Ultrafast recovery of Zn from waste galvanized iron sheet by ultrasound-assisted acid pickling and ion flotation techniques.

High-efficiency dezincification from waste galvanized iron sheets is crucial for resource recovery and environmental protection. In this work, ultrasound-assisted acid pickling and ion flotation techniques were combined to intensify the Zn extraction and separation from the waste galvanized iron sheets. The effects of leaching parameters on the leaching rate of Zn and Fe, Zn leaching kinetics and leaching electrochemistry were compared between conventional leaching and ultrasonic-assisted leaching. It's demonstrated that ultrafast dezincification is realized as the acid pickling time can be reduced from 10 min to 60 s with ultrasound assistance, and the Zn and Fe leaching rates are 99.9 % and 0.02 %, respectively. Ion flotation was adopted to recover the Zn ion from the circulated leaching solution using sodium dodecyl benzene sulfonate (SDBS) as the collector. After the Zn ion flotation, powdery ZnO with size distribution of 1-3 μm is prepared from the froth product after calcining at 600 ℃ for 2 h. In addition, various characterizations involving thermodynamics, XRD, XPS, SEM-EDS, TG-DSC, and FTIR analyses were employed to elucidate the mechanisms underlying the enhancement of Zn dissolution through ultrasound assistance and the Zn capture mechanism via ion flotation. Eventually, the combination of ultrasonic-assisted acid pickling and ion flotation techniques can achieve the rapid selective Zn extraction from waste galvanized iron sheet and fast separation of Zn ion from leachate, which can provide technical reference for the resource utilization of other waste metal coating plates.