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Journal of CO2 Utilization 67 (2023) 102292
Available online 11 November 2022
2212-9820/© 2022 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Review article
A review on CO
2
capture and sequestration in the construction industry:
Emerging approaches and commercialised technologies
Mohd Hanifa
a
,
b
, R. Agarwal
a
, U. Sharma
a
, P.C. Thapliyal
a
, L.P. Singh
a
,
*
a
CSIR- Central Building Research Institute, Roorkee 247667, India
b
Academy of Scientic and Innovative Research (AcSIR), Ghaziabad 201002, India
ARTICLE INFO
Keywords:
CO
2
capture
Mineral carbonation
CO
2
utilization
Commercialized technologies
ABSTRACT
Reducing CO
2
emissions from the construction industry is the most imperative factor in the ght against climate
change, which aims to reduce the average atmosphere temperature below 1.5 ◦C by the end of this century.
Globally, the cement industry is responsible for approximately ~7 % of CO
2
emissions. About 9.95 Gt/y of CO
2
was emitted by the construction sector as of 2019, making it the highest contributor. The construction sector is
forecast to reduce its CO
2
emissions by 16 % by 2030, leading to net-zero emissions by 2050. Thus, several
measures have been implemented to mitigate signicant CO
2
emissions from the construction industry by
capturing and utilizing CO
2
. This paper reviews existing industrial-level CO
2
capture technologies in cement
industries, such as amine scrubbing, oxy-combustion, direct capture, and calcium looping, as well as the costs
and barriers associated with their use. Also presented a summary and comparison of utilizing CO
2
through
accelerated mineral carbonation in cement-based materials, recycled aggregate, and calcium-rich solid waste. In
addition to this, various commercialized technologies for mitigating CO
2
emissions (Carbon8, Calera Corpora-
tion, CarbonCure, Solidia, Blue Planet and Carbstone) and their methods of sequestering CO
2
as well as their
technology readiness levels (TRL), %CO
2
uptake, and patent analysis for their technologies were discussed.
1. Introduction
Over the years, change in climate conditions has been one of the most
signicant concerns, as it affects the economic, social and environmental
aspects of our lives. The increase in greenhouse gases (GHGs) in the
atmosphere results from several human activities, contributing to a
signicant rise in the earth’s temperature and thus threatening life on
the planet [1,2]. Among various GHGs, viz., CO
2
, CH
4
, N
2
O, etc., the
major inuencing gas is CO
2,
which is considered the major cause of
global warming. Absorption of Infrared radiation by CO
2
gas causes its
deformation and stretching-vibration force resulting in a warming effect
[3]. Anthropogenic activities have contributed to global warming of
1.0 ◦C over pre-industrial levels. By 2030, it is likely to reach 1.5 ◦C if
current CO
2
emissions levels continue [4].
Climate change was addressed at the United Nations Conference on
Environment and Development (UNCED) in Rio de Janeiro, Brazil, in
1992 [5]. Under the United Nations Climate Change Secretariat (UNCCS
2009), increased CO
2
levels result in changes in climate indicators such
as rainfall, heat, rise in temperatures and acidication of oceans [6]. The
Paris Agreement in 2016 marked the historical transformation of global
climate change, as the world leaders from 195 nations agreed to combat
climate change and its harmful effects [7]. According to the Paris
Agreement, global warming should be reduced to 2 ◦C below
pre-industrial levels by the end of the century [4]. During the Paris
Agreement, India committed to reducing CO
2
emissions by 30–35 % by
2030 and creating a carbon sink of 2.5–3 billion tons of CO
2
equivalent
by 2030 through additional forest cover [8,9]. At the Katowice Climate
Summit (COP-24), one of the milestones in completing the Paris
Agreement was approving the Paris Agreement Rulebook (Katowice
Rulebook) [10]. To achieve the 1.5 ◦C targets by the end of the century,
the International Panel on Climate Change (IPCC) recommends that CO
2
emissions should be maintained at 25–30 Gt CO
2
per year instead of the
existing 52–58 Gt CO
2
per year [11]. A recent agreement on climate
change COP-26 was held in Glasgow, the UK in November 2021 to re-
view and discuss the status [12].
Globally, three main ways to mitigate CO
2
emissions are discussed in
the literature.
* Corresponding author.
E-mail address: Ipsingh@cbri.res.in (L.P. Singh).
Contents lists available at ScienceDirect
Journal of CO2 Utilization
journal homepage: www.elsevier.com/locate/jcou
https://doi.org/10.1016/j.jcou.2022.102292
Received 29 June 2022; Received in revised form 10 October 2022; Accepted 18 October 2022
Journal of CO2 Utilization 67 (2023) 102292
2
1. Reducing CO
2
emissions by using renewable energy, switching to
cleaner fuels, improving efciency, using nuclear power, and using
carbon capture and storage techniques is possible [13–15].
2. CO
2
mitigation methods or negative emissions technologies will be
deployed in the future to capture and sequester CO
2
from the at-
mosphere [6].
3. Thirdly, solar and terrestrial radiation management can be used to
alter the earth’s radiation balance [16,17].
The current study reviewed CO
2
capture and utilization in con-
struction industries. This paper examines recent CO
2
capture and utili-
zation developments, which concerns about global warming have
driven. In the rst part of the paper, we review the different capture
methods of CO
2
in cement production, such as amine scrubbing, calcium
looping, direct separation, and oxy combustion. We also discuss
commercialized technologies involved in CO
2
capture and their chal-
lenges. In the second section, we discussed the CO
2
utilized in cement-
based materials, recycled aggregate (RA) and solid wastes by ACT
(accelerated carbonation technology). Later, we discussed the different
commercially available technologies for CO
2
utilization in construction
industries, including Carbon8, Calera, CarbonCure, Solidia, Blue Planet,
and Carbstone. Further, patents published by these commercialized
technologies were also reviewed.
2. CO
2
capture in the cement industry
The cement industry plays a signicant role in CO
2
emission, and it
emits 0.5–0.6 tons of CO
2
per ton of cement production, which is ~7 %
of the total CO
2
emission in the world [10,18–22]. At the beginning of
cement production at a large scale, studies were carried out to improve
energy efciency, fuels reduction and optimize cost, however later on,
due to environmental threats and global warming issues, cement in-
dustries were allocated to devote budget and time to mitigate the
pollution strategies [23]. Approximately 576 million tons of CO
2
/year
were emitted from the global cement industry in 1990 and increased to
1.4 billion tons in 2002. Within 24 years, CO
2
emissions increased
almost three times and amounted to ~2.9 billion tons of CO
2
per year in
2021 [24–26]. Three sources mainly generate CO
2
during cement
manufacturing [27,28].
1. 50 % results from calcination (decomposition of CaCO
3
to CaO and
CO
2
) [29,30].
2. 40 % from the fuel combustion in the kiln (coal, waste, sewage
sludge, etc.)
3. 10 % from the manufacturing operations include transportation and
electricity.
Globally CO
2
emissions are estimated to be 35 % from China and
India in 2020, while only 4 % are from the UK, Germany, and France
combined [31]. The countries with the highest contribution of CO
2
from
2005 to 2021 are China, India, Europe, and the USA (Fig. 1) [31]. During
COVID, the cement sector’s CO
2
emissions did not grow but did not
decline as much as oil, gas, and coal [26]. By applying the best strategies
like alternative fuels, energy efciency, clinker substitution and CCU,
CO
2
emissions from cement industries can be reduced to 1.5 billion tons
per year and 0.43-tons CO
2
per ton of cement production by 2050
(Fig. 2) [32]. Among global cement industries, Heidelberg Cement has
pledged to mitigate CO
2
emissions by 25–30 % by 2030 compared to
1999 and was the rst company to be approved by science-based CO
2
capture [33]. CO
2
captured in the cement industry by different tech-
nologies were distinguished, such as amine scrubbing, calcium looping,
oxyfuel combustion and direct separation are summarized [34] and the
pre-combustion process is not well suitable for CO
2
capture in the
cement industry as they are suitable for the energy-related CO
2
emission
source [35].
2.1. Amine scrubbing
The cement industry has used amine scrubbing technology since
1930 [36]. The process involves removing CO
2
from ue gases after
combustion or before vents into the atmosphere. An amine solvent is
used in the absorber column at 50 ◦C to produce a decarbonized gas
stream, which is further regenerated by heating the solvent at around
120 ◦C in the stripper column, where a pure CO
2
gas is recovered [37].
The capturing method involves wet scrubbing with amine solvents such
as monoethanolamine (MEA) and diethanolamine (DEA), as the rate of
reaction of amine solvent is very high and lower cost [38]. During the
process, a carbamate ion and a protonated amine were formed by the
reaction of MEA and CO
2
, which further reacted with H
2
O molecules to
form a bicarbonate ion (Fig. 3) [39].
Among the widely used amines in amine scrubbing technology, MEA
is considered a primary amine, DEA is considered a secondary amine,
and MDEA (methyldiethanolamine) is considered a tertiary amine [40].
According to Sharif et al., 2020 [41], the absorption of CO
2
by amine
solvents is characterized by high CO
2
solubility, lower regeneration
energy for solvent regeneration, and fast kinetic rates. Singh and Ver-
sterg 2008 [42] investigated amine activity performance and reported
that amine solvent activity is highly dependent on chain lengths, alkyl
Fig. 1. Top countries with the highest CO
2
emission annually from cement industry (2005–2019) [31].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
3
group position, and abundance of functional groups. Budzianowski
2016a [43] found that primary and secondary amine solvents’ regen-
eration energy is very high compared to tertiary amine.
Amine scrubbing is considered a benchmark technology for CO
2
capture in the cement industry. The rst globally CO
2
capture technol-
ogy based on amine scrubbing that achieved the milestone in the cement
industry was Norway’s Longship. Aker Solution Advanced Carbon
Capture technology (ACCT
M
) and its S26 solvent used by Norcem’s
cement factory in Brevik, Norway, capture ~400,000 Mt of CO
2
/year.
The plant can capture 40 % of its total CO
2
emissions using only waste
heat, and its technology readiness level (TRL) is 8 [44]. In December
2020, Heidelberg Cement Group, another CO
2
capture technology, will
construct its rst full-scale CCS facility at the NORCEM cement plant in
Brevik, which can capture ~400 kt CO
2
/year [45]. Recently, Heidelberg
Cement Group announced that it would construct CCS facilities at its
cement plant in Slite, Gotland Island, Sweden, which capture ~1.8 Mt
CO
2
/year. This facility is accounted for around 3% of CO
2
emissions in
Sweden [46]. The world’s largest amine-based CCS was built at the
Baimashan cement plant in late 2017 by Anhui Conch Group, Wuhu,
china. The CO
2
capturing capacity of the plant is ~50Mt CO
2
/year
(Table 1) [47].
