Magnesium Leachability of Mg-Silicate Peridotites: The Effect on Magnesite Yield of a Mineral Carbonation Process - MDPI
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minerals
Article
Magnesium Leachability of Mg-Silicate Peridotites:
The Effect on Magnesite Yield of a Mineral
Carbonation Process
Muhammad Imran Rashid *, Emad Benhelal, Faezeh Farhang, Michael Stockenhuber and
Eric M. Kennedy
Department of Chemical Engineering, University of Newcastle, Callaghan, NSW 2308, Australia;
emad.benhelal@newcastle.edu.au (E.B.); faezeh.farhang@newcastle.edu.au (F.F.);
michael.stockenhuber@newcastle.edu.au (M.S.); eric.kennedy@newcastle.edu.au (E.M.K.)
* Correspondence: muhammadimran.rashid@uon.edu.au
Received: 15 November 2020; Accepted: 3 December 2020; Published: 5 December 2020
Abstract: The aim of this study was to increase feedstock availability for mineral carbonation.
Acid dissolution and carbonic acid dissolution approaches were used to achieve higher Mg extractions
from peridotites. Acid dissolution studies of raw dunite, heat-activated dunite, heat-transformed
dunite, and twin sister dunite have not been reported in the literature. Heat-activated dunite is more
reactive as compared to heat-transformed dunite, raw dunite, and twin sister dunite. The fraction of
magnesium extracted from heat-activated dunite was 57% as compared to 18% from heat-transformed
dunite, 14% from raw dunite, and 11% from twin sister dunite. Similarly, silicon and iron extractions
were higher for heat-activated dunite compared to that of heat-transformed dunite, raw dunite,
and twin sister dunite. Materials rich in forsterite (twin sister dunite and heat-transformed dunite)
showed preferential Mg release and exhibited incongruent dissolution similar to that of forsterite.
Heat-activated dunite (amorphous magnesium silicate rich) on the other hand behaved differently
and showed congruent dissolution. Olivine did not dissolve under carbonic acid dissolution
(with concurrent grinding) and acidic conditions. Under carbonic acid dissolution with concurrent
grinding conditions, olivine was partially converted into nanometer sized particles (d10 = 0.08 µm)
but still provided 16% Mg extraction during 4 h of dissolution.
Keywords: acid dissolution; dunite rock; olivine; carbonic acid dissolution; peridotites
1. Introduction
The CO2 concentration in the atmosphere has risen to 411 ppm as compared to 280 ppm in pre-industrial
times [1]. Accumulation of CO2 in the atmosphere is considered the main cause of climate change and
the global warming phenomenon. Warming of 2 ◦ C would release billions of tons of soil carbon [2].
Geological storage, oceanic storage, and recently mineral carbonation, are among different candidates for
CO2 sequestration to prevent its emissions to the atmosphere [3,4]. Mineral carbonation, mainly using
naturally abundant Mg-silicates, can offer safe storage of CO2 in the form of mineral carbonates for many
centuries [5,6].
Single stage [4,6–12] and two-stage carbonation [13–19] are different processes that are being
extensively studied for CO2 capture, utilization, and storage. Initial studies on mineral carbonation
showed relatively slow reaction kinetics [20]. One of the key considerations for developing efficient
mineral carbonation technology is to increase Mg extraction from feedstock. For this purpose,
acid dissolution of magnesium silicate minerals was studied previously [15,21–24]. Park et al. used
different acid solutions and grinding media to increase Mg extraction [25,26]. Sulfuric acid, formic acid,
Minerals 2020, 10, 1091; doi:10.3390/min10121091 www.mdpi.com/journal/minerals
Minerals 2020, 10, 1091 2 of 16
acetic acid, hydrochloric acid, and nitric acid were used to extract Mg from serpentine [27–29].
Farhang et al. studied acid dissolution of heat-activated lizardite at different pH values, solid-to-liquid
ratios, and particle sizes and obtained almost 60% Mg extractions during 1 h of dissolution [22].
Farhang et al. investigated silica precipitation at different pH values and temperatures and determined
that re-precipitation of silica retards dissolution of Mg by forming a diffusion barrier [30]. Dunite is
partially weathered olivine that is the most abundant ultramafic rock available [31,32], which makes it
important for the mineral carbonation process and needs significant consideration. Compared to other
magnesium silicate minerals that have been studied for mineral carbonation, dunite is more complex as
it is usually a mixture of minerals. One example that has previously been studied contains 61%–62%
lizardite, 30%–33% olivine, 3.8%–8.3% brucite, and 0.6% magnetite [4]. Heat activation can be used to
convert the lizardite present in dunite into more reactive amorphous Mg-silicate phases. Heat activation
is a process in which dehydroxylation of serpentine minerals occurs as hydroxyl groups bound within
mineral matrix are destabilized and released from the sample in the form of water vapor. The optimum
decomposition temperature for lizardite has been reported as 635 ◦ C [33]. Lizardite dehydroxylation
converts the material into MgO. SiO2 motifs, Equation (1), can further crystallize at higher temperatures
(or excessive soak times exceeding 4 h) to form forsterite (Mg2 SiO4 ), Equation (2), enstatite (MgSiO3 ),
Equation (3), and silica (SiO2 ) [34]. The formation of intermediate phases, which tend to be X-ray
amorphous, increases the reactivity of the parent mineral [35], while the formation of new crystalline
phases, such as forsterite, is detrimental to the reactivity of the material.
Mg3 Si2 O5 (OH)4 → 3MgO.2SiO2 + 2H2 O (1)
2MgO.SiO2 → Mg2 SiO4 (2)
MgO.SiO2 → MgSiO3 (3)
Dunite is comprised of approximately 61% lizardite, which can be converted into a more reactive
amorphous phase through the heat-activation treatment process. A temperature of 650 ◦ C is sufficient
for lizardite to complete dehydroxylation [36]. In our previous publication, we established that
heat-activated dunite provided higher magnesite yields compared to that of heat-transformed dunite
(forsterite rich) and raw dunite [4]. The aim of this work was to confirm these magnesite yield results
through a second approach, i.e., Mg extraction using acid dissolution experiments. Materials that
provided a higher carbonation extent also showed higher Mg extractions, indicating a direct relationship
between carbonation extent and Mg extractions. Acid dissolution studies of dunite rock, heat-activated
dunite, and heat-transformed dunite have not yet been reported in the literature. The purpose of this
article was to study acid dissolution of dunite rock at room temperature and to investigate if dunite
can be considered as a potential feedstock for mineral carbonation. Furthermore, dissolution of olivine
as a relatively pure peridotite mineral in carbonic acid solution with the aid of concurrent grinding
was studied in this work, which has not been studied previously in the literature.
2. Material, Methods, and Experimental Set-Up
2.1. Dunite
The dunite used in this study was sourced from a dunite quarry, located close to the township of
Bingara (within 5 km), located in The Great Serpentine Belt (GSB) of New South Wales (NSW), Australia.
Samples of rock were handpicked (a total mass of approximately 15 kg) from the center and north walls
of the quarry and then crushed to 2 to 10 cm in diameter. The dunite was tested by stereomicroscopy
and polarized light microscopy (with dispersion staining) to check for the presence of chrysotile,
amosite, and crocidolite asbestos and was only used if it was certified to be asbestos free (Pickford
& Rhyder Consulting Pty Ltd., New South Wales, Australia). Approximately 2 kg of the dunite was
dry crushed in a jaw crusher (200 × 125 mm model, Terex Jaques) to obtain a 2–3 mm size fractions.
A portion of this material was transferred to a ball mill (MTI Corporation, CA, USA) to prepare sub-75
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to prepare sub-75 micron size fractions. Grinding was performed in a stainless-steel jar for 2 h, where
to prepare
micron size sub-75 micron
fractions. size fractions.
