Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.5, pp 339-347, 2009
jmmce.org Printed in the USA. All rights reserved
Model for the Calculation of the Concentration of Dissolved Hematite during
Hydrogen Peroxide Leaching of Iron Oxide Ore
C. I. Nwoye*
1
, C. C. Nwakwuo
2
, C. Nlebedim
3
, U.C. Nwoye
4
, R. A. Umana
5
and G. C. Obasi
6
1
Department of Materials and Metallurgical Engineering, Federal University of Technology,
Owerri, Nigeria.
2
Department of Material Science, Oxford University. United Kingdom.
3
Department of Material Science, University of Cadiff, Wales, United Kingdom.
4
Data Processing, Modelling and Simulation Unit, Weatherford Nig. Ltd. Port-Harcourt Nigeria.
5
Department of Mathematics and Computer Science, Federal University of Technology, Owerri,
Nigeria.
6
Department of Material Science, Aveiro University, Portugal.
*Corresponding Author, contact: [e-mail]
ABSTRACT
Model for the calculation of the concentration of dissolved haematite during hydrogen peroxide
leaching of iron oxide ore has been derived. The model was found to depend on both the %
concentration of dissolved iron and weight input of iron oxide ore from experiment. The validity
of the model is rooted on the expression %Fe
2
O
3
≈ %Fe√(µ)
1/3
where both sides of the
relationship are correspondingly almost equal. The deviation of the model-predicted
concentration of dissolved haematite from the corresponding experimental values is less than
30% which is quite within the acceptable range of deviation limit of experimental results. The
model indicates that the dissolved % ratio of extreme oxidation stage of iron to that of its
extreme reduction stage is approximately equal to one-sixth (1/6th) power of the weight input of
iron oxide ore during the leaching process.
Key Words: Model, Calculation, Haematite dissolution, Hydrogen Peroxide, Iron Oxide Ore,
Leaching

340 C. I. Nwoye, C. C. Nwakwuo, C. Nlebedim, U.C. Nwoye, R. A. Umana and G. C. Obasi Vol.8, No.5
1. INTRODUCTION
Several works have been reported [1-4] involving the use of different acids for the leaching of
iron oxide ore. Also attempts have been made to leach pyrite using strong oxidizing agent like
hydrogen peroxide because of the inert nature of the pyrite.
Ambikadevi and Lalithambika [5] found oxalic acid (0.05-0.15M) to be the best extractant for
removing iron from iron compounds. The dissolution was found to increase with acid
concentration within the range (0.05-0.15M) studied. Both hydrogen ions and oxalate were
increased in this case. Using 0.15M oxalic acid approximately, 70% of the iron could be
extracted from a slurry (20%w/v) containing 0.93% iron oxide (of goethite and haematite phases)
at 100
0
C within 90mins. The iron oxide concentration in the leach is equivalent to 1.86g/L
Fe
2
O
3
. A study of the electrochemical dissolution of haematite (α-Fe
2
O
3
), maghetite, (γ-Fe
2
O
3
),
goethite, (α-FeOOH) and lepidochrocite, (γ-FeOOH) inhydrochloric and oxalic acid using
voltammetry [6] indicated that the hydroxyl-oxides of FeOOH can be reduced also via soluble
Fe(III) species at 0.6-0.8 V (vs Ag-AgCl), where as haematite and maghetite dissolve only via
direct reduction of the solid at -0.55 to -0.60V (vs AG-AgCl). These potentials were determined
as peaks on voltammograms conducted with stationary electrodes made from these iron oxides
and hydroxyl-oxides. This fundamental study [6] on the electrchemical behaviour of different
types of iron oxides confirms the electrochemical nature of haematite reductive dissolution. This
further explains why it is easier to dissolve hydroxyl-oxides such as goethite where dissolution
can take place via both reduction (solid and aqueous species) and complexation [7] whereas
haematite dissolves mainly via solid reduction [8]. Oxalate can easily be reductant for such a
process, as shown in its Eh-pH diagram [9].
