the reducibility of the greek nickeliferous

8122019 The Reducibility of the Greek Nickeliferous

httpslidepdfcomreaderfullthe-reducibility-of-the-greek-nickeliferous 19

P u b l i s h e d b y M a n e y P u b l i s h i n g ( c ) I O M C

o m m u n i c a t i o n s L t d a n d t h e A u s t r a l a s i a n I n s t i t u t e o f M i n i n g a n d M e t a l l u r g y

The reducibility of the Greek nickeliferouslaterites a review

E Zevgolis C Zografidis and I Halikia

This paper refers to a critical review of the Greek nickeliferous laterites roasting reduction studies

for better understanding of the process thermodynamic and kinetic mechanisms affecting

decisively the smelting step in pyrometallurgical extraction of nickel from these ores From this

work it is deduced that iron and nickel oxide reduction degree does not exceed 33 and 76

respectively the reductive reactions being stopped within the first 20ndash30 min Thus part of ferric

iron is transformed into ferrous iron (in the form of magnetite wustite or fayalite) instead of metallic

iron production Also no total conversion to metallic nickel takes place Variation of roasting

temperature (700ndash850uC) grain size of the ores and type of solid reductants affect the reduction

rates and the final reduction degrees obtained Diffusion or mixed control mechanisms have been

found to prevail during reduction Low reduction degrees obtained are attributed to kinetic

phenomena such as the formation of fayalite (2FeOSiO2) which probably covers oxide grains

and impedes reduction

Keywords Reducibility Laterites Review Ferronickel Pyrometallurgy

Introduction

Nickel is a lustrous silvery white metal with a highmelting point (1453uC) high resistance to corrosion and

oxidation good thermal and electrical conductivity

ferromagnetic properties catalytic behaviour ease of

electroplating and excellent strength and toughness at

elevated temperatures1 properties that are indicative of

the wide range of its applications Laterite (oxide) and

sulphide ores constitute the two basic natural resources

of nickel accounting for about 60 and 40 of the

worldrsquos primary nickel reserves respectively Nickel

production and demand has presented an eightfold rise

since 1950 and laterite source nickel though it formed

only a small fraction of the worldrsquos production (10 in

1950) its participation has risen ever since to 42 (2003)and according to laterite projected economic scenarios

and forecasts it is expected to rise further more to 51

by 20122

The three types of nickel laterite deposits with

economic interest for nickel are limonitic intermediate

and saprolitic (or garnieritic) The main mineralogical

phase of the saprolitic ores is garnierite

(NiMg)6Si4O10(OH)8 having a high magnesia and low

iron content with Ni grade 15 t o 35 Limonitic

laterites contain iron oxides as the main mineralogical

phase ndash goethite (a-FeOOH) hematite (Fe2O3) or

magnetite (Fe3O4)- thus having a high iron content

and a lower Ni grade (1ndash2) Laterite ores are classifiedinto three classes3

(i) class A garnieritic type of laterites (Fe 12and MgO 25)

(ii) class B limonitic type of laterites (high Fecontent 15ndash32 or 32 and MgO 10)

(iii) class C intermediate type of laterite ores that liebetween garnieritic and limonitic type of ores (Fe12ndash15 and MgO 25ndash35 or 10ndash25)

Greek nickeliferous laterites chemicalndashmineralogical characterisation andindustrial treatmentGreek nickeliferous laterite deposits are mainly locatedin three different regions Evia Island Lokrida inCentral Greece and Kastoria in Northern GreeceGreek reserves represent 90 of nickel laterite reservesin the European Union the remainder occurring in

Finland Evia Island and Lokrida laterites are classifiedin class B while Kastoria laterite deposit is approachinga typical example of class C laterite In Table 1 a typicalchemical analysis of the Greek nickeliferous laterites isgiven

Evia Kastoria and Lokrida laterite samples have beencharacterised by using techniques such as XRDdifferential thermal analysis and thermogravimetry X-

ray fluorescence ore microscopy and electron microp-robe analysis All laterite types examined are charac-

terised by a pissolitic texture Evia and Lokiridalateritesrsquo main mineralogical constituents were foundto be hematite (Fe2O3) and quartz (SiO2) while the mainnickel bearing mineral phases are the chlorite group[(MgNiFeAl)6(AlSi)4O10(OH)8]45 Some other nickel

Laboratory of Metallurgy School of Mining and Metallurgical EngineeringNational Technical University of Athens Heroon Polytechniou 9 15780Zografou Athens Greece

Corresponding author email zografidismetalntuagr

2010 Institute of Materials Minerals and Mining and The AusIMMPublished by Maney on behalf of the Institute and The AusIMMReceived 12 March 2009 accepted 16 August 2009DOI 101179174328509X431472

Mineral Processing and ExtractiveMetallurgy (Trans Inst Min Metall C) 2010 VOL 1 19 NO 1 9





bearing mineral phases that have been found in selective

Lokrida deposit parts are nepouite [(NiMg)3Si2O5(OH)4]

and takovite [(Ni5Al4O2(OH)86H2O]5 The main miner-

alogical constituent of the Kastoria ore was found to be

serpentine (MgFeNi)6Si4O12(OH)6 The high goethite (a-

FeOOH) content of Kastoria ore indicates a higher

content of the crystallic moisture compared to the other

types of Greek laterites Serpentine and nickeliferous

magnesian crostendite (Fez28 Fez3

4 )(Si4Fez34 )O20(OH)6-

where part of Fez2 can be replaced by Mg- represent the

main nickel carrier minerals in Kastoria ore6

Microcrystallity of the nickel bearing mineral phases

renders their liberation and upgrading by mineral proces-

sing techniques extremely difficult something which would

improve drastically the cost of pyrometallurgical or

hydrometallurgical laterite treatment

Greek nickeliferous laterites are processed by the

pyrometallurgical method lsquoLarco Processrsquo at the metal-

lurgical plant of LARCO GMM SA for the production

of a ferronickel alloy (FendashNi) with y20Ni and low C

S and P suitable for austenitic stainless steel productionlsquoLarco Processrsquo involves the following steps

(i) handling and mixing of raw materials (ie

laterite solid fuels and agglomerated rotary

kiln (RK) dust in form of pellets)

(ii) drying preheating and controlled prereduction

of the metallurgical mixture in RKs and

production of a calcine

(iii) smelting reduction of the calcine in open-bath

submerged-arc electric furnaces (EFs) and

production of an FendashNi alloy with 12ndash15Ni

(iv) refining and enrichment of FendashNi with 12ndash

15Ni to FendashNi with 18ndash23Ni in OBM

converters and granulation of the final market-able alloy product

Mechanisms of laterite solid statereductionThe main reactions that take place during coal based

reduction of iron nickel and cobalt oxides contained in

laterites can be summarised as follows

(i) three-step reduction of hematite

Step 1 hematite to magnetite

3Fe2

O3zCO2Fe

3O

4zCO

2 (1)

