J. Nig. Soc. Phys. Sci. 2 (2020) 128–133

Journal of the
Nigerian Society

of Physical
Sciences

Original Research

Dissolution of a Nigerian sourced Muscovite ore for use as an
ingredient in paint production

Daud T. Olaoluwaa,∗, Abdulhadi E. Abdulmalika, Taoreed A. Murainaa, Sadisu Girigisub, Ayo F.
Balogunc

aDepartment of Science Laboratory Technology, The Federal Polytechnic, P.M.B. 231, Ede, Nigeria.
bDepartment of Science Laboratory Technology, The Federal Polytechnic, P.M.B. 420, Offa, Nigeria
cDepartment of Chemistry, Kogi State College of Education (Technical), Kabba. P.M.B. 242, Nigeria

Abstract

Dissolution and characterization studies on the purification of muscovite ore in hydrochloric acid for use in paint production was investigated.
Specific dissolution parameters including the effects of acid concentration as well as temperature on the dissolution of muscovite ore were studied.
Important instrumentation techniques such as X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM)
were employed for the better explanation of the dissolution process so as to fathom the availability of elements and compounds within the ore.
The results revealed that the dissolution rates were considerably influenced as the acid concentration and temperature increased, while at optimal
leaching conditions, about 85% of the ore was found to have been reacted by 2.5 mol/L at 75◦C temperature and at 120 minutes of leaching time.
The reaction order for the dissolution can be deduced to be half order reaction as the value obtained was in the bracket of 0.50. The reaction
kinetic data revealed the dissolution mechanism to involve diffusion and surface chemical mechanisms as the rate controlling mechanisms while
the different instrumentation techniques corroborated the dissolution as well as purification of the muscovite ore as an ingredient for possible use
in paint production.

Keywords: Characterization, diffusion, dissolution kinetics, hydrochloric acid, leaching, muscovite ore.

Article History :
Received: 17 April 2020
Received in revised form: 09 May 2020
Accepted for publication: 09 June 2020
Published: 01 August 2020

c©2020 Journal of the Nigerian Society of Physical Sciences. All rights reserved.
Communicated by: W. A. Yahya

1. Introduction

Muscovite with the chemical formula KAl2(AlSi3O10)(OH)2,
is an important mineral amongst the mica group that is charac-
terized by layered crystal structure, a density range of 2.77 to
2.88 g/cm3 and majorly described predominantly as of meta-
morphic origin but also found in igneous and sedimentary rocks
as a light coloured phyllosilicate [1]. It is made up of paral-

∗Corresponding author tel. no: +2348032064189
Email address: daudolaoluwa@gmail.com (Daud T. Olaoluwa )

lel sheets of silicate tetrahedrons that are weakly bonded to-
gether by a layer of potassium ions [2]. These sheets are char-
acterized as being chemically inactive, water absorbing, pre-
vents loss of heat, flexible, dielectric, lightweight, reflective,
resilient, refractive, transparent to opaque and stable when ex-
posed to water, electricity, light and extreme temperatures. As
a result of these its superior electrical properties as well as its
abundance, muscovite has been employed as the major mica
used by industries as insulation materials in high voltage and
high power electrical machines, electronic instruments, water

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columns, condensers and radio tubes, high-duty boilers and in
other industrial products and instruments as well as its extensive
use as a pigment extender in paints where it serves purposes
such as; chalking reduction, water penetration and weathering
reduction, tone of coloured pigments brightener, sustains pig-
ments in suspension as well as in the reduction of shrinking and
shearing of the finished surfaces [3, 4, 5].

