minerals

Article
Mineralogical Transformations of Heated Serpentine
and Their Impact on Dissolution during
Aqueous-Phase Mineral Carbonation Reaction in Flue
Gas Conditions
Clémence Du Breuil 1 , Louis César-Pasquier 1, * , Gregory Dipple 2 , Jean-François Blais 1 ,
Maria Cornelia Iliuta 3 and Guy Mercier 1
1 Institut National de la Recherche Scientifique (Centre Eau, Terre et Environnement), University of Quebec,
490 rue de la Couronne, Quebec, QC G1K 9A9, Canada; clemence.jouveau_du_breuil@inrs.ca (C.D.B.);
jean-francois.blais@ete.inrs.ca (J.-F.B.); guy.mercier@ete.inrs.ca (G.M.)
2 Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020–2207 Main
Mall, Vancouver, BC V6T 1Z4, Canada; gdipple@eoas.ubc.ca
3 Chemical Engineering Department, Laval University, Quebec, QC G1V 0A6, Canada;
maria-cornelia.iliuta@gch.ulaval.ca
* Correspondence: louis-cesar.pasquier@ete.inrs.ca; Tel.: +1-418-654-2606; Fax: +1-418-654-2633




Received: 16 August 2019; Accepted: 23 October 2019; Published: 3 November 2019


Abstract: Mineral carbonation is known to be among the most efficient ways to reduce the
anthropogenic emissions of carbon dioxide. Serpentine minerals (Mg3 Si2 O5 (OH)4 ), have shown great
potential for carbonation. A way to improve yield is to thermally activate serpentine minerals prior
to the carbonation reaction. This step is of great importance as it controls Mg2+ leaching, one of
the carbonation reaction limiting factors. Previous studies have focused on the optimization of the
thermal activation by determining the ideal activation temperature. However, to date, none of these
studies have considered the impacts of the thermal activation on the efficiency of the aqueous-phase
mineral carbonation at ambient temperature and moderate pressure in flue gas conditions. Several
residence times and temperatures of activation have been tested to evaluate their impact on serpentine
dissolution in conditions similar to mineral carbonation. The mineralogical composition of the treated
solids has been studied using X-ray diffraction coupled with a quantification using the Rietveld
refinement method. A novel approach in order to quantify the meta-serpentine formed during
dehydroxylation is introduced. The most suitable mineral assemblage for carbonation is found to
be a mixture of the different amorphous phases identified. This study highlights the importance of
the mineralogical assemblage obtained during the dehydroxylation process and its impact on the
magnesium availability during dissolution in the carbonation reaction.

Keywords: serpentinite; X-ray diffraction; rietveld refinement; magnesium leaching; thermal

activation; meta-serpentine; carbonation; heat activation optimization

1. Introduction
The increasing greenhouse gas emissions and particularly anthropogenic carbon dioxide (CO2 ) in
the atmosphere are known to play a major role in climate change [1]. Mitigation solutions are needed
more than ever. Among the methodologies proposed for mitigation, mineral carbonation appears to be
one of the most sustainable [2,3]. This natural and spontaneous phenomenon involves the reaction
between CO2 (aqueous or gas) and divalent cations bearing minerals in order to form the associate
carbonates [3]:

Minerals 2019, 9, 680; doi:10.3390/min9110680 www.mdpi.com/journal/minerals

Minerals 2019, 9, 680 2 of 14

Equation (1) Carbonation reaction [4]

(Mg, Ca)x Siy Ox + 2y + xCO2 = > x(Mg,Ca)CO3 + yCO2 (1)

The reaction products are stable and inert solids where CO2 is sequestered. The composition of
the resulting carbonates depends on the major cations present in the reactant mineral [5]. Carbonation
reaction can be divided in three main steps: (i) the CO2 dissolution in water (ii) the material dissolution
and (iii) the precipitation of carbonates as final products. The process is essentially controlled by
the first two steps [6]. Serpentine minerals, due to their high amount of Mg2+ [7] are considered for
carbonation [8]. Thermal treatment acts on serpentine dissolution by enhancing Mg2+ availability,
making it a key step for the process [9]. Serpentine dissolution first results in a rapid exchange of
surfacing Mg2+ with protons (H+ ) before being extracted from the structure into the solution, during a
much slower phase [10,11]. The dissociation of CO2 added to the solution will generate protons and
HCO3 - ions, therefore enhancing Mg2+ availability (Pasquier et al., 2014b).
Lizardite, antigorite, and chrysotile are the main minerals of the serpentine group (Mg3 Si2 O5 (OH)4 ),
belonging to the phyllosilicate class [7,12–14]. Serpentine structure is made of stacked layers composed
of two sheets: the tetrahedral layer composed of silicon tetrahedral (SiO4 ), linked to the lateral Mg
of the octahedral layer by its apical oxygen atoms, forming a covalent bond [14,15]. Outer hydroxyl
groups contribute to Van der Waals interactions between the two layers, whereas inner hydroxyl
groups contribute to intrafoliar Van der Waals interactions [15–17].
Under high temperatures, hydroxyl groups, linked to Mg atoms, escape the structure. During
this dehydroxylation process, serpentine transformed into amorphous phases (between 550 and
750 ◦ C—Equation (2)), and then recrystallized into forsterite (Mg2 SiO4 > 750 ◦ C), associated with
enstatite (MgSiO3 > 800 ◦ C) as the temperature increased (Equation (3)) [18–20]. Two types of
amorphous phases have been described [21]: pseudo-amorphous phases, named α-meta-serpentine,
appearing at 50% of the total dehydroxylation reaction, and amorphous meta-serpentine, appearing at
90% of the total dehydroxylation. The formation of αmeta-serpentine component can be observed at
a temperature close to 580 ◦ C visualized on a diffractogram by a feature in the lower angle domain
(2θ = ± 6◦ ) [21].
Equations (2) and (3): Serpentine dihydroxylation

Mg3 Si2 O5 (OH)4 (s) → Mg3 Si2 O7 (s) + 2H2 O (g) (2)

2Mg3 Si2 O7 (s) + SiO2 (s) → 3Mg2 SiO4 (s) + MgSiO3 (s) + SiO2 (s) . (3)

It has been observed that amorphous meta serpentine tends to promote Mg2+ leaching and
thus carbonation [21–23]. Therefore, optimized conditions for carbonations have been prescribed
to be between 630 ◦ C and 650 ◦ C for 30 to 120 min [22,24,25]. However, in the previous studies,
carbonation reactions have essentially been performed using pure CO2 gas at high temperature and
high pressure [21,25–27], strong acids or salts to promote dissolution [22,28]. To date no studies have
been conducted on optimizing thermal activation from the mineralogical point of view, especially for
direct aqueous mineral carbonation using diluted gas. In these conditions, serpentine dissolution is
only promoted by carbonic acid at room temperature and low/mild CO2 partial pressure and a good
activation is more than ever critical for reaction.
This study is part of the follow-up work on direct flue gas carbonation process initiated by Mercier
et al. at INRS, Québec [29]. Using mining residues available in the Province of Québec, the process uses
a simulated cement plant flue gas to perform direct flue gas aqueous carbonation [30]. Carbonation
reaction parameters have been optimized by Pasquier [31], optimized conditions for the precipitation
of carbonates have been determined by Moreno [32] whereas a technical and economical evaluation
of the process have shown its feasibility and sustainability in the Province of Québec [33]. However,
a pilot scale test revealed that thermal treatment conditions needed to be optimized for the INRS
process as well [34,35].
Minerals 2019, 9, 680 3 of 14

