Extraction of gadolinium by the electrochemical aerosol formation

Due to their optical, electronic, and metallurgical properties, rare earth elements play a vital role in the production of catalysts, permanent magnets, electric car batteries, electronic components, and in medical applications such as magnetic resonance imaging (MRI) contrast agents. MRI contrast agents are regularly used to detect tumors at early stages and often are gadolinium (Gd)-based. Because of the high toxicity of Gd (III) ions, they first get complexed with potent chelators and administrated to patients who will undergo MRI. These highly stable compounds can readily pass through human bodies and accumulate in wastewater systems. We developed a novel extraction strategy to recover Gd inspired by a natural phenomenon called sea spray aerosol enrichment. We electrochemically generated hydrogen and oxygen bubbles using a Ni foam electrode in a custom-made H-type cell which consists of a low amount (10 ppb to 100 ppb) of Gd (III) ions with a ligand in the presence of phosphate buffer. Once bubbles start to move to the top through the liquid column, the Gd complex can preferentially be adsorbed onto the air/liquid interface of the bubble. When bubbles reach the air/liquid interface at the top of the liquid column, they burst and produce aerosol droplets enriched with Gd(III). We found that bis(ethylhexyl)amido diethylenetriamine pentaacetate (BED) and bis(octaylamido) diethylenetriamine pentaacetate (BOD) binds to Gd(III) and get attached to the rising bubbles. Using 100 ppb Gd (III) and two molar-equivalences of BED, we could obtain the extraction efficiency of Gd up to ~50%. We observed that the extraction efficiency would increase with the ligand concentration. When we increased the molar equivalence of BED from 0.5 to 2, cathodic extraction efficiency increased from ~12% to 53%. The anodic side gives a much lower extraction efficiency, ~39% lower than the cathodic side. When electrolysis takes place, one molar equivalence of H₂O produces, one molar-equivalence of H₂, and half an equivalence of O₂ at cathode and anode, respectively. We are currently improving the extraction efficiency of Gd by ligand modulation and fine-tuning the metal to ligand interactions towards the air/liquid interface of the bubble surface.