Recovery of Uranium, Thorium, and Other Rare Metals from Eudialyte Concentrate by a Binary Extractant Based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and Methyl Trioctylammonium Nitrate

Abstract

Eudialyte-group minerals are of scientific interest as important concentrators of rare elements (mainly Zr and REE) in agpaitic alkaline rocks and a potential source of REE, Zr, Hf, Nb, and Ta for industrial use. Extraction of uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III) by a binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyl trioctylammonium nitrate from eudialyte breakdown solutions is studied. Extraction isotherms were obtained and exhaustive extraction was investigated. It is shown that uranium, thorium, hafnium, zirconium, scandium, and titanium are almost completely recovered in two-stage extraction by a mixture of 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane. Quantitative characteristics were compared for uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III). It was shown that the extraction efficiency of the metals by the binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane is much higher in comparison with the commercially available tributyl phosphate.

Simultaneously Recovery of Thorium and Tungsten through Hybrid Electrolysis–Nanofiltration Processes

“…In order to avoid the loss of thorium in the form of thorium dioxide of nanometric dimensions from the membrane electrolysis process, this process was coupled with the nanofiltration of both the solution from the cathodic space and the solution in the anodic space (Figure 12). The probable reactions in the anodic space (1-4) and cathodic space (5,6) are as follow: Anode…”

“…Thus, by superimposing the Pourbaix diagrams [61][62][63] of the three elements (Figure 13), it is possible to specify, at constant potential, the chemical species for each pH in the anodic space (Table 3). The probable reactions in the anodic space (1-4) and cathodic space (5,6) are as follow:…”

“…• The first stage is at the pH (6)(7)(8)(9)(10)(11)(12) in this space when a permeate, containing the soluble tungstate ion, and a concentrate, containing thorium dioxide and aluminum hydroxide, are obtained; • The second stage is when the concentrate is mixed with the pH 13 solution from the cathodic space, the aluminum is solubilized as aluminate, passing into the permeate, and thorium dioxide remains in the concentrate.…”

“…The performances proven by membrane separation processes in various ecological and greening technologies constitute important arguments for their involvement in the recovery and recycling of various urban wastes, especially those that generate toxic products [ 1 , 2 , 3 , 4 ]. Thus, in order to develop a technology for the separation and valorization of some metallic elements from specific urban waste, baromembrane processes can be applied, when the elements are in a colloidal (nanometric) or suspension (micrometric) state, or processes with electric and/or concentration gradient, if the metals are found in the forms of ions [ 5 , 6 , 7 , 8 ].…”

“…Moreover, tungsten has been the focus of process engineers for its recovery from various residues through electrolytic processes and acid or basic solubilization processes [ 26 , 27 , 28 , 29 , 30 ]. On the other hand, thorium has been the focus of researchers in the field of membranes for concentration, separation or purification, especially when it comes from ores in which uranium or rare earths can also be found [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ] ( Table 1 ).…”