ПОЛУЧЕНИЕ ВЫСОКОЧИСТОГО КАРБОНАТА КАЛЬЦИЯ ИЗ СЫРЬЯ РАКОВИН МОЛЛЮСКОВ И ХАРАКТЕРИСТИКА ЕГО МОРФОЛОГИИ И ЭЛЕМЕНТНОГО СОСТАВА МЕТОДОМ SEM–EDX

УДК 546.3+661.4+504.6

Аннотация

Отходы раковин моллюсков, образующиеся в результате деятельности предприятий пищевой промышленности, представляют собой богатый биогенный ресурс, содержащий значительное количество карбоната кальция и пригодный для получения материалов с высокой добавленной стоимостью. Целью настоящего исследования являлось получение высокочистого карбоната кальция из сырья на основе раковин моллюсков, а также изучение его морфологии и элементного состава методом сканирующей электронной микроскопии в сочетании с энергодисперсионным рентгеновским анализом (SEM–EDX). Раковины моллюсков подвергались промывке, сушке, измельчению, просеиванию и термической очистке для получения тонкодисперсного порошка карбоната кальция. Морфологический анализ показал наличие частиц неправильной формы с относительно однородным распределением и пористой поверхностной структурой, что свидетельствует о благоприятных свойствах материала для использования в качестве наполнителя и адсорбента. EDX-анализ подтвердил, что основными элементами в полученном материале являются кальций, кислород и углерод, тогда как примеси присутствуют лишь в следовых количествах. Элементный состав показал, что чистота полученного продукта превышает 97 мас. %, что подтверждает высокую эффективность применённого процесса извлечения. Количественный EDX-анализ выявил содержание 40,04 мас. % Ca, 47,96 мас. % O и 12,00 мас. % C, что свидетельствует о преобладании карбоната кальция в полученном материале. Полученные результаты демонстрируют высокий потенциал отходов раковин моллюсков как экологически устойчивого и экономически привлекательного источника высококачественного карбоната кальция для применения в строительных материалах, полимерных композициях, лакокрасочных покрытиях и других промышленных областях. Исследование вносит вклад в развитие ресурсосберегающих технологий переработки отходов и способствует более эффективному использованию возобновляемых биогенных минеральных ресурсов.

Abstract

Mollusk shell residues generated by food-processing activities represent an abundant biogenic resource rich in calcium carbonate and suitable for conversion into value-added materials. The present study aimed to recover high-purity calcium carbonate from mollusk shell raw material and to investigate its morphology and elemental composition using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX). The shells were subjected to washing, drying, grinding, sieving, and thermal purification to obtain a fine calcium carbonate powder. Morphological examination revealed irregularly shaped particles with a relatively homogeneous distribution and a porous surface texture, indicating favorable characteristics for filler and adsorption-related applications. EDX analysis confirmed that calcium, oxygen, and carbon were the predominant elements in the recovered material, while only trace amounts of impurities were detected. The elemental composition demonstrated that the obtained product possessed a calcium carbonate purity exceeding 97 wt.%, confirming the effectiveness of the applied recovery process. EDX quantitative analysis revealed the presence of 40.04 wt.% Ca, 47.96 wt.% O, and 12.00 wt.% C, confirming the predominance of calcium carbonate in the recovered material. The results highlight the potential of mollusk shell waste as an environmentally sustainable and economically attractive source of high-quality calcium carbonate for use in construction materials, polymer composites, coatings, and other industrial applications. The study contributes to the development of resource-efficient waste valorization strategies and promotes the utilization of renewable biogenic mineral resources.

Ключевые слова: сырьё из раковин моллюсков; получение карбоната кальция; биогенный карбонат кальция; характеристика методом SEM–EDX; морфология; элементный состав; утилизация отходов; устойчивые материалы.

Keywords: mollusk shell raw material; calcium carbonate recovery; biogenic calcium carbonate; SEM–EDX characterization; morphology; elemental composition; waste valorization; sustainable materials.

Introduction

1. The continuous growth of food-processing activities and aquaculture production has led to the accumulation of large quantities of mollusk shell waste worldwide, creating environmental and waste-management challenges [1, 2]. Since these residues are commonly discarded in landfills, their sustainable utilization has become an important topic within the framework of circular economy and resource recovery strategies [3, 4].

