Interaction mechanism of radionickel on Na-montmorillonite: Influences of pH, electrolyte cations, humic acid and temperature

• Desorption capacity of the Na-montmorillonite increased with decreasing pH.
• Desorption ability for 63Ni(II) was Na+ = K+ > Ca2+ = Mg2+.
• HA influenced 63Ni(II) sorption clearly and promoted the 63Ni(II) desorption.
• 63Ni(II) desorption decreased significantly with increase in temperature.

Understanding the rate and extent of 63Ni(II) sorption and desorption on/from mineral surfaces are important to predict its mobility performance in the natural environment. We herein systematically investigated the effects of pH, electrolyte cations, humic acid (HA) and temperature on 63Ni(II) sorption/desorption on/from Na-montmorillonite. The results indicated that the sorption/desorption of 63Ni(II) on/from Na-montmorillonite were strongly dependent on pH and electrolyte cations. Desorption abilities of 63Ni(II) were Na+ ≈ K+ > Ca2+ ≈ Mg2+ at the cationic concentration of 0.2 mol/L, which was associated with the clay tactoid size. The kinetic results suggested that 63Ni(II) sorption/desorption initially increased rapidly and remained constant as time increasing. The presence of HA influenced 63Ni(II) sorption clearly and promoted 63Ni(II) desorption as a result of the dissolution of ternary surface complexes. Increasing temperature was favorable for the sorption reaction owing to the formation of strong inner-sphere complexes, however, hampered the desorption reaction because of the increased stability of inner-sphere complexes or the aggregation of montmorillonite. The results are crucial to understand the physicochemical behavior of radionickel in the natural environment.

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