Microfluidic process enhancement in liquid-liquid extraction: efficient extraction and recovery of valuable metals

In recent years, the widening gap between supply and demand of key metal resources has promoted the development of microfluidic process intensification technology to replace traditional solvent extraction. This review systematically examines the advancements from 2015 to 2024 in microfluidic technology, particularly microreactors integrated with 3D printing, in enhancing liquid-liquid extraction for metal ion recovery. We highlight the fundamental principles, structural designs, and classifications of micro-extractors, and delve into the pivotal role of 3D printing in fabricating complex geometries and high-precision microchannels, facilitating the transition from the lab-scale to industrial applications. The performance of various micro-extractors in recovering valuable metals is comprehensively evaluated, demonstrating volumetric mass transfer coefficients 2-3 orders of magnitude higher than traditional equipment, with high extraction efficiency and selectivity achieved within millisecond residence times. Furthermore, we emphasize the importance of numerical simulations in optimizing micro-extractor design and operational parameters. Despite challenges in scale-up, material corrosion resistance, and system integration, microfluidic technology offers a promising pathway toward green, efficient, and sustainable metal recovery, especially from secondary resources.