The Bureau of Mines is researching a new technology for dewatering clay suspensions that consists of flocculation by high-molecular- weight polyethylene oxide (peo) polymer and subsequent removal of water from the flocs via a trommel. The minimum amount of peo required to dewater the clays depends on the ions adsorbed on the surface of the clay particles. Infrared studies were performed on clays with li+, nh4+, k+, mg2+, ca2+, ba2+, or sr2+ adsorbed, with and without adsorbed peo, to develop data to aid in understanding the dewatering mechanism. Hydroxyl stretching modes between 3,400 and 3,250 cm-1, associated with water adsorbed on the clay, showed changes in intensity proportional to the ionic charge-to-radius ratio; that is, the ionic potential. In addition, a water-bending vibration of adsorbed water at 1,630 cm-1 showed variations associated with water desorption. The data are consistent with changes in adsorption of peo resulting from variation of the acidity of water coordinated with the exchange ions, induced by the variation in field strength of the ions with the ionic potential.