In this article, the extraction of cytochrome c utilizing various nonionic surfactant microemulsions has been tested to determine the effect of surfactant structure on protein partitioning. Surfactants tested include a linear alcohol ethoxylate (Neodol 91-2.5), two alkyl phenol ethoxylates (lgepal CO-520, Trycol 6985), and a series of alkyl sorbitan esters that are either ethoxylated (Tweens) or un-ethoxylated (Spans). Initial attempts to extract hemoglobin into Neodol 91-2.5 Winsor II microemulsions (oil-continuous) appeared successful based on heme estimation. Careful analysis showed that the hemoglobin had dissociated prior to extraction and that only the heme was extracted with false positive results. In fact, Neodol 91-2.5 microemulsions were unable to extract a variety of proteins with differing biophysical properties. Among all the other nonionic surfactant microemulsions tested only those made using sorbitan esters extracted significant amounts of cytochrome c. The partition coefficients achieved in this study are more than an order of magnitude higher than that seen previously in the literature for comparable sorbitan systems. However, this partition coefficient is extremely sensitive to ionic strength. At an ionic strength as low as 0.001 M, the partition coefficient is reduced to that seen in previous studies. We have found that protein partitioning in sorbitan ester microemulsions is not a function of water content. In addition, extraction is not a function of either alkyl chain length, or polyethylene oxide molecular weight. Hence, the sorbitan group appears to have an important role in extraction, possibly through a weak electrostatic protein-surfactant interaction. (c) 1995 John Wiley & Sons, Inc.

Protein extraction into Tween 85 nonionic microemulsions is characterized. Apparently, a weak electrostatic interaction is the underlying extraction mechanism. The extraction of several proteins is examined as a function of protein size and net charge. The proteins that extracted successfully are positively charged. A size-exclusion limit (60 kDa) is also evident in these extractions. Tween 85 and several other nonionic surfactants possess a net negative charge at neutral pH. Titration measurements are an effective means of quantifying charge on these surfactants. In Tween 85 microemulsion separations, both the sign and the magnitude of surfactant charge play a role in extraction. Blends of Neodol 91−2.5 (capable of extracting 0% protein) and Tween 85 (capable of extracting 100% protein) indicate that a minimum net surfactant charge of 15 mequiv/mol is required for extraction.

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Flotation beneficiation of ores containing fibrous minerals is highly problematic due to transport of such gangue minerals from pulp to the froth phase. Earlier studies have attributed such transport to the entrainment of fibrous minerals. In this work, this problem is investigated for the case of flotation of ultramafic Ni ore with fibrous serpentines (Mg silicates) interfering with their separation. Serpentines are proposed to form large (~1-2 cm) networks in pulp and thus unlikely to be transported by entrainment. Various simulation based studies suggest that the networks are stable under the dynamic flotation conditions. Furthermore, the pores in the networks are relatively small (e.g. < 20 microns -SEM studies) for the bubbles (1-2 mm) to penetrate through the network of fibers in the pulp. This leads to the hypothesis that bubbles which cannot penetrate through the network accumulate below the network in the pulp with the buoyancy force of the bubbles thrusting the network to the froth phase. Model system studies were carried out with nylon fibers of size similar to that of serpentines. The phenomenon, of bubble-flux driven A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT transport of fibrous serpentines was clear from the model system studies, and is proposed to be the key mechanism of transport of fibrous serpentines to flotation concentrate.

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