Calorimetric studies on leaching of mechanically activated sphalerite in FeCl3 solution

Article abstract of DOI:10.1016/j.tca.2003.11.027

The thermal behaviors of the leaching of mechanically activated sphalerite were investigated for the first time by calorimetry. The specific granulometric surface area and the structural disorder sphalerite were also analyzed by X-ray diffraction laser particle size analyzer and X-ray powder diffraction (XRD) analysis, respectively. A new method to measure the mechanically activated storage energy of minerals was proposed by designing a thermochemical cycle that made mechanically activated and non-activated mineral reaching the same final state while leaching in FeCl₃ solution. The results indicate that the mechanically activated storage energy of sphalerite rises with the increased grinding time and is closely related to the lattice distortions and crystallite sizes. The calorimetric results of the products from sieved in water or ethanol medium and the products from 2 h treatment of mechanically activated sphalerite under pure argon (99.99 vol.%) at different temperatures indicate that the mechanically activated storage energy of sphalerite is caused mainly by changes of the crystal structure, and the reactivity of mechanically activated sphalerite is difficult to lose.

Full text of DOI:10.1016/j.tca.2003.11.027

Thermochimica Acta 416 (2004) 5–9
Calorimetric studies on leaching of mechanically activated
sphalerite in FeCl solution
3
a,b,∗
a
a
a
a
Zhongliang Xiao
, Qiyuan Chen , Zhoulan Yin , Huiping Hu , Pingmin Zhang
a
College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, PR China
b
Chemistry Department, Changsha University of Electric Power, Changsha 410077, PR China
Available online 3 February 2004
Abstract
The thermal behaviors of the leaching of mechanically activated sphalerite were investigated for the first time by calorimetry. The specific
granulometric surface area and the structural disorder sphalerite were also analyzed by X-ray diffraction laser particle size analyzer and
X-ray powder diffraction (XRD) analysis, respectively. A new method to measure the mechanically activated storage energy of minerals was
proposed by designing a thermochemical cycle that made mechanically activated and non-activated mineral reaching the same final state while
3
leaching in FeCl solution. The results indicate that the mechanically activated storage energy of sphalerite rises with the increased grinding
time and is closely related to the lattice distortions and crystallite sizes. The calorimetric results of the products from sieved in water or ethanol
medium and the products from 2 h treatment of mechanically activated sphalerite under pure argon (99.99 vol.%) at different temperatures
indicate that the mechanically activated storage energy of sphalerite is caused mainly by changes of the crystal structure, and the reactivity of
mechanically activated sphalerite is difficult to lose.
©
2003 Published by Elsevier B.V.
Keywords: Calorimetric method; Mechanical activation; Sphalerite; Leaching; Structural disorder
1
. Introduction
In this paper, the storage energy behaviors of mechani-
cally activated sphalerite samples prepared by various treat-
ment methods were investigated by calorimetric experiments
to get the essence of mechanically activated storage energy.
Dislocations and various structural defects produced in
crystals as a result of mechanical treatment cause accu-
mulation of large excess of energy. The excess energy is
named as mechanically activated storage energy [1], which
has been given considerable attention recently. Schellinger
2. Experimental
[2] reported that the mechanical activated storage energy in
the minerals were between 10 and 20% of the total energy
after mechanical activation. De Lima and Kim et al. [3,4]
investigated the thermal properties of ball-milled amor-
phous solid using differential scanning calorimetry (DSC).
By the described precision of the DSC method, it is hard to
obtain the accurate mechanically activated storage energy
data. Microcalorimetry has been shown as an important
tool in the study on energy change and its use is increasing
nowadays [5–7]. But applications of microcalorimetry to
determine mechanically activated storage energy has not
been reported due to the complexity of the releasing of
mechanically activated storage energy.
Since the mechanically activated storage energy of spha-
lerite cannot be released completely in the course of heat-
ing, a suitable leaching agent was selected to release all
storage energy by a leaching procedure. A thermochemical
cycle was designed to make mechanically activated and
non-activated mineral reaching the definite final state. Thus
the mechanically activated storage energy can be acquired
by calculating the difference of the reaction enthalpy of
mechanically activated and non-activated minerals in each
process.
The selection of a suitable leaching system is very im-
portant for the calorimetric experiment of sphalerite, which
has been summarized in many publications [8,9]. Although
various acids (H SO , HCl) and bases (ammonia) solutions
∗
Corresponding author. Tel.: +86-731-8877364.
2
4
E-mail address: xiaozhongliang@163.com (Z. Xiao).
have been tested, they did not fit the calorimetry experiment
0
040-6031/$ – see front matter © 2003 Published by Elsevier B.V.
doi:10.1016/j.tca.2003.11.027

