Abstract

In this study, palm shell activated carbon powder (PSAC) and magnesium silicate (MgSiO₃) modified PSAC (MPSAC) were thoroughly investigated for fluoride (F^–) adsorption. F^– adsorption isotherms showed that PSAC and MPSAC over-performed some other reported F^– adsorbents with adsorption capacities of 116 mg g^-1 and 150 mg g^-1, respectively. Interestingly, the MgSiO₃ impregnated layer changed the adsorption behavior of F^– from monolayer to heterogeneous multilayer based on the Langmuir and Freundlich isotherm models verified by chi-square test (X²). Thermodynamic parameters indicated that the F^– adsorption on PSAC and MPSAC was spontaneous and exothermic. PSAC and MPSAC were characterized using FESEM-EDX, XRD, FTIR and XPS to investigate the F^– adsorption mechanism. Based on the regeneration tests using NaOH (0.01 M), PSAC exhibited poor regeneration (<20%) while MPSAC had steady adsorption efficiencies (–70%) even after 5 regeneration cycles. This is due to highly polarized C-F bond was found on PSAC while Mg-F bond was distinguished on MPSAC, evidently denoting that the F^– adsorption is mainly resulted from the exchange of hydroxyl (-OH) group. It was concluded that PSAC would be a potential adsorbent for in-situ F^– groundwater remediation due to its capability to retain F^– without leaching out in a wide range pH. MPSAC would be an alternative adsorbent for ex-situ F^– water remediation because it can easily regenerate with NaOH solution. With the excellent F^– adsorption properties, both PSAC and MPSAC offer as promising adsorbents for F^– remediation in the aqueous phase.

*Abstract online at https://www.ncbi.nlm.nih.gov/pubmed/31520981

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