Headgroup Interactions and Ion Flotation Efficiency in Mixtures of a Chelating Surfactant, Different Foaming Agents, and Divalent Metal Ions

Abstract

The correlation between interaction parameters and ion flotation efficiency in mixtures of chelating surfactant metal complexes and different foaming agents was investigated. We have recently shown that chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) forms strong coordination complexes with divalent metal ions, and this can be utilized in ion flotation. Interaction parameters for mixed micelles and mixed monolayer formation for Mg(2+) and Ni(2+) complexes with the chelating surfactant 4-C12-DTPA and different foaming agents were calculated by Rubingh's regular solution theory. Parameters for the calculations were extracted from surface tension measurements and NMR diffusometry. The effects of metal ion coordination on the interactions between 4-C12-DTPA and the foaming agents could be linked to a previously established difference in coordination chemistry between the examined metal ions. As can be expected from mixtures of amphoteric surfactants, the interactions were strongly pH-dependent. Strong correlation was found between interaction parameter β(σ) for mixed monolayer formation and the phase-transfer efficiency of Ni(2+) complexes with 4-C12-DTPA during flotation in a customized flotation cell. In a mixture of Cu(2+) and Zn(2+), the significant difference in conditional stability constants (log K) between the metal complexes was utilized to selectively recover the metal complex with the highest log K (Cu(2+)) by ion flotation. Flotation experiments in an excess concentration of metal ions confirmed the coordination of more than one metal ion to the headgroup of 4-C12-DTPA.

Influences of the operational variables on electrochemical treatment of chelated Cu(II) in alkaline solutions using a membrane cell

“…To reduce the problems associated with the separation of chelated heavy metals and the degradation of the resulting chelating agents, the substitution of either biodegradable or functionally modified alternatives for conventional ones such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA) has been considered a viable option. In addition, using alternative treatment techniques to minimize the loss of chelating agents and recycle them from industrial effluents has been recommended for economic and practical reasons…”

Electrochemical recovery of copper complexed by DTPA and C12‐DTPA from aqueous solution using a membrane cell

“…The chelation ability of these ligands is the result of their possessing three amines and five carboxylic groups as donor atoms. In theory, the charge can vary from +3 at low pH to −5 at high pH . In solutions with pH between 7 and 12, DTPA ligands could be found in three different ionic species with net charges of −3, −4, and −5, whereas by adding an equimolar concentration of copper ions, CuDTPA 3– is the only stable complex (see Fig.…”

“…On the other hand, chelating surfactants have purpose‐built functionality; besides forming strong coordination complexes with metal ions, they are also surface‐active and will readily adsorb at air–water interfaces. As a result of these properties, a chelating surfactant can be employed to effectively separate metal ions from aqueous solution via an ion flotation technique, and isolate them in a foam phase . From an economic perspective, it is essential that a metal product can be recovered from the foam phase with regeneration of the chelating surfactant …”

“…electrode of high surface area) to make feasible the removal and recovery of the relevant components. One possible approach to overcome the problems of treating dilute metal solutions could be to first employ an ion flotation technique with a chelating surfactant to separate and concentrate the metal ions, and then to apply electrolysis in a membrane cell on the concentrated complex solutions. It would then be possible to recover the chelating surfactant for further reuse and simultaneously collect the metals by electrodeposition in a membrane electrolysis cell, making the process more economical and more environmentally friendly.…”

“…For this purpose, studies have mainly focused on chelating agent modification 1,[4][5][6][7][8] and/or the exploration and development of effective wastewater treatment methods. 2,6,[9][10][11][12][13][14][15][16][17] Chelating agents can only be modified if they have been synthesized to be biodegradable 4,5 and surface-active. 1,[6][7][8] Biodegradable chelating agents have lower long-term environmental effects, due to their degradation.…”