An improved Amine Promoted Buffer Solution (APBS), APBS-
CDRMax®, developed by Carbon Clean Solutions Limited (CCSL), was
used by different commercialized technologies. The solvent designed by
APBS-CDRMax® has a high CO
2
absorption rate, higher capacity of CO
2
capture and lower regeneration energy than MEA solvent. Compared
with the MEA solvent, it also has a lower corrosion rate, solvent
degradation rates and operating costs are also very low [48]. Kentucky
Utilities E.W. Brown Power Generation Station in Harrodsburg, Ken-
tucky, uses the CDRmax solvent for different test conditions campaigns
at the 0.7 MWe pilot scale CO
2
Capture. The solvent regeneration energy
ranged from 2.9 to 3.3 GJ/ton CO
2
, which is a 30 % lower regeneration
rate than MEA [49]. The Dalmia Cement Group built a large CCUS fa-
cility using Carbon Clean’s technology, CDRMax®, at their cement plant
sites in Tamil Nadu, India, in 2019. The facility can capture 0.5 Mt
CO
2
/year and the estimate capturing cost is approximately $40/t CO
2
(Table 1) [50].
In the recent decade, the mixture of amine solvents has solved many
of the current challenges regarding the direct use of primary, secondary
and tertiary amines for CO
2
capture. The mixed amine solution has a
Fig. 2. Globally CO
2
emission from 1990 to 2050 with and without any mitigation strategies [32].
Fig. 3. Mechanism of CO
2
capture in aqueous amine solution (MEA & DEA) [39].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
4
high CO
2
absorption capacity and lower regeneration energy during the
desorption of CO
2
. Table 2 summarizes the recent literature on different
methods of optimizing amine solvent mixtures to enhance CO
2
absorp-
tion efciency and regeneration energy [51–61].
The main disadvantage of the amine scrubbing method is its higher
regeneration energy, as almost 50–80% of energy is used in the solvent
regeneration process of the overall CO
2
capture cost. The estimated cost
of MEA-based scrubbing technology is around $80/t CO
2
[62,63].
Various contaminants in the ue gases, including SO
2
, NO
2
, etc., poison
the absorption solvent, which is crucial to the operation of the scrubber
unit. SO
2
reacts with amine solvent forming corrosive salt. Similarly,
NO
2
reacts with the solvent to form HNO
3
resulting in the degradation of
the amine solvent [64]. The concentration of SO
2
and NO
2
should be
limited to 10 ppmv and 20 ppmv, respectively, in the amine absorption
process [65,66]. Solvent degradation can also occur in the presence of
acidic components like HCl, which reduces the effectiveness of the MEA
absorption process [67]. The environmental risk associated with amine
solutions during CO
2
capture is escaping amine solutions into the at-
mosphere [68]. According to a study, every million tons of CO
2
captured
with 30 % MEA aqueous solutions releases ~80 tons of MEA into the
atmosphere [68]. A study by Xie et al. [69] found that atmospheric re-
actions of ethanolamine produce harmful isocyanic acids and
cancer-causing nitrosamines. The advantages and disadvantages of
amine scrubbing technology are summarized in Table 3.
2.2. Calcium Looping
Shimizu rst proposed calcium looping technology in 1990 [70,71].
This method has a reversible reaction between CaO and CO
2
at high
temperatures to form CaCO
3
. It is a regenerative process that uses
CaO-based energy to effectively release CO
2
from combustion through
carbonation-calcination reaction cycles (Eq.1).
CaO +CO2⇌CaCO3ΔH0= − 178 kJmol (1)
This process comprises two interconnected reactions, i.e., carbon-
ation and calcination. Carbonation reaction occurs in the carbonator
where CO
2
is reacted with CaO at high temperatures (600–750ºC), giv-
ing a solid CaCO
3
, which is an exothermic reaction (Eq. 1) [72,73].
CaCO
3
formed in the carbonator is sent to the calciner for calcination
reaction, where CaCO
3
is heated up to ~950ºC to obtain CO
2
gas and
CaO. The reaction is endothermic. CaO formed in the calciner is further
sent back to the carbonator for reaction (Fig. 4) [72,73]. Impurities such
as NO
2
and SO
2
in the ue gas can remove easily by the CO
2
processing
unit [74,75]. Repeated calcination and carbonation processes are
observed to affect the performance of the sorbent. Sorbent deactivates
due to sintering and irreversible sulphation during the processing
[76–79]. As sintering becomes more severe at higher CO
2
partial pres-
sures and calcination temperatures, the calcination temperature is set as
low as possible to maintain sorbent regeneration [76,79,80]. In a recent
study, Lisbona et al. propose using cement plants as carbon capture hubs
for industrial clusters of carbon emitters by implementing calcium
looping carbon capture, thereby reducing overall CO
2
capture costs. In
the proposed work, carbonators utilize ue gases generated by different
processes within the cluster as calciners. As a result of using a CO
2
Table 1
Different technology and CO
2
captured rates in cement plants worldwide.
Project Location CO
2
capture Ref.
•Amine-based absorption
technology.
•The largest CO
2
capture
plant operated in 2018
almost captured 3% of
the total CO
2
emission
from the cement
industry.
•CO
2
is produced by this
plant with a purity of
99.9%.
•The cost of the project
was $10 M
AnhuiConch’s
Baimashan plant
(Wuhu, China)
50,000 t
CO
2
/year
[259,260]
•Amine-based scrubbing
technology.
•Used of Carbon Clean
CDRMax® technology
combined with
proprietary solvent
(Amine Promoted Buffer
Salts -APBS)
•Produced CO
2
purity
between 95% and
99.9%.
•The project cost was
$40/t CO
2
.
Dalmia Cement
project (Tamil Nadu,
India)
0.5 Mt CO
2
/
year
[261,262]
•Calcium looping
technology
•ITIR (Industrial
Technology Research
Institute) with TCC
(Taiwan Cement
Company) installed a
calcium looping pilot in
2013
•Demonstrate HECLOT
(High-Efciency
Calcium Looping
Technology)
•The captured rate was
about 85%
•The estimated cost was
$30 t CO
2
.
TCC’s Ho Ping cement
plant (Hualien,
Taiwan)
1 t CO
2
/h [89,263]
•Aker Solutions ACCT
M
and its S26 amine
solvent
•capture CO
2
gas emitted
by the Norcem’s cement
factory.
•Complete in 2023.
Brevik, Norway 400,000 Mt
CO
2
/year
[264] {add
reference)
•Direct capture
technology -Low
Emissions Intensity
Lime and Cement
(LEILAC)
•European funded from
2016 to 2020 in which
CO
2
is direct capture
from the lime and
cement industry.
Heidelberg Cement’s
plant (Lixhe, Belgium)
25,000 t
CO
2
/year
•Direct capture
technology
•successful of LEILAC,
LEILAC-2 was launched
on April 7, 2020, and
ended in the year 2025
Western Europe 100,000 t
CO
2
/year
[109,265]
•CEMCAP project was
launched in 2015 and
ended in 2018
•CO
2
is used for cooling
the clinker.
•Cost of CO
2
capture
technology in cement
Hannover – [63]
Table 1 (continued )
Project Location CO
2
capture Ref.
plants is almost $44/t
CO
2
•Oxyfuel combustion
technology-ECRA.
•Three of the four-phase
were completed, and
phase IV was underway.
•The project’s estimated
cost was $84.1 M.
Heidelberg Cement
plant (Italy) & Lafarge
Holcim plant (Austria)
– [119]
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
5
capture hub approach, small plants could save approximately 10% on
operating costs, while cement plants could save about 5% [81].
Calcium looping has two congurations for CO
2
capture in the
cement industry, i.e., integrated conguration and tail-end congura-
tion. Several studies have explored the concept of integrated congu-
ration technology with the cement industry to capture CO
2
[82–85]. A
cement kiln with an integrated calciner performs calcination within the
calciner in an integrated conguration [86]. The tail-end conguration
involves capturing CO
2
from the clinker process using a carbonator at
the end of the pipe. In the cement industry, the tail-end conguration is
more suitable for large-scale exhibitions and more mature than the in-
tegrated conguration [87,88].
The integrated technology was further developed under the Euro-
pean funded CLEAN clinKER (CLEANKER) project from 2017 to 2021,
which aimed the project at TRL7 in Buzzi Unicem’s Cement plant in
Vernasca, Italy. Fuel consumption in the tail-end conguration is more
than in the integrated conguration [87]. The estimated cost of tail-end
and integrated congurations in the cement industry is approximately
$55/t CO
2
and $61/t CO
2
, respectively [63].
Taiwan Cement Company (TCC) and Industrial Technology Research
Institute (ITRI) installed a calcium looping driver at Ho Ping’s cement
plant in Hualien, Taiwan, in 2013 to demonstrate high-efciency Cal-
cium Looping Technology (HECLOT). The plant captured 1 ton of CO
2
per hr. from 3.1 tons of ue gas (having ~25 % CO
2
) (Table 1). The
captured rate was more than 85% and the capturing cost was approxi-
mately $30/t CO
2
[89]. It was the largest calcium looping plant in the
world and ITRI received more than 100 R&D awards for this technology
[90]. An additional calcium looping project, CEMCAP (2015–2018)
(tail-end calcium looping), was tested on two pilot plants: a 30 kWth rig
at INCAR Spain and a 200kWth rig at IFK with an efciency of CO
2
up to
98 % [91] (Table 1).
Currently, calcium looping technology faces the problem of high
calcination temperatures and decaying CO
2
capture efciency. Several
studies have shown that the sintering of CaO gradually intensies with
increased calcination temperature, resulting in the decay of CO
2
capture
performance [76,92]. We have summarized recent literature and
attempted to reduce the calcination temperature. Anbalagan et al. [93]
and Haji-Sulaiman et al. [94] investigated that impurities reduced the
decomposition temperature and increased limestone calcination rates. It
can also be stated that the energy required for the decomposition of
limestone is lower than pure CaCO
3
decomposition [95]. According to
Valverde et al. [96], milled limestone can regenerate CaO at 900 ºC
more than raw limestone calcination at 950ºC. Dolomite (CaMg(CO
3
)
2
)
is an abundant material and also a low-cost precursor used to prepare
CaO-based sorbents because of the homogeneous distribution and inert
MgO within the dolomite-derived sorbents [97]. Doping limestone with
salts having a low melting point, such as KCl, CaCl
2
, NaCl, Na
2
CO
3
,
KMnO
4
, and CaBr
2
is another way to reduce the calcination temperature.
