Removal of Cd(II) from Aqueous Solutions by Aluminium Hydroxide-Modified Attapulgite

Modified attapulgite (ATP-Al) was prepared with aluminium hydroxide through a co-precipitation method, and we used ATP-Al as an adsorbent to investigate the adsorption of Cd(II) from aqueous solutions. Raw ATP and ATP-Al were characterized by TEM, FTIR, XRD and Zeta. Adsorption parameters, such as pH, initial Cd(II) concentration, contact time and adsorbent dose, were evaluated to explain the mechanism of Cd(II) adsorption on ATP-Al. ATP-Al had a better adsorption capacity of Cd(II) than ATP. When the pH value was 7, ATP and ATP-Al had the highest Cd(II) adsorption capacities. The optimal dose of adsorbent was 0.1 g per 25 mL of solution. The Freundlich model better described the adsorption isotherm on ATP and ATP-Al than the Langmuir model. The maximum adsorption capacity for Cd(II) calculated was 4.01 and 6.36 mg g-1, respectively. Adsorption of Cd(II) onto ATP and ATP-Al followed pseudo-second order kinetics. The Gibbs free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) were evaluated by a thermodynamic study. The adsorption processes of ATP and ATP-Al were exothermic, spontaneous and mainly based on physical adsorption.