In the present paper, only the proportion of magnesium prior to precipitation will be studied
and considered as an intermediate product of the carbonation, as thermal activation can only acts
on enhancing serpentine dissolution. Therefore, post-carbonation solids were not considered in the
present study for the given reasons. Furthermore, it serves to give a novel approach of evaluating the
influence of amorphous phases on serpentine dissolution and thus Mg2+ leaching during direct flue
gas aqueous mineral carbonation by introducing a new quantifying method of those phases. Those
new mineralogical data will provide a further understanding of the relation between thermal activation
and serpentine dissolution and therefore, improve this step in the INRS carbonation process.

2. Materials and Methods

2.1. Sample Preparation, Characterization and Analytical Methods

Serpentinite residues were sampled on stockpiles from Jeffrey Mine, near the town of Asbestos,
southern of the Province of Québec. Lizardite is identified to be the major serpentine polymorph [36].
Fibres, representing 20 wt % of the residue, were removed by gravimetric separation based on their
buoyancy. Iron oxides were also removed by wet gravimetric separation using the Wifley table, due to
their potential commercial value for the process.
The sample was ground using a ring mill (Retsch RS200, Dusseldorf, Germany). The grain size
distribution is given in Table 1 Values were obtained and measured using a particle size distribution
analyzer (LA-950V2 Horiba, Kyoto, Japan).

Table 1. Size distribution of the sample.

Mean Size (µm) d90 d50 d10

16.00 1.99 8.16 43.28

The chemical composition of the starting material is given in Table 2. The chemical composition of
liquid and solid samples was obtained using inductively coupled plasma-atomic emission spectrometry
(ICP-AES) analysis (Varian, Palo Alto, CA, USA). Solid samples were first fused using the Claisse
Method [37]. Loss on ignition (LOI) was obtained from mass difference after placing the sample into a
ceramic crucible inside a muffle furnace for 6 h at 1025 ◦ C.

Table 2. Composition of the raw solid feedstock 1 .

Elements Values (wt %)

CaO 0.7
Cr2 O3 0.2
Fe2 O3 6.8
K2 O 0.2
MgO 41.0
MnO 0.1
NiO 0.3
SiO2 39.9
LOI 10.8
1 Major compounds only.

Phases were identified using XRPD analysis (Bruker AXS, 2004, Karlsruhe, Germany), performed
at the University of British Columbia. To prepare the sample, 1.6 g were mixed with 0.4 g of pure
corundum (Al2 O3 ) [38], used as an internal standard, representing a 20.0 wt % spike. Samples were
ground in ethanol using agate grinding pellets for seven minutes, in a McCrone micronizing mill to
ensure homogenization. Scans were acquired for 30 min with 2θ ranging from 3◦ to 80◦ with scanning
step size of 2θ = 0.3◦ with a counting time of 7 s per step, on a Siemens D5000 Bragg-Brentano θ-2θ
Minerals 2019, 9, 680 4 of 14

diffractometer (Bruker AXS, 2004, Karlsruhe, Germany) with radiation CuKα (40kV, 40mA). Matches
were obtained using Bruker identification software DIFFRACplus EVA and the ICDD PDF-2 database.
Quantification of phases was performed using the Rietveld method ([39–42]) based on a calibration
factor obtained from the mass and volume of each phase’s unit cell. However, this method requires that
all of the phases show high degrees of crystallinity with well-defined crystal structures [42]. Serpentine
minerals are known to show discrepancies from their ideal crystal structures [38,43]. Therefore, when
the crystalline structure of a phase is unknown or partially known, it can be quantified through the use
of the Partial Or No Known Crystalline Structure method (PONKCS), combined with the Rietveld
method [44]. A standard sample of pure chrysotile (90.0 wt %) and fluorite (10.0 wt %), provided
by The University of British Columbia (Vancouver, British Columbia, Canada)., whose composition
is well known [38] was used in order to calibrate the PONKCS model. A calibrated mass value for
the unit cell of both phases was acquired by Rietveld refinements and the chrysotile peaks were
fitted using the Le Bail method [45]. The unit cell parameters and the space group were extracted
from Falini [46]. The generated PONKCS model was then used in the Rietveld refinements as a
crystallographic information files in the software TOPAS (Bruker AXS) [44,47].

2.2. Experimental Apparatus and Conditions

2.2.1. Thermal Activation

Heat treatments were performed in a muffle furnace, Furnatrol I33 (Thermolyne Subron
Corporation). Twenty grams of samples were placed in a cast-iron skillet in a thin surface, then
introduced into the furnace. Cast iron was chosen for its resistance to drastic temperature changes.
No major iron contaminations were observed after thermal treatments according to chemical analysis.
Tests were performed under isothermal conditions, meaning that the furnace was set to the targeted
temperature beforehand to the test. At the end of the treatment, the furnace was open to help the skillet
cool down, for five minutes. The skillet and the sample were weighted and the difference between
initial and final masses corresponded to the mass lost induced by heat treatment. A series of seven
tests were conducted at different residence times and temperatures, as shown in Table 3.

Table 3. Treatment conditions.

Temperature (◦ C)
Residence Time (min)
550 650 750
15 A C F
30 - D G
60 B E H

2.2.2. Dissolution in Aqueous Carbonation Conditions

Dissolution reactions were performed using carbonation conditions in order to evaluate thermal
treatment effects on the developing process. Carbonation reactions were conducted in a 300 mL stirred
reactor, model 4561 of Parr Instrument Company (Moline, IL, USA) [29,31]). The tests were performed
using a certified composition gas of 4.0 vol% O2 and 18.2 vol% CO2 , balanced with N2 , simulating
cement plant flue gas. The pulp density was set to 15% (150 g·L−1 ), with a volume of 75 mL of water,
11.25 g of solid and a gas phase volume of 225 mL, as optimized by Mercier et al. [29]. A batch of
10.2 bar of gas was introduced into the stirred reactor and was allowed to react with the pulp for 15 min
at room temperature 22 ◦ C ± 3 ◦ C with the agitation sets to 600 RPM (Figure 1). As the reaction happens,
the pressure decreased between 0.1 and 3.5 bar, depending on the amount of gas initially introduced.
At the end of each batch, the pulp was filtered to obtain the liquid for chemical composition analyses.
The reactivity of the eight thermally treated samples were tested along with an untreated sample (U).
They were only observed throughout the proportion of magnesium leached from the solid during the
reaction, using Equation (4) [Mg]liq corresponds to the measured concentration of Mg2+ at the end of
 Minerals 2019, 9, 680 5 of 14