Al-Jeboori et al. [98] studied that low doses of CaCl
2
or MgCl
2
doping in
limestone increased the pores by around 100 nm, which promotes the
carbonation reaction of CaO.
2.3. Direct Separation
A direct separation technology involves circulating air through
regenerative lters to directly capture CO
2
from the atmosphere. Since
1999, direct separation has decreased atmospheric CO
2
concentration
[99,100]. Carbonates are formed from this reaction, which can be
calcined to generate CO
2
, while hydroxide streams are recirculated in a
closed loop. McLaren [101] states this direct separation technique has a
Technology Readiness Level (TRL) level of 4–6, with a potential CO
2
capture capacity of 10 Gt/year. Currently, the technology has a TRL of 7
[102]. Several companies are developing pilot and commercial facilities,
including Climeworks, Global Thermostats, and Carbon Engineering
[102,103]. With Sunre and Audi, Climeworks built and operated a pilot
Table 2
Summary of mixed amine scrubbing technology studied by various researchers.
Solvent Ratio CO
2
removal efciency % Method Temperature
(ºC)
Regeneration energy (GJ/tCO
2
) Ref.
MEA 35 wt% MEA 85 solvent development 123.7 3.10 [51]
30 wt% MEA 95.9 solvent development 114–130 3.1–5.4 [52]
28 wt% MEA 80.49 modication 120–121 3.98 [53]
30 wt% MEA 90 solvent development 136 3.99 [54]
AMP 30 wt% AMP 96.39 solvent development 95–109 2.1 (MJ/kgCO2) [55]
MDEA
+PZ
10 wt% MDEA+30 wt% PZ modication 110 2.39 [56]
20 wt% MDEA+10 wt% PZ 90 solvent development 95–110 3.0–4.1 (MJ/kg CO2) [57]
MDEA+PZ =30–40 wt% multi-objective optimization 100–120 2.76 [58]
1-MPZ
+PZ
30 wt%1-MPZ+10 wt%PZ 94 solvent development 124.7 2.988 [59]
20 wt% 1-MPZ+10 wt% PZ solvent development 120 2.5 [60]
MEA +sulfolane 4 M MEA +% 5 M sulfolane solvent development 70 1.159 [61]
MEA+1-
propanol
30 wt% MEA+40 wt% 1-propanol 90 solvent development 136 2.40 [54]
TETA +TMPDA 30 wt% MEA+40 wt% TMPDA 90 solvent development 136 1.83 [54]
Table 3
Advantage and disadvantage of different CO
2
capture technologies [102,111,
266,267].
CO
2
capture
Technology
Advantage Disadvantage
Amine
Scrubbing
•Adsorption capacity is high
•The technology is well
known and is widely used
in various industries
•Recovery rate of up to 95%
•Thermally stable
•Loss of sorption capacity over
multiple cycles
•Signicant energy
requirement for the solvent
regeneration
•Degradation and equipment
corrosion
•Solvent emission has negative
impact on environment
Oxy
Combustion
Capture
•Concentration of CO
2
in
ue gas is high (60%)
•CO2 separation is easier
without N
2
•NOx free emission
•Mature ASU system
•Low volume of gases
involves smaller
equipment size
•Energy penalty due to the air
separation unit
•CO
2
recycle required to
control combustion
temperature
•Signicant energy
requirement for separation of
O
2
from air
•May present corrosion
problems
Direct
Separation
•High CO
2
removal
efciency
•Can achieve net zero or
even net negative emission
•The concentration of CO
2
in
air is low (420 ppm) which
make the process energy
intensive
Calcium
Looping
•The technology is well
known
•No thermal formation of
NO
x
•Exhaust gas stream are not
harmful
•Large scale demonstration is
not available
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
6
plant in Dresden in 2014 that captured 80 % of the air’s CO
2
[104].
According to Benhelal et al. [29], CO
2
is captured from the lime and
cement industry without being exposed to air or combustion gases. The
direct separation technology developed by Calix, an Australian com-
pany, captured approximately 64–70 % of the CO
2
produced by a
standard cement plant [105,106]. LEILAC is a low-emission intensity
lime and cement developed through a European-funded project between
2016 and 2020. In the LEILAC system, the heat from the exhaust gas is
transferred to the limestone through a steel vessel called a direct sepa-
rator reactor (DSR). CO
2
gas captured from this system is almost pure
[107] in approximately 25,000 t CO
2
/year, almost 5 % of total CO
2
emissions from the factory (Table 1). After the completion of LEILAC 1,
LEILAC 2 project was launched on April 7, 2020, and will be completed
by 2025. [108]. LEILAC 2 is almost four times larger than LEILAC 1 and
can capture 100,000 t CO
2
/year (Table 1) [108]. After examining
different locations, the LEILAC 2 demonstration project is built at the
Heidelberg Cement plant in Hanover, Germany. The project’s main
features were improved technological advancement at the industrial
level, a complete integration process in the existing cement plant, and
the provision of renewable energy [109].
A signicant advantage of direct separation technology is that it can
be used anywhere. Using this technology, it is theoretically possible to
reach zero net emissions or even to produce negative net emissions. Low
concentrations of SO
2
and NO
2
in atmospheric air result in moderate
degradation of sorbents [110]. Low concentrations of SO
2
and NO
2
in
atmospheric air result in moderate degradation of sorbents [110]. Since
ambient air contains 420 ppm of CO
2
, it is relatively low compared with
ue gases at power plants. As a result, the cost of direct separation is
high. Direct separation technology pilot plants cost $94–232/t CO
2
but
are expected to drop to $60/t CO
2
by 2040, increasing their competi-
tiveness [111,112]. Both direct separation and calcium looping tech-
nology appear to be progressing rapidly. The advantages and
disadvantages of both calcium looping and direct separation technology
are summarized in Table 3.
2.4. Oxy-combustion capture
Oxy-combustion technology is promising for CO
2
capture in the
cement industry (CSI/ECRA, 2009). However, development is expected
to take longer than amine scrubbing technology [113]. Oxy-combustion
technology uses pure O
2
for the combustion of fuels. During this process,
oxygen combustion increases the kiln temperature, which can cause
structural damage [114,115]. Parts of the ue gas rich in CO
2
must be
recycled back into the kiln to maintain the temperature. The resulting
CO
2
stream is puried in a simple cryogenic central processing unit
(CPU), achieving almost 95 % of CO
2
. Higher purity of CO
2
is also
achieved by using cryogenic distillation [116]. Contaminants present in
the ue gas, like SO
2
, particles, etc., are removed with the help of
desulphurization and a standard electrostatic precipitator, respectively.
Oxyfuel combustion can improve fuel efciency and capture CO
2
at a
lower cost in cement plants. According to H¨
oltl et al., oxyfuel combus-
tion applies to the combustion of low-caloric fuels, such as agricultural
waste and municipal waste biomass, and the ame’s temperature can be
controlled by adjusting the ue gas recycling rate [117,118].
The European cement research academy’s (ECRA’s) long-running
research project has been conducting research on CO
2
capture since
2007. Phases I, II, and III of ECRA’s CCS project were completed and
continuing the phase IV project [119,120]. The two European cement
plants demonstrated industrial-scale oxy-combustion CO
2
capture in
2018, the Lafarge Holcim plant in Retznei (Austria) and the Heilderberg
Cement plant in Colferferro (Italy) [121], where clear steps were taken
to build an oxyfuel kiln. Such kilns were intended to provide insight into
the industrial performance of technology that provides high CO
2
emis-
sions for further carbon capture and the cost is approximately $84.1 M.
CEMCAP (2015–2018) is another oxyfuel testing project manufactured
by IKN wherein CO
2
was used for cooling the clinker and incorporated
into the Heilderberg Cement plant in Hannover, Germany. The
oxy-combustion technology produces high purity of oxygen (95 %) in
the Air Separation Unit (ASU) [122]. The estimated cost of the tech-
nology in the cement plants is almost $44/t CO
2
(Table 1) [63]. As the
world’s rst and largest oxy-fuel demonstration power plant retrotting
an existing PC-red boiler, the Callide oxy-fuel power plant with 30 MW
capacity commenced in 2011 in Queensland, Australia [123]. The plant
consists of four units, each with a capacity of 30 MW. A recent literature
review of oxy-fuel combustion demonstrations at pilot and industrial
scales is provided in Table 4 [123–125]. It is expected that the success of
Fig. 4. Principle of calcium looping process [72,73].
Table 4
Projects on oxy-fuel combustion technology (Pilot and industrial demonstration)
[123–125].
Companies Year Project name Capacity
(MW
e
) and
New/Retrot
Location
ENDESA,
CIUDEN and
Foster
2015 Compostilla
(OXY-CFB-300)
320, New Spain
Vattenfall 2015 Janschwalde 250, New Germany
FutureGen
Alliance
2015–2016 FutureGen 210, Retrot USA
Black Hills
Corporation
2016 Black Hills
Power
100, New USA
KEPCO 2016–2018 Youngdong 100, Retrot South
Korea
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
7
these demonstrations will lead to the greater commercial potential.
3. CO
2
utilization in the construction industry
3.1. Mineral carbonation
Mineral Carbonation (CO
2
mineral storage) is an accelerated form of
natural carbonation or weathering carbonation of natural silicate rocks
in which CO
2
is permanently stored in the form of thermodynamically
stable carbonate (CaCO
3
/MgCO
3
) (Eq. 2) [126].
CaO/MgO +CO2→CaCO3+Heat (2)
CO
2
storage by mineral carbonation is more expensive than
geological storage due to pretreatment requirements, including
extracting Ca and Mg from alkaline waste [127]. Standard Gibbs free
energy (ΔG) of carbonate is much lower than CO
2
, which means CO
2
storage through mineral carbonation is safe [128].
Most previous research focused on carbonating natural silicates such
as serpentine, olivine, limestone, wollastonite, and forsterite because
these minerals are rich in Ca and Mg. The carbonation of these minerals
is sufcient to store CO
2
emitted from the combustion of fossil fuels and
the cement industry. But, utilization of these minerals for carbonation is
not cost-effective because of a slow rate of carbonation reaction and
large-scale mining operation [129,130]. As a result, there has been an
increase in the use of alkaline solid wastes such as cement waste, steel
slag, and coal y ash for CO
2
sequestration. Alkaline solid wastes are
more suitable for mineral carbonation because of their faster reaction
rate, energy input is meager, and carbonate conversion efciency is
higher than natural minerals. Mineral carbonation of solid waste offers
the double benets of waste management and reduction of CO
2
gas
[131]. Mineral carbonation is classied into direct and indirect
carbonation; pathways of mineral carbonation are shown in Fig. 5.
