Fluoride removal by palm shell waste based powdered activated carbon vs. functionalized carbon with magnesium silicate: Implications for their application in water treatment.

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Source: Chemosphere 239:124765. | January 17th, 2020 | Authors: Choong CE, Wong KT, Jang SB, Nah IW, Choi J, Ibrahim S, Yoon Y, Jang M.

Location: International

Industry type: Water Treatment

Highlights

MgSiO₃ impregnated on PSAC for fluoride removal was studied for the first time.
MPSAC showed higher fluoride adsorption capacities compared to PSAC.
Anions inhibited F^? adsorption with the following sequence: Cl^–< NO₃^–< SO₄^2-.
PSAC had stable sequestration capacities of fluoride due to strong C–F bond formation.
MPSAC had high regeneration capacities for ex-situ fluoride treatment using NaOH.

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.

*Original abstract online at https://www.sciencedirect.com/science/article/pii/S0045653519320028

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