Grinding Grinding
was performed in awas performedjar
stainless-steel in for
a stainless-steel jar for 2steel
2 h, where stainless h, where
balls
stainless steel balls (diameter, 6 to 20 mm) were used as the grinding media.
stainless steel
(diameter, 6 to balls
20 mm)(diameter, 6 toas20the
were used mm) were used
grinding as the grinding media.
media.
2.2. Heat-Activated Dunite
2.2.
2.2. Heat-Activated
Heat-Activated Dunite
Dunite
Heat activation of dunite (approximately 150 g) was performed in an electrically heated
Heat
Heatactivation
activationof dunite (approximately
of dunite 150 g) was
(approximately 150 performed in an electrically
g) was performed in anheated stainless-steel
electrically heated
stainless-steel rotary kiln (Nabertherm, Lilienthal, Germany) ◦ C underat 630 °C under a nitrogen purge flow
rotary kiln (Nabertherm, Lilienthal, Germany) at 630 a nitrogen purge flow
stainless-steel rotary kiln (Nabertherm, Lilienthal, Germany) at 630 °C under a nitrogen purge flow (80 L/h) for 4 h.
(80 L/h) for 4 h. A ◦temperature of 650 °C is sufficient for lizardite's complete dehydroxylation [36]
A(80
temperature
L/h) for 4ofh.650 C is sufficientof
A temperature for650
lizardite’s complete dehydroxylation
°C is sufficient [36] and above
for lizardite's complete this temperature
dehydroxylation [36]
and above this temperature enstatite formation starts [33]. The rotary kiln is shown in Figure 1, and
enstatite
and aboveformation starts [33].enstatite
this temperature The rotary kiln is shown
formation startsin Figure
[33]. The1,rotary
and akiln
schematic of the
is shown rotary kiln
in Figure is
1, and
a schematic of the rotary kiln is shown in Figure 2.
shown in Figure
a schematic 2. rotary kiln is shown in Figure 2.
of the
Figure 1. Photo of the rotary kiln (Nabertherm, Lilienthal, Germany). (A): Control panel, (B): Mass
Figure1.1.Photo
Figure Photoofofthe rotary
the rotarykiln (Nabertherm,
kiln (Nabertherm,Lilienthal, Germany).
Lilienthal, (A): (A):
Germany). Control panel,
Control (B): Mass
panel, flow
(B): Mass
flow controllers, (C): Stainless steel tube, (D): Heating element, (E): Material collection jar, (F):
controllers, (C): Stainless steel tube, (D): Heating element, (E): Material collection jar, (F):
flow controllers, (C): Stainless steel tube, (D): Heating element, (E): Material collection jar, (F):Thermocouple
Thermocouple connection, (G): Nitrogen cylinder. Th rotary kiln was used for the heat-activation of
connection,
Thermocouple (G):connection,
Nitrogen cylinder. Th rotary
(G): Nitrogen kilnTh
cylinder. was usedkiln
rotary for was
the heat-activation of dunite and
used for the heat-activation of
dunite and lizardite. It was also used for the dunite heat-transformation.
lizardite.
dunite andIt was also used
lizardite. It wasforalso
the used
dunite
forheat-transformation.
the dunite heat-transformation.
Figure 2. Simplified
Figure 2. Simplified process
process schematic
schematic of
of the
the rotary
rotary kiln
kiln and
and gas
gascontrol
controlmanifold.
manifold.
Figure 2. Simplified process schematic of the rotary kiln and gas control manifold.
2.3. Heat-Transformed Dunite
2.3. Heat-Transformed Dunite
2.3. Heat-Transformed Dunite
To study the reactivity of synthesized forsterite and compare it with natural forsterite (i.e., olivine),
To study the reactivity of synthesized forsterite and compare it with natural forsterite (i.e., ◦C
duniteTowas heat-transformed
study the reactivitytoofforsterite in a rotary
synthesized kiln and
forsterite (Nabertherm,
compare Lilienthal, Germany)
it with natural at 800(i.e.,
forsterite
olivine), dunite was heat-transformed to forsterite in a rotary kiln (Nabertherm, Lilienthal, Germany) ◦
for 3 h. Lizardite
olivine), dehydroxylation
dunite was may result
heat-transformed in non-reactive
to forsterite enstatite
in a rotary formation atLilienthal,
kiln (Nabertherm, or above 800 C [33].
Germany)
at 800 °C for 3 h. Lizardite dehydroxylation may result in non-reactive enstatite formation at or above
Heat
at 800transformation was used
°C for 3 h. Lizardite to convert themay
dehydroxylation lizardite
resultpresent in duniteenstatite
in non-reactive into forsterite to compare
formation its
at or above
800 °C [33]. Heat transformation was used to convert the lizardite present in dunite into forsterite to
800 °C [33]. Heat transformation was used to convert the lizardite present in dunite into forsterite to
compare its reactivity with other forms of feedstock via dissolution in mild acidic pH. Heat
compare its reactivity with other forms of feedstock via dissolution in mild acidic pH. Heat
Minerals 2020, 10, 1091 4 of 16
reactivity with other forms of feedstock via dissolution in mild acidic pH. Heat transformation is a process
in which serpentine minerals (here the lizardite fraction in dunite rock) are deliberately transformed
into forsterite at high temperatures (in excess of 780 ◦ C). During the dunite heat transformation process,
lizardite and brucite transform into forsterite and magnesium oxide, respectively, Equations (4) and (5).
2Mg3 Si2 O5 (OH)4 → 3Mg2 SiO4 + SiO2 + 4H2 O (4)
Mg(OH)2 → MgO + H2 O (5)
We adopted the term “heat-transformed” to clearly distinguish this process from “heat-treatment”
that involves heating minerals to a specific temperature and for a specific duration to produce an
amorphous phase. The maximum forsterite yield was calculated based on decomposition of lizardite
and brucite, which is represented in Equations (6) and (7).
2Mg3 Si2 O5 (OH)4 (s) 3Mg2 SiO4 (s)+SiO2 (s)+4H2 O (g) (6)
Mg(OH)2 (s) MgO (s)+H2 O (g) (7)
2.4. Twin Sister Dunite
This reference material was collected from a quarry located in the Twin Sisters Range, approximately
20 miles east of Bellingham, Washington, DC, USA. This dunite had more than 90% forsterite with
minor chromite and trace amounts of lizardite. It had 29.8 wt/wt% Mg and 18.4 wt/wt% Si.
2.5. Olivine
Two olivine samples were imported from Sibelco (Norway), originating from the Aheim plant.
Crushed olivine was ground in a ball mill (MTI Corporation, CA, USA) for 1 h and sub-20 micron size
fractions were prepared. Twin sister dunite (>90% forsterite) and olivine were considered standard
materials and were used to compare results with the Australian dunite.
2.6. Methods and Experimental Set-Up
2.6.1. Reactivity Test Via Acid Dissolution
An acid dissolution experiment previously developed in our research group [22] was used to
determine Mg extraction from different minerals and rocks. The process involved drying solid sample
at 100 ◦ C for two days to remove absorbed moisture. Once dried, 1 g of the dried sample was added to
200 mL buffered acid solution (1 M acetic acid, 1 M sodium acetate, constant pH = 4.7) and stirred by a
magnetic stirrer (Figure 3). Samples of the supernatant solution were taken using a 1 mL syringe at
different time intervals. Samples were filtered immediately using a 0.22 µL syringe filter, diluted by 2%
nitric acid, and analyzed by ICP-OES.
2.6.2. Carbonic Acid Dissolution
To perform dissolution experiments, the grinding media, distilled water, and mineral (olivine)
were added (2% loading) to a liner, the liner was placed inside the reactor (Parr Instrument Company,
IL, USA), and reactor was assembled. The back pressure regulator (BPR) was set at 3 bar and cooling
water was turned on. The stirrer then commenced at 600 rpm and the reactor was heated to 45 ◦ C.
