Table 1.

Overview of research studies applying a mechanochemical approach for the treatment of eggshell waste published recently: experimental techniques, the most important result and application field of the final product.

Milling input	Experimental techniques	Most important results	Final product/application	References
Eggshell	SEM	Statistical approach; milling speed is the most important factor	Hydroxyapatite/bioceramics	(van Hoten et al., 2018)
Eggshell + ethanol/water	XRD, SEM, TEM, TA, optical microscopy, mechanical properties evaluation, biocompatibility	5 wt% nanohydroxyapatite was the ebst, cells grow on the fibers	PLA-nanohydroxyapatite fibers/bioengineering	(Apalangya et al., 2019)
Eggshell + window parapet made of PVC	XRD, FTIR, titration	Comparison of planetary and vibratory milling, scalability	Calcium chloride + harmless organic matrix/dechlorination	(Baláž et al., 2019a)
Eggshell + TiO2/+ Mg	XRD, TA, SEM	Comparison of conventional and high-energy ball milling	CaTiO3 ceramics/electronics	(Cherdchom et al., 2019)
Eggshell/cuttlefish bone+ phosphoric acid	SEM, XRD, Raman, TEM	No sintering, comparison of eggshell and cuttlefish bone as Ca sources	Hydroxyapatite/bioceramics	(Ferro and Guedes, 2019)
Eggshell + rice straw	XRD, SEM, adsorption kinetics and thermodynamics and influence of various factors	Maximum sorption capacity of 231 mg/g was evidenced for balanced eggshell:rice straw ratio	Phosphate ions adsorbent/wastewater treatment	(Liu et al., 2019)
Eggshell + acetone	XRD, SEM	Sintering enriched Ca content and did not result in a significant increase in crystallite size	Nanoization	(Puspitasari et al., 2019)
CaO from eggshell	XRD, FTIR, SEM, fluorescent microscopy, biocompatibility evaluation	Comparison of ball milling, mortar and pestle and Food and Drug Administration (FDA)-approved methodology, post-milling reaction with H3PO4	β-tricalcium phosphate scaffolds/bioceramics	(Roopavath et al., 2019)
CaO from eggshell	XRD, SEM, chemical oxygen demand, biogas and methane production	Size reduction into nano-range resulted in a significant improvement in biogas production	Biogas production from palm oil mill effluent: cow manure mixture	(Sari et al., 2020)
Eggshell + ethanol	XRD, FTIR, SEM, WCA, SPM	Stearic acid favors the transformation into aragonite	Superhydrophobic eggshell/filtration	(Seeharaj et al., 2019)
Eggshell + Li-Ni0.8Co0.1Mn0.1O2	TA, XRD, FTIR, SEM/EDS, XPS, electrochemical measurements	CaO prevents electrolyte dissolution and electrode corrosion	CaO-coated Li-Ni0.8Co0.1Mn0.1O2 electrode/electrochemistry	(Senthil et al., 2019)
Eggshell + acetone	XRD, SEM, FTIR	Comparison of calcined (CaO) and non/calcined (CaCO3) material	Nanoization	(Supriyanto et al., 2019)
Eggshell + stearic acid/water	XRD, TA, TEM	Stearic acid reduces the crystallite size and thermal degradation temperature	Nanoization	(Villarreal-Lucio et al., 2019)
Eggshell + aqueous solution of phosphate precursor	XRD, FTIR, SEM, TA	Pure HA produced from different precursors using three different CaCO3 sources using wet milling and low-temperature treatment	Hydroxyapatite/bioceramics	(Cestari et al., 2020)
Eggshell + ethanol	SBET, particle size distribution, zeta potential, SEM, TEM, EDS, FTIR, Ca2+ concentration determination, XRD	Zeta potential was decreased during treatment	Nanoization	(Huang et al., 2020)
Eggshell membrane + Li2FeSiO4	XRD, TA, SBET, Raman, XPS, TEM	ESM served as a carbon source for improving electrical properties of the LFS ESM composite	LFS-C composite/electrochemistry	(Karuppiah et al., 2020)
Eggshell + Al2O3	SEM, mechanical properties, corrosion, thermal expansion	Toughness and ductility reduced, but tensile strength, hardness, corrosion resistance, thermal stability improved upon addition of CaO derived from eggshell	Al/eggshell/Al2O3 composite	(Kumar, S., Dwivedi, S. P., and Dwivedi et al., 2020)
Eggshell	Particle size distribution, SEM, EDX, XRD	The authors report graphite in the eggshell	Micronization	(Ononiwu and Akinlabi, 2020)
Eggshell/eggshell + TiO2	FTIR, TEM, XRD, acid-resistant and buffering properties	The buffering performance was evaluated against that of four available toothpastes	Eggshell-TiO2 composite/dentistry	(Onwubu et al., 2019a)
Eggshell/eggshell + TiO2	The same as above, but also SEM	The tooth surface is less destroyed when using Colgate toothpaste and the prepared composite in comparison with other toothpastes	Eggshell-TiO2 composite/dentistry	(Onwubu et al., 2019b)
Eggshell	XRD, SEM, TEM, FTIR, mechanical properties, microhardness, erosion resistance	Different amounts of eggshell (from 1-4%) in the composites were beneficial for different mechanical properties	Eggshell-epoxy composite/composites	(Panchal et al., 2020)
Eggshell + acetone	XRD, FTIR, Raman, SEM	Effect of various post-milling sintering temperatures (900–1,200°C) on CaCO3-CaO transformation was investigated	Nanoization	(Puspitasari et al., 2020)
Eggshell	Particle size, SEM, XRD, AFM, mechanical properties, chloride ion permeability	Improvement of mechanical properties of oil well cement and accelerate hydration process	Oil well cement-eggshell composite	(Salman et al., 2020)