Lee et al.[10] reported that dissolution of haematite in oxalic acid is via a reductive mechanism
which made Fe(III) non-existent in the solution. The overall reaction was therefore reported [10]
as a redox reaction, forming two half cells: Oxidation of oxalate to form carbonic acid or carbon
dioxide:
HC
2
O
4-
= H
+
2CO
2
+ 2e
-
(1)
Reduction of haematite forming Fe(II) oxalate:
2H
+
+ Fe
2
O
3
+ 4HC
2
O
4-
+ 2e
-
= 2Fe(C
2
O
4
)
22
- + 3H
2
O (2)
The dissolution reaction is therefore:
H
+
+ Fe
2
O
3
+ 5 HC
2
O
4-
= 2Fe(C
2
O
4
)
22
- + 3H
2
O + 2CO
2
(3)
The overall reaction indicates that species involved in the leaching would be hydrogen ions,
oxalate and iron oxide (haematite particles).
Model for computational analysis of the concentration of dissolved haematite and heat absorbed
by oxalic acid solution during leaching of iron oxide ore has been derived [11].

Vol.8, No.5 Model for the Calculation of the Concentration of Dissolved Hematite 341
The model also indicates that the concentration of haematite dissolved during the leaching
process is directly proportional to the final pH of the leaching solution and inversely proportional
to the weight input of the iron oxide ore. It was also found [11] that values of Q obtained from
both the experiment and model agree to the fact that leaching of iron oxide ore using oxalic acid
solution is an endothermic process, hence the absorbed positive heat energy by the leaching
solution. The quantity of heat energy absorbed by the oxalic acid solution during the leaching
process was found to be directly proportional to the weight input of the iron oxide ore. These
results were obtained at initial pH 6.9, average grain size of 150µm and leaching temperature of
30
0
C. The constants of proportionality K and K
C
associated with the derived model were
evaluated to be 0.0683 and 66.88 respectively.
It has been found [12] that increasing the concentration of HCl results in a significant reduction
in the rate of pyrite dissolution. The report also states that hydrochloric acid has an inhibiting
effect on the oxidation of pyrite. This was attributed to chloride ions which are known to have a
high tendency for adsorption. Also the formation of chloride complexes of iron (III) was found
[12] to be possible, resulting in a decreasing concentration of the free iron (III) ions. However,
no work has been reported on the effect of chloride ions and HCl concentration on the
dissolution of iron during leaching of iron oxide ore.
Nwoye [13] derived a model for the computational analysis of the solution temperature during
leaching of iron oxide ore in hydrochloric acid solution. The model is expressed as:
T = e
(8.9055/γ)
(4)
where
T= Solution temperature during leaching of iron oxide ore using hydrochloric acid.(
0
C)
N= 8.9055(pH coefficient for hydrochloric acid solution during leaching of iron
oxide ore) determined in the experiment [13].
γ = Final pH of the leaching solution at the time t when the solution temperature is evaluated.
The model is dependent on the value of the final pH of the leaching solution which was found to
also depend on the concentration of iron dissolved in the acid. The prevailed process conditions
on which the validity of the model depended on include: initial pH 2.5, leaching time; 30
minutes, leaching temperature; 25
o
C, average ore grain size; 150µm and hydrochloric acid
concentration at 0.1mol/litre.
The mixed potential model of leaching assumes that the charge transfer processes occurring at
the mineral surface are those that control the rate of dissolution [14].
The dissolution of iron ore has been investigated in the presence of oxygen at elevated
temperatures and pressures [15-19]. The result of the works indicates that presence of oxygen
enhances dissolution of iron. The use of hydrogen peroxide as the oxidizing agent for

342 C. I. Nwoye, C. C. Nwakwuo, C. Nlebedim, U.C. Nwoye, R. A. Umana and G. C. Obasi Vol.8, No.5
hydrometallurgical processes has been increasingly studied. McKibben [15] studied the kinetics
of aqueous oxidation of pyrite by hydrogen peroxide at pH 1-4 and 293-313K.
Model for computational analysis of heat absorbed by hydrogen peroxide solution (relative to the
weight of iron oxide ore added) has been derived [20]. The values of the heat absorbed Q as
predicted by the model were found to agree with those obtained from the experiment that the
leaching process is endothermic in nature hence the positive values of Q and the absorbed heat.
