A simple, field-compatible method for accurate pH measurement in hypersaline brines

Accurate pH determination in hypersaline brines is essential for reliable geochemical modeling and simulation, particularly for processes such as direct lithium extraction, carbonate precipitation potential calculations, brine reinjection assessments, and related applications. However, standard pH electrode calibration techniques may produce significant errors in concentrated brines due to elevated liquid junction potential (LJP) and ion interactions with the electrode's glass membrane. Here, we present a robust, field-compatible method for accurate pH measurement in high salinity brines, using standard combined glass pH electrodes and titration-based calibration with tailored buffer solutions. The technique integrates an online PHREEQC (Pitzer model) based software to prepare custom buffer solutions and calibration curves, enabling the re-analysis of field data for correct pH detection. The method was evaluated using data from 16 hypersaline brines across the full evaporation sequence of a lithium production plant in the Salar de Uyuni of Bolivia. pH values obtained using the new method resulted in substantially improved agreement between PHREEQC-simulated and measured total alkalinity compared to standard pH calibration. While simulations based on standard pH calibration showed increased scatter and large errors with increasing ionic strength (up to >95% in total alkalinity simulations), applying the new method reduces these errors to within ±10% across the entire salinity range. This approach provides a simple, generic, low-cost, and effective tool for improving the pH measurement and chemical characterization of hypersaline brine.

Duke Scholars

Author Avner Vengosh Earth and Climate Sciences