Co and Ni extraction and separation in segmented micro-flow using a coiled flow inverter

The segmented micro-flow extraction and separation of the adjacent elements of Co from Ni sulphate solution with Cyanex 272 is developed using a micro-scale coiled flow inverter (CFI). This is compared with the conventional batch extraction in parallel. Continuous operation of a process involving liquid-liquid extraction and then two-phase separation is achieved instantly. For the latter a micro-scale separator is used. Compared with batch extraction, the segmented micro-flow extraction process shows order-of-magnitude faster extraction times, higher extraction ability for Co, lower extraction for Ni, and then a better selectivity between Co and Ni at industrial-matching concentration. Regular columnar slugs are observed at low flow rates and found to be a Gaussian function of the flow rates. Matched in- and outlet flows indicates that extraction in micro-flow is dependent on mass transfer by molecular diffusion. Extraction efficiency is enhanced by the internal circulation flow generated within slugs. Additionally, the characteristic parameters, overall volumetric mass transfer coefficient kLα and overall mass transfer coefficient kL, are measured to determine the mass transfer performance. Compared with batch, much higher kLα of Co (0.26–0.017 s−1) and smaller of Ni (0.053–0.013 s−1) are investigated in CFI. Meanwhile, 4.5 times increasement of the kL value of Co to Ni is observed in CFI indicating the asynchronous extraction between Co and Ni.