6
Z. Xiao et al. / Thermochimica Acta 416 (2004) 5–9
Table 1
of 1:25. Mechanically activated sphalerites were obtained
The chemical analyses of the natural sphalerite
after grinding for tG = 20, 40, 120, 180 and 260 min,
Elements
respectively.
Zn
S
Fe
Pb
Cd
Sb
Bi
In
2
.1.2. Mechanically activated sphalerite sieved in water or
Content (wt.%) 61.39 32.11 2.38 1.92 0.28 0.05 0.01 0.03
ethanol medium
The sieving experiment was completed in a 500 ml beaker
to which 100 ml of distilled water or ethanol and 5 g mechan-
ically activated sphalerite samples were added. The mixture
was introduced sequentially to 60, 100, 120, 140, 160, 180
and 200 mesh sieves to obtain the samples with different
particle size. The samples were then dried in a thermostati-
cally controlled furnace at 343.15 K.
due to gas releasing. FeCl3 solution was selected as a suit-
able lixiviant for sphalerite leaching in our experiments.
Dutrizac, MacDonald and Maurice [10,11,14] stated in their
study of oxidative leaching of sphalerite by FeCl3. In ac-
cordance with the literature data the leaching reaction can
be represented as:
Fe3 + ZnS = Zn2+ + 2Fe2+ + S
+
0
(1)
2
2.1.3. Products from 2 h treatment under an inert
The reaction enthalpy of sphalerite samples in FeCl3 solu-
tion was measured by batch experiments.
atmosphere at different temperatures
Mechanically activated sphalerite grinding for 120 min
was loaded with a porcelain boat reactor in a electric tube
furnace which was kept in higher vacuum (the residue
pressure ≤ 3 Pa), followed by pouring highly pure argon
into it. The vacuum pumping and pure argon gassing oper-
ations were repeated for three times, then the electric tube
furnace was maintained at 323.15, 423.15 and 573.15 K for
2 h, respectively, to obtain the products from 2 h treatment
under an inert atmosphere at different temperatures.
2
2
.1. Preparation of the samples
.1.1. Preparation of mechanically activated sphalerite
Natural pure hand-sorted sphalerite ore was purchased
from a domestic mine, and its chemical compositions are
summarized in Table 1. It was found by X-ray diffraction
analysis that the natural sphalerite contained cubic spha-
lerite as a predominant component (shown in Fig. 1). The
non-activated sphalerite was prepared by crushing the nat-
ural sphalerite in a jaw crusher to a particle size of ≤1 mm,
then stored for more than 6 months. The non-activated
sphalerite (10 g) was added into a stainless vessel with six
stainless steel balls of 18 mm in diameter and 12 balls of
2.2. Calorimetric experiments
A HT-1000 heat flow calorimeter (SETRAM, France) was
used for isothermal heat measurements at 298.15 K. The
sensitivity and temperature scales of the calorimeter were
calibrated carefully [7] before experiments. The enthalpy
8
mm in diameter, then kept in higher vacuum (the residue
3
pressure ≤ 1 Pa), followed by pouring pure nitrogen into
this vessel for 0.5 h (these operations were performed once
again), i.e., non-activated sphalerite was kept under an inert
atmosphere, and then mechanically activated in a planetary
ball mill (QM-ISP planetary ball mill, PR China) under a
rotation rate of 200 rpm, and a powder-to-ball mass ratio
of solution of KCl(s) in water (10.00 cm ) to form about
KCl·1120H2O was measured at T = (298.15 ± 0.05) K to
check the accuracy of the calorimetric method. The results
−
1
was (17.49 ± 0.13) kJ mol , which was in good agree-
−
1
ment with the value 17.503 kJ mol
[18].
from the literature
Fig. 1. XRD pattern of natural sphalerite.

