Kinetics of mercury extraction using oleic acid

Abstract

In the absence of halide ion, Hg2+ is the predominant species in water and can be effectively extracted using oleic acid. The organic phase complex that is formed is HgRi2(RH). The presence of polar modifiers in the organic phase facilitates the formation of a complex dimer, [HgR2'2(RH)12. Kinetics of the extraction reaction have been studied as a function of pH, Hg2+ concentration, oleic acid concentration, and mixing rate in a stirred cell reactor. Extraction kinetics are first order in mercury concentration and zero order with respect to oleic acid concentration and pH. This is consistent with f i l m theory predictions for an instantaneous reaction that is mass transfer controlled. A diffusion/ reaction model for mercury extraction in a batch stirred tank reactor has been developed that incorporates this information, and includes mass transfer of mercuric ion from the bulk solution to the droplet surface, equilibrium between aqueous mercury and organic mercury complex at the droplet interface, and diffusion and dimer formation of the complex within the organic phase droplet. Without the use of adjustable parameters, this model successfully predicts mercury extraction rate and equilibrium.

Mass-transfer model of mercury removal from water via microemulsion liquid membranes

“…boundary conditions: Transport of mercury to the surface of the drop is controlled by mass transfer (eq 4), consistent with the results of the kinetic study which revealed that the mercury-oleic acid reaction is instantaneous (Larson and Wiencek, 1993). Consequently, at the interface, mercury in the aqueous phase is assumed to be in equilibrium with the mercury-oleic acid complex in the emulsion phase (eq 7).…”

“…Equilibration time was 12 h. The internal-phase content was measured to be 15 wt % 6 N H2SO4 on a Mettler Model DL18 Karl Fischer titrator. A volume of 0.5 X 10~3 m3 of emulsion was dispersed into 5 X m3 of an aqueous solution containing 0.0025 kmol/m3 (511 ppm) mercury in a stirred contactor described in our earlier work (Larson and Wiencek, 1993). The agitation speed was 350 rpm.…”

“…This extraction represented a 32-fold improvement in extraction over the equilibrium limited solvent extraction case. The second phase of this research studied extraction kinetics for the mercury-oleic acid system and concluded that the reaction is instantaneous and that mass-transfer resistances are controlling (Larson and Wiencek, 1993). The present study is the final phase of the project where an overall diffusion/reaction model is developed for microemulsion extraction of mercury.…”

Kinetics study on supercritical fluid extraction of zinc(II) ion from aqueous solutions

“…Therefore, the mass-transfer behaviors within both films of liquid and SC CO 2 closely approach the linear driving force model (LDF model) of film theory, which assumes the concentration profile within the film is linear. In fact, the LDF model of film theory has been used to estimate the mass-transfer rate across the liquid film for studies of mercury extraction in a stirred tank under atmosphere [27,28]. In order to estimate the mass-transfer rate of the in situ chelation-SFE process, a simplified LDF model is proposed here.…”

Emulsion Liquid Membranes for Wastewater Treatment: Equilibrium Models for Lead and Cadmium Di-2-ethylhexyl Phosphoric Acid Systems

“…In recent publications from our laboratory, we have demonstrated the advantages of using emulsion liquid membranes (ELMs) to extract heavy metals like mercury, copper, nickel, and zinc from aqueous waste streams (1)(2)(3). ELMs, first invented by Li (4), are made by forming an emulsion between two immiscible phases.…”