the chemistry and processing of jamaican bauxite

8/12/2019 The Chemistry and Processing of Jamaican Bauxite

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The Chemistry and Processing of

Jamaican Bauxite

The first commercial extraction of alumina (Al2O3) from bauxite has been attributed toHenri Sainte-Claire Deville in about !"#$

Soon after this% in !!!% &arl 'oseh a*er described +hat is no+ ,no+n as the a*er

rocess% +hich led to a dramatic reduction in the cost of aluminum metal$ Toda*% it is an

ever*da* commodit*% rather than a recious metal$

Althou.h deosits of aluminous red earth have been ,no+n to occur in the Tertiar*

/imestone areas (+hich covers t+o thirds of the land surface of 'amaica) since the

!201s% it +as not until the #01s that their economic si.nificance as an ore of

aluminum +as reco.nised$

n October% #3% Alcan +as incororated under the name 'amaica auxites /imited as

a 'amaican coman* to investi.ate the commercial otential of 'amaican bauxite$ n the

same *ear% 2"00 tonnes of ore +as shied to the 4SA for rocess investi.ation and it+as realised that the bauxite +as suitable for rocessin. usin. a*er technolo.*$

The &ir,vine +or,s +ere comleted around "2 and the first shiment of alumina +as

consi.ned to a 5or+e.ian smelter in 'anuar* "3$

A a*er lant in 'amaica

The a*er rocess% +hich continues to be the most economical method of

manufacturin. alumina can be schematicall* summarised in a flo+ chart%


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and involves the follo+in. oerations6

-minin.

-dissolution of the alumina at elevated temeratures

-addition of flocculants

-reciitation of ure 7ibbsite

-re.eneration of the solutions for rec*clin.

-heatin. the 7ibbsite to 00C (calcination) to .ive alumina

Mining

mmediatel* rior to minin. an* deosit% the land is cleared and the to soil% to a

minimum of 8 inches% removed and stoc,iled for later relacement +hen minin. is

comleted$

The surface occurrence of the ore (usuall* less than 00 feet) ma,es the deosits

suitable for minin. b* simle oencast methods$ Due to the soft% earth* nature of theore% no drillin. or blastin. is .enerall* re9uired$

Deosits are located in areas var*in. from .entle undulatin. to ru..ed% hill* terrain

involvin. ma:or caital exenditures in establishin. a s*stem of ore transortation$
http://wwwchem.uwimona.edu.jm:1104/lectures/baux1.gif


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;inin. areas in 'amaica

Dissolution of the alumina at elevated temperatures

The exact rocedure re9uired for di.estion% deends on the nature of the ore deosits$

The follo+in. Table outlines a number of minerals commonl* found in bauxites6

7ibbsite (h*drar.illite) -Al2O3$3H2O

oehmite -Al2O3$H2O

Diasore -Al2O3$H2O

Hematite -


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Diaso!e Al2O3.H2O + 2NaOH ---> 2 NaAlO2 + 2 H2O (hi"h # a$% &)

Comlete extraction from diasoric bauxite re9uires stron.er caustic solutions% in

addition to hi.her temeratures and ressures$ n .eneral the reaction e9uilibria above

move to the ri.ht +ith increases in caustic soda concentration and temerature$ n

ractice this means that for deosits containin. the more easil* recovered 7ibbsite onl*%roduction costs are much lo+er than +hen oehmite or Diasore are resent$

The control of silica in the conventional a*er rocess is most imortant and in fact

ores havin. reactive silica .reater than @ cannot be economicall* rocessed$

4nli,e 9uart?% +hich is considered virtuall* non-reactive at 7ibbsite extraction

temeratures% some minerals% includin. ,aolins% dissolve raidl* and the reaction of the

silica can .ive rise to areciable loss of caustic soda and aluminum$

The control of silica is .enerall* carried out durin.% or rior to% the di.estion ste% and

.enerall* involves dissolution% e. for ,aolin Al2O3.2'iO2 + NaOH ---> Na2'iO3

and desilication via reciitation$ Na2'iO3 + NaAlO2 ---> Na2O.Al2O3.2'iO2

Dissolution is necessar* to suersaturate the li9uid to a oint +here the sodalite formed

acts as a seed to reciitate more sodalite$ The rate of reciitation is found to increase

