§ 4.2.5 Electrophoresis -- Super Mineral Separation In Orbit
"Electrophoresis" for mineral separation can work only in zero gravity, but it is an extremely high performance process as well as a simple one. (Indeed, the use of the Space Shuttle for small medical purpose electrophoresis payloads has been and always will be a major program.) Electrophoresis works better than electrostatic beneficiation but is much slower.
How electrophoresis works
A tank is filled with a fluid, and an electric field is created across the tank, say, by charging two opposite walls or plates facing each other, one positive and one negative, as shown in the figure below. The mineral grains to be separated are put into the fluid, where they will be suspended due to the zero gravity environment.
Electric charges will pass through the fluid from one wall to the other, and the minerals will collect electric charges. Due to the differing molecular natures of the different mineral types, each will accumulate a different net electric charge with respect to the fluid. The different minerals will migrate through the fluid to a certain position between the two walls and between other types of minerals of higher and lower "isoelectric" values. Each type of mineral will form a plane of material parallel to the two walls and parallel to planes of the other mineral types.
Electrophoresis has been employed by medical and biological fields since the 1930s for separation and identification of enzymes, proteins, lipids, and blood cells. Electrophoresis has also been used as a separation technique for dissolved clays and limestones.
However, electrophoresis on Earth is limited to very lightweight materials. When it is used, it is performed with difficulty and limited effectiveness because of Earth's gravity, which causes convection currents, as well as gravitational settling. Some medical applications of electrophoresis which were exceedingly difficult, elusive or practically impossible on Earth due to convection currents proved quite easy on the Space Shuttle.
A NASA-supported research report states "One of the most promising properties of lunar soil is the wide range of isoelectric points of the minerals. No two minerals have the same isoelectric point or, in practically all cases, even similar isoelectric points ... [This property of lunar soil] makes it an ideal candidate for electrophoretic separation; it means that for a given suspension material each mineral phase will separate and form a discrete band within the electrophoretic chamber."
An experimental series of studies were supported at the NASA Marshall Space Flight Center to test and develop the concept of electrophoresis of simulated lunar soil, and the results were very encouraging, including separating minerals with close isoelectric points.
Electrophoresis is simple, takes little energy and is highly automatable.
Electrophoresis can also be highly effective for separating trace minerals.