Comparison of Particle Shape, Surface Area, and Color Properties of the Calcite Particles Ground by Stirred and Ball Mill

Round 1

Reviewer 1 Report

1.     There are some improper expressions in the text.

l  The subsection number of the Section 2 needs to be adjusted because there is no Section 2.2.

l  P4, Line 151. “the term d97, [18]”; In addition, it is suggested that the author explain the meaning of d97 in the first place.

l  P5, Table 2. “Ball density (g/cm3)”; In addition, it is suggested that the author explain the meaning of “% of Nc”, “Ball filling ratio (J)” and “Interstitial filling (U)”.

l  P8, Line 255. Please supplement the full form of ECAD in the first place.

l  P8, Line 263-264. The data of EAR is lost.

l  P9, Figure 9. The ordinate data needs to be further normalized.

2.     P4, Line 153-154. Please explain the proper feed sizes of the two mills.

3.     P11, Line 328-336. Different XRD peaks represent different crystal faces, which should be further demonstrated. And, different proportions of crystal faces may be directly related to particle shape.

Author Response

Response 1: Thank you for your constructive comments. Section 2 is revised based on its subheadings as suggested.

Response 2: Thank you for your valuable points and comments. d97, which is known as the sieve aperture through which 97% of the ground calcite products pass in the particle size distribution plot, is the fineness value usually looked at in GCC production. Therefore, in Lines 60-62; the following statements were used in the revised manuscript: “Since the d97 term (97% passing size) is the fineness value usually looked at in GCC production [17], It is well-known that dry GCCs with a d97 value of 74-45 μm are among the cheapest known white fillers [18]”.

Response 3: Thank you for your valuable points and comments. Ball density is revised as media density. In addition, other parameters such as Nc, J and U are explained under Table 2 as footnotes since they were already reported in the previous study [40].

                                            Table 2. Experimental conditions for stirred mill and ball mill followed in this study [37].

* Calculated from Nc = 42.3/(D - d)1/2, rpm (D, d in m).

** Calculated from J=[(mass of balls/ball density)/(mill volume)]/[1.0/0.64]

***Calculated from J=[(mass of balls/ball density)/(mill volume)]/[1.0/0.60]

****U=f_C/0.36J

*****U=f_C/0.40J

Response 4: Thank you for your valuable points and comments. Equivalent circular area diameter (ECAD), represents the diameter of a sphere that would have a volume close to the actual volume of the particle. The following statement is included in Lines 287-290:

“Since the equivalent circular area diameter (ECAD) parameter used in the DIA, represents the diameter of a sphere that would have a volume close to the actual volume of the particle, ECAD values shown in the tables are found similar to compare the particle shape of each sample in terms of mean aspect ratio values.”

Response 5: Thank you for your constructive comments. EAR results are included in the text as:

As seen from Figure 9a, EAR values ranged from 1.421 to 1.415 for stirred-milled calcite particles, while they varied from 1.523 to 1.497 for ball-milled particles

Response 6: Thank you for your constructive comments. It is revised based on the suggestion of the reviewer.

Response 7: Thank you for your constructive comments. This paragraph is written as “The particle size distributions of the calcite sample fed to the stirred mill and the ball mill are given in Figure 3 and it is seen that it is suitable for the material and media size to be fed to the mills used in this experimental study”.

Response 8: Thank you for your constructive comments. This statement is also included in the discussion as “since different XRD peaks represent different crystal faces, different proportions of these crystal faces may be directly related to particle shape”.

Reviewer 2 Report

The paper compares the properties of calcite products obtained from either a stirred or a lab-scale ball mills. I found the paper to be interesting, generally well‐ written and the structure well- organized but, it still needs some English improvements. The paper contains a good Introduction and description of the methods used to measure the shape parameters of the grinding products, as well as adequate references describing the research carried out so far. However, the methods used are well-known and authors simply report results from a few experiments and draw conclusions that already exist in the literature. As a result, a better explanation for the contribution of the present study to scientific literature is required.

