Potential for CO 2 Mineral Carbonation in the Paleogene Segamat Basalt of Malaysia

: Geological storage of carbon dioxide (CO 2 ) requires the host rock to have the capacity to permanently store CO 2 with minimum post-storage monitoring. Mineral carbonation in geological formations is one of the most promising approaches to CO 2 storage as the captured CO 2 is converted into stable carbonated minerals (e.g., calcite and magnesite). In this study, we investigated the geochemical and mineralogical characteristics of Segamat basalt in the Central Belt of Malaysia and evaluated its potential for mineral carbonation by using laboratory analyses of X–ray ﬂuorescence (XRF), X–ray di ﬀ raction analysis (XRD) and petrographic study. The XRF results showed that Segamat basalt samples contain a number of elements such as Fe (21.81–23.80 wt.%), Ca (15.40–20.83 wt.%), and Mg (3.43–5.36 wt.%) that can react with CO 2 to form stable carbonated minerals. The XRD and petrographic results indicated that Segamat basalt contains the reactive mineral groups of pyroxene and olivine, which are suitable for the mineral carbonation process. The results of this study could help to identify the spatial distribution of elements and minerals in the Segamat basalt and to assess its mineral carbonation potential for geological storage in Malaysia. process of mineral carbonation, it is essential to understand their geochemical and mineralogical characteristics. Several reports have shown that only a few basaltic types are suitable to serve as host rocks in CO


Introduction
The atmospheric concentration of carbon dioxide (CO 2 ), as well as other greenhouse gases (GHGs), has become a central issue for researchers due to its significant effect on global warming [1][2][3][4]. The objective of a carbon capture storage (CCS) approach is to help decrease the amount of carbon dioxide (CO 2 ) that is emitted globally from industrial areas through the capture of the produced CO 2 . CCS is considered to be one of the safest ways of achieving this, and storing CO 2 in geological formations, such as in depleted oil and gas reservoirs is one of the proposed solutions in CCS strategies [1,5,6]. These reservoirs used to contain hydrocarbon at high pressure for a certain geological period, which proves that they have the potential to be used for the storage of CO 2 [7]. However, there are some challenges associated with the CCS technique. The most critical issue is the possibility of CO 2 leakage. Understanding the geochemical characterization of the geological formation is crucial to ensure the permanency of the CO 2 storage in the mineral interaction of the host rock with the injected CO 2 [8,9].

Geological Setting
The Malay Peninsula forms an integral part of the SE Asian continental core of Sundaland [25,26]. It comprises two tectonic blocks: the Sibumasu Terrane in the west and the Sukhothai Arc in the east of the Malaya Block [27]. As shown in Figure 1, the Malay Peninsula is characterized by three north-south trending longitudinal belts, including the Western Belt, Central Belt, and Eastern Belt [27,28].
Flows of alkaline basaltic lava has occurred twice in the Malay Peninsula. These have been reported around Kuantan and in the neighborhood of Pekan Jabi in Segamat [29][30][31]. These volcanic rocks are named after the localities as Kuantan basalt and Segamat basalt. The Segamat volcanism includes both lava and shallow intrusive rocks (Figure 1), and individual lava flows vary from 18 m to 42 m in thickness [29,31]. Segamat basalt was formed as post-orogenic flows within the Central Belt of the Malay Peninsula during the Cenozoic Era ( Figure 1). It erupted in the Early Tertiary period and has been dated as Palaeocene (62 ± 3 Ma) by K-Ar dating [32], during a time in which the Malay Peninsula was considered as a tectonically stable block [33]. The main area of Segamat basalt outcrops is located in the State of Johor, Malaysia ( Figure 1).

Field Occurrence of Segamat Basalt
Segamat basalt presents as dark green to black colored outcrops ( Figure 2a) and in the field, it is mainly characterized by its fine-grained porphyritic texture. Segamat basalt contains very fine groundmass with visible phenocrysts of light-green colored minerals (Figure 2b). Olivine and pyroxene occur as the greenish phenocrysts in the groundmass rock specimen. These greenish phenocrysts have undergone a relatively slow rate of cooling at the near surface before reaching the surface. The early-formed phenocrysts represent basic-ultrabasic olivine/pyroxene minerals. The dominant fine groundmass indicates that there was a second phase of relatively fast cooling during the extrusion of the magma to the surface and the atmosphere.

