## 3 Different Sources of Calcium Carbonate Particles (CCPs)
### Incense Sticks Ash  
Inense sticks ash (ISA) is one of the major household wastes in South-east Asian countries like China, Taiwan, Thailand, and India. Incense sticks are majorly used in the temples, churches, mosques, houses, and other religious places. In Taiwan alone, a total of 3580 tons of incense sticks are consumed yearly in temples alone and if household burning is also considered then this value may reach to double or triple and may indicate an environment hazardous situation [33; 35]. The size and composition of an incense sticks varies from one country and one religion to another. Currently, most of the countries, including India, do not have exact data on the incense sticks ash production. The only information we have regarding this is that: Brazil, China, U.S.A and India, are the leading manufacturer of incense sticks. India is the third largest manufacturers of incense sticks and fourth largest consumer of incense sticks. Along with USA, India also exports most of the incense sticks to Gulf countries, and Mexico. In India, the average size of an incense sticks is 8-9 inches and width is about 1-3 mm. Generally, Indian markets have two types of incense sticks: one is charcoal, or coal based (black in color), whereas the other one is non charcoal based whose color could be grey, or any other color. The black color incense sticks ashes have ferrous, silica, alumina, carbon, and calcium oxides. Indian incense sticks manufactures uses calcium phthalate in order to minimize the smoke released during burning of sticks. So, this is the one of the source of high amount of calcium oxides in the ISA. The ISA have nearly 50-56% calcium oxides [36]. The composition of incense are herbal and wood powder 21%, fragrant materials 35%, adhesive powder 11%, bamboo stick 33% by weight [37; 38]. The complete combustion of a 9 inch and 1-2 mm incense stick, produces one-third ash by weight while the remaining 60-70% weight of incense sticks is made up of volatile matters like essential oil, fragrance, and combustible matter. [PERSON] et al., 2018 and [PERSON] et al., 2020, reported that India alone consumes approximately 3-4 million tonnes of incense sticks, while USA was one of the largest importer of incense sticks from India. Based on the above information, we can predict that India alone generates 0.3-0.4 million tonnes of ISA from the various religious places and homes. The same information from other countries would be impossible to estimate as there is hardly any information available from the government or in the literature [36]. The chemical composition of incense sticks ash is given below in Table 3. The X-ray fluorescence analysis reveals that the incense ash has CaO 50-55%, Ferrous oxide (Fe\({}_{2}\)O\({}_{3}\)/Fe\({}_{3}\)O\({}_{4}\)) 4-5%, Aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) 4-5%, Silica oxide 15-20%, magnesium oxide 4-5%. In addition, it also has a high amount of alkali oxides, i.e., Na\({}_{2}\)O, K\({}_{2}\)O, traces of TiO\({}_{2}\), CuO, and other heavy metals. Figure 1 shows the flowchart of the synthesis of CaCO\({}_{3}\) from ISA, while Figure 2 shows field emission scanning electron micrograph (FESEM) of calcium carbonate microparticles from incense sticks ash. [PERSON] and [PERSON] (2018), also reported the calcium carbonate particles of various sizes synthesized by chemical routes. Out of these cuboidal shaped particles were also observed, by varying the temperature of synthesis [39]. In Figure 1, initially ISA was mixed with distilled water (1:5) to form a slurry. Further with the help of an external magnet, the ferrous particles were separated as ferrous will add impurity in the final calcium carbonate particles. Further, it was dried in an oven at 50 \({}^{\circ}\)C, followed by treatment with sulphuric acid at 90 \({}^{\circ}\)C for 90 min to extract alumina along with stirring at 400 rpm. Further, after completion of the reaction, mixture was cooled to room temperature (RT), followed by the centrifugation.