Synthesis and Characterization of Hydroxyapatite from Cockle Shells (Anadara granosa) Originated from Indonesia

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IOP Conference Series: Earth and Environmental Science

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Synthesis and Characterization of Hydroxyapatite of Cockle Shells (Anadara granosa) Originated from Indonesia Through Precipitation Method

To cite this article: E Sinurat et al 2022 IOP Conf. Ser.: Earth Environ. Sci. 1118 012035

View the article online for updates and enhancements.

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11th International and National Seminar on Fisheries and Marine Science IOP Conf. Series: Earth and Environmental Science 1118 (2022) 012035

IOP Publishing doi:10.1088/1755-1315/1118/1/012035

Synthesis and Characterization of Hydroxyapatite of Cockle Shells (Anadara granosa) Originated from Indonesia Through Precipitation Method

E Sinurat^1*, F R Dewi², D Fransiska¹, R Nurbayasari¹

1 Research Center for Marine and Land Bioindustry, Jakarta 14430, Indonesia

2Research Center for Applied Microbiology, Cibinong 16911, Indonesia

* [email protected]

Abstract. The precipitation method successfully synthesized cockle shells into a highly valuable biomaterial in the present investigation. The present work aimed to determine the effect of the technical approach; (1) calcination temperatures of calcium oxide preparation and (2) sintering time of HA synthesis. Thermogravimetric-differential thermal analysis revealed that the cockle shells were calcined at 600 – 1000 °C for 3 hours and had a fine CaO powder. Thus, those sintering temperature is used as the starting point for the calcination of cockle shells. The calcinated CaO powder was then analyzed. The analysis conducted includes yield, functional group analysis using FT-IR, morphological analysis using SEM, and analysis of the composition of Carbon (C), Calcium (Ca), Oxygen (O), and Phosphor (P). Furthermore, hydroxyapatite synthesis (HA) was done with three different sintering times (2, 4, and 6 hours) at 800 ôC. The characterized HA was functional group morphology, major elemental in the apatite constituents, and the crystallinity degree. Obtained the optimum temperature result for calcinated at a temperature of 800 ôC. The results of HA synthesis obtained by HA quality have approached commercial HA products judging from the composition of Ca, O, and P, but the quality still includes type B of commercial HA. The HA particles obtained are micro-sized, which is 304 nm at a temperature sintering of 800 ôC for 4 hours. The micro-sized allows a by-product of cockle shells as raw material HA to be applied as a futuristic biomaterial in bone/teeth implants.

1. Introduction

It is widely established that hydroxyapatite (Ca10(PO4)6(OH)2, HA) has biological applications in medicine. It resembles human hard tissue in terms of morphology and composition. The biggest distinguishing feature of HA is its exceptional stability compared to other calcium phosphates. It is widely utilized in orthopedics and dentistry because of its biocompatibility, bioactivity, and osteoconductivity [1], [2]. However, the thermal stability of HA is governed by a range of factors that might result in its disintegration. When HA breakdown, the final material's physicochemical characteristics are altered. Those conditions will change an implant's solubility, resorption rate, and even biocompatibility in a living body, affecting its performance [3][5]. The synthesis technique may be one of several variables affecting the HA's thermal stability.

Several methods of synthesizing HA, such as chemical 6, thermal 7,8, and irradiation 9, are synthesized. Various chemical compounds are employed in the course of the chemical synthesis operation. As a result, this procedure is more expensive and time-consuming. Thermal synthesis of hydroxyapatite is a more affordable and time-efficient approach. Additionally, sintering fish bones helps remove the organic component and yields calcium phosphate derivatives such as hydroxyapatite.

In addition to production processes, raw materials have a significant influence in determining the characteristics of HA. Investigation of waste materials for HA production has been done extensively in the last decade. This approach creates a new value product from waste resources while also benefitting the environment. HA was previously synthesized using waste materials such as seashells [6][8], fish

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scale [3], [9], fishbone [10], eggshells[11], and snail shells [12], [13]. The waste materials contain a significant amount of calcium and can be employed as a calcium precursor in the formation of HA.

