Beneficiation of Dolomitic Phosphate Ores Using Modified Crago-TVA

Znd. Eng. Chem. Res. 1987,26, 1413-1419

1413

Beneficiation of Dolomitic Phosphate Ores Using Modified Crago-TVA Process S. S. Hsieh Division of Research, National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama 35660

A modified Crago-TVA process has been developed for beneficiating dolomitic phosphate ore containing coarse, weathered dolomite in the flotation feed. In this process, the phosphate mineral first is concentrated with fatty acid and fuel oil in the overflow, in the conventional Crago process, but then is refloated to remove additional coarse dolomite in the underflow. Subsequently, the concentrate is subjected to the conventional deoiling and silica flotation. The remaining dolomite in the phosphate concentrate then is 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. By use of this method, phosphate concentrates containing 31-33% P205 and 0.7-1.0% MgO were obtained from flotation feeds containing 8.1-9.5% Pz05 and 1.5-2.6% MgO. The P205 recoveries were 77-80%. In current beneficiation practices, the Crago “doublefloat” froth flotation process is widely used for commercial phosphate ores that contain silica and silicates as the principal gangue minerals (Hoppe, 1976). Generally, the double-float process is ineffective for beneficiating phosphate ores containing carbonate minerals because the fatty acid collectors used to float the phosphate mineral also collect carbonate minerals. This necessitates the use of a depressant for either the phosphate or carbonate mineral to achieve selectivity. Notable examples include the use of phosphoric acid or its salts (Bushell et al., 1969; Bushell and Hirsch, 1969; Ratobylskaya et al., 1975), aluminum sulfate-tartrate complex (Smani et al., 1975),or fluosilicic acid (Rule et al., 1974, 1975, 1978). Alternative processes use other collectors such as amines (Snow, 1979; Lawver et al., 1980), N-substituted sarcosine (Kiukkola, 19801, or sulfonated fatty acids (Snow, 1982; Lawver et al., 1983) for the flotation recovery of satisfactory phosphate products. Recently some unconventional approaches, such as twostage conditioning (Moudgil and Chanchani, 1985) and surface modification treatment with copper and sulfide (Mair and Soroczak, 1986), also have been proposed. The diphosphonic acid depressant process has been developed at the Tennessee Valley Authority (TVA) to beneficiate the dolomitic phosphate ores (Lehr and Hsieh, 1981). The process used diphosphonic acid as a phosphate mineral depressant and fatty acid as a dolomite collector to remove dolomite from the overflow and recover the phosphate value in the underflow. The process can be performed either before or after the separation of siliceous matter from phosphate minerals by current beneficiation methods (Lehr and Hsieh, 1981). The process has been evaluated on western US. dolomitic phosphate ores (Hsieh and Lehr, 1985). The results indicate that concentrates containing 31-33% P205and 1%or less MgO can be obtained from flotation feed containing 21-26% Pz05and 1.8-3.2% MgO, with about 80% P205recovery. Some phosphate ores, such as those found in the Southern Extension of central Florida, contain relatively coarse, weathered dolomite in the flotation feed. When this occurs, a phosphate concentrate having satisfactory grade and MgO content may not be obtained with reasonable recovery efficiency by using the conventional Crago process followed by TVA’s diphosphonic acid depressant process. The reason for this is that the coarse, weathered dolomite carried over from the phosphate rougher flotation stage usually is difficult to float in the subsequent carbo-

nate flotation stage. The difficult-to-float coarse dolomite particles also have been observed by other investigators (Lawver et al., 1982). Therefore, a different flotation scheme known as the modified Crago-TVA process was developed by TVA for beneficiating this particular type of dolomitic phosphate ore.

Materials The dolomitic phosphate samples used for the present study were obtained from a Florida phosphate producer. The samples were the regular flotation feeds, -28 to +150 mesh in size, prepared by the producer. The materials were maintained in the wet state until used in the flotation trials. Before each flotation test, the flotation feed was scrubbed for 10 min and screened to remove -400-mesh slime. This additional procedure was intended to eliminate residual slime and any possibility of an aging effect. The particle size distribution and chemical analysis of the flotation feeds after scrubbing and desliming are shown in Tables I and 11. The first sample (BL-47) consisted of 3.8% +28-mesh, 9.6% -28-mesh to +35-mesh, 82.9% -35-mesh to +150-mesh, and 3.7% -150-mesh fractions. Chemically it contained 17.6% CaO, 9.5% P205,2.6% MgO, and 58.1% SO2. The mineral composition in the BL-47 sample varied significantly at different size fractions. The dolomite content was particularly high in the +35-mesh and -150mesh fractions. These fractions consisted of more than 6% MgO, while the -48-mesh to +150-mesh fraction consisted of less than 2% MgO. The slime-size dolomite can be removed easily by desliming and/or flotation. However, coarse dolomitic particles were difficult to float in the carbonate flotation circuit, as observed in the present study. The -150-mesh fraction also contained a significant amount of iron-bearing minerals (about 7.5% Fe203). Because of scrubbing and desliming prior to the flotation tests, no noticeable adverse effect had been observed during the flotation study. The second flotation feed (BL-48) obtained from the same commercial source had a lower content of dolomite and phosphate minerals but more silica than the first sample (BL-47); it contained 14.5% CaO, 8.1% P205, 65.4% SO2, and 1.5% MgO. The feed contained 3.5% +28-mesh material and 6.0% below 150 mesh; the bulk of the sample (-71%) fell in the -35-mesh to +100-mesh size range. The mineral composition of the screen fractions

