Adsorption behavior of kenyaite for Cu2+ and Pb2+

Hydrated layered polysilicates (HLPSs) have received considerable attention as adsorbents because of their selective adsorption for heavy metal cations. However, the adsorption behavior of kenyaite, a HLPS, was not elucidated for heavy metal cations yet. The aim of this study is to investigate adsorption behavior of kenyaite for various heavy metal cations and to elucidate selective adsorption. In the quaternary Cu–Pb–Cd–Zn system, kenyaite exhibited selective adsorption, especially for Pb2+ and Cu2+ of which removal rates were 97 and 66%, respectively. It revealed that Pb2+ was more strongly adsorbed than Cu2+ through coordination with interlayer silanol groups, resulting in dehydration in the interlayers and severe collapse of the silicate layers. In the presence of NaCl, on the other hand, adsorption for Cu2+ was less affected showing removal rate of 56% whereas that for Pb2+ was considerably affected as indicated by remarkably decreased removal rate (42%). Such a preferential adsorption of Cu2+ in the presence of NaCl could be explained by the role of interlayer Na+ in inhibiting rapid collapse of the interlayer space to facilitate more adsorption of Cu2+ with a larger hydrated radius. This study provides an insight into understanding selective adsorption of HLPSs and developing potential adsorbents for water purification.