However, HA characteristics and purity might be influenced by the preparation method. Hadiwinata et al., (2021b) concluded that the calcination temperature affected the crystallinity degree and calcium content of CaO as HA raw material. Thus, it is critical to determine the ideal calcination temperature to get HA with a high crystallinity degree. The sintering behavior of hydroxyapatite (HA), as well as the ensuing microstructure and properties, are impacted not only by the features and impurities of the raw materials but also by the fabrication process's thermal history [15].

The small-scale industry in Indonesia discards a considerable number of cockle shells daily. Thus, in this study, cockle shells were utilized through precipitation and thermal synthesis. The study focussed on combining the effect of the technical approach; (1) calcination temperatures of calcium oxide preparation and (2) sintering time of HA synthesis. The effect of the calcination process and sintering time on the CaO physicochemical properties and HA were evaluated.

2. Materials and Methods.

2.1. Raw material preparation

The cockle shells were obtained from Muara Reja beach, Tegal, Indonesia. The first stage involves the handling of raw materials by washing the shells with water to remove all the dirt. The clean shells were then rinsed and dried under the direct sun for a day. On the following day, the shells were dried in the drier cabinet at 50 C for 48 hours. The dried shells are then crushed manually using a hammer mill.

The crushed shells were transferred into a blender (HR2106 Philips, Netherlands) and blended for 3 minutes at 30 rpm to get the finer form. The shells powder was stored in a plastic container at room temperature before use.

2.2. Methods

Two sequence experiments were done in this study. The first experiment was designed to find the effect of calcinating temperature (600 – 1000 C) on the physicochemical properties of the yielded CaO powder. Elemental (carbon (C), calcium (Ca), oxygen (O), and phosphor (P)) content using an Energy Dispersive Spectroscopy (EDS), microstructure, and molecular were done in this stage. The last experiment was aimed at the effect of sintering temperature physicochemical properties of HA.

Functional group, the ratio of calcium and phosphor (Ca/P), particle and morphological, size, and degree of crystallinity were investigated.

2.3. Calcium oxide (CaO) preparation

Shells powder was calcined using a furnace (6000 Barnstead, USA) with temperature variations of 600, 700, 800, 900, and 1000 ° C for 3 hours to decompose calcium carbonate into calcium oxide. Calcium oxide powder is then stored in a dry container prior to analysis.

2.4. HA synthesis

Calcium oxide powder from cockle shells was dissolved in 100 mL aquadest, and then diammonium hydrogen phosphate (NH4)2HPO4 (Merck, 101207) with a Ca/P ratio of 1.67 was dissolved in 100 mL aquadest. Calcium and phosphate solutions were precipitated and homogenized at room temperature for 90 minutes at a stirring speed of 250 rpm, followed by 24 hours of aging. The precipitation products are filtered through filter paper, rinsed with distilled water, and then sintered at 800°C for 2, 4, and 6 hours.

2.5. Morphological and elemental analysis

The morphology of HA was examined using an Energy Dispersive Spectroscopy (EDS)-equipped Scanning Electron Microscope (SEM) (JEOL 6000, Japan). HA was loaded into the sample holder and the coating machine. The samples were coated for 1 minute with a layer of gold (Au) to remove any conductivity. The coated sample was then put into a scanning electron microscope (SEM) at

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magnifications of 2000 and 5000 times. The measurement is carried out at a 20 kV voltage acceleration.

Five elements of the sample were then identified using a feature of the SEM-EDS machine.

2.6. Functional group analysis

Spectrum One FTIR instrument C69526 (Perkin Elmer Precisely, Germany) was used in this analysis.

The FTIR instrument is equipped with a detector in the middle infrared region (4.000-450 cm^-1) at a resolution of 4 cm^-1. The HA was crushed to get a finer form before analysis. The sample was subsequently mixed with KBr salt in 1: 100. Then the mixed sample was placed in the metal chamber to be pressed and vacuumed for 15 minutes at a pressure of 7 tons. The sample was inserted into the FTIR instrument afterward. The data graph was read in the spectrum one application on the computer.

2.7. Analysis of crystallinity degree

X-ray diffraction (X'Pert Powder DY 3688) with Cu K radiation was used to analyze the mineralogy of HA. The resultant HA powder's crystal structure and phase purity were determined using Rietveld refinement with a step size of 0.01o and 7.14 s, respectively.

