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3 Mössbauer Studies of Healthy Brain Tissue

3 Mössbauer Studies of Healthy Brain Tissue

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32 MOSSBAUER

SPECTROSCOPY IN THE STUDY OF LATERITE MINERAL PROCESSING



614

200



1. SiO2 - Quartz

2. Fe2O3 - Hematite

3. (Mg,Fe,Al)6(Si,Al)4O10(OH)8 - Clinochlore

4. (Na,Ca)0.3(Al,Mg)2Si4O10(OH)2 xH2O Montmorillonite

5. FeOOH - Goethite

6. KAl2Si3AlO10(OH)2 - Muscovite

7. CaCO3 - Calcite

8. Mg3(OH)2Si4O10 - Talc



1



Intensity (cps)



150



100

1

2



50



3



3



2

1



4



2



334



66 8



3



12



33



5



1

1,2



1



1



7



2 2



2



1 2



3



1



2



1



3



0

5



10



15



20



25



30



35



40



45



50



55



60



65



70







FIGURE 32.8

X-ray pattern of the bulk hematitic laterite ore. (Reproduced from Ref. 19 with permission of Elsevier.)



microwave power was achieved employing a proportional power controller connected to the furnace magnetron.

Powder samples were placed, without applying pressure, in a cylindrical alumina crucible with r ¼ 4 cm, h ¼ 6 cm and d

(thickness) ¼ 3.3 mm, (r ¼ 7.5, h ¼ 10, and d ¼ 3.3 mm crucible was used in the case of the 477 g sample), which was

positioned at the center of the furnace on a low-density porous alumina platform. Measurements of the real and

imaginary permittivities of hematitic laterite samples were done using the cavity perturbation technique at the Microwave

Properties North laboratory in Canada [24]. The apparatus consists of a cylindrical cavity connected to a network

analyzer and a conventional resistance furnace. The materials, in powder or pellet form, are placed in a long, slim quartz

sample holder tube, and are then loaded vertically into the system Fig. 32.9, whereupon the furnace temperature is

increased in steps. After a soak at each temperature step, the samples are rapidly moved down into the cavity for

measurement ($2 s duration), and then rapidly returned to the furnace. The method is based on measuring the difference

in the cavity resonant frequency and Q factor between the empty sample holder and the holder with sample. The

dielectric constants are derived from the resonant frequency and Q factor changes produced by the sample, and are



FIGURE 32.9

Schematic diagram of the TM0n0

cavity system (in cross section)

showing the linear actuator with

the quartz sample holder and a

sample located on the y axis in

the center of the cavity.

(Reproduced from Ref. 19 with

permission of Elsevier.)



615



32.3 MICROWAVE PROCESSING



0



–4



Fit

Data



(d)



Absorption (%)



0



–4

0



–4



Fe2+

metallic Fe(Ni)



Fe3+ (oxide)

Fe2+/3+(oxide)

alpha-Fe



(c)



(b)



0



(a)

–4

–10



–8



–6



–4



–2



0



2



4



6



8



10



Velocity (mm s–1)



FIGURE 32.10

€ ssbauer spectra of

The Mo

reduced laterite samples at

800 W, with two times the stoichiometric carbon addition and

11.75 g sample mass at 120 (a),

240 (b), 360 (c), and 480 (d) s.

(Reproduced from Ref. 19 with

permission of Elsevier.)



dependent on the sample and cavity shapes and volumes. The laterite samples were measured in powder form in a

stagnant air atmosphere.

M€

ossbauer spectroscopy is again used as a tool to assess the phase composition and the degree of reduction of the

samples with processing. For example, the evolution of iron oxide phases during the reduction of a 10 g laterite sample

with twice the stoichiometric addition of carbon at 800 W is presented in Fig. 32.10, where the spectra of reduced

laterites at 120 (a), 240 (b), 360 (c), and 480 (d) s are recorded.

