during the production of titanium oxide.
  • the gypsum produced is of sufficient purity to be useful in the production of plasterboard.
  • the pH is again raised by the addition of lime to bring the stream to a pH of about 6.
  • the gypsum precipitated at this pH is of low purity, containing significant amounts of iron and other impurities which are also present in the acid stream.
  • the product of this second precipitation step is commonly referred to as "red gypsum" and is mainly used for soil rehabilitation or as a cement additive. It is an object of the present .invention to overcome or alleviate one or more of the disadvantages of the prior art processes, and to provide improved recovery of high purity gypsum from sulfuric acid containing waste streams.
  • the invention provides a process for the production of gypsum from a waste stream containing sulphuric acid including:
  • the process according to the invention allows the recovery of highly pure gypsum at two stages by including an intermediate precipitation step in which impurities are removed.
  • impurities include Fe and Al.
  • the gypsum recovered at both stages may also have an acceptable particle size to be useful in various manufacturing processes, such as the manufacture of plasterboard and plaster-based products, or as an additive for cement.
  • the term "basic material” refers to any alkaline material capable of neutralizing sulphuric acid.
  • suitable basic materials include alkali metal hydroxides, such as NaOH and KOH, alkaline earth metal hydroxides such as Mg(OH) 2 and Ca(OH) 2 , basic oxides such as Na 2 O, MgO and CaO, and carbonates and hydrogen carbonates, such as Na 2 CO 3 , NaHCO 3 and CaCO 3 .
  • the term "calcium containing basic material” refers to a basic material as defined above which includes calcium atoms or cations.
  • suitable calcium containing base materials include Ca(OH) 2 , CaCO 3 , CaO, and lime, including slaked lime and quicklime.
  • the calcium containing basic material is Ca(OH) 2 or lime.
  • waste stream containing sulphuric acid refers to a waste stream resulting from any industrial process which uses or produces sulphuric acid, such that excess or waste sulphuric acid is contained in the waste stream.
  • industrial processes include the production of titanium dioxide, activated bentonite clay, tapioca starch, citric, lactic and tartaric acids and the production of kevlar.
  • high purity and “highly pure” as used in relation to recovered gypsum means having a purity of greater than 85% .
  • step A of the process it is preferred that the pH of the waste acid stream is brought within the range of 2 to 2.4. To maximise the yield while maintaining high purity it is preferred that the pH is brought to about 2.4.
  • the residence time of the calcium containing basic material in the waste acid stream is between 30 minutes and 2 hours. It is also possible to 'seed' the precipitation of the gypsum by adding gypsum to the waste acid stream. Seeding in this way may increase the weight of precipitation of the gypsum or alter the crystal size, or both.
  • the basic material and/or calcium containing basic material is highly dispersed. This may be achieved by any suitable means including grinding or dissolution.
  • the gypsum may be recovered from the waste acid stream using methods known to the art, such as by filtration, clarification or cent ⁇ tugation
  • step B the pH of the waste acid stream is brought to within the range of trom about 3 0 to 3 4, preferably about 3 0
  • a higher pH can be chosen, however this will decrease the total yield of gypsum
  • the 'red gypsum' produced from the sulphuric acid waste stream of the titanium dioxide process otten contains significant amounts of radioactive materials
