Abstract: A cross-linked flexible sponge absorbent medium containing substantially uniformly distributed fibrous reinforcement is prepared under such conditions that swelling of the sponge is controlled to a water retention value of 2 to 6; and simultaneously or subsequently, the cross-linked sponge is reacted with a reagent which introduces functional groups into the modified cross-linked sponge. There is also provided apparatus having an inlet for liquid, an outlet for liquid so as to define a path for liquid flow between the inlet and the outlet, an adsorbent medium, obtainable by the above method, being positioned across the liquid flow path in the apparatus.