Study of the Stability of W/O/W-Type Emulsion During the Extraction of Nickel via Emulsion Liquid Membrane

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Abstract
Considerable effort has been directed toward describing the analysis of mass‐transfer resistance for solute diffusion and reaction in an emulsion liquid membrane (ELM) system but very little attention has been paid to the loss of extraction efficiency often encountered in these systems due to rupture of the emulsion globules. In the present work, batch extraction of nickel(II) with ELM from a dilute sulfate solution by using di‐(2‐ethylhexyl) phosphoric acid (D2EHPA) as an extractant and hydrochloric acid as a stripping agent is reported. However, separation efficiency significantly decreases with breakage of the liquid membrane. Important variables affecting the stability of the emulsion, such as pH of the feed phase, speed of agitation, emulsion drops size per unit specific interfacial area, surfactant concentration, pH in inner aqueous phase, and the presence of different tracers, are systematically investigated during the extraction of nickel(II) ions.