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Iranian Journal of Science & Technology, Transaction B, Engineering, Vol. 31, No. B4, pp 447-450 Printed in The Islamic Republic of Iran, 2007 Shiraz University

Research Note

LAR MOUNTAIN PHOSPHATE ORE PROCESSING USING FLOTATION APPROACH*

M. GHARABAGHI1, M. NOAPARAST**2 AND S. Z. SHAFAEI TONKABONI3 1, 2Dept. of Mining Eng., Faculty of Eng., University of Tehran, Tehran, I. R. of Iran

Email: noparast@ut.ac.ir 3Faculty of Mining and Geophysics, University of Shahrood, , I. R. of Iran

Abstract The sample of Lar Mountain Phosphate deposit which is located in the southwest of Iran, was studied to upgrade its phosphate grade. The results obtained from mineralogical studies showed the presence of apatite, CaO, Al2O3, Fe2O3 and SiO2, in which carbonate was detected as the main gangue. Two sets of direct and reverse flotation tests were performed using samples from this deposit with 10% P2O5. In phosphate flotation (direct approach), the samples were conditioned with sodium silica, oleic acid-fuel oil and Armac T-fuel oil. The direct flotation at pH=9.2 yielded a product with 23.2% of P2O5 and 75.16% recovery. The reverse flotation tests were carried out at pH=5.2, with floating carbonate and pulp de-oiling, using H2SO4 and wash water, and phosphate was then floated from siliceous gangue. In the second sets of the reverse approach, depressing the phosphate and floating silica with Amines in natural pH were done. However the best concentrate assay was 31.2% P2O5 with a 71.12% recovery, which was obtained from reverse tests.

Keywords Mineral processing, phosphate processing, flotation, Lar mountain deposit

1. INTRODUCTION

Separation of phosphate from carbonate gangues by flotation is extremely complex due to their similarities in physico-chemical and surface chemistry properties of constituent minerals. It also becomes complex because of the complicated solution generated by the formation of the dissolved salt-type minerals [1]. The difficulties encountered in the separation of calcite type impurities from phosphate minerals have been attributed to the similarities in the surface chemistry, electrokinetics and dissolution properties of these minerals. Therefore carbonate and phosphate show identical responses to anionic and cationic collectors [2].

Extensive investigation has been conducted on the treatment of natural phosphate ores containing carbonates [3, 4]. The optimum pH value for carbonate flotation is one of the key parameters to maximize carbonate recovery. Improvement on the selectivity in carbonate flotation also depends on the sense and nature of phosphate depression.

This investigation is on the application of the flotation method to process the sample from the Lar Mountain phosphate ore deposit, located in the southwest of Iran with about 81mt phosphate ore reserves. It includes a low grade phosphate ore with a high content of carbonate. Received by the editors September 25, 2006; final revised form March 4, 2007. Corresponding author

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2. MATERIALS AND METHODS To process the Lar Mountain phosphate ore, a sample with a weight of 250kg was prepared. Its complete chemical analysis is 10% P2O5, 42.1% CaO, 6.5% SiO2, 2.4% Al2O3, 3.1% FeO, 2.35% Fe2O3, 0.85% K2O, 0.5% MgO, 0.08% Cl, and 29.87% LOI. Mineralogical studies were carried out using polished and thin sections of size fractions samples. Obtained results indicated the presence of apatite, CaO, Al2O3, Fe2O3 and SiO2, in which Carbonate was detected as the main gangue. Figure 1 shows a microscope photograph of a thin section in a -0.850+0.600 mm size fraction. It also showed that the liberation size for apatite was -150 microns, and to reach the size of -150 microns, the phosphate samples were ground in a rod mill, and desliming was then performed using hydrocyclone to remove the fines at certain cut size (25 microns). Approximately 10% of slime was removed.

Fig. 1. Photo of a thin section in -0.850+0.600 mm size fraction (85)

Table 1. The results obtained from single stage direct flotation

Single stage for phosphate flotation

Tests No. Carbonate depressant Phosphate collector P2O5 (%) L.O.I (%) P2O5 Recovery

(%)

1-1 Oleic Acid-fuel oil 21.48 15.62 73.51

1-2 CMC

Armac T-Fuel oil 23.20 13.88 75.16

2-1 Oleic Acid-fuel oil 17.65 20.55 77.91

2-2 Starch

Armac T-Fuel oil 20.36 16.26 76.70

3-1 Oleic Acid-fuel oil 19.74 17.90 68.62

3-2 Sodium silicate

Armac T-Fuel oil 21.10 15.80 70.13

4-1 Oleic Acid-fuel oil 18.15 19.36 78.20

4-2 Sodium carbonate

Armac T-Fuel oil 18.50 19.78 79.54

3. EXPERIMENTAL

The flotation tests were performed in a 2-litre laboratory Denver flotation cell. In the direct flotation approach, four flotation tests were carried out for the separation of phosphate from carbonate with both Armac T-fuel oil (1.5 kg/t), and Oleic acid-fuel oil (2 kg/t) mixtures. The pH was adjusted at 9.2, the pulp

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Lar mountain phosphate ore processing,

August 2007 Iranian Journal of Science & Technology, Volume 31, Number B4

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conditioning time was 4 minutes, using sodium silica (0.3 kg/t) and then flotation was performed for 5 minutes. The obtained results are shown in Table 1.

Two stages of reverse flotation experiments were carried out. In the first stage carbonates were floated in acidic media, using Oleic acid-fuel oil at pH=5.2. In the second stage phosphate were floated from siliceous gangue, with Armac T-fuel oil and Oleic acid as the collector at pH=8.4 using NaOH as modifier. H2SO4 and H3PO4 were used as phosphate depressants in the first stage. In addition, floating siliceous gangue in natural pH and depressing phosphate minerals with CMC (carboxymethyl cellulose), was another approach which was performed. The obtained results are shown in Tables 2 and 3.

