Calcium Carbonate Production

Reactant-Controlled Calcium Carbonate Synthesis in the Presence of Propionic Acid

Abstract

In this study, the morphology of calcium carbonate (CaCO3) crystals synthesized in the presence of propionic acid (PA) was examined by XRD and SEM analyses, and BET specific surface areas were determined. According to the results obtained, CaCO3 in calcite form is obtained by using initial reactant concentrations between 0.2 M and 0.1 M in the presence of 0.05 M PA. CaCO3 synthesized using 0.1 M and lower initial reactant concentrations is obtained as a mixture of vaterite and calcite forms. The vaterite form is produced as hollow spheres composed of nano-sized particles. With the concentration reduced to 0.1 M, the BET specific surface area begins to be measured around 19 m²/g due to the formation of vaterite.

1. Introduction

CaCO3 is one of the most widely used materials in paints and coatings industries today [1]. Due to ease of application, water-based paints are preferred over solvent-based systems. Apart from water and polymeric binders, inorganic fillers are used as the third main component of water-based coatings, either as functional pigments or spacer extenders [2]. By adding fillers, the cost of water-based paints is reduced. Among the various fillers available, CaCO3 as a filler is widely used due to its availability and low cost [3]. CaCO3 is non-toxic. It has low density, high whiteness value, and is resistant to weather conditions [4]. Beyond all these properties, its interaction with the binder, pigment, and other components in the paint system is minimal. The ability to produce CaCO3 in particle distribution and fineness suitable for all desired processes is its most important characteristic. This property makes it useful in regulating physical properties such as dispersion, gloss, and opacity [5]. As scientists investigate various parameters for CaCO3 production with desired properties [6], the effects of additives used during crystallization on the synthesized crystal morphology and sizes have been known, so the effects of additives on CaCO3 production have also attracted attention [7, 8]. Different studies on the synthesis of CaCO3 in the presence of PA also exist [9].

2. Materials and Methods

2.1 Materials

In this study, calcium chloride dihydrate (CaCl2.2H2O, 99.5% ACS) and sodium carbonate (Na2CO3, 99.9% ACS) used for the reaction were obtained from Merck. PA (99%) used as an additive was obtained from Sigma-Aldrich.

2.2 Method

In the experiments, CaCl2.2H2O and Na2CO3 solutions used to synthesize CaCO3 were mixed in a 1 L double-walled glass reactor and the reaction was carried out for 15 minutes. During the reaction, the reactor temperature was maintained at 25°C using a circulating water bath and the stirring rate was kept at 400 rpm using a magnetic stirrer. To investigate the effect of changes in initial reactant concentration on CaCO3 crystal size and morphology in the presence of additives, PA concentration was kept constant at 0.05 M in all experiments. Initial reactant concentrations were equimolar and concentrations were selected as 0.2, 0.175, 0.15, 0.1, 0.075, and 0.05 M. The obtained residue was filtered with a membrane filter and washed, then dried overnight in a vacuum oven at 80°C. After drying, XRD, SEM, and BET analyses were performed on the obtained powder. XRD structural analysis of the material was performed by scanning between 10° and 90° 2θ values on a Bruker D8 Discover X-ray diffraction instrument. SEM images were acquired using a Carl Zeiss Sigma 300 VP scanning electron microscope. The BET specific surface areas of the synthesized materials were measured using a Quantachrome Nova Touch LX4 instrument. Degassing was performed before BET surface area measurements, and this process was carried out at 80°C for 10 hours. Specific surface area calculations were based on multipoint nitrogen adsorption isotherm measurements at 77 K.

3. Results and Discussion

As the initial reactant concentration is reduced, the amounts of Ca2+ and CO3²⁻ ions in the reactor environment decrease, so the amount of material synthesized by reacting decreases. It was observed through conductivity measurements that the 0.05 M PA used as an additive at the relevant concentrations had no inhibitory or delaying effect on the reaction. From the XRD analyses of materials produced in the presence of PA, it was understood that CaCO3 was synthesized. Figure 3.1 shows the XRD analyses of CaCO3 materials synthesized at initial reactant concentrations of 0.2, 0.175, and 0.05 M in the presence of PA. [caption id="attachment_149996" align="aligncenter"] Figure 3.1 XRD analyses of synthesized CaCO3 crystals (C: Calcite – V: Vaterite)[/caption] As a result of comparison from the ICDD database for the synthesized materials, calcite peaks matched with JCPDS 98-006-0995 card and vaterite peaks matched with JCPDS 98-000-6034. At 0.05 M PA concentration, with the initial reactant concentration used as 0.15 M, the synthesized CaCO3 is seen to consist of cubic agglomerated calcite crystals (Figure 3.2a). Upon examination of SEM images, the surfaces of the synthesized calcite crystals are clean and smooth. At 0.05 M PA concentration, with the initial reactant concentration used as 0.1 M, vaterite crystals in the form of hollow spheres are formed alongside agglomerated cubic calcite crystals (Figure 3.2b). SEM analysis reveals deterioration on the surfaces of the synthesized calcite crystals. At 0.05 M PA concentration, with the reactant concentration used as 0.05 M, a mixture of calcite and vaterite forms is obtained as in the experiments performed at 0.1 M (Figure 3.2c). SEM analyses also show that vaterite spheres are formed by the agglomeration of nano-sized crystals (Figure 3.2d). Upon examination of SEM images, it is understood that as the initial reactant concentration is reduced from 0.15 M to 0.05 M, the average crystal size decreases. [caption id="attachment_149998" align="aligncenter"] Figure 3.2 SEM images of CaCO3 crystals synthesized in the presence of PA (0.05 M): Initial reactant concentration
a) 0.15 M b) 0.1 M c) 0.05 M d) 0.05 M (High magnification)[/caption] BET specific surface area measurements of the obtained materials show that as the initial reactant concentration reaches from 0.2 M to 0.1 M, the specific surface area increases from 6.35 m²/g to 19.98 m²/g (Figure 3.3). [caption id="attachment_149999" align="aligncenter"] Figure 3.3 Effect of initial reactant concentration on BET specific surface area in the presence of PA (0.05 M)[/caption]

