Referee Report on the manuscript # NANO4186R1
We appreciate your advices and comments which lead our manuscript to a sophisticated one helpfully.
Firstly we would like to explain the overview of our manuscript. We conducted the experiments to get the parameters for simulation conditions and to prove the validity of simulation results. Both primary particles in rhombic and spindle granular particles as shown in Figure 3 consist of calcite particles. The model of calcite structure shows Figure 2. In submitted our paper to this Journal, the aggregation of particles was calculated by particles with charges in the center. In case of that, the large spindle particles did not form. However, as you pointed out, we eliminate this result of simulation. On the other hand, the large spindle particles formed in that case of calculating by using unit particles model with surface charges. In summary, we calculated the aggregation process by using unit particle model, in that rhombic system.
We answer your questions as follows.
1. According to the experiment results and some references, the colloid particles and spindle granular particles form by different experimental conditions regardless of the same calcite. As you pointed out, the larger primary particles create spindle-shaped. On the other hand, the smaller primary particles disperse and become colloid particles. The reason is because the effect of surface charge significantly causes the difference between spindle-shaped and colloid particles. The spindle-shaped particles are formed by charge polarization because the unit particle size is larger than that of colloid particles. If the size of primary particles is larger, the charge polarization occurs. It would be driven by the size difference of the primary particles.
The phase transition does not occur from rhombic to hexagonal. The phase transition is supposed to occur by the reaction crystallization due to the gas CO2 and Ca(OH)2 solution. In that, the calcium carbonate is thought to generate by reacting the carbon dioxide with the calcium ion in the suspension. By this reaction, the phase transition would occur. As shown in below, especially the structure of calcite is the hexagonal structure. However, unit structure is rhombic particle as shown in below. Therefore, our description might cause misleading that the phase transition occurs from rhombic to hexagonal structure.
When the surface energy get across the top of energy, the generation of particles starts occurring. In the MC simulation, it could be concluded that the surface charge distribution and the structure of unit particles were determinative factors to form spindle shape. From the point of view of the free energy, it was found that granules with size distribution existed in the solution because of calculating the aggregation process of unit particles with surface charge.
In addition, we adjusted the notation throughout the text.
2. We modeled a rhombic particle as a unit particle because we would like to simulate aggregation process in MC simulation. As you pointed out, we agree with your proposal that the unit particles only appear in MC simulation. Therefore, we revised the primary particles in experiment.
3. As you indicated, we eliminated the term nucleation in this content unless we refer to the formation of the primary particles.
4. As you indicated, we replaced carbonating by carbonation process.
5. As we noted above, we calculated aggregation process by MC Simulation. The unit particles were defined in Sec. 2.2, which cubic unit particle was made as a model for primary particles.
6. We controlled the temperature to circulate the cooling water in the jacket because the experimental carbonation process was carried out in a semi-batch bubble column reactor under different conditions. Therefore, we revised this sentence to make sentence.
7. As you pointed out, we added detailed measured time as below. We measured the Zeta potential and electric double layer at 40, 80, 120, 130, 140 and 150 minutes.
8. Surely we noted that the shape did not change regardless of the number of unit particles. Even if the number of unit particles changes, the aspect ratio as expressed shape did not change. Therefore, we stated the shape would not change over 4000. If the number of unit particle increased, the granular size will approach the actual one but aspect ratio expressed shape will not change. We added a comment in the end of Section 3.2 because it was difficult to get through our intension as you pointed out.
9. As you indicated, we replaced particle diameter in Fig. 5 by particle dimension.