Eggshell valorization : membrane removal, calcium oxide synthesis, and biochemical compound recovery towards cleaner productions

Abstract

As climate change continues to rank high among issues of global concern, industries such as agriculture and construction continue to unearth possible ways to curb carbon dioxide generation and encourage the use or reuse of a variety of by-products and waste materials fostering the implementation of cleaner technologies. Eggshells form a notable component of this waste, making up more than 7.6 million metric tonnes annually. Research works involving the calcination of eggshells have often been done by burning both shell and its constituent proteins and membrane to produce calcium oxide, CaO. This novel research investigated a cleaner means of CaO synthesis by recovering the shell membrane and some valuable chemical compounds from eggshells before calcination. Atomic absorption (AA), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), Ultra-performance-liquid chromatography quadrupole-time-of-flight mass spectrometry (UPLC-Q-TOF-MS), and RGB color analysis were all employed. Acetic and Nitric acid was used to weaken the shell-membrane bond, thereby aiding membrane separation. Shell membrane was easily separated after 17 minutes of soaking time. Calcium oxide, CaO was synthesized from separated shells after calcination for 3 hours at 900 ℃. 99% CaO with an RGB value of 253 was produced. Collagen, as well as other chemical compounds, were recovered. Eggshell was successfully valorized for CaO production. The shell membrane, collagen, and other recovered compounds, which would have been burnt off and left as an impurity in the CaO, can now the put to more profitable use.