Off-campus WSU users: To download campus access dissertations, please use the following link to log into our proxy server with your WSU access ID and password, then click the "Off-campus Download" button below.
Non-WSU users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Access Type
WSU Access
Date of Award
January 2025
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Claudio Verani
Abstract
This dissertation focused on the following objectives: (i) to leverage fundamental coordination chemistry principles and HSAB theory to enhance the efficiency of cobalt removal from solution, and (ii) to examine how coordination chemistry influences the formation of thermodynamically favored complexes, as well as to gain insights into the interactions within metal-chelato and metal-chelator-surfactant systems. The first objective was tested based on the hypothesis that selecting ligands with medium hardness that provide the appropriate cavity or pocket size can drive the formation of the favored thermodynamic product. This involves establishing ligand field energies that lead to improved cobalt recovery. For the second objective, we hypothesized that cyclic and linear ligands containing multiple amines might deliver the appropriate hardness, cavity size, and ligand fields necessary to achieve nickel recovery via ion flotation. As such, amine-based ligands and sodium dodecyl sulfate were used in the recovery of cobalt using the ion flotation technique. We investigated the role of chelators in promoting the solubility of the metal-chelate complex at various pH levels and their adsorption to the surfactant, which leads to higher metal recoveries. Coordination chemistry was employed to determine the binding modes of metal-chelate complexes using chelators with varying charge biting angle and pocket/cavity sizes to drive the formation of octahedral geometry for Co3⁺complexes. Flotation experiments were conducted with a series of chelators: ethylenediamine (en), triethylenetetramine (222), 1,2-bis(3-aminopropylamino)ethane (323), N,N′-bis(3-aminopropyl)-1,3-propanediamine (333), and 1,4,7,10-tetraazacyclododecane (cyclen). The collector surfactants included cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) as cationic surfactants, and sodium dodecyl sulfate (SDS) and sodium dodecanoate (SDD) as anionic surfactants. Co3⁺ recoveries with collector surfactants alone showed pH 11 = 41% for CPC, pH 11 = 47% for CTAB, pH 1 = 34% for SDD, and pH 8 = 97% for SDS. The results indicate that the highest recoveries were achieved with 222 and 323 at pH 11 using SDS, yielding recoveries of > 95%, while cyclen showed a recovery of 78% at the same pH.Coordination chemistry, which was the determining factor, suggested that Co:222 forms a strained 2:3 complex, while Co:cyclen and Co:323 drive the formation of a 1:1 complex. This suggests that the tetradentate ligands coordinate to the metal in a pseudo-square planar geometry, with two solvent molecules coordinating to the metal to form the octahedral geometry of the cobalt complexes. Thus, ligands with larger pocket/cavity sizes facilitate the formation of thermodynamically favored products. We explored the same ligands with SDS for nickel recovery. The recovery studies indicated that 99% of nickel was recovered at a pH of 11. Similar to cobalt, ligands 222 and en faced steric issues when coordinating to nickel, resulting in the formation of 2:3 and 1:3 metal-chelate ratios, respectively. Speciation studies suggested that the smaller cavity sizes led to the formation of multiple species in solution, including nickel hydroxide at basic pH. In contrast, ligands 323, 333, and cyclen coordinated to nickel in a 1:1 ratio, suggesting that the tetradentate amines wrap themselves around the metal in a pseudo-octahedral geometry, with two solvent molecules binding at axial positions to form an octahedral geometry complex with nickel. This confirms that ligands with appropriate cavity sizes drive the formation of the most stable, thermodynamically favored products. Selectivity was observed as a function of pH when the tetradentate ligands 323, 333, and cyclen were used for the recovery of cobalt, nickel, and gadolinium. Gadolinium was recovered at pH 7-8, achieving recoveries of 80%. However, as the pH increased, the recovery of gadolinium decreased to nearly zero, while cobalt and nickel maintained higher recovery values at this pH. Therefore, gadolinium can be selectively removed at a pH of 8 using ligands 333 and cyclen. To investigate the incorporation of both chelators and surfactants, two new chelating surfactants were synthesized with NO₂ and SO₃ functional groups in their ligand framework, potentially for use in ion flotation studies. However, coordination studies could not be conducted because the chelating surfactants were not coordinating with the metals This dissertation has bridged the gap between coordination chemistry and ion flotation. The data suggest that the chelate cavity size, HSAB character, denticity, and donicity of chelators drive the formation of the thermodynamically favored geometry. The research has identified pH as the key factor in selective metal recovery. Understanding the binding modes of metal-chelate and metal-chelate-surfactant interactions will enhance the design of better systems for selective metal recovery through ion flotation.
Recommended Citation
Mwakazi, Eva Dama, "Identification Of The Coordination Compounds Formed In The Ion Flotation Recovery Of Co3+ And Ni2+ Ions Using Amine Chelators And Sodium Dodecyl Sulfate" (2025). Wayne State University Dissertations. 4167.
https://digitalcommons.wayne.edu/oa_dissertations/4167