This article not subject to U.S. Copyright. Published 1987 by the American Chemical Society

1414 Ind. Eng. Chem. Res., Vol. 26, No. 7, 1987 Table I. Size and Chemical Analysis of BL-47 Flotation Feed" size, mesh analysis, % passing retained wt % CaO P2O5 MgO SiOz Fez03 8.8 22.5 12.2 1.2 28 3.81 32.8 9.57 24.5 11.4 5.8 40.7 0.9 28 35 9.9 35 48 21.09 18.4 2.7 57.3 0.9 30.30 14.3 8.1 68.3 1.3 0.9 48 65 24.55 17.7 11.3 1.5 58.1 1.1 65 100 100 150 6.97 12.8 6.5 2.0 65.0 2.6 150 3.71 14.2 2.8 6.0 48.4 7.5 head (calcd) 100.00 17.6 9.5 2.6 58.1 1.3 a

A1203

0.4 0.3 0.4 0.5 0.7 0.6 0.6 0.5

CaO 7.1 13.3 22.1 24.7 24.7 5.1 3.0 100.0

distribution, % MgO SiOz Fez03 5.3 13 1.5 3 11.5 22 6.7 7 22.1 22 20.8 14 25.9 15 35.6 21 29.3 14 24.5 21 4.8 5 7.8 13 1.1 9 3.1 21 100.0 100 100.0 100

CaO 7.8 12.7 23.4 25.6 21.9 6.1 1.7 0.7 99.9

distribution, % SiOz FezOn 7.0 12 1.4 3 12.0 17 6.2 5 23.5 21 19.3 12 26.8 20 29.3 ia 23.6 14 24.1 18 5.8 8 13.1 17 1.0 5 5.8 ia 0.3 3 0.9 9 100.0 100 100.1 100

PzO5

A1203 3 6 16 29 33 9 4

100

After scrubbing and desliming.

Table 11. Size and Chemical Analysis of BL-48 Flotation Feed" size, mesh analysis. % MgO SiOz Fe203 passing retained wt % CaO p2°5 3.45 32.6 28 16.4 5.5 26.1 0.9 8.40 21.9 11.5 3.2 48.3 0.7 2a 35 9.5 1.6 63.1 0.7 20.03 16.9 35 4a 1.1 68.8 7.8 0.8 27.81 13.3 48 65 23.25 13.6 8.2 0.9 0.9 67.7 65 100 4.2 11.0s 8.0 1.1 77.3 1.a 100 150 4.85 5.2 1.6 78.2 1.7 4.6 150 200 2.3 1.12 9.2 4.7 53.0 9.8 200 14.5 99.99 a. 1 1.5 65.4 1.2 head (calcd)

" After scrubbing

A1203

0.6 0.7 0.7 0.8 1.0 1.0 0.9 1.0 0.8

P,Os MgO

A1,0, 2 7 16 2a 2a 13 5 1 100

and desliming.

Table 111. Flotation Conditions and Results for BL-47 Sample-Example 1 I. Operations, 500-g Starting Feed conditioning reagent, kg/ton of starting feed operation % solid pH M05" fuel oil NaOH HZS04 amineb dequest' phosphate flotation rougher 65 9.5 0.5 1.0 0.1 25 5.4 0.75 deoi1ing 7 7.3 silica flotation 0.15 35 6.5 carbonate flotation 0.02 0.1 11. Results analysis, % distribution, '70 product wt% CaO P205 MgO Si02 CaO P205 MgO phosphate flotation 4.8 61.46 1.1 2.0 rougher sink 85.8 16.5 6.8 54 silica float 7.17 6.3 3.4 1.7 74.6 2.5 2.5 5 2.22 28.2 4.4 13.9 0.2 3.5 1.0 carbonate float 14 29.15 47.4 30.3 77.4 89.7 27 2.1 4.6 phosphate sink 100.00 17.8 9.8 2.3 99.9 100.0 head 59.4 100 a Branched-chain fatty acid from Union Camp Corp. content.

