Recovery of zinc from scrap steel using zinc–bromine battery technology

Secondary production of steel is proven to significantly decrease CO2 emissions of steelmaking, but only 40 % of steel is produced via recycling, which is made difficult by contamination of scrap resources with non-ferrous metals and non-metal debris. These contaminants include zinc, which blast furnace and electric arc systems have a low tolerance towards (< 0.02 wt%). In this work, clean and efficient recovery of zinc from the surface of steel substrates was investigated using a custom-made low-cost membrane-free non-flow zinc-bromine battery (ZBB) that enabled rapid and straightforward integration and removal of steel substrates. The electrical performance of the cell was characterised by charge-discharge profiles, and zinc removal and recovery onto electrodes was characterised using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Upon discharging, the cell efficiently removed > 99.9 wt% zinc from steel surfaces. On recharging the cell, zinc was re-electroplated onto a carbon foam electrode in an easily recoverable form and with high purity. The process was repeated over 30 cycles to demonstrate robustness. The work shows the importance of the cut-off voltage upon discharging: if less than 0.5 V, the cell co-extracted iron into the electrolyte solution, affecting cell durability and zinc purity. A two-stage process for recovering zinc from scrap steel is proposed, illustrating how ZBB technology could enable efficient and clean recovery of zinc from complex scrap steel resources in the steel industry.