3. Results and Discussion

3.1. Characterization of CaO

The yield and calcium (Ca) content of CaO are shown in Table 1, and the color of CaO is shown in Figure 1. The result showed that the higher the calcination temperature, the lower the CaO yield. The calcium (Ca) content increased with increasing the calcination temperature. The phosphor (P) content had the same pattern as the CaO yield. Due to the higher calcination temperature, the phosphor content decreased.

Table 1. The yield and calcium (Ca) content of calcinated cockle shell with various temperature Various

temperatures (⁰C) Yield (%) C (%) Ca (%) P (%) O (%)

600 96.49 8.91 84.04 0.20 6.81

700 86.41 6.03 86.11 0.15 7.72

800 60.33 23.10 56.51 0.07 20.29

900 58.07 17.39 63.66 nd 18.95

1000 55.13 7.95 89.95 nd 2.10

Figure 1 showed that the CaO color became whiter due to the increase in the calcination temperature.

Powder at the temperature of 600 is still blackish ash, which indicates high levels of carbonate [14], [16]. In contrast, calcined starting temperature 700-1000 ^oC powder white color produced tends to be increasingly white.

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Figure 1. CaO powder produced by calcination cockle shells from temperature variations

The CaO yield decreased due to the higher the calcination temperature. The yield decreasing showed that the cockle shells had decomposed during the heating process. The decomposed phase was calculated from the change in weight of the sample to the initial weight of sample [17]. It could be seen that the maximum was achieved at a temperature of 1000 ºC, which was 55.13%. At the temperature of 800 ºC, it could be said that cockle shells had optimally decomposed into CaO. This showed from the powder produced in whiter color, which indicates the change of CaCO3 to CaO. Possibility at this temperature process occurs complete calcination, which means that almost all of the CO2 in CaO can be liberated [18].

The structure of the shells caused the high-temperature calcination required by cockle shells to decompose into CaO. The cockle shells consist of three layers: periostracum, a horny substance, prismatic, and a thick layer consisting of CaCO3 crystals. The nacre is the innermost layer composed of fine crystals CaCO3. The third layer forms a very hard shell that requires a higher calcination temperature to get CaO [19]. CaO from these cockle shells had a calcium content (Ca) of 56.51 – 89.95%. The calcium content of CaO was still in the range of values from previous studies. The color of CaO at 600 ºC was blackish gray, and the more the calcination temperature increased, the color changed to bright white. The color change occurs due to the combustion process with very high temperatures, which causes carbon release [20].

3.1.1. Microstructure Analysis

Figure 2 shows SEM pictures of cockle shells estimated at different temperatures. At a magnification of 2,000x, the SEM image was captured. Overall morphology shows that various microstructures, such as rods with a diameter of roughly 5-10 µm, are present. Carbon, calcium, oxygen, and phosphorus were detected by EDS from calcined samples, as shown in Table 1. At 800°C of calcination, the maximum calcium and oxygen levels are disseminated. The basic ingredient for the synthesis of HA is calcium and oxygen (CaO) content, which is weighed.

At a calcination temperature of 800ºC, the optimum oxygen level obtained is found at a calcination temperature of 800 °C, the particle size is smaller than at calcination at a temperature of 600 ^oC and the size is more homogeneous. However, calcined at 1000 ^oC, agglomeration occurs in the particles.

A). Calcinated at 600 ôC B) Calcinated at 700 ôC C). Calcinated at 800 ôC

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D) Calcinated at 900 ^oC E) Calcinated at 1000 ^oC Figure 2. Morphology of CaO powder with temperature variation

3.1.2. Molecular Structure

As a source of calcium, the cockle shells were calcined to CaO form. A source of phosphorus was used diammonium phosphate by adding H3PO4 to obtain a precipitate of Ca10 (PO4) 6 (OH)2. Figure 3 shows FTIR calcined cockle shells of temperature variations in frequencies of 450–4000 cm⁻¹. Significant characteristic peaks at 711 (ʋ1), 874 (ʋ2), 1410-1464 (ʋ3), indicative of the presence of CaCO3

compounds that are carbonated in the sample[21]. In addition, a small uptake at 1700 cm^-1 indicates the presence of a combination of CO32- band. This uptake is not present in calcination results at temperatures of 900 ôC and 1000 ôC. This indicates that the level of CO32- in powder calculated by the temperature is very small. While calcined cockle shells at a temperature of 600 - 800 ôC, there is uptake in wavenumbers of 1700 cm ^-1 reinforced with the uptake of 2511 cm ^-1 and 2910 cm^-1. In addition, the appearance of CaO showed from the absorption band at a wavelength of 2513.25 cm^-1, which is a characteristic of the peak of the C – H functional group. Samples containing CaO showed in the C – H stretching vibration [22].