When the temperature stabilized at 45 ◦ C, the CO2 cylinder was opened, the CO2 pressure regulator
was set at 3 bar, and the reactor inlet valve opened to feed CO2 into the reactor. Dissolution was
performed for 4 h, and the slurry was sampled from the reactor using a sampler (Figure 4). The slurry
was then filtered, and the supernatant was diluted with 2% nitric acid to prevent precipitation of
magnesium carbonate phases.Minerals 2020, 10, 1091 5 of 16
Minerals 2020, 10, x FOR PEER REVIEW 5 of 16
Figure 3. Schematic of the dissolution set-up [22] used to determine relative reactivity of raw, heat-
activated, and heat-transformed dunite.
2.6.2. Carbonic Acid Dissolution
To perform dissolution experiments, the grinding media, distilled water, and mineral (olivine)
were added (2% loading) to a liner, the liner was placed inside the reactor (Parr Instrument Company,
IL, USA), and reactor was assembled. The back pressure regulator (BPR) was set at 3 bar and cooling
water was turned on. The stirrer then commenced at 600 rpm and the reactor was heated to 45 °C.
When the temperature stabilized at 45 °C, the CO2 cylinder was opened, the CO2 pressure regulator
was set at 3 bar, and the reactor inlet valve opened to feed CO2 into the reactor. Dissolution was
performed
Figure for
Figure 3. 4 h, and the
3. Schematic
Schematic slurry
ofofthe was sampled
thedissolution set-up
dissolution from
[22]
set-up the
used
[22] reactor
to
used using
determine a sampler
relative
to determine (Figure
reactivity
relative 4).ofThe
of raw,
reactivity raw,slurry
heat-
was heat-activated,
then filtered,
activated, andheat-transformed
and and the supernatant
heat-transformed was diluted with 2% nitric acid to prevent precipitation of
dunite.
dunite.
magnesium carbonate phases.
2.6.2. Carbonic Acid Dissolution
To perform dissolution experiments, the grinding media, distilled water, and mineral (olivine)
were added (2% loading) to a liner, the liner was placed inside the reactor (Parr Instrument Company,
IL, USA), and reactor was assembled. The back pressure regulator (BPR) was set at 3 bar and cooling
water was turned on. The stirrer then commenced at 600 rpm and the reactor was heated to 45 °C.
When the temperature stabilized at 45 °C, the CO2 cylinder was opened, the CO2 pressure regulator
was set at 3 bar, and the reactor inlet valve opened to feed CO2 into the reactor. Dissolution was
performed for 4 h, and the slurry was sampled from the reactor using a sampler (Figure 4). The slurry
was then filtered, and the supernatant was diluted with 2% nitric acid to prevent precipitation of
magnesium carbonate phases.
Figure4.4. Photo
Figure Photo of
ofthe
thecarbonic
carbonicacid
aciddissolution
dissolutionexperimental
experimental set-up
set-up closed
closed (back
(back pressure
pressureregulator
regulator
(BPR))system,
(BPR)) system,(A):
(A): Carbon
Carbon dioxide
dioxide gasgas cylinder,
cylinder, (B): (B): Sampler
Sampler to sample
to sample slurry,slurry, (C):pressure
(C): Low Low pressure
gauge,
gauge,
(D): (D): vessel,
Reactor Reactor(E):
vessel,
Back (E): Back regulator,
pressure pressure regulator,
(F): Electric(F): Electric
heater heater for
for heating the heating the slurry
slurry during the
during the
reaction, reaction,
(G): (G): Temperature
Temperature andper
and revolution revolution per minute
minute (RPM) (RPM)(H):
controller, controller, (H): Power meter.
Power meter.
2.6.3. Material Characterization
XRD analyses were performed using Philips X’Pert Pro multi-purpose diffractometer with Cu
radiation and the 2 θ used was 10–90◦ . Collection time and step size were 1 s and 0.02◦ , respectively.
Semi-quantitative XRD was performed by addition of silicon reference material inside the original
sample [16]. Inductively coupled plasma-optical emission spectrometry (ICP-OES) (Varian) was used
to determine elemental composition of Mg, Si, and Fe in liquid samples. Olivine feed and concurrent
Figure 4. Photo of the carbonic acid dissolution experimental set-up closed (back pressure regulator
ground products were analyzed using scanning electron microscopy (SEM) (Zeiss Sigma VP FESEM).
(BPR)) system, (A): Carbon dioxide gas cylinder, (B): Sampler to sample slurry, (C): Low pressure
gauge, (D): Reactor vessel, (E): Back pressure regulator, (F): Electric heater for heating the slurry
during the reaction, (G): Temperature and revolution per minute (RPM) controller, (H): Power meter.2.6.3. Material Characterization
XRD analyses were performed using Philips X’Pert Pro multi-purpose diffractometer with Cu
radiation and the 2 θ used was 10–90°. Collection time and step size were 1 s and 0.02°, respectively.
Semi-quantitative XRD was performed by addition of silicon reference material inside the original
sample
Minerals [16].
2020, 10,Inductively
1091 coupled plasma-optical emission spectrometry (ICP-OES) (Varian) was used6 of 16
to determine elemental composition of Mg, Si, and Fe in liquid samples. Olivine feed and concurrent
ground products were analyzed using scanning electron microscopy (SEM) (Zeiss Sigma VP FESEM).
Particle
Particlesize
size analyses
analyses were performedusing
were performed usingMalvern
MalvernMastersizer
Mastersizer 2000.
2000. To identify
To identify and and quantify
quantify the
the different phases present in dunite, samples were heated from 0–1000 ◦ C in TGA, coupled with a
different phases present in dunite, samples were heated from 0–1000 °C in TGA, coupled with a mass
mass spectrometer.
spectrometer. For For
moremore details
details about
about material
material characterization
characterization and
and techniquesused,
techniques used,readers
readersare
are
referred to [14,16].
referred to [14,16].
3.3.Results
Resultsand
andDiscussion
Discussion
3.1. Feedstock Phase Identification and Analysis
3.1. Feedstock Phase Identification and Analysis
X-ray Diffraction (XRD) analysis of the dunite sample indicated that it contained various mineral
X-ray Diffraction (XRD) analysis of the dunite sample indicated that it contained various mineral
phases, i.e., lizardite, olivine, brucite, and magnetite. Semi-quantitative XRD and TGA-MS analyses
phases, i.e., lizardite, olivine, brucite, and magnetite. Semi-quantitative XRD and TGA-MS analyses
revealed
revealedthat
thatthe
thedunite
dunitesample
samplewas
was composed
composed of of 61%–62%
61%–62% lizardite, 30%–33% olivine,
lizardite, 30%–33% olivine, 3.8%–8.3%
3.8%–8.3%
brucite,
brucite,and
anda minor
a minor quantity of magnetite
quantity (0.6%).
of magnetite XRDXRD
(0.6%). analysis of heat-activated
analysis dunite
of heat-activated (Figure
dunite 5) shows
(Figure 5)
that heat activation completely transformed lizardite to more reactive Mg-silicate X-ray
shows that heat activation completely transformed lizardite to more reactive Mg-silicate X-ray amorphous
phases as observed
amorphous phases asandobserved
reportedand
before [24] and
reported dehydroxylated
before brucite to MgO.
[24] and dehydroxylated bruciteThe dominant
to MgO. The
crystalline phases in the heat-activated dunite were olivine and magnetite, which remained
dominant crystalline phases in the heat-activated dunite were olivine and magnetite, which remainedunchanged
after heat activation.
unchanged after heat activation.
Figure5.5.Raw
Figure Rawdunite
dunite(top)
(top)and
andheat-treated
heat-treateddunite (bottom). LL =
dunite(bottom). = Lizardite, B == Brucite,
Brucite,OO ==Olivine,
Olivine,
MM==Magnetite.