* Dodecylamine hydrochloride.

varied significantly, as also was the case with the BL-47 sample. The dolomite content was high in the +35-mesh and -150-mesh fractions. These fractions consisted of 3.2-5.5% MgO, while size fractions between 48 and 150 mesh consisted of 0.9-1.6% MgO. Beneficiation with Crago-TVA Process. The BL-47 sample was evaluated with the Crago-TVA process. Because the sample contained a large amount of silica (60%), it was preferable to first concentrate the phosphate value by using conventional techniques such as the Crago double-float process. The dolomite impurity then was removed by using the TVA diphosphonic acid depressant process. The simplified Crago-TVA process is shown in Figure 1. In bench-scale tests a 520-g sample (dry basis) was scrubbed at about 50% solids for 10 min and then screened to remove the -400-mesh slime fraction (about 4%). The deslimed feed (about 500 g) then was processed with the conventional Crago double-float process. The sample was conditioned a t a pulp density of 65% solids for 2.5 min with a mixture of fatty acid (M05, a branched-chain fatty

oleic acid

0.5

SiOz 88.7 9.0 0.0 2.3 100.0

Hydroxyethylidenediphosphonicacid, 60% active

acid from Union Camp Corporation, Wayne, NJ) and fuel oil (use of trade names does not constitute a TVA endorsement). The pH was adjusted to about 9.5 with NaOH. The pulp then was diluted with tap water and floated to recover the phosphate value in the rougher float and remove silica in the rougher sink. After the deoiling stage with H2S04,additional silica was removed as float with amine, and the phosphate value (with the carbonate mineral impurities) remained in the sink. The phosphate concentrate containing the carbonate mineral impurities from the Crago process was treated further with the TVA diphosphonic acid depressant method. The sample first was conditioned with diphosphonic acid (Dequest 2010, obtained from Monsanto Industrial Chemical Company, St. Louis, MO) for 1 min and then with oleic acid for 2.5 min. The pH was adjusted to about 6.5 with NaOH. The carbonate minerals then were refloated as waste, and the phosphate mineral remained in the sink as concentrate. The detailed specific flotation conditions and their results with the Crago-TVA process are shown in Tables

Ind. Eng. Chem. Res., Vol. 26, No. 7, 1987 1415 Table IV. Flotation Conditions and Results for BL-47Sample-Example 2 I. Operations, 500-g Starting Feed reagent, kg/ton of starting feed conditioning operation % solid pH M05' fuel oil NaOH H2S04 amineb dequestc phosphate flotation rougher 65 9.4 0.5 1.0 0.1 25 5.4 0.75 deoiling 0.15 silica flotation 7 7.2 carbonate flotation 35 6.4 0.03 0.1 11. Results analysis, % distribution, % product wt% CaO P205 MgO SiOz CaO pzo5 MgO phosphate flotation rougher sink 61.27 4.2 0.9 2.0 86.9 14.7 5.8 53 6.3 silica float 8.31 12.2 1.9 65.5 5.8 5.5 7 39.5 18.8 7.4 3.2 14.2 carbonate float 6.28 12.4 20 47.3 30.0 1.9 5.6 65.3 76.3 20 phosphate sink 24.14 head 100.00 17.5 9.5 2.3 60.2 100.0 100.0 100 a Branched-chain fatty acid from Union Camp Corp. content.


Dodecylamine hydrochloride.

111-V. Each table represents one series of tests. The first part of the table shows the operation conditions and reagent dosage, and the second part shows the results of the test. In these experiments the operation conditions and reagent dosage were the same from the phosphate flotation to the silica flotation (Crago process). The main difference was in the carbonate flotation (TVA process), in which the dosage of oleic acid was increased from 0.5 kg/ton in example 1 (Table 111)to 1.0 kg/ton in example 2 (Table IV) and to 1.6 kg/ton in example 3 (Table V). The dosage of diphosphonic acid remained the same at 0.1 kg/ ton. As shown in Tables 111-V, the data indicate that a phosphate concentrate having satisfactory P205grade and MgO content cannot be obtained with reasonable recovery efficiency using the conventional Crago process, followed by TVAs diphosphonic acid flotation step. The coarse, weathered dolomite carried over from the phosphate rougher flotation was difficult to float in the carbonate flotation stage (TVA process). For example, at the highest P205recovery efficiency (89.7%, Table 1111, the phosphate conceritrate contained 30.3 % P205,but the MgO conteht (2.1%) was unacceptable. Allowing the phosphate recovery efficiency to decrease to -72% (Table V) to optimize dolomite separation did not yield the satisfactory concentrate; the MgO content was reduced somewhat to a

