US Patent 10301198 Selective retention of multivalent ions

Disclosed herein are systems and methods in which multivalent ions are selectively retained in an aqueous stream. According to certain embodiments, multiple separations may be used to process an aqueous feed stream containing solubilized monovalent ions and solubilized multivalent ions to produce a stream enriched in the solubilized multivalent ions. The separations may be arranged, according to certain embodiments, to enhance the overall separation process such that the product stream contains—relative to the initial aqueous feed stream—a high amount of solubilized multivalent ions, a high amount of water from the aqueous feed stream, and/or a high ratio of solubilized multivalent ions to solubilized monovalent ions.