Method for purifying by nanofiltration an aqueous sugary solution containing monovalent and polyvalent anions and cations

Purification method by nanofiltration of an aqueous solution containing one or several sugars, multivalent cations, monovalent metal cations, monovalent anions and multivalent inorganic anions and/or organic acid anions, characterized in that it comprises the operations:

• (a) of replacement of at least a part of said multivalent cations and/or of said multivalent inorganic anions and organic acid anions respectively by monovalent metal cations and/or monovalent anions, in order to obtain an aqueous solution depleted in multivalent cations and/or multivalent inorganic anions and organic acid anions, and containing said monovalent metal cations and monovalent anions,
• (b) of nanofiltration of the solution resulting from operation (a) in order to obtain as a retentate, a sugar aqueous juice enriched in sugars, in multivalent cations and in multivalent inorganic anions and/or in organic acid anions, and as a permeate, an aqueous effluent enriched in monovalent anions and monovalent metal cations,
• (c) of additional demineralization of at least a part of the retentate obtained by operation (b), with a cation-exchange resin of which the counter-ion is H+ and an anion-exchange resin of which the counter-ion is OH−, these resins thus charging themselves respectively in residual cations and anions of the retentate, and
• (d) of regeneration, on one hand, of said cation-exchange resin by means of a inorganic acid of which the anion is of the same type as the monovalent anions present in the initial aqueous solution, and on the other hand, of said anion-exchange resin by means of a inorganic base of which the cation is of the same type as the monovalent metal cations present in the initial aqueous solution, which produces regenerated exchange resins and two regeneration effluents mainly containing monovalent anions and monovalent metal cations.