Step 2 magnetite to wustite

Fe3O4zCO3FeOzCO2 (2)

Step 3 wustite to iron

FeOzCOFeozCO2 (3)

One-step reduction of nickel and cobalt oxides as

follows

(a) NiOzCONiozCO2 (1a)

(b) CoOzCOCoozCO2 (1b)

(i) coal de-volatilisation

solid fuel (coal lignite coke)

carbon (C)zVolatile matter (4)

(ii) carbon gasification (Boudouard reaction)

Cz

CO2

2CO (5)

Hydrocarbons are the main gas constituents of the

volatile matter In high temperatures the high hydro-

carbons are cracked into low ones so that gaseous

reductants CO and H2 are evolved7

There is a general acceptance7ndash9 that solid-state

reduction in the Fe-C-O system (in the presence of solid

fuel) is mainly carried out via the gaseous intermediates

(mainly CO) which are produced by the solid fuelrsquos

gasification reaction (5) Regeneration of gaseous reduc-

tant through the Boudouard reaction provides the

reductive atmosphere needed for the transformation of iron nickel and cobalt oxides Direct contact of the ore

with carbon particles is probably responsible for the

production of CO during the very early stages of

reduction according to the following reaction

AxOyzCAxOy1zCO (6)

where A5Fe Ni or Co

But the overall reductive reaction mainly occurs

through the combination of reaction (7) below and

reaction (5) as follows

AxOyzCOAxOy1zCO2 (7)

AxOyzCAxOy1zCO

Physico-chemical parameters affecting reducibility of nickeliferous laterites

Greek lateritesReducibility of Greek laterites has been a subject of

extended research in order to find optimum values of

the physico-chemical parameters affecting their roasting

reduction process Given that energy requirementsconstitute one of the basic pillars for competitiveness

and development of the metallurgical process applied

the highest necessary reduction degree (37) of the

calcine is of decisive importance as it corresponds to

important energy saving during the smelting step of the

process and also because with this reduction degree

Table 1 Typical chemical analysis of Greek nickeliferouslaterites

Component Evia Lokrida Kastoria

SiO2 282 186 322Al2O3 70 109 29Fe2O3 475 450 248Fetot 332 314 173Cr2O3 31 27 14MnO 004 004 001

MgO 32 40 154Ni 103 115 145Co 005 006 006S 04 045 040CaO 30 66 145LOI 50 75 125Total 9888 9741 9903

(ii)

(iii)

Zev gol is et al The reducibility of the Greek nickeliferous laterites

10 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2010 VOL 1 19 NO 1





smelting step is a quiet process since no reduction gasesare evolved through the slag in the EF

Table 2 presents a summary of the conditions

employed and the main conclusions drawn by the

published work on reducibility of Greek nickeliferous

laterites Temperature has proved to be one of the most

important operational parameters in RK roastingreduction of the Greek laterites According to the

equilibrium diagram of the Fe-C-O system as presentedin Fig 1 magnetite reduction (Fe3O4zCO53FeOzCO2) and wustite reduction (FeOzCO5FeozCO2) can take place above 680 and 700uC

respectively10 Chemical analysis of representative sam-

ples taken along the length of industrial RKs indicatedthat up to 700ndash800uC laterite reduction remained in low

levels (up to 5ndash7) but it was drastically increased for

higher temperatures11 (however always 300)

Calcine temperature is not increased above y850uC

due to agglomeration of the calcine Moreover all

experiments carried out in the laboratory by different

researchers regarding reducibility of Greek laterites withsolid fuels in the temperature range of 700ndash900uC

showed that an increase of temperature favours reduc-

tion rate of both iron and nickel oxides Nevertheless

influence of temperature on the reduction degree of iron

oxides is positive between 700 and 750uC1213 or 700 and

800uC according to nickeliferous RK dust and pellets

reducibility tests14 and then it diminishes for higher

temperatures Within the same temperature range

examined nickel oxide reduction degree is increased

for temperatures 700ndash800uC and then it remains

practically constant1213

Reducibility of laterite is considerably affected by the

ore grain size as shown during ore treatment in RKsand EFs of industrial scale for ferronickel produc-

tion1516 The conclusion drawn from this work is that

mean size of the ore and reduction degree are inversely

proportional Indeed even by macroscopic observation

of calcined ore grains topochemical reactions are

taking place that is reductive reactions take place

upon the ore grainrsquos surface within the temperature

range 700ndash850uC So by decreasing ore particle sizefree surface is increased and therefore total rate of

reduction is increased It was proved that gradual

decrease of feed size from 240 to 212 mm had very

satisfactory results in terms of the calcinersquos reduction

degree achieved Additionally a finer ore correspondsto a higher mean temperature of the calcine therefore

it corresponds to a more energy saving during smeltingof the calcine Nevertheless studying the effect of ore

grain size not only in the pre-reduction but also in the

smelting step of the Greek laterites it has been

concluded that a high portion of fine particles fed into

the RKs favoured high levels of dust production

(which means a higher nickel loss in dust operational

problems of the RKrsquos dedusting installation and

additional cost for dust handling and treatment in

order to be pelletised and recycled) and was responsible

for lower height of calcine-self-lining for prevention of EF walls chemical attack from slag Laboratory

studies using Greek laterite ore and solid fuels of

various grain sizes have also confirmed that iron and

nickel oxide reduction rate increases with decreasing

ore and carbonaceous material grain size This

phenomenon is more evident for grain size bigger than

3 mm as the difference in reduction obtained for finer

particles is less significant12

The type of solid fuel used as reductant constitutesanother critical parameter affecting reducibility of

Greek laterites Its role is much more complex than

being just a heat source as for example in cementproduction where fuel calorific value is the ultimate

critical parameter17 In case of laterite reduction solid

fuels are utilised both for heating and reduction thustheir reactivity is of great importance Also they can be

classified according to their reactivity as follows lignite

coal coke and graphite11 Lignite is characterised by its

high volatile matter inherent moisture and low percen-

tage of fixed carbon (Cfix) It evolves its thermal energy

in lower temperatures compared to coal or coke and

graphite which contain a higher percentage of fixed

carbon and a lower percentage of volatile matter than

lignite Laboratory studies of the Greek laterites withdifferent types of solid reductants maintaining the other

parameters fixed (temperature ore and fuel grain size

C

fix

Fe ratio etc) confirmed that the use of lignite

18

resulted in higher iron and nickel oxide reduction

degrees in comparison with the use of coal and pet

coke9 Moreover increasing the amount of carbonac-

eous material relative to iron and nickel oxide content

increased the rate of reduction Also industrial scale

experiments have shown that reduction degree of Greek

laterites decreases as we go from lignite to coke in the

following sequence ligniteRcoalRcoke11

The role of solid fuels used for reduction of Greek

laterites in RKs has also been studied1116 The conclu-

sions drawn after extensive evaluation of operational

data is that optimum results with respect to calcine

reduction are obtained in the appropriate combinationof solid fuels so that the necessary amount of volatiles