+ith temerature% ho+ever at 3"-"0 C it is si.nificantl* slo+er than is re9uired for

comlete 7ibbsite extraction +hich occurs +ithin minutes$ The need for desilication

therefore means that the material must be held at the di.estion temerature lon. enou.h

to allo+ the silica to reciitate$

Still to come

Addition of Flocculants

Precipitation of pure Gisite

!egeneration of solutions

The !ed Mud Ponds

and the latest ideas on dr* stac,in.


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Calcination

=eferences$

see for examle%

=$'$ /ancashire% Bauxite and aluminium roductionB

ducation in Chemistr*% ;a* !2% s 82-8#$

roduction fi.ures on auxitefrom ictoria in Australia are available at the 5ational

=esources and nvironment +ebsite under 1;inerals and etroleum1$


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achievement +as the culmination of several *ears of intensive +or, on this roblem$ t

+as a .oal that he had set as a hi.h school student and that had been encoura.ed +ith

ideas and materials b* rofessor


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mixtures of salts commonl* had lo+er meltin. oints than the hi.her meltin. of the

t+o$ Toda*% this substance is +ritten +ith a formula of 5a3Al


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The cr*olite solvent that Hall found for his rocess has some fortunate roerties in

addition to bein. a solvent for aluminum oxide$ ein. ionic% cr*olite is a .ood

conductor of electricit*$ Althou.h the densit* of solid cr*olite is .reater than the densit*

of solid aluminum at room temerature% the densit* of molten aluminum is .reater than

that of molten cr*olite at the electrol*sis temerature$ As a conse9uence% li9uid

aluminum metal collects in the bottom of the electrol*sis vessel +here the aluminum isrotected from bein. reoxidi?ed b* ox*.en in the atmoshere$

rofessor 'e+ett la*ed a crucial role as Hall1s mentor$


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A recreation of the Hall +oodshed is associated +ith the 'e+ett house$ This house is

art of the Oberlin Historical Societ* site on rofessor Street :ust south of the

Conservator*$ A lecture-demonstration recreatin. Hall1s ori.inal laborator* rocess +as

held in Oberlin in !8 on the centennial of the discover*$


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5orman Crai. standin. next to the aluminum statue of Charles ;artin Hall located in

the &etterin. Hall of Science$

=eturn to the Oberlin Chemistr* Deartment Home a.e$

($te! 'ea!)h

$%M&6 P!%D"CT'%(6 REFINING

Alumina Refining
http://www.oberlin.edu/chem/history/cmh/OCChemistry.htmlhttp://www.world-aluminium.org/default.asphttp://www.world-aluminium.org/production/index.htmlhttp://www.world-aluminium.org/default.asphttp://www.oberlin.edu/chem/history/cmh/OCChemistry.htmlhttp://www.world-aluminium.org/default.asphttp://www.world-aluminium.org/production/index.html


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Overvie+

auxite

;inin.

Alumina

Refining

a*er

rocess

Chemistr*

Smeltin.

rocessin.

=ec*clin.

;as

The aluminium industr* relies on the a*er rocess to

roduce alumina from bauxite$ t remains the most

economic means of obtainin. alumina% +hich in turn is vital

for the roduction of aluminium metal - some t+o tonnes of

alumina are re9uired to roduce on tonne of aluminium$

The Bayer Process

The rimar*

aluminium

industr* is

deendent on a

re.ular sul* of

alumina for fourfunctions6

1. Basic rawmaterialforaluminiumproduction

2. Thermalinsulatorfor the

top ofelectrolytic cells

3. Coating

$')T%!*

P!%D"CT'%(

&(+'!%(M&(T

APP#'CAT'%()

)TAT')T'C)

(&,)

'A'

&n-uiries

#in.s

)ite Map

1.8 million tonne alumina refinery at Gove,orthern Territory, !ustralia
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the chemistry and processing of jamaican bauxite

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