3.1.1. Direct carbonation
3.1.1.1. Gas-solid carbonation. It was rst studied by Lackner and co-
workers, which is the most straightforward reaction between the Ca/
Mg-rich solid with the CO
2
gas [132]. Gas-Solid Carbonation of
olivine shown in Eq. 3.
Mg2SiO4(s) + 2CO2(g)→2MgCO3(s) + SiO2(3)
The reaction rate of Gas-Solid Carbonation is very slow or insuf-
cient, even at elevated temperatures and pressure. Forsterite, serpentine,
and wollastonite have Gibbs free energies (ΔG) of 44.6 kJ/mol, 43.0 kJ/
mol, and 16.9 kJ/mol, respectively. These values indicate that the re-
action is spontaneous, but the reaction rate is very slow. Therefore, It is
necessary to maintain a high temperature (100–500 ºC) and a pressure
of 100–150 bar CO
2
to achieve a reasonable reaction rate [129,130]. In
their study, DaCosta and coworkers passed the ue through ne-grained
silicate rocks (2.5–60 µm). They reported that using 5 g of olivine and 10
% CO
2
at a temperature range of 100–500 ºC, 0.12 g CO
2
per gram of
olivine can be stored. The capacity for capturing CO
2
was increased to
18 % at a concentration of 15 % [133].
3.1.1.2. Direct aqueous carbonation. The addition of water in the two-
phase reaction (gas-solid reaction) converts into the multiple-phase re-
action (gas-liquid-solid reaction), which increases the carbonation re-
action rate.
In this reaction, rstly, CO
2
dissolves into the water to form carbonic
acid, then carbonic acid is further ionized into the H
+
and CO
3
2-
Eqs. 4, 5
and 6 [134].
CO2(g) + H2O(l)→H2CO3(aq)(4)
H2CO3(aq)→H++HCO−
3(5)
HCO−
3→H++CO2−
3(6)
The aqueous solution becomes acidic due to the formation of H
+
ions. Due to the acidic environment, Ca/Mg present in the matrix of the
minerals leaches out and reacts with CO
2
to form calcium/magnesium
carbonate (Eqs. 7 and 8) [134].
(Ca/Mg)SiO2+2H+→(Ca2+Mg2+) + SiO2+H2O(7)
Ca2+Mg2+) + HCO−
3→(Ca
MgCO3+H2O(8)
Direct carbonation of recycled concrete aggregate (RCA), in which
CO
2
penetrated the RCA through the pores and cracks and dissolved in
water present in the pores producing carbonic acid. Calcium ions, which
Fig. 5. Pathways of mineral carbonation [134].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
8
leached from the Calcium hydroxide, calcium silicate hydrate, C
3
S, C
2
S,
ettringite, calcium sulfoaluminate hydrates, etc., react with carbonate
ions to form calcium carbonate and silica gel. Calcium carbonate is
precipitated as calcium carbonate polymorphs like calcite, aragonite,
and vaterite in the pores. Thus, the cracks of RCA are lled, decreasing
the porosity [135,136].
3.1.2. Indirect carbonation
Compared with direct carbonation, indirect carbonation proceeds in
two or more successive steps (leaching step and carbonation step),
where the carbonation step is the rate-the determining step [137,138].
1. Leaching step- Extracting reactive components (Mg/Ca) from the
minerals using acid or other solvents (Table 5).
2. Carbonation step- Reaction of CO
2
with Ca/Mg in alkaline
conditions.
Unlike direct carbonation, indirect carbonation depends more on the
carbonation conditions, such as temperature, pressure, and pH [139].
Extraction of Ca and Mg using acid (HCl and HNO
3
) is accessible from
the alkaline solid waste/silicate matrix. Lackner et al. rst proposed
extraction through HCl in 1995 [140]. The main limitation of this route
is the cost of HCl, the energy consumption during the evaporation of the
aqueous solution and the estimated cost of more than $157/ton of CO
2
[141]. Extraction of magnesium from serpentinite using HNO
3
and
carbonation of magnesium salt was carried out by Teis et al. [142,143].
In both cases, excess acid is required to efciently extract calcium and
magnesium from the alkaline solid waste, which increases the pH of the
solution causing a decrease in carbonation. Therefore, it is necessary to
increase the pH of solid waste before the carbonation reaction by
approximately 8–9 pH by using caustic reagents [142,143].
Adding organic acids such as EDTA increases the extraction of Ca and
Mg in mildly acidic conditions. As a result, less caustic reagent would be
required during the carbonation process. However, extraction through
organic acid is not economically benecial because of the higher cost
and recycling of acid in the leaching steps [144]. Extraction using acetic
acid is another approach and the advantage of this approach is the re-
covery of acetic acid in the carbonation step and recyclability [145,146].
Another extraction process for calcium and magnesium developed by
Kodama et al. used NH
4
Cl, which has the potential for fully recycling the
NH
4
Cl and caustic reagents are not required during the carbonation
steps. It is the most promising method, which has the potential for the
recovery of reagent and reuse [147].
Cement kiln dust (CKD) is a byproduct of Portland cement manu-
facture in high-temperature rotary kilns [148]. CKD is classied as
hazardous waste because it has a caustic nature and the composition of
CKD is 38–48% CaO and 1.5–2.1 % MgO [137,149]. The CKD is already
carbonated and contains 38–45 % CaCO
3
[150]. Cement bypass dust
(CBD) has lower carbonated content than CKD and has more potential to
sequester CO
2
than CKD by indirect carbonation [151]. CKD has
sequestered up to 42 Mt of CO
2
annually or stores approximately 0.1 %
of CO
2
emission globally from the combustion of fuels [152]. The CKD
and CBD have the potential to store 0.08–0.025 t CO
2
/t CKD and CBD at
ambient pressure and temperature in a column reactor [150,151].
Waste cement is a byproduct of concrete, where aggregate is sepa-
rated from the waste cement. According to Bobicki et al., waste cement
generated from the EU, China and the USA was approximately 1100 Mt
and could sequester about 61 Mt CO
2
[137]. Most waste cement is
already used in construction by mineral carbonation [148]. During in-
direct carbonation of the waste cement, extraction of calcium in the
leaching step from the cement waste is achieved by HCl, CH
3
COOH, and
NH
4
Cl (Table 2). When the concentration of CH
3
COOH and HCl is 0.5 M,
the extraction of calcium is approximately 13,220 mg/L and 13,
670 mg/L, respectively, whereas the extraction efciency of 0.5 M
NH
4
Cl is around 6733 mg/L. During carbonation, calcium extraction by
NH
4
Cl in the leaching step sequestrated approximately 0.1 kg CO
2
/kg
cement, whereas extraction by HCl and CH
3
COOH could sequester
1.4Kg CO
2
/Kg cement [127]. Mineral carbonation in waste cement
using the extracting agent NH4Cl is more economically benecial than
HCl and CH
3
COOH because of the fully recycling of solvent and the need
for a caustic reagent to increase pH during the carbonation step.
The following Eq. 9 measures the efciency of indirect carbonation
[124].
Efciency depends on the Ca or Mg content in the minerals, not the
quantity of the minerals used for the carbonation.
3.2. Cement-based materials
In the past, cement carbonation was viewed as a negative factor as it
deteriorates the hydration products with time, called weathering
carbonation. The main component of cement is calcium-silicate-hydrate,
which, when exposed to atmospheric CO
2
, decalcies and eventually
transforms into silica gel, losing its binding properties and durability
[153]. Additionally, the high alkalinity of the cement product protects
the steel reinforcement from corrosion. However, in recent years, studies
have shown positive effects from the carbonation of cement hydrates,
specically in early-age carbonation. CO
2
curing of cement-based ma-
terials has gained more attention since the 1990s due to the increase in
global warming. Carbonation of cement-based materials has been sug-
gested recently for more active sequestration of CO
2
and numerous
research are conducted in this eld [154–156]. The carbonation reac-
tion between the cement-based materials with CO
2
formed a thermo-
dynamically stable carbonate [157,158].
It has been suggested that accelerated carbonation at an early age
accelerates cement’s hardening process in which CO
2
gas reacts with Ca
(OH)
2
, cement clinkers (C
2
S and C
3
S) and C-S-H. The reaction of CO
2
Table 5
Extraction of reactive elements by different reagents.
Extracting
reagent
Chemical reactions involved in the extraction Ref.
HCl/HNO
3
•Mg
3
Si
2
O
5
(OH)
4(s)
+6(HNO
3
/HCl)
(aq)
→ 3Mg
2+
(aq)
+6
(NO
3
-
/Cl
-
)
(aq)
+2SiO
2(s)
+5 H
2
O
(l)
•Mg
2
+(aq)
+2(NO
3
-
/Cl
-
)
(aq)
+xH
2
O
(l)
+y(HNO
3
/HCl)
(aq)
→ Mg((NO
3
)
2
/Cl
2
).6 H
2
O
(s)
+(x-6) H
2
O
(g)
+y
(HNO
3
/HCl)
(g)
•5Mg((NO
3
)
2
/Cl
2
)
(aq)
+10NaOH
(aq)
+4CO
2(g)
→
10Na(NO
3
-
/Cl
-
)
(aq)
+Mg
5
(OH)
2
(CO
3
)
4
0.4 H
2
O
(s)
[140,
141]
CH
3
COOH •CaSiO
3
+CH
3
COOH → Ca
2+
+SiO
2
+2CH
3
COO
-
+H
2
O
•Ca
2+
+2CH
3
COO
-
+H
2
O +CO
2
→ CaCO
3
+2CH
3
COOH
[145,
146]
NH
4
Cl •4NH
4
Cl +2CaSiO
3
→ 2CaCl
2
+2SiO
2
+4NH
3
+2 H
2
O
•2CaCl
2
+2CO
2
+4NH
3
+2 H
2
O → 2CaCO
3 +
4NH
4
Cl
[147]
η
(Carbonation)%=quantatity of Mg or Ca converted into carbonate
quantatity of Mg or Ca available in the minerals ×100 (9)
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
9
with cement paste mainly gives CaCO
3
and silica gel. This early-age
carbonation improves the microstructural compactness of cement-
based materials, resulting in greater strength and performance at an
early age. Carbonation of Ca(OH)
2
occurs in different stages, i.e.,
dissolution of Ca(OH)
2
to form calcium ions, CO
2
gas reacts with water
to form carbonate ions which further reacts with the calcium ions to
form calcium carbonate polymorphs (calcite, vaterite and aragonite)
(Fig. 6) [159].