Muscovite, despite its high density is still not readily and
easily separated from quartz using heavy liquids as a result of
its high surface energy [6] which allows it float and also as a
result of the presence of elements such as aluminium, potas-
sium, iron and titanium etc. which serves as impurities and
could apparently reduce the quality of the muscovite [7, 8].
Muscovite ore processing methods mainly include shape sepa-
ration; a method where particles are separated based on shapes
required for the improvement in quality of powder products,
pneumatic separation; using aerodynamics properties of par-
ticles to heave light, dusty and husky materials out of grains
while heavier materials settle, and flotation; a process for selec-
tively separating hydrophobic materials from hydrophilic sub-
stances [9, 10, 11, 12]. Purification studies of muscovite in-
volves fluoric acid leaching which has been found to show great
effects on processing of muscovite but also found to lead to se-
vere environmental pollution [13, 14]. Other purification stud-
ies such as the oxygen pressure acid leaching involves high acid
consumption and an elongated leaching or reaction time which
ends up leading to consequential declines in equipment life,
production output as well as raise in production costs [15, 16].
Therefore, this research sets out to determine the purification
activities of muscovite ore in hydrochloric acid while critically
examining the effects and extents acid concentrations, reaction
temperature and particle size might have on the ore dissolution
for better interpretation of the optimal purification process as
well as its possible use as a pigment extender in paint produc-
tion.

2. Materials and methods

For this study, the muscovite sample was sourced from Mangu
Local Government Area of Plateau State, Nigeria and the sam-
ple was crushed and milled to yield a fine powder and then
sifted into different particle mesh sizes (53 µm, 63 µm and
90 µm) using the American Society for Testing and Materials
(ASTM) standard sieve fractions, with the size fraction with the
largest surface area used for characterization and leaching stud-
ies.

The EMPYREAN X-ray diffractometer equipped with a Bruter
X-Flash detector using Esprit 1.82 software X-ray Diffraction
Spectroscopy (XRD) was employed in determining the mate-
rial purity assessment as well as to identify compounds of in-

terest present in the ore sample while the MINI PAL 4 EDXRF
spectrometer was used in determining the elemental composi-
tion of the muscovite sample. The samples were carbon coated
and viewed at 5.0kV , 26mm working distance using SEM model
Vega3 TESCAN with LaB6 filament to study the structural mor-
phology of the ore sample. Physicochemical parameters such as
moisture content, loss of mass on ignition as well as the surface
pH of the raw ore were adequately appraised using standard
procedures.

2.1. Leaching Process

Acid dissolution experiments was carried out in a 250 ml
glass beaker erected on a hot plate with automatic temperature
control and magnetically stirred for 120 minutes. The setup was
equipped with a watch glass on the beaker to avoid evaporation,
thereby, enabling the condensation of the leach solution. Dis-
solution parameters including hydrochloric acid (HCl) concen-
tration and leaching temperatures were studied to ascertain the
optimum leaching conditions. Known concentrations of acid
solutions were prepared and placed in the glass beaker till the
solution reached the desired temperature, then the ore sample
was introduced into the beaker and magnetically stirred as the
dissolution proceeded. The amount of ore sample introduced
for the reaction/dissolution was weighed to make up a pulp of
10 g/L. The residue after leaching was filtered, washed, dried
and weighed and the fraction of the ore reacted was calculated
from the initial difference in weight of amount dissolved and
undissolved at various time intervals. Appropriate kinetic curve
was examined using the established shrinking core models for
the establishment of the dissolution mechanism while selected
residues after appropriate treatments were fully characterized
by SEM and XRF [16].

3. Results and Discussion

The elemental composition (Table 1) of the raw muscovite
ore sample by EDXRF and confirmed by XRD spectrum shows
that the ore contains Silicon, Aluminium, Potassium, Rubid-
ium and Tin, occurring as major elements while other elements
such as Calcium, Phosphorus, Manganese, Iron, Nickel, Cop-
per, Zinc, and Molybdenum occur from low to trace levels (≤
0.5%). The XRD pattern (Figure 1) as shown confirms the raw
ore sample to be predominantly muscovite, although with traces
of albite and quartz.

