Dual-site modulated P204-P507/XAD-4 resin separates Pt/Co efficiently. • Alkaline activation of P-OH groups significantly boosts Co(II) capture. • HFIP effectively shields P=O sites to suppress Pt(IV) co-adsorption. • The Co/Pt separation factor achieves a nearly ten-fold improvement. • DFT and XPS reveal decoupled pathways via synergy-through-inhibition. The efficient recovery of platinum (Pt) and cobalt (Co) from spent proton exchange membrane fuel cell (PEMFC) catalysts is vital for the sustainable hydrogen economy, yet their deep separation from acidic leachates is hindered by the inherent affinity property of organophosphorus extractants. In this study, a dual-site regulation strategy was developed using a synergistic P204-P507/XAD-4 solvent-impregnated resin (SIR). By combining alkaline activation to enhance P–OH cation-exchange capacity (boosting Co(II) uptake from 40.19 ± 0.31 to 47.26 ± 0.58 mg/g at pH 7.0) as well as the hexafluoroisopropanol (HFIP) masking to selectively shield P=O sites via competitive hydrogen bonding (suppressing Pt(IV) adsorption from 7.60 ± 0.66 to 3.78 ± 0.47 mg/g at pH 3.0), the competing adsorption pathways were effectively decoupled. Experimental results showed that the dual-modified resin achieved a Co(II) adsorption capacity of 47.26 ± 0.58 mg/g and an exceptional separation factor (SF Co/Pt ) of 248.85 ± 10.19 at pH 7.0, representing an approximately ten-fold improvement over the unmodified composite. Mechanistic investigations via XPS and DFT calculations indicated that Co(II) is predominantly captured through P–OH sites, while the binding energy shifts in P=O groups are primarily attributed to a secondary inductive effect rather than direct coordination. Furthermore, in continuous fixed-bed operation, the resin exhibited a wide separation window with Co(II) breakthrough delayed to 55 bed volumes, delivering a Pt-enriched effluent with 99.1% purity at 97.0% recovery, while the retained Co(II) was quantitatively eluted at 96.6% purity. The resin also retained over 90% of its initial Co(II) adsorption efficiency after three consecutive adsorption–desorption cycles. and offering a mechanism-driven approach for precision metal adsorbent design.
Rong Zha,Ying Huang,Ling Zhu,Jiali Tan,Zhenfeng Xiong,Baoyan Chi
Hydroxamic acid extractants, such as LIX984, demonstrate high efficiency in extracting nickel from electron-free nickel waste solutions; however, they suffer from a slow extraction rate. This study investigated the effect of adding 2–5 vol.% of three organophosphate extractants (P507, P204, and Cyanex272) to LIX984. The results show that incorporating 2–5 vol.% of P507 or Cyanex272 significantly improves both extraction efficiency and kinetics. The addition of organophosphate extractants increased the extraction rate by 1.5–10 times, indicating a direct correlation between the extractant content and the acceleration of the extraction process, with higher concentrations yielding faster extraction. Compared to the use of LIX984 alone, where nickel extraction efficiency was only 46%, the addition of 5 vol.% P507 increased efficiency to over 99%, with a substantial improvement in extraction rate. Similarly, 2 vol.% P204 achieved a nickel removal efficiency of 99.8%. In non-electroplating waste solutions (pH 4–6), selective removal of iron and zinc impurities was achieved by first adding 2–5 vol.% P204 or P507, followed by adjusting the pH to 6–7 and using a mixture of organophosphate extractants. The spent electroless nickel plating baths were then treated with LIX984 combined with organophosphoric acid extractants, yielding nickel salt solutions of higher purity. Thus, P507, P204, and Cyanex272 serve as effective promoters for the hydroxamic acid extractant LIX984, resulting in both enhanced nickel extraction efficiency and faster extraction kinetics.
Driven by surging global lithium demand, highly selective lithium separation from magnesium-rich brines is urgently required. This work systematically investigated the structure–performance relationship of four aryl-substituted phosphates (TOP, DPOP, IPPP, TPP). Moderate aryl substitution widened the coordination difference between Li + and Mg 2+ through electron-withdrawing effects, and DPOP exhibited the optimal balance of extraction capacity and selectivity. A ternary synergistic extraction system was fabricated with DPOP as the primary extractant, P204 to immobilize Fe 3+ , and eco-friendly diethyl succinate (DES) as a polar modifier. DES inhibited third-phase formation at DPOP contents of 10–50 vol.% and produced synergistic solvation via carbonyl groups. Under optimized conditions, the single-stage Li + extraction efficiency achieved ∼73%, and the Li/Mg separation factor reached 1630, nearly 80 times that of the traditional TBP–FeCl 3 system. Synergistic coordination of P204 and DES stabilized Fe 3+ in the organic phase, realizing quantitative lithium stripping with deionized water and avoiding concentrated acid and saponification. The organic phase maintained over 80% extraction efficiency after ten cycles. Slope analysis and FT-IR confirmed the extracted complex LiFeCl 4 •2DPOP•0.1DES. This work transforms DPOP into a sustainable, low-cost, closed loop industrial solution for lithium recovery from high Mg/Li brines.
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