Comparison Of Cadmium
COMPARISON OF CADMIUM
AND NICKEL ADSORPTION BEHAVIOUR
ON DIFFERENT TYPE ZEOLITES
M. Majdan1, P. Staszczuk1, M. Kowalska-Ternes1,
A. Gładysz-Płaska1, E. Marchewka2
1Uniwersytet Marii Curie Skłodowskiej, Wydział Chemii,
Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
2Politechnika Radomska im. Kazimierz Pulaskiego,
Wydział Materialoznawstwa i Technologii Obuwia,
Chrobrego 27, 26-600 Radom, Poland
The unique problem of cadmium/nickel separation appears during reprocessing of wastes from cadmium-nickel batteries industry [1]. The extractive separation methods, however effective and selective, are troublesome in respect to the toxicity of used chemicals. For this reason there is need for elaboration of new, ecologically safe methods of Cd/Ni separation.
In the presented paper we have shown the results of cadmium and nickel adsorption on three different types of synthetic zeolites kindly delivered by Zeolyst International: AD 10N (A type), CBV 100 (Y Type), CBV 10A (mordenite). Experimental results consist of: metal adsorption isotherms, pH dependence of adsorption, ionic strength influence. It results from experiments, that there is preferential adsorption of cadmium on AD 10N zeolite. We have found the following Cd/Ni separation factors: 6.9, 30, 7.9 for pH=4.3, 6 and 6.6 respectively. It\’s interesting, that affinity of Cd toward AD 10N zeolite is higher than Ni, contrary to the ionic radius rule; Ni as small ion should be transferred better to the zeolite phase, however probably its higher hydration energy decides upon relatively (in comparison with Cd) lower distribution constant.
The shape of adsorption isotherms for Ni has sigmoidal character for three types zeolites. Using well known Langmuir-Freundlich model (with 3 adsorption sites) we found the best fit for Ni adsorption data; for Cd data we used Langmuir-Freudlich model with one adsorptive site [2].
The changes of adsorption vs. pH of the aqueous phase are nonlinear both for Cd and Ni. There is sharp increase of adsorption values for low pH, appearance of plateau in medium pH range, repeat increase and second plateau as a result of "saturation" of adsorptive sites of zeolite. The changes of distribution constants Kd vs. pH for Cd and Ni were evaluated using the model, which takes into account the ion exchange and surface hydrolysis of metals.
References
1. I. Szilassy, L. Sumeghy, K. Vadasi, Min. Pro. Extr. Met. Rev., 17 (1997) 227.
2. T. Hiemstra, W.H. Van Riemsdijk, Chemical sorption in the system soil-water-sediment, Department of Soil Science & Plant Nutrition Wageningen Agricultural University, 1996.
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