1.0

SiOl 88.4 9.1 0.3 2.2 100.0

Hydroxyethylidenediphosphonic acid, 60% active

Table V. Flotation Conditions and Resblts for BL-47Sample-Example 3 I. Operations, 500-g Starting Feed conditioning reagent, kg/ton of starting feed operation % solid pH M05" fuel oil NaOH H,SOa amineb deauestc phosphate flotation rougher 65 9.4 0.5 1.0 0.1 deoiling 25 5.3 0.75 0.15 silica flotation 7 7.2 carbonate flotation 35 6.4 0.04 0.1 11. Results analysis, % distribution, % product wt% CaO p,o, Ma0 SiO, CaO P,O, MEO phosphate flotation 2.1 84.8 18.1 9.0 rougher sink 62.19 5.2 1.4 57 3.5 3.2 7.39 7.8 2.0 72.6 2.7 6 silica float 7.93 41.1 20.5 carbonate float 6.5 2.5 18.2 16.7 22 48.1 30.9 1.5 5.8 60.5 71.6 15 phosphate sink 22.49 100.0 17.9 9.7 2.3 59.6 100.0 100 head 100.00 Branched-chain fatty acid from Union Camp Corp. content.

oleic acid

oleic acid

1.5

SiO, 88.5 9.0 0.3 2.2 100.0


-

FEED

I FATTY ACID FUEL OIL NoOH

ROUGHER PHOSPHATE FLOTATION FLOAT

WASTE CONVENTIONAL CRAG0 PROCESS

AMINE

FLOTATION

WASTE

-

4

DIPHOSPHONIC ACID FATTY ACID

CARBONATE FLOTATION

FLOAT CARBONAT[

rvds

CARBONATE SEPARATION PROCESS

si""

PHOSPHATE CONCENTRATE

-

Figure 1. Beneficiation of dolomitic phosphate rock with CragoTVA process.

1416 Ind. Eng. Chem. Res., Vol. 26, No. 7 , 1987 Table VI. Flotation Conditions and Results for BL-47 Sample-Example 4 I. Operations, 500-g Starting Feed reagent, kg/ton of starting feed conditioning operation % solid pH M05” fuel oil NaOH H2S04 amineb dequestc phosphate flotation rougher 65 9.6 0.5 1.0 0.1 cleaner 8.6 0.75 25 5.3 deoi1ing 0.15 7.2 silica flotation 0.02 0.1 carbonate flotation 35 6.1 11. Results analvsis. 5% distribution. % vroduct wt % CaO P,oq Ma0 SiO, CaO P20, MgO phosphate flotation rougher sink 62.89 4.4 1.0 1.9 86.6 15.8 6.7 54 5.8 38.0 13.8 11.0 25 25.2 10.9 cleaner sink 9.54 3 1.5 1.4 5.4 2.3 60.9 2.40 11.3 silica float 4.5 3.2 10 34.6 13.2 9.7 3.0 carbonate float 2.26 0.8 5.4 64.4 77.7 49.1 31.9 8 phosphate sink 22.91 100.0 100.0 100 9.4 2.2 60.9 100.00 17.5 head

