WO1998043741A1

WO1998043741A1 - Methods of beneficiating siliceous phosphates

Info

Publication number: WO1998043741A1
Application number: PCT/US1998/004898
Authority: WO
Inventors: Yingxue Yu; Jinrong Zhang
Original assignee: The Florida Institute Of Phosphate Research
Priority date: 1997-03-28
Filing date: 1998-03-12
Publication date: 1998-10-08
Also published as: AU6461598A; WO1998043741A9; BR9808093A; IL132093A0; CN1251539A

Abstract

A method of beneficiating siliceous phosphate, designated as 'reverse Crago', which includes subjecting a siliceous phosphate-containing flotation feed to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation. A further improved reverse crago process for beneficiating siliceous phosphate includes the steps of subjecting a siliceous phosphate or material to amine flotation so as to obtain a prefloat concentrate, and screening the prefloat concentrate so as to separate it into 1) a fine predominantly phosphate fraction without substantial amounts of silica, and 2) a coarse fatty acid flotation feed fraction containing phosphate and substantial silica. The coarse fraction is subjected to fatty acid flotation so as to recover phosphate as a fatty acid flotation concentrate.

Description

METHODS OF BENEFICIATING SILICEOUS PHOSPHATES

Field of the Invention The present invention relates generally to methods of beneficiating siliceous phosphates. Background of the Invention

Currently, beneficiation of siliceous phosphate ore almost always occurs via the Crago process. In the Crago process, siliceous phosphate ore is deslimed and then subjected to sizing which involves using a hydrosizer to size the deslimed ore into two fractions — coarse (1000 x 420 micron) and fine (420 x 105 micron) (see Fig. 1) - - or three fractions (1000 x 707 micron, 707 x 420 micron and 420 x 105 micron) (see Fig. 2) . The sized, deslimed ore is then subjected to rougher flotation.

Rougher flotation, as depicted in Fig. 3, involves dewatering the ore-containing feed and conditioning it at about 70% or higher solids with a fatty acid/fuel oil mixture for about three minutes at a pH of about 9, after which phosphate is floated to produce a concentrate. As shown in Fig. 4, the rougher flotation concentrate then goes through dewater cycloning, acid scrubbing and washing to remove reagents from the phosphate surface. After rinsing, the concentrate feed is transported into flotation cells where amine is added, sometimes together with diesel, and the silica is floated at neutral pH.

The Crago process just described is inefficient in terms of collector efficiency due to, inter alia, the fact that 30-40% by weight of the silica present in the feed are floated twice, first by fatty acid and then by amine. To illustrate the inefficiency of the Crago process, it is noted that the fatty acid dosage for floating

"pure" phosphate is about 0.18 kg per ton, making the theoretical dosage for floating a feed of 6.86% P₂0₅ (15% BPL) only 0.027 kg/ton of feed (TOF) . However, actual plant consumption of fatty acid for such a feed is about 0.54 kg/TOF, which means that the Crago process is operating at about only 5% of theoretical efficiency. The remainder of the reagents appear to be wasted primarily on the excess silica in the feed.

Despite its inefficiency, the Crago process has been used widely in the phosphate industry in the past. However, due to increasing amine costs and decreasing phosphorous content in currently-mined ore, the Crago process is rapidly becoming obsolete. Thus, there is a need in the art for new methods of economically and efficiently beneficiating siliceous phosphates. Summary of the Invention

In accordance with the present invention, a method of beneficiating siliceous phosphates includes subjecting a siliceous phosphate-containing flotation feed to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation.

Also in accordance with the present invention, a method of beneficiating siliceous phosphates includes subjecting a siliceous phosphate containing feed which also contains a substantial amount of clay to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation.

Further in accordance with the present invention, a method of beneficiating siliceous phosphates includes subjecting a siliceous phosphate containing flotation feed to amine flotation so as to form a prefloat concentrate, wherein the flotation water contains a substantial amount of suspended particles, and subjecting the prefloat concentrate to fatty acid flotation. Also in accordance with the present invention, a method of beneficiating siliceous phosphates includes subjecting a siliceous phosphate containing flotation feed which has not been sized to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation.