Magnetite.
After33hhofofdunite
After duniteheat-transformation,
heat-transformation, aa product
product comprised of 64%64% (semi-quantitative
(semi-quantitativeXRD)
XRD)
forsteritewas
forsterite wasformed,
formed,which
whichwas
waslower
lowerthan
than the
the maximum possible forsterite formation
formation of
of85%
85%based
based
ononreaction
reaction stoichiometry
stoichiometry and and
massmass
balancebalance
shown shown
in Tablein Table longer
1. Much 1. Much
(100 longer (100 h) heat-
h) heat-transformation
istransformation is required
required to achieve to achieve
maximum maximum
forsterite forsterite
formation formation [16,37].
[16,37].Minerals 2020, 10, 1091 7 of 16
Minerals 2020, 10, x FOR PEER REVIEW 7 of 16
Table 1. Mass
Table 1. Mass balance
balance to
to calculate
calculate theoretical
theoretical forsterite.
forsterite.
Input Gram Gram
Input Moles Moles Output
Output Moles
Moles Gram Gram
Forsterite Forsterite
29 29 0.20 0.20 Forsterite
Forsterite 0.33 0.33 46.4 46.4
Lizardite Lizardite
61 61 0.22 0.22 SiO
SiO2 2 0.11 0.11 6.60 6.60
Brucite 8.3 0.14 Water Equation (6) 0.44
Brucite 8.3 0.14 Water Equation (6) 0.44 7.93 7.93
Magnetite 1.3 0.0056 Magnetite 0.0056 1.30
Magnetite 1.3 0.0056 Magnetite 0.0056 1.30
MgO 0.14 5.73
MgO 0.14 5.73
Water Equation (7) 0.14 2.56
Water Equation (7) 0.14 2.56
Forsterite from feed 29
Forsterite from feed 29
Total 100 Total 99.6
Total 100 Total 99.6
Wt % theoretical forsterite formation = (Total Forsterite/(100-water Equation (6)-water Equation
Wt % theoretical forsterite formation = (Total Forsterite/(100-water Equation (6)-water Equation (7) × 100) =
(7)*100) =−(75.4/(99.6-7.93-2.56))
(75.4/(99.6 * 100 = 85%.
7.93 − 2.56)) × 100 = 85%.
XRD
XRD patterns
patterns of
of olivine
olivinecrystals
crystals(Sample
(Sample1)1)and
andcrushed
crushedolivine
olivine(Sample
(Sample2)2)are
areshown
shown inin
Figure 6.
Figure
Olivine crystals
6. Olivine were
crystals wereessentially 100%
essentially pure
100% as determined
pure by semi-quantitative
as determined by semi-quantitativeXRD analysis
XRD andand
analysis the
crushed olivine samples were 94% olivine (based on semi-quantitative XRD analysis).
the crushed olivine samples were 94% olivine (based on semi-quantitative XRD analysis). The The elemental
composition of the crushed
elemental composition olivine
of the sample
crushed wassample
olivine determined by ICP-OES.by
was determined The sample was
ICP-OES. The estimated
sample wasto
comprise
estimated30.7% Mg and30.7%
to comprise 19.1%MgSi, consistent
and 19.1%with the XRF analysis
Si, consistent that
with the XRFshowed Mgthat
analysis andshowed
Si compositions
Mg and
of 29.9% and 19.4%, respectively.
Si compositions of 29.9% and 19.4%, respectively.
Figure 6.6. XRD
Figure XRDpatterns
patterns forfor crushed
crushed olivine
olivine (top)olivine
(top) and and olivine crystals (bottom).
crystals (bottom). O = Olivine,OC = =Olivine, C =
Clinochlore,
Clinochlore,
E = Enstatite,EL==Enstatite,
Lizardite,L T
= Lizardite,
= Talc. ForTcrushed
= Talc. For crushed
olivine, the olivine, the phasesare
phases identified identified are olivine,
olivine, clinochlore,
clinochlore,
enstatite, enstatite,
lizardite, and lizardite, and talc.
talc. For olivine For olivine
crystals, crystals,
the phase the phase
identified identified is olivine.
is olivine.
3.2. Acid Dissolution Experiments
Comparing Mg-leachability
Mg-leachability of of the
the four
four feedstocks
feedstocks chosen
chosen for
for this
this study,
study, i.e.,
i.e., sub-75
sub-75 µm raw,
µm raw,
heat-activated (630 ◦°C, C, 4 h), heat-transformed (800 ◦°C, C, 3 h) (64% forsterite), and twin sister dunite
(more than
than 90%
90% forsterite),
forsterite), provided
provided insight
insight into
into the
the reactivity
reactivity of
of each
each material.
material. Further dissolution
experiments ◦ C, 4 h) to
experiments werewereperformed
performedusingusingdifferent
differentsize
sizefractions
fractionsofof
heat-transformed
heat-transformed dunite
dunite(800
(800 °C, 4 h)
study the the
to study effect of particle
effect size distribution
of particle on reactivity
size distribution and in particular
on reactivity Mg-leachability.
and in particular The fraction
Mg-leachability. of
The
magnesium, silicon, and iron
fraction of magnesium, extracted
silicon, overextracted
and iron a 7 h dissolution
over a 7period is shownperiod
h dissolution in Figures 7–9, respectively.
is shown in Figures
Sub-75 µm fractions of raw, heat-transformed ◦ C, 3 h), heat-activated (630 ◦ C, 4 h), and twin sister
7–9, respectively. Sub-75 µm fractions of raw,(800heat-transformed (800 °C, 3 h), heat-activated (630 °C,
dunite
4 h), andhad similar
twin sisterparticle
dunitesize
haddistribution (PSD),
similar particle sizeasdistribution
shown in Figure
(PSD),10.as shown in Figure 10.Minerals 2020, 10, x FOR PEER REVIEW 8 of 16
Minerals
Minerals 2020,
2020, 10, 10,
1091x FOR PEER REVIEW 8 of 16 8 of 16
-75 um Heat-activated dunite (630 °C, 4 h) -20 um Heat-transformed dunite (800 °C, 4 h)
-75
-75um
umHeat-activated dunite
Heat-transformed (630(800
dunite °C, 4°C,
h) 3 h) -20 um Heat-transformed dunite (800 °C, 4 h)
-75 um Heat-transformed dunite (800 °C, 4 h)
-75
-75 um
umHeat-transformed
Raw dunite dunite (800 °C, 3 h) -75 um Heat-transformed dunite (800 °C, 4 h)
20-45 um Heat-transformed dunite (800 °C, 4 h)
-75
-75um
umRaw
Twindunite
sister dunite 20-45 um Heat-transformed dunite (800 °C, 4 h)
0.7-75 um Twin sister dunite 0.5
Mg Extracted
Mg Extracted
0.6
0.7 0.5
0.4
of Extracted
of Extracted
0.5
0.6
0.4 0.4
0.3
0.5
0.3
0.4 0.3
0.2
of Mg
of Mg
0.2
0.3
Fraction
0.2
Fraction
0.1 0.1
0.2
Fraction
Fraction
0.10 0.10
0 0 2 4 6 8
0 0 2 4 6 8
Time (h) Time (h)
0 2 4 6 8 0 2 4 6 8
Time (h) Time (h)
Figure 7. The extent of Mg extracted from sub-75 µm fractions of raw dunite, heat-activated dunite
Figure
Figure The
(6307.°C, extent
7. 4The
h), extentofofMg
Mgextracted
heat-transformed from
dunite
extracted sub-75
(800
from µmand
°C, 3 µm
sub-75 h), fractions
twin of
fractions of raw
sister
raw dunite,
dunite
dunite, heat-activated
(left). dunite
The extentdunite
heat-activated of Mg
◦ C, 4 h),from
extracted
(630(630 different size fractions of ◦ C, 3 h), and twin
heat-transformed dunite (800 °C, 4 h) (right).