oleic acid

T

~

0.5

~~~

“

Branched-chain fatty acid from Union Camp Corp. content. (I

I


SiO, 89.5 6.0 2.4 0.1 2.0 100.0


Table VII. Flotation Conditions and Results for BL-47 SamDle-Examde 5 I. Operations, 500-g Starting Feed reagent, kg/ton of starting feed conditioning overation % solid pH M05” fuel oil NaOH H2SOa amineb dequestc phosphate flotation rougher 65 9.5 0.5 1.0 0.1 cleaner 8.6 0.75 deoiling 25 5.5 ” 0.15 7.4 silica flotation 0.03 0.1 carbonate flotation 35 6.6 11. Results analysis, % distribution, ?6 wt 70 CaO P206 MgO SiOz CaO p205 MgO product phosphate flotation rougher sink 62.35 4.7 1.3 2.2 85.9 16.9 8.6 58 5.5 42.4 11.9 9.0 22.5 9.3 21 9.16 cleaner sink 70.7 1.2 1.0 3.9 1.9 2 2.48 8.3 silica float 8.5 12.2 2.8 1.87 30.0 3.2 1.7 10 carbonate float 47.9 31.2 0.9 5.3 66.8 9 24.14 79.7 phosphate sink 100.00 17.3 9.4 2.4 60.5 100.0 100.0 100 head ~~~~~

a Branched-chain fatty acid from Union Camp Corp. content.


level of 1.5%. Therefore, a modified process, namely the “modified Crago-TVA process”, was developed further to beneficiate this and other similar types of phosphate ores which contain coarse, weathered dolomite in the flotation feed. Beneficiation with Modified Crago-TVA Process. The simplified flowsheet of the modified Crago-TVA process is shown in Figure 2. The modified process was derived from the 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. In this manner, the coarse dolomite particles, along with silica and some phosphate, then were removed in the sink as waste. The subsequent steps of deoiling, silica flotation, and carbonate flotation were the same as those in the Crago-TVA process. This cleaner flotation step, even though simple in theory and practice, was the crucial step for the later carbonate flotation because the coarse dolomite, typically difficult to float, was essentially removed in this extra step. Three series of flotation tests with the BL-47 sample were performed by using this modified Crago-TVA process. The first series of tests used 500-g samples as starting feed. The tests were intended to evaluate whether an

oleic acid

0.5

SiOz 80.5 6.4 2.9 0.1 2.1 100.0

Hydroxyethylidenediphosphonicacid, 60% active

acceptable phosphate concentrate could be obtained. In the second and third series of tests, the starting feeds were increased to 1000 and 2000 g, respectively. The tests more accurately reflected the reagent consumption in the carbonate flotation circuit because about 250- and 500-g samples, respectively, went into the carbonate flotation circuit, as compared to about 125-g samples when 500 g of starting feed was used. The first series of tests is shown in Tables VI and VII. The test results show that a phosphate concentrate containing 31-32% P205 and 0.8-0.9% MgO can be obtained, with a P205recovery of about 7840%. The best conditioning pH to achieve these results in the carbonate flotation circuit was about 6.6 or slightly lower. These flotation results are quite satisfactory and contrast sharply with those obtained by the Crago-TVA process, in which the phosphate concentrate still contained 1.5% MgO with a phosphate recovery of only 71.6% Pz05(Table V). The reagent consumption, based on 500 g of starting feed, was 0.5 kg/ton fatty acid, 1.0 kgjton fuel oil, 0.12 kgjton NaOH, 0.75 kg/ton H2SQ4,0.15 kgjton amine, 0.1 kg/ton diphosphonic acid (60% active content), and 0.5 kgjton oleic acid. The experimental results using 1OOO- and 2OOO-g samples

Ind. Eng. Chem. Res., Vol. 26, No. 7 , 1987 1417 Table VIII. Flotation Conditions and Results for BL-47 Sample-Example 6 I. Operations, 1000-g Starting Feed conditioning reagent, kg/ton of starting feed operation % solid pH M05" fuel oil NaOH H2S04 amineb dequestc phosphate flotation rougher 65 9.6 0.5 1.0 0.1 cleaner 8.7 50 5.5 0.38 deoi1ing 12 7.5 0.075 silica flotation 65 6.6 carbonate flotation 0.015 0.075 11. Results analysis, % distribution, % product wt % CaO P,O, Me0 SiO, CaO P,O, Me0 phosphate flotation 16.5 4.8 1.1 2.3 84.3 6.8 56 rougher sink 60.43 14.7 11.1 26 11.44 22.6 9.5 5.6 22.6 cleaner sink 2.4 3.00 14.0 2.1 3 silica float 6.8 2.6 55.5 2.20 35.5 14.5 8.8 4.0 4.4 3.2 8 carbonate float 7 22.93 47.5 62.0 76.8 phosphate sink 32.8 0.8 2.8 100.00 17.6 100.0 100.0 100 9.8 2.5 59.6 head

" Branched-chain fatty acid from Union Camp Corp. content.


e Hydroxyethylidenediphosphonic

Table IX. Flotation Conditions and Results for BL-47 Sample-Example 7 I. Operations, 2000-g Starting Feed conditioning reagent, kg/ton of starting feed operation % solid pH M05" fuel oil NaOH HpS04 amineb dequeste phosphate flotation rougher 65 9.6 0.5 1.0 0.1 8.6 c1eaner 65 5.6 0.25 deoi1ing 22 7.6 0.038 silica flotation 65 6.8 carbonate flotation 0.008 0.038 11. Results analysis, % distribution, 90 product wt% CaO P,OS Me0 SiO, CaO P,O, Me0 phosphate flotation 61.84 4.0 1.0 2.0 84.8 14.6 6.4 54 rougher sink 10.42 23.4 10.5 5.6 38.9 14.4 11,3 26 cIeaner sink 16.1 2.3 2.3 2 9.1 1.9 55.8 silica float 2.44 35.1 18.3 7.4 0.4 5.4 2.58 4.9 8 carbonate float 47.2 32.0 1.0 5.4 63.3 75.1 10 phosphate sink 22.72 100.0 100.00 16.9 9.7 2.3 59.1 100.0 100 head

" Branched-chain fatty acid from Union Camp Corp. content.


Branched-chain fatty acid from Union Camp Corp. content.

SiO, 85.4 10.6 2.8 0.1 1.1 100.0

acid, 60% active

oleic acid

0.13

SiO, 88.8 6.9 2.3 0.0 2.0 100.0

oleic acid