Also in accordance with the present invention, a method of beneficiating siliceous phosphate includes the steps of subjecting a siliceous phosphate ore material to amine floatation so as to obtain a prefloat concentrate, and screening the prefloat concentrate so as to separate it into a 1) fine predominantly phosphate fraction without substantial amounts of silica, and 2) a coarse fatty acid floatation feed fraction containing phosphate and substantial silica. The coarse fraction is subjected to fatty acid flotation so as to recover phosphate as a fatty acid flotation concentrate. Brief Description of the Drawings

Fig. 1 depicts a sizing process in which deslimed ore is sized into two fractions .

Fig. 2 depicts a sizing process in which deslimed ore :'.s sized into three fractions. Fig. 3 depicts the rougher flotation step which occurs during the

Crago process to yield a rougher concentrate.

Fig. 4 depicts the cleaner flotation (i.e., amine flotation) and the steps preceding this flotation to which the rougher concentrate is subjected during the Crago process. Fig. 5 depicts the kinetics of oleic acid adsorption onto a silicon phosphate containing flotation feed. This figure indicates that fatty acid adsorption on silica is significant.

Fig. 6 depicts flotation recovery of apatite and silica with dodecylammonium chloride as a function of pH. This figure shows that amine can float more than about 95% of silica from pH of about 3 to about 12 while phosphate flotation by amine is minimal within this same pH range. In contrast, it is well-known that fatty acids do not float phosphate well at neutral pHs . Fig. 7 illustrates the effects of pH on zeta potentials for silica and apatite. This figure shows that at near neutral pHs there is a large difference in zeta potential between silica and phosphate, thereby making separation of silica from phosphate preferable at neutral pHs . Fig. 8 depicts one embodiment of the amine-fatty acid flotation process of the present invention.

Fig. 9 depicts another embodiment of the amine-fatty acid flotation process of the present invention.

Fig. 10 illustrates the effect of stagewise addition of an amine condensate on the amount of silica (sand) floated.

Fig. 11 illustrates the effect of slime-binding polymer on the amount of silica (sand) floated as a function of the amount of amine consumed.

Fig. 12 illustrates the effect of slime-binding polymer on the amount of silica (sand) floated as well as on the amount of P₂0₅ recovery at 0.23 lb/TOF of amine added as one dose.

Fig. 13 is a flow chart showing one embodiment of the invention.

Fig. 14 is a flow chart showing another embodiment of the invention. Description of the Preferred Embodiments

It surprisingly has been discovered that subjecting a siliceous phosphate containing flotation feed to amine flotation so as to form a prefloat concentrate and then subjecting the prefloat concentrate to fatty acid flotation (the "amine-fatty acid flotation" or "reverse Crago process") is particularly and unexpectedly economical and efficient in beneficiating siliceous phosphates.

According to the present invention, methods of beneficiating siliceous phosphates are provided. The methods of the present invention include subjecting a siliceous phosphate-containing flotation feed, where the flotation water contains a substantial amount of suspended particles and/or the feed may be unsized and/or may also contain a substantial amount of clay, to amine flotation so as to form a prefloat concentrate and then subjecting the prefloat concentrate to fatty acid flotation.

According to the present invention, a siliceous phosphate- containing flotation feed is subjected to amine flotation. Typically, amine flotation occurs for between about 1 and about 3 minutes, preferably for about 1.5 minutes, and at a pH of between about 5 and about 8, preferably at about 7. Moreover, pulp density of the feed during amine flotation is generally between about 20% and 40%, with 27% being most preferred.

Amine flotation results in, inter alia, separation of silica, particularly fine silica, from the siliceous phosphate-containing feed. Thus, any amine capable of adsorbing onto silica in the flotation feed so as to facilitate separation of silica from the feed can be used in accordance with the methods of the present invention. Such amines as are currently utilized by the phosphate industry may be used. Most preferably, the least expensive amine condensate is used.

To effect amine adsorption onto silica in the siliceous phosphate- containing flotation feed, an adsorption-effective amount of amine is added to the feed during amine flotation. Preferably, the amount of amine added to the feed is between about 0.2 and about 0.6 lb per ton. Most preferably, about 0.3 lb per ton of amine is added to the feed.