the reaction,
Minerals V
2019, 9, 680and m are the volume of the solution and the mass of solid, respectively, and CMg 5 ofis14the
measured concentration of Mg in the post-thermal treatment solid. Carbonates were not precipitated
treatment
from thesolid. Carbonates
solution were
as thermal not precipitated
activation impacts from
on the the
Mgsolution as thermal
leaching. activation
Mg analysis impacts onon
was performed
theliquid
Mg leaching. Mg analysis
sample after was
reaction. performed
The on liquid
liquid fraction wassample
obtainedafterafter
reaction. The of
filtration liquid fraction was
the resulting pulp.
obtained after infiltration
Consistency of thewas
the procedure resulting pulp.
validated Consistency
by performing in balance
mass the procedure wasany
to highlight validated by
precipitation
performing
occurring mass
during balance to highlight
manipulation any precipitation
or during the pressureoccurring
release ofduring manipulation or during the
the vessel.
pressure release of
Equation (4):the vessel. of Mg2+ leached
Proportion
Equation (4): Proportion of Mg2+ leached
( 𝑀𝑔 ([ 𝑉)]×
×Mg × V ) × 100
liq 100
%𝑀𝑔 =%Mg =  ×. 𝑚).
(𝐶 (4)
(4)

C ×m Mg

In In a successive
a successive batches
batches test,
test, thethe solid
solid was
was used
used forfor
1212 batches
batches of of gas.
gas. Every
Every twotwo batches,
batches, thethe solid
solid
was filtered and reused with fresh liquid in the subsequent batches. After six
was filtered and reused with fresh liquid in the subsequent batches. After six batches, the solid was batches, the solid was
filtered, dried at 60 ◦ C, and ground for 1 min at 700 RPM in a ring mill, to partially remove the silica
filtered, dried at 60 °C, and ground for 1 min at 700 RPM in a ring mill, to partially remove the silica
layer
layer formed
formed around
around thethe grains
grains and
and thenrereused
then usedforforanother
anotherseries
seriesofof66batches
batchesasasdescribed
describedbybyFigure
Figure 2.
2. The liquid phase was sampled and renewed every two batches to prevent
was sampled and renewed every two batches to prevent saturation. Long term saturation. Long term
reactivity ◦ ◦
reactivity of of samples
samples DD andand F treated
F treated at at
650650 C for
°C for 30 30
minmin and
and 750750 C for
°C for 15 15
min,min, respectively,
respectively, were
were
tested
tested in in a successive
a successive batches
batches experiment.
experiment.

±10.2 bar

P
TºC RPM

Flue gas
18.2 vol%
CO2

600 RPM
11.25 g of solid+75 mL of H2O

Filtration

Inert solid Liquid phase for

ICP analyses

Figure
Figure 1. Parr
1. Parr reactor
reactor experimental
experimental setset
up.up.
Minerals 2019, 9, 680 6 of 14
Minerals 2019, 9, 680 6 of 14

Batch 1
Solid Liquid (a)
Batch 2
Batch 3
Solid Liquid (b)
Batch 4
Batch 5
Solid Liquid (c)
Batch 6

ICP analyses
Grinding (700 RPM 1 min)

Batch 7
Solid Liquid (d)
Batch 8
Batch 9
Solid Liquid (e)
Batch 10
Batch 11
Solid Liquid (f)
Batch 12

Figure 2.
Figure Batches dissolution
2. Batches dissolution experiments.
experiments.

3. Results and Discussion

3. Results and Discussion
3.1. Mass Loss
3.1. Mass Loss
The proportion of mass lost by each sample during thermal treatments has been registered and is
The proportion
presented in Table 4.ofAs
mass lost bythe
expected, each sample during
proportion thermal
of mass treatments
lost during has been
treatment registered
increased withand
the
is presented in Table 4. As expected, the proportion of mass lost during treatment
◦ increased with
temperature. It reached a peak at 14.5% for sample F and was treated at 750 C for 15 min. This value the
temperature. It reached
is in agreement with theaexpected
peak at 14.5% for sample
one, between F and
12.0% andwas treated
14.0% at 750 °C for 15 min. This value
[48,49].
is in agreement with the expected one, between 12.0% and 14.0% [48,49].
Table 4. Mass lost during each thermal treatment, expressed as percent of initial mass of sample.
Table 4. Mass lost during each thermal treatment, expressed as percent of initial mass of sample.
Temperature (◦ C) 550 650 750
Temperature (°C) 550 650 750
Residence Time (min) 15 60 15 30 60 15 30 60 LOI
Residence Time (min) 15 60 15 30 60 15 30 60 LOI
Sample Name A B C D E F G H
Sample Name A B C D E F G H
%%Mass LostLost
Mass 5.5 5.55.5 5.5 5.0 5.0 9.99.9 12.5
12.5 14.2
14.2 13.1
13.1 11.7
11.7 10.8
10.8

Mineralogical Transformations
3.2. Mineralogical Transformations Along with Activation Temperatures
Temperatures
The evolution in the mineral mineral composition
composition at at different
different temperatures and residence times has been
studied using
usingXRPD.XRPD. Serpentine
Serpentine shows highhigh
shows crystallinity in samples
crystallinity U, A, and
in samples U, B,A,respectively untreated,
and B, respectively
treated at 550 ◦ C for 15 min, and treated for 60 min. It then decreases in samples C, D, E, and F,
untreated, treated at 550 °C for 15 min, and treated for 60 min. It then decreases in samples C, D, E,
respectively
and F, respectively at 650 ◦ C
treated treated at for
65015°C min,
for 3015min,
min,and 60 min,
30 min, andand60 at ◦ C for 15 min. Crystalline
750 and
min, at 750 °C for 15 min.
features disappear in disappear
samples F and G, respectively, ◦
Crystalline features in samples F and at G,750 C for 15 and
respectively, at 30
750min.
°C Amorphous
for 15 and contents
30 min.
can be identified
Amorphous in allcan
contents of thebe treated
identifiedsamples
in all asofthe
thecrystallinity
treated samplesdecreases.
as theForsterite is observed
crystallinity decreases. in
Forsterite
samples E,isG, observed in samples
and H, shown E, G, and
by highly H, shown
crystalline by highly crystalline peaks.
peaks.
The remaining magnetite (the small proportion not removed during gravimetric separation)
shows peaks in all samples, samples, whereas
whereas the the hematite
hematite (Fe (Fe22O33)) which
which appears
appears during the duration and
temperature of of the
thetest
testincreases.
increases.Due Duetotothethe tests
tests being
being performed
performed in atmospheric
in atmospheric conditions,
conditions, the
the iron
iron
in theinferrous
the ferrous
formform (Fe2+(Fe 2+) contained
) contained in theinserpentine
the serpentine structure
structure is oxidized
is oxidized into ferric
into ferric iron
iron (Fe 3+ (Fe 3+)
) [50].
[50].iron
As Asrichironolivine
rich olivine (fayalite—Fe
(fayalite—Fe 2SiOessentially
4) can essentially
2+
incorporate Festructure
in its structure [51],
2 SiO4 ) can incorporate Fe in its [51], hematite
2+

