Adsorption profiles of some heavy metal ions from aqueous waste solutions using sodium-doped zirconium titanoslicate

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 [K₂(Zr_0.8Ti_0.2)Si₃O₉ × H₂O], Penkvilksite [(Ti_0.9Zr.1)Si₄Na₂O₁₃H₄], and Umbite [K₂(Zr_0.86Ti.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 Cu²/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.

Keywords:

• Adsorption profiles
• Concentration
• Equilibrium and initial pH
• Zirconium titanosilicate and doping effects