Abstract: Disclosed is an improved method of concentrating with respect to a first salt an aqueous solution containing the first salt and a second salt, the solubility of the first salt increasing more with increasing temperatures than the solubility of the second salt, by multiple stage evaporation at progressively higher temperatures and backward feed, wherein first salt and second salt is precipitated in an evaporator stage which communicates with an elutriation leg, wherein an aqueous slurry containing first salt and second salt is withdrawn from the elutriation leg and wherein the concentrated solution is forwarded to a step where the first salt is recovered. In the improved method, slurry withdrawn from the evaporator stages is leached with raw feed and/or mother liquor from this step in which the first salt is recovered to dissolve first salt from the slurry and return the dissolved first salt to the evaporator effect.