Surface-mediated leaching of calcium and magnesium from raw coconut shell powder: Thermodynamic and spectroscopic insights

Abstract

Coconut shell powder (CSP), a low-cost, biogenic material, has been widely explored for water purification, particularly for its ability to adsorb toxic heavy metals. In this study, we examined the interfacial behavior of raw CSP when exposed to calcium (Ca 2+ ) and magnesium (Mg 2+ ) ions in aqueous systems, with a focus on surface interactions and mineral mobility. Using a combination of ICP-MS, FT-IR, SEM, and EDX analyses, we found that CSP does not effectively adsorb these divalent ions. Instead, a mass-dependent increase in ion concentration was observed in treated solutions, indicating spontaneous mineral leaching from the adsorbent. Surface imaging and elemental mapping confirmed the deposition of crystalline residues post-treatment, while FT-IR spectra showed minimal functional group shifts, suggesting weak surface interaction. Thermodynamic analysis supports a dissolution-driven mechanism, governed by favorable entropy gains and low adsorption affinity. These findings emphasize the importance of surface chemistry, material pretreatment, and selectivity in the application of biomass-derived adsorbents for ion remediation. • Raw coconut shell powder (CSP) exhibits spontaneous mineral leaching in aqueous systems. • SEM-EDX and FT-IR revealed minimal adsorption and prominent surface mineral redeposition. • ICP-OES confirmed mass-dependent release of Ca 2+ and Mg 2+ from the adsorbent. • Thermodynamic analysis supports dissolution over adsorption as the dominant interfacial process. • Findings provide new insight into surface-controlled ion release in bio-derived interfaces.