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Electrochemical decarbonation (ED) of CaC O 3 is a promising method to reduce C O 2 emissions from limestone calcination for cement manufacturing. Most cement plants are located near accessible deposits of limestone; therefore, the feasibility of ED deployment depends on the efficiency of natural limestone decarbonation, which has variable CaC O 3 content. Accordingly, this research compares the ED efficiency of different limestones ( CaC O 3 content between 84 % and 68 %) and the chemical and physical characteristics of precipitate materials (PM) obtained from this process. The obtained PMs were comprised mainly of Ca OH 2 (~59 %) and had similar particle size distributions . At the same time, the efficiency of Ca OH 2 precipitation, energy consumption, and CaO recovery were comparable to the ED of a pure CaCO 3 reagent (>99 %). The PMs were found to have higher CaO content and lower loss on ignition than the feedstock material , independent of the type of limestone, facilitating the future ED implementation in cement manufacturing. Introduction Cement is the main active compound of concrete. Portland cement contains 95 % clinker, an artificial mineral mainly comprising lime ( CaO ) and other constituent oxides such as silica ( Si O 2 ), aluminum ( A l 2 O 3 ), and iron oxide ( F e 2 O 3 ). The CaO on average makes up between 64 % and 67 % of portland cement by weight, and is usually obtained through thermal calcination of powdered calcareous rocks such as limestone (mainly calcite), or any other rich source of calcium carbonate ( CaC O 3 ) [1]. Calcination is an early stage of the clinkerization process that occurs at a temperature ranging between 800 and 1000 ° C . As shown in Eq. (1), the carbon dioxide ( C O 2 ) produced during calcination is responsible for about 50 % of the C O 2 emissions associated with clinker production, with the remaining balance mainly caused by the burning of fossil fuels. On average, to yield 1 ton of clinker, about 1.16 tons of CaC O 3 must be calcinated, emitting 0.51 tons of C O 2 [2]. CaC O 3 s + Heat → Ca O s + C O 2 g Nowadays, the cement industry is responsible for about 8 % of global C O 2 emissions due to anthropic activities [3]. Several strategies have been implemented to reduce the carbon footprint of the cement industry (e.g., clinker ratio reduction, use of alternative fuels, enhanced energy efficiency of cement kilns), which have had a positive impact on the reduction of C O 2 emissions per ton of cement [[4], [5], [6]]. These strategies have also included alternative clinkers (e.g., belite-calcium sulfoaluminate-ferrite cement) [6] and sources of CaO other than limestone to reduce emissions derived from the calcination process (e.g., recycled cement paste and civil construction waste) [7,8]. However, the effectiveness and widespread adoption of these strategies is frequently limited by the growing demand for cement, concrete performance requirements, and barriers to its large-scale application that, according to Benhelal et al., [9] includes challenges associated with technical, economic, legislation, policy, distribution and raw materials availability. This last point is especially critical since most cement plants are located close to feasible limestone sources [10], and alternative raw materials are not widely available or can be consumed rapidly [9,11]. Currently, the cement industry has not stabilized its C O 2 emissions, which are expected to grow by 4 % by 2050, while cement demands would increase about 15 % [12]. Consequently, great efforts must be made to change current practices if the cement industry wants to achieve its goal of net-zero carbon emissions by 2050. In 2020, Ellis et al. [13] reported an electrochemical method to decarbonate CaC O 3 . The electrochemical decarbonation (ED) process uses a water electrolysis cell and electricity to precipitate calcium hydroxide ( Ca OH 2 ), while yielding valuable gas streams (see Eq. (2)). Whereas post-combustion gases from conventional cement kilns emit high amounts of C O 2 at concentrations of about 25 % [14], their emissions also include dust and other gases (e.g., N O x , S O x ) that affect the efficiency of carbon capture and storage technologies (CCS) [15]. In the ED process, the C O 2 concentration is significantly higher (~67 %) as the gases generated from the anode chamber of the electrolysis cell is a high purity mix of O 2 and C O 2 (1:2 molar ratio) [13], which is beneficial to reduce the energy penalty of CCS implementation and improve their efficiency. In addition, the mix O 2 / C O 2 also can be considered an oxy-fuel which is highly synergistic with the focus on post combustion capture plus oxy-enhanced