4. Conclusion

In this study, CaCO3 was rapidly synthesized using CaCl2 and Na2CO3 solutions in the presence of PA used as an additive. Morphology and size were determined by XRD and SEM analyses, and BET specific surface areas were measured using nitrogen adsorption isotherms. XRD analyses of materials synthesized in all experiments with PA concentration adjusted to 0.05 M confirm that pure CaCO3 was synthesized. With initial reactant concentration at 0.15 M, the crystal morphology is entirely in the form of agglomerated cubic calcite. Using concentrations of 0.1 M and 0.05 M, vaterite in the form of hollow spheres obtained by combining nano-sized structures accompanies the calcite form. With decreasing initial reactant concentration, the BET specific surface area value increases, and it is presumed that the reason for this is due to the formation of hollow vaterite sphere forms. The fundamental reason for changes in morphology and BET surface areas is the effectiveness of PA concentration used as an additive at the relevant concentrations.   References [1] V. Alvarez and M. Paulis, "Effect of acrylic binder type and calcium carbonate filler amount on the properties of paint-like blends," Prog. Org. Coatings, vol. 112, no. May, pp. 210–218, 2017, doi: 10.1016/j.porgcoat.2017.07.023. [2] V. Alvarez, N. S. J. Williams, and M. Paulis, "Isolation of the interaction between CaCO3 filler and acrylic binder. Part II: Effect of the amount and type of functional monomer," Prog. Org. Coatings, vol. 134, no. May, pp. 281–287, 2019, doi: 10.1016/j.porgcoat.2019.05.024. [3] V. Alvarez, N. S. J. Williams, and M. Paulis, "Isolation of the interaction between CaCO3 filler and acrylic binder. Part I: Effect of the surfactant and functional monomer type," Prog. Org. Coatings, vol. 136, no. March, p. 105212, 2019, doi: 10.1016/j.porgcoat.2019.105212. [4] U.S. Department of Health and Human Services and U.S. Department of Labor, "Occupational Safety and Health Guideline for Calcium Carbonate." pp. 1–7, 1995. [Online]. Available: https://www. cdc.gov/niosh/docs/81-123/pdfs/0090.pdf?id=10.26616/NIOSHPUB81123 [5] TurkChem, "Ideal Filler Properties in Paint Formulations," 2022. https://www.turkchem.net/idealfiller- properties-in-paint-formulations-2.html [6] S. Kirboga and M. Öner, "Application of experimental design for the precipitation of calcium carbonate in the presence of biopolymer," Powder Technol., vol. 249, pp. 95–104, 2013, doi: https:// doi.org/10.1016/j.powtec.2013.07.015. [7] S. Kırboga and M. Öner, "The inhibitory effects of carboxymethyl inulin on the seeded growth of calcium carbonate," Colloids Surfaces B Biointerfaces, vol. 91, pp. 18–25, 2012, doi: https://doi. org/10.1016/j.colsurfb.2011.10.031. [8] S. Kirboga, M. Oner, and E. Akyol, "The effect of ultrasonication on calcium carbonate crystallization in the presence of biopolymer," J. Cryst. Growth, vol. 401, no. September, pp. 266–270, 2014, doi: 10.1016/j.jcrysgro.2013.11.048. [9] G. Ahmed Hussein Hussein and M. B. Akın, "Investigation of Effect of the Parameters on Calcium Carbonate Crystallization," in The 1st International Karatekin Science and Technology Conference, 1-3 September 2022, Çankırı, Turkiye, 2022, pp. 369–373.   Dr. Muhammed Bora Akın, Assistant Professor Çankırı Karatekin University Faculty of Engineering Department of Chemical Engineering   Ghassan Ahmed Hussein Hussein Senior Operations Engineer Northern Oil Refineries, Iraq Ministry of Oil Çankırı Karatekin University Graduate School of Sciences Chemical Engineering Master's Program