title: Mechanisms of boron removal from hydraulic fracturing wastewater by aluminum electrocoagulation.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Actual hydraulic fracturing wastewater containing ∼120mg/L boron from the Eagle Ford shale play was employed. Electrocoagulation was performed over a range of aluminum dosages (0-1350mg/L), pH 6.4 and 8, and high current densities (20-80mA/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.
  
  
  RESULTS
  Boron removal increased monotonically with aluminum dosage and was higher at pH 8, but remained relatively constant at ⩾20mA/cm(2). 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 BO bond shifting toward lower binding energies in XPS. Severe AlO interferences precluded evidence for tetrahedral B(OH)4(-) complexation. No evidence for co-precipitation was obtained.
authors.affiliation: Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, United States.
authors.forename: Mutiara Ayu
authors.initials: MA
authors.lastname: Sari
authors.affiliation: Zachry Department of Civil Engineering, Texas A&M University, College Station, TX 77843-3136, United States. Electronic address: chellam@tamu.edu.
authors.forename: Shankararaman
authors.initials: S
authors.lastname: Chellam
keywords: Aluminum coagulation; Boron; Electrocoagulation; Fourier Transform Infrared spectroscopy; Fracking; Hydraulic fracturing; Industrial wastewater treatment; X-Ray Photoelectron Spectroscopy