  • the pH of the waste stream in step B may need to be higher than 3 4
  • it may also be beneficial to use a higher pH to remove unwanted contaminants although the higher the pH the lower the yield of gypsum in step C
  • the impurities precipitated in step B may be removed using any suitable means known to the art.
  • a flocculant is used The flocculant may cationic, anionic or non- lonic Examples of suitable flocculants include acrylamide polymers, polyaminoacrylate polymers and sulphonated polystyrene
  • the flocculant is anionic
  • a preferred anionic flocculant is Nalco Optimer ® 9960 from Nalco Chemical Company.
  • Other methods for removing the impurities, such as centrifuge separation, are also possible.
  • the impurities removed from the acid waste stream may be useful as landfill.
  • step B If a calcium containing basic material is used in step B then the product will contain gypsum as well as other impurities Vigorous stirring and/or deration may also be used to promote oxidation of Fe and other impurities, thereby assisting removal of these impurities
  • step C the pH of the acid waste stream is brought within the range of from about 4 to 6, preferably about 6 To ensure maximum yield a residence time of between about two and four hours may be required
  • “seeding" of the precipitation with gypsum can be used to increase the yield and/or modify the crystal size produced
  • the gypsum recovered in step C is of a high purity and has a suitable particle size distribution for manufacturing processes
  • the process of the present invention allows the production of gypsum from waste sulphuric acid streams which is of high purity and acceptable particle size for use in the manufacturing processes
  • the gypsum recovered from steps A and C of the process may have the purity of greater than 85%, preferably greater than 90%, and most preferably greater than 92%
  • the highly pure gypsum produced according to the present invention may also have an acceptable particle size making it suitable for use in manufacturing processes
  • the gypsum particles may an average size of between 20 and 120 microns, preferably above 40 and 120 microns and
  • Gypsum was recovered from the waste sulphuric acid stream generated during the production of activated bentonite clay In addition to sulphuric acid the solution contains iron and other dissolved materials
  • the pH of the waste acid stream was initially pH 1 64
  • the solution was filtered to remove residual solids before the pH was increased to 2 42 by the addition of finely divided calcium hydroxide
  • the solution was allowed to mix for 60 minutes before filtration to remove the precipitated gypsum
  • the yield from this step was 3 5 grams per litre of acid effluent and purity of 91 7%o gypsum
  • the gypsum was set aside without washing for use in later step
  • the pH of the solution was ten increased to 3 0 by the addition of calcium hydroxide and an anionic flocculant (Optimer® 9960) added to aid in the separation of the iron and other impurities
  • the solution was vigorously stirred for 60 minutes before filtration
  • the yield for this step was 6 1 grams per litre of effluent
  • the precipitated fraction contained iron and other impurities detrimental to the use of the gypsum
  • the filtrate was then neutralised to a pH of 6 15 using finely divided calcium hydroxide and a portion of the gypsum produced in the first stage was added to increase the rate of crystallisation
  • the solution was allowed to mix for 120 minutes before filtration
  • the overall yield from the precipitation was 18 7 grams per litre
  • the purity of the gypsum produced was 93 6%
  • the dry gypsum was cream in colour and had an average particle size of 53 microns

