Ind. Eng. Chem. Res. 1988,27, 594-596
594
Beneficiation of a Dolomitic Phosphate Pebble from Florida Shuang-shii Hsieh Division of Research, Tennessee Valley Authority, National Fertilizer Development Center, Muscle Shoals, Alabama 35660
A different version of the modified Crago-TVA process was developed for beneficiation of a weathered dolomitic phosphate pebble from Florida. In this process, the phosphate mineral first is concentrated with fatty acid and fuel oil in the overflow and then refloated t o remove additional coarse dolomite in the underflow. The concentrate from the cleaner flotation stage then is subjected t o conventional deoiling, but not silica flotation with amine. The remaining dolomite contaminant in the phosphate concentrate is finally floated as waste by using TVA's diphosphonic acid depressant process. At the reagent dosages of 0.5-0.75 kg/ton of fatty acid and 1.0-1.5 kg/ton of fuel oil in the phosphate flotation circuit and 0.1 kg/ton of diphosphonic acid and 1.0-1.5 kg/ton of oleic acid in the carbonate flotation circuit, a phosphate concentrate containing 29.5-30.6% P205and 0.7-1.0% MgO was obtained from a Florida dolomitic phosphate pebble, which contained about 37.2% CaO, 23.2% Pz05, 2.0% MgO, and 22.5% SiO,. T h e P,05 recovery was 82.6-90%, and the weight recovery was 60.7-67.3%. Over the last 10 years, the Tennessee Valley Authority (TVA) has conducted considerable work on the beneficiation of high-carbonate phosphate ores. During this period, several processes have been developed, including the diphosphonic acid depressant process (Lehr and Hsieh, 1981; Hsieh and Lehr, 1985a), the differential desorption-reflotation process (Hsieh and Lehr, 1984,1985b1,the modified Crago-TVA process (Hsieh, 1987a,b), and the partial deoiling process (Hsieh, 1987~). Among these processes, the modified Crago-TVA process was developed for beneficiating dolomitic phosphate ore containing coarse, weathered dolomite in flotation feed (Hsieh, 1987a,b),and the partial deoiling process was further used to reduce the reagent consumption (Hsieh, 1987~). The modified Crago-TVA process was derived from the conventional Crago-TVA process by returning the rougher float product from the fatty acid phosphate flotation stage to the flotation cell and refloating to collect the phosphate value in a cleaner stage (Hsieh, 1987a,b). In this manner, dolomitic particles carried over in the rougher flotation step are rejected along with some additional silica in the cleaner sink fraction. The subsequent steps of deoiling and silica flotation are the same as those employed in the Crago process. Residual dolomite in the silica flotation step underflow is removed by the TVA diphosphonic acid depressant process (Lehr and Hsieh, 1981; Hsieh and Lehr, 1985a,b). Recently, the concept of the modified Crago-TVA process was successfully applied to weathered dolomitic phosphate pebble from Florida. In flotation feed prepared from phosphate pebble, the SiO, content was much lower than that of regular flotation feed. Silica carried over from the rougher phosphate flotation stage was satisfactorily removed in the cleaner phosphate flotation stage. Therefore, in practicing the modified Crago-TVA process, the silica flotation stage with amine reagents can be eliminated (Figure 1). The flotation scheme in this case includes rougher phosphate flotation, cleaner phosphate flotation(s), deoiling, and carbonate flotation.
