PNNL

Abstract

Boehmite dissolution experiments were conducted at NaOH concentrations of 10 M and 12 M to determine whether the increased aluminum solubility at high hydroxide concentration would offset the increase in added sodium, leading to an overall decrease in the amount of sodium added during the boehmite dissolution process. A shrinking-core dissolution rate model that assumed reversible reaction was used to fit the test data. The resulting model accounted for the effects of temperature, hydroxide concentration, and dissolved aluminum concentration. The rate was found to be dependent on the ~1.5 power of hydroxide molarity. When the dissolution rate model was used in simulations of batch boehmite dissolution, a concentration range of 7 to 9 M NaOH was found to minimize the mass of sodium needed to dissolve a given mass of aluminum, potentially reducing it by as much as two-thirds. The time required to dissolve the boehmite was also found to be decreased by using hydroxide concentrations greater than ~10 M.