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Geology (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

This invention provides a process for the production of gypsum from a waste stream containing sulphuric acid including: (A) adding calcium containing basic material to said waste stream to bring pH within the range of from about 2.0 to 2.7 to precipitate gypsum, and recovering the precipitated gypsum from the waste stream, and (B) adding basic material to the waste stream to bring pH within the range of from about 3.0 to 3.4 to precipitate impurities, and removing the precipitated impurities from the waste stream, and (C) adding calcium containing basic material to said waste stream to bring pH within the range of from about 4 to 6 precipitate gypsum, and recovering the precipitated gypsum from the waste stream.

Description

Process for the production of gypsum from sulphuric acid containing waste streams
This invention relates to the production of gypsum from waste streams containing sulphuric acid, in particular a process for the production of high purity gypsum from industrial waste streams containing sulphuric acid.
The production of gypsum from acidic waste streams containing sulphuric acid is normally carried out using a one or two step process, the key difference between the two processes being the pH at which the precipitation of the gypsum occurs. In the one step process, the pH of the acid stream is raised, typically to the range of 4 to 6, and the gypsum recovered by a range of separation and/or filtration processes. Resultant gypsum has a low gypsum content, typically less than 90%, and not uncommonly less than 80% . The gypsum produced also has a small crystal size. Both of these factors make it unsuitable for use in the manufacture of plaster or other higher value products. The gypsum from this process is commonly used for soil rehabilitation or as a setting control agent for cement.
In the two step process gypsum is recovered from the sulphuric acid waste stream via precipitation at two different pH levels. Typically the gypsum is initially recovered by the addition of lime to the acid stream, increasing the pH to the range 2 to 2.4. The precipitated gypsum is generally of high purity, typically greater than 90% , and has an acceptable particle size distribution for use in manufacturing processes. This method is presently being used to recover gypsum from waste acid streams generated during the production of titanium oxide. The gypsum produced is of sufficient purity to be useful in the production of plasterboard.
After the first precipitation step, the pH is again raised by the addition of lime to bring the stream to a pH of about 6. The gypsum precipitated at this pH is of low purity, containing significant amounts of iron and other impurities which are also present in the acid stream. The product of this second precipitation step is commonly referred to as "red gypsum" and is mainly used for soil rehabilitation or as a cement additive. It is an object of the present .invention to overcome or alleviate one or more of the disadvantages of the prior art processes, and to provide improved recovery of high purity gypsum from sulfuric acid containing waste streams.
Accordingly the invention provides a process for the production of gypsum from a waste stream containing sulphuric acid including:
(A) adding calcium containing basic material to said waste stream to bring pH within the range of from about 2.0 to 2.7 to precipitate gypsum, and recovering the precipitated gypsum from the waste stream, and
(B) adding basic material to the waste stream to bring pH within the range of from about 3.0 to 3.4 to precipitate impurities, and removing the precipitated impurities from the waste stream, and
(C) adding calcium containing basic material to said waste stream to bring pH within the range of from about 4 to 6 to precipitate gypsum, and recovering the precipitated gypsum from the waste stream.
The process according to the invention allows the recovery of highly pure gypsum at two stages by including an intermediate precipitation step in which impurities are removed. Such impurities include Fe and Al. The gypsum recovered at both stages may also have an acceptable particle size to be useful in various manufacturing processes, such as the manufacture of plasterboard and plaster-based products, or as an additive for cement.
As used herein, the term "basic material" refers to any alkaline material capable of neutralizing sulphuric acid. Examples of suitable basic materials include alkali metal hydroxides, such as NaOH and KOH, alkaline earth metal hydroxides such as Mg(OH)2 and Ca(OH)2, basic oxides such as Na2O, MgO and CaO, and carbonates and hydrogen carbonates, such as Na2CO3, NaHCO3 and CaCO3. As used herein the term "calcium containing basic material" refers to a basic material as defined above which includes calcium atoms or cations. Examples of suitable calcium containing base materials include Ca(OH)2, CaCO3, CaO, and lime, including slaked lime and quicklime. Preferably the calcium containing basic material is Ca(OH)2 or lime.
As used herein the term "waste stream containing sulphuric acid" refers to a waste stream resulting from any industrial process which uses or produces sulphuric acid, such that excess or waste sulphuric acid is contained in the waste stream. Such industrial processes include the production of titanium dioxide, activated bentonite clay, tapioca starch, citric, lactic and tartaric acids and the production of kevlar.
As used herein the terms "high purity" and "highly pure" as used in relation to recovered gypsum means having a purity of greater than 85% .
In step A of the process it is preferred that the pH of the waste acid stream is brought within the range of 2 to 2.4. To maximise the yield while maintaining high purity it is preferred that the pH is brought to about 2.4.
