S. Kumari

AN OVERVIEW OF PROCESS OPTIONS AND BEHAVIORAL ASPECTS OF THE COPPER VALUES RECOVERED FROM THE COPPER BLEED STREAM OF A COPPER SMELTER DEVELOPED AT THE NATIONAL METALLURGICAL LABORATORY

In the present research, an effort has been made to prepare copper salt/powder from the copper bleed stream generated during the electrowinning of pure copper from the copper anode in a copper smelter. Various approaches have been opted for the complete recovery of copper values such as: evaporation–crystallization, electrolytic process, and direct hydrogen reduction. Physical and chemical properties of copper powder/salt produced from the large-scale experiments from actual plant and model solutions have been evaluated for P/M applications and compared with the standard properties. Thus, mixed crystal suitable for recycling back to the system as a makeup salt containing nickel in a tolerable range could be recovered by evaporation and crystallization of the bleed stream up, to 50%. Copper powder recovery by the electrolysis process at a current density of 700 A/m2 was about 95%. Scanning electron microscope examination showed that the powder was dendritic in nature. On annealing, the purity of the copper powder was found to be 99.95%. The annealed powder had apparent density of 3.04 g/cc, hydrogen loss 0.72%, and acid insoluble as 0.27%. On compaction of <104-µm sized powder, the green density was found to be 8.7 g/cc. Similarly, the recovery of the copper powder obtained from the model copper solution by the hydrogen reduction process was found to be >99% and the annealed powder had an apparent density of 3.50 g/cc, flow rate 35.6 g/min, hydrogen loss 0.195%, purity 99.8%, and green density of 8.57 g/cc while the powder from the actual plant solution was found to have an apparent density of 3.49 g/cc, flow rate 46.0 g/min, hydrogen loss 0.598%, purity 99.4%, and green density 8.57 g/cc for the powder < 100 µm in size. Thus, the properties of copper powder produced by hydrogen reduction and electrolytic route were compared and were found to be suitable for the P/M applications.

Exploitation of Copper Bleed Stream for the Extraction and Recovery of Copper and Nickel by Bis(2,4,4-trimethylpentyl)phosphinic Acid

Bleed streams from copper electrolysis/electrowinning processes potentially contain high amounts of acid, copper, and nickel which need an effective treatment before disposal. A systematic study was carried out to optimize the parameters for the extraction and recovery of metal values using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) diluted with kerosene. Since pH has a major role to play in the separation of Cu from Ni, a 60% saponified solvent was used for extraction studies. With an increase in equilibrium pH from 3.32 to 5.48 and extractant concentration from 5 to 20%, there is an increase in the percentage extraction of metal ions. With a solvent concentration of 20%, the separation factor for Cu with respect to Ni ( ) increases from 39.1 to 118.8 with the increase in pH from 3.3 to 5.5. Loading capacity of 20% Cyanex 272 was found to be 30.8 g/L Cu and 0.024 g/L Ni. After scrubbing of coextracted Ni(II) with 15 g/L H2SO4, the loaded organic containing 30.59 g/L Cu(II) and 4 ppm Ni(II) was stripped with 75 g/L sulfuric acid. A McCabe-Thiele plot shows the requirement of two counter-current stages at an O:A ratio of 1:1 for extraction and two counter-current stages at O:A ratio of 2:1 for the stripping of copper. Results of the present investigation indicate the possibility of the use of saponified Cyanex 272 for the extraction, separation, and recovery of copper and nickel from the actual spent copper bleed streams.