Factors Affecting the Particle Size of Bio-Calcium Carbonate Synthesized from Industrial Eggshell Waste
2018 Volume 59 Issue 8 Pages 1220-1224
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2018 Volume 59 Issue 8 Pages 1220-1224
Calcium carbonate is broadly used as a catalyst support, filler, additive, and reinforcement in several types of industry e.g. chemical, food, and biomedical industry. Recently, eggshell waste has attracted much attention for the purpose of calcium carbonate production due to its compost about 96% calcium carbonate. However, direct use of egg shells as filler material can probably cause product defects. In this research, calcium chloride was extracted from chicken-eggshell waste followed by precipitation of micron size calcium carbonate. The effect of agitation time, the initial concentration of calcium chloride and synthesis temperature on particle size, and selected physicochemical properties of this precipitated calcium carbonate (PCC) were investigated. Scanning electron micrographs of the prepared materials illustrated that all of the PCCs obtained from these experiments exhibit uniform-round shape. The laser diffraction results show that the median size of the PCC particles increased significantly from about 6 µm to 19 µm with increasing agitation time and with decreasing initial concentration of calcium chloride. However, increasing the synthesis temperature from 30°C to 160°C only slightly increased the median size of the PCC particles. The results of X-ray diffraction indicated that both agitation time and initial concentration also have an effect on the crystalline morphology of the PCCs. In addition, calcite crystalline phase became dominant over the other crystalline phases when agitation time and initial concentration were increased. In comparison, PCCs synthesized from this eggshell waste have much smaller median particle size than commercial calcium carbonate. Furthermore, the purity of the PCC derived from shell waste was comparable to commercial calcium carbonate. This facile synthesis is environmentally friendly and cost effective.
Calcium carbonate is one of the most important materials due to its extensive applications in fundamental research and industry.1–3) It has been broadly used in cement making and used as a filling material in paint, rubber, textile, sealant, and plastics industries in order to reduce product cost and increase some mechanical properties of various materials. Calcium carbonate is also essential for medicine, pharmaceuticals, foodstuffs, and also for environmental aspects.4–6) The most commonly used natural sources of calcium carbonate are limestone, chalk, and dolomite. However, production of calcium carbonate from renewable sources, e.g. cockle shell and avian eggshell, has attracted considerable attention due to the need for sustainable materials.7,8)
In Thailand, more than 660 tons of chicken eggshells are produced annually from large hatchery industry and are commonly disposed into landfills. This disposal method carries major concerns of environmental impact, green house gases emissions, and community conflicts. Eggshells can be used to produce calcium carbonate as they contain about 96% of calcium carbonate with the remaining 4% of the composition being trace elements and the organic matrix.9) Direct use of eggshells as a filler material probably causes detrimental effects on the end use properties of the products. Besides the purity of the solid phase, calcium carbonate with micron size and narrow particle size distribution is preferable for broad use and due to market demand.1,10) Technology for the production of calcium carbonate with the properties mentioned above include two main routes: solid-liquid-gas route and liquid-liquid route. In the former, precipitated calcium carbonate (PCC) occurs on a time scale of seconds in a chemical reaction of two soluble salts, where as in the latter carbon dioxide is bubbled through solution as the source of carbonate ion. The precipitation mechanism of calcium carbonate has been extensively studied but most of the studies pay attention on the synthesis of PCCs from commercially starting chemicals.1,11) However, the complexity of crystal nucleation and growth of PCCs still leads to controversies in regards to the factors that affect the properties of PCCs.12,13) Furthermore, several researches have reported on the synthesis of PCCs from cockle shell and its application on bone graft materials,4) drug delivery,14) and adsorption of heavy metal.15) However, only a few researches have reported on the preparation of PCCs from eggshell.8,16,17)
In the present study, precipitated calcium carbonate was synthesized from chicken eggshell waste via a simple liquid-liquid route. To the best of our knowledge this is the first time that the effects of various factors e.g. agitation time, temperature, and initial concentration of calcium chloride prepared from chicken eggshell waste on the particle size of PCCs were systematically observed.
Commercial grade of calcium chloride, calcium carbonate, sodium hydroxide, and ethylenediaminetetraacetic acid (EDTA) were obtained from Ajax Finechem Pty Ltd., Concentrated (37%) hydrochloric was obtained from RCI Labscan limited. All chemicals in this study were used without any further purification.
