Enhanced removal of heavy metal from stainless steel pickling sludge by sonochemical cavitation: Physical fragmentation and chemical activation

Stainless steel pickling sludge (SSPS) is a noxious solid waste containing heavy metals (Fe, Cr, Mn, and Ni). Herein, an ultrafast ultrasonic-assisted leaching (UAL) extraction method for heavy metals from SSPS is proposed. The effects of key leaching factors, including acid lixiviant, acid dosage, leaching time, liquid-to-solid ratio, and leaching temperature, on the leaching efficiency of Fe, Cr, Ni and Mn in SSPS were systematically studied, followed by the theoretical optimization by response surface methodology. The leaching efficiencies of Fe, Mn, Ni, and Cr were significantly enhanced to 98.6%, 90.74%, 90.83%, and 92.25% within 15 min, which were nearly nine times higher than the acid leaching process. The ultrasonic burst broke up the SSPS and increased the contact area (mass transfer effect) of the heavy metal leaching reaction. In addition, kinetic and thermodynamic studies shown that sonochemical action could significantly promote the initial leaching efficiency of heavy metals. This work provided a super-fast method to recovery of heavy metal from SSPS, which shows great potential for the actual application. [Display omitted] •The efficient removal of heavy metals in ultra-short time was demonstrated.•The optimal process conditions for leaching heavy metals are provided.•The use of ultrasound accelerated the disintegration of SSPS.•The leaching rate achieved is higher compared to conventional methods.