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Article

Impact of Physical Processes and Temperatures on the Composition, Microstructure, and Pozzolanic Properties of Oil Palm Kernel Ash

by
Ramón Torres-Ortega
1,
Diego Torres-Sánchez
2 and
Manuel Saba
1,*
1
Civil Engineering Program, University of Cartagena, Calle 30 # 48-152, Cartagena de Indias 130001, Colombia
2
Department of Civil and Engineering Environmental Engineering, Florida International University, Miami, FL 33199, USA
*
Author to whom correspondence should be addressed.
ChemEngineering 2024, 8(6), 122; https://doi.org/10.3390/chemengineering8060122
Submission received: 21 October 2024 / Revised: 13 November 2024 / Accepted: 28 November 2024 / Published: 2 December 2024
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Abstract

:
In recent decades, the global use of ashes derived from agro-industrial by-products, such as oil palm kernel shells, which are widely cultivated in Colombia and other tropical regions of the world, has increased. However, the application of these ashes in engineering remains limited due to their heterogeneity and variability. This study utilized scanning electron microscopy (SEM) to assess the influence of calcination temperatures, ranging from 500 °C to 1000 °C, as well as the physical processes of cutting, grinding, and crushing, on the silica content of the studied ashes. Specifically, the sample labeled M18A-c-m-T600°C-t1.5h-tr1h, which was subjected to a calcination temperature of 600 °C and underwent cutting and grinding before calcination, followed by post-calcination crushing, exhibited the highest silica concentration. Complementary techniques such as X-ray fluorescence (XRF) and X-ray diffraction (XRD), were applied to this sample to evaluate its feasibility as an additive or partial replacement for cement in concrete. XRF analysis revealed a composition of 71.24% SiO2, 9.39% Al2O3, and 2.65% Fe2O3, thus, meeting the minimum oxide content established by ASTM C 618 for the classification as a pozzolanic material. Furthermore, XRD analysis confirmed that the sample M18A-c-m-T600°C-t1.5h-tr1h is in an amorphous state, which is the only state in which silica can chemically react with calcium hydroxide resulting from the hydration reactions of cement, forming stable cementitious products with strong mechanical properties.

