Hypotheses: Boron uptake from highly saline hydraulic fracturing wastewater by freshly precipitated amorphous Al(OH)(3) precipitates is due to ligand exchange and complexation with surface hydroxyl groups. Consequently, aluminum electrocoagulation can be a feasible approach to remove boron from flowback/produced water. Experiments: Actual hydraulic fracturing wastewater containing -similar to 120 mg/L boron from the Eagle Ford shale play was employed. Electrocoagulation was performed over a range of aluminum dosages (0-1350 mg/L), pH 6.4 and 8, and high current densities (20-80 mA/cm(2)) using a cylindrical aluminum anode encompassed by a porous cylindrical 316-stainless steel cathode. Direct measurements of boron uptake along with its chemical state and coordination were made using Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-Ray Photoelectron Spectroscopy. Findings: Boron removal increased monotonically with aluminum dosage and was higher at pH 8, but remained relatively constant at 20 mA/cm2. Chloride ions induced anodic pitting and super-Faradaic (131% efficiency) aluminum dissolution and their electrooxidation produced free chlorine. ATR-FTIR suggested outer-sphere and inner-sphere complexation of trigonal B(OH)3 with Al(OH)3, which was confirmed by the 8-0 bond shifting toward lower binding energies in XPS. Severe Al-0 interferences precluded evidence for tetrahedral B(OH) i complexation. No evidence for co-precipitation was obtained. (C) 2015 Elsevier Inc. All rights reserved.