Abstract: A solution treatment method in which a solution containing a separation target substance such as a neutral molecule is treated with a combination of a plurality of types of membranes, and a component and water desired to be left as a purified liquid are recovered while the unnecessary separation target substance is separated. More specifically, it could be helpful to provide a solution treatment method which is to be applied to a solution containing at least an electrolyte in an amount of 1000 mg/L or more and containing a low-molecular-weight nonelectrolyte molecule having a molecular weight of 70 or less, and by which the electrolyte and water are recovered while the low-molecular-weight nonelectrolyte molecule is removed, with combination of a plurality of membranes.

Abstract: The present invention relates to a method for recovering a rare metal salt, the method including: an acid treatment step of obtaining a rare metal-containing acidic aqueous solution by bringing a material including a monovalent rare metal and a polyvalent rare metal into contact with an acidic aqueous solution; a separation step of obtaining permeated water including the monovalent rare metal and non-permeated water including the polyvalent rare metal from the rare metal-containing acidic aqueous solution by using a nanofiltration membrane satisfying the condition (1); and a concentration step of obtaining non-permeated water having a higher concentration of the monovalent rare metal and permeated water having a lower concentration of the monovalent rare metal than that of the permeated water in the separation step, by using a reverse osmosis membrane.

Abstract: A method of separating and recovering a cobalt salt and a nickel salt includes a separation step of separating, by using a nanofiltration membrane, a cobalt salt and a nickel salt from a rare metal-containing aqueous solution containing at least both the cobalt salt and the nickel salt as rare metals, in which the nanofiltration membrane has a glucose permeability of 3 times or more a sucrose permeability, the sucrose permeability of 10% or less, and an isopropyl alcohol permeability of 50% or more when a 1,000 mg/L glucose aqueous solution, a 1,000 mg/L sucrose aqueous solution, and a 1,000 mg/L isopropyl alcohol aqueous solution, each having a pH of 6.5 and a temperature of 25° C., individually permeate through the nanofiltration membrane at an operating pressure of 0.5 MPa.

Abstract: The present invention relates to a method for recovering a rare metal salt, the method including: an acid treatment step of obtaining a rare metal-containing acidic aqueous solution by bringing a material including a monovalent rare metal and a polyvalent rare metal into contact with an acidic aqueous solution; a separation step of obtaining permeated water including the monovalent rare metal and non-permeated water including the polyvalent rare metal from the rare metal-containing acidic aqueous solution by using a nanofiltration membrane satisfying the condition (1); and a concentration step of obtaining non-permeated water having a higher concentration of the monovalent rare metal and permeated water having a lower concentration of the monovalent rare metal than that of the permeated water in the separation step, by using a reverse osmosis membrane.

Abstract: The present invention relates to a dialysate regeneration method that reduces a urea concentration of a urea-containing aqueous solution, the method including a reverse osmosis process of obtaining, from the urea-containing aqueous solution, a concentrate having a higher urea concentration and a permeate having a lower urea concentration by using a reverse osmosis membrane element at an operating pressure of 0.5 MPa or more and 2.0 MPa or less, in which the urea concentration of the urea-containing aqueous solution is 0.5 g/L or more, the reverse osmosis membrane element includes a reverse osmosis membrane, and the reverse osmosis membrane has a pore diameter of 7.0 ? or less as measured by a positron annihilation lifetime measurement method.

Abstract: The present invention relates to a membrane separation system including a plurality of separation membrane elements connected to one another, each of the separation membrane elements including a plurality of separation membrane pairs, each separation membrane pair including separation membranes each having a feed-side surface and a permeate-side surface and disposed such that the feed-side surfaces face each other, in which the plurality of separation membrane elements include a first separation membrane element and a second separation membrane element, and at least one first separation membrane element serves as a stage preceding the second separation membrane element.

Abstract: The present invention relates to a membrane separation system including a plurality of separation membrane elements connected to one another, each of the separation membrane elements including a plurality of separation membrane pairs, each separation membrane pair including separation membranes each having a feed-side surface and a permeate-side surface and disposed such that the feed-side surfaces face each other, in which the plurality of separation membrane elements include a first separation membrane element and a second separation membrane element, and at least one first separation membrane element serves as a stage preceding the second separation membrane element.

Abstract: A method is provided for precisely predicting the temporal variation of a membranous filtration resistance, a transmembrane pressure, a membranous filtration flowrate, or a membranous filtration flowrate as occurs in filtrating a liquid with a membrane, in a membranous filtration method wherein the liquid is filtrated by the separation membrane with the transmembrane pressure as a driving force. The method includes calculating: a constituent component quantity value of the liquid that attaches on a surface of the separation membrane at a time t+?t; a constituent component quantity value of the liquid that exists in pores of the separation membrane; a consolidation degree of a constituent component of the liquid that attaches on the separation membrane surface; a membranous filtration resistance value; a transmembrane pressure value; and a membranous filtration flowrate value.

Abstract: A method is provided for precisely predicting the temporal variation of a membranous filtration resistance, the temporal variation of a transmembrane pressure, the temporal variation of a membranous filtration flux, or the temporal variation of a membranous filtration flowrate as occurs in filtrating a liquid to-be-filtrated with a membrane, in a membranous filtration method wherein the liquid to-be-filtrated is filtrated by the separation membrane with the transmembrane pressure as a driving force. The variation of the membranous filtration resistance, the transmembrane pressure or the membranous filtration flowrate (flux) with time is predicted in a case where the membranous filtration is continued while controlling the membranous filtration flowrate (flux) or the transmembrane pressure to a set value.