According to one aspect of the present invention, amine can be added stagewise (i.e., stepwise or in steps) or continuously during amine flotation. Adding amine stagewise or continuously during amine flotation can dramatically decrease the amount of amine needed for flotation. "Stagewise" addition is defined herein as meaning multiple (i.e., at least 2) additions of amine during amine flotation. Preferably, such multiple additions occur on a routine basis (e.g., once every 30 seconds, upon entry of the feed into a new flotation cell, etc.), although it is to be understood that for purposes of the present invention amine can be added stagewise on a non-routine basis. Moreover, the amount of amine added stagewise can vary from addition. to addition. It is preferable, however, to add amine in approximately equal amounts.

Continuous addition of amine during amine flotation preferably occurs at a rate of between about 0.1 and about 0.4 lb/minute per ton of feed, with a rate of about 0.2 lb/minute being most preferred, and the cumulative amount of amine added is preferably between about 0.2 and about 0.6 lb/ton of feed, with about 0.3 lb being most preferred.

Although it is preferred that continuous addition of amine occurs at an approximately constant rate, it is to be understood that for purposes of the present invention the rate of amine addition can be varied throughout amine flotation. According to another aspect of the present invention, an effective amount of a slime binding polymer can be added prior to or during amine flotation. Adding a polymer during amine flotation can dramatically decrease the amount of amine needed for flotation. The polymer can be added either to the siliceous phosphate-containing feed or to the flotation water added to the feed during amine flotation depending on quality of the feed or the water. Moreover, the polymer can be added prior to or during amine flotation regardless of whether amine is added stagewise, continuously or all at once.

Suitable polymers for use in accordance with this aspect of the present invention are polymers capable of at least partially desliming a siliceous phosphate-containing feed which also contains a substantial amount of clay (i.e., enough clay to interfere with or hinder amine flotation, typically up to about 2% by weight of the feed) so as to minimize or diminish the deleterious effects of clay on amine flotation. Such polymers include, but are not limited to, anionic polymers (e.g., anionic polyacrylamides with either carboxylic groups or sulfonate groups), nonionic polymers (e.g., polyethylene oxides, polyacrylamides, and polyvinl alcohol) and cationic polymers (e.g., cationic polyelectrolytes, polyethyleneimine) . Preferably, the slime binding polymers used are anionic polyacrylamides.

Typically, the amount of polymer added prior to or during amine flotation is between about 2 and about 25 grams/ton of feed, with the addition of about 9 grams being most preferred. For example, Percol 90L can be added in amounts between about 5 and about 15 grams/ton of feed, with 9 grams being most preferred.

According to another aspect of the present invention, the siliceous phosphate-containing flotation feed subjected to amine flotation can be sized or unsized. Preferably, the flotation feed is unsized.

According to the present invention, after subjecting a siliceous phosphate-containing flotation feed to amine flotation so as to form a prefloat concentrate, the prefloat concentrate is subjected to fatty acid flotation. Preferably, the prefloat concentrate is dewatered prior to fatty acid flotation, although dewatering is not absolutely necessary. Typically, fatty acid flotation occurs for between about 0.5 and about 4 minutes, preferably for about 1.5 minutes, and at a pH of between about 5 and about 11, with a pH of 9 being most preferred. Moreover, pulp density of the feed during fatty acid flotation is generally between about 20% and about 35%, with about 23% being most preferred. According to one aspect of the present invention, fatty acid flotation occurs in a fatty acid flotation mixture comprising at least one fatty acid and at least one fuel oil. Preferably, the fatty acid flotation mixture further comprises pH modifier such as soda ash and/or at least one surfactant. Suitable fatty acids for use in the fatty acid flotation mixture include, but are not limited to, oleic acid, tall oil fatty acids, crude tall oil, tallow fatty acids, vegetable fatty acids, tall oil pitch soap, or mixtures thereof.

Suitable fuel oils for use in the fatty acid flotation mixture include, but are not limited to, No. 5 fuel oil, recycled motor oil, or mixtures thereof.

Suitable surfactants for use in the fatty acid flotation mixture include, but are not limited to, sulfonated fatty acids, petroleum sulfonates, alkylalcohol ether sulfate, alkylalcohol sulfate, or mixtures thereof.