combustion in cement kilns. Furthermore, the H 2 from the cathode chamber of the electrolysis cell is a valuable energy source that, among other potential industrial applications, could be feedback to the same cement production process as a source of heat and electricity. Recently, other potentialities of the ED have been reported, such as its use in direct C O 2 capture from air based on calcium loops [16], the generation of valuable carbonaceous products [17], and new electrolyzer designs for the direct utilization of H 2 and continuous operation [18]. All the above mentioned advantages in conjunction with the increasing feasibility of using renewable energy in electrochemical processes [19] enables synergistic adoption of several complementary strategies to reach deep decarbonization of the cement industry [13]. 2 CaC O 3 s + 4 H 2 O l → 2 Ca OH 2 s + 2 H 2 g + O 2 g + 2 C O 2 g Regarding cement manufacturing, Ellis et al. demonstrated that the precipitated Ca OH 2 from the ED of a high-purity source of CaC O 3 can be used as an intermediary raw material for Alite synthesis ( 3 CaO . SiO 2 ), which is the main hydraulic clinker phase and responsible for cement performance [20]. Focusing on the clinkerization process, the Ca OH 2 can be considered an alternative CaO carrier free of C O 2 . The ED cell removes the C O 2 from the raw material before introducing it in the cement kiln, replacing the calcination process of Eq. (1) by the dehydration process of Eq. (3), which also occurs in a lower range of temperature between 310 and 470 ° C [21]. All those possibilities mentioned above motivate the study of ED as a convenient intermediary stage for cement production, particularly with respect to the decarbonation of common limestones widely available in the proximity of cement plants. Ca OH 2 s + Heat → Ca O s + H 2 O g Limestones for cement manufacturing may have a very high content of CaC O 3 (~95 %), although their composition can vary within a wide range according to the type of rock exploited [22]. In this sense, although limestone is largely composed of two carbonate minerals, calcite ( CaC O 3 ) and dolomite ( CaMg C O 3 2 ), most natural limestone sources are not pure carbonates and include other components such as quartz ( Si O 2 ) and clay [23]. Requirements for the chemical composition of limestones are well defined by the state of practice in cement manufacturing. Considering as example the requirements listed by Sd et al. [24], limestones are required to contain constituent minerals proportioned as follows: Total carbonates ( xC O 3 ) > 80 % , CaO > 45 % , Si O 2 < 12 % , and F e 2 O 3 < 5 % . Also, the content of secondary oxides such as MgO , S O 3 , alkalis, and chlorides are limited to avoid negative effects in the clinker quality and operative issues during clinkerization [25,26]. Limestones with a higher content of CaC O 3 , and consequently of CaO , can be mixed with clays and corrective materials to reach the chemical composition desired for the raw meal for clinker synthesis [26,27]. On the other hand, low-grade limestones having a lower content of CaC O 3 are more difficult to combine [26] and can be used in low proportions as a corrective material, or in cases of unavailability of high-grade limestones their quality may be augmented through ancillary processes (e.g., flotation) to increase the CaO content [24,28,29]. To the chemical requirements of limestones, the physical properties of the raw materials can be added; in particular, fineness of the material is an important parameter that influences the clinkerization process. The raw materials undergo a grinding process to reach a specified fineness that is commonly defined as the sieve residue at 90 μm mesh [30,31]. In this sense, the objective of the grinding process is to reach fineness values of the raw material where <15 % of its mass has a particle size over the 90 μm [26], which is a critical parameter to facilitate the chemical combination of the CaO and Si O 2 during clinkerization [27,31]. In summary, there are several requirements concerning the chemical and physical characteristics of the raw materials which represent a technical challenge that must be addressed before ED can be incorporated as an intermediary stage for cement production. In this sense, the precipitate material (PM) produced through ED can be considered an intermediary raw material with different physical and chemical characteristics compared to its precursor. To the best of the authors' knowledge, these characteristics and their variability have not been reported before, especially if different-grade limestones from the cement industry are used as a source of CaC O 3 or precursor. Additionally, the amount of impurities and