Boron isotopic fractionation in boric acid solutions during adsorption on synthetic manganese oxides (birnessite "B" and cryptomelane "C") and Mg-Al-layered double hydroxide "LDH" was investigated. The materials were characterized by elemental analyses, powder X-ray diffraction, FUR spectra, BET surface area and zeta potential measurements. Batch experiments were conducted without changing the solution pH to correlate the boron sorption properties of the adsorbents with isotopic fractionation in the associated boric add solutions. The results showed that boron isotopic composition of the contact solution is heavily dependent on the selective adsorption of B(OH)(3) or B(OH)(4)(-) species due to the charge properties of the minerals. With B and C, possessing negatively charged surfaces, B-10(OH)(4)(-) was preferentially fractionated in the solution due to the transfer of the Lewis acidic B-11(OH)(3) species while with LDH selective adsoption of B-10(OH)(4)(-) by positive layers was favorable resulting in the enrichment of the heavier isotope in the solution. (C) 2015 Elsevier B.V. All rights reserved.