and Cfix respectively is contained Moreover increase of

the lignite amount has proved to result in an increased

reduction rate due to burning of the volatile matter in

the first zone of the RKs (drying preheating zone) andtherefore maintaining of the required reductive atmo-

sphere so that a higher reduction is obtained

Nevertheless very high content of volatile matter in

the metallurgical mixture corresponds to high tempera-

ture of RK flue gases which cause increased thermal

losses and risk for fire in the dedusting installation For

this reason decrease of lignite participation in the

metallurgical mixture is required and increased amountof less reactive coal with higher content of the main

reductive agent Cfix resulting in a lower specific

consumption of fuel per ton of natural laterite

There are various approaches published in interna-

tional literature concerning the effect of solid fuel

volatile matter in iron ore reduction All of them

however seem to agree that volatiles increase the rate of

reduction There is also an agreement among different

researchers that participation of volatiles in reductiondepends mainly on temperature Thus at temperatures

below 900ndash1000uC78 reduction by volatile matter is

regarded as quite significant whereas at higher tem-peratures the role of volatiles is negligible so that at

higher temperatures reduction mainly takes place

through solid carbon This is due to the fact that most

of volatiles are evolved at temperatures 1000uC11 Liu

et al and Strezov et al1920 also investigated the

fundamental mechanisms for iron ore fines reduction


Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2010 VOL 1 19 NO 1 11





T a b l e

2

L a b o r a t

o r y

a n d

i n d u s t r i a l r e s u l t s

o n

r e d u c i b

i l i t y

o f G r e e k

n i c k e l i f e r o u s

l a t e r i t e s

R e f e r e n c e

Z e v g o l i s 1 1

H a l i k i a - N e o u

e t

a l 1 2

H a l i k i a

a n d

S k

a r t a d o s

1 8

N e o u

e t

a l 9

N e o u

e t a l 1 3

Z e v g o l i s

e t

a l 1 4

O r i g i n o f

l a t e r i t e o r e

E v i a ndash L o k r i d a ndash P e l l e t s

( f r o m

r o t a r y k i l n d u s t )

7 0 ndash 3 0 ndash 5 w t -

E v i a

ndash L o k r i d a ndash K a s t o r i a

6 0 ndash 2 5 ndash 1 5 w t -

E v i a ndash L o k r i d a ndash K

a s t o r i a


E v i a ndash L o k r i d a ndash K a s t o r i a


K a s t o r i a

G r e e k N i -

f e r r o u s l a t e r i t e

ndash r o t a r y k i l n d u s t

O r e g r a i n s i z e

O r e 2 1 5 m m

p e l l e t s 2 1 2 m m

2 2 0

8 z 3 8 m m

2 1 0

0 z 3 8 m m

2 5 3

z 3 8 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

O r e 2 0 2 5 0 z 0 0 3 8 m m

p e l l e t s 2 1 0 z 5 6 m m

2 1 4 z 1 0 m m

D u s t 2 1 0 5 m m p e l l e t s 9 m m

R e d u c t a n t

C o a l l i g n i t e

C f i x

( o f d u s t )

L i g n

i t e

L i g n i t e c o a l

P e t c o k e

C o a l

C f i x

( o f d u

s t )

C f i x F e t o t

1 5 2 4

1 4

3 1

1 6 0 2 ndash 1 5 0 1

1 4 6 3

1 3 5 1

1 2 4 ndash 1 2 6

R e d u c t a n t

g r a i n s i z e

2 3 0 m m 2 5 m m

2 1 0 0 m m

2 2 0

8 z 1 4 7 m m

2 1 4

7 z 1 0 4 m m

2 1 0

4 z 7 4 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

2 0 1 5 0 z 0 1 0 6 m m

hellip

S p e c i m e n f o r m

B u l k o r e a n d s o l i d f u e l s

G r o

u n d l a t e r i t e

a n d

l i g n i t e

B u l k o r e a n d

s o l i d f u e l s

G r o u n d l a t e r i t e

a n d p e t c o k e

P u l v e r i s e d o r e ndash

p e l l e t s b i n d i n g a g e n t

b e n t o n i t e 1

R o t a r y k i l n d u s t p e l l e t s

( o f s a m e

d u s t )

T e m p e r a t u r e

u C

9 2 0

7 0 0

ndash 8 5 0

8 6 0 ndash 9 0 0

7 5 0 ndash 9 0 0

7 0 0 ndash 9 0 0

7 0 0 ndash 8 5 0

M a x i m u m

r e d u c t i o

n

d e g r e e ndash

c o n d i t i o n s

2 5

3 2 7

3

2 9 5 5

2 3 1 6

3 1 7 4

2 8

9 2 0 u C

8 5 0

u C

9 0 0 u C

9 0 0 u C

9 0 0 u C

8 5 0 u C

2 1 5 m m

o r e

2 1 2 m m

p e l l e t s

2 3 0 m m

c o a l

2 5 m m

l i g n i t e

2 5 3

z 3 8 m m

o r e

2 1 0

4 z 7 4 m m

l i g n i t e

L i g n i t e

P u l v e r i s e d o r e

R o t a r y k i l n d u s t

A c t i v a t i o n

e n e r g y E k J m o l 2

1

hellip

4 0 1

7 ( i r o n o x i d e )

hellip

7 2 4 ( i r o n o x i d e )

hellip

4 2 E 8 4

( 7 0 0 ndash 7 5 0 u C )

8 7 4

5 ( n i c k e l o x i d e )

E 4 2 ( 8 0

0 ndash 8 5 0 u C )

R a t e c o n t r o l l i n g s t e p

hellip

D i f f u s i o n ( i r o n o x i d e )

M i x e d k i n e t i c m o d e l

c h e

m i c a l r e a c t i o n

ndash d i f f u s i o n ( n i c k e l o x i d e )

hellip



c h e m i c a l

r e a c t i o n ndash d i f f u s i o n

( n i c k e l o x i d e )

hellip

M i x e d k i n

e t i c m o d e l c h e m i c a l

r e a c t i o n ndash

d i f f u s i o n ( i r o n o x i d e )







in coalndashore mixtures and the role of the fuel volatile

matter They reported that volatile matter constituents

were methane (CH4) within the temperature range 450ndash

700uC and CO kai H2 for temperatures 800uC Gas

agents CO kai H2 are mainly responsible for hematite

(Fe2O3) reduction up to 800uC while additional CO

generated due to the Boudouard reaction at elevated

temperatures resulted in acceleration of the reduction

procedure Concerning laboratory work with Greek

laterite the fact that remaining carbon in the calcine is

in most cases much higher than the theoretically

expected indicates according to researchers that evolvedvolatiles participate in the oxide reduction912 but this