2.2 Preparation of powder eggshellsChicken eggshell wastes in this study were derived from large hatchery farms in the northeast of Thailand. The eggshell wastes were rinsed with water 2 to 3 times to separate the shell membrane and dred in a hot air oven at 105°C for 24 hours. Then, the dried eggshell samples were crushed with Panasonic MX-AC400 crushing machine followed by screening through a 425 micrometer sieves to obtain the eggshell powder. Results from laser diffraction particle size analyzers indicated that the eggshell powder had median size of 110.6 µm. This powder mainly consisted of calcium oxide CaO 68.2% with loss on ignition of 30.5%.
2.3 Preparation of calcium chloride solutionMethod for preparation of calcium chloride was adapted from Oladoja et al.18) Briefly, calcium chloride solution was prepared via immersin 10 g of eggshell powder in 100 ml of 2 M HCl. Then, the mixture was agitated at 1,000 rpm for 2 hours. The extraction mixture was then filtered to obtain calcium chloride solution. Subsequently, concentration of the obtained calcium chloride solutions was determined via EDTA titration method and this concentration was determined to be 1.74 M.
2.4 Synthesis of precipitated calcium carbonatePrecipitation of calcium carbonate was conducted through gradual addition of sodium carbonate solution to the prepared calcium chloride solution. In addition, agitation time, initial concentration of calcium chloride, and temperature were varied as shown in Table 1. Then, the precipitation mixture was filtered and washed with distilled water 2–3 times to obtain the PCC. The synthesized PCC was dried at 105°C for 24 hours and kept in vacuum desiccators.
The following instruments were employed for observation and characterization of the eggshell powder and the prepared PCCs. Microstructure of PCC surface was analyzed by using a scanning electron microscopy (SEM – LEO 1455VP). Particle size diameter of the both the eggshell powder and PCC samples was analyzed by laser diffraction particle size analyzers (Beckman Coulter LS 230). The crystal phase and elemental composition of the samples was examined by X-ray powder diffraction (XRD - PW 3040/60 X’PERT PRO Console) with Cu-K radiation and X-ray fluorescence analyzer (XRF Bruker S4 Explorer), respectively.
Figure 1 shows that both agitation time and initial concentration of CaCl2 play an important role on particle size of the synthesized PCCs. Results from laser particle size analyzer show that median particle size of the PCCs increased with increasing agitation time. This is probably due augmented agglomeration of small PCC particles into so called secondary particles with increased agitation time. Increasing the agitation time allows these secondary PCC particles to grow continuously.19,20) The increase of the particle size with agitation time prepared from the 1.74 M CaCl2 starting solution was rather modes in comparison to the size increases observed for the PCCs prepared from CaCl2 solutions with lower concentrations. It should be noted that the smallest particle size of the synthesized PCCs was obtained at the shortest agitation time (30 s). Altiner et al.10) pointed out that precipitation of 98% of PPCs occurred rapidly within 1 min. For the effect of initial concentration, median particle size of the PCCs decreased with increasing starting concentration of CaCl2. It appears that, particle size of the PCCs obtained from various agitation time and at the concentration of 1.74 M CaCl2 was between 6.4–11.2 µm, which is smaller than median particle size of both analytical grade (11.4 µm) and industrial filler grade (11.8 µm) of CaCO3. Table 2 shows the results from the X-ray fluorescence reveled that the obtained PCCs and analytical grade CaCO3 consist of 98.20 and 97.49% of CaO, respectively. Furthermore, the yields of PCCs derived from eggshell and PCCs derived from dolomite21) were 80% and 79%, respectively. These results indicate that the purity and yield of the PCCs produced from eggshell waste is comparable to commercial chemicals.
The effect of agitation time and initial concentration of CaCl2 on particle size of synthesized PCCs.
Figure 2 and Fig. 3 present the SEM images of the precipitated CaCO3 obtained from various experimental conditions. It is clear that PCCs produced with 30 seconds and with 40 minutes agitation time exhibit spherical shape with a rough surface. When the agitation time is increased to 90 minutes, the morphology of the PCCs changes to an irregular shape. This is because long agitation period allows microcrystal of PCCs to form large aggregates.12) This irregular shape of the PCCs is also found for samples made with low initial concentration of CaCl2.
