Modeling the Sodium Recovery Resulting from Using Concentrated Caustic for Boehmite Dissolution

Boehmite dissolution experiments were conducted at NaOH concentrations of 10 and 12 M to determine whether the increased aluminum solubility at high hydroxide concentration would offset the increase in added sodium, causing a decrease in the amount of sodium added during boehmite dissolution. A shrinking-core dissolution rate model with a reversible reaction was fitted to the test data. The resulting model included the effects of temperature, hydroxide concentration, and dissolved aluminum concentration. The rate was found to depend on the similar to 1.5 power of hydroxide molarity. When the rate model was used to simulate batch boehmite dissolution, a concentration range of 7-9 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 could be decreased by using hydroxide concentrations greater than similar to 10 M.