1. Introduction

The composition, microstructure, and pozzolanic properties of a material can be influenced by the combustion temperature at which it is produced [1,2,3,4]. It has been established that various types of ashes derived from agro-industrial by-products, such as rice husk, sugarcane bagasse, banana peel, etc., exhibit varied responses to different combustion temperatures [5,6,7,8,9]. Specifically, it has been demonstrated that temperature significantly affects the concentrations of silica, a crucial element in the manifestation of pozzolanic activity [10,11]. Furthermore, both the pre- and post-calcination grinding processes play a decisive role in the quality and final properties of the resulting ashes [12,13].
The findings reported by Amin et al. (2019) [14] provide a detailed insight into the pozzolanic reactivity of rice husk ash (RHA) and its impact on early shrinkage and compressive strength in high-performance concrete. Using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) analyses, they determined the basic oxide contents present. The rice husk was burned at 700 °C and 950 °C for 3 h to obtain amorphous silica, whose quantity and phase depend on the temperature and duration of incineration. The composition of the RHA was measured by EDX, revealing that RHA burned at 950 °C had a slightly higher silica content compared to that burned at 700 °C. The percentages of SiO2, Al2O3, and Fe2O3 indicated that both samples were pozzolanic, with values of 89.61% and 90.44% for RHA burned at 700 °C and 950 °C, respectively [15].
Ruviaro et al. (2023) [16] investigated the influence of combustion temperature on the characteristics of oat husk ash (OHA) and its use as a supplementary cementitious material (SCM). Additionally, the authors evaluated its effect on the properties of cementitious materials in both fresh and hardened states. To characterize the oat husk ash burned at different temperatures (500 °C–800 °C), analytical techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) were employed. The combustion process was conducted in the laboratory at temperatures of 500 °C, 600 °C, 700 °C, and 800 °C. In this context, the ashes met the requirements of ASTM C618 for Class N pozzolans, where SiO2 + Al2O3 + Fe2O3 represent more than 70% of the constituents. However, at a combustion temperature of 500 °C, the OHA showed a higher content of residual organic matter. On the other hand, although the organic matter content is lower at higher temperatures (700 °C and 800 °C), the crystallization of silica made the OHA less reactive. Therefore, the characterization results indicated that the optimal combustion temperature for oat husk is 600 °C, which was later corroborated by tests conducted on cement pastes [16].
In the study conducted by Nogueira Sallaberry (2019) [17], the pozzolanic potential of banana leaf ash (BLA) was evaluated using the Portland cement performance index at 28 days—NBR 5752:2014 and electrical conductivity. To obtain the ash, Nogueira used a muffle furnace at temperatures of 450 °C and 900 °C, subjecting them to different grinding times, both 1 h and 3 h each. For the chemical and physical characterization of the BLA, specific mass analysis, fluorescence and X-ray diffraction (XRF and XRD), scanning electron microscopy (SEM), and organic matter content analysis were performed. The results revealed pozzolanic properties in all the ashes, concluding that the optimal production temperature for the material was 900 °C, with a grinding time of 1 h [17].
In their research, Bie et al. (2015) [18] analyzed rice husk ash (RHA) obtained under different temperature conditions in a muffle furnace and its impact on the mechanical properties of mortar. Scanning electron microscopy with energy dispersive analysis (SEM-EDX) was conducted to examine the microstructure and chemical composition. The samples were subjected to temperatures of 600 °C and 700 °C for one and two hours and denoted as RHA600-1h, RHA600-2h, and RHA700-1h. The analyses showed that the surface of the rice husk is smooth and dense, with orderly protrusions, primarily composed of SiO2. The compositions for RHA600-1h, RHA600-2h, and RHA700-1h were 92.09%, 93%, and 93.42% SiO2, respectively, along with traces of Al2O3 and Fe2O3. The results indicated that burning rice husk at low temperatures (600 °C–700 °C) produces RHA with high reactivity, making it useful as an additive for concrete and mortars. Additionally, the authors highlight that 600 °C is the optimal temperature for obtaining RHA with a higher specific surface area due to the presence of SiO2 [18].
In their study, Cordeiro et al. (2021) [11] investigated the effect of calcination temperature on the pozzolanic activity of sugarcane bagasse ash (SCBA). X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were employed for the analysis. The bagasse samples were subjected to combustion in a ventilated electric furnace at varying temperatures between 400 °C and 800 °C for a period of 3 h. After the calcination and cooling process, the samples were ground in a planetary mill. The results obtained by the authors revealed that SCBA generated by calcination at 600 °C for 3 h exhibited amorphous silica characteristics, low carbon content, and a high specific surface area, suggesting its potential pozzolanic activity [19].
Similarly, Joshaghani and Moeini (2017) [20] conducted a study to evaluate the effects of sugarcane bagasse ash (SCBA) and nanosilica on the mechanical properties and durability of mortar. Various combustion temperatures were investigated, including 500 °C, 600 °C, 700 °C, 800 °C, and 1000 °C. X-ray diffraction (XRD) was used to analyze the crystalline composition of the bagasse ash obtained at these temperatures. The results indicated that the quality of bagasse ash, in terms of pozzolanic activity, was influenced by the combustion conditions, particularly temperature and exposure time. It was concluded that bagasse ash produced at a temperature of 800 °C with a combustion time of 30 min demonstrated optimal pozzolanic activity [20].
The composition, microstructure, and pozzolanic properties of materials derived from agro-industrial by-products are significantly influenced by thermal and mechanical treatments. While extensive research has been conducted on various biomass-derived ashes, such as rice husk ash, sugarcane bagasse ash, and banana leaf ash, there is a scarcity of studies focusing on oil palm kernel shell ash (POFA). Previous studies have demonstrated that the calcination temperature plays a crucial role in determining the pozzolanic activity of biomass-derived ashes. However, the impact of physical processes, such as cutting, grinding, and crushing, on the pozzolanic properties of POFA remains largely unexplored. This study aims to fill this knowledge gap by investigating the influence of these physical processes, along with thermal treatment, on the microstructure, chemical composition, and pozzolanic potential of POFA. By understanding these factors, the authors propose how to optimize the production of high-quality POFA and its utilization as a sustainable construction material.
The primary objective of this study is to analyze, using scanning electron microscopy (SEM), the effect of physical processes such as cutting, grinding, and crushing, along with combustion at various temperatures, on the ash obtained from oil palm kernel shells sourced from the northern region of the Bolívar department, Colombia, for its potential use as a cementitious material. This research aims to establish a theoretical precedent for future studies, enabling the selection of an optimal calcination temperature for obtaining palm kernel shell ash, based on a robust scientific analysis. It also seeks to evaluate physical processes, such as pre-treatment, which can yield significant silica content in the ashes, making them suitable for use as pozzolans in concrete. To achieve this, the samples were subjected to different calcination temperatures, ranging between 500 °C and 1000 °C, as well as cutting, grinding, and crushing processes. Subsequently, a comprehensive analysis of their chemical and mineralogical composition was conducted. This analysis involved the use of SEM to provide a detailed evaluation of the morphology and microstructure of the ash particles, as well as the distribution of elements present. SEM offers high-resolution images and compositional data through energy-dispersive X-ray spectroscopy (EDS), which is essential for determining the properties and potential applications of ash as a cementitious material. Furthermore, the study aims to evaluate the chemical composition of the samples subjected to various processes, identifying which sample presents the highest silica content, which is crucial for its pozzolanic reaction with cement. Following this, X-ray fluorescence (XRF) and X-ray diffraction (XRD) tests were performed to determine the potential of the ash as an additive or partial substitute for cement in concrete.

