title: Removal of Cd2+ from water by Friedel's salt (FS: 3CaO x A12O3 x CaCI2 x 10H2O): sorption characteristics and mechanisms.
abstract: The development of low-cost and efficient new mineral adsorbents has been a hot topic in recent years. In this study, Friedel's salt (FS: 3CaO x A12O3 x CaCl2 x10H2O), a hexagonal layered inorganic absorbent, was synthesized to remove Cd2+ from water. The adsorption process was simulated by Langmuir and Freundlich models. The adsorption mechanism was further analyzed with TEM, XRD, FT-IR analysis and monitoring of metal cations released and solution pH variation. The results indicated the adsorbent FS had an outstanding ability for Cd(II) adsorption. The maximum adsorption capacity of the FS for Cd(II) removal can reach up to 671.14 mg/g. The nearly equal numbers of Cd2+ adsorbed and Ca2+ released demonstrated that ion-exchange (both surface and inner) of the FS for Cd(II) played an important role during the adsorption process. Furthermore, the surface of the FS after adsorption was microscopically disintegrated while the inner lamellar structure was almost unchanged. The behavior of Cd(II) adsorption by FS was significantly affected by surface reactions. The mechanisms of Cd2+ adsorption by the FS mainly included surface complexation and surface precipitation. In the present study, the adsorption process was fitted better by the Langmuir isotherm model (R2 = 0.9999) than the Freundlich isotherm model (R2 = 0.8122). Finally, due to the high capacity for ion-exchange on the FS surface, FS is a promising layered inorganic adsorbent for the removal of Cd(II) from water.
authors: Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China.
authors: Juanjuan
authors: J
authors: Zhang
authors: National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Beijing 100190, China.
authors: He
authors: H
authors: Zhao
authors: Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China.
authors: Hongbin
authors: H
authors: Cao
authors: College of Chemical and Biologic Engineering, Changsha University of Science and Technology, Hunan 410004, China.
authors: Heping
authors: H
authors: Li
authors: National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Beijing 100190, China.
authors: Zhibao
authors: Z
authors: Li
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide / Q000737:chemistry*; D002104:Cadmium / Q000302:isolation & purification*; D002122:Calcium Chloride / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D013816:Thermodynamics; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: C586815:Friedel's salt; D014874:Water Pollutants, Chemical; D002104:Cadmium; D000537:Aluminum Oxide; D002122:Calcium Chloride