Simultaneous recovery and retention of fluoride resources using esterified cellulose filter papers loaded with environmentally friendly calcium and magnesium extracted from seawater.

[Display omitted] • Mining seawater C a 2 + and M g 2 + for recovering F - was proposed. • This was achieved through the high affinity between carboxyl and C a 2 + / M g 2 + . • The C a F 2 / M g F 2 colloids were recovered and retained by the filter papers. • Additional flocculation was avoided. Resource reclamation with low carbon emissions is highly desirable from the perspective of the circular economy. We propose a green solution in this study, which involves mining calcium and magnesium from seawater as an effective reagent for the recovery of valuable fluoride. This was achieved by esterifying the cellulose filter papers with citric acid to associate carboxyl groups onto their surfaces. Consequently, the high affinity between the carboxyl group and alkaline earth elements enabled efficient and selective loading of C a 2 + (0.193 ± 0.001 mmol- C a 2 + /g) and M g 2 + (0.127 ± 0.001 mmol- M g 2 + /g) onto the filter papers, reaching up to 96% and 60% of the available active sites, respectively. When applied in natural seawater, the esterified filter papers successfully captured both C a 2 + (0.110 ± 0.007 mmol- C a 2 + /g) and M g 2 + (0.078 ± 0.005 mmol- M g 2 + /g) simultaneously. The presence of IR singlet symmetric (ν s COO, ≈ 1450 cm−1) stretching vibrations indicated that both C a 2 + and M g 2 + ions were complexed with carboxyl groups in a bridging unidentate mode. The adsorption capacity of C a 2 + and M g 2 + was likely influenced by the varying thickness of their hydration shells within the highly overlapped electric double layers presented in the micropores of the esterified filter papers. The papers loaded with C a 2 + and M g 2 + were subsequently utilized for fluoride recovery in simulated HF wastewater. The formation of C a F 2 / M g F 2 colloids effectively recovered the stoichiometric amount of fluoride (C a F 2.46 and M g F 1.72), which were retained on the surface of the filter papers. Additional flocculation for colloid separation is thus avoided, resulting in a significant increase in the content of reclaimed fluoride. Increasing the density of associated carboxyl groups is crucial for effectively complexing a greater amount of seawater C a 2 + / M g 2 + and, consequently, enhancing the capacity of fluoride reclamation by esterified filter papers. [ABSTRACT FROM AUTHOR]