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2 Beneficiation methods and Characterization. Scrubbing: each pulp prepared by different size fractions with 70% solid concentration was added into a scrubbing cell. It was stirred for 20 min with 1000 rpm. After wet attrition scrubbing, the upper layer of pulp was removed. Calcination: the ore particles with different sizes were calcinated at 950 oC for 120 min in atmosphere. Flotation: The pH value of the pulp with 100 g of ore sample was adjusted by phosphoric acid (H3PO4) to 6. 5. Then, an alkyl amine collector (signed as DAH, dosage 0. 5 kg/t) was added and pulp concentration was 20%. Whole flotation continued for 3 min. The concentrate was chemically analyzed [] M. Mahmoud, A. I. Ahmed Galal and M. A. Hassan Mohamed: Int. J. Miner. Process Vol. 83(2007).
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1 Effect of pairwise combination of different beneficiation techniques on ore grade. (1) Different ore samples treated by scrubbing first and then by calcination（S + C） The results of chemical analysis of different size fractions treated by scrubbing first and then by calcinations (S+C) are shown in Table 1. It can be clearly seen that the grades of the coarse fractions (-30+60 #, -60+80 #, -80+160 # and -160+200 #) are all higher than 30%, and the A.I. contents decrease obviously. Especially, the grade of -80+160 # is 35. 00%, and the A.I. content is 3. 39%. Compared with the chemical analysis results of untreated coarse fractions [3], it indicates that the combination of scrubbing and calcinations (S+C) can upgrade the phosphate and remove quartz effectively. For the fine fraction, the grade of -200 # fraction increases to 29%. The A.I. content decreases from 11. 12% to 10. 35%. Because of the high content of A.I. in untreated fine fraction, the scrubbing cannot remove the quartz from the -200 # fraction as effectively as from the coarse fractions. This is possible to produce more new silicates on the high temperature of the calcination in the second stage [3]. So the A.I. content decreases indistinctively. Table1Chemical analysis of different size fractions treated by scrubbing first and then by calcination Particle size interval (#) Main element concentration（w %） P2O5 A.I. -30+60.
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35 (2) Different ore samples treated by flotation first and then by calcination（F + C） For these different size fractions, the quartz is the main gangue mineral because of the higher content of A.I. than that of L.O.I. So an alkyl amine collector was used in quartz reverse flotation. The results of chemical analysis of different size fractions treated by flotation first and then by calcinations (F+C) are shown in Table 2. The grades of the coarse fractions (-30+60 #, -60+80 #, -80+160 # and -160+200 #) are all higher than 30%. These results are better than those in Table 1. Especially, the grades of -60+80 # and -80+160 # are 34. 73% and 35. 43%. The A.I. contents decrease obviously too. Compared with the results in Table 1, the grade of -200 # fraction processed by flotation first and then by calcination is still below 30%, but the A.I. content decreases from 11. 12% to 5. 14%, which is lower than that in Table 2. This indicates that the combination of flotation and calcination (F+C) can upgrade the phosphate and remove quartz more effectively than the combination of scrubbing and calcination (S+C). The results shown in Table 1 and 2 are better than those treated by one beneficiation method obtained in the first phase of work [3]. It indicates that P2O5 grade of different size fractions is increased obviously by combination beneficiation techniques, especially, by flotation first and then by calcination (F+C). For the fine -200 # fraction, ordinary scrubbing, calcination or single flotation process conditions cannot improve its grade to 30%. It may be upgraded more availably by investigating feasible double reverse flotation conditions to separate the calcite and quartz. This is the focus of our further research. Table 2 Chemical analysis of different size fractions treated by flotation first and then by calcination Particle size interval (#) Main element concentration（w %） P2O5 A.I. -30+60.
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2 Results of Scanning electron microscope. It can be seen that, after scrubbing treatment, the surface of the large size particle is apparently clean because of the amount reduction of ultrafine particulates (Fig. 3 (a). Figure 1 (b) shows that the surface characteristics of -200 # and -80+160 # fractions treated by calcination are different from those treated by scrubbing. And they are also different from each other. It is perhaps due to the differences of chemical composition analysis between untreated -200 # and -80+160 # fractions. (a) -200 # after the scrubbing (×5000) -80+160 # after the scrubbing (×5000) (b)-200 # fraction treated by calcination(×10000) -80+160 # fraction treated by calcination(×10000) Figure 1 SEM images of different samples Summary Effects of pairwise combination of three beneficiation techniques on chemical composition content of different size fractions of a siliceous-calcareous phosphate ore are investigated. The grades of the coarse fractions processed by scrubbing or flotation first and then by calcination are all improved and higher than 30%. The grade of -80+160 # can be up to 35. 43%. And the A.I. contents decrease obviously. Especially, the A.I. content of the fine fraction processed by flotation first and then by calcination decreases from 11. 12% to 5. 14%, which is lower than that processed by scrubbing first and then by calcination about 5%. The SEM images indicate that scrubbing can effectively remove the ultrafine particulates. With the calcination treatment, the surface characteristics of the fine fraction are different from those of the coarse fraction, which are also different from those treated by scrubbing. Acknowledgements This work was financially supported by the National Natural Science Foundation (21206202), the Scientific and Technological Project of Chongqing (CSTC, 2011AC4124), the Project Foundation of Chongqing Municipal Education Committee (KJ120806) , the Basic & Frontier Research Foundation of Chongqing（cstc2013jcyjA50002）and Youth Core Teachers' Scheme of Colleges and Universities of Chongqing. References.
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