icsoba 2010 - beneficiation of bauxite-akw a v rev2

8/19/2019 ICSOBA 2010 - Beneficiation of Bauxite-AKW a v Rev2

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Beneficiation of Bauxite – Upgrading of Recoverable Al2O3

Dr. Stephan Buntenbach1, Thomas Baumann, Fred Donhauser

AKW Apparate+Verfahren GmbH, Germany

1 Abstract

Bauxite deposits are commonly classified in three genetic types according to

mineralogy, chemistry and host-rock lithology. The major part of known deposits

belong to the laterite-type, while less deposits are of the karst-type and only a

minor part of bauxite deposits are classified as tikhvin-type deposits.

Bauxite quality is impacted by the content of alumina and alumina-containing

minerals, like gibbsite, boehmite and diaspor and the amount of reactive silica,

goethite, haematite and other impurities.

The wide range in the composition of the different bauxite ores derives from thedifferences in the origin and geologic history of the individual deposits. In the

Bayer plant, bauxite mineralogy affects process efficiency by driving the chemical

reactions that occur in the process.

If the Run Of Mine (ROM) bauxite is of lower quality, in some cases the

beneficiation by means of physical separation process is economical feasible.

These generally low-cost processes can extend the lifetimes of existing bauxite

mines considerably, and substantially improve the technical and economic basis of

the Bayer process itself.

In this paper some examples are presented to show results of various processes to

upgrade the content of recoverable Al2O3 or to decrease the natural impurities byusing traditional Mineral Processing Technologies.

(Key words: Bauxite Beneficiation, Classification, Density Separation, Magnetic

Separation; Mineral Processing)

2 Characteristics for metallurgical-grade bauxite

The approximate mineralogical composition of lateritic and karst bauxites are

given in table 1.

Table 1: Approximate mineralogical composition of lateritic and karst

bauxites [1]

Element Lateritic KarstAl2O3 Gibbsite, Boehmite Boehmite, Diaspore

SiO2 Kaolinite; Quartz Kaolinite, Quartz, Chamosite, Illite

Fe2O3 Goethite, Hematite Hematite, Goethite, Maghemite, Magnetite

TiO2 Anatase, Rutile Anatase, Rutile, Ilmenite

CaO Calcite, Apatite Calcite, Apatite, Crandallite

Bárdossy and Bourke published in 1993 the ideal characteristics for metallurgical-

grade bauxite and the impact of inadequate values. [2]

The following list is an excerpt from this publication.

1 Dr. Stephan Buntenbach; Independent Consultant for Mineral Processing


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High extractable alumina (+49%) – Low content increases CAPEX and OPEX

Low “reactive silica” (3.0 – 1.5 %, kaolinite) – High content increases causticusage.

Low boehmite (


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Magnetic separation

Electrostatic separation

Froth flotation

The use of gravity concentration methods for processing of metallic ores are wellknown since ancient time. The principles of the operations which were used more

than 2000 years ago are still valid.

Picture 1: Mineral processing in ancient times [4], [5]

4 Bauxite Beneficiation

The idea of bauxite beneficiation is neither new nor out of fashion. In the

” Alumina Technology Roadmap” developed at a workshop in Fremantle, WA in

May 2001, following statements were enunciated:

Impurity Removal: Bauxite and Bauxite Beneficiation

Efficient use of the world´s bauxite resources requires maximizing both the

quantity and quality of the alumina that is extracted. A major cause of Bayer

process inefficiency is the introduction of impurities contained in the bauxite. The

industry lacks technically and economically viable methods for controlling and

removing these impurities. The trend toward lower grades of bauxite available in

the future will only exacerbate this problem.The challenges for the beneficiation of bauxite were identified as

Conduct economic bauxite beneficiation

Address declining grades of bauxite reserves

Reduce impurity content of the liquor

Reduce scale

And the impacts were described as

Increased liquor productivity (lower caustic consumption)

Increased refinery output and lower capital cost per ton of alumina

Better energy efficiency from increased caustic concentration


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Maximized used of bauxite reserves

Less degradation of alumina quality [6]

The aim of the beneficiation is to get a refinery input with quality characteristics

as close to the ”ideal characteristics” as feasible.

