Regeneration of Mixed Bed Ion Exchange Columns For several years in our laboratory we have purified our water by reverse usrnosis followed by ion exchange. Tapwater here contains the equivalent uf about 100 ppm Ca2' and reverae mmosis (Osmonics #3319) removes ahout 9 5 % d the di9solved sulids. A small commercial ion exchange column (Hamstead #DO8091will purify about 1032 I of this partrally purified water to a specific conductance of shout 2 x 10-7 mhos per cm in'bne pass. WL also use a recirculating high purity water system built around a pair of Bion 3X ion exchange columns. We have found it attractive to reduce substantially the expense of the operation hy regenerating the commercial columns. For the Barnstead column it is possible to cut the column with a sharp knife just below the upper plastic closure. If this is done carefully, the column can he resealed by putting the top back on, wrapping the joint with fiber glass tape and then clamping the seal with a hose clamp. The Bion Columns sold by Pierce Chemical Company can he opened by drilling a hole with a cork borer in the side of the plastic column near the top. The column can then he resealed with a rubber stopper. Once the resin is removed from the column it is placed in a 4-ft length of 60 mm glass tubing which has a coarse fritted disk sealed to the bottom. Tapwater is passed upward through this tuhe and the two resins separate so the anion exchange resin rises to the top and the cation exchange resin falls to the bottom. Once separation is accomplished the anion resin is allowed to run out through a side arm of the glass tuhe into a second tube also fitted with a fritted disk in the bottom. Regeneration is performed by running 4 l of 1M HCI slowly downward through the cation resin and 4 l of 1M NaOH through the anion resin. Each resin is then washed with about 6 1of purified water. The regenerated resins are then slid out of the glass tubes and mixed together in a large beaker. The mixed resins can then he returned to the ion exchange tuhe. With the Barnstead type equipment we have found it quite important to fill the column full. Since the water passes upward through the Barnstead column there is atendency for the resins toseparate which can be prevented if the column is sufficiently full. For the Bion columns the water flow is nonnallv downward so there is no tendency for the resins to separate and filling the columns full is not critical to good operation and high capacrty unlike the ~ a r n s t e a dcolumns. Over a period of several years operation our columns have heen regenerated many times. Abide from mechanical loss of small amounts of resin nu difflcultie~have been experienced.
Earlham College Richmond. Indiana 47374
268 / Journal of Chemical Education
George A. Scherer Laurence E. Strong