~~~


as starting feed are shown in Tables VI11 and IX, respectively. A satisfactory phosphate concentrate con-

0.25


Table X. Flotation Conditions and Results for BL-48 Sample-Example 8 I. Operations, 1000-g Starting Feed conditioning reagent, kg/ton of starting feed operation % solid DH M05" fuel oil NaOH H,SO, amineb deouestc phosphate flotation rougher 65 9.7 0.5 1.0 0.12 cleaner 7.5 50 5.3 deoiling 0.5 silica flotation 12 6.7 0.075 carbonate flotation 65 6.3 0.025 0.075 11. Results analysis, % distribution, % product wt% CaO P205 MgO Si02 CaO P206 MgO phosphate flotation 54.56 3.1 11.3 6.4 44 1.0 1.3 rougher sink 94.8 8.3 13.71 cleaner sink 3.3 2.3 83.8 7.6 5.3 19 6.80 7.9 7 3.7 1.6 3.6 3.0 silica float 80.5 21 34.0 7.4 4.6 carbonate float 3.25 12.0 10.5 7.9 48.6 9 21.68 70.2 80.7 phosphate sink 31.6 0.7 6.7 15.0 100.1 100.0 100 100.00 8.5 1.6 head 70.4 ~~

oleic acid

0.25

Si02 73.5 16.3 7.8 0.4 2.0 100.0


taining about 32-33% Pz05and 0.8-1.070MgO was obtained. The Pz05recovery was slightly decreased to

1418 Ind. Eng. Chem. Res., Vol. 26, No. 7, 1987 Table

XI. Flotation Conditions a n d Results for BL-48 Sample-Example conditioning pH

Yo solid

operation phosphate flotation rougher cleaner deoiling silica flotation carbonate flotation

65 50 12 65

9.7 7.5 5.3 6.7 6.5

0.5

1.0

0.5 0.075 0.025

Droduct

wt %

CaO

phosphate flotation rougher sink cleaner sink silica float carbonate float phosphate sink head

49.31 17.98 8.33 3.69 20.69 100.00

2.7 6.5 6.3 36.5 47.5 14.2

0.8 3.0 3.1 17.0 31.2 8.3

WASTE

SILICA AND CARBONATE WASTE

+

PHOSPHATE CONCENTRATE

1.4 1.1

7.3 0.7 1.3

0.25

distribution, % MnO

CaO

PZOS

93.0 85.2 81.4 4.9 8.2 69.8

9.4 8.2 3.7 9.5 69.2 100.0

4.8 6.5 3.1 7.6 78.0 100.0

42 19 7 21 11

100

SiOl 65.7 21.9 9.7 0.3 2.4 100.0


experimental results show that a phosphate concentrate containing 31-32% P205and 0.7% MgO can be obtained, with a P205recovery of about 78-81 % (Tables X and XI). These tests further confirm that a phosphate containing coarse, weathered dolomite in the flotation feed can be beneficiated with this modified Crqgo-TVA process.

ROUGHER PHOSPHATE

SILICA FLOTATION

1.1

0.075

SiO,


Branched-chain fatty acid from Union Camp Corp. content.

4

oleic acid

0.12

11. Results analysis, % P,O, MEO

FUEL OIL NaOH

9

I. Operations, 1000-g Starting Feed reagent, kg/ton of starting feed M05“ fuel oil NaOH H2S04 amine* dequestC

MODIFIED CRAG0 PROCESS

si L ~ C A WASTE

J

Figure 2. Beneficiation of dolomitic phosphate rock with modified Crago-TVA process.