The deviations of the predicted Q values from the experimental values were found to be within
the acceptable range. The model was found to be dependent on the weight of iron oxide ore
added to solution in the course of leaching.
The model is stated as:
Q = e
1.04(√W)
(5)
where
Q= Quantity of heat energy absorbed by hydrogen peroxide solution during the leaching
process (J)
N= 1.04 (Weight-input coefficient) determined in the experiment[20].
W = Weight of iron oxide ore used (g)
The present work is aimed at deriving a model for the calculation of the concentration of
dissolved haematite during leaching of Itakpe (Nigeria) iron oxide ore in hydrogen peroxide
solution.
2. MODEL
Hydrogen ions from the hydrogen peroxide attack the iron oxide ore within the liquid phase in
the presence of oxygen. This simultaneously facilitates and enhances the reductive dissolution of
haematite. The ore (solid phase) was assumed to be stationary, and contains the un-leached iron.
2.1. Model Formulation
Results of research work [21] previously reported (as in Table 1) were used for this work for the
formulation of the model.
Computational analysis carried out on the experimental data from the previous work [21] as
shown in Table 1, resulted to Table 2 which indicate that;
%Fe
2
O
3
≈ %Fe√(µ)
1/3
(6)
Rearranging equation (1)

Vol.8, No.5 Model for the Calculation of the Concentration of Dissolved Hematite 343
%Fe
2
O
3
= (µ)
1/6
(7)
%Fe
Where
%Fe
2
O
3
= Concentration of dissolved haematite in hydrogen peroxide solution during leaching.
%Fe = Concentration of dissolved iron in hydrogen peroxide solution during leaching.
µ= Weight input of iron oxide ore (g).
Equation (6) is the derived model.
Table 1: Variation of the concentrations of dissolved haematite and iron with weight input of
iron oxide ore.[21]
3. BOUNDARY AND INITIAL CONDITION
Leaching solution of hydrogen peroxide was placed in a cylindrical flask 30cm high just after
iron oxide ore was placed in the same flask. The leaching solution was stationary. The flask
(containing the extractant and ore) was assumed to be initially devoid of attached bacteria and
other micro organisms. Oxygen (atmospheric) was assumed to have affected the leaching process
at its initial stage. Weights input ranging from 6-42g of iron oxide ore was used. The leaching
process conditions used include: initial pH6.8, leaching time; 30 minutes, leaching
temperature;25
o
C, average ore grain size;150µm and hydrogen peroxide concentration at
0.28mol/litre.
Since the cylinder was open at the top, the boundary conditions were assumed to include
atmospheric levels of oxygen at the top and bottom of the ore particles in the liquid and gas
phases respectively. The sides of the iron oxide ore particles were assumed to be symmetrical.
Also a zero gradient for the liquid scalar were assumed at the bottom of the particles and also for
the gas phase at the top of the particles.
%Fe
2
O
3
%Fe µ (g)
0.0078
0.0024
0.0017
0.0019
0.0017
0.0017
0.0016
0.0009
0.0017
0.0049
0.0055
0.0016
0.0012
0.0013
0.0012
0.0012
0.0011
0.0006
0.0012
0.0034
6
10
14
18
22
26
30
34
38
42

344 C. I. Nwoye, C. C. Nwakwuo, C. Nlebedim, U.C. Nwoye, R. A. Umana and G. C. Obasi Vol.8, No.5
Table 2: Showing computed values of %Fe√(µ)
1/3
4. MODEL VALIDATION
The formulated model was tested for its validity by evaluation and statistical analysis of the
deviations (of the model-predicted values of dissolved haematite) from the corresponding
experimental values [21]. Comparison between these values (model-predicted and experimental)
reveals deviations. This was believed to be as a result of non-consideration of the
physiochemical interactions between the ore and leaching solution as well as the surface
properties of the ore which were found to have played vital roles during the leaching process
[21].
