Mixture of CaCO₃ Polymorphs Serves as Best Adsorbent of Heavy Metals in Quadruple System

Abstract

This study compares and analyzes removal of Pb (II), Cu (II), Mn (II), and Zn (II) from aqueous solution as individual ions (monometal system) or as mixed ions (quadruple system) by commercial laboratory-grade calcium carbonate (C–CaCO3) and as-synthesized CaCO3 (S–CaCO3) as adsorbents. This was performed to determine whether heavy metal ion adsorption can be influenced by the polymorphic phases of CaCO3. C–CaCO3 and S–CaCO3 were equally efficient in the removal of Pb (II) and Cu (II) from a monometal system. However, S–CaCO3 exhibited only 49.3% ± 0.14 heavy metal removal when compared with 96.7% ± 0.08 by C–CaCO3 in a quadruple system. FTIR and HR-SEM analysis revealed C–CaCO3 consisted of a mixture of calcite and aragonite polymorphs, whereas S–CaCO3 was pure calcite polymorph. These results indicated the importance of identification of the polymorphic phase and phase transformation in any experiment while utilizing CaCO3 as adsorbent.