Study On The New Process For Treatment Of Electroplating Sludge Via Ultrasonically Enhanced Two-stage Acid Leaching

Electroplating sludge, containing high concentrations of heavy metals such as Cu, Ni, Zn, Cr, Fe, etc. and others, is a discharged residue generated from the treatment processes of electroplating waste waters. The metal-grade of electroplating sludge is often higher than metal ore. The sludge is recognized as one of the public hazards at home and abroad. On the other hand, sludge contains lots of valuable metals is actually a cheap secondary renewable resource of metals.A new technology is developed, described as"separation of valuable metals (Cu, Ni and Zn) from less valuable metals (Fe and Cr) in electroplating sludge via ultrasonically enhanced two-stage acid leaching, recovery of heavy metals from leachate of electroplating sludge using solid-liquid-liquid three-phase extraction, separation of Cr from Fe in residue of electroplating sludge via ultrasonically enhanced two-stage alkali leaching". It is used to treat the electroplating sludge in which the primary heavy metals are Cu, Ni, Zn, Cr and Fe. The process conditions of leaching, extraction and product preparation are investigated.An ultrasonically enhanced two-stage acid leaching process on extracting and recovering multiple heavy metals from electroplating sludge was studied. The separation efficiencies of each metal from acid leaching with assistance of ultrasound was compared with the one without assistance of ultrasound and the effects of pH value, leaching temperature, fineness of raw material, ultrasonic power and leaching time have been investigated in the paper. As a result, the more desirable process conditions of the whole process were obtained. The study results demonstrated that ultrasonic energy greatly enhanced metal selectivity of an acid leaching process. On the first-stage acid leaching, when the pH value at 3.2, leaching temperature at 25°C, ultrasonic power at 200 W, leaching time at 60 minutes, fineness of raw material at 100 heads, the leaching rates of 96.72%, 97.77%, 98.00%, 53.03%, and 0.44% for Cu, Ni, Zn, Cr, and Fe respectively, effectively separated half of Cr and almost all of Fe from mixed metals. The subsequent second-stage leaching achieved leaching rates of 75.03%, 81.05%, 81.39%, 1.02%, and 0% for Cu, Ni, Zn, Cr, and Fe that further separated Cu, Ni, and Zn from mixed metals under the conditions of pH value 4.0, leaching temperature 25°C, fineness of raw material at 100 heads, ultrasonic power at 100 W, leaching time at 100 minutes. With the stabilized two-stage ultrasonically enhanced leaching, the resulting over all recovery rates of Cu, Ni, Zn, Cr and Fe from electroplating sludge could be achieved at 97.42%, 98.46%, 98.63%, 98.32% and 100% respectively, with Cr and Fe in solids and the rest of the metals in an aqueous solution discharged from the leaching system. The lab results showed the technical feasibility of the process and had been successfully applied to pilot-scale test.In conclusion, the study demonstrated: the process recovered heavy metals from electroplating sludge successfully. Meanwhile, the whole process did not produce waste water, while the generated minimum discharged solids reached the standard of safe emission. Thus, the technology program has dual economic and environmental benefits and the study results has some reference value and guiding significance for the treatment of electroplating sludge in an industrial test.