Abstract: The invention is concerned with a process of separation and refining of rare earths in which a dilute solution of rare earths, resulting from the step of separating and refining the rare earths by using an ion exchanger, is subjected to reverse osmosis membrane separation treatment to concentrate the solution and reduce its volume, while the water which has passed through the membrane is circulated for reuse in the step of separating and refining the rare earths.

Abstract: A composite semipermeable membrane and a process for preparation thereof are described, wherein said membrane comprises (1) a porous substrate, (2) an ultrathin film as a surface layer formed by polymerization by crosslinking of polyvinyl alcohol and an amino compound having at least two secondary amino groups using a polyfunctional crosslinking reagent capable of reacting with secondary amino groups and hydroxyl groups, and (3) a porous inner layer composed of water insoluble polyvinyl alcohol which is present between the porous substrate and the ultrathin film.

Abstract: A membrane separation apparatus comprising: a cylindrical case provided with an outlet for a membrane permeated fluid; a plurality of tubular or capillary membranes which are inserted into the cylindrical case in a substantially parallel state with each other and in a closely bundled state, the membranes each other and also the bundled membranes and the cylindrical case being bonded and fixed with a casting resin at both end portions thereof; a cap having a nozzle for a feed inlet and a nozzle for a membrane permeated fluid outlet, provided at one end of the cylindrical case; and a cap having a nozzle for a concentrated fluid provided at another end of the cylindrical case, wherein at least one open end of the tubular or capillary membranes is arranged with a slope with respect to the axis of the cylindrical case, and the nozzle for the feed inlet and the nozzle for the membrane permeated fluid are provided on the substantially same axis.

Abstract: A composite semipermeable membrane is described, wherein said membrane comprises (1) a porous substrate, (2) an ultrathin film as a surface layer formed by polymerization by crosslinking of polyvinyl alcohol and an amino compound having at least two secondary amino groups using a polyfunctional crosslinking reagent capable of reacting with secondary amino groups and hydroxyl groups, and (3) a porous inner layer composed of water insoluble polyvinyl alcohol which is present between the porous substrate and the ultrathin film.

Abstract: A composite semipermeable membrane which comprises a porous substrate and an ultrathin dense layer having solute removal performance formed on said substrate by polymerization by crosslinking of a reactive material composed of at least one material selected from the group consisting of(a) a mixture of triazine represented by the general formula: ##STR1## (wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms), and polyamine monomer,(b) said triazine modified with amine,(c) a mixture of said triazine modified with amine, and polyamine monomer,(d) a oligomer composed of said triazine and polyamine monomer, and(e) a mixture of an oligomer composed of said triazine and polyamine monomer, and polyamine monomer,as a main component, with a polyfunctional crosslinking reagent having two or more functional groups capable of reacting with amino groups in the molecule, and a process for preparing the same.

Abstract: A process is described for preparing a selective permeable membrane comprising coating a solution consisting essentially of(i) a polyimide polymer consisting essentially of a repeating unit of the formula (I): ##STR1## wherein R.sup.1 is a divalent organic group, (ii) a swelling agent selected from the group of compounds represented by formula (II) and (III):R.sup.3 O----CH.sub.2 CHR.sup.2 O).sub.n R.sup.4 (II)R.sup.5 ----OH).sub.m (III)wherein R.sup.2, R.sup.3 and R.sup.4, which may be the same or different, can be hydrogen, a methyl group, or an ethyl group, and when R.sup.2 is hydrogen, n can be an integer of from 1 to 5, and when R.sup.2 is a methyl or ethyl group, n can be an integer of from 1 to 3, R.sup.