SORPTION BEHAVIOR OF PERRHENATE ION ON REILLEX™-HP ANION EXCHANGE RESIN FROM NITRIC ACID AND SODIUM NITRATE/HYDROXIDE SOLUTIONS

Abstract

ABSTRACT The distribution coefficients (K' d) are reported for perrhenate on the nitrate form of Reillex™-HP, a weak base anion exchange resin, as a function of nitric acid concentration from 0.100 to 10.0 M. Perrhenate K' d values were determined in 1.00 M NaNO3 from pH 2 to 13. The K'd values were determined in solutions containing 1.35 M NaNO3 and variable NaOH, 0.155 to 4.66 M, and in solutions containing 0.655 M NaOH and variable NaNO3,0.46 to 5.35 M. Maximum perrhenate loadings were <2.7% of theoretical capacity. The K' d is defined by the following equation: The total mmol of rhenium initially added is Retotal and [Re]sol is the analytical molarity of rhenium in Vsot mL of solution after a batch contact. At 1.0 M HNO3 the value of K'd is 73 mL/g. The behavior of the perrhenate system in acid can be described by assuming that perrhenic acid, HReO4, is formed with a derived acid dissociation constant of about 6.5 M. In 1.00M NaNO3from pH 2 to 13 the sorption behavior is initially what is expected for a weak base resin with an acid dissociation constant of 1.24 × 10−55 M. Thus, the K' d value decreases with pH values above the pKa value. However, instead of the value of K' d decreasing to zero at higher pH values, it becomes constant at 15 mL/g. In a solution containing 1.00 M NaOH and 1.00 M NaNO3, the value of K'd is 25 mL/g. The unusual behavior of the Reillex™-HP anion exchange resin suggests that the resin's unprotonated pyridine functionality is solvating a {Na+,ReO4 −} ion pair. The interaction of the perrhenate ion with Reillex™-HP is more involved than a simple ion exchange phenomenon and the presence of NaOH affects the resin-perrhenate interactions.