In accordance with this aspect of the present invention, the fatty acid flotation mixture comprises 30-80% by weight fatty acid, 15-60% by weight fuel oil, and 2-20% by weight surfactant. Preferably, the fatty acid flotation mixture comprises 35 - 60% by weight fatty acid, 40 - 50% by weight fuel oil, and 5 - 10% by weight surfactant. Subsequent to fatty acid flotation, phosphates can be recovered by any suitable means.

For siliceous phosphate-containing flotation feeds containing a substantial amount of coarse particles (i.e., +420 micron), two additional steps optionally can be added to the amine-fatty acid flotation process described supra, either individually or together. First, prefloat concentrate can be sized to obtain a mini-pebble (e.g., sizing at 14 mesh) . Second, the siliceous phosphate- containing flotation feed can be scavenged subsequent to fatty acid flotation and another fatty acid floatation step can take place. The above is particularly advantageous for feeds containing 20% or above of +35 mesh particles.

According to one preferred embodiment of the present invention, a method of beneficiating siliceous phosphates comprising the steps of subjecting a siliceous phosphate-containing flotation feed which contains a substantial amount of clay (as defined supra) to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation is provided. According to one aspect of this embodiment, amine is added stagewise or continuously during amine flotation as described supra to a siliceous phosphate-containing feed which also contains a substantial amount of clay to minimize or diminish the deleterious effects of clay on amine flotation as well as the loss of phosphate during flotation. Amine flotation is typically conducted in a series of banks of flotation cells, each bank containing four to six flotation cells. Conventionally, all of the amine is added to the first flotation cell at the same time. However, it surprisingly has been found that adding a small amount of amine to the initial flotation cell permits not only amine flotation but also desliming, thereby diminishing or minimizing the deleterious effect of clay on amine flotation.

According to another aspect of this embodiment of the present invention, an effective amount of polymer is added to a siliceous phosphate-containing feed which also contains a substantial amount of clay. It has surprisingly been found that adding a polymer prior to or during amine flotation as described supra "binds" the clays in a siliceous phosphate-containing feed. According to another preferred embodiment, a method of beneficiating siliceous phosphates comprising the steps of subjecting a siliceous phosphate-containing flotation feed to amine flotation so as to form a prefloat concentrate, wherein the flotation water comprises a slime enhancing amount of suspended particles, and subjecting the prefloat concentrate to fatty acid flotation is provided.

The use of flotation water containing a substantial amount of suspended particles (generally between about 50 and about 1000 ppm suspended solids) during amine flotation generally results in slime problems similar to those resulting from the presence of a substantial amount of clay in the siliceous phosphate-containing feed. Thus, according to this embodiment, amine is added stagewise or continuously as described supra and/or an effective amount of polymer is added during amine flotation as described supra so as to minimize or diminish the deleterious effects of slime on amine flotation. In this embodiment, the siliceous phosphate-containing feed may or may not also contain a substantial amount of clay (as defined supra) . According to yet another preferred embodiment of the present invention, a method of beneficiating siliceous phosphates comprising the steps of subjecting a siliceous phosphate-containing flotation feed which has not been sized to amine flotation so as to form a prefloat concentrate and subjecting the prefloat concentrate to fatty acid flotation is provided.

According to this embodiment of the present invention, an unsized siliceous phosphate-containing flotation feed is subjected to the reverse Crago process as described supra. It surprisingly has been found that flotation of unsized feeds can occur via the reverse Crago process without sacrificing metallurgical recovery.

In a preferred embodiment, the invention relates to an efficient processing technique for concentrating phosphate from deslimed siliceous phosphate ore. The deslimed flotation feed is first subjected to amine flotation to remove fine silica. The reagent schedule for this stage of flotation includes a commercially available amine condensate or any other amine collector added stagewise with a polymer added either in the feed and/or flotation water. Amine may also be added in a continuous manner to further reduce its consumption and improve selectivity. The prefloat concentrate is sized at an optimal mesh, typically 35 mesh, or finer depending on size and P₂0₅ distribution of pre-float concentrate. The fine fraction of the pre-float concentrate is recovered as a final product. The coarse fraction of the pre-float concentrate is dewatered, conditioned with a pH modifier, a commonly used fatty acid collector and a fuel oil, and floated using either mechanical cells or flotation columns to recover the phosphate, leaving coarse silica in the sink. Figure 13 shows the flowsheet of this process. For feed with a substantial amount of coarse (+16 M) phosphate, it may be desirable to size the pre-float concentrate at 16 mesh as well. Coarse phosphate recovery is further improved by high-pH conditioning followed by low-pH flotation. These additional steps are shown in Figure 14.

