Cadmium adsorption onto aluminum hydroxide-modified attapulgite prepared with basic aluminum acetate.

Cadmium pollution in water is becoming increasingly serious. Thus, the effective removal of Cd(II) from water has garnered attention. Aluminum hydroxide-modified attapulgite (ATP-AC) was prepared from basic aluminum acetate through a coprecipitation method that could efficiently adsorb Cd(II) in aqueous solution. Seven characterization methods were utilized to investigate the properties of ATP-AC. Batch experiments were carried out to research the effects of pH, adsorption time, Cd(II) concentration and dosage on the Cd(II) adsorption ability of ATP-AC. The results revealed that the optimal conditions for the adsorption of Cd(II) by ATP-AC were pH = 7, a dosage of 0.4 g L, and and equilibrium time of 6 h. The Freundlich adsorption isotherm model better described Cd(II) adsorption by ATP-AC than did the Langmuir model. The maximum adsorption capacities at temperatures of 293, 303 and 313 K were 5.55, 10.35 and 12.95 mg g, respectively. The pseudo-second-order kinetic equation was more appropriate for describing the adsorption of Cd(II) by ATP-AC than the pseudo-first-order kinetic equation was. The thermodynamic parameters indicated that Cd(II) adsorption by ATP-AC is endothermic and spontaneous and proceeds in the direction of disorder. The increased specific surface area and increased number of hydroxyl group active sites are the main reasons for the improved Cd(II) adsorption capacity of ATP-AC.