2. Materials and Methods

2.1. Materials and Sample Preparation

The oil palm kernel used to extract the ashes originates from the northern region of the Bolívar department, Colombia. In the laboratory, a dehydration process was conducted at 100 °C for 24 h in an oven for all the oil palm kernel samples. Once the samples were dried, three different methods were applied to obtain the ashes. Figure 1 shows the palm oil core subjected to the dehydration process.
In the first procedure, after dehydration, the kernels were fractionated using an electric machine that cuts solely based on the material’s nature. In the second process, after cutting, the samples were subjected to a manual grinding process prior to calcination in a muffle furnace (see Figure 2).
For the muffle calcination process, temperatures ranging from 500 °C to 1000 °C were used, for a period of 1.5 h, a situation that is illustrated in Figure 3.
The third physical process involved ball milling for 1 h, which was carried out after calcination in a muffle furnace at temperatures between 500 °C and 1000 °C for 1.5 h (see Figure 4). The ball mill cannot be used before calcination, as the nature of the aggregate does not allow for effective crushing to increase the fineness of the cementitious material.
Table 1 presents the nomenclature used to identify each sample according to the procedure employed to obtain the ash.

2.2. Testing

For the study of oil palm kernel ash, a total of 19 samples were collected and analyzed in a specialized laboratory. The analysis employed scanning electron microscopy (SEM), complemented by energy-dispersive X-ray spectroscopy (EDS), and energy-dispersive X-ray analysis (EDX). This methodology provides a powerful tool for detailed characterization of the samples, as it delivers high-resolution images that allow for a thorough examination of particle morphology and determination of elemental composition. The combined use of SEM-EDS and SEM-EDX ensures a comprehensive evaluation of the physical and chemical properties of the ashes, facilitating a deeper understanding of their potential as a cementitious material (Figure 5).
Subsequently, once the physical processes and temperature that result in the highest silica content have been determined through SEM-EDX analysis, the characterization and determination of the basic oxide content (SiO2, Al2O3, and Fe2O3) will be performed using XRF. This is performed with the goal of verifying whether the sample meets the requirements of ASTM C618, which mandates that the combined content of SiO2, Al2O3, and Fe2O3 exceeds 70%, thus making the material viable for use as pozzolans in concrete.
Following this, X-ray diffraction (XRD) analysis will be employed to fully characterize the sample by determining whether it is in an amorphous or crystalline state, considering that amorphous silica exhibits excellent properties in terms of concrete’s mechanical strength and durability. Figure 5 graphically presents the experimental methodology described here.

3. Results and Discussion

The calcination temperature and grinding processes play a crucial role in the quality and characteristics of the ash obtained from oil palm kernels. By adjusting the calcination temperature, one can directly influence the chemical composition and structure of the ash, which in turn affects its physical and chemical properties [21,22,23]. Conversely, grinding methods are decisive as they impact the material’s reactivity and its potential use in industrial applications [24,25]. The choice of the appropriate grinding method depends on the final application of the material and its physical and chemical properties [26,27,28]. These two interrelated factors are essential for optimizing the properties of the final product.

