Treatment of shale gas flowback water by adsorption on carbon- nanotube-nested diatomite adsorbent

Abstract

A carbon-nanotube-nested diatomite adsorbent (CND-composite adsorbent) was successfully prepared and introduced to remove organic contaminants from shale gas flowback water. The CND-composite adsorbent was then characterized using Scanning Electron Microscopy, Brunauer Emmett Teller, Mercury Intrusion Porosimetry and X-ray Diffraction (XRD) analyses. The changes in the organic species present in the shale gas flowback water before and after adsorption were characterized via Gas Chromatography-Mass Spectrometer. The kinetics, isotherms and thermodynamics of the adsorption of organic matter in shale gas flowback water on the CND-composite adsorbent were investigated on the basis of static experiments. The CND-composite adsorbent had hierarchical mesoporous/ macroporous structures. The adsorption experiments indicated that the maximum removal efficiency for total organic carbon was 78.91 %. The adsorption mechanisms mainly involved intermolecular interactions, electrostatic interaction and hydrogen bonds. Results showed that the Freundlich isothermal model and pseudo-second-order model were suitable for the characterization of the adsorption process in this work. The changing values of thermodynamic parameters, including the Gibbs free energy, entropy, and enthalpy, indicated that the adsorption process was spontaneous and endothermic. In addition, the adsorption process was jointly controlled by physical and chemical mechanism. In summary, the CND-composite adsorbent has potential for utilization in the removal of organic pollutants in real wastewater.