The active facilitated transport and separation of cobalt in mixed solution of cobalt and nickel sulfate were studied using hollow-fiber supported liquid membrane (HF-SLM). The HF-SLM contained 2-ethylhexylphosphonic acid mono-2 ethylhexyl ester [HEH(EHP)], which was diluted in kerosene as a carrier. The permeation rates and separation factors were found to be dependent on the operational variables such as the 1519 ORDER REPRINTS concentrations of metal and hydrogen ions in the feed solution, the carrier concentration in the liquid membrane, and the flow rate of feed solution. The permeation rate of cobalt was 10 26 -10 27 mol/m 2 s and the separation factor of Co/Ni was 10 -220 under the experimental conditions. By recirculating the strip solution, a tenfold enrichment of cobalt was possible and cobalt with 95% purity was recovered from the low concentration solution in which the concentrations of both cobalt and nickel were 17 mol/m 3 .

PACS 72.15.Eb, 75.20.Ck, 75.47.Pq, 75.50.Gg Mn-Zn ferrites among iron oxide magnetic materials are widely used for high frequency magnetic core materials because they have low power loss and high initial permeability up to several MHz range. In this paper, the small amount of Nb 2 O 5 and TiO 2 were added to the Mn-Zn ferrites to study their effects on electrical and magnetic properties of the Mn-Zn ferrites. The amount of Nb 2 O 5 and TiO 2 was in the range of 0 ~0.02 wt% and 0-0.6 wt% respectively. The effects of additives were studied in view of change in core loss, maximum flux density, specific resistivity, inductance and permeability. Adding both TiO 2 (0.6wt%) and Nb 2 O 5 (0.01wt %), the core loss was lowest. It was decreased to 50% at 500 kHz. In this case, the maximum flux density was depressed by only 2%. This means that the additives could drastically decrease the minimum core loss with penalty of a little decrease in magnetic flux density. IntroductionIn general, the core loss of magnetic core materials increases when they are used at high frequency. This fact limits the efficiency of magnetic core materials. This requires the development of iron oxide magnetic materials with low core loss. For transformers, especially, magnetic core materials with high magnetic flux density, high initial permeability and low core loss are essential. Mn-Zn ferrites among iron oxide magnetic materials are used for high frequency magnetic core materials because they have relatively low power loss and high permeability up to several MHz [1]. However, their magnetic characteristics such as core loss are not good enough for high frequency operation. To improve electro-magnetic properties of Mn-Zn ferrites, many researchers tried to add additives to them. There are three approaches for these additives. First one is to segregate additives on grain boundaries to increase electrical resistance. It was known that core loss decreased adding Nb 2 O 5 up to 0.03 wt % to Mn-Zn ferrites. By precipitation along grain boundaries, core loss was decreased by 30% at 100 kHz/100 mT compared to the Mn-Zn ferrites without additives. Other additives such as V 2 O 5 , B 2 O 3 , SiO 2 and ZrO were also reported to decrease the core loss [2]. Second one is to form solid solution and then improve magnetic characteristics. Additives such as TiO 2 , SnO 2 , Al 2 O 3 , CoO and MgO were tried for this purpose [3,4]. Third one is to form liquid phase and then enhance grain growth. Additives such as Bi 2 O 3 and In 2 O 3 were used for this purpose [5]. As mentioned above, one additive was used for each case. It will also be very interesting to add two additives simultaneously. Therefore, in this paper, the additive effects of both TiO 2 and Nb 2 O 5 on electromagnetic properties of Mn-Zn ferrites were investigated.

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