°C, 4 h), heat-transformed dunite (800 °C, 3 h), and twin sister dunite (left). The extent of Mgof Mg
heat-transformed dunite (800 sister dunite (left). The extent
extracted from different size ◦
extracted from different sizefractions
fractionsof
of heat-transformed dunite
heat-transformed dunite (800
(800 °C, C,
4 h)4 (right).
h) (right).
-75 um Heat-activated dunite (630 °C, 4 h) -20 um Heat-transformed dunite (800 °C, 4 h)
-75 um Heat-activated dunite (630 °C, 4 h) -20 um Heat-transformed dunite (800 °C, 4 h)
-75 um Heat-transformed dunite (800 °C, 3
-75 um Heat-transformed dunite (800 °C, 4 h)
h)
-75 um Heat-transformed dunite (800 °C, 3
-75 um Twin sister dunite -75 um Heat-transformed dunite (800 °C, 4 h)
h)
20-45 um Heat-transformed dunite (800 °C, 4 h)
-75 um Twin sister dunite
-75 um Raw dunite 20-45 um Heat-transformed dunite (800 °C, 4 h)
-75 um Raw dunite
0.4 0.3
Si Extracted
Si Extracted
0.4 0.3
0.25
0.3
ofExtracted
ofExtracted
0.25
0.2
0.3
0.2 0.2
0.15
0.2 0.15
0.1
of Si
of Si
0.1
Fraction
Fraction
0.1 0.1
0.05
Fraction
Fraction
0 0.050
0 0 2 4 6 8 0 0 2 4 6 8
0 2 4
Time (h) 6
4 (h) 6
Time 8 8 0 2
Time (h) Time (h)
Figure 8. Fraction of silicon extracted from sub-75 µm fractions of raw dunite, heat-activated dunite
(630 ◦ C, 4 h), heat-transformed dunite (800 ◦ C, 3 h), and twin sister dunite (left). Fraction of magnesium
Figurefrom
extracted 8. Fraction
sub-75ofµm
silicon extracted
fraction, fromµm
sub-20 sub-75 µm fractions
fraction, of raw
and 20–45 µm dunite, heat-activated
fraction dunite
of heat-transformed
(630 °C,
Figure 4 h), heat-transformed
8.◦Fraction dunite
of silicon extracted from(800 °C,µm
sub-75 3 fractions
h), and twin
of rawsister dunite
dunite, (left). Fraction
heat-activated duniteof
dunite (800 C, 4 h) (right).
magnesium
(630 extracted
°C, 4 h), from sub-75
heat-transformed µm fraction,
dunite (800 °C,sub-20
3 h), µm
andfraction, and dunite
twin sister 20–45 µm fraction
(left). of heat-
Fraction of
transformedextracted
magnesium dunite (800
from°C,sub-75
4 h) (right).
µm fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-
transformed dunite (800 °C, 4 h) (right).Minerals 2020, 10, x FOR PEER REVIEW 9 of 16
-75 um Heat-activated dunite (630 °C, 4 h)
-20 um Heat-transformed dunite (800 °C, 4 h)
Minerals -75
2020,
Minerals 2020, um
10,
10, x Raw
1091 dunite
FOR PEER REVIEW
9 of 16
-75 um Heat-transformed dunite (800 °C, 49h)
of 16
-75 um Twin sister dunite
20-45 um Heat-transformed dunite (800 °C, 4 h)
-75
-75um
umHeat-activated dunite
Heat-transformed (630(800
dunite °C, °C,
4 h)3
-20 um Heat-transformed dunite (800 °C, 4 h)
h)
-75 um Raw dunite
of Fe Extracted
0.3 0.18
-75 um Heat-transformed dunite (800 °C, 4 h)
of Fe Extracted
-75 um Twin sister dunite 0.16
0.25 0.14
20-45 um Heat-transformed dunite (800 °C, 4 h)
0.2
-75 um Heat-transformed dunite (800 °C, 3 0.12
h) 0.1
0.15
Extracted
0.3 0.18
0.08
Extracted
0.1 0.16
0.06
Fraction
0.25 0.14
0.04
Fraction
0.05
0.2 0.12
0.02
Fraction of Fe
0.10
0.150
Fraction of Fe
0 2 4 6 8 0.08 0 2 4 6 8
0.1 0.06
Time (h) 0.04 Time (h)
0.05 0.02
0 0
0 2 4 6 8 0 2 4 6 8
Time (h) Time (h)
Figure 9. Fraction of iron extracted from sub-75 µm fractions of raw dunite, heat-activated dunite (630
°C, 4 h),
Figure heat-transformed
9. Fraction dunite (800from
of iron extracted °C, 3sub-75
h), andµmtwin sister dunite
fractions (left).
of raw Fraction
dunite, of magnesium
heat-activated dunite
extracted
◦ from sub-75 µm fraction, sub-20 ◦µm fraction, and 20–45 µm fraction of heat-transformed
(630 C, 4 h), heat-transformed dunite (800 C, 3 h), and twin sister dunite (left). Fraction of magnesium
dunite (800
extracted from°C,sub-75
4 h) (right).
µm fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-transformed
Figure(800
dunite ◦ C, 4 h)
9. Fraction of(right).
iron extracted from sub-75 µm fractions of raw dunite, heat-activated dunite (630
°C, 4 h), heat-transformed dunite (800 °C, 3 h), and twin sister dunite (left). Fraction of magnesium
-75 um
extracted Rawsub-75
from duniteµm fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-transformed
-20 heat-transformed dunite (800 °C, 4 h)
dunite (800 °C, 4 h) (right).
-75 um Heat-activated dunite (630 °C, 4 h)
20-45 um heat-transformed dunite (800 °C, 4 h)
-75 um Heat-transformed dunite (800 °C, 3
h) um Raw dunite
-75
-75 um Twin Sister dunite -75heat-transformed
-20 um heat-transformed dunite
dunite (800(800
°C, 4°C,
h) 4 h)
-75 um Heat-activated dunite (630 °C, 4 h)
18 20-45 um heat-transformed dunite (800 °C, 4 h)
6
-75 um Heat-transformed dunite (800 °C, 3
h) 16
5
(%) density (%)
(%) density (%)
14 -75 um heat-transformed dunite (800 °C, 4 h)
-75 um Twin Sister dunite
4 12
6 10
18
3
168
5
Volume
Volume
2 146
4 124
Volume density
Volume density
1
102
3
0 80
2 0.1 1 10 100 1000 6 0.1 1 10 100 1000
Size classes (µm) 4 Size Classes (µm)
1
2
Figure 10. Particle size distribution (PSD) for sub-75 µm fractions of raw dunite, heat-activated dunite
0 0
(630 ◦ C, 4 h), heat-transformed dunite (800 ◦ C, 3 h), and twin sister dunite (left), PSD for sub-75 µm
Figure0.1 1 size distribution
10. Particle 10 100
(PSD) for1000 0.1
sub-75 µm fractions 1 dunite,
of raw 10heat-activated
100
◦
1000
dunite
fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-transformed dunite (800 C, 4 h) (right).
Size classes (µm)
(630 °C, 4 h), heat-transformed Size Classes
dunite (800 °C, 3 h), and twin sister dunite (µm)
(left), PSD for sub-75 µm
fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-transformed dunite (800 °C, 4 h) (right).
