Cd(II) Removal by Novel Fabricated Ground Calcium Carbonate/Nano-TiO 2 (GCC/TiO 2 ) Composite from Aqueous Solution

The heavy metal Cd(II) in wastewater is highly toxic to organisms and must be removed. In this work, an efficient Cd(II) adsorbent consisting of ground calcium carbonate (GCC) and nano-TiO 2 (GCC/TiO 2 ) was harvested through a facile two-step strategy. Firstly, GCC was immersed in titanium sol which prepared from titanium butoxide to form the precursor. Secondly, GCC/TiO 2 was obtained via hydrothermal reaction and the optimal hydrothermal condition was determined to be pH of 3, temperature of 200 °C and reaction time of 12 h. The removal of Cd(II) from aqueous solution by adsorbents under different hydrothermal conditions and adsorption experiments was studied by means of SEM, FT-IR, XPS, and ICP. The maximum Cd(II) removal capacity was approximately 124.07 mg/g at 25 °C and the adsorption equilibrium was attained in only 8 min (at 100 mg/g initial Cd(II) concentration, 0.8 g/L adsorbent dosage, and an initial Cd(II) solution pH of 5). Furthermore, the Cd(II) removal capacity of GCC/TiO 2 was significantly higher than that of isolated GCC and TiO 2 and exhibited an excellent self-settlement property, which is beneficial for adsorbent separation in practical applications. The Cd(II) removal mechanisms include ion-exchange reaction between Cd(II) and the Ca 2+ ions on the GCC/TiO 2 surface and electrostatic attraction. Moreover, the GCC/TiO 2 adsorbent could be regenerated by ethylenediaminetetraacetic acid disodium salt and exhibited a high reusability. The adsorption data could be well fitted by the Langmuir model, and the adsorption kinetic follows the pseudo-second-order model indicating that the removal processes are controlled by the chemisorption mechanism.