the way they are distributed in the CaC O 3 matrix, as well as the physical characteristics of the limestone, such as particle size distribution, porosity, and specific surface area, are relevant in several chemical processes that occur with this type of natural rock [32]. Consequently, this could implicate process parameters such as a longer duration of the ED reactions or an increase of the unreacted CaC O 3 that would affect the performance and efficiency of the electrochemical process. These effects on the ED performance also represent another knowledge gap that must be addressed. Based on the above approaches, this research aims to identify statistically significant differences in the PM characteristics and ED process when feeding an ED cell with different-grade limestones from the cement industry. The PM's chemical parameters compared include: i) Ca OH 2 proportion, ii) remanent CaC O 3 content, and iii) presence and quantity of impurities (i.e., other mineral compounds). The main physical characteristic evaluated is the fineness of the PM. Regarding the ED reactor performance, the parameters compared are: i) efficiency of Ca OH 2 precipitation, ii) CaO recovery, and iii) energy consumption of the electrochemical process. Additionally, the PM's quality as an intermediary raw material compared with its respective precursor limestone is also discussed. Section snippets Preparation of precursor materials ( CaC O 3 sources) Four sources of CaC O 3 were studied. The first was a high purity CaC O 3 powder reagent (Sigma-Aldrich, > 99.2 % ) that was used as a control group (C-99), which was similar to that used by Ellis et al. [13]. The other three CaC O 3 sources correspond to the natural limestone groups, which were three different-grade limestones supplied by two cement plants (L-84, L-74, and L-68, where the number corresponds to the CaC O 3 content in percent). The rocks were crushed in a jaw press and ground using a ball Chemical and physical characteristics of precursor materials ( CaC O 3 sources) Table 1 summarizes the chemical composition of the CaC O 3 sources studied. The CaC O 3 content of all samples was quantified using Eq. (4) and the TG/DTG results that are shown in Fig. 3. It is important to highlight that the slight differences in the decomposition temperature of the control sample C-99, and the limestones L-84, L-74, and L-68 were mainly attributed to the different samples' mass introduced to the TG/DTG analyzer because the samples presented different packing densities that Conclusions This study has shown the application of the electrochemical decarbonation (ED) process on limestones from the cement industry containing different CaC O 3 contents. Based on the results obtained in this research, the following conclusions can be drawn: • The results showed that ED was suitable for the decarbonation of limestones with different contents of CaCO3. In this research, the CaC O 3 content varied between 99 % and 68 % , which represents a wide range of limestone quality used in the cement CRediT authorship contribution statement Dario Ramirez-Amaya: Conceptualization, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing – original draft, Writing – review & editing. Paulina Dreyse: Conceptualization, Formal analysis, Supervision, Resources, Funding acquisition, Validation, Writing – original draft. Natalia P. Martínez: Conceptualization, Investigation, Formal analysis, Validation, Writing – original draft. Felipe Troncoso P.: Conceptualization, Investigation, Formal analysis, Validation, Declaration of competing interest Authors declare that there's not a conflict of interest in the research data and information published on this paper. Acknowledgments This work was supported by the Agencia Nacional de investigación y Desarrollo (ANID) of Chile, through the project ANID FONDEF/CONCURSO IDeA I+D, FONDEF/ANID 2021 ID21I10323, and the ANID-Subdirección de Capital Humano/Doctorado Nacional/2023-21230724; Departamento de Química from the Universidad Técnica Federico Santa María ; Departamento de ingeniería y gestión de la construcción from the Pontificia Universidad Católica de Chile ; VRI-UC for funding the postgraduate studies of the first author. References (39) F. Belaïd How does concrete and cement industry transformation contribute to mitigating climate change challenges? Resour. Conserv. Recycl. Adv. (Nov. 2022) E. Kwon et al. A study on development of recycled cement made from waste cementitious powder Constr. Build. Mater. (May 2015) F.N. Costa et al. Reduction in CO2 emissions during production of cement, with partial replacement of traditional raw materials by civil construction waste (CCW) J. Clean. Prod. 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