Deviation (Dv) (%) of model-predicted values of dissolved haematite from the corresponding
experimental values [21] is evaluated by:
Dv = α
P
– α
E
x 100 (8)
α
E
Where α
P
= Model-predicted values of dissolved haematite
α
E
= Experimental values of dissolved haematite
Correction factor (CR) is evaluated as the negative of the deviation (of model-predicted values
from those of the experiment).
Therefore,
CR = -Dv (9)
CR = -100 α
P
– α
E
(10)
α
E
%Fe√(µ)
1/3
0.0074
0.0023
0.0019
0.0021
0.0020
0.0021
0.0016
0.0011
0.0022
0.0063

Vol.8, No.5 Model for the Calculation of the Concentration of Dissolved Hematite 345
The model-predicted values of the dissolved haematite become exactly equal to those of the
corresponding experimental values on addition of the CR values evaluated from equation (10).
5. RESULTS AND DISCUSSION
Statistical analysis and comparison of the concentrations of dissolved haematite as predicted by
the model and as obtained from the experiment [21], show positive and negative deviations,
which invariably depicts the reliability and validity of the model. This is shown in Table 3. These
deviations (positive and negative) of the model-predicted concentration of dissolved haematite
were found to be less than 30% which is quite within the acceptable deviation limit of
experimental results. The validity of the formulated model is rooted on equation (6) where both
sides of the equation are almost equal (comparing Tables 1 and 2). Table 2 also agrees with
equation (6) considering the values of %Fe
2
O
3
from the experimental result [21] and the values
of %Fe√(µ)
1/3
evaluated from Table1. The model indicates in equation (7) that the dissolved %
ratio of extreme oxidation stage of iron to that of its extreme reduction stage is approximately
equal to one-sixth (1/6th) power of the weight input of iron oxide ore during the leaching
process.
Table 3: Comparison between %Fe
2
O
3
as predicted by model and as obtained from experiment
[21].
Where %Fe
2
O
3 exp
= %Fe
2
O
3
values from experiment [21]
%Fe
2
O
3 M
= %Fe
2
O
3
values predicted by model
%Fe
2
O
3exp
%Fe
2
O
3 M
Dv (%) CR (%)
0.0078
0.0024
0.0017
0.0019
0.0017
0.0017
0.0016
0.0009
0.0017
0.0049
0.0074
0.0023
0.0019
0.0021
0.0020
0.0021
0.0016
0.0011
0.0022
0.0063
-5.13
-4.17
+11.76
+10.53
+17.65
+23.53
+18.75
+22.22
+29.41
+28.57
+5.13
+4.17
-11.76
-10.53
-17.65
-23.53
-18.75
-22.22
-29.41
-28.57

346 C. I. Nwoye, C. C. Nwakwuo, C. Nlebedim, U.C. Nwoye, R. A. Umana and G. C. Obasi Vol.8, No.5
6. CONCLUSION
The model calculates the concentration of dissolved haematite in relation to the concentration of
dissolved iron and weight input of iron oxide ore during hydrogen peroxide leaching of Itakpe
iron oxide ore. The validity of the model is rooted on equation (6) where both sides of the
equation are correspondingly almost equal. The deviation of the model-predicted concentration
of dissolved haematite from the corresponding experimental values is less than 30% which is
quite within the acceptable range of deviation limit of experimental results. The model indicates
that the dissolved % ratio of extreme oxidation stage of iron to that of its extreme reduction stage
is approximately equal to one-sixth (1/6th) power of the weight input of iron oxide ore during the
leaching process.
ACKNOWLEDGEMENTS
The authors wish to thank Dr. Ekeme Udoh, a modelling expert at Linkwell Modelling Centre
Calabar for his technical inputs. The management of SynchroWell Nig. Ltd. Enugu is also
appreciated for permitting and providing the experimental data used in this work.
REFERENCES
[1] Panias, D., Taxiarchou, M., Paspaliaris, I., and Kontopoulos, A., 1996, “Mechanism of
dissolution of iron oxides in aqueous oxalic acid.” Hydrometallurgy, Vol. 42, pp. 257-265.
