Seawater desalination by gas hydrate process and removal characteristics of dissolved ions (Na+, K+, Mg2 +, Ca2 +, B3 +, Cl−, SO42 −)

• We evaluated an application possibility of hydrate-based desalination process.
• Increasing hydraulic pressure increased the removal efficiency of ions.
• CO2 as a guest gas is more suitable than CH4 for the HBD process.
• The property of ionic behavior depending on its concentration should be examined further in the future.

In order to evaluate hydrate-based desalination (HBD), experiments with seawater samples were carried out at various conditions (i.e. hydraulic pressure, washing step, and hydrate-forming gas). Before and after the hydrate process, cations (Na+, K+, Mg2 +, Ca2 +, and B3 +) and anions (Cl− and SO42 −) were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC). In a single stage of CO2 hydrate process without any pretreatment, 71%–94% of each cation was removed in the following order: K+ > Na+ ≈ Mg2 + ≈ Ca2 + > B3 + and 73%–83% of each anion was removed. When the brines on the surface of hydrate pellets were removed, the ion removal efficiency increased above 4%. It was also found that the desalting efficiency depended on the hydrate-forming gas (CO2 > CH4) and the hydraulic pressure (6–10 MPa) to produce hydrate pellets. In this study, the removal efficiency of cations and anions in a real seawater sample using HBD processes were reported for the first time.