To ensure maximum recovery of pure gypsum it is preferred that the residence time of the calcium containing basic material in the waste acid stream is between 30 minutes and 2 hours. It is also possible to 'seed' the precipitation of the gypsum by adding gypsum to the waste acid stream. Seeding in this way may increase the weight of precipitation of the gypsum or alter the crystal size, or both.
In order to provide for better crystal growth and to increase the particle size of the gypsum it is preferred that the basic material and/or calcium containing basic material is highly dispersed. This may be achieved by any suitable means including grinding or dissolution. The gypsum may be recovered from the waste acid stream using methods known to the art, such as by filtration, clarification or centπtugation
In step B the pH of the waste acid stream is brought to within the range of trom about 3 0 to 3 4, preferably about 3 0 A higher pH can be chosen, however this will decrease the total yield of gypsum In some situations it may be beneficial to use a higher pH to remove unwanted contaminants In this regard the 'red gypsum' produced from the sulphuric acid waste stream of the titanium dioxide process otten contains significant amounts of radioactive materials In order to remove these radioactive impurities the pH of the waste stream in step B may need to be higher than 3 4 In some other circumstances it may also be beneficial to use a higher pH to remove unwanted contaminants, although the higher the pH the lower the yield of gypsum in step C
The impurities precipitated in step B may be removed using any suitable means known to the art. In a preferred method a flocculant is used The flocculant may cationic, anionic or non- lonic Examples of suitable flocculants include acrylamide polymers, polyaminoacrylate polymers and sulphonated polystyrene Preferably the flocculant is anionic A preferred anionic flocculant is Nalco Optimer® 9960 from Nalco Chemical Company. Other methods for removing the impurities, such as centrifuge separation, are also possible. The impurities removed from the acid waste stream may be useful as landfill. If a calcium containing basic material is used in step B then the product will contain gypsum as well as other impurities Vigorous stirring and/or deration may also be used to promote oxidation of Fe and other impurities, thereby assisting removal of these impurities
In step C the pH of the acid waste stream is brought within the range of from about 4 to 6, preferably about 6 To ensure maximum yield a residence time of between about two and four hours may be required As with step A, "seeding" of the precipitation with gypsum can be used to increase the yield and/or modify the crystal size produced As with the product of step N the gypsum recovered in step C is of a high purity and has a suitable particle size distribution for manufacturing processes The process of the present invention allows the production of gypsum from waste sulphuric acid streams which is of high purity and acceptable particle size for use in the manufacturing processes In this regard the gypsum recovered from steps A and C of the process may have the purity of greater than 85%, preferably greater than 90%, and most preferably greater than 92% The highly pure gypsum produced according to the present invention may also have an acceptable particle size making it suitable for use in manufacturing processes In this regard the gypsum particles may an average size of between 20 and 120 microns, preferably above 40 and 120 microns and most preferably above 60 and 120 microns
In order to facilitate an understanding of the invention, reference will now be made to the accompanying example which describes an embodiment of the invention However, it is to be understood that the particularity of the following description is not to supersede the generality of the invention described above
Example
Gypsum was recovered from the waste sulphuric acid stream generated during the production of activated bentonite clay In addition to sulphuric acid the solution contains iron and other dissolved materials
The pH of the waste acid stream was initially pH 1 64 The solution was filtered to remove residual solids before the pH was increased to 2 42 by the addition of finely divided calcium hydroxide The solution was allowed to mix for 60 minutes before filtration to remove the precipitated gypsum The yield from this step was 3 5 grams per litre of acid effluent and purity of 91 7%o gypsum The gypsum was set aside without washing for use in later step
The pH of the solution was ten increased to 3 0 by the addition of calcium hydroxide and an anionic flocculant (Optimer® 9960) added to aid in the separation of the iron and other impurities The solution was vigorously stirred for 60 minutes before filtration The yield for this step was 6 1 grams per litre of effluent The precipitated fraction contained iron and other impurities detrimental to the use of the gypsum The filtrate was then neutralised to a pH of 6 15 using finely divided calcium hydroxide and a portion of the gypsum produced in the first stage was added to increase the rate of crystallisation The solution was allowed to mix for 120 minutes before filtration The overall yield from the precipitation was 18 7 grams per litre The purity of the gypsum produced was 93 6% The dry gypsum was cream in colour and had an average particle size of 53 microns
Those skilled will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described It is to be understood that the invention includes all such variations and modifications The invention also includes all of the steps and features referred to or indicated in the specification, individually or collectively and any and all combinations of any two or more of said steps or features

