Porous glass partly filters dissolved salt from aqueous solutions passed through it under pressure. Rejection of salt can be increased by increase in the pH of the solution or by addition of Th(IV). The filtration seems to accord with a mechanism of salt exclusion characteristic of ion exchangers.
The consotldatfcki and loss of permeability of salt crystal aggregates, importa.it in assessing the effects of water in salt repositories, has been studied as a function of several variables. The kinetic behavior was shatter to that often observed in sinter ing and suggested the following expression for the time dependence of the void fraction: • ft) • •«>)-W/fi)ln(1 • «/z(0) s) , where A and B are rate constants and z(0) is initial average particle size. With brine present, A and 4(0) varied linearly with stress. The initial void fraction was also dependent to some extent on the particle size distribution. The rate of consolidation was most rapid In brine and least rapid In the presence yf only air as the fluid. A brine containing 6 m MgC1 2 showed an Intermediate rate, presumably because of the greatly reduced ^ofubHity of NaCt. A substantial «all effect was Indicated by an observed increase in the void fraction of consolidated columns with distance from the top where the stress was applied and by a dependence of consolidation rate on the column height and radius. The distance through which the stress fell by a factor of e was estimeted to change Inversely as the fourth power of the column diameter. With increasing temperature (to 86*C), consolidation proceeded somewhat more rapkRy and the wail effect was reduced. The permeability of the columns dropped rapidly with consolidation, decreasing with about the sixth power of the void fraction. In general, extrapolation of the results to repository conditions confirms the eeif-eeaOng properties of bedded sett as a storage medium for radioactive waste.
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