Field Occurrence of Segamat Basalt
Segamat basalt presents as dark green to black colored outcrops ( Figure 2a) and in the field, it is mainly characterized by its fine-grained porphyritic texture. Segamat basalt contains very fine groundmass with visible phenocrysts of light-green colored minerals (Figure 2b). Olivine and pyroxene occur as the greenish phenocrysts in the groundmass rock specimen. These greenish phenocrysts have undergone a relatively slow rate of cooling at the near surface before reaching the surface. The early-formed phenocrysts represent basic-ultrabasic olivine/pyroxene minerals. The dominant fine groundmass indicates that there was a second phase of relatively fast cooling during the extrusion of the magma to the surface and the atmosphere.
As shown in Figure 2a, the presence of calcite veins has been documented in the Segamat basalt outcrops. The calcite veins have sharp and straight edges with minimal irregularity on the contact As shown in Figure 2a, the presence of calcite veins has been documented in the Segamat basalt outcrops. The calcite veins have sharp and straight edges with minimal irregularity on the contact surfaces with the host rock. The genesis of the calcite veins in Segamat basalt is associated with its hydrothermal origin [35]. surfaces with the host rock. The genesis of the calcite veins in Segamat basalt is associated with its hydrothermal origin [35].

Sample Preparation and Experimental Analysis
The following analyses were conducted to obtain an overview of the characteristics of the Segamat basalt samples. Sampling was carried out to characterize the host rock of the Segamat basalt with regard to its geochemical and mineralogical properties. Standardizing the grain size is essential in order to prevent biased results regarding the elements in these grain, and reducing the grain size enhances the precision of the analyses [36,37]. Therefore, the samples of Segamat basalt were crushed and prepared in a powder form with a grain size of <63 µm, which was determined by a MASTERSIZER-2000 from Malvern Instruments. The samples were studied by a microscope (Zeiss Axioskop-40, Oberkochen, Germany) to study the petrography of the Segamat basalt samples. To this aim, thin sections were prepared by slabbing and polishing the samples before they were glued onto the glass. Then, thin sections were examined under a plane-polarized light (PPL) and crosspolarized light (XPL) microscope (Zeiss Axioskop-40, Oberkochen, Germany), equipped with a Jenoptik ProgRes CF Scan microscope camera at the Southeast Asia Carbonate Research Laboratory, Universiti Teknologi PETRONAS. The PPL and XPL were used to identify the minerals and determine the textural components of the samples, respectively.
The powdered rock samples were analyzed to determine the major elemental composition of the Segamat basalt by using X-ray fluorescence (XRF) S8 TIGER Series 2 from Bruker HighSense Technology. The samples were ground to a grain size of <63 µm and were then combined with a cellulose wax mixture to produce homogeneous samples. Interaction between the atoms of the sample and radiation from the XRF instrument made the analysis of the chemical composition possible. Subsequently, the Segamat basalt sample was ionized by radiation of short wavelength and high-energy. A tightly-held inner electron was forced out when enough radiation was consumed. Then, an outer electron was replaced by an inner one. After that, the energy was released because the binding energy of the inner electron was decreased in comparison to the outer one. Moreover, because the amount of energy emitted was less than the initial incident X-rays, it is labeled as "fluorescent radiation". A transition between definite electron orbitals in a specific element was