CO2+H2O→H2CO3+2H++CO2−
3(10)
Similarly, carbonation of C-S-H forms calcium carbonate and amor-
phous silica gel (Eq. 11), which promotes the removal of Ca
2+
from the
C-S-H, leading to a reduced C/S ratio and a decline in C-S-H stability
[160]. Both Ca(OH)
2
and C-S-H carbonate sequentially; however,
Glasser et al. [114] reported that thermodynamically carbonation of Ca
(OH)
2
took precedence over C-S-H. Morandeau et al. [161] contradicted
this by reporting that both Ca(OH)
2
and C-S-H carbonation occur
simultaneously. Thermogravimetric analysis (TGA) concluded that
initial carbonation rates for Ca(OH)
2
and C-S-H appeared to be com-
parable. However, carbonation of Ca(OH)
2
reached a relatively suf-
cient level with steady utilization of Ca(OH), and C-S-H gel continued to
carbonate.
C−S−H+CO2→CaCO3+SiO2+nH2O(11)
C
3
S, C
2
S, tricalcium aluminate (C
3
A), and tetracalcium alumi-
noferrite (C
4
AF) are the main mineral compositions of C-S-H based
cement clinker. According to Liu et al., the carbonation of cement
clinker is in the order of C
3
S >C
2
S >C
3
A >C
4
AF [162]. C
2
S and C
3
S are
the dominant carbonatable reactants compared to C
3
A and C
4
AF, as they
are in small quantities [163]. In the presence of water, C
2
S and C
3
S
carbonated to form CaCO
3
and silica gel rather than Ca(OH)
2
. Carbon-
ation of C
3
S, β-C
2
S and γ-C
2
S was generally faster than the hydration
[164]. The mechanism of early-age carbonation was different from the
weathering carbonation. The carbonation reaction of anhydrous alite
C
3
S and belite (C
2
S) is given in Eqs. 12 and 13 [165] and these reactions
are spontaneous and exothermic.
3C3S+ (3−y)CO2+mH →CySHm + (3−y)CaCO3−347 kJ/mol
(12)
2β−C2S+ (2−y)CO2+mH →CySHm+ (2−x)CaCO3−184 KJ /mol
(13)
In Eqs. 12 and 13, C
y
SH
m
represents the (CaO)
y
(SiO
2
)(H
2
O)
m
, which
can be described simply by C-S-H. Formation of C-S-H gel on
carbonation was also supported by the result of Berger et al. [166], in
which β-C
2
S and C
3
S powders are cured by CO
2
gas and the heat release
is 347 kJ/mol and 184kJ/mol for C
3
S and β-C
2
S, respectively and the
result also proved that compressive strength of CO
2
cured mortar
increased and further strength is gained by subsequent water curing. The
same result is also reported in the other literature [167,168]. C
2
S has
ve distinct polymorphs and can be activated by CO
2
for strength gain.
Among the ve polymorphs, γ-C
2
S is non-hydraulic and the rests of them
are hydraulic and this CO
2
curing of γ-C
2
S was studied by Bukowski and
Bergen in 1972 [169] and later complemented by FTIR and NMR [170,
171]. CO
2
uptake by γ-C
2
S is higher than β-C
2
S. They form different
CaCO
3
polymorphs [170] and provide more mechanical strength [171].
Tricalcium aluminate (C
3
A) had minimal to no reactivity with CO
2
[172]. Ettringite is another cement phase produced by C
3
A and C
4
AF as
a reaction product of hydration [173], which is prone to CO
2
reaction
and decomposes to produce gypsum, alumina gel, calcite, amorphous
gel and water [174,175]. No evidence exists in any literature on the
carbonation of aluminoferrite (C
4
AF) [176].
A study of the percentage of CO
2
uptake by different cement-based
materials is presented in Table 6. Overall, the CO
2
uptake was signi-
cantly increased by an increase in CO
2
concentration and pressure. Even
though a higher temperature of up to 100 ◦C is benecial for CO
2
sequestration, room temperature (about 20 ◦C) is usually preferred to
avoid more energy consumption, which causes extra CO
2
emissions
[177]. In the RH range of 50–70 %, the carbonation of cement paste is
the highest [177]. Water content also plays a signicant role in this
process, so the pre-curing of samples is done before carbonation. A
three-step curing procedure is usually used to achieve more effective
carbonation, starting with pre-curing followed by standard carbonation
and subsequent carbonation [178,179].
Due to CaCO
3
precipitation, the cement pastes’ chemical composi-
tion changed, which changed its microstructure. Shi et al. [180] studied
Fig. 6. . (a) % CO
2
reduction due to mineralization (b) worldwide CO
2
reduction through mineralization of alkaline solid waste [131].
Table 6
CO
2
uptake % by cement-based materials.
Cement-based materials Mineral composition
%
CO
2
uptake
%
Ref.
CaO MgO
Lightweight concrete masonry
unit
– – 22.0–24.0 [268]
Waste hydrated cement paste 61.0 2.0 15.0–24.0 [269]
Belite-rich Portland cement 62.5 – 16.9 [270]
Precast concrete – – 12.7 [190]
Calcium silicate concrete 63.1–63.9 2.0–3.5 8.1–14.0 [271]
Early curing of cement paste
subject
63.1 2.0 7.5–19.2 [272]
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
10
carbonated concrete microstructure and showed the lling effect, which
decreased the porosity of the concrete. These changes remarkably
improved the mechanical and durability of samples. The pores with
50–100 nm is largely lled during carbonation, whereas 10–50 nm
pores size prevails throughout the volume size for the uncarbonated
cement paste. Early carbonation occurred due to the rapid dissolution of
cement and subsequent carbonation reaction in the pore solution [181].
Carbonation results in a low Ca/Si ratio in cement paste, promoting
early-age hydration due to a higher degree of polymerization [182]. A
study by Zhan et al. [183] found that CO
2
cured cement paste had a
compressive strength twice that of water-cured cement paste after 24 h.
3.3. Recycled aggregates
Recycling construction and demolished (C&D) waste into a recycled
aggregate (RA) is an important method for waste disposal worldwide.
Natural disasters, rapid industrialization and urbanization, mainly in
developing countries, generated a vast amount of C&D waste and will
remain for the next few decades [184,185]. China produced around 1.65
billion and 1.85 billion tons of C&D waste in 2016 and 2017, respec-
tively and was the largest C&D producer in the world [186,187].
Counties such as Germany, Japan and The Netherlands have recycled
more than 80% of C&D waste. The rate of recycled waste in other
developed countries is almost 20–40 % [188] and the recovery rate of
developing countries is almost negligible [84,85]. Replacement of virgin
aggregate with recycled aggregate (100 %) reduced the compressive
strength of concrete by almost 30–40 % [189,190]. Accelerated
carbonation improved the RA properties and captured CO
2
permanently
as a stable CaCO
3
. RA carbonation is a very slow process, and to over-
come it, CO
2
concentrations, temperatures, and relative humidity are
increased, known as accelerated carbonation and the reaction occurs in
a few hrs. [136]. According to the different types of carbonation
methods (Table 7), standard and pressurized carbonation are the most
commonly used methods for carbonating RA [187].
CO
2
uptake by RA is distinct from the concrete structure and
generally. Both rate and amount of CO
2
uptake by RA increase with a
decrease in particle size due to the more surface area exposed to the CO
2
.
The carbonation of concrete structures takes a minimal amount of CO
2
over a long period due to the minimum surface area exposed to CO
2
gas
[135,191]. The amount of CO
2
uptake by RA with particles size
5–10 mm is almost 50 % higher than that of 14–20 mm [192] and the
CO
2
uptake of 1.18 mm is almost 100 % higher than 7.5 mm [193]. CO
2
uptake is further increased by pressured carbonation and pre-soaking
treatment [194,195]. There are two types of RA, a new type RA and
an old type of RA. The CO
2
uptake by the old type RA is lower than the
new type because the natural carbonation already occurred in the old
type RA during storage and demolition [136]. Rapid carbonation is
occurred in the RA after demolition during 1–2 years due to exposed
surface area [135,196]. New RA’s with particles between 5 mm and
20 mm sequestrate almost 7.9 kg CO
2
per ton [136]. During the
carbonation of RA, thermodynamically stable CaCO
3
is formed,
increasing the solid phase volume by ~11.9 % [197]. Pores and cracks in
RA are satisfactorily lled by the CaCO
3
and silica gel (formed in the
reaction between C-S-H and CO
2
) which enhances the property of RA.
Carbonation of RA improved the compressive strength and the elastic
modulus. Compressive strength increased with increased RA content
and the compressive strength reached almost equal to the natural
aggregate concrete at 28 days [198]. The elastic modulus of RA is
increased by almost 13 % [198] and 8–27 % [199] on carbonation. An
increase in the compressive strength and elastic modulus (3.1–27.0 %)
of concrete with CRA is reported in different literature [198–203].
3.4. Solid wastes
In recent decades, solid waste generation has expanded dramatically
worldwide. In 2020, 12 billion tons of solid waste were generated
globally, which is anticipated to rise to 19 billion by 2050 [204]. Around
4.4 billion tons of trash are generated in Asia, with 48 million tons (6 %)
annually in India alone [205], causing many economic, environmental,
and social issues. Therefore, solid waste management in an effective way
is necessary for the development of sustainable and habitable cities.
Using ACT, various solid wastes were treated with CO
2
gas and con-
verted into value-added products to address this problem. ACT changes
the chemistry of the materials by stabilizing the contaminants [206,
207].
Regarding fundamental research, engineering applications, and
economic evaluation [208], Xie et al. recently published a comprehen-
sive review of CO
2
mineralization methods for natural ores and indus-
trial solid wastes. The researchers predicted that CO
2
mineralization and
natural resource extraction would be combined with industrial solid
waste treatment in the future. Around the world, alkaline solid wastes
include iron/steel slags, coal and fuel combustion products, mining/-
mineral processing wastes, incinerator residues, cement and concrete
wastes, and pulp and paper mill waste for CO
2
mineralization. It is re-
ported that ~310 Mt CO
2
can directly reduce CO
2
through mineral
carbonation of alkaline solid waste across the globe, wherein 43% CO
2
reduction is achieved by carbonation of steel slag only. Further, it is
reported that the total amount of CO
2
reduction by mineral carbonation
in China is more than four times (~45 %) that of any country (Fig. 6)
[131]. Gunning et al. [151] described the production of light-weight
carbonated aggregates with individual pellet compressive strengths
exceeding 0.10 MPa. Further, they expanded this study by discussing the
Table 7
Carbonation of RA using various methods.
