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The laboratory conditions used to synthesize the uranyl silicate minerals are almost identical to the evaporator conditions under which high caustic nuclear wastes are processed to reduce total liquid waste volume. The only significant difference lies in the sodium ion concentration in such caustic nuclear wastes, which typically averages around 5.6 M Na+. In this investigation, synthetic uranyl silicate minerals (sodium weeksite, sodium boltwoodite and uranophane) were produced only under low Na+ concentration (less than 0.02 M), while attempts to synthesize these same uranyl silicates minerals in the presence of high Na+ concentration (high ionic strength reacting media), which is typical of caustic nuclear waste evaporator processing conditions proved unfruitful. In the presence of high Na+ concentration the main product for the same soluble silica-uranium reaction mixture shifts towards the formation of mainly clarkeite (Na[(UO2)O(OH)](H2O)0-1), a hydrated sodium uranate and not to wards the formation of uranyl silicates. Thus, the presence of high Na+ concentration in the reaction mixture of dissolved uranium and silica inhibits or suppresses the formation of crystalline uranyl silicates. We therefore conclude that evaporator fouling by uranyl silicate minerals is not easily produced under nuclear waste processing conditions because of the high Na+ concentration in the liquid wastes

Conditions Conducive to Forming Crystalline Uranyl Silicates in High Caustic Nuclear Waste Evaporators