Material The dolomitic phosphate pebble sample used for the present study was obtained from a producer in Florida. The particle size distribution and chemical analysis of this pebble sample are shown in Table I. The sample contained 36.9% CaO, 22.2% P205,2.2% MgO, and 21.2% S O 2 . In this sample, the dolomitic content was particularly high in the coarser fractions, about 9.3% MgO in the
+4-mesh fraction and 5.5% MgO in the -4- to +6-mesh fraction, but only 1.0-1.1%MgO content was in the size fractions less than 8 mesh. The pebble sample was stage wet ground in a 7-in. X 14-in. Denver laboratory rod mill to prepare a -28- to +400-mesh flotation feed. This flotation feed was maintained in the wet state until used in the flotation tests. Before each flotation test, the flotation feed was scrubbed for 5 min and screened to remove -400-mesh slime. This additional procedure was intended to reduce residual slime and the possibility of an aging effect. The particle size distribution and chemical analysis of the -28- to +400-mesh flotation feed are shown in Table 11. The flotation feed contained 37.2% CaO, 23.2% Pz05, 2.0% MgO, and 22.5% Si02,which is about the same as that of the original pebble sample (Table I). Except for the -400-mesh fraction, which is higher in MgO and lower in SiO,, the size fractions do not show significant differences in chemical compositions and therefore in mineral compositions. Experiment. The simplified flotation scheme is shown in Figure 1. In bench-scale tests, a 510-g sample (dry basis) was scrubbed a t about 50% solids for 5 min and then screened to remove the -400-mesh slime fraction. The deslimed feed (about 500 g) then was processed with the conventional fatty acid flotation of the Crago process. The sample was conditioned at a pulp density of 65% solids for 2.5 min with a mixture of fatty acid (Century M05 from Union Camp; use of trade names does not constitute a TVA endorsement) and fuel oil. The pH was adjusted to about 9.1-9.4 with NaOH. After conditioning, the pulp then was diluted with tap water and floated to recover the phosphate value in the rougher float and to remove silica in the rougher sink. After the rougher phosphate flotation, the phosphate concentrate was returned to the flotation cell and diluted with tap water. The phosphate minerals were refloated, and coarse dolomite and some silica were rejected in the sink. The cleaner phosphate flotation procedure was repeated to remove additional coarse dolomite as waste. After two cleaner phosphate flotations, the phosphate concentrate was subjected to deoiling with H,SO,. No silica flotation with amine was performed because most of the free silica was removed in the rougher and cleaner flotation stages. The carbonate flotation was performed after the deoiling stage. The deoiled phosphate concentrate was conditioned a t 65% solids with hydroxyethylidenediphosphonicacid
This article not subject to U.S.Copyright. Published 1988 by the American Chemical Society
Ind. Eng. Chem. Res., Vol. 27, No. 4, 1988 595 Table I. Size and Chemical Analysis of Dolomitic Phosphate Pebble from Florida analysis, % size, mesh passing retained wt % CaO P,O, MgO SiO, 4 6 8 10 14 20
4 6 8 10 14 20
head (calcd)
5.69 5.96 12.69 21.75 30.23 16.59 7.09 100.00
36.8 38.8 39.3 41.3 36.8 34.2 24.1 36.9
13.4 19.5 22.1 25.2 23.8 22.6 15.4 22.2
9.3 5.5 3.1 1.8 1.2 1.0 1.1 2.2
11.8 14.5 13.8 15.2 21.7 27.6 49.3 21.2
CaO 5.7 6.3 13.5 24.4 30.2 15.4 4.6
100.1
Table 11. Size and Chemical Analysis of Flotation Feed PreDared bv Stage Grindin@ size, mesh analysis, % CaO Pz05 MgO SiOz passing retained wt% CaO 28 35 48 65 100 150 200 270 400
35 48 65 100 150 200 270 400
head (calcd)
16.07 27.65 17.87 13.68 8.01 6.91 4.29 3.55 1.97 100.00
37.3 37.7 37.2 35.2 35.5 37.6 38.8 39.6 39.4 37.2
23.9 23.8 23.2 21.9 22.2 23.2 24.3 24.0 21.1 23.2
1.7 1.8 2.1 2.0 2.1 2.1 2.1 2.3 4.4 2.0
24.5 21.1 22.6 25.9 25.5 20.9 18.3 16.6 12.8 22.5
16.1 28.0 17.9 13.0 7.6 7.0 4.5 3.8 2.1 100.0
distribution, % P,O, Ma0
SiO,
3.4 5.2 12.6 24.6 32.4 16.9 4.9 100.0
24 15 18 17 16 7 3 100
3.2 4.1 8.2 15.6 30.9 21.6 16.4 100.0
distribution, % MgO
SiOz
16.5 28.3 17.8 12.9 7.6 6.9 4.5 3.7 1.8 100.0
17.5 26.0 18.0 15.8 9.1 6.4 3.5 2.6 1.1 100.0
P205
14 25 19 14 8 7 5 4 4 100
Flotation feed was further deslimed at 400 mesh before each flotation test.
