Competitive adsorption of boric acid and chromate onto alumina in aqueous solutions

The competitive adsorption of boric acid and chromate from aqueous solutions by alumina has been investigated by spectrophotometry at pH 8, ionic strength = 0.0, 0.1 and 1.0 M NaClO4, T = 22 +/- 3 degrees C and under normal atmospheric conditions. The experimental data show that addition of excess boric acid in the system leads to the increase of Cr(VI) concentration in solution, indicating the replacement of adsorbed chromate by boron on the alumina surface. Data evaluation results in the determination of the competition reaction constant and the formation constant of the Cr(VI) surface complexes, which are logK(Cr(VI)-B(III)) = 3.5 +/- 0.2 and log beta(star)(Cr) = 7.6 +/- 0.3, respectively.