The presence of CaO can also show in the indicated conversion of CaCO3 to CaO. As well, the appearance of the absorption band at a wavelength of 709.80 cm^-1 is a fingerprint indicating the presence of Ca-O bonds [23]. This absorption peak was obtained at a calcination temperature of 600-800 ^oC, but the absorption peak disappeared when the temperature started at 900-1000 ^oC.

Figure 3. Spectra FTIR of the calcined cockle shells with various temperature (black band (600 ^oC);

blue band 700 ôC); red band (800 ôC); green band (900 ôC); purple band (1000 ôC)).

Absorption bands on cookie shell powder after calcination at several time variations in general, the absorption pattern is not much different, although there is a difference in the absorption intensity.

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

20.2 25 30 35 40 45 50 55 60 65 70 75 80 86.3

cm -1

%T

3460.24,74.99

2918.94,79.23

2512.53,79.15

1798.92,74.52

1420.06,54.22

873.93,65.07

712.15,72.41

3642.63,34.10

2512.33,75.67

1799.98,73.44

1467.48,60.80

711.82,68.51

2511.86,58.83

1800.97,61.24

1410.31,44.69

874.25,52.85 711.52,51.54 3642.77,48.77

3447.65,67.22

2919.15,72.99

1637.80,76.65 1409.06,74.53

1114.31,77.25

3641.20,21.50

2362.73,38.25 2341.64,40.76

1471.76,56.62

1117.42,65.26

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However, the temperature variation is enough to affect the IR spectrum results, which is indicated by the widening spectrum peaks and the increase in the calcination temperature. This can be seen in the absorption of 700s ^{-1 cm}at a temperature of 600-800 ^o C. There are sharps at a peak [22]. However, at a temperature of 900-1000, the peak is seen widening. The indicating that CaOis reduced, the possibility of evaporating so that the intensity is weakened.

3.2. Characterization of HA

3.2.1. Characteristic Analysis of Calcium Phosphate (Ca/P) Ratio

The HA powder resulting from 2, 4 and 6 h of sintering has fine solid white particles (Figure 4). The ratio of calcium (Ca) and phosphate (P) of the yielded HA indicates that the longer the sintering time resulted in a low ratio of Ca/P (Table 2).

Figure 4. HA powder by sintering cockle shells from during time variations

The Ca/P ratio of yielded HA is similar to the commercial HA. The Table also shows that sintering for two hours gave a higher Ca concentration than 4 and 6 h of sintering time and even the commercial HA.

The P concentration of HA is lower compared to commercial HA.

The clinical behaviors of HA are influenced by stoichiometry, crystallinity, and morphology. Hence precise control of the synthesis parameters and their effect on sample properties is required [24], [25].

A Ca/P ratio of 1.67 is desirable due to its similarity to the mineral element of mammalian bones and teeth. HA has gained significant attention in the context of bone and teeth implants.

Table 2. Percentage of Calcium, Phosphate, and (Ca/P) Ratio in Hydroxyapatite.

No Sintering Time at 800

oC Calcium (Ca) (%) Phosphate (P) (%) Ca/P ratio

1 2 h 59.03 8.09 7.30

2 4 h 23.59 8.76 2.69

3 6 h 38.51 12.41 3.10

4 Commercial HA 57.28 28.45 2.01

3.2.2. Microstructure Analysis

The morphological analysis of HA particles can be seen in Figure 5. This study shows that the longer the sintering temperature, the more ha produced tends to be more agglomerated. Compared to standards, the size of HA produced in this study was larger.

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a) b)

c) d)

Figure 5. Morphology of cockle shell HA at different sintering times: a) 2 hours, b) 4 hours, c) 6 hours, d) HA commercial

HA particles that undergo agglomeration are more commonly found at a temperature of 1000 C.

