New insights into ball-milled zero-valent iron composites for pollution remediation: An overview

Ball milling is an effective and economical method, which has an important application prospect in overcoming the passivation problem of zero-valent iron (ZVI) and improving its decontamination efficiency. This work provides a systematic and comprehensive summary of the two intersecting areas of ball milling and ZVI materials from a holistic perspective. The results show that the interface structure of ZVI is changed and the particle size is reduced, resulting the enhanced activity of ZVI. Different from single-component mechanical crushing, multi-component mechanical synthesis can improve the agglomerations, alleviate surface passivation, and promote electron transfer. The variation of one or more parameters will affect the particle size, shape and type of the ball milling product. Therefore, for a specific composite system, it is necessary to optimize the process parameters and evaluate the practical application effect. In the ball-milled zero-valent iron (ZVIbm) system, the formation of micro-electrolysis, the unstable interfacial phase and matrix between reinforcers, and the microstructure changes lead to the large amount of generated Fe2+, which is the key to its efficient removal of pollutants. Notably, different from the low activity of ZVI and the high toxicity of nano zero-valent iron (nZVI), ZVIbm has greater application potential in the future because of its moderate activity and low toxicity. Although the mechanochemical reactions induced by ball milling can effectively increase the activity of ZVI, the positive effects of mechanochemical modification and the negative effects of particle agglomeration and over-compaction under the condition of continuous energy input need to be further evaluated. This study has important guiding significance for the application of ball-milling technology in the field of ZVI pollution remediation.