Chromatographic observation of boron isotopic fractionation between kaolin clay and boron bearing solution: A high pressure experiment

In order to determine the boron isotopic fractionation factor between boron adsorbed onto kaolin clay and boron in solution (S), as a first attempt, a break-through column chromatography at a high pressure (12.0 MPa) was performed. A boric acid standard solution (9.25 mmol/l, NIST SRM 951) was fed into a stainless steel column packed with boron-free kaolin clay with the flow rate of 0.8 ml/h. The S value obtained at 293 K was 1.0023, indicating that the lighter isotope (10B) was preferentially enriched into the clay. The magnitude of the S was apparently smaller than the previously reported values obtained by the batch method with seawater boron at atmospheric pressure. Besides the effect of pH and the influence of coexisting ions that would lead to a larger S value, as an aspect, dependence of pressure on the boron isotopic fractionation was a possible candidate reducing the S value. Assuming an occurrence of the molecular volume isotope effect (MVIE) on boron species, the S value would decrease with increasing pressure.