The XRD also gave the formulas of each of these com-
ponents as muscovite (K3.60Na0.28Al9.60Fe0.88Mg0.66Ti0.08Si2.80
O48.00H8.00), albite (Na2.60Al2.00Si6.00O16.00) and quartz (Si3.00O6.00).
The scanning electron image (SEI) at different magnifications

to investigate the structural morphology of the raw muscovite
ore samples is as shown in Figure 2 and it was observed that

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Table 1. EDXRF Result of the raw ore

Elements Si Al K Rb Sn S Ca P Mn Fe Ni Cu Zn Mo

% composition 10.2 4.2 9.3 3.55 1.2 0.54 0.1 0.22 0.41 0.43 0.05 0.05 0.08 0.22

Figure 1. Identified compounds as shown by XRD with their respective Joint Committee on Powder Diffraction Standard file number for peaks assignments showing
Muscovite (K3.60Na0.28Al9.60Fe0.88Mg0.66Ti0.08Si2.80O48.00H8.00) 96-900-5188, albite (Na2.60Al2.00Si6.00O16.00) 96-900-1633 and quartz (Si3.00O6.00) 96-901-2604

throughout the wide size range of the samples, the ore particles
has irregular shapes.

Figure 2. SEI of raw muscovite ore at different magnifications

On ignition in a muffle furnace, the ore sample and its weight
was estimated and affirmed in percentages with an average LOI
value of 1.5 suggesting that the organic component of the ore is
just in low volume while the moisture content obtained was an
average of 2.5%. The pH range of the muscovite ore solution
suspension taken in a period of five (5) days gave values be-
tween 7.35 and 7.47 with the mean pH being 7.42, this affirmed

that the surface of the mineral is neutral.

3.1. Purification studies

Extent of HCl concentration. Muscovite ore dissolution was
carried out using HCl solution in the concentration range of
0.1 mol/L to 3.0 mol/L at 55◦C and at different leaching times
while being moderately stirred at about 300 r pm. The fraction
of the ore dissolved at these different leaching times is plotted
for the separate HCl concentrations as evidenced in Figure 3.

Figure 3 shows that as the HCl concentration at various
leaching times increases, the rate of dissolution increases, there-
fore, 2.5mol/L HCl is considered to be the optimum acid con-
centration and hence, for economic consideration, the optimum
HCl concentration for this study was 2.5 mol/L and hitherto
used in the advancement of some other leaching parameters
such as reaction temperature.

Effect of reaction temperature. The optimal acid concentration
obtained was employed to study the extent of reaction temper-
ature on the dissolution rate of muscovite ore dissolution over
the temperature ranges of 28 − 75◦C and its result is as shown
in the Figure 4.

From the plot, it can be observed that the dissolution of
muscovite is positively influenced as the leaching time rises at

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Figure 3. Extent of HCl concentrations on muscovite ore dissolution per
different leaching time (min.). Experimental conditions: HCl concentration
= 0.1 − 3.0 mol/L; Temperature = 55◦C, Particle size = −90 + 53 µm; Solid-
liquid ratio = 10 g/L with moderate stirring

Figure 4. Extent of temperature on HCl muscovite ore dissolution. Experi-
mental conditions: HCl = 2.5 mol/L; Temperature = 25 − 75◦C, Particle size
= −90 + 53 µm; Solid-liquid ratio = 10 g/L with moderate stirring

different temperature. In other words, muscovite dissolution
rate is greatly affected by reaction temperature as the amount
of muscovite ore leached increased at 75◦C and 120 minutes of
leaching which could be attributable to the certainty of particles
reacting faster when they collide with a rapid rise in tempera-
ture.

3.2. Dissolution kinetics analysis

The reaction between a solid and fluid can be represented as
presented in equation (1) where the rate of reaction may be con-
trolled by either of the mechanisms namely: diffusion through
fluid films, diffusion through ash/product layer, or the chemical
reaction at the surface of the core of unreacted materials [17].

aA(fluid) + bB(solid) → Products (1)

Data collected from leaching with various acid concentrations
and at optimal dissolution conditions was used to estimate the
leaching kinetics as well as the reaction order and activation

energy for better understanding of the dissolution mechanisms
while employing the following shrinking core models to de-
scribe the kinetic models [18, 19].

1 − (1 −α)
1
3 = kct (2)

1 −
2
3
α− (1 −α)

2
3 = kd t, (3)

where α is the fraction reacted, k is the reaction rate constant
and t is the leaching time. Equation (2) is used to predict the
chemical reaction as the leaching rate controlling step occur-
ring at the mineral particle surface while equation (3) predicts
the diffusion through the product layer on the particle surface
as the rate controlling step.