hematite
(Fe2 O3 ) is(Fe 2O3) is preferentially
preferentially formed. formed.
Table
Table 55 presents
presentsphases
phasesquantification
quantificationasas measured
measured using
using thethe Rietveld
Rietveld refinement.
refinement. Three
Three issues
issues are
are
faced:faced: (i) these
(i) these valuesvalues
do notdo not consider
consider the massthe mass
loss loss occurring
occurring during
during thermal thermal(ii)
treatment treatment
amorphous (ii)
amorphous
components components
are identified are identified
in the untreated insample,
the untreated
due to thesample, due
stacking to the of
disorder stacking disorder
serpentine, making of
serpentine, making the identification of thermally induced amorphous components difficult, and
finally (iii) a small peak is observed in the low angle that can be attributed to illite thus undermining
Minerals 2019, 9, 680 7 of 14

the identification of thermally induced amorphous components difficult, and finally (iii) a small
peak is observed in the low angle that can be attributed to illite thus undermining the observation
of the formation of meta-serpentine as described by [21]. Wilson et al. [38] determine that absolute
quantification errors (wt %) for serpentine (chrysotile) and non-serpentine phases, regardless of their
abundance in a sample, to be under 5.0 wt %. Consequently, illite is not considered in the Rietveld
refinement as their peaks are too low and would fall under the estimation limit.

Table 5. Mineral composition using Rietveld refinements on XRD patterns, given in wt %.

Amorphous Serpentine Forsterite Magnetite Hematite

Untreated U 39.6 55.8 0.0 4.4 0.0
A (15 min) 40.4 54.9 0.0 4.1 0.4
550 ◦ C
B (60 min) 39.2 56.3 0.0 3.5 0.8
C (15 min) 44.5 50.8 0.0 3.6 0.9
650 ◦ C D (30 min) 43.5 51.6 0.0 3.4 1.3
E (60 min) 46.9 46.3 2.4 2.4 1.8
F (15 min) 70.1 19.8 0.0 6.0 4.1
750 ◦ C G (30 min) 67.9 0.0 28.5 0.0 3.6
H (60 min) 61.8 0.0 34.6 0.0 3.7

In an attempt to overcome these issues, a mass factor (MF in Equation (5)) is computed based on
the mass loss of each sample (Table 4). Using this factor, the abundance of each phase can be expressed
as grams per 100 g of starting material as given in Equation (5).
Equation (5): Proportion of phases expressed in mass

100
 
mphase = %phase × = %phase × MF. (5)
100 + %mass loss

As dehydroxylation is considered to be the loss of H2 O from the structure, the mass of H2 O lost
per gram of serpentine is computed in order to obtain the proportion of dehydroxylated serpentine
(Equation (6)). The value used as maximum mass loss “%mass loss max ” was obtained experimentally
and found to be 14.2% for this material.
Equation (6): Proportion of dehydroxylated serpentine

%mass loss/ (m
P
amorphous + mserpentine ) mH2O lost
% dehydroxylated serpentine = = . (6)
% mass lossmax %mass lossmax
The initial remaining material is decomposed into a non-reacted serpentine (serpentine(i) )
associated with a non-reacted amorphous phase (amorphous(i) ) induced by the layered structure of the
serpentine. Their masses are calculated according to Equation (7), assuming that amorphous phase
and crystalline initial serpentine both dehydroxylated in the same proportion.
Equation (7): Mass of initial phases

mphase(i) = (mphase ) − (m phase × % dehydroxylated serpentine). (7)

The amount of dehydroxylated serpentine and amorphous phase corresponding to the first
amorphous observed, (respectively named serpentine(d) and amorphous(d) ) are given by Equation (8).
Equation (8): Mass of intermediate amorphous phases

mphase(d) = mphase − mphase(i). (8)

Minerals 2019, 9, 680 8 of 14

Further dehydroxylation leads to the formation of meta-serpentine, whose mass is obtained by

Equation (9) This formation is marked by the total loss of the hydroxyls groups at close to 10 wt % of
the starting material mass.
Equation (9): Mass of meta-serpentine

mmeta−serpentine = (m amorphous × mH2O lost ) − mamorphous . (9)

(i)

As a result, three phases emerge from this calculation: first an initial serpentine, resulting from
the sum of amorphous(i) and serpentine(i) , then an intermediate amorphous components which is
the sum of amorphous(d) and serpentine(d) corresponding to the first stage of amorphization, and
finally meta-serpentine. Forsterite and iron oxides (magnetite and hematite) remain unaltered by
the calculation.
As shown in Table 6, Serpentine is gradually replaced by intermediate amorphous phases in
samples treated at temperatures lower than 650 ◦ C and peaks for 60 min treatment at 70.3 g/100 g of
starting material. Meta-serpentine is first found in samples treated at 650 ◦ C for 15 min. Its proportion
increases with the temperature and peaks at 27.2 g/100 g of starting material in the sample treated
at 750 ◦ C for 15 min. The increase of meta-serpentine is combined with a decrease of intermediate
amorphous components contents. As seen previously (Table 5), forsterite is observed in samples E,
G and H, respectively treated at 650 ◦ C for 60 min and at 750 ◦ C for 30 and 60 min. A treatment at 750 ◦ C
for 15 min produced a sample with no initial serpentine and no forsterite but only amorphous phases,
associated with iron oxides. These observations are in agreement with previous studies which observed
the formation of an intermediate amorphous component, α meta-serpentine, progressively replacing
serpentine below 580 ◦ C. It is then followed by the appearance of an amorphous meta-serpentine
material by 650 ◦ C prevailing by 750 ◦ C [21].

Table 6. Mineralogical compositions based on Rietveld refinements, expressed in grams per 100 g of
starting material) at given temperature and residence times. In. Serp: Initial serpentine, Inter. Am.:
Intermediate amorphous components, Meta-serp.: Meta-serpentine, For.: forsterite, Mag: magnetite,
Hem: hematite and ML: Mass loss.

