Sorption hysteresis in natural sorbents has important environmental implications for pollutant transport and bioavailability. We examined sorption reversibility of Cd(II) and Pb(II) on zeolite and bentonite. Sorption isotherms were derived by sorption of Cd(II) and Pb(II) from solutions containing a range of the metal concentrations corresponding to 10-100% maximum sorption capacity (SCmax) of the sorbents. The desorption experiments were performed immediately following the completion of sorption experiments. Sorption and desorption isotherms of Cd(II) and Pb(II) were well described by the Freundlich model. The results revealed that the desorption isotherms of Cd(II) and Pb(II) from zeolite significantly deviated from the sorption isotherms indicating irreversible or very slowly reversible sorption. For bentonite sorption/desorption isotherms were similar indicating reversible sorption. The extent of hysteresis was evaluated from sorption and desorption Freundlich parameters (K(f) and n) through the apparent hysteresis index (HI = n(desorb)/n(sorb); n is the exponent in the Freundlich equation) and differences in Freundlich K(f) parameters. Higher sorption irreversibility was obtained for Pb(II) as compared to Cd(II). The amounts of Cd(II) and Pb(II) desorbed from bentonite were more than from zeolite, indicating that zeolite was a more effective sorbent for water and wastewater treatment.

中文翻译：

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Cd（II）和Pb（II）在天然沸石和膨润土上的吸附滞后。

天然吸附剂的吸附滞后对污染物的运输和生物利用度具有重要的环境影响。我们研究了Cd（II）和Pb（II）在沸石和膨润土上的吸附可逆性。吸附等温线是通过从溶液中吸附Cd（II）和Pb（II）得出的，该溶液的金属浓度范围对应于吸附剂的10-100％最大吸附容量（SCmax）。吸附实验完成后立即进行解吸实验。Freundlich模型很好地描述了Cd（II）和Pb（II）的吸附和解吸等温线。结果表明，Cd（II）和Pb（II）从沸石的解吸等温线明显偏离吸附等温线，表明不可逆或非常缓慢的可逆吸附。对于膨润土的吸附/解吸等温线相似，表明可逆吸附。通过表观磁滞指数（HI = n（desorb）/ n（sorb）; n是Freundlich方程中的指数）从吸附和解吸Freundlich参数（K（f）和n）评估滞后程度。 Freundlich K（f）参数。与Cd（II）相比，Pb（II）获得了更高的吸附不可逆性。从膨润土中解吸的Cd（II）和Pb（II）的量大于从沸石中解吸的量，这表明沸石是用于水和废水处理的更有效的吸附剂。n是Freundlich方程的指数）和Freundlich K（f）参数的差。与Cd（II）相比，Pb（II）获得了更高的吸附不可逆性。从膨润土中解吸的Cd（II）和Pb（II）的量大于从沸石中解吸的量，这表明沸石是用于水和废水处理的更有效的吸附剂。n是Freundlich方程的指数）和Freundlich K（f）参数的差。与Cd（II）相比，Pb（II）获得了更高的吸附不可逆性。从膨润土中解吸的Cd（II）和Pb（II）的量大于从沸石中解吸的量，这表明沸石是用于水和废水处理的更有效的吸附剂。