3.1. Scanning Electron Microscopy (SEM/EDX)

The chemical composition of oil palm kernel ash exhibits notable variability depending on the different processes it has undergone during its preparation. This heterogeneity in chemical composition is a significant factor in assessing the pozzolanic reactivity of both oil palm kernel ash and other agricultural materials [29,30]. Among the chemical elements in the ash, the presence and proportion of certain components, such as silica, aluminum, and iron, can significantly influence its pozzolanic capacity [31,32]. It is highlighted that silica content has a considerable impact on the ash’s ability to chemically react with calcium hydroxide and form additional cementitious compounds during the cement hydration process [33,34]. Therefore, a detailed analysis of the chemical compositions of all samples considered in this study is essential to adequately understand their pozzolanic potential and suitability for application in the construction industry. The detailed compositions of all the samples considered in this study are presented in Table 2.
According to the findings, the samples exhibited a predominance of silica, carbon, and oxygen. Additionally, traces of other elements, including magnesium, aluminum, potassium, iron, and calcium, were identified. The occasional presence of sodium, sulfur, phosphorus, chlorine, titanium, barium, and tin was also recorded in some samples, though in minimal quantities. These results reveal the varied and complex elemental composition of the analyzed samples. The analysis of silica concentrations across different samples, as shown in Figure 6, indicates significant variation depending on the treatment conditions.
The ash samples with the highest silica concentrations are M18A-c-m-T600C-t1.5h-tr1h (31.92%), M21A-c-m-T900C-t1.5h-tr1h (17.06%), M22A-c-m-T1000C-t1.5h-tr1h (22.6%), and M13A-c-T700C-t1.5h-tr1h (23.47%). Among these, the first three were obtained using the third procedure, while the last sample was obtained through the second procedure. These results indicate that calcination temperatures have a significant impact on silica concentrations in the samples [35]. Additionally, it is observed that both the pre- and post-calcination crushing processes play a crucial role in the outcomes [36,37]. Specifically, sample M18A-c-m-T600C-t1.5h-tr1h, subjected to a calcination temperature of 600 °C and both pre- and post-calcination crushing processes, exhibited the highest silica concentration among all the analyzed samples. This aligns with other research suggesting that calcination temperatures close to 600 °C are optimal for accurately determining ash properties [38,39,40,41,42].
The analysis of SEM-EDX and EDS images reveals a wealth of information about the samples under study and their structural and compositional properties. Comparing different images of the samples shows distinctive patterns in the shape and elemental distribution of the samples. A prominent feature of the particles in certain samples is their irregular constitution, evidenced by the absence of a defined and uniform shape. This structural irregularity is manifested through a variety of non-uniform shapes present in the particles. However, other samples exhibit more defined edges and angular shapes. Additionally, the presence of burned carbon particles within the sample has been observed, which also exhibit irregular structures, contributing to the morphological diversity of the analyzed samples.
The sample M11-c-T500C-t1.5h shown in Figure 7a,b, was subjected to a cutting and calcination process at 500 °C, and exhibited a reduction in porosity and more defined particles compared to sample M0-T100C-t24h, which has a similar chemical composition but a different elemental distribution. On the other hand, sample M11A-c-T500C-t1.5h-tr1h shown in Figure 7c,d, which underwent an additional ball milling process, shows a more homogeneous structure with a high proportion of carbon and oxygen. In the case of sample M17A-c-m-T500C-t1.5h-tr1h shown in Figure 7e,f, the carbon content remains constant, indicating the presence of organic material (see the circle), suggesting the need for an increase in temperature to eliminate these traces. Additionally, the increase in oxygen is attributed to the formation of oxides [43].
By increasing the temperature to 600 °C, the SEM images of sample M12-c-T600C-t1.5h shown in Figure 8a,b reveal more compact particles with a composition similar to that of sample M11-c-T500C-t1.5h. However, a further reduction in carbon content is observed, along with an increase in oxygen, silica, and calcium. For sample M12A-c-T600C-t1.5h-tr1h shown in Figure 8c,d, which was calcined at 600 °C and subsequently subjected to crushing, an increase in carbon content and a decrease in oxygen and silica levels are observed. Sample M18A-c-m-T600C-t1.5h-tr1h shown in Figure 8e,f exhibits a further reduction in carbon content and a notable increase in silica.
Thus, it can be concluded that increasing the temperature allows for greater combustion of organic content, considering that unburnt carbon interferes with the hydration reaction and increases the water demand, ultimately affecting the final properties of concrete. Additionally, jaw milling followed by ball milling results in a sample with a more uniform elemental distribution. These three physical processes produce finer particles that are easier to burn, promoting higher silica content compared to the sample subjected only to cutting and the sample with only cutting and post-combustion crushing.
At a temperature of 700 °C, sample M13-c-T700C-t1.5h shown in Figure 9a,b, exhibits more pronounced changes in particle structure, showing a slight decrease in carbon and oxygen, as well as a low concentration of silica. The SEM images of sample M13A-c-T700C-t1.5h-tr1h shown in Figure 9c,d show a significant reduction in carbon content, indicating an almost complete decomposition of the organic compounds present. Additionally, there is an increase in the concentration of silica and a more noticeable presence of other minerals, such as iron. In contrast, sample M19A-c-m-T700C-t1.5h-tr1h shown in Figure 9e,f, shows a notable increase in carbon concentration, accompanied by a decrease in the concentration of other elements. Furthermore, a significant reduction in silica content is observed compared to M13A-c-T700C-t1.5h-tr1h. These results highlight differences in thermal behavior and the interaction between components during the treatment process.
Sample M14-c-T800C-t1.5h, observed in Figure 10a,b and calcined at a temperature of 800 °C, exhibits a notably dense structure, characterized by a high concentration of carbon and the presence of small traces of other elements. Sample M14A-c-T800C-t1.5h-tr1h shown in Figure 10c,d, after undergoing an additional crushing treatment, shows similar behavior to the previous sample, without significant variations in carbon and silica content. On the other hand, sample M20A-c-m-T800C-t1.5h-tr1h shown in Figure 10e,f maintains the trend of a high carbon proportion, with minimal oxygen and silica content, as well as other minerals. This indicates that the elemental distribution and structural characteristics vary considerably depending on the treatment applied and the calcination temperature, reflecting the complex interactions between material components under extreme temperatures and mechanical processing conditions.
When the temperature reaches 900 °C, sample M15-c-T900C-t1.5h shown in Figure 11a,b, reveals a dense microstructure characterized by a predominance of carbon and low concentrations of oxygen, silica, calcium, and other minerals. A similar case occurs with sample M15A-c-T900C-t1.5h-tr1h in Figure 11c,d, which was subjected to additional crushing, showing a high carbon content, accompanied by a slight increase in oxygen, silica, and calcium concentrations. This trend suggests that the post-calcination crushing process induces significant changes in the sample’s elemental composition [39,44]. Furthermore, sample M21A-c-m-T900C-t1.5h-tr1h shown in Figure 11e,f, also calcined at 900 °C and subjected to milling, exhibits a reduction in carbon content, while the concentrations of oxygen and silica increase considerably. These changes indicate that the ash production processes cause substantial alterations in the elemental distribution and microstructure of the samples.
At a temperature of 1000 °C, sample M16-c-T1000-t1.5h shown in Figure 12a,b, shows more compact particles, with a high concentration of carbon and low levels of other constituent elements. On the other hand, in sample M16A-c-T1000C-t1.5h-tr1h shown in Figure 12c,d, which underwent ball milling, a similar trend in elemental distribution is observed. There is a high concentration of carbon and consistent amounts of oxygen and silica compared to sample M16-c-T1000-t1. Additionally, sample M22A-c-m-T1000C-t1.5h-tr1h shown in Figure 12e,f, reveals a decrease in carbon content and a significant increase in oxygen and silica.
When comparing samples with higher concentrations of silica, differences in morphology and chemical composition are observed. In Figure 8e,f, a particle with a rough surface, and irregular and angular edges is noted, suggesting possible processes of formation or modification. Furthermore, a high concentration of silica in the elemental distribution is evident, which may indicate a direct association between particle morphology and the presence of this element. In contrast, Figure 9c,d shows a distinct configuration with a high concentration of silica merely accompanied by a porous texture in its structure. This finding suggests that formation conditions during the ash extraction processes may have influenced the final particle configuration, resulting in a different morphology compared to that observed in Figure 8e,f.
By contrasting the representations in Figure 6, Figure 7, Figure 8, Figure 9, Figure 10 and Figure 11, clear similarities or patterns in the configuration and surface appearance of the particles are observed. These similarities can be attributed to the grinding processes to which they were subjected, as demonstrated by previous studies [45,46,47,48,49]. However, it is important to highlight the significant variability in the distribution and concentration of elements in the samples. This variability strongly suggests the influence of calcination temperatures on the observed results, as noted by recent research [50]. The effect of calcination temperatures could be related to changes in crystalline structure, chemical composition, and particle porosity, which in turn would affect their properties and behavior in various industrial applications [51,52].
Thus, after analyzing all the samples, a consistent pattern is observed: there is a similarity in the silica and carbon contents between the samples that underwent only cutting and those that underwent both cutting and post-calcination crushing. However, when the third process—pre-calcination milling—is added, the samples exhibit a higher silica content, indicating that finer particles may perform better in concrete. Considering that a temperature of 600 °C resulted in higher silica content and lower carbon levels, this condition was selected as the reference sample due to its potential for use as pozzolans, and it was subjected to XRF and XRD tests.

