Effects of pH, ionic strength and humic acid on the sorption of neptunium(V) to Na-bentonite

• DOI: 10.1016/j.molliq.2015.02.014
• Publication Date: 2015-02-14T02:49:59Z
• Authors: Ping Li; Zhi Liu; Feng Ma; Quanlin Shi; Zhijun Guo; Wangsuo Wu
• Keywords: Bentonite; Neptunium

Abstract Effects of ionic strength, pH, temperature, humic acid (HA) and adsorbate concentration on Np(V) sorption to Na-bentonite were investigated in detail. The sorption of Np(V) to Na-bentonite was significantly dependent on pH and independent of temperature. In the presence of HA, Np(V) sorption was enhanced significantly at low pH; while an obvious negative effect was observed in higher pH range. Np(V) sorption followed the Freundlich isotherm indicating a heterogeneous sorption of Np(V) on the surface of Na-bentonite. The surface complexation model (SCM) suggests that sorption of Np(V) on Na-bentonite was mainly dominated by ion exchange at low pH values, and two dominant monodentate inner-sphere complexes of ≡ SiONpO20 (logK = − 4.55) and ≡ AlO(NpO2OH)− (logK = − 13.80) contributed to Np(V) sorption on Na-bentonite over high pH range.