Removal of Cd(II) and Pb(II) ions from aqueous solutions by synthetic mineral adsorbent: Performance and mechanisms

Abstract

A synthetic mineral adsorbent (SMA) was prepared by mechanochemical treatments of a solid-state mixture containing illite, wollastonite, gypsum, limestone and dolomite powder at a molar ration of 1:1:1:12:3. The XRD patterns revealed that many newly-generated minerals, namely montmorillonite, laumonite and gismondine (zeolite facies), grossular, gehlenite and calcium silicate were observed in SMA residual after full hydration. The potential of SMA for the removal of Cd(II) and Pb(II) ions from aqueous solution was investigated by batch mode. The effects of pH, concentration of adsorbate, contact time, SMA concentration and temperature on adsorption performance of SMA for Cd(II) and Pb(II) over SMA were studied. The results indicate that the adsorption process was found to follow pseudo-second-order kinetic model and Freundlich isotherm model. The maximum monolayer capacity obtained from the Langmuir isotherm at 25°C was 47.0 and 143.3mgg−1 for Cd(II) and Pb(II) ions, respectively. The adsorbed Cd(II) and Pb(II) can hardly be recovered at pH 3.0 but can completely recovered at pH 1.0 and 0.5, respectively. Ion exchange of Cd(II) and Pb(II) for Ca2+ was found to be the principal mechanism in the removal of Cd(II) and Pb(II) from aqueous solution by SMA, followed by adsorption and precipitation. From the investigation, it is concluded that SMA could be a useful environment-friendly, inexpensive and effective tool for removal of high amounts of toxic Cd(II) and Pb(II) ions from aquatic ecosystems.