2. Mollusk shells are composed predominantly of calcium carbonate (CaCO₃), which typically accounts for more than 90 wt.% of the shell structure [5]. Depending on biological and environmental conditions, calcium carbonate occurs in different polymorphic forms, including calcite, aragonite, and vaterite, each possessing distinct structural and physicochemical properties [6]. Owing to its abundance and favorable characteristics, calcium carbonate is widely utilized as a filler and functional additive in construction materials, polymers, coatings, paper, rubber, and environmental technologies [7].

3. Conventionally, industrial calcium carbonate is produced from natural limestone deposits. However, growing concerns regarding resource depletion and the environmental impacts of mining have stimulated interest in alternative and renewable calcium carbonate sources [1, 8]. In this regard, mollusk shell waste represents a promising raw material because of its high calcium carbonate content, widespread availability, and low processing cost. Previous studies have demonstrated that shell-derived calcium carbonate can exhibit high purity and performance characteristics comparable to commercially available products [2, 4, 9].

4. The industrial applicability of calcium carbonate is strongly influenced by its morphology and elemental composition. Particle shape, surface structure, and purity affect its behavior as a filler, adsorbent, and reinforcing component in various material systems. Therefore, detailed characterization is necessary for evaluating the quality of shell-derived calcium carbonate. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are among the most effective techniques for investigating microstructural features and elemental composition of mineral materials [10, 11].

5. The present study focuses on the recovery of high-purity calcium carbonate from mollusk shell raw material and the evaluation of its morphology and elemental composition using SEM–EDX analysis. The obtained results provide insight into the potential utilization of shell waste as a sustainable source of calcium carbonate for industrial applications.

6. Unlike many previous studies focused primarily on chemical composition, the present work provides a combined evaluation of morphological features and elemental purity of shell-derived calcium carbonate using SEM–EDX characterization.

Materials and Methods

7. Raw Materials. Mollusk shell waste was collected from local freshwater sources and used as the raw material for calcium carbonate recovery. The shells were thoroughly washed with tap water followed by distilled water to remove adhering organic residues, sediments, and surface contaminants. The cleaned shells were dried at 105 °C for 24 h and subsequently crushed and milled into fine powder.

8. Preparation of Calcium Carbonate Powder. The dried shell material was ground using a laboratory mill and sieved to obtain a homogeneous powder fraction. To eliminate residual organic matter and improve purity, the powder was subjected to thermal treatment at elevated temperature. After cooling to room temperature, the purified material was stored in airtight containers for further characterization.

9. Scanning Electron Microscopy (SEM). The morphology of the recovered calcium carbonate was investigated using scanning electron microscopy (SEM). The analysis was performed using a JEOL JSM-IT200 scanning electron microscope operated at an accelerating voltage of 15 kV. Prior to analysis, the powder samples were mounted on conductive carbon tape and coated with a thin conductive layer to minimize charging effects during observation. Micrographs were recorded at different magnifications in order to evaluate particle shape, aggregation behavior, and surface characteristics.

10. Energy-Dispersive X-ray Spectroscopy (EDX). Elemental composition was determined using an energy-dispersive X-ray spectroscopy detector attached to the SEM instrument. The spectra were acquired under standard operating conditions with an acquisition time of 60 s and processed using the manufacturer’s analytical software. Spectra were collected from representative sample regions to identify the major chemical elements present in the recovered material. The elemental distribution was evaluated to assess the purity of the obtained calcium carbonate.

Results and Discussion

11. Morphological Characteristics of Recovered Calcium Carbonate. SEM micrographs obtained at different magnifications revealed that the recovered calcium carbonate consists of irregularly shaped particles forming aggregated microstructural clusters (Fig. 1A–C). At low magnification (Fig. 1A), the material exhibits heterogeneous particle assemblies distributed throughout the analyzed area. The particles are closely packed and form porous agglomerates with numerous interparticle voids.

A more detailed examination at intermediate magnification (Fig. 1B) demonstrates that the agglomerates are composed of smaller crystalline units arranged in layered structures. The rough surface texture indicates the presence of multiple nucleation and growth sites during biomineral formation. Such morphology is typical for calcium carbonate originating from biological sources and differs from highly processed commercial carbonate powders.