In. Serp. Inter. Am. Meta-Serp. For. Mag. Hem. ML

Untreated U 95.6 0.0 0.0 0.0 4.4 0.0 0.0
A (15 min) 52.8 36.5 0.0 0.0 3.9 0.4 5.5
550 ◦ C
B (60 min) 53.5 37.0 0.0 0.0 3.3 0.8 5.5
C (15 min) 54.0 31.9 4.8 0.0 3.4 0.9 5.0
650 ◦ C D (30 min) 21.6 60.3 4.0 0.0 3.0 1.2 9.8
E (60 min) 4.2 70.3 7.2 2.1 2.1 1.6 12.5
F (15 min) 0.0 49.9 27.2 0.0 5.2 3.5 14.2
750 ◦ C G (30 min) 0.0 33.6 25.5 24.8 0.0 3.1 13.1
H (60 min) 0.0 34.3 20.3 30.5 0.0 3.2 11.7

3.3. Impact of Mineralogy on Dissolution

3.3.1. Two Batches Dissolution

It is known that the amount of Mg2+ available for leaching will directly control, along with
the amount of CO2 treated, the quantity of carbonates being precipitated from the liquid phase
after carbonation [30,31]. This study focuses on the proportion of Mg2+ leached from thermally
treated serpentine samples. Figure 3 shows the mass of intermediate amorphous components and of
meta-serpentine added up and plotted against the proportion of Mg2+ leached into the liquid phase
during the carbonation reaction. As the amount of amorphous components increases from none (U-
untreated sample) to 77 g/ 100 g of starting material (F—750 ◦ C 15 min), the proportion of Mg2+
Minerals 2019, 9, 680 9 of 14

leached during two batches of gas increases too, respectively from 3.3 wt % to 13.5 wt % of initial
Mg 2+ concentration in solid. Samples D, G and H show similar proportions of Mg2+ leached and a
Minerals 2019, 9, 680 9 of 14
close amount of amorphous components. However, initial serpentine constitutes a third of the former
the solubility 2+ ions is first increased by thermal treatment until it is reduced with ◦the
of Mgforsterite
composition, whereas is formed in the two latter. As observed in previous studies at 650 C,
decreasing
the of Mg2+ofions
solubilitycontent amorphous phases and
is first increased the formation
by thermal of forsterite.
treatment The amount
until it is reduced with of
theMg 2+ leached
decreasing
from the
content of heat activated
amorphous serpentine
phases appears
and the to beof
formation linearly dependent
forsterite. The amount 2+
on theofproportion
Mg leached of amorphous
from the
phases.
heat activated serpentine appears to be linearly dependent on the proportion of amorphous phases.

Figure3. 3.
Figure Extracted
Extracted plotted
plotted against
against the quantity
the quantity of amorphous
of amorphous phases,
phases, being being
the sum theintermediate
of the sum of the
intermediate
amorphous amorphous
components andcomponents and meta-serpentine.
meta-serpentine. (Squares,
(Squares, triangle, triangle,
and circles standsand circles
for test stands for
temperature
oftest ◦ C, 650 ◦ C, and
550temperature of 550 ◦ C,
750°C, 650 °C, and 750 °C, respectively).
respectively).

3.3.2.
3.3.2.Successive
SuccessiveBatches
BatchesDissolution
Dissolution
Thermal ◦ for 30 min and 750 ◦ C for 15 min) are
Thermaltreatment
treatmentconditions
conditionsofofsamples
samplesDDand andFF(650
(650 C °C for 30 min and 750 °C for 15 min) are
chosen
chosentotobe betested
testedon onsuccessive
successivebatches
batchesasasthey theyrespectively
respectivelyare arethetherecommended
recommendedconditions conditionsinin
literature 2+
literature[22][22]andandthetheconditions
conditions giving
giving the
the highest
highest proportion
proportion of of Mg
Mg2+ leached
leachedafter aftertwo
twobatches
batchesof
ofgas
gas in our conditions. Figure 4 shows the cumulative proportion of Mg 2+ leached after twelve
in our conditions. Figure 4 shows the cumulative proportion of Mg leached after twelve batches
2+

batches
of gas.ofAfter
gas. After two batches
two batches of gas,
of gas, thethe proportionofofMg
proportion Mg2+2+leached
leached demonstrates
demonstrates aasignificant significant
discrepancy ◦ for
discrepancy from the previous results and the present one. Indeed, the sample treated at 650 C
from the previous results and the present one. Indeed, the sample treated at 650 °C for
30 2+ ◦
30minminshows
showsaasimilar
similarproportion
proportionof ofMgMg2+ leached
leached to to the
the one
one treated
treated at at 750
750 °C C for
for 15
15 min.
min. After
After4
4batches,
batches,the the sample
sample treated
treated at
at 750 ◦ C for 15 min is catching up with a proportion of Mg2+ leached
750 °C for 15 min is catching up with a proportion of Mg2+ leached
higher 2+
higher by 5 wt % compared to the othersample.
by 5 wt % compared to the other sample.At Atthe
theendendofofthe
the1212batches,
batches,44.6 44.6wtwt%% ofof
Mg Mg2+has
has
been ◦ C for 15 min against 32.4 wt % for the one treated at
beenleached
leachedfromfromthe the sample
sample treated
treated at at 750
750 °C for 15 min against 32.4 wt % for the one treated at 650
650 ◦ C for 30 min. For the sample treated at 650 ◦ C for 30 min, the proportions of Mg2+ leached reached
°C for 30 min. For the sample treated at 650 °C for 30 min, the proportions of Mg2+ leached reached a
aplateau
plateau close
close toto 0.5
0.5 wt
wt % 2+
% during
during the
the tenth
tenth batch,
batch,suggesting
suggestingthat thatalmost
almostall allofofthetheMgMg2+available
availableinin
the ◦
thepresent
presentdissolution
dissolution conditions
conditionsmight
might have been
have leached.
been ThisThis
leached. occurred withwith
occurred at 750at C 750after
°C 15 min,
after 15
which indicates that the plateau has not been reached yet, suggesting that more
min, which indicates that the plateau has not been reached yet, suggesting that more batches of CO2 batches of CO 2 could
allow
coulda allow
highera proportion of Mg2+of
higher proportion leached. As the As
Mg2+ leached. solution is refreshed
the solution for every
is refreshed fortwo batches
every of gas,
two batches
the limiting factor is factor
the availability of the Mg 2+ and not the saturation of the solution.
of gas, the limiting is the availability of the Mg 2+ and not the saturation of the solution.
Minerals 2019, 9, 680 10 of 14
Minerals 2019, 9, 680 10 of 14

50%

Re-grinding
45%
Cumulative proportion of leached Mg2+

40%
(% of initial Mg concentration)

35%

30%

25%

20%

15%

10%

5%

0%
0 2 4 6 8 10 12 14
Batches of CO2
D (650°C 30 min) %Mg leached F (750°C 15 min) %Mg leached
2+ leached (expressed in percent of initial Mg2+
Figure 4. The
Figure 4. The Mg
Mg2+ leached concentration in
(expressed in percent of initial Mg2+ concentration in the
the solid)
solid) for
for samples
samples
treated at 650 ◦ C for 30 min (blue) and at 750 ◦ C for 15 min (green).
treated at 650 °C for 30 min (blue) and at 750 °C for 15 min (green).

The
The increase
increase in
in the
the slope
slope of
of the
the curves
curves between
between the the batches
batches 66 and
and 88 demonstrate
demonstrate thethe slight
slight effect
effect
of
of the grinding on the material after the batch 6. Pasquier et al. [30] demonstrated that the effect of
the grinding on the material after the batch 6. Pasquier et al. [30] demonstrated that the effect of
the
the passivation
passivation silica
silica layer,
layer, formed
formed during
during dissolution,
dissolution, can can be
be reduced
reduced by by grinding
grinding and
and so
so revive
revive the
the
leaching 2+ Nevertheless, studies from the Carmex project [52,53]) show that a continuous
leaching ofof Mg
Mg2+.. Nevertheless, studies from the Carmex project [52,53]) show that a continuous
mechanical
mechanical exfoliation of the passivation layer
exfoliation of the passivation layer as
as itit forms
forms on
on the
the grains
grains would
would be
be aa promising
promising wayway to
to
avoid the need for regrinding after six batches of
avoid the need for regrinding after six batches of gas. gas.