One embodiment of the invention comprises the following steps: 1) pre-floating fine silica (sands) from a deslimed phosphate ore with an amine collector plus a small amount of polymer, 2) sizing the prefloat concentrate at 35 mesh (or finer depending on feed characteristics) to obtain a final product, the -35 mesh fraction, and a fatty acid flotation feed, the +35 mesh fraction, 3) conditioning the coarser fraction of the prefloat concentrate with soda ash, fatty acid and fuel oil, and 4) floating phosphate from silica. Sizing of the prefloat concentrate could cut fatty acid/fuel oil consumption required for the original Reverse "Crago" process by up to 50%, with substantial savings in other operating costs as well.

In these processes, fine silica is first floated with an inexpensive amine, and the prefloat concentrate is further cleaned by either floating phosphate (the amine-fatty acid flotation process, Reverse "Crago") or floating silica (the all cationic process) . The

Reverse "Crago" is unique in the following aspects: stepwise addition of amine, novel fatty acid flotation reagent scheme that improves recovery of coarse phosphate particles, higher collector efficiency, simplified flowsheet, and non-sizing flotation without sacrificing metallurgical recovery.

Amines are more selective collectors than fatty acids, and amine adsorbs instantaneously on sand. Amine can float more than 99% of silica from pH 3 to 12, while phosphate flotation by amine is minimal within this pH range. It was also discovered that at near neutral pHs, there is a large difference in zeta potential between silica and phosphate. Therefore, it is ideal to separate silica from phosphate at neutral pHs . Fatty acids do not readily adsorb on phosphate surfaces at neutral pH as readily as at higher pHs . We therefor float silica first. Since amine adsorbs on silica vary rapidly, the effect of clay on amine consumption may be reduced by adding amine stagewise. Flotation is conducted in a series of banks of flotation cells. Each bank consists of three to six cells. In the conventional process all the amine is added as one dose in the first flotation cell. If a small amount of amine is added in the first cell, this cell not only acts as a flotation machine, but also serves as a desliming device. Since amine flotation does not require conditioning, the number of conditioners currently used for flotation may be reduced by floating silica first. Because amine flotation is conducted at neutral pH, pH modifier consumption is significantly reduced by floating silica first. Finally and perhaps most importantly, for amine is more selective than fatty acid, collector efficiency is improved by floating silica first.

After removing fine silica in the pre-float stage, the fine fraction of the pre-float concentrate is mainly phosphate.

Therefore, screening of the pre-float concentrate at an appropriate mesh gives a fine fraction which does not require fatty acid flotation thereby further reducing fatty acid and fuel oil consumption for the Reverse "Crago" process. As the following examples show, as much as 50% of the prefloat concentrate may be considered acceptable product without going through the second stage (fatty acid) flotation. This not only cuts reagent consumption by nearly half, but also reduces the number of conditioners and flotation cells. The optimal cut size varies from feed to feed. Figures 13 and 14 show improved flowsheets.

The invention can involve the following aspects. In preferred embodiments, the siliceous phosphate ore material which is the starting material is a deslimed siliceous phosphate ore material which has been deslimed with conventional techniques. Preferably, amine flotation also takes place in the presence of a small amount of the polymer, which can be added in the flotation feed and/or in water so as to obtain the prefloat concentrate. In particularly preferred embodiments prior to subjecting the fatty acids flotation feed to fatty acid flotation, the fatty acid floatation feed is subjected to fatty acid conditioning.

During amine flotation, the amine can be added as one dose, stagewise during amine flotation or continuously during amine flotation.

Amine floatation preferably is conducted at a pH of from about 5 to about 8.

