preparation of copper ferrocyanide
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Explanation:
(mol−1 K−1)), ΔGo (kJ mol−1) are in the enthalpy change, entropy change and Gibbs free energy for the adsorption process, respectively. The values of ΔHo and ΔSo can be obtained from the slope and intercept of the Van't Hoff linear plots of ln Kdversus 1/T. The results were shown in Fig. 11. Meanwhile, the values of thermodynamic parameters for the adsorption of cesium at different temperatures were given in Table 3.
Fig. 11 The relationship between ln Kd and 1/T for Cs+ adsorption of CMC–KCuFC particles.
Table 3 Thermodynamic parameters for the adsorption process of cesium on CMC–KCuFC
T (K) ln Kd ΔGo (kJ mol−1) ΔHo (kJ mol−1) ΔSo (J (mol−1 K−1))
288.15 10.723 −24.843 69.087 325.974
298.15 10.871 −28.102
308.15 11.945 −31.362
318.15 13.633 −34.622
328.15 13.750 −37.882
It can be found that all the ΔGo values were negative at the temperature range of 288.15 to 328.15 K, conforming that the adsorption of cesium onto CMC–KCuFC particle was thermodynamically feasible and spontaneous in nature. For the adsorption of cesium the positive values of ΔHo indicated that the adsorption was endothermic. Moreover, the positive value of ΔSo was interpreted as the result of an increase in the randomness at the solid/liquid interface during the adsorption of cesium on the adsorbent.33
3.1.6. Effect of competing ions on the adsorption of cesium The influence of competing cations (e.g. Na+, K+, Li+, Ca2+ and Mg2+) on the Kd value of cesium ion onto the CMC–KCuFC particle was investigated. These five cations were selected due to their natural abundance in wastewater. The effect was studied by keeping the concentration of Cs+ constant (20 mg L−1), and varying the concentrations of Na+, K+, Li+, Ca2+ and Mg2+ under pH (5 ± 0.02) at 298.15 K. In the absence of added cations, the value of Kd was 9493.094 mL g−1. The results under competition with added cations were presented in Fig. 12. As the concentration added cations increase from 50 to 250 mg L−1, the Kd value was substantially increased in the following sequence: K+ < Na+ < Ca2+ < Mg2+ < Li+. The Kd value was lowest in the presence of K+, which could be attributed to the closer similarity in hydration radius between K+ (3.30 Å) and Cs+ (3.25 Å) than that of the other cations.34 Meanwhile, the influences of Ca2+ and Mg2+ cations on the adsorption might be involved in other process or steps except ion exchange, such as nonspecific surface adsorption.35
Fig. 12 Effect of competing ions on the remove of 50 mL 20 mg L−1 Cs+ for 24 h at 298.15 K.
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