Z. Xiao et al. / Thermochimica Acta 416 (2004) 5–9
7
Fig. 2. Thermochemical cycle for the leaching of the activated sphalerite.
Sphalerite sample of 0.15 g (± 0.0001 g) weighed with
2.3. Surface structural characteristics
BP190S electronic balance (Sartorius, Germany) in a sealed
glass ampoule of 3 ml in volume was broken and reacted
The structural disorder of mechanically activated spha-
lerites was characterized by X-ray diffraction analysis on a
diffractometer (Rigaku, Japan) using Cu K␣ radiation (λ =
1.54 Å, voltage: 40 kV, current: 20 mA) with time constant
0.5 s, limit of measurement 10 impulses per second, step size
0.03 and collection time 3 s per step (no internal standard).
The recorded X-ray powder diffraction (XRD) spectra were
used for calculation of the degree of structural disorder—the
distortion (ε) of crystal lattice (presented as a percentage)
and the crystallite size (D), which were determined from the
changes in profile of the diffraction peaks, such as (1 1 1)
and (3 3 1) of sphalerite. As the diffraction line broadening
depends mainly on the increase of ε and the decrease of D,
ε and D can be calculated by using the model of Gaussian
function [12,13]. In this experiment, ε and D were obtained
by dealing with the integral width of diffraction peaks (1 1 1)
and (3 3 1) of non-activated or mechanically activated spha-
lerites at different grinding time.
−
1
with 10.00 ml 1.0 mol l FeCl3 solution for 4 h after the
baseline of the calorimeter reached a stable state. The heat
flow data were recorded by a data acquisition computer un-
til the system reached thermal equilibrium. At the end of
the experiment, the sample was removed from the calorime-
ter and frozen at once. The amount of solubilized zinc ion
was determined by PS-6 ICP atomic emission spectrome-
ter (Baird, USA). Then the reaction enthalpy for 1 mol zinc
leached from sphalerite was obtained by data treatment as
follows:
ꢀ t
0h dt
Qp = ꢀrHm =
c
2+
V
Zn
where ꢀrHm (kJ mol 1), h (W), t (s), cZn2+ (mol l
−
−1
)
and V (l) are the reaction enthalpy of 1 mol zinc leached,
the heat flow, the reaction time, the zinc ion concentra-
tion of leaching solution and solution volume, respec-
tively.
In accordance with Eq. (1), a thermochemical cycle was
designed (shown in Fig. 2). The storage energy of the acti-
vated sphalerite can be given by
The specific granulometric surface area (SG) of mechan-
ically activated sphalerites was calculated from the corre-
sponding average particle size measured using Mastersizer
2000 Laser Diffraction Particle Size Analyzer (Malvern,
Great Britain), where distilled water was used as a dispers-
ing agent.
E = ꢀrHm1 − ꢀrHm2 = ꢀrHm1 − ꢀrHꢀ − ꢀrHꢀꢀ
m2
m2
ꢀ
ꢀꢀ
where E, ꢀrHm1, ꢀrH , and ꢀrH are the mechanically
m2
m2
3. Results and discussion
activated storage energy of sphalerite, the reaction enthalpy
of non-activated sphalerite in leaching, the reaction enthalpy
of mechanically activated sphalerite in leaching and the en-
thalpy of dilution, respectively.
The mean of the enthalpy of non-activated sphalerite
in leaching obtained from data in Table 2 (ꢀrHm1:
3.1. Mechanically activated storage energy of
non-activated sphalerite and sphalerite mechanically
activated for different time
The mechanically activated storage energy, crystal-
lite sizes, the deformations of the crystal and specific
−
1
−
11.50 kJ mol ).
Table 2
The reaction enthalpy of non-activated sphalerite
No.
1
Mean
2
3
4
5
−
1
ꢀ
rHm1 (kJ mol
)
−11.46
−11.52
−11.54
−11.48
−11.50
−11.50 ± 0.04