Therefore, the HCl solution treatment was subjected to the
two aforementioned mathematical model equations. Thus, treat-
ing Figures 3 and 4 accordingly using the above kinetic equa-
tions as a function of reaction time gives a perfectly straight line
for equation (3) only.

Figure 5. Plot of 1 − 23 α − (1 −α)
2
3 versus leaching time at different HCl

concentrations. Experimental conditions: Same as in Figure 3

The results of the influence of HCl concentration (Figure 3)
were also subjected to this kinetic models with the experimen-
tal rate constant, kd values and correlation coefficients for each
concentration evaluated. The graph of ln Kd versus ln[HCl] was
then plotted to give the reaction order of 0.4057 as presented in
Figure 6.

As evidenced in Figure 6, the slope of the resulting plot es-
timated the reaction order to be 0.4057 with respect to H+ ion
and a correlation coefficient of 0.9157.

The data from Figure 4 was also linearized using equation
(3) to obtain the result represented in Figure 7.

The apparent rate constant Kd calculated from the slopes of
the straight lines in Figure 7 was then used to obtain Arrhenius
relation as a function of time as shown in Figure 8 below.

From the plot (Figure 8), the calculated activation energy Ea
was 53.38 kJmol−1 which clearly suggests a surface chemical

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Figure 6. ln Kd against ln[HCl]

Figure 7. Plot of 1− 23 α−(1 −α)
2
3 versus reaction time at varying temperatures.

Experimental conditions: Same as in Figure 4

Figure 8. ln Kd versus 1/T

controlled reaction for the dissolution process as proposed by
several investigators [20, 21]. The calculated value of the acti-
vation energy obtained in the present study is above 40 kJ/mol;
which supports that leaching is controlled by surface chemical
mechanism, however, the high Ea could be as a result of 2-stage
mechanism which involves diffusion and surface chemical con-
currently as all the subjected dissolution kinetics data gave a

perfect fit for diffusion controlled mechanism.

3.3. Residual Product Analysis
The residual product formed after leaching at optimal con-

ditions of 2.5 mol/L HCl, 75◦C and 120 minutes of dissolu-
tion was analyzed using XRF and the result shows the pres-
ence of 5.7% Al, 18.3% Si, 7.8% K, 3.1% Rb, 3.4% S and
0.67% Sb. The XRF result suggests that there was an increase
in the amount of these elements as compared to the raw ore,
therefore, it could be said that this process purified the mus-
covite ore and increased the presence of other elements which
could also be used to produce these compounds.

From the SEM images of the leached muscovite ore par-
ticles presented in Figure 9 below, it can be deduced that the
SEM photograph shows that the residual products were closely
packed with shining surface which suggests that the ore was
greatly enhanced by the hydrochloric acid processing. It also
shows charged surfaces which corroborates its use in literature
as a cosmetic ingredient [4, 5].

Figure 9. SEM images of HCl residual products

4. Conclusion

This research studied the dissolution of muscovite ore to
obtain a high grade material which could be used as extender
for paint production in acidic solution - HCl at a set of opti-
mal experimental conditions of 2.5 mol/L HCl solution, within
120 minutes of agitation/dissolution and at 75◦C. The effects
of solution concentrations and reaction temperatures were in-
vestigated to ascertain the level of ore dissolution while com-
paring the detailed characterization of the raw ore sample with
the products obtained after dissolution. On this basis, these sub-
sequent conclusions can be drawn:

• the dissolution rate increases as the leachant concentra-
tion and temperature are increased as the rate of dissolu-
tion of muscovite ore in HCl solution was found to en-
hance the ore dissolution.

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• the calculated activation energy obtained in the present
study is above 40 kJ/mol; which supports the fact that
the leaching process is controlled by a 2-stage mecha-
nism which involves diffusion and surface chemical con-
currently.

• the residual product analysis by XRF and SEM confirms
the purification of the ore and an increased elemental
constituents in the products.

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