Boron partitioning and isotopic fractionation between synthesized amorphous silica and water

Abstract

We studied boron partitioning and isotopic fractionation between amorphous silica and water to understand a pH proxy in paleo-ocean. The pH of solvents ranged from 8.5 to 9.9, and the boron concentration was adjusted to 5 mg/L. The boron partitioning coefficient showed a bell-shaped pattern having a maximum value at pH 9.3. The isotopic fractionation factor ranged between -37 per mil and -28 per mil, decreasing at pH 9.1. Our result suggests that the precipitation experiment of amorphous silica can reproduce the pH dependent boron isotopic fractionation during the formation of biogenic silica.