Pyrite removal from several clays by high gradient magnetic separation (HGMS) method was investigated. Effects of magnetic susceptibility (MS) values of pyrite and clays, and operation conditions on the pyrite removal were studied. Following results are discussed.
(1) MS values of pyrite in the Itaya clay A and Sendatsu clay C were 1.01×10^-6 emu/g and 0.64×10^-6 emu/g, respectively. In spite of their low SM values, pyrite particles could be separated from clays by HGMS method because of their large particle size.
(2) Efficiency of pyrite removal from clays were mainly dependent on the MS values of origin clays, and the good results were naturally obtained for low value clays. Pyrite removal from Itaya clay D (MS =0.08×10^-6 emu/g), Itaya clay A (MS =0.63×10^-6emu/g) and Sendatsu clay C (MS =1.91×10^-6emu/g) was examined under the following condition ; matrix : FW, magnetic field strength : 14.5 kG and linear velocity : 38.4 m/hr. The XRD peak intensities of pyrite (200) in the N-mag clays were 0 cps, 10 cps and 45 cps for Itaya clay D, Itaya clay A and Sendatsu clay C, and their Fe₂O₃ content were 0.34 wt.%, 0.54 wt.% and 1.92 wt.% respectively.
(3) Good results for pyrite removal from Itaya clay A by HGMS method were obtained at the high magnetic field strength (9.7-14.5 kG) and rather low linear velocity (22.1-38.4 m/hr). The matrix FW was best suitable for the pyrite removal.
(4) By treating of Itaya clay A at 14.5 kG and 22.1 m/hr with matrix FW, whiteness increased from 80.5 to 87.4 with decreasing Fe₂O₃ content from 1.46 wt.% to 0.38 wt.%, and N-mag clay yield was 89.00.
(5) Also titanium oxide was easily removed from clays under the HGMS conditions which pyrite removal from clays resulted in good success.

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In this study, the floatability of xenotime was examined using some kinds of collectors.
First of all, electrokinetic property and flotation behaviour of xenotime were considered in the presence of sodium oleate. Electrophoresis data indicate zpc of 6.5 without sodium oleate, but zpc in presence of sodium oleate indicates negative charge all over the pH ranges. From Hallimond tube flotation tests with sodium oleate, floatability of xenotime revealed maximum values at both pHs of 3 to 4 and 7 to 8. On the other hand, floatability of xenotime at pH of 4 to 7 was very poor. The authors discussed concerning the depression phenomenon of xenotime at pH of 4 to 7 from the point of view of ionic equilibrium. From logarithmic concentration diagram, we pointed out that it was caused by the formation of mono-and poly-hydroxide complexes. Besides sodium oleate, the effects of sodium dodecylsulphate and sodium dodecylbenzene-sulphonate as anionic collectors was also examined on the floatability of xenotime as a function of pH.
Secondly, the effect of dodecylammonium acetate as a cationic collector was considered from a series of electrophoresis measurement and Hallimond tube test. The maximum floatability of xenotime in the presence of dodecyl-ammonium acetate occurred at pH of 10.5 to 12. In the case of use of amine collector, it was found that such phosphate ion as polyvalent cation played the role of surface active ion.

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