The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, Mn+, metalate anions, MXxn−, or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.

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Solvent extraction: the coordination chemistry behind extractive metallurgy

Extractive metallurgy of uranium, The

A review of acid leaching of uraninite

In this work, a novel three dimensional graphene oxide sponge composite material was synthesized by functionalized GO sheets with phytic acid (PA). The as-synthesized samples were characterized and employed to investigate the removal of U(VI) from aqueous solution. Results show that higher pH favored the sorption of uranium on PA–GO. Ionic strength puts insignificant influence on the sorption. The maximum adsorption capacity is 124.3 mg g−1 at pH 5.5. The adsorption isotherms can be well described by Langmuir isotherm model and the sorption kinetics has been successfully modeled by pseudo-second-order kinetic model.

Three-dimensional graphene oxide/phytic acid composite for uranium(VI) sorption

Abstract The performance of the hollow fiber renewal liquid membrane (HFRLM) in the continuous and recycling modes for the extraction of uranium(VI) from the acidic sulfate solution has been investigated. Alamine 336 diluted in kerosene was used as a carrier in liquid membrane (LM) phase. In the batch experiments, the effects of sulfuric acid, extractant and uranium(VI) concentration were studied and the optimum concentration of the donor and LM phases were determined 0.15 mol L−1 and 0.0125 mol L−1, respectively. Various parameters affecting the HFRLM performance including the lumen and shell side flow rate, organic/aqueous volume ratio, acceptor phase type and concentration of carrier and acceptor phase were studied. The mass transfer flux increases with increasing the lumen side flow rates and the shell side flow rate did not have any significant effect. The uranium transfer flux increases with increasing O/A ratio, acceptor and Alamine 336 concentration, and reaches a maximum value at 1/20, 0.5 mol L−1 and 0.0125 mol L−1, respectively. Further increase in these parameters result in uranium transfer decrement. The results show that liquid membrane phase is a rate-controlling step. Among the investigated acceptor phases, 0.5 mol L−1 NH4Cl result in 60.35% uranium(VI) recovery in the recycling mode.

Performance evaluation of hollow fiber renewal liquid membrane for extraction of uranium(VI) from acidic sulfate solution

This paper describes the solvent extraction studies carried out on an acidic low assay uranium bearing leach liquor generated during sulfuric acid leaching of a refractory uranium ore using alamine 336–isodecenol–kerosene reagent combine. The leach liquor has a U3O8 content of about 270 mg/L, free acidity 2.4 N H2SO4 and total dissolved solids concentration of 260 g/L. Process parameteric variation studies indicated strong influence of free acidity of the leach liquor, alamine 336 concentration and aqueous to organic phase ratio on the extraction efficiency of uranium. An extraction efficiency of about 95% was achieved when the free acidity of leach liquor was 1 N H2SO4 or lower, using 2% (v/v) alamine 336 at ambient temperature with an aqueous to organic phase ratio of 1:1. The loading capacity under these conditions was 1.2 g/L of U3O8. About 98% of the uranium values could be stripped from the loaded organic using 1 N NaCl in 0.2 N H2SO4. The solvent extraction studies aided in developing a suitable process flowsheet for treating refractory uranium ores which need high acidity during leaching and relatively lower acidity for purification by solvent extraction.

G. Ramadevi

Papers

Solvent extraction of uranium from lean grade acidic sulfate leach liquor with alamine 336 reagent