Reduction of Low Grade Egyptian Manganese Ore via Hydrogen at 800℃ - 950℃

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How to cite this paper: El-Gawad, H.H.A., Ahmed, M.M., El-Hussiny, N.A. and Shalabi, M.E.H. (2014) Reduction of Low

Grade Egyptian Manganese Ore via Hydrogen at 800˚C - 950˚C. Open Access Library Journal, 1: e427.

http://dx.doi.org/10.4236/oalib.1100427

Reduction of Low Grade Egyptian

Manganese Ore via Hydrogen

at 800˚C - 950˚C

Hala H. Abd El-Gawad1, M. M. Ahmed2, N. A. El-Hussiny3, M. E. H. Shalabi3*

1Faculty of Science and Arts, Mohail Asser, King khalid University, Mahil, Saudi Arabia

2Faculty of Engineering (Mataria), Helwan University, Helwan, Egypt

3Centeral Metallurgical Research and Development Institute (CMRDI), Cairo, Egypt

Email: *shalabimeh@ho tmail.com

Received 17 April 2014; revised 25 May 2014; accepted 16 July 2014

This work is licensed under the Creative Commons Attribution International License (CC BY).

http://creativecommons.org/licenses/by/4.0/

Abstract

Low grade manganese ore fine was briquetted with different amounts of molasses under different

pressure was studied in this investigation. In this study, the characterizations of raw materials

were studied by different methods of analyses such as X-ray and chemical analyses. The results of

briquetting show that as the pressing pressure load increased both the drop damage resistance

and crushing strength increased and the optimum amount of molasses added was 2% and the

pressing pressure was 216.7745 MPa. The produced briquettes were reduced by different flow

rate of hydrogen at different temperatures, and the reduction kinetics was determined. The re-

sults indicated that: 1) The reduction rates by hydrogen increased with increasing temperature of

the reduction; 2) Increase hydrogen flow rate at constant temperature of reduction leads to in-

crease rate of reduction; 3) The zero order is control step at time 0 - 5 min and from 5 to 20 min

the gaseous diffusion in case of cylindrical products and from 20 to 60 min the reaction controlled

by nucleation and growth.

Keywords

Low Grade Manganese Ore, Briquetting, Reduction Kinetic by Hydrogen

Subject Areas: Chemical Engineering & Technology, Mineral Engineering

1. Introduction

Manganese plays an important role in several industrial applications, such as steel production, preparation of di-

*Corresponding a uthor.

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etary additives, fertilizers, cells and fine chemicals, as well as colorants for bricks, dyes and medicines [1]-[3].

Manganese metal is readily available at a low price and is mostly used in the form of ferromanganese in

steelmaking. The major use of manganese is as an alloying addition to steel, where it acts as a desulphuriser and

a deoxidizer which is a very important function in steelmaking. Manganese also provides improved rolling and

forging characteristics, improved strength, toughness, harden ability and wear resistance by suppressing the

hardening transformation of steel on quenching. It is also added to Al, Ag, Mg, Ni, Ti and Zn alloys as an alloy-

ing element. Manganese is added in the form of its ore during iron making or as ferromanganese alloy at the

steelmaking stage.

The normal classification of manganese ore is as follows [4]:

1) Manganese ores, containing more than 35% Mn suitable for the manufacture of high or low-grade ferro-

manganese;

2) Ferruginous m a nga ne s e ores conta i ning 5% - 35% Mn suitable for the manufacture of spiegeleisen;

3) Manganiferous iron ores with 5% - 10% Mn used for the manufacture of manganiferous pig iron.

In practice, manganese ores and concentrates have a wide and complex range of chemical and physical speci-

ficati ons most often empl oy ing a specifi c e n d-use prefix [5].

Metallurgical-grade used in the iron and steel industry requires 35% - 55% Mn, generally with a Mn/Fe ra tio

larger than 5. Battery-grade requires 70% - 85% MnO2 th at is equiv alent to 44% - 54% Mn, and should contain

less than 0.05% of metals more electronegative than zinc, such as copper, nickel, cobalt, and arsenic.

Chemical-grade has various specifications depending on the specific end use such as feedstock for electrolytic

manganese and manganese dioxide, manganese chemicals, colorants, and uranium processing.

Fertilizer and feed grade requires 30% - 60% Mn; ferrites need particularly low levels of CaO, K2O, Na2O,

BaO, and SiO2.

The world annual consumption of manganese is above 1,300,000 annual tons and it is destined to increase.