SEM images demonstrating the different morphology of CaCO3 precipitated from CaCl2 solutions with initial concentration of 1.74 M at room temperature with agitation time of (a) 30 seconds (b) 40 minutes and (c) 90 minutes.
SEM images of precipitated CaCO3 prepared at room temperature and 30 second agitation time with various initial CaCl2 concentrations (a) 1.74 M, (b) 1.40 M, (c) 1.05 M and (d) 1.07 M.
In this experiment, the initial CaCl2 concentration of 1.74 M was chosen and reactions were carried out at temperatures 30, 60, 100, and 160°C. As can be seen in Fig. 4, the median particle size of the prepared PCCs slightly decreases with increasing the reaction temperature from 30 to 60°C. Further increases of reaction temperatures from 60 to 160°C increased the median particle size of the obtained PCCs. Additionally, particle size distribution of the PCCs also shifted up to larger particle sizes (Fig. 5). This is in accordance with the Oswald ripening rule in which high temperature increase mass transport from smaller particles to larger particles.22) Median particle sizes produced at 30, 60, 100, and 160°C were 6.38, 4.41, 5.85, and 7.19 µm, respectively. Figure 6 shows the effect of reaction temperatures on morphology of the PCCs. This revealed that the PCCs still exhibited round shapes at 30 and 60°C while PCCs produced at 100 and 160°C were found to be cubic in shape. Changing the PCC morphology is probably due increased solubility at high temperatures, which has an effect on the morphology of PCCs.1,20)
The effect of temperature on particle size of PCCs.
Particle size distribution of PCCs prepared at different temperatures.
SEM images of precipitated CaCO3 prepared from 1.74 M CaCl2, at 30 second agitation time with various reaction temperature (a) 60°C, (b) 100°C and (c) 160°C.
Calcite, vaterite, and aragonite are the common polymorphs of CaCO3 but these polymorphs are different in their crystallographic characteristics and its applications.1) Thus, optimum conditions for production of pure morphology are useful. Figure 7 shows X-ray diffraction patterns of PCCs prepared at various temperatures with different condition compared with the XRD patterns of eggshell and commercial CaCO3. The XRD peaks at 2θ values of 23.0°, 29.3°, 35.9°, 39.4°, 43.7°, 47.4°, and 48.4° confirm the represence of calcite (JCPS card No. 47-1743). Additionally, The XRD peaks at 2θ values of 20.9°, 24.9°, 27.0°, 32.7°, 43.8°, and 49.9° also reveal the presence of vaterite (JCPS card No. 72-0506). It is clear that the mixture of calcite and vaterite polymorphs formed with high starting CaCl2 concentration (1.74 M). The intensity of vaterite slightly decreased with increasing agitation time from 30 s to 10 min. In contrast, only calcite phase was found for PCCs made at low starting concentration of CaCl2 (1.40 and 1.05 M). It seems that agitation time did not show any effect on the polymorph distribution at low concentration of CaCl2. These results are similar to some research reports, which indicate that vaterite crystals grow more rapidly than calcite crystals at high CaCl2 concentrations. In contrast, low concentration of CaCl2 favores crystal growth of calcite instead of vaterite.10,12,13) Increasing reaction temperature from 30 to 160°C can also change the crystalline form of PCC from aragonite to calcite. The absences of vaterite phase at long reaction times and at high temperatures are probably due to the transformation of the relatively unstable vaterite crystal form to the more stable calcite phase.13,22) There was no trace of aragonite found in the synthesized PPCs.
X-ray diffraction patterns of eggshell, commercial CaCO3, and PCCs prepared at various temperature with different initial CaCl2 concentrations and agitation times.
In this study, PCCs were synthesized from eggshell waste via a simple liquid-liquid precipitation method. This liquid-liquid precipitation method allowed us to produce micron particle sizes of the PCCs ranging from 4 to 11 µm with narrow particle size distribution. It has been observed that small median particle size of PCCs with round shape could be produced at high initial concentration of CaCl2 and at short agitation time. Also, cubic shape of PCCs was found to be formed at high reaction temperatures. In addition, pure calcite phase has been synthesized when low initial concentration of CaCl2 was used. These results provide supplementary guidance on the production and control of particle size, morphology, and polymorphism of PCCs derived from eggshells, which are crucial for industrial applications.
Charoen Pokphand Foods Public Company Limited (CPF) and Research and Researcher for Industry (RRI) project are highly appreciated for their financial support in this study.