Other comments, 1) the results obtained from this study were derived after performing grinding experiments under specific conditions. The authors should mention how the change of operating conditions, e.g. media shape (balls vs. cylpebs), mill speed, etc. should affect the measurements of the shape parameters of the products, 2) the authors should explain how the slight difference of the product’s parameters, e.g. 3 vs. 2.11 SSA (m2/g) or 1.4 vs. 1.5 BRAR aspect ratio, for the stirred and ball mills, respectively, should be considered crucial for their use in various industries such as paint, paper etc.     

Author Response

Response 1: Thank you for the constructive comment. The introduction is revised based on the reviewer’s comment. For the use of GCC as a filler in industries such as paper, paints, and plastics, the mill products must be white, have a high degree of mineral purity, and have controlled particle size, shape, surface area, and liquid absorption. Since DIA is a reliable, and quick method of shape characterization technique it can give an answer to this question: Can the stirred mill, which can produce finer grains with less energy consumption and be an alternative to the traditional ball mill, produce the appropriate grain shape for GCC production? Although there are lots of studies related to the relationship between particle size and GCC properties, quantitative shape analysis by dynamic image analysis of calcite minerals ground by conventional ball mill and stirred mill is still lacking. Therefore, The aim of this study is to compare the aspect ratio at d97=50 μm and evaluate other properties like color and surface area for the intended use of GCC. This is the main novelty that distinguishes it from other studies in the literature. Furthermore, the contribution of our article is that it is about the effect of the ball shape on the grain shape by DIA, especially for the calcite mineral. In addition, other properties (psd, surface area, and whiteness) used in these industries were also measured and compared in this study. Nevertheless, it is quite reasonable to use the results of previous studies with the same material in the comments to contribute to the literature. In other words, we use literature to support our measurement. Besides, the manuscript is revised based on this comment of the reviewer.     Response 2: Thank you for your constructive comments. Cylpebs, which are light conical cylindrical grinding media with a length-to-diameter ratio of one, have been reported to provide finer grinding under the same operating conditions compared to conventional steel balls since the two grinding media have a different surface area, bulk density, and contact mechanisms in grinding action. According to the literature, the cylpebs generate a product with roughly the same sizing at the fine end as that produced with the balls, but slightly less oversize because of their larger surface area.   Since the breakage modes used in grinding mills establish the quality of the particles in terms of their size, size distribution, and shape (Palaniandy et al., 2008). Stirred mills have high intensity attrition breakage mode, whereas conventional ball mills have mainly impact breakage mode (Allen, 2011; Wang, 2009; Palaniandy et al., 2008). It has been suggested that this may be because the advantage of the larger surface area is offset by the line contact and area contact grinding actions with the cylpebs [56].   This explanation also takes place in Lines 321-324; 389-332.   Allen, J. Advances in stirred milling - improving profitability of copper ore processing. Bulk Solids Handl. 2011, 31, 3, 144.   Wang, C. Comparison of HPGR - Ball Mill and HPGR - Stirred Mill Circuits to the Existing AG/SAG Mill - Ball Mill Circuits, MSc. Thesis, University of Science and Technology Beijing, 2009.   Palaniandy, S.; Azizli, k. A. M.; Hussin, H.; Hashim, S. F. S. Effect of operational parameters on the breakage mechanism of silica in a jet mill, Miner. Eng. 2008, 21, 5, 380-388, https://doi.org/10.1016/j.mineng.2007.10.011        Response 3: Thank you for your constructive comments. The aim of this study is to compare the aspect ratio at d97=50 μm and evaluate other properties like color and surface area for the intended use of GCC.   While Hicyilmaz et al. (2005) measured the surface area values of 8-minute ball milled calcite (-250 μm) particles as 0.27 m²/g using steel balls, Ercan et al. (2018) reported that the surface area of marble grains crushed to -2 mm is 0.227 m²/g (98.15 whiteness) and the surface area of GCC with a d50 value of 5 μm produced by a stirred mill is 2.14 m²/g (99.05 whiteness). On the other hand, Huo et al. (2011) have also reported that SSA of 3.9 m²/g and whiteness of 92.9 values for GCC powder with an average grain size of 3.3 μm. Therefore, the magnitude of the specific surface area values depends on the feed size, ball size, and ratio as well as the grinding time. In addition, it is obvious that it will increase even more when the grain size is reduced further. It should be noted that the mill product’s fineness requires more energy input. Moreover, the main aim of this study is to compare the aspect ratio at d97=50 μm and evaluate other properties like color and surface area for the intended use of GCC.   Finally, the surface area values obtained by stirred and ball mills in this study are suitable for the paper, and plastic industries according to the reported study by Ercan et al. (2018).   Hiçyılmaz, C.; Ulusoy, U.; Bilgen, S.; Yekeler, M.; Flotation responses of morphological properties of particles measured with a 3-dimensional approach, Int. J. Miner. Proces. 2005, 75, 3-4, 229-236, https://doi.org/10.1016/j.minpro.2004.08.019.   Ercan, M.; Koltka, S.;  Sabah, E. The Production of Ground Calcium Carbonate (GCC) from Marble Wastes: Comparison of Wet and Dry Grinding Products, Scientific Mining J. 2018, 57, 1, 35-43, https://doi.org/10.30797/madencilik.422868   Huo, C.;  Jiayuan Shen, J.; Xia, Q.  Preparation of Composite Ground Calcium Carbonate in Ca(OH)2–H2O–CO2 System and Characterization, Adv. Mater. Res. Online. 2011, 287-290, 548-552, doi:10.4028/www.scientific.net/AMR.287-290.548.   Although products with equivalent d97 dimensions have been examined, there are differences in the d10 dimensions of the products due to the difference in the grinding mechanism of the two mills. This is also evident from the difference in surface area values. It is thought that a high SSA value is obtained due to the finer fractions in the stirred ball mill, while a difference is observed in terms of particle shape originating from the cylpebs ball in the ball mill. It can be thought that these two product differences will create diversity in terms of industrial use. For example, in industries such as paint where calcite is used as an extender, the surface area is prioritized (Siesholtz and Cohan, 1949), while in the plastic industry calcite with a high aspect ratio may be preferred because it improves mechanical properties (Thenepalli et al., 2015).  