Method Condition Procedure Conclusion Ref.
Standard carbonation RH=70 ±5 % •Carbonation proceeded in standard Chinese GB50082–2009.
•RA is placed in a chamber.
•CO
2
is maintained at ambient pressure.
Carbonation was low and the time of CO
2
curing was
also higher.
[197,
273] Temp.=20 ±2
CO
2
conc.=20
±3
Pressurized
carbonation
RH=50 ±5 •RA was rst dried in a drying chamber.
•Vacuumed the chamber to −0.6 Bar.
•CO
2
pressure is controlled until a required constant is
reached.
Carbonation was higher than standard. [190,
193] Temp.=25 ±3
Flow-through CO
2
curing
RH=50 ±5 •Exposure to RA with CO
2
gas
•CO
2
is injected from one side and discharged through the
opposite side.
•RH was maintained by using a saturated Mg(NO
3
)
2
solution.
•The ow rate of CO
2
was almost 5 L/min.
Low energy consumption and higher efciency than
standard.
[157,
181] CO
2
conc.=10 %
Water CO
2
cooperative
•RA was rst placed in the chamber, which contained water.
•A mixture of CO
2
, N
2
and O
2
gas was injected into the water.
•The CO
2
nano bubble was also mixed with the water to
increase efciency.
Higher efciency condition for CO
2
curing. [274,
275]
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
11
commercial possibilities of aggregates formed from municipal solid
waste [209].
Fernandez-Bertos et al. [154] examined waste streams for CO
2
gas
reactivity. It is reported that due to the formation of CaCO
3
, there is an
increase in volume and reduction in porosity, which helps in the
retention of contaminants and also reduces the pH of waste below a
threshold value (11.5) (Table 8), making them less hazardous [206].
CO
2
uptake percentage is dependent on the Ca and Mg content of the
waste and reactivity of CO
2
increases with the Ca content, but the phase
of the mineral is also important in which calcium is bonded because
CWIA (clinical waste incineration ash) and SSA (sewage sludge ash)
contain the signicant amount of calcium 28.1 (wt%), 14.8 (wt%)
respectively and is expected the carbonation reaction. Still, the reaction
was almost negligible because calcium in these solid wastes bounded in
a different phase [194,195,197]. CO
2
uptake percentage also depends on
the carbonation methods, as some waste requires pre-treatment with
different additives. Table 9 represents the Ca and Mg content and the
CO
2
uptake% of different solid wastes and Table 10 represents the
different carbonation methods of solid wastes.
4. Commercialized approaches
Accelerated carbonation of industrial waste may be utilized to pro-
duce engineered products. In a study by Gunning et al. [151], articial
aggregates were produced from alkaline solid wastes such as cement kiln
dust, wood ash, and paper ash etc. The process was licensed in 2012 for
using MSW air pollution control residue to produce articial aggregates
for construction purposes [209]. Morone et al. [210] produced
pilot-scale carbonate bonded aggregates from BOF steel slags using
mineral carbonation. After 28 days of curing (pure CO
2
at 140 ◦C and
20 bar), the products captured up to 10 % CO
2
(v/v). According to
Quaghebeur et al. [211], monolithic compacts made from stainless steel
waste had a compressive strength of 55 MPa. A commercially available
pre-cast building block made from moist carbonated steel slag was
introduced in 2017 [212]. Natural sand and nely ground steel slag are
used in the products. Since 2009, there has been a continuous increase in
the percentage of commercialized CO
2
usage technologies. Fig. 7 shows
the number of CO
2
usage patents led each year from 2009 to 2021.
Several commercial processes have been developed to sequester CO
2
from the atmosphere in response to an increased interest in waste
mineralization as a technology for CCU. Some of these are summarized
in Table 11 and discussed below.
4.1. Carbon8
The University of Greenwich founded Carbon8 Systems Ltd. (UK) in
2006 to commercialize Accelerated Carbonation Technology (ACT)
[213,214]. ACT produces articial limestone by combining CO
2
with
various industrial wastes (thermal wastes from cement manufacturing
sites, waste energy, steel slags, etc.). The alkaline solid waste is mixed
with liquid CO
2
and water in a pretreatment mixer. Binders and llers
are added to carbonated waste during batch mixing. To produce
rounded aggregates, the slurry passes through a pelletizer where
gaseous CO
2
is introduced to speed up cementation (Fig. 8) [215].
In 2012, ACT was commercialized and licensed as Carbon8 Aggre-
gates, supported with an investment by Grundon Waste Management
and producing >150,000 tons of product per year. It can permanently
absorb over 1 million tons of CO
2
using only 20 % of the waste available
in Europe [216]. Furthermore, for every ton of Carbon8 aggregate, 1.4
tons of natural aggregate are preserved, and 0.5 tons of waste are
Table 8
pH changes before and after carbonation [206].
Biomass
ash
MSWI-BA APC CKD PS-AI WA
Before carbonation 10.6 12.4 11.1 13.2 12.7–13.0 13.4
After carbonation 9.9 9.1 8.4 11.0 9.9–11.4 11.0
*PSIA (paper sludge incineration ash), MSW-BA (municipal solid waste incin-
eration bottom ash), WA (wood ash), CKD (cement kiln dust), APC (Air pollution
control)
Table 9
Ca and Mg content (wt%) of different waste and CO
2
uptake %.
Waste Chemical composition (wt%) CO
2
uptake (wt%) Ref.
CaO MgO Ref.
PS-IA (paper sludge incineration ash) 45–69 1.3–5.3 [206] 17 [206]
MSWI-BA (municipal solid waste incineration bottom ash) 32–53 2.8 [206,276,277] 3–14 [278]
MSWI-FA/APC (municipal solid waste incineration y ash) 50–60 8 [278–280] 7–25 [281]
RCA (recycled concrete aggregate) 15–24 2–3 [282,283] 7.5, 16.5 [281,284]
WA (wood ash) 24–46 8–9 [206] 8 [206]
CKD (cement kiln dust) 34.5–46.2 1.5–2.1 [149,206] 10 [206]
BF slag (blast furnace slag) 15–41 8–11 [146,285,286] 7, 22.7 [73,283]
Steel slag EAF (electric arc furnace slag) 25–47 4–15 [146,287] 12–18 [280,288]
BOF (basic oxygen furnace slag) 34–55 1.5–10 [146,287] 21 [289]
Table 10
Method for carbonation of different solid waste.
Waste Condition Method Ref.
RCA RH=70 % •Waste was treated with pure CO
2
in
a pressured vessel.
•A Saturated NaCl solution was used
to maintain the humidity.
[290]
CO
2
conc.=100 %
Pressure=2 bar
BFS CO
2
conc. =100 % •Reaction proceeded in a batch
reactor.
•Calcium was extracted by an acidic
solution.
•Precipitated by stirring
600–700 rpm for almost 2 hrs. in the
presence of CO
2
gas and NaOH
solution.
[286]
Temp.=70 ºC
Pressure=40 bar
Acidic sol.=20%
EAF CO
2
conc. =100 % •Carbonation proceeded in the
stainless-steel reactor.
•A Saturated NaCl solution was used
to maintain RH
•Maintain liquid to solid ratio of
0.4 L/kg
[280]
Temp.=50 ºC
Pressure=10 bar
RH =75 %
MSW-
BA
Temp =30 ºC •The reaction proceeded in stainless
steel pressurized reactor
•100% CO
2
and 30 ºC temperature
for almost 24 hrs.
•Maintain liquid to solid ratio of
0.3 L/kg
[279]
CO
2
conc.=100 %
Pressure =10 bar
APC/
MSW-
FA
Temp.=200–500 ºC •Carbonation proceeded in a mufe
furnace
•Constant CO
2
100% owed for 6
hrs.
•Ranging the temperature from 200
to 500ºC
[291]
CO
2
conc.=100 %
BM RH =75 % •The reaction proceeded in a reactor
vessel
•100%CO
2
atm and 2 bar pressure
were maintained.
[206]
CO
2
conc.=100 %
Pressure =2 bar
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
12
diverted from landlls [151,206,217]. A total of 350,000 tons of
aggregate are now produced in the United Kingdom each year using this
technology, and this number will grow to over 750,000 tons in the next
ve years [218]. In April 2017, Carbon8 Systems received the UK’s
highest corporate honor award (Queen’s Award) for its breakthrough
technology [219].
Carbon8 demonstrated the rst CO2ntainer project in 2018 at a
cement factory owned by Cement Roadstone Holdings (CRH) in Mis-
sissauga, Ontario. The project demonstrated direct CO
2
capture from
ue gases and the potential to produce two commercially viable prod-
ucts, i.e., mineral-rich fertilizers and lightweight aggregates [220]. In
the CO2ntainer, the volume of trash that will be processed corresponds
to a xed place’s trash output (8000–12,000 Mt/year), eliminating the
transportation of waste materials and the emissions of CO
2
. In addition
Fig. 7. No. of patents published by different companies with respect to the year [306].
Table 11
Status of selected Commercialized technologies.
Technology CO
2
sequestration method TRL CO
2
uptake Location Patent led & year Ref.
Carbon8 Permanent capture of CO
2
through ACT 9 100–200 kg CO
2
/ton of
aggregate
UK U.S.Patent No. 10,343,199, 2019 U.S.
Patent No. 20190119158, 2019
[213,214]
Carbon Cure Injection of CO
2
in the concrete mix. 8–9 161713 MT CO
2
save till
now
UK,
Canada
U.S.Patent No. 8845,940, 2014
U.S. Patent No. 9492,945, 2016
U.S.Patent No. 9376,345, 2016
U.S.Patent No. 10,570,064, 2020
[228–230,
292]
Solidia CO
2
curing cement concrete 8 1.5 gigatons of CO
2
sequestrated/year &
250–300 kg CO
2
/ton of
cement.
