Process for the preparation of low-bleeding cation exchangers

Process for the preparation of strongly acid cation exchangers having a particle size of 50 to 2000 μm comprising sulphonating crosslinked styrene polymers under an inert gas atmosphere at a temperature ranging from 130 to 150° C. with chlorosulphonic acid, sulphuric acid or sulphuric acid monohydrate, in the presence of a swelling agent selected from the group consisting of chlorinated aliphatic and aromatic hydrocarbons, for a time sufficient to produce cation exchangers which, when washed with 3 bed volumes of deionised waiter at a rate of 0.2 bed volumes per hour through a column containing 100 ml of said cation exchangers, at a temperature sufficient to produce an elutate having a temperature of 70° C., have a conductivity profile of less than 50 μS/cm.