Recycling Waste Seashells to Produce Calcitic Lime: Characterization and Wet Slaking Reactivity

The present work aimed at valorizing marine bivalve shells. First, clam, mussel, edible cockle, wedge, razor, oyster, dog cockle and scallop shells wastes were thoroughly characterised for their mineralogical, chemical and thermal properties. Then, the materials were calcined at 1000 °C, milled and sieved to lower than 0.250 mm. The obtained calcium oxide was subjected to wet slaking test to evaluate its reactivity in the production of hydrated lime. The reactivity results of the calcined materials showed that, dog cockle (60 °C in 7:54 min:s) and edible cockle (60 °C in 9:20 min:s) can be classified in the most reactive class (R5) in which 60 °C is reached in less than 10 min. The remaining species were classified in the R4 class, reaching 60 °C between 10 and 25 min, with the lowest reactivity being found for oyster shell (60 °C in 19:09 min:s). Interestingly, the hydrated limes from seashells typically presented a white tonality superior that of the lime from commercial limestone used as reference. Overall, seashell wastes can be used in the production of lime, with several benefits, including, the inexistence of environmental impacts related to the exploitation of limestone on quarry, lesser energy spent in the comminution process, or, inexistence of disposal costs related with landfill tariff. These wastes could thus be used as raw materials in other industrial sector.The authors are grateful to VAC Minerais, S.A.(Rio Maior, Portugal) for the supply of the commercial limestone. Thiswork was supported by Sistema de Incentivos à Investigação e Desen‑volvimento Tecnológico financed by Quadro de Referência EstratégicaNacional (QREN) and Research Unit: UID/GEO/04035/2013 financedby Fundação para a Ciência e a Tecnologia (FCT).