Changes in physical and chemical characteristics and reactivity to hydrogen sulfide of calcined oyster shells

Hiroshima Bay contains the largest cultured oyster production area in Japan. Oyster feces causes deterioration of sediment quality and decay of the benthic ecosystem by generation of hydrogen sulfide and oxygen depletion. The main aim of this study is to utilize oyster shells effectively to suppress the hydrogen sulfide generation in the sediments. The main component of oyster shells, CaCO 3 , was transformed to CaO at calcination temperatures higher than 500 °C. The specific surface area of the shell did not increase with elevated calcination temperature, but remained at an average of 0.69 m 2 /g at 100–500 ℃. In contrast, the area decreased to 0.36 m 2 /g at 600 ℃ and further to 0.21 m 2 /g at 700 ℃. Adsorption of hydrogen sulfide by the calcined oyster shells increased from 1.7 mg S/g without calcination to 3.3 mg S/g at 400 ℃. A budgeting calculation of sulfur revealed that adsorption was the main process for hydrogen sulfide removal, while oxidation was subordinate. It is concluded that oyster shells calcined with temperature at 400 ℃ is most effective for remediation of deteriorated sediments by adsorbing hydrogen sulfide. Using such a by-product would also create a recycle oriented society.