Experimental Study On Electrodeposition Recovery Of Heavy Metals From Simulated Wastewater Containing Heavy Metals

Heavy metals contained in wastewater are difficult to be biodegraded. Wastewater containing heavy metals pollutes environment and endangers human's life seriously. Searching for the treatment methods of this wastewater to recover both water and heavy metals has attracted more and more researchers'attention. In this work, electrodeposition recovery of heavy metals contained in membrane filtration-electrodeposition process was studied.The experiments were carried out with a model electrolysis set-up. Simulated wastewater solutions including Cu(Ⅱ) or Ni(Ⅱ) were used. The effects of basic parameters on current efficiency and metal recovery were investigated. The results indicate that current efficiency of copper and nickel decreased with increasing current density under the same electrolytic time, current efficiency of nickel dropped more sharply. Recovery of copper and nickel increased with increasing current density. Appropriate feed pH value could inhibit hydrogen evolution and hydrolysis reaction of Cu2+ and Ni 2+. It also prevented these heavy metal ions from precipitating. In the scale of this work, the optimum feed pH value of copper and nickel recovery were 2.5~3 and 3~5, respectively. When the metal concentration was lower, the overpotential of metal was higher, and thus the metal precipitation became more difficulty. In this work, under the conditions of feed pH value 3, current density 250 A/m2 , Cu2 + concentration 10 g/L and electrolytic time 1h, average current efficiency of copper was 97.63%. When Ni2+ concentration was above 2000 mg/L and current density was in the range of 0~570 A/m2, the minimum current efficiency of nickel retained about 20%. An increase in temperature or flow rate can cause increasing current efficiency and metal recovery of copper. Appropriate distance between the electrodes also cause increasing current efficiency and metal recovery of copper. The results indicate that the optimum distance between the electrodes was 21~26 mm. Under steady current density, concentration of heavy metals decreased and H+ concentration increased with increasing electrolytic time. Hence, current efficiency of heavy metals decreased.A 0.22μm porous membrane was used to separate the cathode and anode. The effects of current density, feed pH value and temperature on current efficiency and recovery of copper were investigated. Current efficiency and recovery of copper were found to behave the same as no microporous membrane under different current density, feed pH or temperature. The detection with gas chromatography shows that hydrogen content in cathode cell was above 89% and oxygen content in anode cell was above 94%. These results indicate that 0.22μm microporous membrane can separate the products of two eletrodes effectively while did not affect electrolysis process greatly.