Table 2. The results obtained from reverse flotation tests

First stage (carbonate flotation) Second stage Oleic Acid-Fuel oil collector Phosphate flotation

Percent of: Percent of: Tests No. Phosphate depressant P2O5 L.O.I

Phosphate collector P2O5 L.O.I

P2O5 Rec.(%)

1-1 Oleic Acid-fuel oil 28.34 11.5 71.67

1-2 H3PO4 pH=5.2 16.80 21.34

Armac T-Fuel oil 29.46 10.87 68.8

2-1 Oleic Acid-fuel oil 28.73 11.1 69.55

2-2 H2SO4 pH=5.2 15.42 22.06

Armac T-Fuel oil 26.90 12.3 66.35

3-1 Oleic Acid-fuel oil 31.75 9.18 71.12

3-2

H2SO4 and H3PO4

pH=5.2 17.92 19.84 Armac T-Fuel oil 30.40 10.1 70.44

5-1 Oleic Acid-fuel oil 27.55 11.7 65.33

5-2

Sodium silicate pH=5.2 14.25 24.18 Armac T-Fuel oil 26.33 12.5 68.81

Table 3. The results obtained from reverse flotation

First stage (carbonate flotation) Second stage

Oleic Acid-Fuel oil collector Silica flotation

Percent of: Percent of: Tests No. Phosphate depressant P2O5 L.O.I

Silica collector P2O5 L.O.I

P2O5 Rec.(%)

1 H3PO4 pH=5.2 16.80 21.34 Amin 28.83 12.1

74.25

2 H2SO4 pH=5.2 15.42 22.06 Amin 27.68 12.25

75.63

3 H2SO4 and H3PO4 pH=5.2 17.92 19.84 Amin 29.32 11.5 77.29

5 sodium silicate pH=5.2 14.25 24.18 Amin 25.77 12.68 71.29

4. RESULTS AND DISCUSSION The direct flotation results showed that it has failed, as the grade of P2O5 in the products was up to 23.2% with a 75.16% recovery (Table 1). The main reason for these poor results could be due to the precipitation of calcium carbonate on the surface of the apatite. This surface change was probably responsible for apatite depression and decreasing phosphate recovery. It should be mentioned that the depression of

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apatite is related to its physico-chemical instability with the presence of calcite and pH decrease [5]. It should be noticed that CaHPO4 becomes more stable than apatite in the flotation system. The formation of water molecules in the aqueous CaHPO4 on the apatite surface can depress it in this process.

The first stage of reverse flotation was performed at pH=5.2, and H2SO4 and H3PO4 were used. The best results were achieved using a mixture of H2SO4 and H3PO4 and Armac T and Oleic acid. By adding H3PO4, phosphate ions from apatite are hindered owing to the selective chemisorptions of H2PO4- at the surface of apatite with the subsequent formation of (CaH2PO4)2. Then the Oleic acid was not adsorbed on the surface of apatite. At a pH of 5 to 6, the concentration of (CaH2PO4)2 will be less than CaH2PO4+ [5]. In reverse flotation, both approaches (two stages tests) yielded good results. With these approaches it is possible to produce marketable phosphate concentrate. The results obtained from the first method in reverse flotation (Table 2) are more convenient than those of the second method (Table 3). However the best concentrate assay was 31.75% P2O5 with a 71.12% recovery.

5. CONCLUSIONS The sample of Lar Mountain Phosphate deposit with 10% P2O5 was studied to upgrade the phosphate grade. The mineralogical studies showed apatite, CaO, Al2O3, Fe2O3 and SiO2. It also showed that the liberation size for apatite was -150 micron. Two direct and reverse flotation approaches were applied to this sample. In phosphate flotation (direct approach), the samples were conditioned with sodium silica, oleic acid-fuel oil and Armac T-fuel oil, respectively, at pH=9.2. The best results obtained in this step were 23.2% P2O5 and 75.16% recovery. In reverse flotation, at pH=5.2, two sets of tests were carried out, which, in the first ones, carbonate was floated, then pulp was de-oiled, using H2SO4 and wash water. Phosphate was then floated from siliceous gangue, after a brief conditioning step. The second stage was performed with depressing phosphate and floating silica with Amines at natural pH. However the best concentrate was from the second stage of reverse tests with 31.2% P2O5 and a 71.12% recovery.

REFERENCES 1. El-Shall, H., Zhang, P. & Snow, R. (1996). Comparative analysis of dolomite/francolite flotation techniques.

Minerals and Metallurgical Processing, pp. 135-140. 2. Somasundaran, P. & Zhang, L. (1999). Role of Surface Chemistry of Phosphate in Its Beneficiationin the Book

entitled of "Beneficiation of Phosphates, Advances in Research and Practice," Edited by Zhang, P., El-Shall, H., and Wiegel, R., published by Society of Mining, Metallurgy, and Exploration, Inc, pp. 141-154.

3. El-Midani, A. (2004). Separating Dolomite from phosphate rock by reactive flotation: Fundamental and application. Ph.D. Thesis, University of Florida.

4. Lawendy, T. A. B. & McClellan, G. H. (1993). Flotation of Dolomitic and calcerous phosphate ores. in the Book entitled of The beneficiation of phosphate, theory and practice, Edited by El-Shall, H., Moudgil, B.M., Wiegel, R., SME pub., pp231-243.

5. Elgillani, D. A. & Abouzeid, A. Z. M. (1993). Flotation of carbonate from phosphate ores in acidic media. International Journal of Mineral Processing, Vol. 38, No. 3-4, pp. 235-256.

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