Manganese-coated granular oyster shells: a novel approach for heavy metal removal from urban stormwater runoff
2025
Quynh Thi Phuong Tran | Trung Thanh Nguyen | Oanh Nguyen Song Dao | Chia-Yu Lin | Po-Hsun Lin
Abstract This study introduces manganese oxide (MnOx)-coated granular oyster shells (MnOx@GOS) as an advanced adsorbent for heavy metal removal from urban stormwater runoff. The MnOx coating increased the surface area of granular oyster shell (GOS) by 132% (from 1.0534 to 2.4420 m2/g), enhancing the adsorption capacity. Selective adsorption followed the order of Pb(II) > Cu(II) > Zn(II) > Ni(II), influenced by ionic radius compatibility, hydration energy, and MnOx redox interactions. Kinetic studies showed that the adsorption process was fit to the pseudo-second-order (R 2 = 0.9590–0.9931), confirming chemisorption as the dominant mechanism. The highest kinetic rate constant (K 2 = 0.0766 g/mg·min) was observed for Ni(II), whereas Pb(II) exhibited the strongest affinity. The Freundlich model provided a better fit (R 2 = 0.9900–0.9969) than the Langmuir model (R 2 = 0.9433–0.9826), confirming that adsorption primarily occurred through a multilayer process on a heterogeneous surface. Fixed-bed column studies demonstrated over 90% removal efficiency for Pb(II) and Cu(II) over eight days, confirming MnOx@GOS as an effective adsorbent. With abundant oyster shell waste and a simple synthesis process, MnOx@GOS has great potential for cost-effective, large-scale use in low impact development (LID) systems such as bioretention cells and permeable pavements. However, ensuring long-term stability, efficient regeneration, and consistent performance under a wide range of environmental conditions remains a key challenge for real-world deployment. Graphical Abstract
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