Kc. Liddell et Rg. Bautista, SIMULATION OF IN-SITU URANINITE LEACHING .1. A PARTIAL EQUILIBRIUM-MODEL OF THE NH4HCO3-(NH4)2CO3-H2O2 LEACHING SYSTEM, Metallurgical and materials transactions. B, Process metallurgy and materials processing science, 25(2), 1994, pp. 171-183
In situ leaching of uraninite and calcite by H2O2-NH4HCO3-(NH4)2CO3 so
lutions has been simulated using a partial equilibrium model which inc
orporates a one-parameter mixing cell model of solution flow. Rate law
s for UO2 dissolution and for CaCO3 dissolution/precipitation were tak
en from the literature, as were equilibrium constants for solution pha
se reactions. Parameters of the model include the UO2 and CaCO3 ore gr
ades, the concentrations of the H2O2, NH4HCO3, and (NH4)2CO3 component
s, porosity, exit solution flow rate, ore and mineral densities, and m
ineral rate constants and surface areas. Mineral conversions, componen
t and species concentrations, and porosity are among the time-dependen
t quantities calculated using the model. For the conditions simulated,
calcite dissolved somewhat faster than uraninite. The results emphasi
ze the importance of the coupling between the mineral reactions and so
lution flow. Changes in the concentrations of the CO32- and HCO3- spec
ies are particularly complicated and not predictable from the calcite
kinetics alone or from a purely equilibrium model; although the simula
tions did not reveal any conditions under which the solution would bec
ome saturated with CaCO3, the pH continued to change throughout the ca
lcite dissolution and is buffered only after calcite has been consumed
.