Preparation of Metal Oxide Gel Spheres with Hexamethylenetetramine as an Ammonia Donor

Gel spheres containing UO₃, (Th,U)O_x, Al2O₃, Al₂O₃-ZrO₂, and mixtures of various other metal oxides (including Fe, Zr, Al, and Si) have been produced by the internal gelation process by the same general flowsheet. In the internal gelation process, hexamethylenetetramine (HMTA) decomposes to produce ammonia which precipitates hydrous metal oxides gels. The process conditions (metal molarities, HMTA/unneutralized metal ratio, urea/metal ratio, and gelation temperatures) are within the same ranges for all of the products. Selection of the feed compositions and process conditions can be guided by the general criteria described, but optimum conditions need to be determined empirically. General process requirements are discussed in detail, and products made under these conditions are described.