Calcium carbonate (CaCO3) powder is a common filler in many industries, including in the cement industry where it is used in the production process. The properties of calcium carbonate are shown in Table 1.
Types of calcium carbonate
- Natural calcium carbonate: natural CaCO3 can be obtained from calcite and aragonite in mines. This CaCO3 can be found in limestone, spot disland and other types of rock. Waste CaCO3 powder is produced as a byproduct in stone sawing factories with a typical particle size of 0.5 – 1 µm. CaCO3 powder can also be produced from the reaction of carbon dioxide with calcium hydroxide: Ca(OH)2 + CO2 --> CaCO3.
- Precipitated calcium carbonate: the precipitated CaCO3 has a high purity (98 – 99%) and can be produced with a specific crystal morphology.
In this research, the application of waste CaCO3 powder as a raw material in cement production was investigated.
Samples were collected from stone sawing factories around Neyriz, Iran. There are approximately 175 stone sawing factories in this region and all of them produce CaCO3 powder. Each factory produces about 10 tpd of pure and micronised CaCO3 powder, which could be used as a filler and raw material in many industries, such as cement.
The samples were dried before analysis. Particle size analysis (PSA) (SALD-2101, Shimadzu, Kyoto, Japan) was conducted at the Pharmacological School of Shiraz University, Iran, and included the measurement of the number of particles, as well as their longitudinal and surface area equivalent diameters. X-ray fluorescence (XRF) (PW 1480, Philips, Amsterdam, Netherlands) was used to determine 32 elements in the samples. This analysis was conducted at Kansaran Binaloud in Tehran, Iran.
Results and discussion
Characterisation of the CaCO3 powders
All four CaCO3 samples gave similar results for PSA. Therefore, the results for only one of these samples are presented in this article. The particle size distribution (Figure 1) showed that the mean particle size was 0.546 µm (range 0.365 – 19.112 µm), the mode was 0.562 µm and the median was 0.532 µm. Based on the longitudinal equivalent diameter (Figure 2), the mean particle size was 0.616 µm (range 0.365 – 66.689 µm), the mode was 0.562 µm and the median was 0.572 µm. Based on the surface area equivalent diameter (Figure 3), the mean particle size was 0.974 µm (range 0.365 – 101.150 µm), the mode was 0.562 µm and the median was 0.671 µm.
The XRF results (Table 2) showed that the samples contained 0.198% Al2O3 + Fe2O3 and 0.808% MgO on average.
The results from the characterisation of the four waste CaCO3 powder samples are summarised in Table 3. The mean particle size ranged from 0.533 – 1.925 µm; the mean longitudinal equivalent diameter was 0.668 µm, and mean surface area equivalent diameter was 1.424 µm. When sieved through a 325 mesh sieve (44 µm), the average percentage of the CaCO3 that remained on the sieve was 0.02%. These results indicate that the powders are suitable for use as fillers and raw material in the production of cement.
Waste calcium carbonate from marble sawing was analysed by XRF and DLS. The results showed it was similar to the fillers currently used in the cement industry. Therefore, the waste powder could be used as an inexpensive replacement filler.
M.H. Azadi, Young Researchers Club, Shiraz Branch, Islamic Azad University, Shiraz, Iran and Ph.D Student of Economic Geology, North-Tehran Branch, Islamic Azad University, Tehran, Iran; P. Moshksar, M.Sc Student of Urban planning, Shiraz University, Shiraz, Iran; M.R. Vaseghi, Department of Polymer Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran; M.A. Azadi, Young Researchers Club, Shiraz Branch, Islamic Azad University, Shiraz, Iran; Z. Azadi, B.Sc Student of Electronic Engineering, Zimens, Science-Applied University, Shiraz, Iran.
The authors would like to thank Mr Masoud Azadi and Miss Zahra Azadi.
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Written by M. H. Azadi, et al.
Read the article online at: https://www.worldcement.com/africa-middle-east/31052012/the_use_of_waste_calcim_carbonate_powders/