Yuzhu Xue,Weinan Wang,Yanhong Zhang,Qinhua Fan,Ying Zhang,Chen Ling,Yuwei Pan
This study proposes a green purification strategy in which mild decomplexation of Ni-EDTA into other Ni complexes facilitates the efficient removal and recovery of nickel through resin adsorption. Decomplexation of Ni-EDTA by boron/Fe 2+ /H 2 O 2 (B/Fe 2+ /H 2 O 2 ) followed by resins adsorption was conducted for Ni(II) removal in Ni-EDTA. The Ni(II) removal efficiency could only achieve 1.3 % and 6.2 % while Ni(II) coexisted with EDTA but more than 10 times of higher when Ni(II) coexisted with EDTA-relatives via the single adsorption of commercial heavy metal-affined resins (D001 and D463), which attributed to the increased binding energies of these Ni-EDTA’s degradation products complexes than Ni-EDTA based on density functional theory (DFT) calculation. In comparing to precipitation, the resin adsorption required much less mineralization of EDTA to have a better removal efficiency of Ni(II). B improved the efficiency of Ni-EDTA decompexation by accelerating the recycle of Fe 3+ /Fe 2+ . The EDTA (and TOC) removal enhanced from 48.7 % (4.7 %) to 94.7 % (11.9 %) by B/Fe 2+ /H 2 O 2 process comparing to Fe 2+ /H 2 O 2 process. With the high EDTA but low TOC removal efficiency after B/Fe 2+ /H 2 O 2 treatment, Ni(II) removal efficiency via resins adsorption could maximum achieve 80.5 %, 2–3 times of that via regular precipitation method. In addition, B and resins exhibited good reusability in five cycles, and B/Fe 2+ /H 2 O 2 -resins process had excellent adaptability to different heavy metal complexes. B/Fe 2+ /H 2 O 2 -D463 system not only could reduce 78.4 % reagents cost compared with that of Fe 2+ /H 2 O 2 -precipitation process, but also could save much cost than other processes. The results provide new insights for the cost-effective treatment of EDTA-complexed heavy metal wastewater.
Electro-enhanced metal-free boron/peroxymonosulfate (B/PMS) system has demonstrated potential for efficient metal-organic complexes degradation in an eco-friendly way. However, the efficiency and durability of the boron activator are limited by associated passivation effect. Additionally, the lack of suitable methods utilizing in-situ recovery of metal ions liberated from decomplexation causes huge resource waste. In this study, B/PMS coupled with a customized flow electrolysis membrane (FEM) system is proposed to address above challenges with Ni-EDTA used as the model contaminant. Electrolysis is confirmed to remarkably promote the activation performance of boron towards PMS to efficiently generate • OH which dominated Ni-EDTA decomplexation in the anode chamber. It is revealed that the acidification near the anode electrode improves the stability of boron by inhibiting passivation layer growth. Under optimal parameters (10 mM PMS, 0.5 g/L boron, initial pH = 2.3, current density = 68.87 A/m 2 ), 91.8% of Ni-EDTA could be degraded in 40 min, with a k obs of 6.25 × 10 −2 min −1 . As the decomplexation proceeds, nickel ions are recovered in the cathode chamber with little interference from the concentration of co-existing cations. These findings provide a promising and sustainable strategy for simultaneous metal-organic complexes removal and metal resources recovery.
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