Sorption and mechanism studies of Cu^2þ, Sr^2þ and Pb²þ ions on mesoporous aluminosilicates/zeolite composite sorbents

The research aimed to develop a novel mesoporous aluminosilicate/zeolite composite by the template co-precipitation method. The effect of aluminosilicate (AlSi) and zeolite (NaY) on the basic properties and adsorption capacity of the resultant composite was conducted at different mass ratios of AlSi/NaY (i.e., 5/90, 10/80, 15/85, 20/80, and 50/50). The adsorption characteristics of such composite and its feedstock materials (i.e., aluminosilicates and zeolite) towards radioactive Sr²þ ions and toxic metals (Cu^2þ and Pb^2þ ions) in aqueous solutions were investigated. Results indicated that BET surface area (S_BET), total pore volume (V_Total), and mesopore volume (V_Meso) of prepared materials followed the decreasing order: aluminosilicate (890 m²/g, 0.680 cm³/g, and 0.644 cm³/g) > zeolite (623 m²/g, 0.352 cm³/g, and 0.111 cm³/g) > AlSi/NaY (20/80) composite (370 m²/g, 0.254 cm³/g, and 0.154 cm³/g, respectively). The Langmuir maximum adsorption capacity (Q_m) of metal ions (Sr^2þ, Cu^2þ, and Pb^2þ) in single-component solution was 260 mg/g, 220 mg/g, and 161 mg/g (for zeolite), 153 mg/g, 37.9 mg/g, and 66.5 mg/g (for aluminosilicate), and 186 mg/g, 140 mg/g, and 77.8 mg/g for (AlSi/NaY (20/80) composite), respectively. Ion exchange was regarded as a domain adsorption mechanism of metal ions in solution by zeolite; meanwhile, inner-surface complexation was domain one for aluminosilicate. Ion exchange and inner-surface complexation might be mainly responsible for adsorbing metal ions onto the AlSi/NaY composite. Pore-filling mechanism was a less important contributor during the adsorption process. The results of competitive adsorption under binary-components (Cu^2þ and Sr^2þ) and ternary-components (Cu^2þ, Pb^2þ, and Sr²) demonstrated that the removal efficacy of target metals by the aluminosilicate, zeolite, and their composite remarkably decreased. The synthesized AlSi/NaY composite might serve as a promising adsorbent for real water treatment.