3.2. X-Ray Fluorescence (XRF)

The chemical composition of the POFA sample M18A-c-m-T600°C-t1.5h-tr1h was determined using a sequential wavelength-dispersive X-ray fluorescence spectrometer. The results were expressed as weight percentages of the oxides present in the sample. XRF revealed content of 71.24% SiO2, 9.39% Al2O3, and 2.65% Fe2O3, thereby meeting the minimum basic oxide content established by ASTM C618 for classification as a pozzolanic material, which is 70%. This behavior indicates that a temperature of 600 °C, along with the three evaluated physical processes, promotes the release and formation of reactive silica, which is essential for the pozzolanic properties of the material.

3.3. X-Ray Diffraction (XRD)

The XRD evaluation of sample M18A-c-m-T600°C-t1.5h-tr1h produced the diffractogram shown in Figure 13. The sample M18A-c-m-T600°C-t1.5h-tr1h was also subjected to XRD analysis to confirm its silica structure. Figure 13 illustrates that the main phase of this sample was SiO2 (Q = Quartz), while calcite and aluminum oxide were present in smaller proportions. This indicates that the sample is in an amorphous state, allowing the amorphous silica to chemically react with Ca(OH)2, which is produced from cement hydration, to form hydration products, primarily calcium silicate hydrate (C-S-H). With the fineness obtained for this material, it will be capable of reducing the porosity of the cement paste and refining its pore structure, as the pozzolanic activity of POFA primarily derives from the internal surface area of the particles.

