Advancements of heavy metals control in the environment from detection to separation and recovery: Emerging microfluidics strategy

Investigating the fate of heavy metals, especially natural environmental processes, requires innovation and precise technologies that can offer knowledge at the microscopic scale. Breakthrough of the microfluidics involved in heavy metals control has accelerated in recent years along with realization of the ubiquity, non-degradability, bioaccumulation, mobility and reactivity of heavy metals in the environment. This review explores recent advances in microfluidic applications for heavy metal control, spanning detection, separation, and recovery. Among microreactors, droplet-based systems demonstrate exceptional performance in detecting trace contaminants, achieving detection limits below 0.5 µg/L through enhanced mixing and reaction efficiency. For separation, liquid-liquid extraction microreactors stand out, with optimized interfaces yielding extraction efficiencies of up to 99.3% for cadmium (Cd) under specific flow and pH conditions. In the realm of recovery, electrochemical microreactors have shown potential for selective deposition, achieving high recovery rates at optimized current densities and tailored electrode materials. Future work will focus on the design and development of functional integration and scale-up of microfluidic systems/platforms, particularly in terms of the flexibility of microfluidic device design and assembly, as well as the efficiency of mass and heat transfer and reactions. The precise process control characteristics of microfluidic systems make them highly promising for applications in environmental monitoring, pollution control, and resource recovery.