Adsorption of Pt(IV) and Pd(II) from Aqueous Solution by Calcined Gibbsite (Aluminum Hydroxide)

In the present study, calcined gibbsite (GB) was prepared by calcination treatment between 200 and 1000 degrees C (GB200-GB1000). The properties of GBs (i.e., the amount of hydroxyl groups, specific surface area, mean pore diameter, and pore volume) were evaluated. GB400 had the highest amount of hydroxyl groups (0.46 mmol/g), as well as the highest specific surface area (295.3 m(2)/g) and micropore volume (0.036 mL/g). It also provided the highest amount of the adsorbed Pt(IV) and Pd(II), which suggests that the adsorption of Pt(IV) and Pd(II) onto GB is related to the amount of hydroxyl groups, specific surface area, and micropore volume. The optimal pH values for the adsorption of Pt(IV) and Pd(II) onto GB400 were 4.5-5.0 and about 6.0, respectively. The equilibrium adsorption of both cations onto GB400 was reached within 30 min. Moreover, the experimental data of the adsorption of Pt(IV) and Pd(II) onto GB400 was fitted by pseudo-second-order model (r = 0.997-0.999) and the Langmuir equation (r = 0.934-0.953). The calculated thermodynamic parameters Delta G, Delta H, and, Delta S indicate that the adsorption of Pt(IV) onto GB400 is feasible, spontaneous, and exothermic. In addition, the amount of Pt(IV) and Pd(II) adsorbed onto GB400 decreased with increasing chloride ion concentration.