4. Conclusions

  • The chemical composition and morphology of oil palm shell ash are critical elements influencing its pozzolanic reactivity and applicability in the construction industry. Therefore, a comprehensive characterization of oil palm shell ash was conducted using scanning electron microscopy (SEM). After analyzing, using scanning electron microscopy (SEM), the effect of physical processes such as cutting, grinding, and crushing, along with combustion at various temperatures, it was concluded that the sample M18A-c-m-T600°C-t1.5h-tr1h, subjected to a calcination temperature of 600 °C, along with a pre-calcination cutting and grinding process and subsequent crushing, exhibited the highest concentration of silica. For this reason, the oil palm kernel shell ash obtained at this temperature (600 °C) with the three indicated physical processes has potential use as a cementitious material.
  • It was determined that the carbon, silica, and oxygen content is similar in samples subjected only to cutting and those with cutting and post-combustion crushing, while samples that also underwent milling showed a higher silica content. This highlights the influence of material fineness on its chemical behavior. Additionally, temperature emerges as a crucial factor in altering the chemical composition of the studied materials. The variation in silica concentrations indicates that thermal conditions during the calcination process have a direct effect on the redistribution and reaction of siliceous components present in the samples.
  • These findings underscore the importance of carefully considering pre-calcination physical processes to optimize the quality and properties of palm kernel shell ash for industrial applications. Finally, XRD results confirm that the basic oxide content of sample M18A-c-m-T600°C-t1.5h-tr1h exceeds 70%, demonstrating its pozzolanic capacity and potential use in concrete. Moreover, the XRF results indicate that this sample is in an amorphous state. The amorphous nature of the sample suggests that its amorphous silica will chemically react with Ca(OH)2, produced during cement hydration, to form hydration products, primarily calcium silicate hydrate (C-S-H).

Author Contributions

Conceptualization, R.T.-O. and D.T.-S.; methodology, R.T.-O.; software, R.T.-O.; validation, R.T.-O., D.T.-S. and M.S.; formal analysis, R.T.-O.; investigation, R.T.-O. and M.S.; resources, R.T.-O.; data curation, R.T.-O.; writing—original draft preparation, R.T.-O.; writing—review and editing, R.T.-O. and M.S.; visualization, R.T.-O.; supervision, R.T.-O.; project administration, R.T.-O.; funding acquisition, D.T.-S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Dataset available on request from the authors.

