Impact of environmental conditions on the sorption behavior of Pb(II) in Na-bentonite suspensions

In this study, a local bentonite from Lin'an county (Zhejiang province, China) was converted to Na-purified form and the Na-bentonite sample was characterized by using FTIR and XRD to determine its chemical constituents and micro-structure. The removal of lead from wastewaters by Na-bentonite was studied as a function of various environmental parameters such as contact time, pH, ionic strength, foreign ions, humic substances and temperature under ambient conditions. The results indicated that the sorption of Pb(II) on Na-bentonite was strongly dependent on pH and ionic strength. The Langmuir, Freundlich and D-R models were used to simulate the sorption isotherms of Pb(II) at three different temperatures of 298, 318 and 338 K. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Pb(II) on Na-bentonite was endothermic and spontaneous. At low pH, the sorption of Pb(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-bentonite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that Na-bentonite has good potentialities for cost-effective disposal of lead bearing wastewaters.