Water flow rates, effects leaching

PESCATORE AND MACH1ELS Effects of Water Flow Rates on Leaching 351... 

Waste form leach rates in a geologic repository will be affected by unknown water flow rates and by extensive cracking of the waste form monolith. An understanding of these effects is important in predicting the geochemical behavior of disposed radioactive waste forms over the full range of possible scenarios. The dependence of the waste form source term on the rate of renewal of aqueous solution is first established for the simple but important case of solubility-limited network dissolution control. 

A distinguishing effect of flow rate is that saturation of the solution is never achieved under dynamic leaching conditions. Thus, network dissolution, a solubility limited process, is never allowed to halt. A steady-state condition is eventually established whereby leach rates of network formers equalize the rate of removal of species from the leachant due to the flowing solution. This can be illustrated by formulating a network dissolution model which incorporates the dependence of leaching of network formers on solubility limits and water flow rates. 

D8. In the leaching of sugar from sugar cane, water is used as the solvent. Typically about 11 stages are used in a countercurrent Rotocel or other leaching system. On a volumetric basis liquid flow rate/solid flow rate = 0.95. The effective equilibrium constant is i% = 1.18, where m = (concentration, g/liter, in liquid)/(concentration, liter, in solid) fSchwartzberg. 19801. If pure water is used as the inlet solvent, predict the recovery of sugar in the solvent. 

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