Siesholtz, H. W.; Cohan, L. H. Calcium Carbonate Extender Pigments, Ind. Eng. Chem. 1949, 41, 2, 390–395. https://doi.org/10.1021/ie50470a031.

Thenepalli, T.; Jun, A. Y.; Han, C.; Ramakrishna, C.; Ahn, J. W. A strategy of precipitated calcium carbonate (CaCO3) fillers for enhancing the mechanical properties of polypropylene polymers, Korean J. Chem. Eng. 2015, 32, 6, 1009-1022, https://doi.org/10.1007/s11814-015-0057-3

    This is also included in the revised manuscript Lines 395-419     Finally, the English language and style were checked by using a grammar and paraphrasing software tool (Open Grammarly, QuillBot.com).

Reviewer 3 Report

This paper looks good to me. It reads very well and is easy to follow from a metallurgist perspective. I only have minor suggestions for the authors for further improving the paper.

1) the current title is too long and I suggest revise it.

2) some of the charts and figures presented in the paper are too small and are not too clear. They should be revised. 

Author Response

Response 1: Thanks for your valuable points and comments. The title is revised as “Comparison of particle shape, surface area, and color properties of the calcite particles ground by stirred and ball mill”   Response 2: Thanks for your valuable points and comments. They are revised and their quality is improved based on the suggestion of the reviewer.

Round 2

Reviewer 2 Report

Dear Editor,

based on the authors' response, I still believe that they have not provided an accurate and convincing explanation of how the results obtained from the present study could differ when the grinding conditions are changed. Also, a better explanation is needed as to how the small difference of product parameters between the two mills could be considered critical for the industrial use of GCC.