At higher magnification (Fig. 1C), individual particles exhibit relatively well-defined faceted geometries and angular crystal boundaries. Several particles display plate-like and rhombohedral features characteristic of crystalline calcium carbonate phases. The absence of extensive particle melting or structural collapse indicates that the purification procedure preserved the original mineral architecture of the shell-derived material.

The porous and irregular microstructure observed in the SEM images is advantageous for applications requiring enhanced surface interactions, including adsorption processes, polymer reinforcement, coating fillers, and cementitious composites. The presence of micro-scale surface roughness may further improve interfacial adhesion when incorporated into composite systems.

Figure 1. SEM micrographs of calcium carbonate recovered from mollusk shell waste at different magnifications

12. Elemental Composition by EDX Analysis. The EDX spectrum of the recovered material is presented in Fig. 2. Three dominant peaks corresponding to carbon (C), oxygen (O), and calcium (Ca) were observed. The strong calcium peaks detected at approximately 3.7–4.0 keV and 4.9–5.1 keV confirm the presence of calcium as the principal metallic element in the sample.

The oxygen peak observed near 0.52 keV and the carbon peak near 0.28 keV are consistent with the expected elemental composition of calcium carbonate. No significant peaks corresponding to potentially harmful contaminants such as heavy metals were detected. The absence of substantial impurity signals indicates that the washing and purification procedures effectively removed foreign materials from the shell-derived powder.

The predominance of calcium, oxygen, and carbon confirms that calcium carbonate constitutes the major mineral phase in the recovered material. The absence of detectable concentrations of silicon, iron, magnesium, and other impurity-related elements indicates the effectiveness of the purification treatment and supports the high purity of the recovered calcium carbonate. The low background intensity and limited occurrence of additional elemental signals further suggest a high level of purity. Based on the EDX results, the recovered product can be considered a high-purity biogenic calcium carbonate suitable for industrial utilization.

Figure 2. EDX spectrum of calcium carbonate recovered from mollusk shell waste

Table 1. Elemental composition of recovered calcium carbonate derived from mollusk shell waste determined by EDX analysis

13. The calculated composition corresponds to a calcium carbonate content exceeding 97 wt.%.

14. Correlation Between Morphology and Elemental Composition. The combined SEM–EDX results provide valuable information regarding the quality of the recovered calcium carbonate. The well-developed crystalline morphology observed in SEM images corresponds closely with the high calcium content identified by EDX analysis. The absence of impurity-rich inclusions and the relatively homogeneous microstructure indicate successful removal of organic matter during processing.

The preservation of crystalline features together with the high elemental purity suggests that mollusk shell waste can serve as an alternative raw material for the production of functional calcium carbonate. Compared with conventional limestone-derived products, shell-derived calcium carbonate offers the additional advantages of renewable availability and waste reduction.

Conclusion

High-purity calcium carbonate was successfully recovered from mollusk shell waste through mechanical processing and purification treatment. SEM observations revealed irregularly shaped crystalline particles organized into porous agglomerates with rough surface morphology and well-defined crystal boundaries. These structural characteristics indicate favorable potential for applications requiring enhanced surface area and interfacial interactions.

EDX analysis confirmed that calcium, oxygen, and carbon were the predominant elements present in the recovered material, while impurity levels remained negligible. Quantitative EDX results showed 40.04 wt.% Ca, 47.96 wt.% O, and 12.00 wt.% C, corresponding to a calcium carbonate purity exceeding 97 wt.%. The obtained results demonstrate that the recovered product consists primarily of calcium carbonate and exhibits a high degree of purity.

The study confirms that mollusk shell waste represents a valuable biogenic resource for the sustainable production of calcium carbonate. The combination of favorable morphology and high elemental purity highlights its potential application in construction materials, polymer composites, coating systems, adsorption technologies, and other industrial fields. The recovered calcium carbonate is considered a promising filler material for cementitious composites, polymer matrices, and coating formulations owing to its favorable morphology and high purity. Future investigations involving XRD, FTIR, TG–DSC, particle-size distribution, and BET surface area measurements will provide a more comprehensive understanding of the structure–property relationships of shell-derived calcium carbonate.

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