Abstract
Adsorption profiles of Co2+, Cu2+, Ni2+, and Cr6+ ions from aqueous waste solutions were studied on novel sodium-doped zirconium titanoslicate (SDZTS) that was topographically transient pH characterized by a step change in ionic strength of buffer solutions. Using XRD, FTIR, and DTA-TGA, SDZTS-I, II, and III with single orthorhombic phases of Umbite [K-2(Zr0.8Ti0.2)Si3O9 x H2O], Penkvilksite [(Ti0.9Zr.1)Si4Na2O13H4], and Umbite [K-2(Zr0.86Ti.14)Si3O10H], with P 21 21 21 (19), P n c a (60), and P 21 21 21 (19) space groups, were recognized, respectively. According to the transient pH procedure, they could be classified as cation ion-exchange chromatographic supports; the order of strength is SDZTS-III > SDZTS-II > SDZTS-I. The duration of the pH transient was linearly proportional to the total ionic capacity and was used to estimate active binding capacity of the resin. The breakthrough capacities, BTCs, obtained during dynamic measurements through the column experiments were less than the recorded static ion-exchange capacities, SIECs. The BTCs recorded for Cu2+, Co2+, Ni2+, and Cr6+ /SDZTSs were SDZTS-III (2.45, 2.76, 2.25, and 3.97 meq/g), SDZTS-II (2.23, 2.65, 1.95, and 3.85 meq/g), and SDZTS-I (2.11, 2.42, 1.86, and 2.97 meq/g). The STIECs for Cu2+, Co2+, Ni2+, and Cr6+ were in the order of SDZTS-III (6.42, 6.45, 4.57, and 5.25 meq/g)> SDZTS-II (5.82, 5.25, 4.14, and 4.96 meq/g > SDZTS-I (4.93, 4.35, 3.96, and 5.92 meq/g), respectively. Kinetic approaches, including the Lagergren first-order kinetic model (LFOKM), pseudo second-order kinetic model (PSOKM), and Morris-Weber kinetic model (MWKM), were used. They indicated that particle and/or film diffusion is the rate-determining step for Co2+, Ni2+, and Cr6+/SDZTS-III, while chemical reaction is the controlling step in case of Cu-2/SDZTS-III. Langmuir and Freundlich models were selected as basic models for studying the different isotherms. Freundlich approach is a better fit for Co2+, Ni2+, and Cr6+/SDZTS-III, while Langmuir is more appropriate in case of Cu2+/SDZTS-III.