John M. Wiencek

Emulsion Liquid Membranes for Wastewater Treatment: Equilibrium Models for Some Typical Metal-Extractant Systems

Emulsion liquid membranes are capable of extracting metals from dilute waste streams to levels much below those possible by equilibrium-limited solvent extraction. Binary equilibrium data are reported for copper, nickel, and zinc with extractants that can be used in emulsion liquid membrane formulations. Predictive models that incorporate aqueous-phase nonidealities and all aqueous-phase ionic reactions have been developed. For the Cu-LIX and Zn-D2EHPA systems, a single value for the equilibrium constant (K) is accurate over a large range of pH and ionic strength. For the Ni-D2EHPA system, an average single K value was obtained for loadings (fraction of D2EHPA dimers complexed to the metal in the organic phase) less than 0.1. At higher loadings, the organic-phase nonidealities become significant, and the equilibrium constant was fitted as an exponential function of the loading. Emulsion liquid membrane extractions of Cu, Ni, and Zn from aqueous phases were successfully carried out. The effects of various parameters such as mixing speed, stripping reagent concentration, and extractant concentration on the extraction process are reported. 36 refs., 10 figs., 1 tab.

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

Extraction and recovery of heavy metals from wastewater is more attractive than methods such as precipitation which result in sludges that have to be disposed in landfills. Emulsion liquid membranes are capable of extracting metals from dilute waste streams to levels much below those possible by equilibrium-limited solvent extraction. Binary equilibrium data are reported for lead and cadmium with extractants that can be used in emulsion liquid membrane formulations. Predictive models that incorporate aqueous phase nonidealities and all aqueous phase ionic reactions have been developed. Equilibrium constant values have been reported for Pb- and Cd-di-2-ethylhexyl phosphoric acid systems. Emulsion liquid membrane extractions of Pb and Cd from aqueous phases are successfully demonstrated.

Electrical and chemical demulsification techniques for microemulsion liquid membranes

Abstract Recent work has focused on removing mercury from contaminated water via microemulsion liquid membranes. Electrostatic coalescence and butanol addition are evaluated as potential demulsification techniques for recovery of the components of mercury-rich microemulsions. Unlike coarse emulsions, electrical demulsification with heat is not effective for microemulsions due to the smaller size of the internal phase droplets in microemulsions. This explanation is confirmed by the photomicrographs of the two emulsion systems. Microemulsions can be demulsified using butanol as an additive. The demulsification kinetics are proportional to the butanol concentration and the temperature and inversely proportional to the surfactant concentration. Reduced mercury extraction efficiency with microemulsions formulated from recovered oil phase is attributed to some surfactant degradation during the demulsification processing as well as residual butanol in the recycled organic phase.

Lysozyme crystal growth reduced at high pressure

In studies of hen egg-white lysozyme batch crystallization under high pressure, there was an apparent arrest of the crystallization process in samples subjected to hydrostatic pressures of 1 kbar in seeded batches. Crystallization resumed at a normal rate upon restoration of atmospheric pressure. Lack of crystallization at high pressure does not appear to be due to a change in the solute/crystal equilibrium at high pressures, but may be due to either a decrease in the inherent rate of crystal growth or a reversible change in lysozyme confirmation under high pressure. According to our analysis, the activation volume of the crystal growth reaction would have to be on the order of +60 cm3/mol in order for the growth rate to have slowed to the extent measured at 1 kbar pressure.

Application of temperature control strategies to the growth of hen egg-white lysozyme crystals

Abstract Solubility data were combined with mass balances and growth kinetics to derive a temperature control algorithm which maintains a constant level of supersaturation. This constant supersaturation control (CSC) algorithm attempts to maximize the size of protein crystals by maintaining the growth conditions in the metastable zone. Using hen egg-white lysozyme as a model protein system, four temperature programming strategies were employed in seeded and unseeded systems: the CSC algorithm, a linear ramp derived from the CSC algorithm, isothermal 20°C, and isothermal 4°C. Both the CSC-derived linear and the CSC temperature programs yielded large, well-formed crystals which were significantly larger than crystals grown isothermally at 20 and 4°C. The isothermal 4°C program resulted in poorly formed crystals due to the high initial growth rates. The seeded systems displayed much higher levels of nucleation than the unseeded systems which is attributed to secondary nucleation. The results indicate that moderate deviations (∼ 20%) from constant supersaturation can be tolerated, while still producing large, well-formed crystals appropriate for X-ray crystallography.