requires further investigation

Reducibility tests have been conducted by different

researchers on Greek laterites in the form of dust and

pellets as well Dust produced during industrial treat-

ment of laterite in the RKs has a higher Ni content than

the ore and a carbon content 8 which is higher than

the stoichiometrically required (y65) for FendashNi 13

production Thus it is evident that agglomeration and

recycling of dust which is y7 of the laterite feed

contribute to the economics of the metallurgical process

So the reductive behaviour of the industrially produced

cement bonded laterite pellets has been studied forcomparison with the behaviour of same origin laterite

dust14 Reducibility tests of pulverised Kastoria laterite

ore have been also conducted using coal as a reductant

in order to compare with the reductive behaviour of

agglomerated mixture (pellets) of Kastoria pulverised

ore and coal (the stoichiometrically required for FendashNi

13 production) with bentonite as the binding agent13

The temperature range of the experimental procedure

was 700ndash900uC It was deduced from both series of tests

that iron oxide reduction degree obtained for pellets was

lower than for dust (with same laterite) under the same

conditions though no serious difference is observed

concerning nickel oxide reduction This difference in thereductive behaviour between laterite dust and pellets can

be attributed to the fact that the binding agent covers

part of the oxide grains decreasing their reactive surface

area

The conclusion drawn from all reducibility studies of

Greek nickeliferous laterites either conducted in an

industrial or in a laboratory scale within the tempera-

ture range of 700ndash900uC is that independently of the

conditions employed ie ore grain size temperature and

type and amount of the solid reductant in no case

calcine reduction degree exceeds 33 though the

remaining carbon in the calcine is almost always higher

than the theoretically required for further progress of reductive reactions Given that the conversion of Fe2O3

1 Equilibrium curves of CO-CO2 versus temperature for Fe-C-O system10

2 Reduction degree versus time typical diagrams at various temperatures of a laterite ore mixture (Evia IslandndashLokridandash

Kastoria 60ndash25ndash15 wt- 20053z0037 mm) with lignite (20149z00940 mm)12 b electrostatic filter dust14 and c elec-

trostatic filter pellets14







to Fe3O4 and to FeO corresponds to a reduction of 111and 333 respectively it comes that magnetite and

wustite should coexist in the calcine and no furtherconversion to metallic iron exists Additionally it is

concluded that reductive reactions occur within the first 20

to 30 min of the process and then they practically stop for

all cases examined This can be attributed to kineticphenomena such as the formation within the temperature

range examined of iron-silicate minerals such as fayalite

(2FeOSiO2) which probably covers oxide grains thusimpeding progress of the reduction In Fig 2 typical

reduction degree diagrams versus time within a tempera-

ture range 700ndash850uC are presented for reduction of

pulverised laterite ore mixture (Evia islandndashLokridandash Kastoria 60ndash25ndash15 wt- 20053z0037 mm) with lig-

nite (20149z00940 mm) and also the reduction of

electrostatic filter dust from RKs as well as the reduction

of laboratory made pellets from this dust From these

diagrams it comes that reduction degree does not exceed

33 The same is shown in Fig 3 with reduction in

industrial RKs (In Fig 3 reduction is defined as the ratio

Fe2z

Fetot

|100 so the real reduction degree ie

Oi Of eth THORN=Oifrac12 |100 where Oi is the initial oxygen and

Of is the final oxygen in iron oxides is 333)

Industrial operation with garnierite type of ores shows

that reduction in the RK goes up to 37 which meansthat we have metallic iron in the calcine21

World experienceReducibility tests concerning different types of nickelifer-

ous laterites according to international literature2223

indicate that chemical mineralogical composition of the

laterite ore is a critical parameter for the final degree of reduction obtained Reducibility of several types of

nickeliferous laterites from the Dominican Republic22

(grain size 20074 mm) has been studied within the

temperature range 400ndash1000uC using hydrogen as a

reductant The aim of the study was to compare the

reductive behaviour of garnieritic limonitic and inter-

mediate type of ores The experimental results clearly

indicated that reducibility of each oxide (iron nickel and

cobalt oxide) depends on the ore type Moreover

chemical and mineralogical analysis of the reduced

samples indicated that nickel and iron (oxide) degree of

metallisation was higher in limonitic than in garnieritic

and intermediate type of ores Specifically both iron andnickel oxide degree of metallisation obtained after 40 minprocessing of the garnieritic type of ore at 1000uC was

y10 Temperature variation between 400 and 1000uC

did not affect significantly the reduction process The

respective degrees of metallisation were 80 and 70 at

1000uC concerning limonitic type of ore and they were

dramatically increased 800uC Cobalt degree of metal-

lisation at 1000uC was slightly lower (y65) in limonitic

compared to garnieritic type of ore (70) and the effect of

temperature variation was negligible concerning the first

and significant 850uC concerning the second one This

is different from what happens in reduction by solid fuelsThat is in solid fuel reduction limonitic type of ores

cannot be reduced to metallic iron so reduction stops

when reduction degree of iron oxides is 333 Low

nickel oxide reducibility in the garnieritic type ores was

attributed to the formation of olivine a nickelndashironndash

magnesium orthosilicate and the tendency of nickel to

3 Temperature and reduction degree in RK







exchange places with magnesium in silicates which are

stable in high temperatures On the contrary the low

magnesia and silica content of the limonitic type of ores is

not adequate to result in hosting nickel in the olivine

phase thus the per cent of nickel oxide reduction degree

increases for high temperatures Cobalt oxide reducibility

was higher for the garnieritic laterite type and the effect of

temperature was more evident for lower temperatures

due to the cobalt tendency to replace iron in the limonitelattice Reductive reactions concerning all types of laterite

ores examined after 40 min practically stopped In the

Greek laterite reducibility tests as it has already been

mentioned above reductive reactions practically stopped

after 20 to 30 min

Reducibility tests of a garnieritic type of laterite ore in

the form of pellets in the range 700ndash1000uC using a CO

CO2 mixture as a reducing agent has also been

conducted23 Olivine (MgFe)2SiO4 formation was

proved to be critical for the reduction progress since it

is stated that reducibility (determined by percentage of

weight loss after first calcined in the same temperaturelaterite ore pellets) reaches the highest possible values for

temperatures above serpentine (Mg Fe Ni)6Si4O12(OH)6decomposition (y600uC) and below transformation

temperature of amorphous olivine to a stable miner-

alogical phase (y810uC) It was also deduced that a

strongly competitive relation exists among reduction

progress and olivine formation ie a slow reduction rate

(by employment of mild reducing atmosphere through

gas reducing agent) relative to olivine formation results to

a lower reduction degree On the contrary rapid

reduction rate (by employment of intensive reducing

atmosphere during the first minutes of the reductive

procedure) relative to the crystallisation of the olivinephase results in higher reduction degree values

