Effect of environmental conditions on the adsorption behavior of Sr(II) by Na-rectorite

The adsorption behavior of Sr(II) by Na-rectorite was investigated as a function of various environmental parameters such as pH, ionic strength, humic acid (HA) and temperature under ambient conditions. The results indicated that the adsorption of Sr(II) on Na-rectorite was strongly dependent on pH and ionic strength. The presence of HA enhanced the adsorption of Sr(II) on Na-rectorite at low pH, whereas suppressed Sr(II) adsorption on Na–rectorite at high pH. The Langmuir model simulated the adsorption isotherms of Sr(II) better than the Freundlich model at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature dependent adsorption isotherms indicated that the adsorption process of Sr(II) on Na–rectorite was spontaneous and endothermic. The adsorption of Sr(II) was dominated by outer-sphere surface complexation and ion exchange at low pH, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH. The results indicate that Na-rectorite may be a promising candidate for the treatment of radionuclides from large volume solution.