## 4 Extraction of Calcium Oxide Particles from Eggshell Waste  
The bioconversion of waste material like eggshell from poultry industries into a valuable material is highly significant for economic development and waste management [40]. The eggshell waste is classified in both industrial wastes as well as in agricultural waste. The utilization of these wastes for the production of valuable materials like fertilizers, feed supplements, adsorbents, and CCNPs not only provides a solution to the disposal of eggshell but also minimizes the pollution in the environment [41; 42]. Among all the countries, China, USA, and India is the leading producer of eggs which contributes near about 80 million metric tonnes, where China s share is 458, USA's share is 109, and India's share is 95 billion eggs per shell as per the 2017 literature. While in 2018, the global egg production was approximately, 78 million metric tonnes. These 78 million metric tonnes produced about 8.58 million metric tonnes of eggshells which are mainly dumped of as waste, while some parts of the world, it is used as landfills, and for fillers, etc. [43]. The eggshell consists of about 10-11% weight of the total weight of an egg. Annually around, 250,000 tons of eggshell waste is generated during processing [44]. There are 150,000 tons of chicken eggshell disposed of in landfills every year in the U.S alone. The eggshell comprises about 95% CaCO\({}_{3}\) as calcite and 5% organic materials such as type X collagen, sulfated polysaccharides, and other proteins which is provided below in Table 4[45]. The disposal methods for waste eggshells are 26.6% as fertilizer, 21.1% as animal feed ingredients, 26.3% discarded in municipal dumps, and 15.8% used in other ways [41]. [PERSON] et al., 2020 reported the synthesis of microsized (10-30 \(\upmu\)m) aragonite calcium carbonate particles from eggshell waste by carbonation method along with calcination at high temperature. India is also one of the major poultry industry countries which have a poultry population of 489 million, producing 47 billion eggs per year. India ranks third among the highest egg producing countries in the world [46]. The outermost cover of the egg is called \begin{table}
\begin{tabular}{c c c} \hline \hline
**S. No.** & **Chemical Elements** & **Concentration (mg/L)** \\ \hline
1. & Ca & 2296–2304 \\
2. & Mg & 849–852 \\
3. & Na & 33–35 \\
4. & K & 16–19 \\
5. & Fe & 1.01–1.43 \\
6. & Zn & 0.95–1.03 \\
7. & Cu & 0.062–0.064 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The chemical composition of chicken eggshell. Figure 2: Field emission scanning electron micrograph (FESEM) of the calcite phase of calcium carbonate microparticles from incense sticks ash. eggshell whose weight is 10-11% to that of the total weight of the egg and made up of mainly CaCO\({}_{3}\) (96%) and trace elements. The chemical composition of eggshell waste is given below in the table. Currently, it is mainly dumped as landfills in most of the developed or developing countries. Disposal of eggshell and the underlying membrane further contributes to environmental pollution [47]. [PERSON] et al. (2013) reported the synthesis of CCPs from the chicken eggshell waste, which encompasses the following steps cleaning and size reduction of eggshell, followed by surface modification by the sonochemical method for enhanced dispersion [48; 49]. [PERSON] et al. (2014) reported the successful synthesis of calcite NPs from eggshell waste using gelatin [50; 51]. The calcite polymorph of CaCO\({}_{3}\) was synthesized using from chicken eggshells employing gelatin via precipitation method and the confirmation of the nano calcite was done by X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-Visible (UV-Vis) spectroscopy and scanning electron microscopy (SEM). The identified particles were calcite polymorphs with a particle size of 25 nm. The analysis results confirmed the formation of calcite NPs and the obtained results were compared with CaCO\({}_{3}\) synthesis without using gelatin. [PERSON] et al.