Characterisation of electrokinetic properties of clinoptilolite before and after activation by sulphuric acid for treating CSG water

• Examination of surface electrokinetics of activated clinoptilolite for treating CSG water.
• Modelling and experiments of surface potential by GSG theory and electrophoresis.
• Importance of surface dealumination of clinoptilolite by acid activation.
• Dealumination increased cation exchange capacity of activated clinoptilolite.

Clinoptilolite, an abundant and low cost natural zeolite, activated by sulphuric acid has been shown to be useful for treating coal seam gas (CSG) co-produced saline water. This paper aims to further examine the effect of the acid activation on changes in physicochemical properties of clinoptilolite which underpin the treatment of CSG saline water by clinoptilolite. Microelectrophoresis was applied to measure surface (zeta) potential of clinoptilolite particles before and after the acid activation as function of pH. The change in the surface potential was theoretically analysed applying the theory on the electrical double layers at solid-solution interfaces. The proton donor–acceptor reactions occurring simultaneously on amphoteric alumina and silica sites of clinoptilolite were considered. The mass balances were applied to link the zeolite active sites with the zeolite charge and potential. Comparing the model with the experimental data reveals the important role of the dealumination process occurred by the acid activation. The dealumination is the main reason for the increase in the surface charge and cation exchange capacity of clinoptilolite after the acid activation due to the increased defects in the crystal structure/lattice, which result in increasing numbers of charge vacancies. These results support our previous findings on the effectiveness of the acid activation of clinoptilolite in treating saline CSG co-produced water.

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