Table 111. Typical Example of Flotation Conditions and Results (Test 6 ) I. Operations conditioning reagent, kg/ton of starting feed operation % solid pH M05n fuel oil NaOH H,SO, deauestb phosphate flotation rougher 65 9.3 0.75 1.5 0.2 first cleaner 17 7.5 second cleaner 17 7.4 deoi1ing 50 4.6 1.5 carbonate flotation 65 5.6 0.15 11. Results analysis, % distribution, % product wt % CaO Pz05 MgO SiOz CaO P205 MgO phosphate flotation 2.5 78.4 5.1 3.3 25 9.8 3.8 rougher sink 19.30 8.8 3.2 58.0 2.7 2.2 9 first cleaner sink 5.56 18.0 second cleaner sink 3.26 25.0 13.5 3.2 43.9 2.2 2.0 5 41.6 18.7 7.2 4.3 9.3 6.9 31 carbonate float 8.32 63.56 47.2 30.3 phosphate sink 0.9 6.0 80.7 85.7 30 37.2 22.5 1.9 24.0 head 100.00 100.0 100.1 100 a
Branched-chain fatty acid.
oleic acid
1.0
SiOz 63.1 13.5 6.0 1.5 15.9 100.0
Hydroxyethylidenediphosphonic acid, 60% active content.
Figure 1. Simplified flotation process for beneficiation of dolomitic phosphate pebble from Florida.
(Dequest 2010 from Monsanto, 60% active content) for 1 min and then conditioned with oleic acid for 2.5 min. The pH a t the end of conditioning was about 5.4-5.9. No pH adjustment was performed. After conditioning, the pulp was transferred to the flotation cell and diluted with tap water. The residual carbonate mineral then was refloated as waste and the phosphate mineral recovered from the sink as product. The reagent dosages in these tests were 0.5-1.0 kg/ton of branched chain fatty acid, 1.0-2.0 kg/ton of fuel oil, 0.14-0.2 kg/ton of NaOH, 1.5 kg/ton of H8SO4,0.10-0.15 kg/ton of diphosphonic acid (60% active content), and
1.0-1.5 kg/ton of oleic acid. The reagent dosages were based on the weight of feed to the rougher phosphate flotation stage. The products analyzed by X-ray fluorescence (XRF) spectrometry included rougher sink, first and second.cleaner sinks from the phosphate flotation circuit, and the carbonate float and phosphate sink from the carbonate flotation circuit. Compositions of the head samples were calculated from the analytical results of the products.
Results and Discussion A typical example of the experimental conditions and results of the flotation tests is shown in Table 111. The first section of the table shows the operation conditions and reagent dosages, and the second section gives the results of the test. This test and other trials are further summarized in Tables IV and V. The flotation experiment can be classified into two unit operations. The first unit operation is phosphate flotation, which includes rougher phosphate flotation, first cleaner
596 Ind. Eng. Chem. Res., Vol. 27, No. 4, 1988 Table IV. Summary of Phosphate Flotation with Different Amounts of Fatty Acid and Fuel Oil' reagent, kg/ton analysis, % b no.ofteste
M05
fuel oil
4 4 4
1.0 0.75 0.50
2.0 1.5 1.0
product float float float
wt% 73.03-75.95 67.36-71.88 69.01-72.87
p2°5
27.9-29.0 29.0-29.5 28.6-29.4
Including rougher, first cleaner, and second cleaner phosphate flotation.
distribution, %
MgO
p206
MgO
1.6-1.9 1.3-1.6 1.5-1.6
94.0-95.1 89.1-92.6 88.9-93.3
63-75 48-61 54-62
By calculation.