Sample Preparation and Experimental Analysis
The following analyses were conducted to obtain an overview of the characteristics of the Segamat basalt samples. Sampling was carried out to characterize the host rock of the Segamat basalt with regard to its geochemical and mineralogical properties. Standardizing the grain size is essential in order to prevent biased results regarding the elements in these grain, and reducing the grain size enhances the precision of the analyses [36,37]. Therefore, the samples of Segamat basalt were crushed and prepared in a powder form with a grain size of <63 µm, which was determined by a MASTERSIZER-2000 from Malvern Instruments. The samples were studied by a microscope (Zeiss Axioskop-40, Oberkochen, Germany) to study the petrography of the Segamat basalt samples. To this aim, thin sections were prepared by slabbing and polishing the samples before they were glued onto the glass. Then, thin sections were examined under a plane-polarized light (PPL) and cross-polarized light (XPL) microscope (Zeiss Axioskop-40, Oberkochen, Germany), equipped with a Jenoptik ProgRes CF Scan microscope camera at the Southeast Asia Carbonate Research Laboratory, Universiti Teknologi PETRONAS. The PPL and XPL were used to identify the minerals and determine the textural components of the samples, respectively.
The powdered rock samples were analyzed to determine the major elemental composition of the Segamat basalt by using X-ray fluorescence (XRF) S8 TIGER Series 2 from Bruker HighSense Technology. The samples were ground to a grain size of <63 µm and were then combined with a cellulose wax mixture to produce homogeneous samples. Interaction between the atoms of the sample and radiation from the XRF instrument made the analysis of the chemical composition possible. Subsequently, the Segamat basalt sample was ionized by radiation of short wavelength and high-energy. A tightly-held inner electron was forced out when enough radiation was consumed. Then, an outer electron was replaced by an inner one. After that, the energy was released because the binding energy of the inner electron was decreased in comparison to the outer one. Moreover, because the amount of energy emitted was less than the initial incident X-rays, it is labeled as "fluorescent radiation". A transition between definite electron orbitals in a specific element was characterized by the energy of Minerals 2020, 10, 1045 5 of 14 the emitted photon, which suggested that XRF analysis could be applied to identify the concentration of the elements in the Segamat basalt sample.
X-ray diffraction (XRD) analysis was also applied to identify the mineral phases in the Segamat basalt samples. Thus, 1 g of each sample with a grain size of <63 µm was dried in an oven (at 45 • C) for 24 h and then introduced into the XRD instrument. The scan speed was set at 1 • /min from 5 • to 50 • under 40 kV/40 mǺ X-ray tube. The XRD patterns were attained from a Rigaku Geiger flex D-MAX/A diffractometer with the Cu-Kα radiation along with a wavelength of 1.54Ǻ [4].
Field-emission scanning electron microscopy (FESEM, SU8030 Hitachi) was applied to assess the morphology of the grains and identify the surface roughness. The FESEM was linked with an energy-dispersive X-ray (EDX) spectroscopy to find the elemental composition of the sample at a specific surface location [38]. The FESEM analysis was performed at 2.2 nm (1 kV) and a 1 nm (15 kV) probe current. The Segamat basalt samples with a grain size of <63 µm were coated with gold and sputtered in the environment with an inert argon for the FESEM analysis. The samples were also qualitatively analyzed in terms of their chemical and crystalline phases by using the FESEM in combination with the EDX technology.

Geochemical Analysis
Tables 1 and 2 provide an overview of the significant elements found in the four samples of Segamat basalt by XRF analysis. As shown in Table 1 [4,7,11]. What is notable about these results is that Segamat basalt has a high percentage of reactants, and thus it has remarkable potential for the process of CO 2 mineral carbonation.    Figure 3g,f show that the minerals of olivine, orthopyroxene, and feldspar appear as phenocrysts. Figure 3 shows that the texture of Segamat basalt is porphyritic, it contains fine groundmass and shows phenocrysts as the minerals identified above. The porphyritic texture that is shown under microscope is similar to that observed in the sample shown in Figure 2b. The average porosity of the samples is 16%, based on the study of more than 75 thin sections of the Segamat basalt.  Tables 1 and 2, the XRF results strongly support the mineralogical identification of oxides and elements that are considered to have potential in the process of CO 2 mineral carbonation.  Tables 1 and 2, the XRF results strongly support the mineralogical identification of oxides and elements that are considered to have potential in the process of CO2 mineral carbonation.  30.7° refer to microcline (KAlSi3O8) while 21.09°, 23.6° and 27.0° donate orthoclase (KAlSi3O8). Both microcline and orthoclase are categorized as alkali feldspars. Also, the plagioclase group presents as anorthite (Ca(Al2Si2O8)) at the 2θ position of 22.0°, 23.7°, 28.1°, and 30.6°. The peaks of 15.78° and 25.97° donate analcime (Na(AlSi2O6)·H2O) as the zeolite group. A shown in Tables 1 and 2, the XRF results strongly support the mineralogical identification of oxides and elements that are considered to have potential in the process of CO2 mineral carbonation.      The XRD results from the thin sections were consistent with the XPL results, which clearly showed the texture of the Segamat basalt including orthopyroxene, olivine, and augite (see Figure 3). Aside from that, other phenocrysts such as calcite, feldspar, and chlorite minerals were identified in the thin sections, and this was also supported by the XRD analysis (see Figures 4-7).

