Enhanced detoxification and valuable metal extraction from electroplating sludge via ultrasonic-assisted ferric sulfate bio acid

Electroplating sludge (ES), a hazardous waste rich in toxic heavy metals, is produced through CaO/Ca(OH)₂ precipitation. Despite its hazardous nature, the sludge is also a valuable secondary source of metals, making its recycling crucial both environmentally and economically. This study introduces an innovative ultrasonic-assisted ferric sulfate bio acid (FSBA) process to leaching of chromium (Cr), copper (Cu), and nickel (Ni) from ES. The bacterial supernatant of Acidithiobacillus ferrooxidans was employed to produce ferric ion and sulfuric acid for the ultrasonic-assisted leaching experiments. The impact of various parameters on the leaching efficiency in the presence of biogenic acids was systematically investigated. Ultrasonication significantly improved metal extraction rates and reduced the leaching time, achieving extraction efficiencies of 92.51% for Cr, 86.91% for Cu, and 91.25% for Ni within 8 min at an S/L ratio of 10 g/L, 400 rpm agitation speed, and 45 °C. Elemental analyses confirmed the enhanced metal extraction facilitated by ultrasonic. Furthermore, field emission scanning electron microscopy and X-ray diffraction analyses have detected the formation of hydronium jarosite on residue surfaces at 75 °C temperature. Finally, both the synthetic precipitation leaching procedure and toxicity characteristic leaching procedure tests demonstrated effective detoxification of the ES through FSBA.