Ion Exchange Adsorption of Molybdenum with Zeolitic Adsorbent

Zeolitic adsorbents have been developed for molybdenum recovery from various sources. The batchwise adsorption ability of molybdenum ion (Mo) with zeolite A type adsorbent could be improved when the counter cation (Na) was exchanged by divalent ions (Sr and Ca), while no significant difference was observed in the case of zeolite X type adsorbent. The adsorption ability for Mo was therefore based on the pore size and cation exchange capacity of the zeolitic adsorbents. The column operations were also conducted with the granulated zeolitic adsorbents, to achieve the quantitative adsorption-elution processing of Mo. *Corresponding author Email: [email protected] INTRODUCTION The demand for rare metals has been increasing in recent years, and thus the separation and recovery of the rare metals are still active issues. Recycle of rare metals from various wastes, such as electric appliances and automobile catalysts, are especially quite important issues for establishing a sound materialcycle society. Among the several recovery technologies of rare metals, ion exchange adsorption is one of the most effective methods and is quite green process. Most of ion exchangers are based on the polymer matrix immobilizing various functional groups for uptake of metal ions. Also, inorganic adsorbent has been paid more attention, due to both separation ability and physical properties such as resistance against heat and radioactive irradiation [1-3]. Molybdenum (Mo) is one of the rare metals used for additive of ferrous alloys based on the nature of melleabil and ductil. Mo is also included in high level liquid waste (HLLW) solution of spent nuclear fuel. The separation and recovery of Mo from HLLW is required for nuclear fuel cycle process, since the solubility of Mo for vitrification is quite low. There are two ways for the hydrometallurgical separation of molybdenum ion (Mo) in the aqueous solution: solvent extraction [4] and ion exchange [5-7]. In case of solvent extraction, acidic organophosphorus compounds, such as bis(2-ethylhexyl)phosphoric acid and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, were occasionally employed as extractants [8-10], and effective extraction of Mo from acid solution could be achieved. In case of ion exchange, anion exchange method was mostly applied, since molybdenum mainly exists as anionic species in the aqueous solution [11]. The cation exchange adsorption is also expected to be available in the acidic region where Mo exists as cationic species, as well as solvent extraction system, though there are few reports. Zeolite is the crystalline alumino-silicate, mainly based on SiO2 and Al2O3, and possesses molecular sieve property due to its regulated pore size. The zeolite has thus been used for the separation of gas components. Zeolite A and zeolite X have been also used for the water softening, since these possesses high cation exchange abilities for Ca and Mg. Recently, the zeolite has been attempted to be applied as the cation exchange adsorbent for heavy metals, especially in the field of nuclear fuel cycle [2,12], indicating the zeolitic adsorbents possess high adsorption ability for various heavy metals in HLLW. In the present work, cation exchange adsorption of Mo with zeolitic adsorbents has been investigated, as a fundamental investigation for the recovery of Mo from the solution of hydrometallurgical recycle process of catalysts and also HLLW in nuclear fuel cycle process. Zeolite A and zeolite X were prepared by hydrothZZermal synthesis, and were characterized with X-ray diffraction (XRD) and filed emission scanning electron microscope (FE-SEM). The zeolitic 366 J. Environ. Eng. Manage., 19(6), 365-369 (2009) adsorbents were then applied for evaluating the adsorption of Mo using batchwise and column operation.