Low grade ores are gaining increasing attention due to developments in exploitation technologies [2].

The utilization of the low grade manganese ore has become necessary. There are several physicochemical

differences among the components in manganese ores, which can be used for the enrichment of manganese. In

particular, the abundant low-grade manganese ores, which contain iron oxide, may be upgraded by pre-reduction

and magnetic separation [6].

Swamy et al. [7] studied this phenomenon with TGA tests. They found that the optimum pre-reducing tem-

perature for increasing the Mn/Fe ratio of the ore non-magnetic part would be 850˚C, and they also observed

that a finer particle size (−0.15 mm) gave a better Mn/Fe ratio compared to the coarser ore (−6 to +3 mm). Ru-

dramuniyappa et al. [8] reported that reduction roasting followed by magnetic separation is considered to be the

best method for upgrading the Chikkanayakanahalli manganese ores. They also showed that tabling studies car-

ried out were not encouraging, probably due to the similar behavior of Mn and Fe. Rao et al. [9] reported, that in

reduction roasting of low grade manganese ore followed by magnetic separ atio n, 60 % of phosphorus can also be

removed [10].

Main purpose of this study was to find the reduction rate of low grade manganese ore briquette by hydrogen.

2. Materials and Experimental

Material

The low grade of manganese ore used in this work was provided by Sinai ferromanganese Co. The sample was

submitted to chemical and X-ray analysis. The chemical analysis of low grade manganese ore is illustrated in

Table 1.

The X-Ray analysis is illustrated in Figure 1. From which it is clear that low grade manganese ore mainly

consists of pyrolusite, hematite an d quartz.

3. Experimental Procedures

3.1. Preparation of Samples

The low grade of manganese ore was grinding in vibrating mill to powder with size less than 75 micrometers.

The low grade of manganese ore powder (10 g) are mixed with 2% molasses and then pressed in the mould (12

mm diameter and a height 22 mm using MEGA KSC-10 hydrau lic press. Under different pressure (the pressure

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Table 1. Chemical analysis of Egyptian low grade of manganese ore.

Weight (%) Constituent

23.2

Fe total

0.25

K2O

2.3

Al2O3

0.95

MgO

2.4

CaO

0.2

28.6

15.3

SiO2

0.2

Na2O

Figure 1. X-ray of low grade of manganese ore.

ranges from 75 MPa up to 250 MPa). The produced briquettes were subjected to drop damage resistance tests

(drop number tests) and compressive strength tests (crushing strength tests). The drop number indicates how of-

ten green briquette can be dropped from a height 46 cm before they show perceptible cracks or crumble. Ten

green briquettes are individually dropped on to a steel plate. The number of drops is determined for each bri-

quette. The arithmetical average values of the crumbing behavior of the ten briquettes yield the drop number

[11]-[14].

3.2. Reduction Procedures

The reduction of low grade manganese ore with hydrogen was performed in thermogravimetric apparatus. This

scheme is similar to that present elsewhere [14] [15] (Figure 2). It consisted of a vertical furnace, electronic

balance for monitoring the weight change of reacting sample and temperature controller. The sample was placed

in a nickel chrome crucible which was suspended under the electronic balance by Ni -Cr wire. The furnace tem-

perature was raised to the required temperature (650˚C - 950˚C) and maintained constant to ±5˚C. Then samples

were placed in hot zone.

The nitrogen flow rate was 0.5 l/min pass through furnace in all the experiments. At initial time air should be

removed before each experiment and also after the end of reduction. The weight of the sample was continuously

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Figure 2. Schematic diagram of the reduction apparatus.

recorded at the end of the run; the samples were withdrawn from the furnace and put in the desiccators.

The percentage of reduction was calculated according to the following equations:

( )

Percent of reductionWoWt100Oxygen mass= −×





where:

Wo: the initial mass of mill scale sample after r e mova l of moistu re.

Wt: mass of sample after each time, t.

Oxygen mass: indicates the mass of oxygen percent in low grade of manganese ore in form FeO, Fe2O3 and

mangane se oxide.

4. Results and Discussions

4.1. Effect of Adding Molasses as Binding Materials on the Q uali ty of Produced Briquettes

Figure 3 and Figure 4 Illustrate the effect of percentage of molasses added on the drop number (drop damage

resistance) and cold crushing strength of the briquette (the pressing load is constant = 216.7745 MPa.). It is clear

that as the percentage of binding materials increased both the drop damage resistance and crushing strength in-

creased; this may be due to the effect of binding material.