75-77%. The reagents used in the deoiling, silica flotation, and carbonate flotation stages were noticeably reduced. For example, in the carbonate flotation circuit using 2000 g as starting material, diphosphonic acid (60% active content) was reduced from 0.1 to 0.038 kg/ton and oleic acid from 0.5 to 0.13 kg/ton. The modified Crago-TVA process was further evaluated with the BL-48 sample. The reagent dosages were the same as those described for BL-47, except that the amounts of H2S04used for deoiling and NaOH for pH adjustment were different. Based on a 1000-g sample as starting feed, the reagent dosages were 0.5 kg/ton fatty acid, 1.0 kg/ton fuel oil, 0.5 kg/ton H2S04,0.15 kg/ton NaOH, 0.075 kg/ton amine, 0.075 kg/ton diphosphonic acid (60% active content), and 0.25 kg/ton oleic acid. The

Conclusions It may be concluded that a phosphate ore containing coarse, weathered dolomite in the flotation feed, such as that from the Southern Extension of central Florida, can be beneficiated with this modified Crago-TVA process. In this process, the phosphate mineral first is concentrated with fatty acid in the overflow, as in the conventional Crago process, but then is refloated to remove additional coarse dolomite in the underflow. The concentrate then is subjected to conventional deoiling and silica flotation. The remaining dolomite contaminant in the phosphate concentrate is floated further as waste by using TVA’s diphosphonicacid depressant process, where diphosphonic acid is used as a phosphate mineral depressant and fatty acid is used as a dolomite collector. By use of this method, a phosphate containing 31-33% P205 and 0.7-1.0% MgO was obtained from flotation feeds containing 8.1-9.5 % Pz05and 1.5-2.6% MgO. The Pz06recoveries were 77-80 % . Registry NQ. Dodecylamine hydrochloride, 929-73-7; hydroxyethylidenediphosphonic acid, 2809-21-4; oleic acid, 112-80-1; dolomite, 16389-88-1.

Literature Cited Bushell, C. H. G.; Hirsch, H. E. US.Patent 3462017, 1969. Bushell, C. H. G.; Hirsch, H. E.; Lauer, R. M. U S . Patent 3462016, 1969. Hoppe, R. Eng. Min. J. 1976,177, 81-93. Hsieh, S. S.; Lehr, J. R. Miner. Metall. Process. 1985, 2(1), 10-13. Kiukkola, K. “Selective Flotation of Apatite From Low-Grade Phosphorus Ore Containing Calcite, Dolomite and Phlogopite”, 2nd International Congress on Phosphorus Compounds Proceedings, Boston, April 1980; pp 219-229. Lawver, J. E.; McClintock, W. 0.;Snow, R. E. U S . Patent 4372843, 1983. Lawver, J. E.; Snow, R. E.; McClintock, W. 0. U S . Patent 4 189 103, 1980. Lawver, J. E.; Wiegel, R. L.; Snow, R. B.; Hwang, C. L. Min. Congr. J. 1982, 68(12), 27-31. Lehr, J. R.; Hsieh, S. S. U.S. Patent 4287053, 1981.

Ind. Eng. Chem. Res. 1987,26, 1419-1424 Mair, A. D.; Soroczak, M. M. U S . Patent 4588498, 1986. Moudgil, B. M.; Chanchani, R. Miner. Metall. Process. 1985, 2(1), 13-25. Ratobylskaya, L. D.; Klassen, V. I.; Boiko, N. N.; Baskakova, M. I.; Smirnov, Yu. M. “Development and Industrial Introduction of New Concentration Processes for Phosphorites of Complex Mineral Composition”, Proceedings of the 11th International Mineral Processing Congress Seminar on Beneficiation on Lean Phosphates with Carbonate Gangue, Cagliari, Sardinia, April 1975; pp 17-39. Rule, A. R.; Clark, C. W.; Butler, M. 0. “Flotation of Carbonate Minerals From Unaltered Phosphate Ores of the Phosphoria Formation”, Report of Investigation No. 7864,1974; U.S.Bureau of Mines, Washington, DC.

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Rule, A. R.; Clark, C. W.; Butler, M. 0. “Flotation of Carbonate Minerals From Unaltered Phosphate Ores of the Phosphoria Formation”, Proceedings of the 11th International Mineral Processing Congress Seminar on Beneficiation on Lean Phosphates with Carbonate Gangue, Cagliari, Sardinia, April 1975; pp 167-186. Rule, A. R.; Kirby, D. E.; Dahlin, D. C. Min. Eng. 1978,30(1),37-40. Smani, M. S.; Blazy, P.; Cases, J. M. AIME Trans. 1975, 258, 168-182. Snow, R. E. U.S. Patent 4 144 969, 1979. Snow, R. E. U S . Patent 4 364 824, 1982.

