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Adsorption and pre-concentration of Co(II) from aqueous solution using a heteropoly acid prepared sorbent

Abstract PM-MFL (phosphomolybdate-Mg-Fe-LDH) adsorbent was prepared and characterized using infrared spectra (FT-IR), X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), thermal analysis (TGA and DTA), and scanning electron microscopy (SEM). The removal percent results of Co(II) adsorption increased with the increase in contact time and the adsorbent weight while the pH had nearly no effect. The adsorption data was found to fit with the Langmuir isotherm model within the range 25–60 ± 1 °C. The kinetics and mechanism of diffusion of Co(II) was studied as a function of reaction temperature and the adsorption process was found to follow the pseudo-second-order kinetic. The heat of activation of the adsorption, ΔH and ΔS were calculated and found to be 47.24 kJ mol−1 and 0.176 kJ mol−1 K−1, respectively. The maximum loading capacity of the prepared sorbent was 33.5 mg/g and was obtained after 5 adsorption stages. The possibility of reuse of the adsorbent after desorption of the metal ions was studied and the results indicated that it could be used for three cycles. The feasibility of pre-concentration of Co(II) on PM-MFL indicated that the concentration of the metal ions in the leaching solutions recovered was concentrated three times compared with its initial concentration.