Segamat Basalt Potential for CO2 Mineral Carbonation
To determine whether the selected samples are suitable for the process of mineral carbonation, it is essential to understand their geochemical and mineralogical characteristics. Several reports have shown that only a few basaltic types are suitable to serve as host rocks in the CO2 mineral carbonation The XRD results from the thin sections were consistent with the XPL results, which clearly showed the texture of the Segamat basalt including orthopyroxene, olivine, and augite (see Figure 3). Aside from that, other phenocrysts such as calcite, feldspar, and chlorite minerals were identified in the thin sections, and this was also supported by the XRD analysis (see Figures 4-7).

Segamat Basalt Potential for CO 2 Mineral Carbonation
To determine whether the selected samples are suitable for the process of mineral carbonation, it is essential to understand their geochemical and mineralogical characteristics. Several reports have shown that only a few basaltic types are suitable to serve as host rocks in the CO 2 mineral carbonation process [21,39,40]. The results of this study indicated that the Segamat basalt samples have the proper geochemical and mineralogical properties for applying the CO 2 mineral carbonation process. These properties involve an appropriate content of Fe-, Mg-, and Ca-bearing minerals. The EDX spectrum (Figure 8) shows that the Segamat basalt samples are mainly composed of C, O, Na, Mg, Al, Si, K, Ca, Ti and Fe. Also, Figure 9 indicates that Ca, C, and O were the main elements detected by the EDX analysis. Additionally, the FESEM images show micro-pores ranging from 0.1-1.5 µm in diameter ( Figure 9).
Based on the XRF results (see Table 2), Segamat basalt, as an ultramafic rock, is very suitable for the process of mineral carbonation because it contains a considerable amount of oxides such as CaO (11.20-15.74 wt.%) and MgO (4.14-6.54 wt.%) that can potentially be carbonated. These oxides are favored by divalent reactants to form another carbonate mineral (i.e., calcite and magnesite). Equations (1) and (2) show the reactions of these oxides with CO 2 . The products of these two potential reactants would be calcite (CaCO 3 ) and magnesite (MgCO 3 ).
Equations (1) and (2) show the reactions of these oxides with CO2. The products of these two potential reactants would be calcite (CaCO3) and magnesite (MgCO3).  Moreover, mineral carbonation requires the dissolution of reactive minerals during CO2-rich water interaction with the feedstock. It has been reported that the presence of water can increase the amount of carbonated minerals during the interaction of basalt samples with the injected CO2 [41]. In this regard, the XRD analysis (see Figures 4-7) provides more precise results for identifying the minerals in the samples. It shows that Segamat basalt contains the pyroxene group (enstatite (MgSiO3) and augite ((Ca,Na)(Mg,Fe,Al)(Si,Al)2O6)), and the olivine group (fayalite (Fe2SiO4) and forsterite (Mg2SiO4)), which enhance the mineral carbonation process in the feedstock (see Figure 4). At first, carbon dioxide is dissolved in water causing it to become acidic. When these reactive minerals Moreover, mineral carbonation requires the dissolution of reactive minerals during CO 2 -rich water interaction with the feedstock. It has been reported that the presence of water can increase the amount of carbonated minerals during the interaction of basalt samples with the injected CO 2 [41]. In this regard, the XRD analysis (see Figures 4-7) provides more precise results for identifying the minerals in the samples. It shows that Segamat basalt contains the pyroxene group (enstatite (MgSiO 3 ) and augite ((Ca,Na)(Mg,Fe,Al)(Si,Al) 2 O 6 )), and the olivine group (fayalite (Fe 2 SiO 4 ) and forsterite (Mg 2 SiO 4 )), which enhance the mineral carbonation process in the feedstock (see Figure 4). At first, carbon dioxide is dissolved in water causing it to become acidic. When these reactive minerals react with the carbonated water, the dissolution process occurs and the cations of Ca, Mg, and Fe are released into the water. Later, these leached out cations precipitate into stable carbonated minerals like calcite (CaCO 3 ), magnesite (MgCO 3 ), and siderite (FeCO 3 ) when combined with the dissociated carbonic acid (Equations (3) and (4)

