A kinetic and thermodynamic study of cd(Ii) removal by hexylamine-clinoptilolite nanoparticles composite

Abstract

Natural clinoptilolite tuff was pre-treated and changed to micro (MCP) and nano (NCP) particles by mechanical method. Modification of MCP and NCP particles and also their Cd-exchanged forms was done by alcoholic-aquatic Hexylamine (HA) solution. The raw and modified samples were characterized by XRD, FT-IR, SEM, TEM, BET and TG. Removal of Cd(II) by the modified and unmodified samples confirmed that NCP-HA sorbent is better sorbent with respect to MCP, NCP-HA, MCP-HA, NCP-Cd-HA and MCP-Cd-HA. The modified samples showed good selectivity for cadmium among various investigated multivalent cations. Obeying the adsorption isotherms from Langmuir equation indicates the monolayer sorption of Cd(II) onto the sorbent. Fitting the adsorption kinetic in the pseudo-second-order rate equation indicates that the chemical reaction rate limiting step for the process. The negative ∆H and ∆G indicate an exothermic and spontaneous process. The negative ∆S indicates that during the adsorption of cadmium cations from solution onto the sorbent shows that total entropy of the system was decreased.