High local supersaturation formation for precipitated calcium carbonate synthesis by applying a rotating disk reactor

doi:10.21203/rs.3.rs-2635605/v1

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High local supersaturation formation for precipitated calcium carbonate synthesis by applying a rotating disk reactor

https://doi.org/10.21203/rs.3.rs-2635605/v1

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Journal Publication

published 01 Dec, 2023

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In this paper, a spinning disk reactor (SDR) was applied and tested successfully for precipitated calcium particle synthesis. The proposed SDR reactor consists of a spinning disk rotating at 4,000–16,000 rpm. The proposed SDR resulted in high local supersaturation due to the intense energy dissipation produced by a high-speed spinning disk. The higher rotational speed of SDR results in the production of calcium carbonate nanoparticles with smaller mean particle sizes and higher aragonite content. At the rotating speed of 15,000 rpm, precipitated calcium carbonate nanoparticles with a size of around 975 nm were produced. In addition, aragonite content increased from 10 wt% to 95 wt% by increasing disk speed from 4,000 rpm to 15,000 rpm.

Supersaturation

Micromixing efficiency

Nanoparticle

Precipitation

high-speed spinning disk

Precipitated calcium carbonate (PCC) is an abundant element on earth that can be produced experimentally by applying the precipitation method while having a higher control on its purity and specifications (i.e., mean particle size, particle size distribution, morphology, and surface) [1]. As shown in Table 1, PCC has three polymorphs that they are calcite, aragonite, and vaterite.

Table 1

Various Polymorphs of Calcium Carbonate at 25°C.
Polymorph	Crystal structure	Stability	Density, g/cm³	K_sp [M²]
Calcite [2]	Hexagonal	Stable	2.8	1.3×10^–9
Aragonite [2]	Orthorhombic	Metastable	2.9	1.7×10^–9
Vaterite [2]	Hexagonal	Unstable	2.7	1.2×10^–8

The reactive precipitation consists of nucleation, growth, and agglomeration stages that affect mean particle size (MPS), and morphology of synthesized PCC [3], and these three steps can be affected by the extent of supersaturation [4–6].

Mixing can change the specification of synthesized PCC due to the relatively short reaction time (i.e., in order of microsecond) that can be applied using different methods such as mechanical starrier, micro-mixers, ultrasound, etc. [7–13]. Different micromixing systems are applied for nano-materials synthesis including two-impinging-jets reactors [14], confined impinging-jet reactors [15], spatially impinging-jets [16, 17], and double spinning disks reactors (DSDR) [18].

SDRs were applied for the production a of a wide range of nanomaterials such as barium sulfate, and it is reported that they have 1000 times lower energy consumption compared to T-mixers [19]. In addition, increasing the rotational speed of the disk can reduce the residence time of ions in the reactor and result in smaller particle size [20]. Bagheri Farahani et al. [18] reported by employing double rotating disks more uniform barium sulfate particles can be synthesized.

In this work, an SDR reactor was applied to examine the effect of operating and design parameters including disk rotating speed, feed entrance radius, and supersaturation, on MPS and polymorph of PCC nanoparticles. The main objective of the present work is the production of PCC nanoparticles with the smallest possible MPS and with high selectivity for the production of a certain polymorph, i.e., aragonite or calcite. Table 2 shows the effectiveness of SDR for synthesizing precipitated calcium carbonate.

Table 2

Different Techniques for Production of Calcium Carbonate Nanoparticles
Author	Method	MPS, nm
Naka et al.[21]	Double-jet reactor by permeation supply method	~ 2000
Vacassy et al.[22]	Segmented flow tubular reactor	~ 5000
Hu et al.[23]	Two-membrane method	~ 70–200
Nishida.[24]	Ultrasonic irradiation method	~ 1000
This work	Spinning disk reactor	~ 600

The reaction that takes place in the present work is as follows:

$${\text{N}\text{a}}_{2}{\text{C}\text{O}}_{3\left(\text{a}\text{q}\right)}+\text{C}\text{a}\text{C}{\text{l}}_{2\left(\text{a}\text{q}\right)}\to \text{C}\text{a}\text{C}{\text{O}}_{3}\downarrow +2\text{N}\text{a}\text{C}\text{l}$$

Calcium carbonate synthesis follows three main steps including nucleation, growth, and agglomeration, and each stage has a significant effect on the properties of the final product [21, 27, 28]. Different models were proposed to explain crystal growth. For instance, according to Kossel’s theory crystals in the solution tend to form on the sites with minimum energy [3]. Nucleation and growth stages are significantly dependent on supersaturation [29]. Supersaturation can be calculated as follow:

$$S={{\sqrt{\frac{{a}_{{{\text{C}\text{a}}^{2+}}^{+}}{a}_{{\text{C}\text{O}}_{3}^{2-}}}{{K}_{sp}}}=\gamma }_{\pm }\left[\frac{\left({C}_{{\text{C}\text{a}}^{2+}}\right)\left({C}_{{{\text{C}\text{O}}_{3}}^{2-}}\right)}{{K}_{sp}}\right]}^{\frac{1}{2}}$$

where ${a}_{{\text{C}\text{a}}^{+2}}$, ${a}_{{\text{C}\text{O}}_{3}^{-2}}$, ${K}_{\text{s}\text{p}}$, ${\gamma }_{\pm }$, ${C}_{{\text{C}\text{a}}^{2+}}$, and ${C}_{{{\text{C}\text{O}}_{3}}^{2-}}$ are the activity of calcium ions, the activity of carbonate ions, solubility, the activity coefficient, the molar concentrations of calcium ions, and the molar concentration of carbonate ions, respectively.