[2] Taxiarchour, M., Panias, D., Doumi, I., Paspaliaris, I., and Kontopoulos, A., 1997, “Removal
of iron from silica sand by leaching with oxalic acid.” Hydrometallurgy, Vol. 46, pp. 215-
227.
[3] Taxiarchou, M., Parnias, D., Douni. I., Paspaliaris, I., and Kontopoulous, A., 1997,
“Dissolution of haematite in acidic oxalate solutions.” Hydrometallurgy, Vol. 44, pp. 287-
299.
[4] Lee, S. O., Tran, T., Park, Y.Y., Kim, S. J., and Kim, M.J., 2006a, “Study on the kinetics of
iron Leaching by oxalic acid.” Int. J. Miner. Process, Vol. 80, pp. 144-152.
[5] Ambikadevi, V. R., and Lalithambika, M., 2000, “Effects of organic acids on ferric iron
removal from iron-stained kaolinite.” Appl. Clay Sci., Vol. 16, pp. 133-145.
[6] Cepria, G., Uson, A., Perez-Arantgui, J., and Castillo, J. R., 2003, “Identification of Fe(III)
oxide and hydroxyl-oxides by voltammetry of immobilized microparticles.” Anal. Chim.
Acta., Vol 477, pp. 157-168.
[7] Stumm.,W., and Furrer, G., 1987, “The dissolution of oxides and aluminum silicates:
examples of surface-coordination-controlled-kinetics.” Aquatic Surface Chemistry. J Wiley
and Sons, New York, pp. 97-219.
[8] Banwart, S., Davies, S., and Stumm, W., 1989, “The role of oxalate in accelerating the
reductive dissolution of haematite (α-Fe
2
O
3
) by ascorbate.” Colloids Surf. Vol. 39, pp. 303-
309.

Vol.8, No.5 Model for the Calculation of the Concentration of Dissolved Hematite 347
[9] Pourbaix, M., 1958, Atlas of Electrochemical Equilibria in Aqueous Solution, Pergamon
Press.
[10] Lee, S. O., Tran, T., Park, Y.Y., Kim, S.J., and Kim, M.J., 2006b, “Study on the kinetics of
iron Leaching by oxalic acid.” Int. J. Miner Process, Vol. 80, pp.144-152.
[11] Nwoye, C. I., 2008, “Model for computational analysis of dissolved haematite and heat
absorbed by oxalic acid solution during leaching of iron oxide ore, J. Eng.& App. Sci., Vol.
4, pp. 22-25.
[12] Dimitrijevic, M., Antonijevic, M. M., and Dimitrijevic, V., 1999, “Investigation of the
kinetics of pyrite oxidation by hydrogen peroxide in hydrochloric acid solutions.” Min.
Eng., Vol. 12, pp. 165-174.
[13] Nwoye, C. I., 2006, SynchroWell Research Work Report, DFM Unit, No. 2021196, pp. 28-
43.
[14] Kanevskii, E. A., and Filippov, A. P., 1963, “Influence of the ionic composition of solutions
of Fe(iii) of the solution of uranium dioxide.” Soviet Radiochemistry (Eng. Trans. Of
Radiokhimiya).
[15] McKibben, M.A., 1984, Ph.D Thesis, Pennsylvania State University.
[16] Bailey, L. K., and Peter, E., 1976, Can. Metall. Q., Vol. 15, pp. 333-344.
[17] Gerlach, J., Hahne, and H., Pawlek, F., 1966, Erzmetall, Vol. 19, pp. 66-74.
[18] McKay, D. R., and Halpern, J., 1958, Trans Metall. Soc. AIME, Vol. 6, pp. 301-309.
[19] Vracar, R. Z., 1987, Prikl.Khim. Vol. 60, pp. 1458-465.
[20] Nwoye, C. I., 2009, “Model for computational analysis of quantity of heat absorbed by
hydrogen peroxide solution relative to weight-input of iron oxide ore during leaching.” J.
Eng.& App. Sc., Inter. Res. J. Eng. Sc. Tech., Vol. 5, pp. 40-52.
[21] Nwoye, C. I., 2006, SynchroWell Research Work Report, DFM Unit, No. 2021196, pp. 28-
43.