The Effects of Calcined Waste Oyster Shells on Physicochemical Changes in Coastal Sediments

Approximately 300,000 tons of waste oyster shells (OS) are generated annually in the Republic of Korea. Comprehensive research is required on the effects of OS on coastal environments for direct application of OS. This study aimed to investigate the physicochemical property changes in coastal sediments caused by the application of calcined OS. OS were pyrolyzed at 300 degrees C, 600 degrees C, and 800 degrees C, and mixed with coastal sediment at 10% (P31, P61, P81), 20% (P32, P62, P82), and 30% (P33, P63, P83). The mixed sediments' calcium content varied depending on the calcination temperature and mixing ratio of the OS, leading to accompanying physicochemical changes. OS in P31-P33 without residual organic matter could be used as a sand replacement. The calcium produced calcium silicate hydrate, densifying and increasing the sediment's shear strength by 1.4 times (P63) and 2.8 times (P81) compared to the control. The release of hydroxide ions from calcined OS alleviated acidification in P61-P63. Although P81-P83 had a high pH, they exhibited the highest PO4-P fixation ability. OS calcined at different temperatures showed potential as a material for sand replacement, acidification mitigation, and strength improvement in coastal sediments. Therefore, the appropriate calcination temperature on OS can potentially improve the coastal sediment environment.