The co-adsorption of Cu2+ and Zn2+ with adsorption sites surface-lattice reforming on calcined layered double hydroxides

Abstract

In this paper, nano-amorphous Mg/Al oxides-calcined layered double hydroxides (CLDHs) were employed to evaluate the adsorption capacity of Cu²⁺ or Zn²⁺ in wastewater and to investigate the adsorption mechanism. The results demonstrated that the maximal adsorption capacities of Cu²⁺ and Zn²⁺ were 422.08 mg g⁻¹ and 508.21 mg g⁻¹, respectively, whereas the initial Cu²⁺ or Zn²⁺ concentration in single-ion solutions was 500 mg L⁻¹. Certain competitive and inhibitory effects were observed during the Cu²⁺ and Zn²⁺ binary ions adsorption process. During the process, CLDHs were hydrated, and heavy metal ions were adsorbed rapidly onto the surface of CLDHs with crystalline phase inversion and formation of octahedral sheets with positive charges. Then, the sheets were stripped into the solution and the hydroxyls intercalated into the interlayer to make sheets combined together. Consequently, CLDHs recovered their hydrotalcite structure, which reflected the transition from surface adsorption to bulk phase. Thermodynamics study indicated that the adsorption isotherm was of the Langmuir-type. The kinetic model was of the pseudo-second-order-type. The regenerative adsorption experiments suggested that CLDHs could remove Cu²⁺ or Zn²⁺ with high efficiency after 4 repetitions. Both the high density bulk adsorption sites and the superior performance indicate a vast potential application prospect of the material.