The invention is directed to an improvement in operation of wash columns, and more in particular to an apparatus for separating solid particles from a slurry and to a process for separating solid particles from a mother liquor slurry. The apparatus of the invention comprises a wash column (1), which comprises a melting circuit (8,10,11,21), wherein means (22,23) are present to introduce a compound or composition to said wash column between a wash front (6b) formed in said wash column in operation and a product outlet and/or in the melting circuit. The process of the invention comprises separating the liquid from the solid particles by filtration with the aid of at least one filtering element (4), while a packed bed of solid particles coming from the mother liquid slurry forms near said filtering element (4), and wherein a wash front (6b) forms which is obtained by bringing a washing liquid in counter current to the solid particles in the bed, the bed being subjected to a movement in the direction of said wash front (6b), while a product stream comprising the material of said solid particles is obtained by continuously discharging a portion of said washing liquid, wherein a portion of said bed is continuously disintegrated, characterized in that a compound or composition is introduced into said wash column (1) between the wash front (6b) and a product outlet and/or in a melting circuit (8,10,11,21), and wherein the introduction of the said compound or composition decreases the equilibrium temperature of the contents of the melting circuit (8,10,11,21), further characterized by the feature that the introduced compound or composition is completely miscible with the product suspension and/or molten product being present in the said melting circuit (8,10,11,21).