The fraction of magnesium extracted from heat-activated dunite was higher than that from other
materials, 57% as compared to 18% from heat-transformed dunite, 14% from raw dunite, and 11% from
Figure 10. Particle size distribution (PSD) for sub-75 µm fractions of raw dunite, heat-activated dunite
twin sister dunite (Figure 7). Acid-dissolution results indicated higher Mg leachability in materials rich in
(630 °C, 4 h), heat-transformed dunite (800 °C, 3 h), and twin sister dunite (left), PSD for sub-75 µm
amorphous magnesium silicates (e.g., heat-activated dunite) compared to that of forsterite-rich materials
fraction, sub-20 µm fraction, and 20–45 µm fraction of heat-transformed dunite (800 °C, 4 h) (right).
(e.g., heat-transformed dunite), raw dunite or twin sister dunite (> 90% forsterite). Mg extraction results
were consistent with the trends in magnesite yield reported for the carbonation experiments using these
same materials [4]. Farhang et.al. [22] has previously obtained 60% Mg extraction during 1 h dissolution
using an optimized −75 µm heat-activated lizardite compared to 48% Mg extraction achieved in thisMinerals 2020, 10, 1091 10 of 16
work using −75 µm heat-activated dunite. This finding indicates that in addition to serpentine, if dunite
is properly heat activated, it can be used as an abundant feedstock for mineral carbonation.
Heat-transformed dunite showed a slightly elevated level of Mg extraction as compared to that of
raw and twin sister dunite because it contained an approximately 32% amorphous magnesium silicate
(Table 1, mass balance and quantitative XRD) phase. Mg extraction was slightly higher for raw dunite
as compared to that of twin sister dunite because of the 8% brucite present in it. The sub-20 micron
fraction of heat-transformed dunite (800 ◦ C, 4 h) resulted in Mg extraction levels of 43% as compared
to 34% from the sub-75 micron fraction and 20% from the 20–45 micron fraction (Figure 7). The reason
for the higher Mg extraction is the higher quantity of fine particles in the sub-20 micron fraction as
compared to that in the sub-75 micron and 20–45 micron fractions (Figure 10). This indicates that
higher Mg extractions can be achieved by reducing the particle size of the feedstock.
Similar to Mg extraction, the fraction of silicon extracted from heat-activated dunite was higher
than that of the other samples, 33% from heat-activated dunite compared to 13% from heat-transformed
dunite, 9% from twin sister, and 3% from raw dunite (Figure 8 left). This again highlights that materials
rich with amorphous magnesium silicates (e.g., heat-activated dunite) are more reactive (soluble)
than forsterite-rich materials such as heat-transformed dunite, twin sister dunite, and raw dunite.
Si extraction was significant here compared to 90% forsterite). This preferential release of Mg continued
(but at a reduced rate after the initial 30 min) for 2 h, after which time the dissolution was close to
stoichiometric. The incongruent dissolution of Mg from dunite (Figure 11b) is thought to be due to
the presence of 30% forsterite and high levels of Mg dissolution is due to the presence of 8% brucite
(which lacks silicon in its structure). Heat-transformed dunite (64% forsterite) also showed preferential
release of Mg, as did forsterite, but this trend quickly stabilized and trended towards stoichiometric
dissolution (Figure 11c–f). This preferential Mg release was higher for sub-20 µm heat-transformed
dunite, especially at the initial stages of dissolution and is attributed to the high fraction of smaller
particle size material. Materials rich in forsterite (twin sister dunite and heat-transformed dunite) show
preferential Mg release and exhibit incongruent dissolution similar to that of forsterite (Figure 11a–f).
Heat-activated dunite (amorphous magnesium silicate rich) on the other hand behaves differently and
shows congruent dissolution (Figure 11g). This trend of heat-activated dunite has been also observed
by others but for heat-activated lizardite [40].size material. Materials rich in forsterite (twin sister dunite and heat-transformed dunite) show
preferential Mg release and exhibit incongruent dissolution similar to that of forsterite (Figure 11a–
f). Heat-activated dunite (amorphous magnesium silicate rich) on the other hand behaves differently
and shows congruent dissolution (Figure 11g). This trend of heat-activated dunite has been also
observed by10,others
Minerals 2020, 1091 but for heat-activated lizardite [40]. 11 of 16
(a) (b)
14
4 12
10
Mg /Si
3 8
Mg /Si
6
2 4 -75 um Raw dunite
-75 um Twin sister dunite (90+ 2
1
forsterite) 0
0 0 2 4 6 8
0 2 4 6 8 Time (h)
Time (h)
(c) (d)
3 3
2.5 2.5
2 2
Mg /Si
Mg /Si
1.5 -75 um Heat-transformed 1.5 -75 um Heat-transformed
1 dunite (800 °C, 3 h) 1 dunite (800 °C, 4 h)
0.5 0.5
0 0
0 2 4 6 8 0 2 4 6 8
Time (h) Time (h)
(e) (f)
5 10
4 8 -20 um Heat-
transformed dunite
3 6
Mg /Si
Mg /Si
20-45 um Heat- (800 °C, 4 h)
2 transformed dunite 4
1 (800 °C, 4 h) 2
0 0
Minerals 2020, 10, x FOR PEER REVIEW 12 of 16
0 2 4 6 8 0 2 4 6 8
Time (h) Time (h)
3
2.5
2
Mg /Si
1.5 Heat-activated dunite
1
Heat-activated lizardite
0.5
0
0 2 4 6 8
Time (h)
(g)
Figure11.
Figure 11.The
TheMg/Si
Mg/Siratio
ratiofor
fordifferent
differentmaterials:
materials:(a)(a)sub-75
sub-75µmµmtwintwinsister
sisterdunite
dunite(more
(morethan
than90%
90%
forsterite) taken as reference; (b) sub-75 µm raw dunite; (c) sub-75 µm heat-transformed
forsterite) taken as reference; (b) sub-75 µm raw dunite; (c) sub-75 µm heat-transformed dunite (800 C, dunite
◦
3 (800 °C,sub-75
h); (d) 3 h); µm
(d) heat-transformed
sub-75 µm heat-transformed dunite
dunite (800 ◦ C, (800
4 h); (e) °C, 4µm
20–45 h);heat-transformed
(e) 20–45 µm heat-transformed
dunite (800 ◦ C,
4 dunite (800 °C,µm
h); (f) sub-20 4 h); (f) sub-20 µm heat-transformed
heat-transformed dunite (800 ◦ C, 4 dunite
h); and(800 °C, 4 h);
(g) sub-75 µmand (g) sub-75 µm
heat-activated heat-
dunite
activated
◦
(630 C, 4 h). dunite (630 °C, 4 h).
3.4. Carbonic Acid Dissolution of Raw Olivine
Sub-20 micron olivine was treated by carbonic acid solution (3 bar CO2, 45 °C, 2 wt % solid) with
the aid of concurrent grinding (1 mm zirconia, 60 wt %) to enhance Mg extraction from this feedstock.
Mg extraction of 16% was achieved in 4 h dissolution (Figure 12 left). The trend of Mg extraction
shows that it continuously increased over time. Therefore, a much longer dissolution period is
required for higher Mg extractions. PSD analysis (Figure 12, Table 2) showed that olivine wasFigure 11. The Mg/Si ratio for different materials: (a) sub-75 µm twin sister dunite (more than 90%
forsterite) taken as reference; (b) sub-75 µm raw dunite; (c) sub-75 µm heat-transformed dunite
(800 °C, 3 h); (d) sub-75 µm heat-transformed dunite (800 °C, 4 h); (e) 20–45 µm heat-transformed
dunite (800 °C, 4 h); (f) sub-20 µm heat-transformed dunite (800 °C, 4 h); and (g) sub-75 µm heat-
Minerals 2020, 10, 1091 12 of 16
activated dunite (630 °C, 4 h).
3.4.
