Microfluidic solvent extraction of La(III) with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) by a microreactor

• A micro solvent extraction system is developed to extract rare earth element La(III).
• Two phases successfully flow in a micro-channel without mixing.
• The extraction residence time of the aqueous phase in the micro-channel is only 0.37 s.

A new solvent extraction system of extracting La(III) with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (P507) has been investigated to intensify the extraction process in microreactor, and solve the problems like long mixing time, low processing capacity, large factory area occupation, and high energy consumption in the conventional rare earth solvent extraction equipment. In this work, extraction equilibrium studies show that the initial aqueous pH value 4.00 and saponification rate 40% are the optimal operation condition. The effects of volumetric flow rate on extraction efficiency are analyzed, and the results indicate that increasing flow ratio could improve the extraction efficiency greatly, up to almost 100%, and the two phases keep parallel flow while keeping an aqueous-organic interface in the microchannel. The mass transfer rate is proportional to the initial pH and P507 concentration, and approaches almost a constant value at high pH and extractant concentration, and the transfer process between the two phases accompanied with an interface chemical reaction is confirmed to proceed satisfactorily in a short time (residence time = 0.37 s). The features of the microreactors, i.e., large specific surface area and short diffusion distance are effective for the efficient extraction of La(III).

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