The specific energy dissipation ($ϵ$) on a rotating disk can be calculated as follows [30]:

$$ϵ=\frac{\left({u}_{2}-{u}_{1}\right)}{4\left({r}_{2}-{r}_{1}\right)}\left({\omega }^{2}\left({r}_{2}^{2}-{r}_{1}^{2}\right)+\left({u}_{2}^{2}-{u}_{1}^{2}\right)\right)$$

where $ϵ$ is the specific energy dissipation, ${r}_{1}$ and ${r}_{2}$ are the entrance radius of feedstocks in the disk, $\omega$ is the rotational speed of disk, and $u$ is the average velocity of liquid on the disk.

3.1. Spinning disk reactor

To investigate the effect of operating and design parameters such as supersaturation, disk rotational speed, and feedstock entrance on MPS and polymorph of produced PCC particles a new high-speed SDR reactor (up to 15,000 rpm) was employed. The disk was made of aluminum that was placed horizontally in the reactor (see Fig. 1).

As shown in Fig. 1, CaCl₂ (1) and Na₂CO₃ (2) solutions were injected into the reaction chamber by applying two calibrated peristaltic pumps (model: Heidolph Pump Drives 5101) from the storage tanks (1 and 2). Subsequently, the solutions were introduced to the surface of the disk using two nozzles. In addition, water was injected simultaneously into the reaction chamber for solution dilution of preventing particle agglomeration.

3.2. Chemicals

In this work, we used double-distilled water, sodium carbonate (${Na}_{2}{CO}_{3}$ Merck code: 106393), and calcium chloride (CaC${l}_{2}$, Merck code: 102378) for PCC synthesis.

3.3. Analysis

For morphology analysis and particle size measurement of synthesized PCC nanoparticles, scanning electron microscopy (SEM; ZEISS, Evo 18) was employed. Digimizer image analysis software was applied to calculate the MPS of synthesized calcium carbonate nanoparticles. In addition, the samples were examined by X-rays (XRD; STOE-MP Stady-Germany analyzed using Cu, Kα = 1.5405) to study calcite and aragonite contents in the final product. The weight content of aragonite can be calculated by applying Eq. (4) [31].

$$y=1-\frac{1}{\left(1+3\bullet 9\frac{{I}_{a}}{{I}_{c}}\right)}$$

where $y$ is the weight content of aragonite, ${I}_{c}$ is the intensity of the strongest characteristic peak of calcite, and ${I}_{a}$ is the intensity of the strongest characteristic peak of aragonite.

The design and operating conditions employed in this study are presented in Table 3. In sections 4.1, 4.2, and 4.3 the effects of supersaturation, rotational disc speed, and feedstock entrance radius on MPS and polymorph of synthesized PCC are discussed. In addition, Table 4 shows the design of the experiment that was applied in this work.

Table 3

Design and Operating Parameters
Parameter	Value
Disk radius$\left(r\right)$	10 cm
Calcium chloride-to-sodium carbonate flow ratio	1:1
Supersaturation	986–1467
Total volumetric flow rate	150–450 mL/min
Nozzle diameter	5 mm
Rotational disk speed	5,000–15,000 rpm

Table 4

Design and Operating Parameters, MPS, and Calcite (wt%)
Experiment No.	Rotational disk speed $\left({r}{p}{m}\right)$	Feedstock entrance radius ($\mathbf{m}\mathbf{m})$	Supersaturation	Calcite (wt%)	MPS (PSD)$\left(\mathbf{n}\mathbf{m}\right)$
E-01	5000	50	1389	90	2780
E-02	7000	50	1389	75	2150
E-03	9000	50	1389	21	1540
E-04	11000	50	1389	14	1410
E-05	13000	50	1389	10	1302
E-06	15000	50	1389	5	975
E-07	9000	10	1389	95	2640
E-08	9000	30	1389	84	2250
E-09	9000	70	1389	18	1450
E-10	9000	90	1389	5	780
E-11	9000	50	986	90	3150
E-12	9000	50	1257	75	2500
E-13	10	50	1467	5	600

4.1. Effect of Supersaturation

Supersaturation is one of the main parameters that can affect the properties of final products in the precipitation method for PCC synthesis. Figure 3 shows the SEM micrographs on synthesized PCC particles in different levels of supersaturation. Supersaturation in PCC synthesis systems can be calculated by applying Eq. (2). After the first contact between calcium and carbonate irons in the SDR reactor the supersaturation will be enhanced significantly. At high supersaturation, primary nucleation is the controlling stage which results in smaller MPS and higher content of aragonite phase (see Fig. 2) [26]. However, at a lower extent of supersaturation, secondary nucleation is the process controlling stage and therefore, particles with larger MPS will be produced [26]. In addition, as shown in Fig. 3, at higher supersaturation the content of the aragonite phase increased. Figure 4 presents XRD pattern of produced PCC particles under different supersaturations.