4.2. Effect of the Pressure Load with Constant Amount of Molasses on the Quality of the

Briquettes

Figure 5 and Figure 6 show the relation between the change of pressure load at constant amount of molasses

(2%) on the drop number (drop damage resistance) and cold crushing strength of the briquette. It is evident that

as the pressing pressure load increased both the drop damage resistance and crushing strength increased. This

may be due to the fact that increase pressure load increase the compaction of briquette and subsequently the

Vander Waals forces increased [16] [17], also this may be due to the increase of briquetting pressure leads to

progressive crushing of the macropores [18].

4.3. Effect of Hydrogen Flow Rate on the Reduction Degree

Figure 7 illustrates the relation between the reduction degree and hydrogen flow rate when the reduction was

done at constant temperature (900˚C) and constant weight of the sample. It is clear that as the flow rate of hy-

drogen increased the reduction percentage increased This may be the increase of flow rate leads to an increase of

number of hydrogen mole in the bulk phase, which in turn leads to the raise of hydrogen adsorption and subse-

quently the rate of reaction increased [19] or the increase of flow rate increased the gas diffusion across the

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Figure 3. Effect of molasses addition on the drop damage

resistance of produced briquettes compressed at 216.8845

MPa.

Figure 4. Effect of molasses addition on the compressive

strength of produced briquettes compressed at 216.8845

MPa.

Figure 5. Effect of pressing pressure on the compressive

strength of produced briquettes at 2% molasses added.

boundary layer subsequently the reduced ion increased [20]. Also may be the h igher flow rate prevailing in the

reaction zone which enhances the rate of hydrogen absorption and subsequently the rate of chemical reaction

steps increased [21].

4.4. Effect of the Reduction Temperature on the Reduction Degree

The reduction was carried out at different temperatures ranging from 800˚C to 950˚C, where the weight of the

Drop damage resistance of

briquett e s, dro p /briqut te

Amount of molasses added, %.

Compressive strength of

briquettes, MPa.

Amount of molasses added, %.

Compressive strength of

briquettes, MPa

Pressing pressur, MPa

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Figure 6. Effect of pressing pressure on the drop damage

resistance of produced briquettes at 2% molasses added.

Figure 7. Effect of hydrogen flow rates (L/min.) on the re-

duction percentage of produced briquettes compressed at

216.88 MPa. at 900˚C.

briquette were constant and the hydrogen flow rate = 1.5 liter /min. The results of the investigation are shown in

Figure 8 for the briquette binding by 2% molasses. It is clear that the increase of temperature favors the reduc-

tion rate and degree. The analyses of the curve relating the reduction percentage and time of reduction, shows

that each curve has 3 different values of reduction rates. The first value is high, while the second is somewhat

slower and the third is slowest one. The increase of reduction percentage with rise of temperature may be due to

the increase of number of reacting moles having excess of energy which leads to the increase of reduction rate

[19] [22]. Also the raise of temperature leads to an increase of the rate of mass transfer of the di ffusio n a nd rat of

desorption [20]-[23].

4.5. Kinetics Reduction of Low Grade Manganese Briquette

It is clear that from Figure 8 there are three rates; therefore we try applied three models First model from time 0

to 5 min.

Zero order

R kt=

Second model from 5 to 20 min for gaseous diffusion in case of cylindrical products can be written as [24]:

() ()

R 1Rln1Rkt

+−− =

Third model from 20 to 60 min

( )

lnln 1Rk t−=





(Avrami equation, this mean the reaction controlled by

nucleati on and growth [25]-[27]).

Where R is fractional reduction, t is time of redu ction, k1,2,3 is the rate constant for each model.

Drop damage resistance of

briquett e s, Dro p / briquett e

Pressing pressure, MPa

Reduction percentage

Flow rate, Liter/min.

0.5 L

1 L

1.5L

2 L

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Figure 8. Effect of reduction temperatures on the reduction

percentage of produced briquettes compressed at 216.88

MPa. at 1.5 flow rate of hydrogen gas/min.

Figure 9 illustrates the relation between R against time of reduction for different reduction temperature (at

time range 0 to 5 min.). From which it is clear that the straight line was observed.

The natural logarithms were used according to the Arrhenius equation to calculate the activation energies of

reduction reaction. The results illustrate in Figure 10 from which it is clear that the activation en ergy = 23.4 kJ/

mole .

Figure 11 illustrates the relation between

() ()

R 1Rln1R+− −

against time of reduction for different reduc-

tion temperature (at time range 5 to 20 min.). From which it is clear that, the straigh t line was observed and this

mean the reaction controlled by gaseous diffusion in case of cylindrical products in this range [24].