The relative amounts of iron in each phase are directly determined from their subspectral areas and are given in

Table 32.2. Divalent iron is found in nonmagnetic silicate mineral phases and in the magnetic nonstoichiometric magnetite

phase. The presence of Fe2ỵ is already significant (42%) after 120 s, considering that the Fe2ỵ content in the initial laterite

is zero (all the iron is in the form of hematite), while the metallic iron (i.e., bcc Fe(Ni)) recovery reaches 11%. Metallic

iron–nickel alloy is also present as a nonmagnetic phase, probably nonmagnetic g-FeNi that can form for 10at% Ni alloys,

the approximate composition of the FeNi metallic phase.

Scanning electron microscopy data combined with EDS analysis on these samples [19] have shown that the reduced

samples consist of a silicate matrix within which the phases FeNi, spinel, Mg–ferrosillite, and chromite are dispersed. A

layer of metallic iron (FeNi) adjacent to an iron oxide phase, which is normally observed in the case of conventionally

carbothermic reduced laterites, is not observed.

Particles of the Fe(Ni) alloy are visible in the processed materials, Fig. 32.11. The slightly negative isomer shift

observed for the nonmagnetic metallic phase agrees with published values for g-FeNi. Another possibility is that a

nonmagnetic component could arise from superparamagnetic nanoparticles of a-Fe(Ni). In some other samples, lowtemperature measurements do indicate the existence of a-FeNi superparamagnetic nanoparticles. In whichever of these

two phases the iron is present, a or g, this iron is metallic, that is, completely reduced. At 240 and 360 s, the reduction

process progresses as can be seen by the further elimination of hematite, Fe3ỵ oxide, and the respective increase of



TABLE 32.2 Iron-Containing Phase Content (wt%) of the Reduced Laterite Samples

Samples

a

b

c

d



Fe3ỵ oxide



Fe2ỵ



Fe2ỵ3ỵ Oxide



Nonmagnetic Fe(Ni)



a-Fe(Ni)



31

9

4

13



42

72

69

29



16

5

2

7



7

4

6

18



4

10

19

34



Source: Reproduced from Ref. 19 with permission of Elsevier.



616





32 MOSSBAUER

SPECTROSCOPY IN THE STUDY OF LATERITE MINERAL PROCESSING



FIGURE 32.11

A spherical Fe(Ni) alloy particle

0.7 mm in diameter formed after

240 s of microwave reduction.

(Reproduced from Ref. 19 with

permission of Elsevier.)



a-Fe(Ni). After 480 s of reduction, the Fe2ỵ content decreases, indicating its reduction to a-Fe(Ni), which has increased

significantly. It should be noted that during the reduction process, the content of Fe2ỵ/3ỵ oxide, which refers to a

nonstoichiometric magnetite phase, is low. The nonmagnetic Fe2ỵ component is in the form of the iron silicate minerals

fayalite, ferrosilite, and kilchoanite that have been detected using X-ray diffraction. No significant w€ustite content is

indicated. Finally, the continuing presence of Fe3ỵ oxideprobably hematiteeven after 8 min of microwave reduction

is likely due to the temperature heterogeneity of the sample (Fig. 32.12), indicating that the external surface of the laterite

has not reduced.

In Fig. 32.13, the reduction degrees of 10 g laterite samples with stoichiometric addition of carbon (1.75 g of lignite) at

three microwave power levels (200, 400, and 800 W) are presented. It is apparent that power supply has a great effect on

the reduction degree and rate. A reduction degree of 60% has been achieved at 600 s using an input power of 800 W,

while only a 32% reduction degree has been achieved in the same time using 200 W. The experimental data in the case of

double the stoichiometric addition of carbon (3.5 g of lignite) are presented in Fig. 32.14. These data show that the

reduction degree is significantly affected by the amount of the reducing agent (lignite) added. The doubling of carbon

content results in an increase in reduction degree from 60 to about 70% at 600 s and 800 W power.

In Fig. 32.15, the effect of laterite–lignite mass on the reduction degree of laterite at an input power of 800 W and

two times the stoichiometric addition of carbon is presented. By increasing the laterite’s mass from 10 g (13.5 g of

mixture) to 365.5 g (493.5 g of mixture), a strong decrease of the reduction degree is observed, from about 70 to 25%.

The effect on the reduction degree of sample mass should be correlated with the temperatures achieved for the

respective samples under a given microwave radiation, Fig. 32.16.

