College of Environment and Ecology, Hunan Agricultural University, Changsha, 410128, China.
Hunan Research Academy of Environmental Sciences, Changsha, 410002, China.
Environ Sci Pollut Res Int. 2023 Dec;30(57):120820-120831. doi: 10.1007/s11356-023-30323-z. Epub 2023 Nov 9.
Sorptive removal of cadmium (Cd) from the aqueous solutions using the easily available natural materials is an attractive method. However, the adsorption efficiencies of these materials, such as clays, are typically low. Besides, they are generally in relatively low stability and renewability, which restrict their application. Thus, modification of these materials to enhance their performance on Cd removal has gained growing attentions. Herein, the integration of calcination and ferric chloride (FeCl) was used to modify a typical clay, i.e., attapulgite, to increase the adsorption sites, and thus to develop a robust adsorbent for Cd. Under the optimum conditions for attapulgite modification (i.e., the mass ratio of FeCl to attapulgite was 1:2, calcination temperature was 350 °C, and calcination time was 1.5 h) and Cd adsorption (i.e., initial pH of 6.0, adsorption temperature of 25 °C, and adsorbent dosage of 1.0 g/L), the maximum adsorption capacity of the modified attapulgite toward Cd was 149.9 mg/g. Mechanisms of surface complexation and electrostatic attraction were involved in the efficient removal of Cd. The adsorption of Cd increased with pH due to the increased electrostatic attraction. Metal cations inhibited the Cd adsorption through competing with the adsorption sites. The changes of Gibbs-free energy during the adsorption of Cd were lower than zero and decreased with temperature, suggesting the process was spontaneous and endothermic. The removal efficiency of Cd after 5 times of recycle maintained at 82% of that of the raw modified attapulgite demonstrated the stability of the adsorbent. These results suggested that the modified attapulgite is robust for Cd removal and is promising for land application.
使用易得的天然材料从水溶液中吸附去除镉（Cd）是一种很有吸引力的方法。然而，这些材料（如粘土）的吸附效率通常较低。此外，它们通常稳定性和可再生性相对较低，这限制了它们的应用。因此，对这些材料进行改性以提高其对 Cd 去除的性能已引起越来越多的关注。在此，采用煅烧和氯化铁（FeCl）的结合来改性一种典型的粘土，即凹凸棒石，以增加吸附位点，从而开发出一种用于 Cd 的强吸附剂。在凹凸棒石改性的最佳条件（即 FeCl 与凹凸棒石的质量比为 1:2、煅烧温度为 350°C 和煅烧时间为 1.5 h）和 Cd 吸附的最佳条件（即初始 pH 值为 6.0、吸附温度为 25°C 和吸附剂用量为 1.0 g/L）下，改性凹凸棒石对 Cd 的最大吸附容量为 149.9 mg/g。表面络合和静电吸引机制参与了 Cd 的有效去除。由于静电吸引的增加，Cd 的吸附随 pH 值的增加而增加。金属阳离子通过与吸附位点竞争而抑制 Cd 的吸附。Cd 吸附过程中吉布斯自由能的变化小于零且随温度降低，表明该过程是自发的和吸热的。经过 5 次循环后 Cd 的去除效率仍保持在原始改性凹凸棒石的 82%，表明该吸附剂具有稳定性。这些结果表明，改性凹凸棒石是一种用于去除 Cd 的强吸附剂，有望在土地应用中得到应用。