Reduction kinetics of Greek nickeliferous lateritesKinetic analysis carried out for the Greek nickeliferous

laterite roasting reduction is based on the unreacted

shrinking core model Roasting reduction kinetics of

Greek laterite fine particles (EviandashLokridandashKastoria ore

mixture 60ndash25ndash15 wt- granulometry 20250z

0037 mm temperature range 700ndash900uC) with lignite

and pet coke as reductants respectively were con-ducted912 The methodology of work used for

approaching the rate controlling step of the process is

the application of the diagnostic equation

lnln 1aeth THORNfrac12 ~n ln tzln b (8)

where a is reduction degree () of iron or nickel oxides t

is time (s) b is constant and n is constant depending on

the rate controlling mechanism and the geometrical

characteristics of the ore and solid reductant particles

The obtained n values from application of the experi-

mental data a ndash t which represent the slopes of the linear

graphic representation of equation (8) are comparedwith the theoretical values of the widespread used kinetic

equations of Table 3 It is noted that equations (D1)ndash

(D5) correspond to the diffusion rate controlling step

equations (F1) (R1) and (R2) correspond to chemical

reaction mechanism and equations (A2) and (A3)

correspond to the nucleation rate controlling step

Linearity assessment of diagrams ln[2ln(12a)] versus

lnt and determination of the slope n were obtainedthrough the application of the least squares method It isnoted that no time greater than 15 min was used for the

kinetic analysis given that after the first 20 min thereactions tended to stop in all cases examined Theconclusion deduced from this work was that diffusion

kinetic equations (D1)ndash(D5) best fitted the experimental

data concerning iron oxide reduction Moreover it hasbeen reported that the ValensindashCarter equation was themathematical model that best represented the proposeddiffusion mechanism with Z value equal to 05 Another

value of coefficient Z would probably result in an evenmore representative mathematical model With respectto the nickel oxide reduction kinetics it was reported

that chemical reaction is the rate controlling step for thelower temperatures (up to 800uC) but no certain kineticmodel from Table 3 (equations (F1) (R1) and (R2)) canbe stated to be the best fitting due to the fact that all of

the aforementioned three equations fit very well

The rate controlling step though changes for highertemperatures (up to 900uC) but there has not been a

conclusion based on reported approaches about themechanism that prevails within the temperature range800ndash900uC

Reduction kinetics of RK dust and laboratory made

pellets of the same origin in the temperature range 700ndash 850uC were studied14 The experimental data obtainedconcerning iron oxide reduction were applied to thefollowing mathematical models

(i) CrankndashGinstlingndashBrounshtein (CGB) kineticmodel

1(2=3)a(1a)2=3~Kt (D4) (9)

rate controlling step diffusion through the

product layer

(ii)(1a)1=3

~Kt (R2) (10)

rate controlling step chemical reaction at the

interface between the unreacted core and the

product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)

Generalised equation that is a combination of

equations (9) and (10) based on the additivity of

reaction times

rate controlling step mixed controlled mechanism

Table 3 n values of kinetic equations for gasndashsolidreactions

Kinetic equation n

D1 a 25Kt 062D2 (12a )ln(12a )za 5Kt 057D3 [12(12a )13]25Kt 054D4 12(23)a 2(12a )235Kt 057D5 Kt 5Z z[1z(Z 21)a ]232(Z 21)(12a )23(Z 21) (ValensindashCarter equation)

F1 2ln(12a )5Kt 10R1 12(12a )125Kt 111R2 12(12a )135Kt 107A2 [2ln(12a )]125Kt 20A3 [2ln(12a )]135Kt 20

Z coefficient representing the product volume per volume ofthe reactants consumed Z is assumed to be 05







It was deduced from the kinetic analysis that the

mixed kinetic model equation (11) fits well the experi-mental data for all dust samples and pellets of a certainorigin (the washing tower) up to 750uC This kinetic

model also verified the experimental data for pellets of different origin (ie electrofilter and polycyclone dusts)up to 800uC At higher temperatures ie up to 850uC ithas been confirmed the predominance of diffusion

mechanism according to the CGB equation (9)The activation energy value of the rate-determining

step at various conditions has been evaluated concern-ing coal based laterite reduction by means of thewidespread rate expression (12) that follows

r~kC n (12)

where r is the reaction rate k the rate constant C thefluid reactant concentration (mol L21) and n the orderof the reaction Assuming that the fluid reactantconcentration is constant the Arrhenius law[lnk 5lnAo ndash E R(1T )] can be used for calculation of the

activation energy through slope determination of thefollowing linear equation

lnr~ln(AoC n)(E =R)(1=T ) (13)

where r is the mean initial reduction rate valuecalculated through the expression r5DaDt21 (a is thereduction rates obtained from the experimental data)

Ao is the frequency factor of the Arrhenius law C is thefluid reactant concentration (mol L21) n the order of the reaction E the activation energy T the temperatures

(K) examined for the kinetic analysis and R the universalgas constant Activation energy has also been calculatedby Zevgolis et al concerning RK dust and laboratory

made pellets of the same origin through application of the Arrhenius law to the slopes of the generalisedequation (13) lines mixed controlled mechanism at 700and 750uC ie by means of the relationship

ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)

The activation energy values concerning iron oxidereduction912 (724 and 402 kJ mol21) indicate that theprevailing kinetic mechanism may be either the mixedcontrolled mechanism (diffusionndashchemical reaction) ordiffusion Activation energy value reported concerningnickel oxide reduction (874 kJ mol21) indicates thepredominance ndash at least for a certain temperature rangeof chemical reaction mechanism The mixed controlledmechanism for iron oxide reduction was proposed byZevgolis et al for low temperatures (700ndash750uC) and

diffusion through the product layer for higher tempera-tures (800ndash850uC)14

The conclusions drawn from the kinetic analysis of the Greek nickeliferous laterite solid state reductionare in agreement with the conclusions drawn by otherstudies concerning reducibility tests of different originlaterite samples either in pellet form23 or in form of cement bonded laterite briquettes with CO-CO2 gas

reducing mixture24

within the temperature range (700ndash 1000uC) Mixed control (chemical reaction and diffu-

sion of the reducing gas agent through the productlayer) is the mechanism that seems to prevail duringthe reductive procedure It is apparent from theaforementioned that diffusion constitutes a seriouskinetic factor affecting solid state reduction of laterites

either on its own or in combination with chemicalreaction in the interface product layer ndash gas reactantKinetic analysis of Greek nickeliferous lateritesenhances the conclusion drawn by all the reportedreducibility tests according to which iron silicatemineralogical phases formed in the temperature rangeexamined (700ndash900uC) like fayalite (2FeOSiO2)probably cover the iron oxide grains and thus impede

the progress of the reaction

ConclusionsThe main physicochemical parameters affecting reduci-bility of the Greek nickeliferous laterite ores have beenreviewed It is concluded that no matter if controllingthe values of physicochemical parameters such astemperature grain size of materials and type of solidreductant to be optimum iron and nickel oxide

reduction degrees obtained do not exceed 33 and 76respectively though the remaining carbon in the calcineis adequate for further progress of the reductive