3.4. Mineralogical Assemblage and Carbonation

3.4. Mineralogical Assemblage and Carbonation
As the hydroxyl groups escape the serpentine octahedral sheets, the remaining atoms of Mg and
As the hydroxyl groups escape the serpentine octahedral sheets, the remaining atoms of Mg and
Si are reorganized through the amorphous components. As the temperature increases, serpentine is
Si are reorganized through the amorphous components. As the temperature increases, serpentine is
transformed into amorphous phases, then recrystallizes into forsterite.
transformed into amorphous phases, then recrystallizes into forsterite.
The best mineralogical assemblage is shown to be a mixture of amorphous phases, as observed
The best mineralogical assemblage is shown2+to be a mixture of amorphous phases, as observed
in sample F with the highest proportion of Mg leached after both two batches and successive
in sample F with the highest proportion of Mg2+ leached after both two batches and successive batches
batches carbonation tests. McKelvy et al. [21] observed significantly higher carbonation reaction
carbonation tests. McKelvy et al. [21] observed significantly higher carbonation reaction rates in the
rates in the presence of amorphous meta-serpentine, formed above 610 ◦ C, than in the presence of
presence of amorphous meta-serpentine, formed above 610 °C, than in the presence of α-meta-
α-meta-serpentine formed below 580 ◦ C and identified as intermediate amorphous components here.
serpentine formed below 580 °C and identified as intermediate amorphous components here. When
When structurally stable Mg-bearing phases are present in the assemblage, such as serpentine or
structurally stable Mg-bearing phases are present in the assemblage, such as serpentine or forsterite,
forsterite, material reactivity decreases. In serpentine, Mg atoms are bonded to the hydroxyls groups
material reactivity decreases. In serpentine, Mg atoms are bonded to the hydroxyls groups whereas
whereas in forsterite, they are ionically bonded to silica tetrahedron [54]. The differentiation of the
in forsterite, they are ionically bonded to silica tetrahedron [54]. The differentiation of the two
two amorphous phases based on the proposed calculation in this paper were revealed to be accurate
amorphous phases based on the proposed calculation in this paper were revealed to be accurate
because the sample showing the highest value of metaserpentine appeared to be the one demonstrating
because the sample showing the highest value of metaserpentine appeared to be the one
the highest proportion of Mg2+ leached, in accordance with observations proposed in the literature.
demonstrating the highest proportion of Mg2+ leached, in accordance with observations proposed in
Moreover, reactivity appears to be affected more by mineralogy than by surface area.
the literature.
Larachi et al. [15] provide surface area measurements on calcined samples, from 300 ◦ C to 1200 ◦ C,
Moreover, reactivity appears to be affected more by mineralogy than by surface area. Larachi et
showing that it tends to decrease with increasing temperature as dehydroxylation occurs.
al. [15] provide surface area measurements on calcined samples, from 300 °C to 1 200 °C, showing
Furthermore, observations made here are in accordance to those made by other authors regarding
that it tends to decrease with increasing temperature as dehydroxylation occurs.
the mineralogical transformations occurring during thermal activation and dehydroxylation [21,22].
Furthermore, observations made here are in accordance to those made by other authors
Nevertheless, a shift of ideal temperature is observed, as observations made by others suggest that
regarding the mineralogical transformations occurring during thermal activation and
reactions at 650 ◦ C were more likely to occur, rather than at 750 ◦ C as occurred in the present study. Such
dehydroxylation [21,22]. Nevertheless, a shift of ideal temperature is observed, as observations made
by others suggest that reactions at 650 °C were more likely to occur, rather than at 750 °C as occurred
in the present study. Such a change can be attributed to numerous factors such as the initial material
Minerals 2019, 9, 680 11 of 14

a change can be attributed to numerous factors such as the initial material mineralogy, the experimental
set up, and the methodology used to evaluate activation efficiency. For instance, Li et al., [22] used
hydrochloric acid to perform lixiviation tests, which is far from neutral pH and weak acid conditions
used in the present study. On the other hand, McKelvy et al.’s [21] work set the basis of serpentine
dehydroxilation understanding using TGA/DTA and XRD. Conversely, their carbonation conditions
used high temperature and supercritical CO2 , which is again far from the conditions tested here. Based
on their results, past ideal activation conditions were shown to be effective, but not necessarily optimal.
Therefore, the present results highlight the importance of considering the mineralogical assemblage
alongside the thermal treatment parameters (temperature and residence time). Such an approach will
allow us to take into account the effect of the initial material composition and potential specificity of
the activation conditions/technique. Indeed, conditions in a rotary kiln will be very different from a
furnace or a fluidized bed. As results, a study of the mineralogical assemblage can lead to an accurate
optimization of heat activation operating conditions in accordance with the material activated and the
equipment used.

4. Conclusions
In this study, a novel approach of amorphous phase quantification, resulting from serpentine
thermal activation, is introduced. It enables a better understanding of their implications in serpentine
dissolution using carbonic acid as a lixiviant, in similar conditions to those used in the direct flue
gas mineral carbonation process developed at INRS. The following conclusions can be made from
this study:
(i) It is possible to differentiate and quantify intermediate amorphous phases and metaserpentine
formed during dehydroxylation of serpentine and correlate these values to the efficiency of
carbonation reaction. In a static furnace, treatment at 750 ◦ C for 15 min leads to the formation of
27.2 g/100 g of starting material of meta-serpentine.
(ii) Thermally produced amorphous phases enhance Mg2+ solubility during carbonation reaction.
Furthermore, the formation of meta-serpentine, resulting in a complete dehydroxylation,
significantly upgrades Mg2+ leaching yield.
(iii) The crystallization of forsterite decreases the sample dissolution potential by limiting the amount
of Mg2+ accessible for leaching in the present dissolution conditions.
(iv) Adjusting thermal activations parameters (temperature and residence time) led to an increase of
39% of Mg2+ leached during the carbonation reaction.

Author Contributions: Methodology, C.D.B., L.C.-P., G.D., J.-F.B., M.C.I., G.M.; formal analysis, C.D.B.;
writing—original draft preparation, C.D.B., L.C.-P., G.D., J.-F.B., M.C.I. and G.M.; writing—review and editing,
C.D.B., L.C.-P.; supervision, L.C.-P., G.D., J.-F.B., M.C.I. and G.M.; project administration, G.M.; funding acquisition,
L.C.-P., G.D., J.-F.B., M.C.I. and G.M.
Funding: This research was funded by Fond de Recherche Quebecois en Nature et Technology, projet de recherche
en équipe 2015–2016.
Acknowledgments: This research was funded by ‘projet de recherche en équipe’ grant from FRQNT. The authors
would like to thank Matti Raudsepp. Kate Carroll. Ian Power from the University of British Columbia (Vancouver.
Canada) and Connor Turvey from Monash University (Melbourne. Australia) for their advice and help on the
XRD and Rietveld refinement application to the serpentine minerals.
Conflicts of Interest: The authors declare no conflict of interest.