4.2. Effect of rotational disk speed

Rotational disk speed is an important parameter that affects the micromixing of ions solutions in the precipitation process. Figure 4 shows SEM micrographs of synthesized PCC particles at different rotational disk speeds. A higher degree of micromixing results in higher local supersaturation and smaller residence time and consequently smaller MPS [26]. As shown in Fig. 5 by increasing disk speed from 5,000 to 15,000 rpm, the MPS of PCC particles decreased from 2780 to 975 respectively. In addition, due to the indirect impact of high rotational disk speed on supersaturation, by increasing rotational disk speed from 5000 to 15,000 rpm the content of the aragonite phase increased from 10 to 95 wt%. In addition, Fig. 6 and Table 5 show the EDXS image and atomic composition of PCC powder synthesized in E-1.

Table 5

Atomic composition of PCC particles obtained in E-1.
Element	Weight%	Atomic%
C K	15.04	23.85
O K	50.03	59.56
Ca K	34.93	16.60
Totals	100.00	100.00

4.3. Effect of feed entrance radius

The entrance radius of feeds is one of design parameters that can affect MPS and morphology of synthesized PCC particles. Figure 9 shows SEM micrographs of produced PCC particles at different feeds entrance radius. The inlet nozzles were placed at radius of 10, 30, 70, and 90 mm. The rotational speed was set at 9,000, see Table 4.

As shown in Fig. 8 by changing the feed entrance of CaCl2 and Na2CO3, MPS of PCC particles are decreased. At higher feeds radius entrance, a higher linear velocity and consequently higher degree of micromixing can be achieved. Therefore, higher local supersaturation due to micromixing effect results in lower MPS and higher aragonite content.

SDR reactor was applied for PCC particle synthesis. The effect of supersaturation, rotational disk speed, and the position of the feed entrance was studied. Results showed by increasing supersaturation particles with smaller MPS and higher content of aragonite phase were produced. In addition, a high extent of micromixing in the SDR reactors results in a higher local supersaturation that can be intensified by increasing the rotational disk speed and increasing the radius of the feed entrance. Therefore, applying SDR is practical for controlling MPS and polymorph of PCC particles which is necessary for specific applications such as medicine, filler, and drug delivery..

${a}_{{\text{C}\text{a}}^{2+}}$ = activity of calcium ions [mol/m³]

${a}_{{\text{C}\text{O}}_{3}^{2-}}$ = activity of carbonate ions [mol/m³]

${C}_{{\text{C}\text{a}}^{2+}}$ = molar concentrations of calcium ions [mol/m³]

${C}_{{{\text{C}\text{O}}_{3}}^{2-}}$ = molar concentrations of carbonate ions [mol/m³]

${I}_{a}$ = intensity of the strongest characteristic aragonite peak [-]

${I}_{c}$ = intensity of the strongest characteristic calcite peak [-]

${K}_{\text{s}\text{p}}$ = solubility [ M²]

$r$ = disk radius [m]

$S$ = supersaturation [-]

$u$ = average velocity of liquid on disk [m/s]

$y$ = weight content of aragonite [-]

Greek Symbols

${\gamma }_{\pm }$ = activity coefficient [-]

$\epsilon$ = energy loss rate per unit mass [W/kg]

$\omega$ = rotational disk speed [rad/s]

Subscripts/Superscripts

$\text{1,2}$ =inner and outer side on the disk

${\text{N}\text{a}}_{2}{\text{C}\text{O}}_{3\left(\text{a}\text{q}\right)}$ = sodium carbonate solution

$\text{C}\text{a}\text{C}{\text{l}}_{2\left(\text{a}\text{q}\right)}$ = calcium chloride solution

$\text{C}\text{a}\text{C}{\text{O}}_{3}$ =calcium carbonate

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

CRediT authorship contribution statement

Kazem Adavi: Conceptualization, Investigation, Writing - original draft, Formal analysis, Methodology, Writing - review & editing. Danial Tahery: Formal analysis, Methodology, Writing - review & editing, Mohammad Khajouei: Formal analysis, Methodology, Writing - review & editing.

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You are reading this latest preprint version

High local supersaturation formation for precipitated calcium carbonate synthesis by applying a rotating disk reactor

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

3. Experimental Section

3.1. Spinning disk reactor

3.2. Chemicals

3.3. Analysis

4. Results And Discussion

4.1. Effect of Supersaturation

4.2. Effect of rotational disk speed

4.3. Effect of feed entrance radius

5. Conclusion

Abbreviations

Declarations

References

Status:

Journal Publication

Version 1

Parameter	Value
Disk radius\(\left(r\right)\)	10 cm
Calcium chloride-to-sodium carbonate flow ratio	1:1
Supersaturation	986–1467
Total volumetric flow rate	150–450 mL/min
Nozzle diameter	5 mm
Rotational disk speed	5,000–15,000 rpm