Table V. Summary of Carbonate Flotation with Different Amounts of Diphosphonic Acid and Oleic Acid reagent, kg/ton analysis, % distribution, % no. of tests
dequest 2010
oleic acid
3
0.15
1.5
3
0.15
1.0
3
0.10
1.5
3
0.10
1.0
product float sink float sink float sink float sink
wt% 7.53-8.27 59.61-64.76 6.17-8.32 63.56-69.78 7.52-11.25 62.49-64.04 4.36-10.34 60.73-67.32
phosphate flotation, and second cleaner phosphate flotation. The second unit operation is carbonate flotation. The results of phosphate flotation (at the end of the second cleaner phosphate flotation) a t different levels of fatty acid and fuel oil dosages are summarized in Table IV. The data show that a t the reagent dosages of 0.5 kg/ton of fatty acid and 1.0 kg/ton of fuel oil, a phosphate concentrate (float) containing 28.6-29.4% Pz05 and 1.5-1.6% MgO was obtained. The P205recovery was 88.9-93.3%. The phosphate flotation results did not show significant differences when the dosages of fatty acid and fuel oil were increased to 0.75 and 1.5 kg/ton, respectively. When fatty acid was further increased to 1.0 kg/ton and fuel oil to 2.0 kg/ton, the Pz05 recovery was increased to 94.0-95.1 % . At the high dosages, the P205content in the concentrate was decreased slightly to 27.9-29.0% and the MgO content was increased to 1.6-1.9%. Based on these tests,it is concluded that a reagent consumption of 0.5-0.75 kg/ton of fatty acid and 1.0-1.5 kg/ton of fuel oil is sufficient for phosphate flotation, with a reasonable P205 recovery. The results of carbonate flotation a t different levels of diphosphonic acid and oleic acid consumption are summarized in Table V. The dosage of diphosphonic acid (60% active content) ranged from 0.1 to 0.15 kg/ton of starting feed, and the dosage of oleic acid was from 1.0 to 1.5 kg of starting feed. Since the carbonate flotation was a continuation of the phosphate flotation, the weight of sample subjected to the carbonate flotation varied from 67.37% to 75.95% of the starting feed. This constituted a maximum of 13% feed variation entering the carbonate flotation circuit. This feed weight variation, however, was not considered a significant factor in the deviation of subsequent carbonate flotation results. As shown in Table V, the experimental results indicate that about 0.1 kg/ton of diphosphonic acid was sufficient to depress the phosphate mineral and to allow dolomite to be floated with oleic acid. The appropriate amount of oleic acid used was 1.0-1.5 kg/ton of starting feed. At these reagent dosage ranges, the total P205 recovery was 82.6-90.0% and the phosphate product contained
pzo5 20.4-22.7 30.1-30.4 13.5-20.2 29.8-30.3 18.2-20.1 30.1-30.6 13.3-22.4 29.5-30.5
MgO
pzo5
MgO
5.2-6.7 0.8-1.0 6.9-9.8 0.9-1.1 6.7-7.2 0.7-0.9 5.4-9.6 0.8-1.0
7.5-7.9 81.4-86.5 3.7-6.9 85.7-92.3 6.6-10.2 84.4-86.0 2.6-8.4 82.6-90.0
22-29 26-34 27-33 30-42 28-39 24-32 21-43 26-33
29.5-30.6% Pz05and 0.7-1.0% MgO. The weight recovery was 60.73-67.32%. Conclusions These tests confirm that the concept of the modified Crago-TVA process can be applied to weathered dolomitic phosphate pebble. In this process the phosphate mineral first is concentrated with fatty acid and fuel oil in the overflow, as in the conventional Crago process, but then is refloated to remove additional coarse dolomite in the underflow. The concentrate from the cleaner flotation then is subjected to conventional deoiling. The silica flotation with amine may be eliminated because the Si02 carried over from the phosphate flotation is small. The remaining dolomite contaminant in the phosphate concentrate is finally floated as waste by using TVA's diphosphonic acid depressant process where diphosphonic acid is used as a phosphate mineral depressant and fatty acid is used as a dolomite collector. Using this method, a phosphate product containing 29.5-30.6% P205 and 0.7-1.0% MgO was obtained from a Florida dolomitic phosphate pebble, which contained about 37.2% CaO, 23.2% P205,2.0% MgO, and 22.5% SiOz. The Pz05recovery was 82.6-90.0%. The best reagent dosage ranges were 0.5-0.75 kg/ton of fatty acid and 1.0-1.5 kg/ton of fuel oil in the phosphate flotation circuit and 0.1 kg/ton of diphosphonic acid (60% active content) and 1.0-1.5 kg/ton of oleic acid in the carbonate flotation circuit. Registry No. Dolomite, 16389-88-1.
Literature Cited Hsieh, S. S. Znd. Eng. Chem. Res. 1987a, 26(7), 1413-1419. Hsieh, S. S. U.S. Patent 4636303, 1987b. Hsieh, S. S. US. Patent 4648966, 1987c. Hsieh, S. S.; Lehr, J. R. US.Patent 4486301, 1984. Hsieh, S. S.; Lehr, J. R. Miner. Metall. Process 1985a, 2(1), 10-13. Hsieh, S. S.; Lehr, J. R. Znd. Eng. Chem. Process Des. Dew. 1985b, 24(4), 937-941.
Lehr, J. R.; Hsieh, S. S. US.Patent 4287053, 1981.
Received f o r review July 20, 1987 Accepted November 30, 1987