CaO + CO → CaCO
As discussed above, the identification of pyroxene and olivine minerals in Segamat basalt is crucial because these minerals are the prerequisite for further reaction with CO 2 and water, which allows the process of mineral carbonation to occur [19]. Forsterite (Mg 2 SiO 4 ) and anorthite (Ca(Al 2 Si 2 O 8 )) minerals in basalts act as the potential source minerals for CO 2 sequestration. According to Oelkers et al. [19], 5.86 tons of forsterite and 23.1 tons of anorthite are required to sequester 1 ton of carbon dioxide. This means that olivine and pyroxene are more reactive than plagioclases for the process of mineral carbonation. Also, the existence of carbonated minerals such as calcite in the Segamat basalt proves that this feedstock has a natural potential for the process of mineral carbonation during geological time. There is no record in previous studies of the presence of calcite as phenocrysts in Segamat basalt.
Furthermore, the outcrops of Segamat basalt present a potential site for sequestering carbon dioxide. The Segamat basalts are located in Johor Province, Malaysia, with a strong source of CO 2 emissions in this area. The CCS approaches are applicable through the H 2 O-CO 2 interaction to sequestrate CO 2 in the Segamat basalt. As can be seen in the FESEM images (see Figures 8 and 9), the CO 2 mineral carbonation process is increased since pore-space is highly available in the Segamat basalt samples. On the other hand, the Segamat basalts have been formed in the Paleogene period and are relatively less-altered by volcanic exposure, thus they are more feasible in the process of CO 2 mineral carbonation [41]. Furthermore, Koukouzas et al. [41], have calculated the CO 2 storage capacity (SC CO2 ) using Equation (5).
The outcrop volume (V) of the Segamat basalt is 52 km 3 with an area of about 200 km 2 and a depth of 260 m. A potential plot with a volume of 0.0042 km 3 (length 400 m, width 250 m, depth 42 m) was used to estimate the CO 2 storage of the Segamat basalt outcrop. Also, the average porosity (ϕ) of the Segamat basalt samples is 16%. Studies in [42] and [43] have shown that the specific gravity of the carbon dioxide is 400 kg/m 3 at a pressure of 10 MPa and temperature of 50 • C. The CO 2 storage ratio (ε) is 5% [44]. Therefore, the Segamat basalt provides a site that could sequester 91,520 tons of carbon dioxide.

Conclusions
This study was undertaken in order to characterize samples of the Paleogene Segamat basalt in the Central Belt, Malaysia, to assess their potential in the process of CO 2 mineral carbonation. The findings from the petrographic and mineralogical studies indicate that Segamat basalt contains silicate minerals that are well favored in the process of CO 2 mineral carbonation. These are enstatite, augite, fayalite, and forsterite, which can form carbonate minerals (i.e., calcite, magnesite, and siderite) during reaction with CO 2 . The results also show that the Segamat basalt samples have the necessary, appropriate physicochemical characteristics to be considered as potential sites for implementing the CO 2 mineral carbonation approach. Based on these characterizations, Segamat basalt might be considered as having the potential for mineral carbonation either for CO 2 storage purposes or ex situ mineral carbonation feedstock. Therefore, the Segamat basalt could be used in further studies to better understand the process of mineral carbonation in basalts.