USA,
Canada
U.S.Patent No. 9221,027, 2015
U.S.Patent No. 10,016,739, 2018
U.S.Patent No. 10,668,443, 2020
[293–295]
Carbstone Developed high-quality materials by adding
CO
2
from ue gas to steel slag
9 180–200 g CO
2
/kg of steel
slag
Belgium US Patent No. 8709,151, 2014
U.S. Patent Application 14/354,024,
2014
[296,297]
BluePlanet Capture CO
2
is coated over the calcium rich
substrate to form aggregate
6–7 440 kg CO
2
/ton of
aggregate
California
USA
U.S. Patent No. 9993,799, 2018
U.S. Patent No. 10,766,015. 2020
U.S. Patent No. 9714,406, 2017
U.S. Patent 10,197,747, 2019
[298–301]
Carbicrete Carbonation of steel slag to replace cement
(cement free concrete)
6–7 200 kg CO
2
/day Canada U.S. Patent No. 10,112,871, 2018
U.S. Patent No. 10,633,288, 2020
[302,303]
Calera
corporation
Carbonated precipitates from CO
2
in water/
brines
8–9 3.4MT CO
2
/year & 460 kg
CO
2
/ton
USA U.S.Patent No. 7887,694, 2011
U.S. Patent No. 8333,944, 2012
U.S.Patent No. 7771,684, 2010
U.S. Patent 8006,446, 2011
[222,223,304,
305]
Fig. 8. Flow Chart of Carbon8 aggregate production [215].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
13
to precast concrete blocks, pipe bedding, and road sub-base, the proc-
ess’s outputs can be used in high-value goods like lightweight ooring
and green roong substrates or as fertilizers according to the source of
the industrial waste. The Carbon8 company announced its rst global
licensing agreement with a signicant French cement company in 2019
[220].
Both Carbon8 and CEMEX Systems recognize mineralization’s po-
tential as a carbon sink, and they have partnered to develop a line of low-
carbon building products. This technology can be applied to the pro-
duction of byproducts as well as to the production of alternative ag-
gregates and cementitious materials [221]. Fig. 9 illustrates some
carbon8 facts.
4.2. Calera corporation
Calera is a Los Gatos, CA-based startup company which develops a
new carbon capture system wherein mineral carbonate is converted into
a stable carbonate slurry that can be used to make cement-based ma-
terials or building materials [222,223]. The ue gas reacts with alkaline
solutions rich in Ca or Mg to form a thermodynamically stable CaCO
3
solid. They further used carbonate as a cement building material and
Supplementary Cementitious Materials (SCM) (Fig. 10) [134]. This
process has offset carbon emissions compared with traditional cement
production and generated positive revenue. In a cost-analysis of carbon
capture and storage, Charles Kolstad found that the Calera process
would be the cheapest way to retrot an existing coal-red power plant
to capture CO
2
[224,225]. A research team at Calera has identied re-
gions in the United States and China that may have sufcient alkalinity
and calcium for the process. A series of projects are now being developed
in these areas. Calera’s technology might prove useful in developing
nations, such as China and other countries where the cement and power
industries are growing rapidly [226].
A demonstration facility developed by Calera in Moss Landing, Cal-
ifornia, can capture 30,000 tons of CO
2
per year, equivalent to the
efuent of a 10-megawatt natural gas power plant. Using ue gas from a
100-megawatt output, the company claims that this facility can produce
almost 550,000 tons of valuable construction materials annually from
CO
2
[227]. According to the company, using Calera ne and coarse
aggregate creates the most carbon-neutral concrete. Portland
cement-based concrete has a 600 lb CO
2
/yd
3
. Reducing Portland cement
with y ash (50%) decreases its carbon footprint by 300 lb CO
2
/yd
3
.
Replacing the natural ne and coarse aggregate with Calera ne and
coarse aggregate reduces the carbon footprint by 1146 lb CO
2
/yd
3
(Table 12) (Fig. 11). In 2009, Calera SCM replaced 20 % of OPC in the
US, resulting in a decrease in cement output from 75 Mt/year to
60 Mt/year, reducing CO
2
emissions by roughly 13 Mt/year. With
Calera SCM replacing 20 % of OPC in China, cement output would be
reduced from 1.4 Gt/year (2009) to 1.12 Gt/year, resulting in a
246 Mt/year CO
2
emissions reduction [226].
4.3. CarbonCure
A process developed by CarbonCure (Nov. Scotia, Canada) acceler-
ates concrete curing and enhances strength by directly injecting CO
2
into
the mixture (Fig. 12) [228–230]. Injection of CO
2
accelerated the hy-
dration and strength of the concrete mix without altering its properties.
The initial and nal setting times were accelerated by 95–118 min (25 %
time reduction) and 103–126 min (23 % time reduction), respectively
[231]. The reaction of mature concrete with CO
2
results in shrinkage,
decreased pH, and corrosion induced by carbonation. Fresh concrete
does not undergo the same effects as carbonated concrete. The strength,
absorption, chloride permeability, and freeze-thaw performance of
precast or masonry concrete improved after exposure to early-age
carbonation [232]. It is possible to reduce cement without
Fig. 9. Facts of Carbon8 [213,214].
Fig. 10. Process ow diagram of Calera corporation technology [134].
Table 12
A comparison of different concrete mixes illustrates different formulations in lb.
CO
2
/yd
3
concrete to reduce the carbon footprint in the concrete product via
offsetting and CO
2
sequestration [226].
Ordinary Portland concrete
Ingredient Ordinary
Portland
cement
Water Fine
aggregate
Coarse
aggregate
Total
lb. CO
2
/
yd
3
concrete
494.1 2.8 16.9 23.4 537
High volume y ash concrete
Ingredient Ordinary
Portland
cement &
Fly ash
Water Fine
aggregate
Coarse
aggregate
Total
lb. CO
2
/
yd
3
concrete
247.0
&12.7
2.7 15.9 23.4 302
Carbon native concrete (rst carbon native concrete)
Ingredient Ordinary
Portland
cement &
y ash
Water Calera
SCM
Calera
ne
aggregate
Calera
coarse
aggregate
Total
lb. CO
2
/
yd
3
concrete
269.1 &
5.1
2.7 -50.9 -562.5 -810.0 -1146
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
14
Fig. 11. Comparing concrete mixes lb. CO
2
/yd
3
of 100% OPC, 50% replacement by y ash and 100% Calera aggregate to offset and sequester CO
2
[226].
Fig. 12. Chemistry of CarbonCure process [228–230].
Fig. 13. Carbon Cure technology produces reduced cement content concrete without sacricing the compressive strength [134].
Table 13
CarbonCure mission by 2030 [233].
CarbonCure for ready
mix
CarbonCure for reclaimed
water
CarbonCure for masonry &
precast
CarbonCure for recycled
aggregate
Total CO
2
reduced
CO
2
sequestered 4.2 65.3 0.4 95.8 166
Reduce cement
impact
126.1 229.6 12.3 – 368
Net Impact 130.3 294.9 12.7 80.7 519
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
15
compromising its compressive strength through performance improve-
ment by carbonation. Adding CO
2
to a concrete mix would restore
compressive strength after a reduction of 7–8 % cement (Fig. 13), and
the CO
2
emissions are also reduced by approximately 150 kg/m
3
[134].
Through CarbonCure, the concrete industry strives to reduce CO
2
emissions by 500 million tons per year by 2030 (Table 13) [233].
Several CarbonCure ready-mix concrete producers are located in
Alberta; these plants produce 22 million m
3
of concrete with 8.3 million
tons of CO
2
and save 354 million tons of CO
2
emissions. The Calgary
Airport location, where 50.5 tons of CO
2
were utilized, produced
70,535 m
3
of concrete and avoided 425 tons of cement. Over 25 years,
raised in concrete production to 55 million m
3
, the utilization of CO
2
was up to 21 million tons, and 884 million tons of CO
2
emissions were
saved [234]. The life cycle assessment (LCA) of CarbonCure shows that
this process reduces the net CO
2
emission of around 18 kg/m
3
of con-
crete (Table 14) [235].
4.4. Solidia
In 2008, Solidia Technologies was founded in Piscataway, New
Jersey, USA, a company offering green building materials that use CO
2
[236]. The company developed Solidia Cement and Solidia Concrete,
which reduce net CO
2
emissions compared to traditional construction
materials [237]. Solidia Cement is a nonhydraulic cement containing
less lime minerals than ordinary cement, primarily composed of
wollastonite (CaOSiO
2
) and rankinite (3CaO
2
SiO
2
). In contrast, ordinary
cement is composed of alite (3CaOSiO
2
) and belite (2CaOSiO
2
) [238].
Since less lime is required per cement unit, less limestone must be cal-
cinated, reducing emissions by approximately 30 % [239]. Solidia
Cement clinker is manufactured at about 1200 ºC, about 250 ºC lower
than Portland cement clinker, which is sintered at a temperature of
1600 ºC. The lower calcination temperature reduces thermal fuel con-
sumption, reducing emissions by 30 % [239]. Ordinary cement produces
around 500 kg CO
2
/ton in process emissions and another 300 kg
CO
2
/ton in thermal fuel combustion, totaling 800 kg CO
2
/ton. Solidia
Cement, on the other hand, emits 550 kg CO
2
/ton (process & thermal)
[240].
Concrete manufactured with Solidia Cement is characterized by its
patented curing method and formula, consisting of ne and coarse
aggregate, CO
2,
and Solidia Cement. Solidia cement reacts only with
CO
2
, not with water, like ordinary cement. CO
2
interacts with Solidia
Cement during curing to form thermodynamically stable calcium car-
bonate. Calcite polymorphs of CaCO
3
and silica gel are formed during
the carbonation reaction and are crucial for developing strength within
the concrete (Fig. 14) [238]. In contrast to ordinary concrete, Solidia
Concrete cures in 24 h, saving cement and concrete producers time,
money, and inventory space. During the curing process of Solidia con-
crete, it can sequester 290–310 kg of CO
2
per ton of Solidia cement used
in Solidia concrete [240].
In comparison with the Solidia, carbonation of natural concrete over
40 years sequesters up to 48% of the process emissions from the cement
used in the concrete (non-energy) (Fig. 15) [241]. As previously stated,
500 kg of CO
2
emissions per ton of ordinary cement, implying that
natural sequestration will eventually sequester 240 kg of CO
2
per ton of
cement used in the concrete, approximately the same amount as Solidia
during the curing process today (Fig. 15). [241]. The Solidia technology
has shown it can save 1.5 Gt of CO
2
, save 3 trillion liters of fresh water
every year, reduce the cement industry’s energy consumption by 67
million tons of coal, and remove 100 million tons of landlls each year
[237].
LafargeHolcim and Solidia Technologies signed a Joint Development
Agreement in August 2013 and a Commercial Agreement in January
2015 to bring Solidia cement and concrete solutions to market. With a
novel CO
2
curing method, they can reduce the overall carbon footprint
of concrete by up to 70 % compared to conventional Portland cement
concrete [242]. The LafargeHolcim group’s Whitehall (USA) and Pecs
(Europe) facilities conducted the rst two non-hydraulic cement
manufacturing campaigns. The rst precast (in the United States) was
manufactured using Solidia cement and concrete solutions. Durability
testing and characterization are proceeding in compliance with PC re-
quirements in the United States and the European Union [242].