In Fig. 32.17, differential thermal analysis (DTA) data (obtained using a TG Labys-DSC system in the temperature

range 25–970  C with a 10  C minÀ1 heating rate and in a stagnant air atmosphere) for the laterite–lignite mixture are

compared with both the real (e0 ) and the imaginary (e00 ) permittivities at 2.45 GHz in the temperature range 25–970  C.

The dielectric constant data present a significant increase in the values of e0 and e00 , noticeable after 300  C. The increase,

especially in the case of the imaginary permittivity (e00 ), is sharp and acquires its maximum value at 585  C (from 1.8 at

300  C to 5.2 at 585  C). Given that the formation of the magnetite phase occurs at 572.5  C, and that the Curie point of

magnetite is 585  C, the concurrence of the temperature in which e00 maximizes with the magnetite Curie point (585  C)

should be noted. Several research studies on the measurement of the dielectric properties of magnetite, in powder and

pellet forms, have shown a dramatic increase in e00 at the Curie temperature (from 5 at 300  C to about 35 at 585  C)

[25,26]. Between 585 and 980  C, the value of e00 gradually decreases as the volume of magnetite decreases, it being

reduced to w€

ustite in this temperature interval.

Thus, the dielectric constant of the laterite–lignite mixture increases in the temperature range of 450–750  C.

However, these results may not be directly related to the actual dielectric properties of the mixture under microwave

heating conditions. The extremely high rate of temperature increase during microwave heating cannot be achieved during

the cavity perturbation measurement. Thus, the high temperatures developed in the core of the sample in the case of

microwave heating result in the formation of phases (e.g., ferrosilicates), which are not formed in the cavity perturbation



617



32.3 MICROWAVE PROCESSING



FIGURE 32.12

Infrared images of the crucible containing laterite–lignite mixtures. Lateral images at (a) 120, (b) 240, and (c) 360 s

of microwave heating and a vertical image (d) at 120 s. (Reproduced from Ref. 19 with permission of Elsevier.)



instruments. Nevertheless, the data on the dielectric properties of laterite–lignite mixture give a useful order of

magnitude indication of their evolution in the temperature range between 25 and 980  C.

From the study of the microwaved materials we can deduce the following

(1) The laterite–lignite mixture is susceptible to microwave radiation and can reach a temperature of 900  C after

120 s of heating using a power of 800 W. The heating behavior of the mixture is strongly affected by the power



Reduction degree (%)



70

200 W



60



400 W



50



800 W



FIGURE 32.13



40

30

20

10

0

0



100



200



300

400

Time (s)



500



600



700



Reduction degree as a function

of time and microwave power

supply for a laterite–lignite

mixture sample of 11.75 g

(stoichiometric carbon addition).

(Reproduced from Ref. 19 with

permission of Elsevier.)





32 MOSSBAUER

SPECTROSCOPY IN THE STUDY OF LATERITE MINERAL PROCESSING



618



Reduction degree (%)



80



FIGURE 32.14

Reduction degree as a function

of time and microwave power

supply for a laterite–lignite

mixture sample of 13.50 g and

double the stoichiometric carbon

addition. (Reproduced from

Ref. 19 with permission of

Elsevier.)



70



200 W



60



400 W

800 W



50

40

30

20

10

0

0



100



200



300

400

Time (s)



500



600



700



Reduction degree (%)



80



FIGURE 32.15

Logarithmic scale diagram of

reduction degree as a function of

sample mass for a laterite–lignite

mixture with two times the

stoichiometric carbon addition at

800 W. (Reproduced from Ref. 19

with permission of Elsevier.)



70

60

50

40

30

20

10

0

10



100

Mass (g)



1000



1000

m = 47 g



FIGURE 32.16

Microwave heating of laterite–

lignite mixtures (stoichiometric

addition of carbon) of various

masses at 800 W. (Reproduced

from Ref. 19 with permission of

Elsevier.)



Temperature (°C)



900



m = 117.5 g



800



m = 493.5 g



700

600

500

400

300

200

100

0

0



100



200



300



400



500



600



700



800



Time (s)



supplied and the mass of the sample. A power setting of 800 W is insufficient to heat laterite–lignite mixture

samples with masses over 47 g effectively.