During the 134th

TMS Annual Meeting in February 2005 in San Francisco Zhao

Qingjie et al stated in their paper “ Fundamental Research on Alumina Production

of the Future” [7] that China has rich bauxite resources, mainly diasporic type,

with high content of alumina, silica and low content of ferric oxide (except

Guangxi bauxite). For China it is reported that bauxite ore with the ratio of

aluminium and silica greater than 10 accounts for only 10% among all the bauxite

in China, and the bauxite with the ratio of aluminium and silica between 7 and 10

accounts for only 20%, and between 4 and 7 accounts for 60%, and between 2.6

and 4.0 accounts for 10%. The average ratio is 5.56.

The authors identified following trends for China's alumina industry:

Beneficiation Bayer process improves the ratio A/S in bauxite from 4-7 tomore than 10, which makes it possible for China's alumina industry to

develop sustainably.

Intensified sintering process with refined or high-grade bauxite as chargeincreases greatly output under the present condition, which reduces the

energy consumption and operation cost, thus traditional sintering process

revives.

Investigating new separation technology of alumina and silica; substituting

high – efficiency equipments for traditional high- energy- consumption ones

to improve the output ,save energy and reduce the cost; further improving

alumina quality and precipitation yield .

4.2 Classification with Hydrocyclones

As an average, the process to get bauxite as input material for a refinery the Run

Of Mine Ore (ROM) is processed by,

Crushing and Milling

Screening

And for some mines these process steps are supplemented by,

Elutriation (Scrubbing)

Cycloning (in combination with dewatering screens)

The elutriation in combination with classification by cyclones is carried out todecrease the amount of reactive silica (kaolinite). Mine sites which are using these

processes are: Juruti, Trombetas (Brazil), Awaso (Ghana), Weipa (Australia),

Coermotibo (Suriname).

4.2.1 Example of a semi-mobile bauxite beneficiation plant

At a South American bauxite area it was the target of the mine operator to

increase the remaining lifetime of the established mine areas by extracting those

parts of the deposit that had not been mined in the past owing to an excessive

content of reactive silica.

The high content of reactive silica of up to 15 wt. % is caused mainly by the

kaolinite contained in the rock. Thanks to its small particle size, this can be fully


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removed by classification after a reasonable elutriation. Following a successful

test programme conducted at the AKW A+V test centre, this plant was put into

operation in 2007.

The material with a particle size of up to 1,000 mm is fed to a roller grizzly with a

variable cut-point. Depending on the composition of the raw material, material inthe size range from 100 - 150 mm is already product. The WLT completely dissolves any kaolinite

contained. At the end of the WLT, a strainer basket removes the fraction >16 mm.

The underflow from the strainer basket is sized at around 2 mm on a vibrating

screen. The screen overflow is discharged together with the material >16 mm on

to a belt conveyor at the side. The screen underflow is collected in a pump sump

and fed to a hydrocyclone with a centrifugal pump. Its overflow has a high content

of kaolinite, the underflow is dewatered on a dewatering screen and fed to the

product belt conveyor. In the plant – installed next to the independent feed unit in

three (3) containers – a hydrosizer can be added in future if the bauxite quality

requires this. Some pictures of the plant on site are shown in picture 2. [9]

Picture 2: Pictures of a semi-mobile bauxite washing plant ,

built by AKW A+V

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ROM Bauxite

Al2O3total / SiO2 total ratio 5,6

Size

Mass.-%-0,09mm

41,5

49,8

10,8

64,3

32,7

5,0

2,2

35,7

55,0

2,9

2

Process Water

+2mm

Al2O3 [%]

Re.-SiO2 [%]

TiO2 [%]

-2mm

6,0

22,8

52,31,9

2,2

Feed

90 µm

M as s Re co ve ry [ %] 1 00

Al2O3 [%] 52,3

Re.-SiO2 [%] 6,0

TiO2 [%] 2,9

0,09-2mm

58,5

54,0

2,5

2,1

7,2

Mass Recovery [%]

Al2O3 [%]

Re.-SiO2 [%]

TiO2 [%]

Al2O3total / SiO2 total ratio

Picture 3: Flow diagram of the semi-mobile bauxite washing plant ,

built by AKW A+V


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Picture 4: Flowsheet of the bauxite beneficiation plant at Itamarati de Minas,

CBA [10]

4.4 Flotation

During World War II, the United States Congress charged the Bureau of Mines to

investigate processes for the production of alumina from low-grade bauxite,

alunite and clay. As one part of the program, the application of ore-dressingmethods for the beneficiation of Arkansas Bauxite was investigated by the

Mississippi Valley Experiment Station in Rolla, Missouri. The reports of Gandrud

and DeVaneyl and Clemmer, Clemmons, and Stacy show the possibilities of

flotation as a means of beneficiating bauxite. Their work has also developed

reagent combinations that are satisfactory for flotation of gibbsite. [11]

