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.