Interaction of vanadates with Mg/Al and Mg/Fe LDH intercalated with carbonates and sulphates based on experimental data and surface complexation modelling

The mechanisms of unmodified, pure LDH and aqueous V(V) interaction have not been extensively studied yet, despite the important role of both layered material and element in the industry. The performed studies revealed that maximum capacity of LDH was heavily influenced by different layer and interlayer chemistry of the materials. Several possible mechanisms of V(V) removal from aqueous solutions were identified, depending on the chemical composition of LDH, V(V) initial concentration and background electrolyte concentration. Based on the Raman spectroscopy and application of 1-site 2-pK non-electrostatic model (herein reported for the first time for LDH-V), the formation of inner-sphere monodentate VO₃⁻ complexes at the surface of the LDH layers was confirmed at lower initial V(V) concentrations (0.05–1.0 mmol/L). At high initial V(V) concentration (5 mmol/L), the polymerized (V₁₀O₂₈)⁶⁻ form was identified and the precipitation of Mg and V-bearing phases was revealed by XRD. Additionally, the interlayer anion-exchange mechanism could not be explicitly excluded. The XPS method, however, excluded the reduction of V(V). The study clearly showed that V(V) bonding mechanism is affected by different reaction conditions which should always be considered during applications involving LDH and vanadium compounds.