The tailings of the beneficiation plant described in chapter 4.3 (Itamarita de

Minas) still contain bauxite, which can be separated by reverse froth flotation

(flotation of the quartz and depression of the bauxite), using starch as a depressant

and amine as a promoter at a pH of approx. 10. The iron and titanium bearing

minerals are depressed with the bauxite and an additional magnetic separation

operation is necessary on the depressed bauxite. [12]

In [14] X. Cheng et al are reporting that by using reverse flotation and a new

developed reagent scheme (DTAL, SFL and MIBC) it is possible to obtain a

bauxite concentrate (A/S > 10, Al2O3 recovery > 86%), which can be

economically processed by the Bayer technology.

5 Conclusion

The scientific investigations to use mineral processing technologies like

classification, gravity separation, magnetic separation and flotation to improve the

quality of the ROM bauxite have quite a long history, but these technologies were

not commonly adapted by the industry. Due to the increasing economic and


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ecologic pressure on the aluminium industry, these technologies have nowadays

been introduced on a large scale to the industry. This trend will continue in the

future and more and more bauxite ores will be processed by using traditional

mineral processing technologies to improve the overall process of the production

of aluminium.References

[1] Smith, Peter, Economic processin of High Silica Bauxites – Existing and

Potemtial Processes, Parker Centre, CSIRO Light Metals Flagship,

puplished as part of the Asia-Pacific Partnership Project (ATF-06-4), High

Silica Bauxite Processing, 2008 (http://www.asiapacificpartnership.org)

[2] Bárdossy,G., and Bourke,D.J., 1993, “ An assessment of world bauxite

deposits as source for Greenfield alumina plant developments -

Aluminium 69”)

[3] Solymár, Mádai, Papanastassiou, Effect of Bauxite Microstructure on

Beneficiation and Processing , Light Metals 2005, TMS 134th

AnnualMeeting, San Francisco, California, February 13-17, 2005, Page 47 ff.

[4] Agricola, Georgius, De re metallica,1556

[5] Wang, D.Z. et al, Evolution and Innovation of Mineral Processing in

China, Proceedings of XXIV International Mineral Processing Congress,

Beijing China 24-28, September 2008, ISBN 978-7-03-022711-9 (Beijing)

pp 3-14

[6] Alumina Technology Roadmap, (http://www.amira.com.au/Web/sites)

[7] Zhao Qingjie, Yang Qiaofang, Qi Lijuan, Chen Qiyuan, Yin Zhoulan,

Zhang Lingxian, Fundamental Research on Alumina Production of the

Future, Light Metals 2005, TMS 134th Annual Meeting, San Francisco,California, February 13-17, 2005, Page 29 ff.

[8] Buntenbach, Stephan, Mineral Processing Technologies in the Bauxite and

Alumina Industry, Proceedings of the 8th

International Alumina Quality

Workshop, 7-12 September 2008, Darwin, NT, Australia, Page 149ff.

[9] Papoutes, A.: , Beneficiation plant for the bauxite of Silver & Baryte Ores

Mining Co. S.A., TRAVAUX de l’ICSOBA, No. 30. 1999. pp. 85-88

[10] A. P. Chaves, M. Bergerman, C. A. V. Abreu, N. Bigogno, Concentration

of bauxite fines via gravity concentration, Revista Escola de Minas, vol.62

no.3 Ouro Preto July/Sept. 2009, Print version ISSN 0370-4467,

http://www.scielo.br[11] Runke, S.M.; O`Meara, R.G., Aluminium – Beneficiation of Arkansas

Bauxite, Mining Technology, May 1944, American Institute of Mining,

Metallurgical and Petroleum Engineers

[12] Renata Salles Kurusu; Arthur Pinto Chaves et al, Concentration of bauxite

fines via froth flotation, Revista Escola de Minas, vol.62 no.3 Ouro Preto

July/Sept. 2009, Print version ISSN 0370-4467, http://www.scielo.br

[14] X. Cheng, A. Ren, G. Zheng, Study on improved silicates removal

technology in direct Bauxite Flotation, XXIII International Mineral

Processing Congress 2006; Istanbul, Turkey, Volume 1, pp 719 - 722
http://www.amira.com.au/Web/siteshttp://www.amira.com.au/Web/siteshttp://www.amira.com.au/Web/siteshttp://www.scielo.br/http://www.scielo.br/http://www.scielo.br/http://www.scielo.br/http://www.amira.com.au/Web/sites

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