References
1. IPCC. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change; Core Writing Team, Pachauri, R.K., Meyer, L.A., Eds.;
IPCC: Geneva, Switzerland, 2014; p. 151.
2. Lackner, K.S.; Wendt, C.H.; Butt, D.P.; Joyce, B.L.; Sharp, D.H. Carbon dioxide disposal in carbonate minerals.
Energy 1995, 20, 1153–1170. [CrossRef]
Minerals 2019, 9, 680 12 of 14

3. Seifritz, W. CO2 disposal by means of silicates. Nature 1990, 345, 486. [CrossRef]
4. Maroto-Valer, M.M.; Fauth, D.J.; Kuchta, M.E.; Zhang, Y.; Andrésen, J.M. Activation of magnesium rich
minerals as carbonation feedstock materials for CO2 sequestration. Fuel Process. Technol. 2005, 86, 1627–1645.
[CrossRef]
5. Hänchen, M.; Prigiobbe, V.; Baciocchi, R.; Mazzotti, M. Precipitation in the Mg-carbonate system: Effects of
temperature and CO2 pressure. Chem. Eng. Sci. 2008, 63, 1012–1028. [CrossRef]
6. Harrison, A.L.; Power, I.M.; Dipple, G.M. Accelerated carbonation of brucite in mine tailings for carbon
sequestration. Environ. Sci. Technol. 2012, 47, 126–134. [CrossRef]
7. Page, N.J. Chemical differences among the serpentine polymorphs. Am. Mineral. 1968, 53, 201–215.
8. Goff, F.; Guthrie, G.D.; Lipin, B.; Fite, M.; Chipera, S.; Counce, D.A.; Kluk, E.; Ziock, H. Evaluation of Ultramafic
Deposits in the Eastern United States and Puerto Rico as Sources of Magnesium for Carbon Sequestration; Los Alamos
National Laboratory: Los Alamos, NM, USA, 2000; p. 30.
9. Nagamori, M.; Plumpton, A.J.; Le Houillier, R. Activation of magnesia in serpentine by calcination and the
chemical utilization of asbestos tailings, A review. C. Bull. 1980, 73, 144–156.
10. Luce, R.W.; Bartlett, R.W.; Parks, G.A. Dissolution kinetics of magnesium silicates. Geochim. Cosmochim. Acta
1972, 36, 35–50. [CrossRef]
11. Stumm, W.; Morgan, J.J. Aquatic Chemistry: An Introduction Emphasizing Chemical Equilibria in Natural Waters;
John Wiley and Sons: Hoboken, NJ, USA, 1981.
12. Aruja, E. An X-ray study of crystal-structure of antigorite. Mineral. Mag. 1994, 27, 11.
13. Nagy, B.; Faust, G. Serpentines: Natural mixtures of Chrysotile and antigorite. Am. Mineral. 1956, 41,
817–838.
14. Wicks, F.J.; Whittaker, E.J.W. Serpentine textures and serpentinization. Can. Mineral. 1977, 15, 459–488.
15. Larachi, F.; Daldoul, I.; Beaudoin, G. Fixation of CO2 by chrysotile in low-pressure dry and moist carbonation:
Ex-situ and in-situ characterizations. Geochim. Cosmochim. Acta 2010, 74, 3051–3075. [CrossRef]
16. Mellini, M.; Zanazzi, P.F. Crystal structures of lizardite-1T and lizardite-2H1 from Coli, Italy. Am. Mineral.
1987, 72, 943–948.
17. Turci, F.; Tomatis, M.; Mantegna, S.; Cravotto, G.; Fubini, B. A new approach to the decontamination of
asbestos-polluted waters by treatment with oxalic acid under power ultrasound. Ultrason. Sonochem. 2008,
15, 420–427. [CrossRef] [PubMed]
18. Ball, M.C.; Taylor, H.F.W. The dehydration of chrysotile in air and under hydrothermal conditions.
Mineral. Mag. 1963, 33, 467–482. [CrossRef]
19. Brindley, G.W.; Hayami, R. Mechanism of formation of forsterite and enstatite from serpentine. Mineral. Mag.
1965, 35, 189–195. [CrossRef]
20. Brindley, G.W.; Hayami, R. Kinetics and mecanisms of dehydration and recrystallization of serpentine.
Clays Clay Miner. 1965, 12, 35–37. [CrossRef]
21. McKelvy, M.J.; Chizmeshya, A.V.; Diefenbacher, J.; Béarat, H.; Wolf, G. Exploration of the role of heat
activation in enhancing serpentine carbon sequestration reactions. Environ. Sci. Technol. 2004, 38, 6897–6903.
[CrossRef]
22. Li, W.; Li, W.; Li, B.; Bai, Z. Electrolysis and heat pretreatment methods to promote CO2 sequestration by
mineral carbonation. Chem. Eng. Res. Des. 2009, 87, 210–215. [CrossRef]
23. Farhang, F.; Rayson, M.; Brent, G.; Hodgins, T.; Stockenhuber, M.; Kennedy, E. Insights into the dissolution
kinetics of thermally activated serpentine for CO2 sequestration. Chem. Eng. J. 2017, 330, 1174–1186.
[CrossRef]
24. Gerdemann, S.J.; O’Connor, W.K.; Dahlin, D.C.; Penner, L.R.; Rush, H. Ex situ aqueous mineral carbonation.
Environ. Sci. Technol. 2007, 41, 2587–2593. [CrossRef] [PubMed]
25. O’Connor, W.K.; Dahlin, D.C.; Rush, G.E.; Gedermann, S.J.; Penner, L.R.; Nilsen, D.N. Aqueous Mineral
Carbonation; Final Report DOE/ARC-TR-04-002. 2005, p. 462. Available online: https://www.researchgate.net/
profile/William_Oconnor8/publication/315844800_Aqueous_Mineral_Carbonation_Mineral_Availability_
Pretreatment_Reaction_Parametrics_and_Process_Studies/links/58ebb247a6fdcc965767765f/Aqueous-
Mineral-Carbonation-Mineral-Availability-Pretreatment-Reaction-Parametrics-and-Process-Studies.pdf
(accessed on 3 November 2019).
Minerals 2019, 9, 680 13 of 14

