Chorghe, Darpan Atul (2017-04). Boron Removal from Hydraulic Fracturing Wastewater using Conventional Aluminum and Iron Coagulation: Processes and Uptake Mechanisms. Master's Thesis.
Thesis
One promising strategy to manage the large volumes of water needed for and wastewater generated by hydraulic fracturing is on-site treatment and reuse. In particular, the saline flowback water contains many of the chemicals employed for fracking, which need to be removed before possible reuse as "frac water." This manuscript targets one chemical of concern: borate based cross-linkers. To this end, coagulation-flocculation-sedimentation was evaluated for boron removal from saline flowback water obtained from a well in the Eagle Ford shale. Very high dosages reaching Al/B and Fe/B ratios of ~70 were necessary to remove ~80% boron at an optimal pH of 8. X-ray photoelectron spectroscopy revealed B-O bonding on surfaces of freshly precipitated Al(OH)3(am) and Fe(OH)3(am) suggesting boron uptake was predominantly via ligand exchange. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy provided direct evidence of inner- and outer-sphere boron complexation with coagulant surface hydroxyl groups. Only trigonal boron was detected on aluminum flocs since possible presence of tetrahedral boron was masked by severe Al-O-Al and Al-O interferences. In contrast, both trigonal and tetrahedral conformation of boron complexes was identified on Fe(OH)3 surfaces. Direct Al-B or Fe-B bonding was not observed demonstrating boron was complexed largely with surface hydroxyl groups. Considering vast complexity of flowback water, it is important to develop in-depth understanding of chemistry of different flowback components like organic carbon compounds, silica compounds to scale up this bench scale experiment on an industrial level.