8
Z. Xiao et al. / Thermochimica Acta 416 (2004) 5–9
Table 3
ꢀ
ꢀꢀ
m2
The values of ꢀrH , ꢀrH , E, SG, D and ε for non-activated sphalerite and sphalerites mechanically activated for different time leaching condition:
m2
−1
CFeCl , 1 mol l ; temperature, 298.15 K; reaction time, 4 h
3
Grinding time (min)
0
20
40
60
120
260
ꢀ
−1
−1
ꢀ
ꢀ
rH
rH
(kJ mol
(kJ mol
)
)
−11.50
−14.50
−18.93
−21.98
−27.21
−28.46
m2
ꢀ
ꢀ
0
0
−0.0032
−0.0092
−0.0086
10.48
7.04
−0.0106
15.71
7.45
−0.0113
16.96
7.70
m2
−
1
E (kJ mol
SG (m g
D (Å)
ε (%)
)
1.90
4.94
615
0.32
7.43
6.02
472
0.45
2
−1
)
3.15
964
0
339
0.92
230
0.99
163
1.15
granulometric surface area of non-activated sphalerite and
sphalerites mechanically activated for different time were
listed in Table 3. Chen and Xiao et al. [9,17] reported that
no elemental sulfur was produced during mechanical ac-
tivation of sphalerite and this mechanical activation was
performed under inert atmosphere, therefore, the chemical
reaction of this mechanical activation for sphalerite can be
neglected.
Table 5
The storage energy of the products from the 2 h treatment of mechanically
activated sphalerite under inert atmosphere
Without the
treatment
Treating temperature
23.15 K 423.15 K 573.15 K
3
rHm2 (kJ mol 1) −27.21
−
−25.84
14.42
−25.83
14.41
−25.36
13.94
ꢀ
−
−1
1
E (kJ mol
SG (m g
)
15.71
16.64
2
)
9.123
8.612
6.404
Table 3 indicates that the mechanically activated storage
energy of sphalerite increases with the increased grinding
time, and the crystallite sizes decrease and the deformations
of the crystal increase gradually with the increased grinding
time, which is similar with the study of mechanically acti-
vated chalcopyrite and pyrite [15,16]. Therefore, it can be
deduced that non-activated sphalerite undergoes the struc-
tural distortion during the mechanical activation under an
inert atmosphere, which leads to the formation of metastable
sphalerites. The metastable sphalerites containing accumu-
lated excess energy, so the mechanically activated storage
energy of sphalerite is closely related to the structural dif-
ferences between non-activated and mechanically activated
sphalerites.
medium and the particle size of mechanically activated spha-
lerite. It indicates that the decrease of the particle size of
mechanically activated sphalerite is not the major factor of
the increase of the storage energy of mechanically activated
sphalerite.
3.3. Mechanically activated storage energy of the
products from 2 h treatment of mechanically activated
sphalerite under an inert atmosphere
The storage energy of the products from the 2 h treat-
ment of mechanically activated sphalerite under an inert at-
mosphere at different temperatures is listed in Table 5. The
products were also characterized by XRD analysis (shown
in Fig. 3).
3
.2. Mechanically activated storage energy of
mechanically activated sphalerite sieved in water
or ethanol medium
Table 5 shows that the storage energy of the products
remains almost constant with increased treating tempera-
ture. Fig. 3 and Table 5 indicate that the average surface
area of mechanically activated sphalerite changes with the
2 h treatment but does not change the lattice structure of
The mechanically activated storage energy of sphalerite
sieved in water or ethanol medium is shown in Table 4.
Table 4 shows that the mechanically activated storage en-
ergy of the samples is almost independent of the sieving
Table 4
Storage energy of mechanically activated sphalerites sieved in different mediuma
Particle size (mesh)
60–100
120–140
160–180
180–200
−
ꢀ
rHm2, sieved in H2O (kJ mol 1)
−22.89
11.39
−23.10
11.60
−23.05
11.55
−22.87
11.37
−1
E, sieved in H2O (kJ mol
ꢀ
)
rHm2, sieved in C2H5OH (kJ mol 1)
−
−23.81
−23.77
−23.99
−24.34
−1
E, sieved in C2H5OH (kJ mol
)
12.31
12.27
12.49
11.84
a
rHm2 = ꢀrHꢀ + ꢀrHꢀꢀ
ꢀ
.
m2
m2

Z. Xiao et al. / Thermochimica Acta 416 (2004) 5–9
9
Fig. 3. XRD patterns of mechanically activated sphalerite (1) and its treated product (2): (1) mechanically activated sphalerite without the 2 h treatment;
2) the product obtained from the 2 h treatment under inert atmosphere at 573.15 K.
(
mechanically activated sphalerite. This is another support
for the opinion that the decrease of particle size of mechani-
cally activated sphalerite is not the major factor of resulting
in the increase of the storage energy of mechanically acti-
vated sphalerite.
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6
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2
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