The Basic Chemistry Involved in the Internal-Gelation Method of Precipitating Uranium as Determined by pH Measurements

Abstract

Internal gelation jUranylnitrate IHexamethylenetetramine/Urea / pH /PrecipitationAbstiact Studies were conducted to investigate the chemical reactions thought to be important during hydrolysis and gelatinous precipitation of acid-deficient uranyl nitrate (ADUN) in the internalgelation process for microsphere preparation. Investigations performed to determine pH profiles during urania gelation in conjunction with hexamethylenetetramine (HMTA) decomposition experiments were useful in defining important characteristics of four reactions and in determining process variables that affect reaction rates as well as pH regions in which ADUN precipitates. These variables are the nitrate-to-uranium and the HMTA-touranium mol ratios, the uranium concentration, and the gel formation temperature. The influenae of these process variables on the Solution pH and precipitation reactions is discussed.only limited supporting data were given.) Our study suggests that an increased understanding of these reactions and their kinetics should facüitate control of the product characteristics, which can vary widely with variations in process parameters. It is this inherent capability to produce metal oxide microspheres with precise properties that makes these processes uniquely useful for many applications.The major objectives of this study were to define and better understand the principal reactions that occur during hydrolysis and gelatinous precipitation of ADUN and to determine the effects of process variables on these reactions. A secondary objective was to determine the pH at which precipitation and gelation occur as a function of key process variables.

A Uranium Nitride Doped with Chromium, Nickel or Aluminum as an Accident Tolerant Fuel

“…An estimated chemical form of metals after gelation is a oxy-hydroxide UO 2 (OH) 2 or hydrated oxide UO 3 xH 2 O [21] . The internal sol-gel method is based on the precipitation of metals, which is governed by a pH shift in the solution towards alkaline.…”

Determination of Ideal Broth Formulations Needed to Prepare Hydrous Aluminum Oxide Microspheres via the Internal Gelation Process

“…This study found the gel spheres could be washed with ammonium hydroxide (NH 4 process. 4 The most important of these reactions are as follows: Urea serves as a complexing agent for the metal (reaction 1).…”

“…In this process, chilled clear broth droplets containing the salt of the metal, hexamethylenetetramine (HMTA), and urea are heated, which causes homogenous gelation and solidification of the droplets. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] After washing treatments, the gel spheres can be either air dried for use as engineered ion-exchange materials 7−11 or, depending upon the metal, dried, calcined, and sintered to ceramic microspheres for use as nuclear fuel, 1−6 catalysts, 7−11 getters, 7−10 or dielectrics. [12][13][14] A previously reported test-tube methodology, 15 which was employed to determine the optimum process parameters for preparing hydrous metal oxide microspheres, was also used in this study to determine the optimum process parameters for preparing hydrous aluminum oxide microspheres.…”

“…4 The most important of these reactions are as follows: Urea serves as a complexing agent for the metal (reaction 1). For broths of certain concentrations, the urea allows stable broths to be prepared at 0°C.…”

Determination of Ideal Broth Formulations Needed to Prepare Hydrous Cerium Oxide Microspheres via the Internal Gelation Process

“…5 The most important reactions are as follows: Urea serves as a complexing agent for the metal (reaction 1). For broths of certain concentrations, the urea allows stable broths to be prepared at temperatures of 0°C.…”