Another study [26] also stated that HA particles undergo agglomeration at a temperature of 1000 C.

This happens because of the influence of HA's hygroscopic nature. So that chemosorption processors form an O-H bridge in the apatite hydroxyl group through the Van Der Waals bond, causing the formation of the physical bond between particles. The resulting hydroxyapatite does not have a dispersing agent that can limit the chemosorption process. The hydroxyapatite particles formation consists of two main factors: hydrothermal temperature pressure and the calcination process.

Hydrothermal temperature pressure causes saturation of suspension, resulting in deposition and impact on the particle nucleation process. The nucleation process continues at the densification stage during the calcination process so that there is the hydroxyapatite particles formation [24].

The study showed that reaction times increase Ca/P ratios. Aging the precipitated powder might add trace amounts of carbonate [24]. Adding carbonate ions to the apatitic structure does not require monovalent cations. In addition, according to Suchanek (1998), the challenge with most traditional precipitation procedures is synthesizing specified orthophosphates [28]. However, the study of (Chai 2018) showed that the ratio of Ca/P did not have a significant effect on the crystalline size and pore properties [29]. In the work of Chai 2018, rich calcium of HA (Ca/P= 1.90 – 2) was produced from fish scales [29]. The fish scales were immersed in Na2HPO4 solution for 5 min at 37 C and then washed using H2O. After washing, the scales were immersed in CaCl2 and tris (hydroxymethyl) aminomethane.

The process went for 5 and 10 cycles and went to a double calcination process (at 250C and then 550C).

A calcium-rich HA produced in this study might be formed due to a calcium-rich HA foams were made and investigated for their degradation behavior on blood differentiation [30]. The study reveals that the foams were biocompatible when cultured human endothelial cells on their surfaces. Calcium ion release, disintegration, and endothelial cell differentiation indicate that this biphasic ceramic is a contender for bone marrow in vitro cultivation and as a prospective bone substitute material. As a result, the calcium-rich HA obtained in this work may be employed as a bone replacement material.

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3.2.3. FTIR Spectra

Hydroxyapatite synthesized is characterized using FTIR to look at the functional groups contained in synthesized HA. In the HA, based on the sintering length seen in Figure 6, there are peaks in the wavenumber (wavenumber) 3600-3572 cm^-1, indicating the presence of oh groups derived from H2O in the apatite crystals formed. While the absorption band at wavenumber 633-602 cm^-1 comes from the OH ̄ group bound to the HA phase [31]. Wavenumbers at 1456 cm^-1 and 1415 cm^-1 indicate the presence of carbonate groups (CO32-). The carbonate groups indicate that the HA obtained still contains CaCO3. The absorption peaks mentioned above are all treatments (two, four, and six hours) and commercial HA.

However, high-intensity uptake in wave numbers ν3-1450s cm^-1 for commercial HA does not indicate ion carbonate (CO32-). The presence of carbonate ions in HA is classified as type BCHA. At 962 cm^-1, the symmetrical stretching mode v1 PO43- is obtained[32] [29]. The asymmetric stretching mode v3 P – O of the estimated sample orthophosphate group is represented by absorption peaks in wavenumbers 1047, 1091, and 1119 cm^-1 in the IR spectra.

Figure 6. Spectra FTIR of HA sintering the cockle shells with various temperatures (black band (HA commercial); blue band (sintering 2 hours); red band (sintering 4 hours); green band (sintering 6 hours))

HA elements or chemical compositions that differ in sintering temperature are determined via EDS analysis. Figure 7 shows the EDS spectra of all samples sintering at 800°C for 2, 4, and 6 hours and commercial HA. Table 2 calculates the presence of the Ca:P ratio based on these findings and compares it to the theoretical ratio of 1.67. The HA closest to commercial HA is sintering for four hours during cockle shell sintering.

The spectra analysis result using FTIR shows an apatite compound marked with the vibration peak of P-O and PO43-. The cluster of PO43- with the calcium could be seen with No. NH cluster adsorption of ammonia or ammonium on the 3150 – 3500 cm^–1. The FT-IR analysis shows all typical absorption characteristics of hydroxyapatite. The HA powder generates two characteristic stretching modes of O-H bands at over 3000 cm^-1 from calcium carbonate molecules. The bands of 1400 cm-¹ indicate the presence of CO2 in the synthesized HA. These groups may have been adsorbed by the HA samples from the atmosphere and replaced the PO^3-4 group in HA during the HA synthesis process [32].

