Regeneration of ion-exchange resins with rock salt solutions frequently does not give completely satisfactory results because of the presence of iron in the rock salt and in the resin. During regeneration, especially with neutral solutions of rock salt, insoluble iron oxide forms tubercules in the resin chambers, thus preventing free flow through the resin. The addition of 0.5 to 1 pound of ammonium citrate dibasic per 100 pounds of rock salt has been successful in preventing this resin plugging, and at very nominal costs.
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