[Recovery of copper from sewage sludge by bioleaching-solvent extraction-electrodeposition process]

Sewage sludge contains not only a lot of organic matter and plant nutrients, but also some harmful metals. Recovery of sludge-born metals for sewage sludge of high metal content is very important for safe reutilization of sewage sludge and for economic consideration. Here, we reported a recovery technique for sludge-born copper using bioleaching-solvent extraction-electrodeposition (L-SX-EW) process through batch experiments. The tested sludge containing 7 432 mg/kg Cu was collected from Suzhou Wastewater Treatment Plant located in industrial zone of Suzhou City, Jiangsu, China. The results showed that more than 90% of sludge-born Cu could be solubilized into aqueous phase within 72 h through bioleaching process. Furthermore, soluble Cu in the form of Cu2+ in bioleached sludge filtrate could be concentrated into organic phase through the extracting operation using 2% solvent extractant M5640 under the optimized condition of 1/3 phase ratio (O/A) and pH 2.0, in which Cu2+ extraction efficiency reached more than 95%, whereas the co-existing soluble iron extraction efficiency was less than 10%. Stripping results showed that the Stripping rate of Cu was 80.07% when the phase ratio (O/A) was 2/1 using 1.5 mol/L H2SO4 as stripping solvent. After the concentrated Cu2+ in acidic aqueous phase was electrolyzed for 6 h at 2.1 V bath voltage and 55 degrees C, more than 90% of the Cu2+ recovery efficiency was achieved in the form of elemental Cu powder. There wasn't any wastewater generation in this process. Therefore, this L-SX-EW technique exhibited a potential application for the recovery of metal for heavy metal-loaded sludge.