Claims

Claims
1 A process tor the production ot gypsum trom a waste stream containing sulphuric acid including
(A) adding calcium containing basic material to said waste stream to bring pH within the range of from about 2 0 to 2 7 to precipitate gypsum, and recovering the precipitated gypsum trom the waste stream, and
(B) adding basic material to the waste stream to bring pH within the range ot trom about 3 0 to 3 4 to precipitate impurities, and removing the precipitated impurities from the waste stream, and
(C) adding calcium containing basic material to said waste stream to bring pH within the range of from about 4 to 6 to precipitate gypsum, and recovering the precipitated gypsum from the waste stream.
2 A process according to claim 1 wherein, in step A, the pH is brought to about 2 4
3 A process according to claim 1 wherein, in step B, the pH is brought to about 3 0
A process according to claim 1 wherein, in step C, the pH is brought to about 6
5 A process according to claim 1 wherein the calcium containing basic material is selected from Ca(OH)2, CaCO3, CaO and lime
6 A process according to claim 5 wherein the calcium containing basic material is Ca(OH)2
7 A process according to claim 1 wherein, in step B, the precipitated impurities are removed by flocculation A process according to claim 7 wherein the precipitated impurities are removed by flocculation with an anionic flocculant
A process according to claim 1 wherein, in step C, the calcium containing basic material has a residence time in the waste-stream of between about 2 and 4 hours
Gypsum of high purity when produced by a process according to claim 1
A process according to any one of claims 1 to 9 wherein the particle size of the gypsum produced in step A or step C is 20 to 120 microns
PCT/AU1998/000347 1997-05-12 1998-05-12 Process for the production of gypsum from sulphuric acid containing waste streams WO1998051616A1 (en)

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AU73253/98A AU7325398A (en) 1997-05-12 1998-05-12 Process for the production of gypsum from sulphuric acid containing waste st reams

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SG9701492 1997-05-12
SG9701492-2 1997-05-12

Publications (1)

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WO1998051616A1 true WO1998051616A1 (en) 1998-11-19

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2192088A1 (en) 2008-11-25 2010-06-02 Ferro Duo GmbH Method of producing calcium hydroxide
KR20160111875A (en) * 2015-03-17 2016-09-27 스미토모 오사카 세멘토 가부시키가이샤 Method of producing gypsum and method of producing cement composition
CN111527052A (en) * 2017-12-27 2020-08-11 三菱综合材料株式会社 Method for treating waste water
US11479490B2 (en) 2017-12-27 2022-10-25 Mitsubishi Materials Corporation Method of treating wastewater
US12172905B2 (en) 2018-12-14 2024-12-24 Avertana Limited Methods of extraction of products from titanium-bearing materials

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4457848A (en) * 1981-09-10 1984-07-03 Hoechst Aktiengesellschaft Process for after-treating extraction residues originating from the decontamination of phosphoric acid
US5156746A (en) * 1990-07-20 1992-10-20 Csir Treatment of water
US5427691A (en) * 1992-12-02 1995-06-27 Noranda, Inc. Lime neutralization process for treating acidic waters

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4457848A (en) * 1981-09-10 1984-07-03 Hoechst Aktiengesellschaft Process for after-treating extraction residues originating from the decontamination of phosphoric acid
US5156746A (en) * 1990-07-20 1992-10-20 Csir Treatment of water
US5427691A (en) * 1992-12-02 1995-06-27 Noranda, Inc. Lime neutralization process for treating acidic waters

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2192088A1 (en) 2008-11-25 2010-06-02 Ferro Duo GmbH Method of producing calcium hydroxide
KR20160111875A (en) * 2015-03-17 2016-09-27 스미토모 오사카 세멘토 가부시키가이샤 Method of producing gypsum and method of producing cement composition
JP2016172682A (en) * 2015-03-17 2016-09-29 住友大阪セメント株式会社 Manufacturing method of gypsum and manufacturing method of cement composition
CN105985037A (en) * 2015-03-17 2016-10-05 住友大阪水泥株式会社 Method of producing gypsum and method of producing cement composition
KR102449716B1 (en) * 2015-03-17 2022-09-30 스미토모 오사카 세멘토 가부시키가이샤 Method for manufacturing gypsum and method for manufacturing cement composition
CN111527052A (en) * 2017-12-27 2020-08-11 三菱综合材料株式会社 Method for treating waste water
US11479490B2 (en) 2017-12-27 2022-10-25 Mitsubishi Materials Corporation Method of treating wastewater
US11505480B2 (en) 2017-12-27 2022-11-22 Mitsubishi Materials Corporation Method of treating wastewater
US12172905B2 (en) 2018-12-14 2024-12-24 Avertana Limited Methods of extraction of products from titanium-bearing materials

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TW440552B (en) 2001-06-16
AU7325398A (en) 1998-12-08

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