(2) The mineralogical analysis of laterite-reduced samples after 120, 240, 360, and 480 s of heating indicates the

rapid reduction of hematite to magnetite, metallic iron, and iron silicate phases. Also, the occurrence of

temperature heterogeneity is supported by the presence of materials that are not stable at the same

temperature conditions (e.g., after 240 s of heating, although the metallic iron–nickel alloy has been formed,

the calcite phase has still not been totally calcined).

(3) The comparison of DTA data of laterite–lignite heating with the dielectric properties shows an important

increase in the value of the imaginary permittivity (e00 ) after 300  C, which maximizes at 585  C (from 1.8 at



619



REFERENCES



Dielectric constants



7



12

10

8

6



6

5

4



4

2

0

–2



3

2



ε΄

5xε''



1



DTA



0

0



100



200



300



400



500



600

o



Temperature ( C)



700



800



900



–4

–6

1000



Heat flow (μV)



16

14



8



FIGURE 32.17

Comparison of the real and

imaginary permittivities (e0 and

e00 ) of the laterite–lignite mixture

at 2.45 GHz with the DTA data.

(Reproduced from Ref. 19 with

permission of Elsevier.)



300  C to 5.2 at 585  C). It is the Curie point of magnetite, which forms at 572  C, as the DTA curve

demonstrates. The values of the measured dielectric constants do not accurately correspond to the “real”

respective constants of the mixture while being heated with microwaves, because the heating rates are much

higher and a number of different mineralogical phases are formed where topically high temperatures are

achieved. However, the measured constants approach the “real” values in parts of the sample that were heated

relatively smoothly with microwaves, that is, the external surface.

(4) The scanning electron microscopy combined with EDS analysis showed that the reduced samples consist of a

silicate matrix within which the phases FeNi, spinel, Mg–ferrosillite, and chromite are dispersed. A layer of

metallic iron (FeNi) adjacent to an iron oxide phase, which is normally observed in the case of conventionally

carbothermic reduced laterites, was not observed.

(5) The reduction degree of laterite was measured using M€

ossbauer spectroscopy and was examined as a function

of the reducing time, the added carbon content, and the mass of sample. It was demonstrated that the optimum

conditions in case of a 10 g reduced laterite sample were two times the stoichiometric addition of carbon and a

power supply of 800 W. Under these conditions, a 70% reduction degree has been achieved after 480 s of

heating. The reduction degree is strongly affected by the laterite–lignite sample mass. A power supply of 800 W

was not efficient to heat a 493.5 g laterite–lignite sample effectively. In this case, only a 25% reduction degree was

achieved after 480 s.

In these studies, we can see the power of M€

ossbauer spectroscopy for shedding light on many important aspects of

mineral processing in this example of laterite processing.



REFERENCES

1. International Nickel Study Group Press Release, Lisbon, Sept 2011.

2. D.A. Davli, G.W. Bacon, C.R. Osborne,“The past and the future of nickel laterites”. PDAC (Prospectors and Developers

Association of Canada) International Convention, March 7–10, 2004, Canada, pp. 1–27.

3. G.M. Mudd,“Nickel Sulfide Versus Laterite: The Hard Sustainability Challenge Remains.” Proceedings of the 48th Annual

Conference of Metallurgists, August 2009, Canadian Metallurgical Society, Sudbury, Ontario, Canada, 2009,

4. C.A. Pickles, Microwaves in extractive metallurgy: Part 2: A review of applications, Miner. Eng. 2009, 22(13), 1102–1111.

ossbauer and X-ray diffraction study of the ilmenite reduction process in a

5. B. Saensunon, G.A. Stewart, R. Pax, A combined 57 Fe-M€

commercial rotary kiln, Int. J. Miner. Process. 2008, 86(1–4), 26–32.

6. D. Bandyopadhyay, R.M. Singru, A.K. Biswas, Study of the roasting of chalcopyrite minerals by 57 Fe M€

ossbauer spectroscopy, Miner.

Eng. 2000, 13(8–9), 973–978.

7. A. Navarra, J.T. Graham, S. Somot, D.H. Ryan, J.A. Finch, M€

ossbauer quantification of pyrrhotite in relation to self-heating, Miner.

Eng. 2010, 23(8), 652–658.



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