Membrane Percrystallization for Production of Lithium Salt and Basic Compounds

Membrane percrystallization is an emerging and productive crystallization technology. In this research, experiments using sugar-derived carbon membranes demonstrate the production of lithium hydroxide, carbonate, chloride, sulfate and acetate, from feed solutions with concentrations ranging from 1 to 20 wt.% (weight solute/weight solution). Sugar-derived carbon membranes were coated on a porous alumina substrate via vacuum impregnation and pyrolysis resulting in a tailorable porosity and homogenous membrane which was chemically robust over a wide range of solution chemistries. The highest flux was for 20 wt.% lithium chloride solution, equivalent to an annual salt production rate of 70 t for 1 m² of membrane. The percrystallizer productivity was 54 times higher than evaporative crystallization, shown by comparing the membrane surface area to the exposed surface area of a stirred solution–vacuum interface of an evaporative crystallizer at equivalent conditions of initial solution composition, temperature, and vacuum. The percrystallized solids were characterized in terms of their microstructures, crystal structure, and chemical compositions via scanning electron microscopy, x-ray diffraction, and thermogravimetric analysis, providing the first information of this type for lithium salts and basic compounds produced using this new technology.