Assessing the role of detergent–detergent interactions in membrane protein crystallization

Abstract Static light scattering may be used to probe the solution behavior of complexes of integral membrane proteins with detergents. As has been observed with soluble proteins, the crystallization behavior of protein–detergent complexes can be reliably predicted by the second osmotic virial coefficient ( B 22 ), which is obtained from light scattering. Conditions which yield crystals map to a narrow window of B 22 values falling within the “crystallization slot” previously described for soluble proteins. This slot lies near the cloud point of the detergent used for crystallization. The detergent portion of the protein–detergent complex appears to be an important factor in determining the B 22 values for the complex. This suggests a strategy for the design of membrane protein crystallization screens which focuses principally on optimization of detergent–detergent interactions. Cloud point assays have been developed to facilitate collection of the data necessary to construct such screens.

Effects of PEG on detergent micelles: implications for the crystallization of integral membrane proteins

The solubilization of integral membrane proteins with detergents produces protein-detergent complexes (PDCs). Interactions between the detergent moieties of PDCs contribute significantly to their behavior. The effects of the precipitating agent polyethylene glycol (PEG) upon these detergent-detergent interactions have been examined, focusing on the detergent system used to crystallize the bacterial outer membrane protein OmpF porin. Static and dynamic light scattering were used to assess the effects of temperature and concentration upon the hydrodynamic size distribution and the aggregation state of detergent micelles and a phase diagram for micellar solutions was mapped. Estimates of the second osmotic virial coefficient obtained from static light-scattering measurements on micelles were shown to accurately reflect the thermodynamic quality of the solvent. Solvent quality decreases as the consolute boundary is approached, suggesting micelle-micelle attractive forces help to organize PDCs into crystalline aggregates near the cloud point. An apparent increase in micelle mass is observed as the solution approaches the cloud point. These results raise the possibility that the detergent-mediated aggregation of PDCs and/or slight changes in micelle geometry may prove to be important in the nucleation of membrane protein crystals.

Copper—LIX 84 Extraction Equilibrium

Extraction of copper from water using LIX 84 extractant was investigated. Binary equilibrium data are reported and predictive models have been developed. With a simple, concentration-based equilibrium model, an equilibrium constant of 3.9 was obtained. This model is adequate when no acid is present in the aqueous phase. As the acidity of the aqueous phase increases, nonideality becomes significant and needs to be considered to predict extraction equilibrium properly. Our second model incorporates activities and major ionic reactions for the aqueous phase species; nonideality of the aqueous phase is successfully modeled. Nonideality of the organic phase is lumped into a concentration-dependent equilibrium constant. Equilibrium constants of 27.2, 13.1, and 6.2 were obtained for 5, 10, and 20 v/v% LIX 84 in tetradecane, respectively. This model can effectively predict the extraction equilibrium over a wide range of pH.

Improvements in lysozyme crystal quality via temperature-controlled growth at low ionic strength

In previous work, large high quality crystals of tetragonal lysozyme were grown using constant supersaturation control (CSC) growth algorithms. Working toward the goal of inducing increased temperature sensitivity in protein crystallization, these results have been extended to low ionic strength systems using salts such as NaSCN and NaNO 3 in lieu of NaCl. Using the combination of calorimetrically-determined growth rate parameters and constant supersaturation temperature control algorithms; large, well formed, single crystals have been grown in NaSCN and NaNO 3 buffer systems. The improvement in quality of these lysozyme crystals upon employing temperature controlled growth is striking. When compared to crystals grown using more traditional methods these crystals are quite large, and show few, or no, obvious defects. Preliminary crystal quality assessment via X-ray diffraction studies are encouraging. A single monoclinic CSC grown crystal had an average signal to noise ratio of 8.4 at a resolution of 1.62 A. In addition, this crystal showed excellent resistance to radiation damage and continued to diffract well after more then 45 h of continuous beam exposure.

Emulsion Liquid Membrane Extraction in a Hollow-Fiber Contactor

This article describes how ELMs (emulsion liquid membranes) can be used for extraction. The article addresses the disadvantages of ELM extraction in a stirred contactor, and the advantages of SELMs (supported emulsion liquid membranes). The introduction of the article provides background information on liquid-liquid solvent extraction and dispersion-free solvent extraction.