Author Response

Response 1: Thank you for your constructive comments.  Since the primary purpose of grinding is to obtain an appropriate product size with the least possible energy consumption we aim to compare the properties of GCC by using two different mill particles with the same particle size (d97=50 μm) produced. Because the ball mill produces limited product particle size. In addition, there are studies in the literature examining GCC pigment grains in sizes close to the product grain size we obtained. For instance, Siesholtz and Cohan (1949) have also investigated 80 μm GCC pigment particles for comparison with other fine-size GCC products. Using a ball mill with cylpebs and a stirred mill with alumina balls (Table 2) has produced the GCC products with particles the same particle size (d97=50 μm) but different aspect ratios (supported by both ANOVA hypothesis testing, SEM, and XRD), surface area values (Table 4), and whiteness values (Table 5). By using two different grinding systems, such as ball mills and stirred mills, different surface areas, aspect ratios, and color characteristics of GCC particles with the same product size were the expected result. These differences are thought to be due to the different grinding mechanisms of the mills and different grinding media. Using a ball mill with cylpebs and a stirred mill with alumina balls caused different breakage and thereby different aspect ratio since the predominant breakage process in ball mills is commonly thought of as impact breakage in the mill's toe (Tavares, 2009; Weerasekara et al., 2013). While the breakage mechanisms in stirred mills are typically known as abrasion and attrition, or more simply shear breakage (Gao and Forssberg, 1995; Sinnott et al., 2006; Ye et al., 2010). The more rounded particle shape produced by stirred mill compared to the ball mill may be due to the abrasion effect of stirring mills (Little et al., 2017; Cleary and Morrison, 2016; Kaya et al., 2002; Pourghahramani, 2012; Roufail, 2011; Vizcarra et al., 2011; Ye et al., 2010). It has been suggested that, under impact stress, the fragmentation mechanism may be due to essentially simultaneous rupture and fracture, which produces particles of nearly round shape and uniform size during fragmentation. On the other hand, it has been reported that the main mechanism of fracturing by attrition is primarily the rupture of grain joints leading to the dissociation of crystallites, and secondly, the chipping and the breakage of these crystallites (Frances et al., 2001; Rácz, 2014) Siesholtz, H. W.; Cohan, L. H. Calcium Carbonate Extender Pigments, Ind. Eng. Chem. 1949, 41, 2, 390–395. https://doi.org/10.1021/ie50470a031. Tavares, L.M., 2009. Analysis of particle fracture by repeated stressing as damage accumulation. Powder Technol. 190, 327–339. http://dx.doi.org/10.1016/j.powtec.2008. 08.011. Weerasekara, N.S., Powell, M.S., Cleary, P.W., Tavares, L.M., Evertsson, M., Morrison, R.D., Quist, J., Carvalho, R.M., 2013. The contribution of DEM to the science of comminution. Powder Technol. 248, 3–4. http://dx.doi.org/10.1016/j.powtec.2013. 05.032. Gao, M., Forssberg, E., 1995. Prediction of product size distributions for a stirred ball mill. Powder Technol. 84, 101–106. Sinnott, M., Cleary, P.W., Morrison, R., 2006. Analysis of stirred mill performance using DEM simulation: Part 1–Media motion, energy consumption and collisional environment. Miner. Eng. 19, 1537–1550. http://dx.doi.org/10.1016/j.mineng.2006. 08.012. Ye, X., Gredelj, S., Skinner, W., Grano, S.R., 2010. Regrinding sulphide minerals—breakage mechanisms in milling and their influence on surface properties and flotation behaviour. Powder Technol. 203, 133–147. http://dx.doi.org/10.1016/j. powtec.2010.05.002. 35.          Little, L.; Mainza, A. N.; Becker, M.; Wiese, J. Fine grinding: How mill type affects particle shape characteristics and mineral liberation. Miner. Eng. 2017, 111, 148–57, https://doi.org/10.1016/j.mineng.2017.05.007. Cleary, P.W., Morrison, R.D., 2016. Comminution mechanisms, particle shape evolution and collision energy partitioning in tumbling mills. Miner. Eng. 86, 75–95. http://dx. doi.org/10.1016/j.mineng.2015.12.006. Kaya, E., Hogg, R., Kumar, S.R., 2002. Particle shape modification in comminution. KONA 20, 188–195. Pourghahramani, P., 2012. Effects of ore characteristics on product shape properties and breakage mechanisms in industrial SAG mills. Miner. Eng. 32, 30–37. http://dx.doi. org/10.1016/j.mineng.2012.03.005. 33.          Roufail, R.A. The Effect of Stirred Mill Operatıon on Particles Breakage Mechanism and Their Morphological Features. PhD thesis, University of British Columbia, 2011. Vizcarra, T.G., Wightman, E.M., Johnson, N.W., Manlapig, E.V., 2011. The effect of breakage method on the shape properties of an iron-oxide hosted copper–gold ore. Miner. Eng. 24, 1454–1458. http://dx.doi.org/10.1016/j.mineng.2011.07.007. Frances, C.; Le Bolay, N.; Belaroui, K.; Pons, M.N. Particle morphology of ground gibbsite in different grinding environments, Int. J. Mineral Proc. 2001, 61, 41, https://doi.org/10.1016/S0301-7516(00)00025-9. 23.          Rácz, A. Reduction of Surface Roughness and Rounding of Limestone Particles in a Stirred Media Mill, Chem. Eng. Technol. 2014, 37, 5, 865–872, https://doi.org/10.1002/ceat.201300671.  Response 2: Thank you for your constructive comments. This research article aims to compare the physical properties such as aspect ratio, surface area, and whiteness of GCC products produced by different grinding processes. It has been concluded that two GCC products with the same size but different values of aspect ratio, surface area, and color property, produced by stirred and ball mill grinding are obtained. Therefore, it can be said that one of the grinding systems is better than the other for one of these properties desired in one of the industries such as paper, paint, and plastic. 

