COLLOIDAL ZEOLITE SUSPENSIONS

A method is presented whereby it is possible to synthesize colloidal z eolite sols containing discrete zeolite particles with an average part icle size of less than 150 nm and with a narrow particle-size distribu tion. The zeolite sols exhibit typical colloidal characteristics such as Tyndall light scattering and a low rate of sedimentation and coagul ation due to electrolyte concentrations in excess of the critical coag ulation concentration. The effect of sodium on the crystallization kin etics, product distribution, and particle size has been investigated. Relatively high Na2O/Al2O3 ratios favor the formation of large crystal s of zeolite A. Low Na2O/Al2O3 ratios result in colloidal crystals of zeolite Y, whereas intermediate ratios yield zeolite Y and/or zeolite A with particle sizes of ca. 100 nm. Midsynthesis addition of sodium a llows for a fivefold increase in zeolite yield.