reactions This means that practically no metallic ironis formed during roasting reduction of Greek lateritesand nickel oxide is partially transformed to metallicnickel Decrease of the ore and solid reductant grain size(mainly for granulometry z3 mm) and use of reactivesolid fuels (lignite) instead of less reactive (coal or coke)favour considerably iron and nickel oxide degree of

reduction Increase of temperature within the tempera-ture range 700ndash900uC examined results in increase of oxides reduction rate but its influence on iron and nickeloxide degree is evident up to 750ndash800uC and then itdiminishes Reduction process progresses initially with arelatively high rate for the first ten minutes then the rate

starts to decrease until it diminishes to zero after thefirst 20 min reaction The conclusion that reductivereactions practically stop after a time of 20ndash40 min isverified by published approaches concerning reducibility

studies of different origin laterite ores It can beattributed to the formation within the temperaturerange examined of iron silicate minerals such as fayalite(2FeOSiO2) or forsterite (Mg2SiO4) which probablycover oxide grains and impede further progress of thereduction Thus future reducibility studies of Greeknickeliferous laterites should be focused on mineralogi-cal analysis of the reduction products in relation withthe factors affecting the formation and reduction of complex nickelndashironndashmagnesium silicate phases so that

the highest possible reduction degree is obtainedKinetic studies of the reductive procedure showed thatmixed control and diffusion mechanisms have been

found to prevail during reduction of oxides

References1 wwwlibmurdocheduauadtpubfilesadt-MU20051004114504

02Wholepdf

2 A D Dalvi W Bacon and C Osborne lsquoThe past and the future of

nickel lateritesrsquo Proc PDAC 2004 Int Convent Toronto

Canada March 2004 PDAC 1ndash27

3 E N Zevgolis lsquoExtractive metallurgy of nickel part I

Pyrometallurgical methodsrsquo 2000 Athens National TechnicalUniverity of Athens

4 E Mposkos A Orfanoudaki and Th Perraki lsquoThe Ni distribution

in the mineral phases of Greek FendashNi laterite depositsrsquo Proc 3rd

Symp on lsquoMineral wealthrsquo Athens Greece November 2000

Technical Chamber of Greece 107ndash115

5 N Albadakis lsquoNi-minerals in the deposits of the sub-pelagonic

zonersquo Miner Wealth 1984 31 9ndash32







6 S Agatzini lsquoA new approach to the metallurgical treatment

of nickeliferous lateritesrsquo Report within the framework of the

CEC BRITE-EURAM Programme ECU 368000 (In cooperation

with University of Hertfordshire University of Minho) 1993 1ndash

12

7 Q Wang Z Yang J Tian W Li and J Sun lsquoMechanisms of

reduction in iron orendashcoal composite pelletrsquo Ironmaking

Steelmaking 1997 24 (6) 457ndash460

8 E Donskoi D L S McElwain and L J Wibberley lsquoEstimation

and modeling of parameters for direct reduction in iron orecoal

composites part II Kinetic parametersrsquo Metall Mater Trans B 2003 34B 255ndash266

9 P Neou-Syngouna I Halikia and K Skartados lsquoPrereduction

of laterites with petroleum coke influence of the granulometric

size on its progress and kineticsrsquo Min Metall Ann 1997 1 25ndash

49

10 E N Zevgolis lsquoIron-cast iron metallurgy ndash theory and technologyrsquo

2004 Athens National Technical Univerity of Athens

11 E N Zevgolis lsquoA contribution to the study of problems of rotary

kilns in roasting reduction of greek nickeliferous lateritesrsquo Thesis

for lectureship National Technical Univerity of Athens Athens

Greece July 1982

12 I Halikia P Neou-Syngouna and M Katapotis lsquoReductive

roasting of iron-nickel ore using greek lignite thermodynamic and

kinetic approachrsquo In honor of Professor Emeritus of NTUA A Z

Fragiskos 1998 Athens National Technical Univerity of Athens

13 P Neou-Syngouna I Halikia C Skartados L Papadopoulou

and G Portokaloglou lsquoComparative study of laterite roasts in the

form of powder and pelletsrsquo Min Metall Ann 1999 1ndash2 85ndash

118

14 E N Zevgolis I Halikia and I-P Kostika lsquoReductive behavior of

the recycled dust during nickeliferous laterite treatmentrsquo Erzmetall

ndash the World of Metallurgy 2006 59 (6) 350ndash359

15 E N Zevgolis lsquoThe importance of iron ore grain size in rotary kiln

operationrsquo Miner Wealth 1986 45 103ndash110

16 E N Zevgolis lsquoThe ore grain size effect in ferroalloys production

by the rotary kiln ndash electric furnace methodrsquo Miner Wealth 1988

54 39ndash46

17 E N Zevgolis and A Tzamtzis lsquoThe role of solid fuels used for

reduction in rotary kilnsrsquo Techn Chron C 1987 7C (2) 5ndash19

18 I Halikia and K Skartados lsquoEffect of solid reductant on themetallurgical behaviour of laterite calcinersquo In Memory of NTUA

Professor Emeritus J Papageorgarakis 294ndash303 2001 Athens

National Technical Univerity of Athens

19 G-S Liu V Strezov L A Lucas and L J Wibberley lsquoTermal

investigations of direct iron ore reduction with coalrsquo Thermochim

Acta 2004 410 133ndash140

20 V Strezov G-S Liu J A Lucas and L J Wibberley

lsquoCalorimetric study of the iron ore reduction reactions in mixtures

with coalrsquo Ind Eng Chem Res 2005 44 621ndash626

21 E N Zevgolis Report from visit to FENIMAK Ferronickel Plant

Kavadarci Fyrom 24 February 2000

22 M Kawahara J M Toguri and R A Bergman lsquoReducibility of

laterite oresrsquo Metall Trans B 1988 19B 181ndash185

23 S Li and K S Coley lsquoKinetics and mechanism of reduction of

laterite ore high in serpentinersquo Proc J M Toguri Symp onlsquoFundamentals of metallurgical processingrsquo (ed G Kaiura et al)

179ndash192 2000 Ottawa CIM

24 H Purwanto T Shimada R Takahashi and J Yagi lsquoReduction

rate of cement bonded laterite briquette with CO-CO2 gasrsquo ISIJ

Int 2001 41 S31ndashS35







bearing mineral phases that have been found in selective

Lokrida deposit parts are nepouite [(NiMg)3Si2O5(OH)4]

and takovite [(Ni5Al4O2(OH)86H2O]5 The main miner-

alogical constituent of the Kastoria ore was found to be

serpentine (MgFeNi)6Si4O12(OH)6 The high goethite (a-

FeOOH) content of Kastoria ore indicates a higher

content of the crystallic moisture compared to the other

types of Greek laterites Serpentine and nickeliferous

magnesian crostendite (Fez28 Fez3

4 )(Si4Fez34 )O20(OH)6-

where part of Fez2 can be replaced by Mg- represent the

main nickel carrier minerals in Kastoria ore6

Microcrystallity of the nickel bearing mineral phases

renders their liberation and upgrading by mineral proces-

sing techniques extremely difficult something which would

improve drastically the cost of pyrometallurgical or

hydrometallurgical laterite treatment

Greek nickeliferous laterites are processed by the

pyrometallurgical method lsquoLarco Processrsquo at the metal-

lurgical plant of LARCO GMM SA for the production

of a ferronickel alloy (FendashNi) with y20Ni and low C

S and P suitable for austenitic stainless steel productionlsquoLarco Processrsquo involves the following steps