Received for review August 14, 1986 Accepted April 10,1987

Selective Oxidation of Propene on a Mo-Pr-Bi Catalyst Gojko Kremeni6,* Jose M. L. Nieto, Juan M. D. TascGn, and Luis G. Tejuca Instituto de Catdlisis y Petroleoqulmica, C.S.I.C.,28006 Madrid, Spain

Sol W . Weller Department of Chemical Engineering, State University of New York at Buffalo, Buffalo,New York 14260

The adsorption of oxygen and propene and the kinetics of formation of acrolein during the oxidation of propene over a Mo-Pr-Bi catalyst were studied. Preadsorption of propene a t 373 K does not appreciably affect the total adsorption of oxygen. The total adsorption of propene on a surface with preadsorbed oxygen a t 373 K is about 25% lower than that on a clean surface. This decrease is assumed to result from steric hindrance. The oxygen isobar exhibits an ascending branch, indicating a change in the nature of the adsorbed species, probably associated with the appearance of dissociatively adsorbed oxygen above 550 K. The kinetic data are best fitted by equations derived from the redox Mars-van Krevelen mechanism and from the stationary state of the adsorption model assuming in both cases nondissociative adsorption of oxygen. Reasonably good fits are also obtained with the power rate law. It is concluded that the data- and model-fitting procedures are useful in arriving a t rate equations that best describe the kinetic results, but it is hazardous to extend this analysis to conclusions concerning the detailed mechanism. Propene can be oxidized to acrolein in the gas phase over a number of catalysts. In recent years a large number of patents has been reported for this reaction (Hucknall, 1974). However, only in a limited number of cases have the kinetic aspects been studied, mainly due to the complexity of this catalytic reaction. The dependence of acrolein formation with propene or oxygen partial pressure gives reaction orders ranging from 1to 0. Activation energy values have been found to be from 50 to 210 kJ mol-l (Isaev and Margolis, 1960; Keulks et al., 1971; Crozart and Germain, 1973; Aso et al., 1980). Many selective oxidation reactions proceed according to a redox mechanism (Cullis and Hucknd, 1982) although other mechanisms where surface oxygen is involved have been proposed for the partial oxidation of olefins (Cartlidge et al., 1975; Cort6s Corber6n et al., 1985). Praseodymium oxide has unstable lattice oxygen (Takasu et al., 1981) (up to 7.5% total lattice oxygen is desorbed between 298 and 873 K). On the other hand, this oxide exhibited a maximum in the rate of exchange of molecular oxygen in a series of lanthanide oxides (Minachev et al., 1977; Klissurski, 1979). Other studies showed that these oxides have a promoting effect for partial oxidation (Khiteeva and Rzakulieva, 1981). From these considerations it seems of interest to study the preparation of new selective catalysts by modification of known systems using praseodymium oxide. As part of a more comprehensive work on this type of material, in this paper the adsorption of propene and oxygen and the kinetics of acrolein formation over a Mo-Pr-Bi catalyst were studied. The rate equations that best describe the kinetic data are 0888-5885187 12626- 1419$01.5010

given and the methodology of “best fit” is examined.

Experimental Section Catalyst Preparation and Gases. The catalyst sample was prepared by double impregnation of silica (BASF D-11-11) previously heated for 4 h at 1073 K. After this treatment, the support had a BET specific surface area (measured by N2 adsorption at 77 K) of 135 m2 g-l and a pore volume of 0.8-1.1 cm3 g-l. First, the support was impregnated at pH 7 with 1.4 cm3 (per g of SO2)of an aqueous solution of (NH4)6M07024a4H20 (Merck, p.a.). The resulting precursor was first dried in a rotary evaporator at 323 K and 200 mmHg (1 mmHg = 133.3 N and then in an oven at 383 K. Finally it was calcined for 4 h at 723 K in flowing air. Second, the impregnation was effected with an acid solution of Pr(N0J2-5H20(Fluka AG) and Bi(N03)3(Koch Light). This precursor was dried as above and calcined for 16 h at 823 K in flowing air. The final catalyst has an atomic ratio Mo:Pr:Bi of 4:0.50.5 and a concentration in MOO, of 20 w t %. Its BET specific surface area was 55.6 m2 g-l; its pore volume and mean pore radius, both determined by mercury porosimetry, were 1.31 cm3 g-l and 40.3 nm, respectively. By means of X-ray diffraction, the phases Moo3, a-Bi203,and yBi2Mo06were found. No praseodymium compound was detected in the diffraction pattern. The gases used were propene (199%), oxygen (199.98%), and helium (99.998%) from Sociedad Espaiiola del Oxigeno. Adsorption Experiments. The adsorption experiments were carried out in a conventional high-vacuum volumetric apparatus (dynamic vacuum, lo4 mmHg) 0 1987 American Chemical Society

Beneficiation of Dolomitic Phosphate Ores Using Modified Crago-TVA

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