The weaker absorption band indicates fewer CO2 or carbonate levels [33], [34]. It can be shown from the results of the peak that appears sintering for 6 hours shows a weaker peak. This product is obtained because moisture allows the O to absorb it and form Ca (OH) easily.

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Figure 7. EDX Spectra of HA at different sintering times: a) 2 hours, b) 4 hours, c) 6 hours, d) HA commercial

3.2.4. Characterize hydroxyapatite by XRD

The results of XRD characterization are presented in Figure 8. The peaks of XRD hydroxyapatite appear at an angle of 2θ of 18.8322°, 25.980ô; 31.70ô; 32,960ô; 39,880ô; 46.80ô; and 49,540ô. The analysis results showed that the sample was hydroxyapatite for all treatments (2, 4, and 6 hours). The peaks that appear are HA at the highest peak of 2θ = 37,140, with a very strong peak intensity. The XRD pattern indicates that the sample is hydroxyapatite Ca10 (PO4)6(OH)2 by JCPDS data 09-0432. The data showed that the highest peak was at 2θ = 37,140. So from these results, it can be concluded that the hydroxyapatite synthesis from the initial compound Ca(OH)2 with H3PO4 has been formed with the following reactions: 10 Ca(OH)2 + 6H3PO4→ Ca10 (PO4)6(OH)2 + 18 H2O. In Fig 8b, there is a moderate peak intensity at an angle of 2θ of 29.37ô, a calcium carbonate compound with calcite crystal type and rhombohedral crystal structure after being synthesized into PCC. This reinforces the indicator that the synthesis process of PCC from shells has been successfully carried out.

The peaks that appear are HA at the highest peak of 2θ = 37.140, with a very strong peak intensity.

The longer the sintering time shows an intensity decreased at 2θ = 37.140, at a sintering time of 2 hours indicates an intensity of 40.000, at 4 hours by 30.000 and 6 hours by 9900. Nevertheless, the XRD pattern of the sintering cockle shell closest to commercial HA is sintering for 4 hours.

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Figure 8. XRD Pattern of Hydroxyapatite of HA at different sintering times: a) 2 hours, b) 4 hours, c) 6 hours, d) HA commercial

The XRD pattern indicates that the sample is hydroxyapatite Ca10 (PO4)6(OH)2 by JCPDS data 09-0432.

Referring to the Joint Cristal Powder Diffraction Standard (JCPDS 9-0432), hydroxyapatite has a diffraction peak at values = 25.9; 29.0; 31.8; 32.2; 32.9 34.0; 39.8; 46.7; 49.5; 50.5; and 53.1. So from these results, it can be concluded that the synthesis of hydroxyapatite from the initial compound Ca (OH)2 with H3PO4 has been formed with the following reactions: 10 Ca(OH)2 + 6H3PO4→ Ca10 (PO4)6(OH)2 + 18 H2O. In Fig 8b, there is a moderate peak intensity at an angle of 2θ of 29.37^o, a calcium carbonate compound with calcite crystal type and rhombohedral crystal structure after being synthesized into PCC. This reinforces the indicator that the synthesis process of PCC from shells has been successfully carried out. Based on the data analysis of peaks, the peaks of hydroxyapatite dominated the XRD pattern. However, the monetite (CaHPO4) presence may still be attributed to the incomplete transformation of monetite during calcination. This happens likely due to the rudimentary calcination process. this happens likely due to the rudimentary calcination process [26].

4. Conclusion

The higher the calcination temperature resulted, the lower the CaO yield. The calcium (Ca) content tended to rise, and phosphor content declined with increasing the calcination temperature. The ratio of calcium (Ca) and phosphate (P) content of the HA indicates that a longer sintering time resulted in a low ratio of Ca/P. Two hours of sintering gave a higher Ca concentration than four and six hours of sintering time or even the commercial HA. HA has a lower P content compared to commercial HA. Sintering HA for four hours close to pattern XRD HA commercial.

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