Fig. 5: Phosphate recycling.

a, Recovery of phosphate salts. b, Identification of C/F/P contents of PTFE mix^CYC after first cycle and efficacy of recovered phosphate salts. Ball milling conditions: PTFE (1 equiv.; 86 mg) milled with K₃PO₄ (0.625 equiv. per F; 457 mg) or K₃PO₄^CYC (457 mg) in a 15-ml stainless-steel milling jar, two chrome steel balls (2 × 7 g) at 35 Hz for 6 h. ^aThe total yield of released fluoride (F⁻ and PO₃F²⁻) as well as F⁻:PO₃F²⁻ ratio was determined by quantitative ¹⁹F NMR spectroscopy (in 10% D₂O in H₂O using NaOTf as an internal standard). ^bYields for isolated KF are reported. ^cThe total yield of recovered phosphate (PO₄³⁻ and P₂O₇⁴⁻), as well as PO₄³⁻:P₂O₇⁴⁻ ratio was determined by quantitative ³¹P NMR spectroscopy (in 10% D₂O in H₂O using PO(OEt)₃ as an internal standard); recovered phosphate salts contain up to 8% carbonate.