For example, GCC particles with a higher surface area due to their particle shape will have a better contact interface with the polymer matrix due to their larger specific surface area when used as polymer filling material. In addition, a higher surface area and higher whiteness are important for the composite polymer filler due to its superior mechanical properties (Huo et al., 2011). Furthermore, it is well known that with the addition of a GCC filler, the most desirable mechanical properties for the plastics industry are the tensile strength and impact resistance of the polymer, it is reported that as the filler aspect ratio increases, their mechanical properties increase (Adams 1993) [45]. Therefore, the stirred mill is preferred in the plastic and rubber industries when compared to the ball mill.

In the paper industry, since loading higher filler content is always desired by the paper manufacturer due to reduced cost and increased optical properties, aspect ratios and surface areas of the particles to be used as fillers become important, e.g., it is known that the filler's particle size and shape have the biggest effects on how the light scatters (Chauhan and Bhardwaj, 2017) [14]. Since the size and shape of the GCC particles used in paper coating provide the gloss properties of the system, higher composite stiffness is suggested to be caused by a higher particle aspect ratio and a higher modulus. It is also well known that platy particles of uncoated GCC fillers decrease porosity and improve printing performance by enhancing the smoothness and gloss of the papers (Adams 1993) [45]. Thus, the ball mill is favored for the paper industry compared to the stirred mill.

In paint making, the surface area is important for hiding power properties. While hiding power increases with an increase in the surface area of the GCC extender for the rheological properties of the fluid paint (Siesholtz and Cohan, 1949) [69], the filler's intrinsic high surface area causes it to debond fibers when employed to generate brightness and opacity (Wilson, 2006) [67]. Therefore, the stirred mill is preferred in the paint industry compared to the ball mill.

 Huo, C.; Shen, J.; Xia, Q. Preparation of Composite Ground Calcium Carbonate in Ca(OH)2–H2O–CO2 System and Characterization, Advanced Materials Research. Trans Tech Publications, Ltd., July 2011 287-290, pp. 548-552. https://doi.org/10.4028/www.scientific.net/amr.287-290.548.

Chauhan, V.S.; Bhardwaj, N.K. Efficacy of Dispersion of Magnesium Silicate (Talc) in Papermaking. Arabian J. Chem. 2017 10, S1059–S66, https://doi.org/10.1016/j.arabjc.2013.01.012

Wilson, I. Filler and Coating Pigments For Papermakers, In Industrial Minerals & Rocks, Kogel, J.E.; Trivedi, N.C.; Barker, J.M.; Krukowski, T.S. Eds.; Littleton, SME: Colorado. USA, 2006, pp.1287–1300.

 Siesholtz, H. W.; Cohan, L. H. Calcium Carbonate Extender Pigments, Ind. Eng. Chem. 1949 41, 2, 390–395. https://doi.org/10.1021/ie50470a031. Adams, J. M. Particle Size and Shape Effects in Materials Science: Examples From Polymer and paper Systems, Clay Min. 1993 28, 509-530.   

Prof. Dr. Ugur Ulusoy

On behalf of my co-authors