26. Gerdemann, S.J.; Dahlin, D.C.; O’Connor, W.K.; Penner, L.R. Carbon dioxide sequestration by aqueous
mineral carbonation of magnesium silicate minerals. In Greenhouse gas Technologies; Albany Research Center
(ARC): Albany, OR, USA, 2003; p. 8.
27. Mann, J. Serpentine Activation for CO2 Sequestration. Ph.D. Thesis, University of Sydney, Sydney, Australia,
2014; p. 274.
28. Sanna, A.; Wang, X.; Lacinska, A.; Styles, M.; Paulson, T.; Maroto-Valer, M.M. Enhancing Mg extraction from
lizardite-rich serpentine for CO2 mineral sequestration. Miner. Eng. 2013, 49, 135–144. [CrossRef]
29. Mercier, G.; Blais, J.-F.; Cecchi, E.; Veetil, S.P.; Pasquier, L.-C.; Kentish, S. Carbon Dioxide Chemical
Sequestration from Industrial Emissions by Carbonation. U.S. Patent 9.440,189 B2, 13 September 2016.
30. Pasquier, L.-C.; Mercier, G.; Blais, J.F.; Cecchi, E.; Kentish, S. Reaction mechanism for the aqueous-phase
mineral carbonation of heat-activated serpentine at low temperatures and pressures in flue gas conditions.
Environ. Sci. Technol. 2014, 48, 5163–5170. [CrossRef] [PubMed]
31. Pasquier, L.-C.; Mercier, G.; Blais, J.F.; Cecchi, E.; Kentish, S. Parameters optimization for direct flue gas
CO2 capture and sequestration by aqueous mineral carbonation using activated serpentinite based mining
residues. Appl. Geochem. 2014, 50, 66–73. [CrossRef]
32. Moreno Correia, M.J. Optimisation de la Précipitation des Carbonates de Magnésium pour L’application
dans un Procédé de Séquestration de CO2 par Carbonatation Minérale de la Serpentine. Master’s Thesis,
Université du Québec, Québec, QC, Canada, 2018; p. 125.
33. Pasquier, L.-C.; Mercier, G.; Blais, J.-F.; Cecchi, E.; Kentish, S. Technical and economic evaluation of a mineral
carbonation process using southern Québec mining wastes for CO2 sequestration of raw flue gas with
by-product recovery. Int. J. Greenh. Gas Control 2016, 50, 147–157. [CrossRef]
34. Kemache, N.; Pasquier, L.-C.; Cecchi, E.; Mouedhen, I.; Blais, J.-F.; Mercier, G. Aqueous mineral carbonation
for CO2 sequestration: From laboratory to pilot scale. Fuel Process. Technol. 2017, 166, 209–216. [CrossRef]
35. Kemache, N.; Pasquier, L.-C.; Mouedhen, I.; Cecchi, E.; Blais, J.-F.; Mercier, G. Aqueous mineral carbonation
of serpentinite on a pilot scale: The effect of liquid recirculation on CO2 sequestration and carbonate
precipitation. Appl. Geochem. 2016, 67, 21–29. [CrossRef]
36. Aumento, F. Serpentine Mineralogy of Ultrabasic Intrusion in Canada and on the Mid-Atlantic Ridge; Department
of Energy, Mines and Resources: Ottawa, ON, Canada, 1970.
37. Tertian, R.; Claisse, F. Principles of Quantitative X-ray Fluorescence Analysis; Wiley-Heyden: London, UK, 1982.
38. Wilson, S.A.; Raudsepp, M.; Dipple, G.M. Verifying and quantifying carbon fixation in minerals from
serpentine-rich mine tailings using the Rietveld method with X-ray powder diffraction data. Am. Mineral.
2006, 91, 1331–1341. [CrossRef]
39. Bish, D.L.; Howard, S. Quantitative phase analysis using the Rietveld method. J. Appl. Crystallogr. 1988, 21,
86–91. [CrossRef]
40. Pawley, G.S. Unit-Cell Refinement from Powder Diffraction scans. J. Appl. Crystallogr. 1981, 14, 357–361.
[CrossRef]
41. Raudsepp, M.; Pani, E.; Dipple, G. Measuring mineral abundance in skarn; I, The Rietveld method using
X-ray powder-diffraction data. Can. Mineral. 1999, 37, 1–15.
42. Rietveld, H.M. A Profile Refinement Method for Nuclear and Magnetic Structures. J. Appl. Crystallogr. 1969,
2, 65–71. [CrossRef]
43. Turvey, C.C.; Wilson, S.A.; Hamilton, J.L.; Southam, G. Field-based accounting of CO2 sequestration in
ultramafic mine wastes using portable X-ray diffraction. Am. Mineral. 2017, 102, 1302–1310. [CrossRef]
44. Scarlett, N.V.Y.; Madsen, I.C. Quantification of phases with partial or no known crystal structures. Powder Diffr.
2006, 21, 278–284. [CrossRef]
45. Le Bail, A. Whole powder pattern decomposition methods and applications: A retrospection. Powder Diffr.
2005, 20, 316–326. [CrossRef]
46. Falini, G.; Foresti, E.; Gazzano, M.; Gualtieri, A.F.; Leoni, M.; Lesci, I.G.; Roveri, N. Tubular-Shaped
Stoichiometric Chrysotile Nanocrystals. Chem. A Eur. J. 2004, 10, 3043–3049. [CrossRef]
47. Du Breuil, C.; Pasquier, L.C.; Dipple, G.; Blais, J.F.; Iliuta, M.C.; Mercier, G. Impact of particle size in serpentine
thermal treatment: Implications for serpentine dissolution in aqueous-phase using CO2 in flue gas conditions.
Appl. Clay Sci. 2019, 182, 105286. [CrossRef]
48. Jolicoeur, C.; Duchenes, D. Infrared and thermogravimetric studies of the thermal degradation of chrysotile
asbsestos fibers: Evidence for matrix effects. Can. J. Chem. 1981, 59, 1521–1526. [CrossRef]
Minerals 2019, 9, 680 14 of 14

49. Viti, C. Serpentine minerals discrimination by thermal analysis. Am. Mineral. 2010, 95, 631–638. [CrossRef]
50. Balucan, R.D.; Dlugogorski, B.Z. Thermal activation of antigorite for mineralization of CO2 .
Environ. Sci. Technol. 2013, 47, 182–190. [CrossRef]
51. Hora, Z. Ultramafic hosted chrysotile asbestos. In Fieldwork; British Columbia Geological Survey: Victoria,
BC, Canada, 1997; p. 4.
52. Bodénan, F.; Bourgeois, F.; Petiot, C.; Augé, T.; Bonfils, B.; Julcour-Lebigue, C.; Guyot, F.; Boukary, A.;
Tremosa, J.; Lassin, A.; et al. Ex situ mineral carbonation for CO2 mitigation: Evaluation of mining waste
resources, aqueous carbonation processability and life cycle assessment (Carmex project). Miner. Eng. 2014,
59, 52–63. [CrossRef]
53. Julcour, C.; Bourgeois, F.; Bonfils, B.; Benhamed, I.; Guyot, F.; Bodénan, F.; Petiot, C.; Gaucher, É.C.
Development of an attrition-leaching hybrid process for direct aqueous mineral carbonation. Chem. Eng. J.
2015, 262, 716–726. [CrossRef]
54. Birle, J.; Gibbs, G.; Moore, P.; Smith, J. Crystal structures of natural olivines. Am. Mineral. 1968, 53, 807.

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).