【正文】 with monazite and they are both recovered inthe form of a bulk concentrate as a byproduct of iron ore mining. Currently, there is aneed for further treatment of the bulk concentrate since its hydrometallurgical processinginvolves high costs due to the high content of monazite. Numerous investigations havebeen carried out pursuing a flotation scheme for selectively separating bastnaesite and monazite. Gu and Zhu 1988 reported on the flotation separation of bastnaesite and monazite using Nhydroxylphthalimade as collector. Phthalic acid in a weakly acidic. slurry was used by Zhang 1985 as a selective collector to produce a bastnaesite concentrate of 98% purity, but with only 38% recovery. Other collectors have been also remended, namely Hydroxynaphthlyl hydroxamic acid and Nhydroxyl phthalicimide Ren, 1993。 Ren et al., 1997 . Not only effective collectors, but also efficient depressants play an important role inthe flotation of rare earth minerals( Pradip and Fuerstenau, 1991 ). While searching for collectors to selectively float bastnaesite over monazite, investigations were also performed in our laboratory to find a depressant that could be used to achieve the separation between the two minerals. Of all the inanic and anic depressants 內(nèi)蒙古科技大學(xué)本科畢業(yè)論文 21 tested,potassium alum was found to be the most promising paper shows the results on the applicability of potassium alum as a depressant inthe selective flotation of bastnaesite from monazite in a rare earth bulk concentrate using benzoic acid as a collector. In addition, the methodology used to establish the flotation scheme for the separation process through studies on flotability of single particles of both bastnaesite and monazite is presented. 2. Experimental The mineral samples of bastnaesite and monazite used in this work were obtained from the Haoniuping mine and Southern rare earth mine, in China, sieving, 37 100 mm size particles were obtained for flotation tests, and y37 mm size particles for zeta potential measurements. Through this procedure, the purity of thebastnaesite and monazite samples were % and %, bastnaesite and monazite bulk concentrate, assaying % total REO, % CaO,% F and % P O , from the Baiyunebo mine, in China, was used as sample for 25flotation studies to separate bastnaesite and monazite. The concentrate, with % REOas bastnaesite and % REO as monazite, also contained % SiO and % Fe as 2martite. In order to determine the relative proportion of bastnaesite and monazite in thevarious flotation products, both the total REO content and the REO content of bastnaesite were assayed in the products. Benzoic acid used in this work was prepared in our laboratory and found to have % purity. Potassium alum (KAl (SO4)), hydrochloric acid, sodium hydroxide and octanol were all analytical grade reagents. 3. Results and discussions . Flotation of bastnaesite and monazite The effect of pH on the flotability of single particles of both bastnaesite and monazite using benzoic acid as a collector in the presence and absence of potassium alum is shown in Fig. 1. It can be noted that both minerals present flotability peaks about pH 5 in the absence of potassium alum. These results indicate that there is no selectivity between bastnaesite and monazite in the whole pH range studied if only the 內(nèi)蒙古科技大學(xué)本科畢業(yè)論文 22 collector benzoic acid is used. However, with 300 mgrl potassium alum, monazite is strongly depressed, while the flotability of bastnaesite is affected only slightly. Around pH 5, the flotability difference between the two minerals is over 60%. Clearly, potassium alum seems to be an efficient selective depressant for the separation of bastnaesite and monazite. Fig. 1. Flotability of bastnaesite and monazite as a function of pH in the presence and absence of potassium alum(KAl (SO4)) with benzoic acid as collector. The effect of potassium alum addition on the flotability of both bastnaesite and monazite with benzoic acid at pH 5 is shown in Fig. 2. These results indicate that a high dosage of potassium alum not only depressed monazite, but also bastnaesite. The flotability curve for monazite exhibits a steep slope in the low potassium alum addition。 內(nèi)蒙古科技大學(xué)本科畢業(yè)論文 23 range, whereas that for bastnaesite decreases only slightly as increasing the depressant addition in the low range before it declined sharply. There is an optimum potassium alum addition for the best selectivity in the flotation separation of bastnaesite and monazite. From the results shown in Figs. 1 and 2, it can be seen that potassium alum preferentially depresses monazite over bastnaesite in a narrow addition range at –. Potassium alum dissociates into K+,Al3+,SO2 ions and hydrolyzed aluminum species upon dissolution in water. In order to clarify which ions are responsible for the depressing effect on monazite and bastnaesite, the effect of potassium sulfate K2SO 4 and aluminum sulfate Al2（ SO4） 3on the flotation of the two minerals were investigated separately. The results shown in Fig. 3 indicate that aluminum sulfate depresses monazite and bastnaesite in the same manner as potassium alum, whereas potassium sulfate does not have a significant influence on flotation. From these results, it can be readily concluded that the depressing effect of potassium alum on monazite and bastnaesite was originated from aluminum ions and not from potassium or sulfate. However, there could be a bined effect of aluminum and sulfate ions, caused by the specific adsorption of sulfate ions . Fig. 4 depicts a diagram showing the different species resulting from hydrolysis of aluminum ions for a 104 mol/l total concentration in aqueous solution . In