Eggshell waste to produce building lime: calcium oxide reactivity, industrial, environmental and economic implications

Eggshells wastes are produced in huge amounts worldwide. The recycling or valorization of this waste, which otherwise is usually disposed in landfills, represents an opportunity within a circular economy perspective. In the present work, the potential of chicken eggshell waste to produce calcitic lime was explored. After collection from an industry supplier, the waste was thoroughly characterized for its mineralogical, chemical, and thermal properties. The material was calcined at 1000 °C, and the obtained calcium oxide was evaluated for its reactivity in wet slaking tests. Comparison was made with commercial limestone used as reference. It was found that the calcium oxide from eggshell waste belonged to the most reactive class (R5—60 °C within 10 min), the same of the calcium oxide from limestone. However, different times were obtained to reach 60 °C (25 s and 4:37 min:s) and for 80% of the reaction (28 s and 5 min) for calcium oxide from limestone and eggshell waste, respectively. The lower reactivity of calcium oxide from eggshell waste was related to its larger size particles with smoother surfaces and lower specific surface area in comparison to limestone calcium oxide. Industrial, environmental and economic implications concerning the use of this waste to produce lime were also evaluated. The eggshell waste could be all consumed at an industrial scale in Portugal allowing for approximately 2.6% partial substitution of limestone in a lime factory.