In particularly preferred embodiments, during fatty acid flotation, one or more acids is added, selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, fluosilicic acid, phosphoric acid, organic acids and mixtures thereof.

In preferred embodiments, fatty acid conditioning is conducted at a pH from about 9 to about 11, and fatty acid flotation is conducted at a pH from about 5 to about 11.

Amine flotation can be conducted at a pulp density from about 20% to about 40% solids, and fatty acid flotation can be conducted at a pulp density of from about 20% to about 35% solids. The prefloat concentrate can be sized by screening to at least two or more fractions at sizes ranging from about 14 mesh to about 100 mesh.

The polymer can be an anionic polymer, a non-ionic polymer, e.g. selected from the group consisting of polyethylene oxide and polyacrylamide, or the polymer can be a polyacrylic acid or salt thereof.

The deslimed phosphate ore material can be subjected to comminution prior to amine flotation. In accordance with this aspect of the present invention, the fatty acid flotation mixture comprises 30-80% by weight fatty acid, and 15-

60% by weight fuel oil. Preferably, the fatty acid flotation mixture comprises 35 - 60% by weight fatty acid, 40 - 50% by weight fuel oil.

Subsequent to fatty acid flotation, phosphates can be recovered by any suitable means.

The following examples are for illustrative purposes only, and are not to be construed in a limiting sense.

EXAMPLE 1

Two unsized flotation feeds were collected from a northern Florida mine and tested using both the amine-fatty acid flotation process of the present invention with and without scavenging for the coarser feed. Feed characteristics and testing results are shown in Tables 1-3. Prefloat was conducted using about 0.3 lb/ton of feed of amine condensate, at natural pH and about 25% solids for approximately 1.5 minutes. Fatty acid floatation was conducted at pH 9 with soda ash as pH modifier. Floatation time is about 1.5 minutes.

Table 1. Size (mesh) Distribution (wt. %) of the

Flotation Feeds

Sample ID +20 20/28 28/35 35/150 -150

Plant A Fine 1.3 3.3 10.2 83.7 1.5

Plant A Coarse 4.7 6.1 15.6 73.1 0.5 Table Chemical Analysis of the Flotation Feeds

Sample ID PO, Insol

Plant A Fine 9.26 70.60 Plant A Coarse 9.44 70.45

Table 3. Performance of the Reverse Crago Process on Plant A Unsized Fine and Coarse Feeds

Concentrate Concentrate

Feed % P₂0₅ % Insol Recovery Cost

Fine 31.20 5.18 95.2 $1.41

Coarse 31.80 4.24 92.5 $1.50

Coarse with scaveng [ing 32.08 3.69 94.7 $1.79

EXAMPLE 2

Another relatively coarse, unsized flotation feed from a mine in central Florida was also subjected to the process of the present invention. Tables 4-5 show feed analysis and results. Conditions were about the same as in Example 1.

Table 4. Size (mesh) Distribution (wt. %) and Chemical Analysis of the Flotation Feed From Plant B

P₂0₅ Insol +28 28/35 35/150 -150

5.43 83.49 6.1 7.8 82.6 3.5

Table 5. Performance of the Reverse Crago Process on Plant B Unsized Feed

Concentrate Concentrate % P₂05 Reagent

Process % P₂0₅ % Insol Recovery Cost

No Scavenging 32.09 8.50 89.4 $2.04 With Scavenging 31.58 7.4 94.4 $1.96 EXAMPLE 3

The process of the present invention was also used on a coarser (+35 mesh) flotation feed. Table 6 shows chemical analysis of the feed and concentrate. Conditions used were about the same as Examples 1 and 2 except that amine dosage was about 0.21 lb/ton of feed.

