ICSOBA 2010 - Beneficiation of Bauxite-AKW a v Rev2
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Transcript of 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
4,15
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