Removal of impurities from electrolyte solution to produce pure metals

Hossain, Mirza M. Rashed (2010) Removal of impurities from electrolyte solution to produce pure metals. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (8MB)

Abstract

The impurities present in the electrolyte solution not only deteriorate the quality of the metal product, but also may have large impact on the overall process efficiency. Therefore, solution purification before electrowinning process is an essential step for the metal to be electrowon. In this study, cobalt electrolyte solution was purified to produce pure cobalt and to improve process efficiency. A solvent extraction (SX) method has been examined to remove impurities such as manganese (Mn) and cadmium (Cd) from a cobalt electrolyte solution in a laboratory scale batch wise test work using modified D2EHPA (Di-2-ethylexhyl phosphoric acid). The organic reagent D2EHPA is an organophosphorous acidic extractant, which has an affinity to extract and remove metals from the electrolyte solution. The real cobalt electrolyte solution collected from Vale Inco's demo plant at Argentia has been used in this experiment. -- By the SX method, metals were selectively removed from the cobalt electrolyte solution using modified D2EHPA, after converting its functional group with Na⁺ or Co²⁺ ions. The distribution ratio and separation factors were the key measures, in this experiment, to selectively remove the impurity metals from the cobalt electrolyte solution, and the separation of metals was greatly dominated by the equilibrium pH of the solution. It was found that D2EHPA modified by Co²⁺ was more favorable for controlling the pH of the solution. The concentration of organic extractant and the equilibrium pH of the solution were the important parameters to selectively remove the impurities from the cobalt electrolyte solution. A kinetic study was carried out showing the equilibrium position (rate of transfer of metals) between two phases. The stripping of metals from the loaded organic extractant was conducted using different concentrations of sulphuric acid (H₂SO₄). Finally, a fixed concentration of H₂SO₄ was used for the stripping of the metals of interest. Mn and Cd were stripped with same concentration of H₂SO₄ which was the added benefit for the process. The kinetics for the extraction of Mn and Cd observed in the study were also found to be similar. -- The screening tests with different ion exchange resins were also investigated in this study, to selectively remove manganese and other impurities. It was found that, among others, Amberjet 4400 CL followed by Amberlite IRC 7481 and Lewatit TP-207 are suitable resins for the extraction of manganese and cadmium from a cobalt electrolyte solution.

Actions (login required)

View Item