4.5. Blue planet
Blue Planet has developed and commercialized a scalable, econom-
ically and technically sustainable climate change mitigation solution.
Blue Planet manufactures articial ne and coarse aggregate by mineral
carbonation, similar to the natural formation of ooids [243,244].
Demolished concrete, cement kiln dust, steel slag, y ash, bauxite res-
idue, and silicate rocks are calcium-rich geomass sources, which pro-
duce a carbon-sequestering coating aggregate that is 44% by mass CO
2
(Fig. 16) [245]. Blue Planet concrete’s aggregate absorbs so much CO
2
in
concrete that the whole structure becomes carbon-negative [245]. Each
ton of CO
2
-sequestered limestone prevents the accumulation of 440 kg
of CO
2
. The Blue Planet process reduces CO
2
emissions by 100 kg per ton
of concrete. This equates to about 220 kg CO
2
/m
3
of concrete. Consid-
ering a cement content of 320 kg/m
3
of concrete, this results in a
reduction of about 0.65 tons of CO
2
per ton of Portland cement, and
would therefore compensate for the raw material CO
2
emissions of the
cement production [246].
The company says employing this aggregate is the most efcient
method of providing carbon-neutral concrete. A cubic yard of standard
Portland cement-based concrete has a carbon footprint of around 600
pounds of embodied CO
2
. Reducing the cement component of a mixture
with SCM (supplementary cementitious material, such as y ash) re-
duces the carbon footprint by just 300 lb/yd
3
. By substituting traditional
ne and coarse aggregate with Blue Planet synthetic limestone aggre-
gate, it is possible to offset the carbon footprint of Portland cement by
1320 lb/yd
3
. If the Portland cement in the mixture comes from a cement
kiln where Blue Planet has collected CO
2
, the normal 600-pound carbon
footprint of cement in the mix is excluded from the computation. The
total CO
2
offset per cubic yard of concrete is 1320 pounds of industrial or
atmospheric CO
2
sequestered in aggregate and 600 pounds captured
during Portland cement manufacturing, resulting in the total 1920 lb
CO
2
offset per cubic yard of concrete (Fig. 17) [247,248].
San Francisco Bay Aggregates is planning and constructing the rst
commercial plant using Blue Planet Systems’ patent-protected carbon
mineralization process. The plant will gather CO
2
from the nearby Los
Medanos Energy Center and permanently deposit it in synthetic lime-
stone aggregate via mineralization. SF Bay Aggregates is at the forefront
of developing this paradigm-shifting technology and will provide
carbon-negative aggregate to Bay Area projects by 2022 [249]. Blue
Planet technology was used to construct a temporary boarding area at
San Francisco International Airport. MC and Blue Planet will perform a
feasibility study on potential Silicon Valley use until the scal year 2021,
following which the partners hope to make the technology commercially
accessible [250]. Blue Planet has launched a pilot program and Sulzer to
reduce CO
2
emissions and reshape the cement industry sustainably.
Sulzer Chemtech, the industry leader in separation and mixing tech-
nology, is creating an efcient and effective carbon capture unit at Blue
Planet’s pilot plant, which is now under construction in Pittsburg,
Table 14
Life cycle assessment of concrete production by CarbonCure [235].
CO
2
emission g CO
2
/m
3
concrete
Gas processing & transport 55.5
Equipment production & operation 9.3
Avoided from Materials transport -123.6
CO
2
sequestered -289.1
Avoided from cement reduction -17584.8
Total -17932.7
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
16
Fig. 14. Mechanism of carbonation in Solidia concrete [238].
Fig. 15. Comparing CO
2
emissions from ordinary concrete and Solidia at different stages of concrete life (net thermal +process) [241].
Fig. 16. A ow chart showing the process of manufacturing coated aggregates [245].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
17
California, United States, and will capture emissions from a nearby
natural gas-red power plant. The plant will use Sulzer Chemtech’s
technology to achieve high CO
2
absorption performance with minimal
energy usage [248,251].
4.6. Carbstone
In the 1990s, the slag was dumped after being separated from the
ore. Nowadays, it is converted into bricks by carbonation. Slag from
steel mills is rich in magnesium and calcium silicates, which convert to
high-quality products when reacted with captured CO
2
(Fig. 18) [252,
253]. The steel industry in Belgium generates approximately 500,000
tons of steel slag per year [254]. The recycling company Orbix discov-
ered in 2004 that CO
2
and H
2
O could harden the nest steel slag par-
ticles. Orbix, a company specializing in slag processing in the steel
industry, recovers residual steel. Carbonation (Fig. 18) involves three
steps: pre-handling of slag; forming the building blocks with a hydraulic
press at a pressure between 75 and 609 kg/cm
2
and subsequent com-
pacting to achieve the desired porosity; and diffusion of CO
2
into slag at
high temperatures and pressures (0.5–10 MPa) in autoclaves [211,255,
256]. In this reaction, CO
2
is reacted with calcium silicate to form cal-
cium carbonate, an effective substitute for cement (a binding material in
the building block) that effectively sequestered CO
2
for a long time
[257]. As an alternative to conventional concrete-making, this block has
a negative carbon footprint (200 g CO
2
/kg slag less than conventional
concrete-making) [258].
A patented process developed in partnership with the Flemish
Institute for Technological Research (VITO) led to the founding of
Carbstone Innovation in 2009. Although the carbonation process is
straightforward, it still took us almost ten years to rene the basic
technology. Towards the end of 2013, a pilot plant was built in Farci-
ennes, near Charleroi, to produce large blocks. With this facility in
Farciennes - Walloon Municipality, Slag from various sources will be
processed and used to produce high-value construction products
through carbonation [256]. In 2016, Carbstone Innovation signed its
rst deal with RuwBouwGroep CRH of the Netherlands, which produces
the stones in its factories. Since the market for building materials is
highly competitive, they are partnering with a company that can bring
the carbstone to market in the most efcient possible way. In 2017,
carbstone aimed to set up a production installation for the Belgian
market. At the same time, it developed a license to commercialize the
technology globally [256].
5. Future challenges
Over the past 30 years, the technology of CO
2
sequestration by
mineral carbonation has developed signicantly. The fundamental
characteristics of mineral carbonation have been discovered to acquire
mineral carbonation. The carbonization efciency can be improved by
Fig. 17. Comparing four concrete mixes shows the consequences in lb. CO
2
/yd
3
of using different formulations to offset and sequester CO
2
[252,253].
Fig. 18. Schematic representation of the accelerated carbonation of stainless-
steel slag [252,253].
M. Hanifa et al.
Journal of CO2 Utilization 67 (2023) 102292
18
varying various parameters, such as high CO
2
pressure, high tempera-
ture, ne particle size, and adding a catalyst. Despite the apparent ad-
vantages of mineral carbonation over other geological CO
2
storage
technologies, the following research gaps need to be addressed:
1. Reducing the total emission of CO
2
is one of the most important goals
that must be addressed broadly.
2. Additional energy consumption during mineral carbonation leads to
direct or indirect emissions of CO
2
, which must be addressed while
calculating the CO
2
sequestration in a particular process.
3. The life cycle assessment technique should be introduced to evaluate
mineral carbonation and optimization.
4. The mineral carbonation mechanism has not yet been precisely
established. Further study of mineral structural transitions and
phases during CO
2
mineral carbonation is possible with the devel-
opment of in-situ tools such as XRD and IR techniques.
6. Conclusions
The purpose of this paper was to review CO
2
capture technologies in
the cement industry and the utilization of CO
2
in the construction in-
dustry. In addition, the number of commercialized CO
2
sequestration
technologies was discussed. The following are the main conclusions:
1. Based on the current climate situation, the development of different
methods for mitigation and adaptation is essential to meet the 1.5 ◦C
targets by the end of the century.
2. CO
2
capture methods used in the cement plant included amine
scrubbing with $84.1/t CO
2
and oxy-combustion with $44.1/t CO
2
,
roughly half that of MEA scrubbing. Calcium looping in the tail end
and integrated congurations were approximately $54.6/t CO
2
and
$59.7/t CO
2,
respectively.
3. Mineral carbonation is one of the most promising technologies for
reducing CO
2
emissions. The process has the double benet of
reducing CO
2
emission and utilizing solid wastes in the carbonation
to produce certain value-added products.
4. Indirect carbonation using extracting agent NH
4
Cl is better for CO
2
sequestration than extracting agents such as HCl, HNO
3
, and
CH
3
COOH. An advantage of using NH
4
Cl is that it is easily regen-
erated and does not need basic reagents during the precipitation of
calcium carbonate.
5. CO
2
uptake by mineral carbonation of different cement-based ma-
terials was 7–25 %. Both hydration products (Ca(OH)
2
and C-S-H)
and unhydrated cement clinker (C
3
S and C
2
S) react with CO
2
. The
uptake of CO
2
by γ-C
2
S (non-hydrated) was higher than by β-C
2
S. On
the other hand, C
3
A had a minimal reactivity with CO
2
, and the study
of C
4
AF with CO
2
is still unavailable in the literature.
6. Carbonation of RA has signicantly reduced water absorption,
porosity and crushing value while increasing the apparent density.
Concrete prepared with CRA has better compressive strength and
elastic modulus, with increased solid phase volume by 11.8 % than
untreated RA. RA has a particle size between 5 and 20 mm seques-
ters, almost 7.9 Kg CO
2
per ton.
7. Carbonation is maximum in those solid wastes with a higher con-
centration of CaO content (but the phase of the mineral is also
important in which calcium is bonded), more surface area and op-
timum relative humidity of 50–70 %. Carbonation decreased the pH
of solid waste from the threshold value (11.5), making them less
hazardous.
8. Currently, waste-derived construction products are cost-competitive
on the market. Different companies have successfully produced
construction materials from different solid wastes by mineral
carbonation. Articial aggregates completely replace the use of
natural stone in a variety of construction applications.
Declaration of Competing Interest
The authors declare the following nancial interests/personal re-
lationships which may be considered as potential competing interests:
Mohd Hanifa reports nancial support was provided by University
Grants Commission. Usha sharma reports nancial support was pro-
vided by Council for Scientic and Industrial Research.
Data availability
No data was used for the research described in the article.
Acknowledgments
Authors, Mohd. Hanifa and Usha Sharma thank UGC, New Delhi, and
CSIR, New Delhi, India, for nancial support.
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