Acknowledgments

The authors acknowledge the University of Cartagena and Maria Salome Luna Velasco.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Palm oil core dried for 24 h at 100 °C.
Figure 1. Palm oil core dried for 24 h at 100 °C.
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Figure 2. Palm oil core with physical cutting processes using an electric machine and grinding in a manual mill.
Figure 2. Palm oil core with physical cutting processes using an electric machine and grinding in a manual mill.
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Figure 3. Palm oil core with physical processes of cutting using an electric machine and grinding in a manual mill and calcining in a muffle furnace at different temperatures.
Figure 3. Palm oil core with physical processes of cutting using an electric machine and grinding in a manual mill and calcining in a muffle furnace at different temperatures.
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Figure 4. Palm oil core with physical processes of cutting using an electric machine and grinding in a manual mill, calcining in a muffle at different temperatures and grinding in a ball mill after calcining.
Figure 4. Palm oil core with physical processes of cutting using an electric machine and grinding in a manual mill, calcining in a muffle at different temperatures and grinding in a ball mill after calcining.
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Figure 5. Experimental methodology.
Figure 5. Experimental methodology.
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Figure 6. Silica concentrations in the samples.
Figure 6. Silica concentrations in the samples.
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Figure 7. (a) M11-c-T500C-t1.5h SEM EDS; (b) M11-c-T500C-t1.5h SEM EDX; (c) M11A-c-T500C-t1.5h-tr1h SEM EDS; (d) M11A-c-T500C-t1.5h-tr1h SEM EDX; (e) M17A-c-m-T500C-t1.5h-tr1h SEM EDS; (f) M17A-c-m-T500C-t1.5h-tr1h SEM EDX.
Figure 7. (a) M11-c-T500C-t1.5h SEM EDS; (b) M11-c-T500C-t1.5h SEM EDX; (c) M11A-c-T500C-t1.5h-tr1h SEM EDS; (d) M11A-c-T500C-t1.5h-tr1h SEM EDX; (e) M17A-c-m-T500C-t1.5h-tr1h SEM EDS; (f) M17A-c-m-T500C-t1.5h-tr1h SEM EDX.
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Figure 8. (a) M12-c-T600C-t1.5h SEM EDS; (b) M12-c-T600C-t1.5h SEM EDX; (c) M12A-c-T600C-t1.5h-tr1h SEM EDS; (d) M12A-c-T600C-t1.5h-tr1h SEM EDX; (e) M18A-c-m-T600C-t1.5h-tr1h SEM EDS; (f) M18A-c-m-T600C-t1.5h-tr1h SEM EDX.
Figure 8. (a) M12-c-T600C-t1.5h SEM EDS; (b) M12-c-T600C-t1.5h SEM EDX; (c) M12A-c-T600C-t1.5h-tr1h SEM EDS; (d) M12A-c-T600C-t1.5h-tr1h SEM EDX; (e) M18A-c-m-T600C-t1.5h-tr1h SEM EDS; (f) M18A-c-m-T600C-t1.5h-tr1h SEM EDX.
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Figure 9. (a) M13-c-T700C-t1.5h SEM EDS; (b) M13-c-T700C-t1.5h SEM EDX; (c) M13A-c-T700C-t1.5h-tr1h SEM EDS; (d) M13A-c-T700C-t1.5h-tr1h SEM EDX; (e) M19A-c-m-T700C-t1.5h-tr1h SEM EDS; (f) M19A-c-m-T700C-t1.5h-tr1h SEM EDX.
Figure 9. (a) M13-c-T700C-t1.5h SEM EDS; (b) M13-c-T700C-t1.5h SEM EDX; (c) M13A-c-T700C-t1.5h-tr1h SEM EDS; (d) M13A-c-T700C-t1.5h-tr1h SEM EDX; (e) M19A-c-m-T700C-t1.5h-tr1h SEM EDS; (f) M19A-c-m-T700C-t1.5h-tr1h SEM EDX.
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Figure 10. (a) M14-c-T800C-t1.5h SEM EDS; (b) M14-c-T800C-t1.5h SEM EDX; (c) M14A-c-T800C-t1.5h-tr1h SEM EDS; (d) M14A-c-T800C-t1.5h-tr1h SEM EDX; (e) M14A-c-T800C-t1.5h-tr1h SEM EDS; (f) M14A-c-T800C-t1.5h-tr1h SEM EDX.
Figure 10. (a) M14-c-T800C-t1.5h SEM EDS; (b) M14-c-T800C-t1.5h SEM EDX; (c) M14A-c-T800C-t1.5h-tr1h SEM EDS; (d) M14A-c-T800C-t1.5h-tr1h SEM EDX; (e) M14A-c-T800C-t1.5h-tr1h SEM EDS; (f) M14A-c-T800C-t1.5h-tr1h SEM EDX.
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Figure 11. (a) M15-c-T900C-t1.5h SEM EDS; (b) M15-c-T900C-t1.5h SEM EDX; (c) M15A-c-T900C-t1.5h-tr1h SEM EDS; (d) M15A-c-T900C-t1.5h-tr1h SEM EDX; (e) M21A-c-m-T900C-t1.5h-tr1h SEM EDS; (f) M21A-c-m-T900C-t1.5h-tr1h SEM EDX.
Figure 11. (a) M15-c-T900C-t1.5h SEM EDS; (b) M15-c-T900C-t1.5h SEM EDX; (c) M15A-c-T900C-t1.5h-tr1h SEM EDS; (d) M15A-c-T900C-t1.5h-tr1h SEM EDX; (e) M21A-c-m-T900C-t1.5h-tr1h SEM EDS; (f) M21A-c-m-T900C-t1.5h-tr1h SEM EDX.
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Figure 12. (a) M16-c-T1000-t1.5h SEM EDS; (b) M16-c-T1000-t1.5h SEM EDX; (c) M16A-c-T1000C-t1.5h-tr1h SEM EDS; (d) M16A-c-T1000C-t1.5h-tr1h SEM EDX; (e) M22A-c-m-T1000C-t1.5h-tr1h SEM EDS; (f) M22A-c-m-T1000C-t1.5h-tr1h SEM ED.