The natural logarithms were used according to the Arrhenius equation to calculate the activation energies of

reduction reaction. The r esu lts illustrate in Figure 12 from which it is clear that the activation energy = 23.05 kJ/

mole .

Figure 13 illustrates the relation between

( )

lnln 1R−





against

ln t

, time of reduction for different reduc-

tion temperature (at time range 20 to 60 min.). From which it is clear that the straight line was observed this

mean the reaction controlled by nucleation and growth [25]-[27].

The natural logarithms were used according to the Arrhenius equation to calculate the activation energies of

reduction reaction. The results illustrate in Figure 14 from which it is clear that the activation en ergy = 55.5 kJ/

mole .

4.6. X-Ray Analyses of the Reduced Sample

It is clear that the phases of the sample after reduction at 950˚C (time of reduction 60 min.) (Figure 15) are me-

tallic iron, MnO, Mn3O4 and SiO2.

The metallic iron formed according the following reaction:

23 22

Fe OHFeH O+ →+

While Mn3O4 and MnO formed a c cording the follo wi ng reactions:

22 342

3MnO 2HMnO 2HO

+→ +

and

34 22

Mn OH3MnOHO+→ +

5. Conclusions

Manganese plays an important ro le in several indu stria l application s. The utilization of the low grade manganese

ore has become necessary. There are several physicochemical differences among the components in manganese

ores, which can be used for the enrichment of manganese. In particular, the abundant low-grade manganese ores,

which contain iron oxide, may be upgraded by prereduction and magnetic separation. The reduction of Egyptian

Reduction percentage , %.

Time of reduction, min

800 °C

850 °C

900 °C

950 °C

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Figure 9. The relationship between time of reduction and R at different tempera-

tures.

Figure 10. The relation between 1/T and

ln K

for reaction at time 0 - 5 min.

(Arrhenius plot for reduction reaction).

Figure 11. The relationship between time of reduction from 5 to 20 min. and

( )( )

R 1Rln1R+− −

at d if f erent temp er atu re.

y = 9.639x -0.000

R² = 1

y = 10.65x -0.005

R² = 1

y = 12.10x -0.006

R² = 1

y = 13.23x -0.000

R² = 1

Reduction percentage, %.

Time of reduction, min.

800 °C

850 °C

900 °C

950 °C

y = -2827.x + 4.895

R² = 0.995

y = -2827.x + 4.895

R² = 0.995

ln k

1/T

y = 0.008x + 0.11

R² = 0.941

y = 0.008x + 0.11

R² = 0.941

y = 0.010x + 0.138

R² = 0.961

y = 0.010x + 0.138

R² = 0.961

y = 0.009x + 0.205

R² = 0.933

y = 0.009x + 0.205

R² = 0.933

y = 0.011x + 0.254

R² = 0.942

y = 0.011x + 0.254

R² = 0.942

R+(1-R)ln(1-R)

Time, min

800 °C

850 °C

900 °C

950 °C

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Figure 12. The relation between 1/T and

ln K

for reaction at time 5 to 20 min.

(Arrhenius plot for reduction reaction).

Figure 13. The relation between

( )

lnln 1R −



against

ln t

at different reduc-

tion temperatures (at time range 20 to 60 min.).

Figure 14. The relation between 1/T and

ln K

for reaction at time 20 to 60 min.

(Arrhenius plot for reduction reaction).

y = -2785.x -2.231

R² = 0.999

ln K

1/T

y = 0.148x -0.405

R² = 0.979

y = 0.149x -0.264

R² = 0.991

y = 0.076x + 0.071

R² = 0.907

y = 0.079x + 0.246

R² = 0.927

ln[ln(1-R)]

ln t

800 °C

850 °C

900 °C

950 °C

y = 6705.x - 8.087

R² = 0.770

ln K

1/T

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Figure 15. X-ray of produced briquettes compressed at 216.88 MPa. under 1.5 flow rate of hydrogen gas/min at 950˚C.

low grade of manganese ore by hydrogen in tempera ture indicated that:

1) The reduction rates increased with increasing temperature of the reduction.

2) Increase hydrogen flow rate at constant temperature of reduction leads to increase rate of reduction,

3) The zero order is control step at time 0 - 5 min and from 5 to 20 min the gaseous diffusion in case of cylin-

drical products and from 20 to 60 min the reaction controlled by nucleation and growth.

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