The effect of impurities, smootheners and other factors on the recovery of copper from solutions

Abstract

The electrochemical refining of copper was investigated at different temperatures, distances between electrodes, different levels of overvoltage, current density, metal impurities, smootheners, electrode-active area and concentration of electrolyte using the parallel-plate model. The purpose of the investigation was to evaluate the effect of smootheners, impurities and other factors on the recovery of copper from solutions. The results showed that the metal impurities, with more negative oxidation potentials, did not affect the electro-deposition of copper whilst metals with oxidation potentials close and equal to that of copper reduced the current efficiency. The current density increased with the increase in temperature, overvoltage and concentration of electrolyte. The increase in overvoltage and current density above limiting values produced increased rates of deposition resulting in efficiencies greater than 100% to be attained. The increase in the limiting current density at concentration below 10.8g/L produced low values of current efficiency ranging from 100 to 30%. The 2 and 3cm distance between electrodes produced stable efficiencies of between 92-100% and 96-100% respectively. The temperature was found to have indirect effect on the current efficiency but direct effect on the dissociation of electrolyte in solution, current density and overvoltage. An increase of 20cm2 of electrode active area reduced the current efficiency by about 40%. The increase in concentration of electrolyte produced an increase in the current density and efficiency ranging from 75-100%. The use of smootheners; thiourea and EDTA (Ethylenediaminetetraacetic acid) reduced the current density and current efficiency (100>CE>30%). However increased concentration of Kglue, B-glue and G-Arabic in conjunction with EDTA or thiourea and NaCl improved the current efficiency even at increased levels of overvoltage to levels of 96-100%, 100% and 90-100% respectively. Therefore, the presence of impurities, the use of high current densities, inadequate distance between electrodes, and too low concentration of electrolyte and the absence of glue disadvantaged the recovery process while the presence of K-glue and B-glue reduced the inhibition effects of thiourea and EDTA and thus improved the recovery of copper from solutions.