Table 6. Performance of the Reverse Crago Process on A Screened Coarse Feed

Reagent cost,

Sample Insol Recovery $/TOC

Feed 13 . 82 60 . 06 Concentrate 31 . 17 10 . 56 98.1 $0.98

EXAMPLE 4

Because of high maintenance costs for desliming hydrocyclones and the limited capacity of clay settling ponds, some plants are frequently floating slimy feed using unclean water (with high suspended solids) . To test the robustness of the reverse Crago process and its performance against the standard Crago process, a comparative testing was conducted on sized flotation feeds with relatively high slime in the feed and using plant water. This plant processes about 20% coarse (+35 mesh) and 80% fine feeds . The plant water was rather cloudy, containing 0.1144 grams/liter of total suspended solids and 0.3741 grams/liter of total dissolved solids. Analysis of the flotation feeds is shown below:

I-tern Fine Feed Coarse Feed

% BPL 8.89 16.34

% Insol 86.81 76.04

+16 mesh 0.09 3.22

16x35 5.91 32.79

35x150 90.84 63.63

-150 3.16 0.36

Tables 7-8 show the significant advantages of the reverse Crago process in terms of both reagent costs and total consumption. Conditions were approximately the same as Example 1, with amine added stagewise. Table 7. Overall Comparison Between Crago and Reverse Crago

Processes on a Plant Fine Feed with Plant Water (TOC = Ton of Concentrate)

Total

ConcenConcenReagent Reagent trate trate % P₂0₅ Cost, Usage,

Procedure % P₂0₅ % Insol Recovery $/TOC lbs/TOC

Crago 72.49 3.36 82.83 4.53 67.41

Reverse

Crago 69.44 6.38 84.93 1.49 8.84

Difference -3.05 3.02 2.10 -3.04 -58.57

Table 8. Overall Comparison Between Crago and Reverse Crago Processes on a Plant Coarse Feed with Plant Water

Total

ConcenConcen* Reagent Reagent trate trate P₂0₅ Cost, Usage,

Procedure % P₂0₅ % Insol Recovery $/TOC lbs/TOC

Crago 70.40 4.85 90.48 2.44 41.57

Reverse

Crago 67.49 7.41 89.94 0.97 5.40

Difference -2.91 2.56 -0.54 -1.47 -36.17

EXAMPLE 5

A. Flotation Feeds. Numerous flotation feeds from Florida were also subjected to the process of the present invention. Table 9 shows the basic chemical analyses of the individual feeds, and Table 10 shows the size distribution within the feeds.

Table 9. Basic Chemical Compositions of Flotation Feeds

Sample ID 5P205 %Insol

Al 9.62 70.60

A2 9.44 70.45

B 5.43 83.49

Cl 8.60 74.86

C2 6.77 79.75

D 13.82 60.2

Table 10. Size (in microns) Distribution of Flotation Feeds

Sample ID +841 841x595 595x420 420x105 -105

Al 1.3 3.3 10.2 83.7 1.5

A2 4.7 6.1 15.6 73.1 0.5

B 3.0 3.1 7.8 82.6 3.5

Cl 3.1 4.5 13.3 76.5 2.6

C2 1.4 4.3 12.7 79.6 2.0

D >420

All the flotation feeds tested were unsized and were collected from secondary hydrocyclone underflows. Most of the flotation experiments were conducted on the as-received feeds.

B. Flotation Reagents. The quartz collector used was an amine condensate designated as Custamine-738 and provided by Westvaco. A blend of commercially-available fatty acid, a surfactant and fuel oil (45% fatty acid, 47% fuel oil, and 8% sulfactants) was used as phosphate collector. Soda ash and sulfuric acid were used as pH modifiers. Bartow tap water was utilized in the initial tests, and plant water was used for studying the slime effect.

C. Flotation Procedure. All the flotation tests were conducted in a standard one-liter Denver cell with a charge of about 500 gram dry feed. Apart from the stepwise addition of amine, all the tests followed standard flotation procedures. Slight desliming (rinsing with tap water) was practiced for comparison in a few instances as noted below.

RESULTS AND DISCUSSION

Table 11 summarizes the flotation test results. In every case, over 90% flotation recoveries at reagent costs of around $1.5 per ton of concentrate were achieved. In contrast, a typical industrial operation has flotation recovery of about 80% at reagent costs of $2.2-3.

Table 12 shows phenomenal reduction in total chemical usage by adopting the reverse Crago process. The first row was obtained by averaging data from two plants during a two-week period. The numbers for the reverse Crago process were averaged on the six feeds evaluated.

Table 11. Performance of the Reverse Crago Process

Feed ID Conc.%P₂0₅ Conc.%Insol %P₂0₅ Recov. $/Ton Cone.

