Preparation of sodium-substituted xonotlite from eggshell and its adsorption behavior for cadmium(ii)

Abstract

Sodium-substituted xonotlite (NaCSH) was prepared from eggshell by using hydrothermal method and doping technology, and was used to remove cadmium(II) from aqueous solution. NaCSH had porous structure and large surface area as characterized by BET surface area, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). Batch adsorption experiments showed that the removal efficiency and adsorption capacity came to 98.01% and 98.01 mg/g, respectively, at pH 6.0, temperature 313 K and contact time of 45 min. Further analysis revealed that cadmium(II) adsorption onto NaCSH2 was best described by Langmuir isotherm model (R2 > 0.988), and kinetics data were best fitted by pseudo-second order kinetics (R2 > 0.99). The calculated maximum adsorption capacity of cadmium(II) on NaCSH2 was 150.07 mg/g at 313 K, which is much higher than pure xonotlite. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. Moreover, NaCSH2 was found to retain greater adsorption capacity for cadmium(II) after five cycles of adsorption–desorption. Thus, NaCSH2 may be a good adsorbent to remove cadmium(II) from wastewater.