Solid mineral and regenerant recovery for ion-exchange resins

Abstract

Recovery of ion-exchange regenerants and precipitation of mineral salts is disclosed. The spent cation and anion regenerant streams are combined to form a weak dissociable complex of the regenerants and to reconstitute the removed inorganic mineral salt. The mixture is adjusted stoichiometrically to balance the anion and cation of the removed salt. The salt is precipitated by limiting solubility thereof either by concentrating the mixture or by reducing the solubility of the salts therein, suitably by the addition of a water-miscible solvent such as methanol. The complex is dissociated to reconstitute the separate anion and cation regenerants which are adjusted to the appropriate solvent concentration for recycle and reuse. Excess water in the system provided by water of hydration released by the resin during regeneration or by washing steps is removed prior, during or after separation of the regenerants depending on the nature of the separation technique employed and the optimum time for precipitation and removal of the mineral salts. Separation and recovery of the regenerants may be accomplished by distillation of regenerants having disparate volatilities, solvent extraction using an immiscible solvent having preferential solubility for one of the regenerants or by forming an insoluble complex of one of the regenerants. The recovered regenerants are reused as regenerants for spent anion and cation resin columns and the precipitated slats are removed by filtration, sedimentation or centrifugation.