(i) handling and mixing of raw materials (ie

laterite solid fuels and agglomerated rotary

kiln (RK) dust in form of pellets)

(ii) drying preheating and controlled prereduction

of the metallurgical mixture in RKs and

production of a calcine

(iii) smelting reduction of the calcine in open-bath

submerged-arc electric furnaces (EFs) and

production of an FendashNi alloy with 12ndash15Ni

(iv) refining and enrichment of FendashNi with 12ndash

15Ni to FendashNi with 18ndash23Ni in OBM

converters and granulation of the final market-able alloy product

Mechanisms of laterite solid statereductionThe main reactions that take place during coal based

reduction of iron nickel and cobalt oxides contained in

laterites can be summarised as follows

(i) three-step reduction of hematite

Step 1 hematite to magnetite

3Fe2

O3zCO2Fe

3O

4zCO

2 (1)

Step 2 magnetite to wustite

Fe3O4zCO3FeOzCO2 (2)

Step 3 wustite to iron

FeOzCOFeozCO2 (3)

One-step reduction of nickel and cobalt oxides as

follows

(a) NiOzCONiozCO2 (1a)

(b) CoOzCOCoozCO2 (1b)

(i) coal de-volatilisation

solid fuel (coal lignite coke)

carbon (C)zVolatile matter (4)

(ii) carbon gasification (Boudouard reaction)

Cz

CO2

2CO (5)

Hydrocarbons are the main gas constituents of the

volatile matter In high temperatures the high hydro-

carbons are cracked into low ones so that gaseous

reductants CO and H2 are evolved7

There is a general acceptance7ndash9 that solid-state

reduction in the Fe-C-O system (in the presence of solid

fuel) is mainly carried out via the gaseous intermediates

(mainly CO) which are produced by the solid fuelrsquos

gasification reaction (5) Regeneration of gaseous reduc-

tant through the Boudouard reaction provides the

reductive atmosphere needed for the transformation of iron nickel and cobalt oxides Direct contact of the ore

with carbon particles is probably responsible for the

production of CO during the very early stages of

reduction according to the following reaction

AxOyzCAxOy1zCO (6)

where A5Fe Ni or Co

But the overall reductive reaction mainly occurs

through the combination of reaction (7) below and

reaction (5) as follows

AxOyzCOAxOy1zCO2 (7)

AxOyzCAxOy1zCO

Physico-chemical parameters affecting reducibility of nickeliferous laterites

Greek lateritesReducibility of Greek laterites has been a subject of

extended research in order to find optimum values of

the physico-chemical parameters affecting their roasting

reduction process Given that energy requirementsconstitute one of the basic pillars for competitiveness

and development of the metallurgical process applied

the highest necessary reduction degree (37) of the

calcine is of decisive importance as it corresponds to

important energy saving during the smelting step of the

process and also because with this reduction degree

Table 1 Typical chemical analysis of Greek nickeliferouslaterites

Component Evia Lokrida Kastoria

SiO2 282 186 322Al2O3 70 109 29Fe2O3 475 450 248Fetot 332 314 173Cr2O3 31 27 14MnO 004 004 001

MgO 32 40 154Ni 103 115 145Co 005 006 006S 04 045 040CaO 30 66 145LOI 50 75 125Total 9888 9741 9903

(ii)

(iii)












































































C

fix


18














































T a b l e

2

L a b o r a t

o r y

a n d


o n

r e d u c i b

i l i t y

o f G r e e k


l a t e r i t e s

R e f e r e n c e

Z e v g o l i s 1 1


e t

a l 1 2

H a l i k i a

a n d

S k

a r t a d o s

1 8

N e o u

e t

a l 9

N e o u

e t a l 1 3

Z e v g o l i s

e t

a l 1 4

O r i g i n o f



( f r o m



E v i a




a s t o r i a




K a s t o r i a

G r e e k N i -




O r e 2 1 5 m m

p e l l e t s 2 1 2 m m

2 2 0

8 z 3 8 m m

2 1 0

0 z 3 8 m m

2 5 3

z 3 8 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

O r e 2 0 2 5 0 z 0 0 3 8 m m

p e l l e t s 2 1 0 z 5 6 m m

2 1 4 z 1 0 m m


R e d u c t a n t


C f i x

( o f d u s t )

L i g n

i t e


P e t c o k e

C o a l

C f i x

( o f d u

s t )

C f i x F e t o t

1 5 2 4

1 4

3 1

1 6 0 2 ndash 1 5 0 1

1 4 6 3

1 3 5 1

1 2 4 ndash 1 2 6

R e d u c t a n t

g r a i n s i z e

2 3 0 m m 2 5 m m

2 1 0 0 m m

2 2 0

8 z 1 4 7 m m

2 1 4

7 z 1 0 4 m m

2 1 0

4 z 7 4 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

2 0 1 5 0 z 0 1 0 6 m m

hellip



G r o


a n d

l i g n i t e

B u l k o r e a n d

s o l i d f u e l s


a n d p e t c o k e



b e n t o n i t e 1


( o f s a m e

d u s t )


u C

9 2 0

7 0 0

ndash 8 5 0

8 6 0 ndash 9 0 0

7 5 0 ndash 9 0 0

7 0 0 ndash 9 0 0

7 0 0 ndash 8 5 0

M a x i m u m

r e d u c t i o

n

d e g r e e ndash

c o n d i t i o n s

2 5

3 2 7

3

2 9 5 5

2 3 1 6

3 1 7 4

2 8

9 2 0 u C

8 5 0

u C

9 0 0 u C

9 0 0 u C

9 0 0 u C

8 5 0 u C

2 1 5 m m

o r e

2 1 2 m m

p e l l e t s

2 3 0 m m

c o a l

2 5 m m

l i g n i t e

2 5 3

z 3 8 m m

o r e

2 1 0

4 z 7 4 m m

l i g n i t e

L i g n i t e



A c t i v a t i o n


1

hellip

4 0 1

7 ( i r o n o x i d e )

hellip

7 2 4 ( i r o n o x i d e )

hellip

4 2 E 8 4

( 7 0 0 ndash 7 5 0 u C )