Figure 12. (a) M16-c-T1000-t1.5h SEM EDS; (b) M16-c-T1000-t1.5h SEM EDX; (c) M16A-c-T1000C-t1.5h-tr1h SEM EDS; (d) M16A-c-T1000C-t1.5h-tr1h SEM EDX; (e) M22A-c-m-T1000C-t1.5h-tr1h SEM EDS; (f) M22A-c-m-T1000C-t1.5h-tr1h SEM ED.
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Figure 13. X-ray diffraction (XRD) for sample M18A-c-m-T600°C-t1.5h-tr1h.
Figure 13. X-ray diffraction (XRD) for sample M18A-c-m-T600°C-t1.5h-tr1h.
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Table 1. Nomenclature of the Samples Analyzed According to Processing Techniques.
Table 1. Nomenclature of the Samples Analyzed According to Processing Techniques.
Calcination Temperature (°C)Samples with Cutting in Electric Crusher (Process #1). Calcination in Muffle Furnace for 1.5 hSamples with Cutting in Electric Crusher (Process #1). Calcination in Muffle Furnace for 1.5 h. Ball Milling for 1 h (Process #3)Samples with Cutting in Electric Crusher (Process #1), Grinding in Jaw Crusher (Process #2). Calcination in Muffle Furnace for 1.5 h. Ball Milling for 1 h (Process #3)
500M11-c-T500C-t1.5hM11A-c-T500C-t1.5h-tr1hM17A-c-m-T500C-t1.5h-tr1h
600M12-c-T600C-t1.5hM12A-c-T600C-t1.5h-tr1hM18A-c-m-T600C-t1.5h-tr1h
700M13-c-T700C-t1.5hM13A-c-T700C-t1.5h-tr1hM19A-c-m-T700C-t1.5h-tr1h
800M14-c-T800C-t1.5hM14A-c-T800C-t1.5h-tr1hM20A-c-m-T800C-t1.5h-tr1h
900M15-c-T900C-t1.5hM15A-c-T900C-t1.5h-tr1hM21A-c-m-T900C-t1.5h-tr1h
1000M16-c-T1000-t1.5hM16A-c-T1000C-t1.5h-tr1hM22A-c-m-T1000C-t1.5h-tr1h
c = Cutting in Electric Crusher, T = Temperature, C = Calcination (Degrees Celsius), t = Time, tr = Ball Milling, m = Grinding in Manual Jaw Mill.
Table 2. Chemical Composition of Oil Palm Kernel Ash with Different Processing Techniques.
Table 2. Chemical Composition of Oil Palm Kernel Ash with Different Processing Techniques.
SamplesProcessWeight %
°CCuttingTriturationGrindingCOMgAlSiKCaTiFe
M0-T100C-t24h100 58.7736.170.440.142.440.70.7800.57
M11-c-T500C-t1.5h500yes 76.3160.590.33.451.480.9400.44
M11A-c-T500C-t1.5h-tr1h500yesyes 83.3114.100.140.220.491.180.5500
M17B-c-m-T500C-t1.5h-tr1h500yesyesyes89.679.48000.320.53000
M12-c-T600C-t1.5h600yes 42.8812.86000.370.594.964.421.64
M12A-c-T600C-t1.5h-tr1h600yesyes 85.3410.930.390.211.071.300.4900.26
M18B-c-m-T600C-t1.5h-tr1h600yesyesyes28.339.780031.920000
M13-c-T700C-t1.5h700yes 77.6716.790.8001.482.040.8000.43
M13A-c-T700C-t1.5h-tr1h700yesyes 37.5222.450.753.323.40.8400.910.8
M19B-c-m-T700C-t1.5h-tr1h700yesyesyes89.168.3800.361.270.58000.26
M14-c-T800C-t1.5h800yes 77.9611.350.930.241.953.341.6400.93
M14A-c-T800C-t1.5h-tr1h800yesyes 87.768.5500.212.640.560.2800
M20B-c-m-T800C-t1.5h-tr1h800yesyesyes84.369.820.250.591.821.290.3700.67
M15-c-T900C-t1.5h900yes 83.7910.730.221.191.522.070.4700
M15A-c-T900C-t1.5h-tr1h900yesyes 85.759.130.220.612.550.740.3800.62
M21B-c-m-T900C-t1.5h-tr1h900yesyesyes59.6020.520.300.3617.060.860.7700.54
M16-c-T1000-
t1.5h		1000yes 85.918.900.310.161.552.360.8200
M16A-c-T1000C-t1.5h-tr1h1000yesyes 81.3712.820.410.592.580.880.6700.68
M22B-c-m-T1000C-t1.5h-tr1h1000yesyesyes47.5725.880.210.2922.60.790.1902.22
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Torres-Ortega, R.; Torres-Sánchez, D.; Saba, M. Impact of Physical Processes and Temperatures on the Composition, Microstructure, and Pozzolanic Properties of Oil Palm Kernel Ash. ChemEngineering 2024, 8, 122. https://doi.org/10.3390/chemengineering8060122

AMA Style

Torres-Ortega R, Torres-Sánchez D, Saba M. Impact of Physical Processes and Temperatures on the Composition, Microstructure, and Pozzolanic Properties of Oil Palm Kernel Ash. ChemEngineering. 2024; 8(6):122. https://doi.org/10.3390/chemengineering8060122

Chicago/Turabian Style

Torres-Ortega, Ramón, Diego Torres-Sánchez, and Manuel Saba. 2024. "Impact of Physical Processes and Temperatures on the Composition, Microstructure, and Pozzolanic Properties of Oil Palm Kernel Ash" ChemEngineering 8, no. 6: 122. https://doi.org/10.3390/chemengineering8060122

APA Style

Torres-Ortega, R., Torres-Sánchez, D., & Saba, M. (2024). Impact of Physical Processes and Temperatures on the Composition, Microstructure, and Pozzolanic Properties of Oil Palm Kernel Ash. ChemEngineering, 8(6), 122. https://doi.org/10.3390/chemengineering8060122

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