3.4.Carbonic
CarbonicAcid
AcidDissolution
DissolutionofofRaw
RawOlivine
Olivine
Sub-20
Sub-20micron
micron olivine
olivine was
was treated
treated by
by carbonic
carbonic acid
acid solution
solution (3 (3 bar
bar CO
CO22,, 45
45 °C,
◦ C,22wtwt%%solid)
solid)with
with
the
the aid of concurrent grinding (1 mm zirconia, 60 wt %) to enhance Mg extraction from thisfeedstock.
aid of concurrent grinding (1 mm zirconia, 60 wt %) to enhance Mg extraction from this feedstock.
Mg
Mg extraction
extraction of of 16%
16%waswasachieved
achieved inin
4 h4dissolution
h dissolution (Figure
(Figure 12 left).
12 left). The trend
The trend of Mgofextraction
Mg extraction
shows
shows that it continuously increased over time. Therefore, a much longer
that it continuously increased over time. Therefore, a much longer dissolution period is required dissolution period for
is
required for higher Mg extractions. PSD analysis (Figure 12, Table 2) showed
higher Mg extractions. PSD analysis (Figure 12, Table 2) showed that olivine was converted into very that olivine was
converted into(dvery fine powder (d10 = 0.08 µm (80 nanometres), d50 = 0.32 µm) using concurrent
fine powder 10 = 0.08 µm (80 nanometres), d50 = 0.32 µm) using concurrent grinding. Very fine
grinding. Very fine
concurrent ground product concurrent ground
(Figure 13b)product (Figurein13b)
was identified SEMwas identified
analysis in SEM to
as compared analysis as
relatively
compared
large feed to relatively
particles large13a).
(Figure feed Formation
particles (Figure
of nano 13a). Formation
particles of nano
of olivine wasparticles of olivine
also identified was
by SEM
also identified by SEM analysis of concurrent ground product (Figure 13c).
analysis of concurrent ground product (Figure 13c). Even though olivine was converted into nanoEven though olivine was
converted into nano particles, the extent of dissolution was still very low, indicating
particles, the extent of dissolution was still very low, indicating the low reactivity of olivine under the low reactivity
of olivine
these under these
conditions. conditions.
Formation, Formation,
presence, presence,
and growth and growth
of secondary of secondary
phases on olivine phases onsurfaces
particle olivine
particle surfaces reduce olivine
reduce olivine dissolution [41]. dissolution [41].
Sub 20 micron olivine Sub 20 micron olivine feed
Concurrent ground product
0.2 8
0.18
Fraction of Mg Extracted
7
Volume density (%)
0.16
6
0.14
5
0.12
0.1 4
0.08 3
0.06 2
0.04 1
0.02 0
0 0.01 1 100
0 1 2 3 4 5 Size classes (μm)
Time (h)
Figure 12. Mg extraction for sub-20 micron olivine (left), PSD analysis for sub-20 micron olivine feed
and concurrent ground product (right).
Table
Figure 12. 2. PSD analysis
Mg extraction for sub-20
for sub-20 micron
micron olivine
olivine (left),feed
PSDand concurrent
analysis ground
for sub-20 product.
micron olivine feed
and concurrent ground product (right).
d10 d50 d90
Feed and Concurrent Ground Product
µm µm µm
Sub-20 micron olivine feed 3.04 13 31
Sub-20 micron olivine concurrent ground 0.08 0.32 5.1Table 2. PSD analysis for sub-20 micron olivine feed and concurrent ground product.
d10 d50 d90
Feed and concurrent ground product
µm µm µm
Sub-20 micron olivine feed 3.04 13 31
Minerals 2020, 10, 1091 Sub-20 micron olivine concurrent ground 0.08 0.32 5.1 13 of 16
(a)
(b)
(c)
Figure 13.
13. SEM
SEMmicrograph
micrograph for for
sub-20 micron
sub-20 olivine
micron feed and
olivine feedconcurrent ground ground
and concurrent products: (a) sub-
products:
20 sub-20
(a) micronmicron
olivineolivine
feed, feed,
(b) concurrent ground
(b) concurrent groundproduct, and
product, and(c)(c)concurrent
concurrent ground
ground product
nanometer-sized particles.
4. Conclusions
4. Conclusions
Heat-activated
Heat-activated dunite
dunite can
can be
be used
used asas a feedstock for
a feedstock for mineral
mineral carbonation.
carbonation. Heat-activated
Heat-activated dunite
dunite
showed
showed higher
higher Mg, Si, and
Mg, Si, and Fe
Fe extractions
extractions compared
compared toto that
that of
of heat-transformed
heat-transformed dunite,
dunite, raw
raw dunite,
dunite,
and twin sister dunite. These results are in agreement with magnesite yield results obtained for
and twin sister dunite. These results are in agreement with magnesite yield results obtained for these these
materials [4]. This study showed that carbonation extent and Mg extractions have a direct relationship.
Elevated Fe extraction from twin sister dunite compared to heat-transformed dunite was due to the presence
of a small amount of chromite (FeCr2 O4 ) in this mineral. When different fractions of heat-transformed
dunite were dissolved, the sub-20 micron fraction showed higher Mg, Si, and Fe extractions followed by
the sub-75 micron and 20–45 micron fractions. Heat-activated dunite showed congruent dissolution whileMinerals 2020, 10, 1091 14 of 16
forsterite rich materials showed incongruent dissolution. Forsterite/olivine does not dissolve properly
under acidic and carbonic acid dissolution (with concurrent grinding) conditions. Only 16% Mg extraction
was achieved from olivine during 4 h of dissolution. Further research is required to investigate different
acid dissolution approaches, medias, media mixtures, and reactor configurations to increase Mg extraction
from olivine. Different buffer solutions and or acid solutions need to be investigated to increase Mg
extraction from peridotites. Outstanding research questions include the following: Why does sub-75 µm
twin sister dunite show a higher Si extraction compared to that of sub-75 µm raw dunite? Why does raw
dunite show a higher Fe extraction compared to that of twin sister dunite and heat-transformed dunite?
Author Contributions: Conceptualization, M.I.R.; Data curation, M.I.R.; Formal analysis, M.I.R.; Roles/Writing-original
draft, M.I.R.; Investigation, E.B. and F.F.; Methodology, E.B. and F.F.; Writing-review and editing, E.B., F.F., M.S., and
E.M.K.; Validation, E.B. and F.F.; Visualization, E.B. and F.F.; Funding acquisition, M.S. and E.M.K.; Project administration,
M.S. and E.M.K.; Supervision, M.S. and E.M.K. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by Mineral Carbonation international.
Acknowledgments: M.I.R. thanks the University of Newcastle, Australia for a postgraduate scholarship.
Jennifer Zobec and Yun Lin from EMX unit are acknowledged for support in XRD and SEM, respectively.
Kitty Tang is acknowledged for support in particle size analysis.
Conflicts of Interest: The authors declare no conflict of interest.
References
1. Global Monitoring Laboratory, Trends in Carbon Dioxide. Available online: https://www.esrl.noaa.gov/gmd/
ccgg/trends/ (accessed on 1 November 2020).
2. Varney, R.M.; Chadburn, S.E.; Friedlingstein, P.; Burke, E.J.; Koven, C.D.; Hugelius, G.; Cox, P.M. A spatial
emergent constraint on the sensitivity of soil carbon turnover to global warming. Nat. Commun. 2020,
11, 5544. [CrossRef]
3. Rashid, M.I.; Benhelal, E.; Rafiq, S. Reduction of Greenhouse Gas Emissions from Gas, Oil, and Coal Power
Plants in Pakistan by Carbon Capture and Storage (CCS): A Review. Chem. Eng. Technol. 2020, 43, 2140–2148.
[CrossRef]
4. Rashid, M.I.; Benhelal, E.; Farhang, F.; Oliver, T.K.; Rayson, M.S.; Brent, G.F.; Stockenhuber, M.; Kennedy, E.M.
ACEME: Direct Aqueous Mineral Carbonation of Dunite Rock. Environ. Prog. Sustain. Energy 2019, 38, e13075.
