A liquid membrane approach for removal of metallic species from resinous extracts under imposed electrical fields

The application of externally imposed electrical fields to a bio-purification process is illustrated for crude guayule resin. The specific emphasis of this study is on removal of solubilized species consisting of soil nutrients that partition into the resin phase from the soils of growth origin and heavy metals that come from other possible sources of contamination. Heavy metals include lead and zinc, whereas soil nutrients include magnesium, sodium, calcium and potassium. Other preferentially water-soluble species are also removed but have not yet been identified. Separation demonstrations were carried out in a 21 capacity coalescer with a flat and parallel insulated electrode configuration. A liquid membrane type of emulsion of relative stability (phase disengagement in less than 12 h) of guayule resins and water was used to assess separation rates at different field strengths and frequencies for a.c. and half-wave rectified, non-smoothed d.c. (i.e. pulsing d.c.). Maximum separation rates were determined by measuring output flow rates (separated resins and water), under steady-state conditions. Metal removal efficiencies were determined for a 1000 Hz a.c. field under a potential gradient of 4 kV/cm at the maximum rate of coalescence. Methods to increase removal efficiencies are discussed. In addition to enhancing the rate of phase disengagement, electrostatic coalescence was shown to be particularly effective in removal of lead, zinc and iron as compared to 12 h of gravitational settling. Applications of this technology to removal of toxic heavy metals and/or radioisotopes from multi-phase hydrocarbon-based media are discussed.