Ni0.5Zn0.5Fe2O4 nanocomposite was synthesized and used for the removal and preconcentration of Cr(VI), Mo(VI), V(V) and W(VI) ions. The effect of various parameters such as pH, amount of the adsorbent and contact time on the adsorption efficiency of Cr(VI), Mo(VI), V(V) and W(VI) ions on the adsorbent were studied. The maximum adsorption occurred at pH 4.0 for Cr(VI) and W(VI) and at pH 5.0 for Mo(VI) and V(V). Maximum adsorption capacity (qmax) was estimated using Langmuir adsorption model as 48.5, 38.8, 28.0 and 72.0 mg g−1 for Cr(VI), Mo(VI), V(V) and W(VI) ions, respectively. The adsorbed oxyanions were then desorbed by NaOH solution. The concentration of the ions in desorbed solution was determined spectrophotometrically. Calibration curves were linear for Cr(VI), Mo(VI), V(V) and W(VI) ions in the range 0.7–150.0, 0.9–70.0, 2.0–50.0 and 1.0–40.0 ng mL−1 for an initial sample solution of 100 mL, respectively.