[CrossRef]
5. Lackner, K.S. A Guide to CO2 Sequestration. Science 2003, 300, 1677–1678. [CrossRef] [PubMed]
6. Rashid, M.I.; Benhelal, E.; Farhang, F.; Oliver, T.K.; Rayson, M.S.; Brent, G.F.; Stockenhuber, M.; Kennedy, E.M.
Development of Concurrent grinding for application in aqueous mineral carbonation. J. Clean. Prod. 2019,
212, 151–161. [CrossRef]
7. Farhang, F.; Oliver, T.K.; Rayson, M.; Brent, G.; Stockenhuber, M.; Kennedy, E. Experimental study on the
precipitation of magnesite from thermally activated serpentine for CO2 sequestration. Chem. Eng. J. 2016,
303, 439–449. [CrossRef]
8. Benhelal, E.; Rashid, M.I.; Holt, C.; Rayson, M.S.; Brent, G.; Hook, J.M.; Stockenhuber, M.; Kennedy, E.M.
The utilisation of feed and byproducts of mineral carbonation processes as pozzolanic cement replacements.
J. Clean. Prod. 2018, 186, 499–513. [CrossRef]
9. Benhelal, E.; Oliver, T.K.; Farhang, F.; Hook, J.M.; Rayson, M.S.; Brent, G.F.; Stockenhuber, M.; Kennedy, E.M.
Structure of Silica Polymers and Reaction Mechanism for Formation of Silica-Rich Precipitated Phases in
Direct Aqueous Carbon Mineralization. Ind. Eng. Chem. Res. 2020, 59, 6828–6839. [CrossRef]
10. Rim, G.; Wang, D.; Rayson, M.; Brent, G.; Park, A.-H.A. Investigation on Abrasion versus Fragmentation of
the Si-rich Passivation Layer for Enhanced Carbon Mineralization via CO2 Partial Pressure Swing. Ind. Eng.
Chem. Res. 2020. [CrossRef]
11. Benhelal, E.; Rashid, M.I.; Rayson, M.S.; Prigge, J.-D.; Molloy, S.; Brent, G.F.; Cote, A.; Stockenhuber, M.;
Kennedy, E.M. Study on mineral carbonation of heat activated lizardite at pilot and laboratory scale.
J. CO2 Util. 2018, 26, 230–238. [CrossRef]Minerals 2020, 10, 1091 15 of 16
12. Benhelal, E.; Rashid, M.I.; Rayson, M.S.; Brent, G.F.; Oliver, T.; Stockenhuber, M.; Kennedy, E.M. Direct aqueous
carbonation of heat activated serpentine: Discovery of undesirable side reactions reducing process efficiency.
Appl. Energy 2019, 242, 1369–1382. [CrossRef]
13. Werner, M.; Hariharan, S.; Mazzotti, M. Flue gas CO2 mineralization using thermally activated serpentine:
From single- to double-step carbonation. Phys. Chem. Chem. Phys. 2014. [CrossRef] [PubMed]
14. Benhelal, E. Synthesis and Application of Mineral Carbonation By-Products as Portland Cement Substitues.
Ph.D. Thesis, University of Newcastle, Newcastle, Australia, 2018.
15. Benhelal, E.; Rashid, M.I.; Rayson, M.S.; Oliver, T.K.; Brent, G.; Stockenhuber, M.; Kennedy, E.M. “ACEME”:
Synthesis and characterization of reactive silica residues from two stage mineral carbonation Process.
Environ. Prog. Sustain. Energy 2019, 38, e13066. [CrossRef]
16. Rashid, M.I. Mineral Carbonation of CO2 Using Alternative Feedstocks. Ph.D. Thesis, The University of
Newcastle, Newcastle, Australia, 2019.
17. Oliver, T.K.; Farhang, F.; Hodgins, T.W.; Rayson, M.S.; Brent, G.F.; Molloy, T.S.; Stockenhuber, M.;
Kennedy, E.M. CO2 Capture Modeling Using Heat-Activated Serpentinite Slurries. Energy Fuels 2019,
33, 1753–1766. [CrossRef]
18. Mouedhen, I.; Kemache, N.; Pasquier, L.-C.; Cecchi, E.; Blais, J.-F.; Mercier, G. Effect of pCO2 on direct flue
gas mineral carbonation at pilot scale. J. Environ. Manag. 2017, 198, 1–8. [CrossRef] [PubMed]
19. Rashid, M.I.; Benhelal, E.; Farhang, F.; Oliver, T.K.; Stockenhuber, M.; Kennedy, E.M. Application of a
concurrent grinding technique for two-stage aqueous mineral carbonation. J. CO2 Util. 2020, 42, 101347.
[CrossRef]
20. Hänchen, M.; Prigiobbe, V.; Storti, G.; Mazzotti, M. Mineral carbonation: Kinetic study of olivine dissolution
and carbonate precipitation. Proceedings of 8th International Conference On Greenhouse Gas Technology,
Trondium, Norway, 19–22 June 2006.
21. Werner, M.; Hariharan, S.; Zingaretti, D.; Baciocchi, R.; Mazzotti, M. Dissolution of dehydroxylated lizardite
at flue gas conditions: I. Experimental study. Chem. Eng. J. 2014, 241, 301–313. [CrossRef]
22. 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]
23. Hariharan, S.; Mazzotti, M. Kinetics of flue gas CO2 mineralization processes using partially dehydroxylated
lizardite. Chem. Eng. J. 2017, 324, 397–413. [CrossRef]
24. Benhelal, E.; Hook, J.M.; Rashid, M.I.; Zhao, G.; Oliver, T.K.; Rayson, M.S.; Brent, G.F.; Stockenhuber, M.;
Kennedy, E.M. Insights into chemical stability of Mg-silicates and silica in aqueous systems using 25Mg and
29Si solid-state MAS NMR spectroscopy: Applications for CO2 capture and utilisation. Chem. Eng. J. 2020.
[CrossRef]
25. Park, A.-H.A.; Jadhav, R.; Fan, L.-S. CO2 mineral sequestration: Chemically enhanced aqueous carbonation
of serpentine. Can. J. Chem. Eng. 2003, 81, 885–890. [CrossRef]
26. Park, A.-H.A.; Fan, L.-S. CO2 mineral sequestration: Physically activated dissolution of serpentine and pH
swing process. Chem. Eng. Sci 2004, 59, 5241–5247. [CrossRef]
27. 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]
28. Teir, S.; Kuusik, R.; Fogelholm, C.-J.; Zevenhoven, R. Production of magnesium carbonates from serpentinite
for long-term storage of CO2 . Int. J. Miner. Process. 2007, 85, 1–15. [CrossRef]
29. Teir, S.; Revitzer, H.; Eloneva, S.; Fogelholm, C.J.; Zevenhoven, R. Dissolution of natural serpentinite in
mineral and organic acids. Int. J. Miner. Process. 2007, 83, 36–46. [CrossRef]
30. Farhang, F.; Oliver, T.K.; Rayson, M.S.; Brent, G.F.; Molloy, T.S.; Stockenhuber, M.; Kennedy, E.M. Dissolution
of heat activated serpentine for CO2 sequestration: The effect of silica precipitation at different temperature
and pH values. J. CO2 Util. 2019, 30, 123–129. [CrossRef]
31. Li, J.; Hitch, M. Mechanical activation of magnesium silicates for mineral carbonation, a review. Miner. Eng.
2018, 128, 69–83. [CrossRef]
32. Styles, M.T.; Sanna, A.; Lacinska, A.M.; Naden, J.; Maroto-Valer, M. The variation in composition of ultramafic
rocks and the effect on their suitability for carbon dioxide sequestration by mineralization following acid
leaching. Greenh. Gases Sci. Technol. 2014, 4, 440–451. [CrossRef]You can also read