8 7 4


E 4 2 ( 8 0

0 ndash 8 5 0 u C )


hellip



c h e



hellip



c h e m i c a l



hellip

M i x e d k i n
















































area




































Fe2z

Fetot
























































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140

























































































C

fix


18














































T a b l e

2

L a b o r a t

o r y

a n d


o n

r e d u c i b

i l i t y

o f G r e e k


l a t e r i t e s

R e f e r e n c e

Z e v g o l i s 1 1


e t

a l 1 2

H a l i k i a

a n d

S k

a r t a d o s

1 8

N e o u

e t

a l 9

N e o u

e t a l 1 3

Z e v g o l i s

e t

a l 1 4

O r i g i n o f



( f r o m



E v i a




a s t o r i a




K a s t o r i a

G r e e k N i -




O r e 2 1 5 m m

p e l l e t s 2 1 2 m m

2 2 0

8 z 3 8 m m

2 1 0

0 z 3 8 m m

2 5 3

z 3 8 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

O r e 2 0 2 5 0 z 0 0 3 8 m m

p e l l e t s 2 1 0 z 5 6 m m

2 1 4 z 1 0 m m


R e d u c t a n t


C f i x

( o f d u s t )

L i g n

i t e


P e t c o k e

C o a l

C f i x

( o f d u

s t )

C f i x F e t o t

1 5 2 4

1 4

3 1

1 6 0 2 ndash 1 5 0 1

1 4 6 3

1 3 5 1

1 2 4 ndash 1 2 6

R e d u c t a n t

g r a i n s i z e

2 3 0 m m 2 5 m m

2 1 0 0 m m

2 2 0

8 z 1 4 7 m m

2 1 4

7 z 1 0 4 m m

2 1 0

4 z 7 4 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

2 0 1 5 0 z 0 1 0 6 m m

hellip



G r o


a n d

l i g n i t e

B u l k o r e a n d

s o l i d f u e l s


a n d p e t c o k e



b e n t o n i t e 1


( o f s a m e

d u s t )


u C

9 2 0

7 0 0

ndash 8 5 0

8 6 0 ndash 9 0 0

7 5 0 ndash 9 0 0

7 0 0 ndash 9 0 0

7 0 0 ndash 8 5 0

M a x i m u m

r e d u c t i o

n

d e g r e e ndash

c o n d i t i o n s

2 5

3 2 7

3

2 9 5 5

2 3 1 6

3 1 7 4

2 8

9 2 0 u C

8 5 0

u C

9 0 0 u C

9 0 0 u C

9 0 0 u C

8 5 0 u C

2 1 5 m m

o r e

2 1 2 m m

p e l l e t s

2 3 0 m m

c o a l

2 5 m m

l i g n i t e

2 5 3

z 3 8 m m

o r e

2 1 0

4 z 7 4 m m

l i g n i t e

L i g n i t e



A c t i v a t i o n


1

hellip

4 0 1

7 ( i r o n o x i d e )

hellip

7 2 4 ( i r o n o x i d e )

hellip

4 2 E 8 4

( 7 0 0 ndash 7 5 0 u C )

8 7 4


E 4 2 ( 8 0

0 ndash 8 5 0 u C )


hellip



c h e



hellip



c h e m i c a l



hellip

M i x e d k i n
















































area




































Fe2z

Fetot
























































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140




















T a b l e

2

L a b o r a t

o r y

a n d


o n

r e d u c i b

i l i t y

o f G r e e k


l a t e r i t e s

R e f e r e n c e

Z e v g o l i s 1 1


e t

a l 1 2

H a l i k i a

a n d

S k

a r t a d o s

1 8

N e o u

e t

a l 9

N e o u

e t a l 1 3

Z e v g o l i s

e t

a l 1 4

O r i g i n o f



( f r o m



E v i a




a s t o r i a




K a s t o r i a

G r e e k N i -




O r e 2 1 5 m m

p e l l e t s 2 1 2 m m

2 2 0

8 z 3 8 m m

2 1 0

0 z 3 8 m m

2 5 3

z 3 8 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

O r e 2 0 2 5 0 z 0 0 3 8 m m

p e l l e t s 2 1 0 z 5 6 m m

2 1 4 z 1 0 m m


R e d u c t a n t


C f i x

( o f d u s t )

L i g n

i t e


P e t c o k e

C o a l

C f i x

( o f d u

s t )

C f i x F e t o t

1 5 2 4

1 4

3 1

1 6 0 2 ndash 1 5 0 1

1 4 6 3

1 3 5 1

1 2 4 ndash 1 2 6

R e d u c t a n t

g r a i n s i z e

2 3 0 m m 2 5 m m

2 1 0 0 m m

2 2 0

8 z 1 4 7 m m

2 1 4

7 z 1 0 4 m m

2 1 0

4 z 7 4 m m

2 6 z 0 0 3 8 m m

2 2 0 8 z 3 7 m m

2 0 1 5 0 z 0 1 0 6 m m

hellip



G r o


a n d

l i g n i t e

B u l k o r e a n d

s o l i d f u e l s


a n d p e t c o k e



b e n t o n i t e 1


( o f s a m e

d u s t )


u C

9 2 0

7 0 0

ndash 8 5 0

8 6 0 ndash 9 0 0

7 5 0 ndash 9 0 0

7 0 0 ndash 9 0 0

7 0 0 ndash 8 5 0

M a x i m u m

r e d u c t i o

n

d e g r e e ndash

c o n d i t i o n s

2 5

3 2 7

3

2 9 5 5

2 3 1 6

3 1 7 4

2 8

9 2 0 u C

8 5 0

u C

9 0 0 u C

9 0 0 u C

9 0 0 u C

8 5 0 u C

2 1 5 m m

o r e

2 1 2 m m

p e l l e t s

2 3 0 m m

c o a l

2 5 m m

l i g n i t e

2 5 3

z 3 8 m m

o r e

2 1 0

4 z 7 4 m m

l i g n i t e

L i g n i t e



A c t i v a t i o n


1

hellip

4 0 1

7 ( i r o n o x i d e )

hellip

7 2 4 ( i r o n o x i d e )

hellip

4 2 E 8 4

( 7 0 0 ndash 7 5 0 u C )

8 7 4


E 4 2 ( 8 0

0 ndash 8 5 0 u C )


hellip



c h e



hellip



c h e m i c a l



hellip

M i x e d k i n
















































area




































Fe2z

Fetot
























































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140


























































area




































Fe2z

Fetot
























































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140




































Fe2z

Fetot
























































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140
































after 20 to 30 min






















































1(2=3)a(1a)2=3~Kt (D4) (9)


product layer

(ii)(1a)1=3

~Kt (R2) (10)



product layer

(iii) 1(2=3)a(1a)2=3z1(1a)1=3

~Kt (D4zR2) (11)



reaction times



Kinetic equation n















r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140

























r~kC n (12)








ln k (T 2)

ln k (T 1)~

E

R

1

T 2

1

T 1

(14)




reducing mixture24














02Wholepdf






















12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140
























12










49






Greece July 1982








118








54 39ndash46








Acta 2004 410 133ndash140
















the reducibility of the greek nickeliferous

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