Al 31.10 6.23 93.1 1.41

A2 31.87 4.17 92.1 1.50

B 32.13 7.30 94.6 1.96

Cl 33.42 5.69 94.1 1.10

C2 31.06 7.85 92.6 1.77

D 31.17 10.56 98.1 0.98 Table 12. Reagent Consumption (kg/toc) Comparison

Between the "Crago" and Reverse Crago Processes

Fatty acid Process +fuel oil Amine Soda ash H₂S0₄

Crago 7.35 0.54 2.49 2.90

Reverse Crago 1.98 1.78 1.30

All the above results were generated using plant feeds with tap water. There was a concern that amine consumption would be economically prohibitive when slimy feed and plant recycled water are used. Therefore, more flotation tests were conducted for parallel comparison between the Crago process and the reverse Crago process using plant feed and plant water. Table 5 shows similar metallurgical performance on a low-grade (3.5% P₂0₅) fine feed.

Table 13. Flotation Performance Comparison Between the "Crago" and

Reverse Crago Processes Using Plant Water on a Plant Feed

Item Crago Process Reverse Crago

Concentrate %P₂0₅ 30.04 30.32

Concentrate %Insol 10.15 9.08

%P₂0₅ Recovery 84.94 84.49

However, the reagent consumption made a big difference in terms of both total kilograms and dollars, Table 14. Table 14. Reagent Consumption Comparison between the Crago and Reverse Crago Processes Using Plant Water on a Plant Fine Feed

Reagent Dosage, kg/ton Concentrate ■ Crago Process Reverse Crago

Fatty acid/fuel oil 11.20 1.89

Amine 0.33 2.18

Polymer 0.15

Sodium silicate 1.17

Starch 1.87

Sulfuric acid 2.79

Soda ash 2.79 0.71

Total reagent usage 20.16 4.93

Total reagent cost $3.95 $2.24

EXAMPLE 6

An unsized flotation feed was collected from a northern Florida mine, and tested using the improved Reverse "Crago" process. Characteristics of the feed are shown in Table 15. Table 15. Size, P₂O_s and Insol Distribution (wt.%) of the Fine Feed

Mesh size wt.% %P₂Ω5 %Insol

+20 1.77 14.20 50.71

20/28 6.27 9.20 71.71

28/35 20.53 8.50 73.82

35/48 31.88 10.60 67.72

48/65 30.17 10.40 68.74

65/100 7.10 21.20 37.00

100/150 1.83 22.60 33.51

-150 0.46 13.52 59.89

Total Feed 100 11.06 65.54 About 2000 grams of the fine feed was prefloated with a pound of amine condensate and 0.016 pound of polymer per ton of feed. This floated 71% of the silica in the feed. The prefloat concentrate was sized at 16 and 35 mesh. The -35 mesh fraction accounts for 52% by weight of the prefloat concentrate, and is an acceptable product with 31.4% P₂0₅ and 9.2% Insol. The +16 mesh fraction accounts for 1.6% by weight of the prefloat concentrate, and may be blended in the final product. The +35 mesh pre-float concentrate was conditioned at about 72% solids with 0.27 pound of soda ash and 0.45 pound of fatty acid/fuel oil per ton of feed, and then floated to separate phosphate from silica. Table 16 summarizes the flotation results.

Table 16. Material Balance on the Fine Feed Using the Improved

Reverse "Crago"

Stream Weiαht Wt.% i£₂o₅ Insol %P₂Q₅ (g) Distribution

Head 1995.2 100 11.97 64.35 100

Pre-float tails 1043.0 52.28 1.80 93.82 7.79

Pre-float Concentrate 952.2 47.12 23.13 32.07 92.21

-35 M, product #1 492.1 24.66 31.40 9.20 64.12

+16 M, product #2 16.1 0.81 19.00 42.17 1.27

Fatty acid tails 238.0 11.93 0.32 98.60 0.32

Fatty acid concentrate, 206.0 10.32 31.00 9.07 26.50 product #3

Total product 714.2 35.80 31.01 9.91 91.89

(#l+#2+#3) EXAMPLE 7

A relatively coarser flotation feed from the same plant was also tested using the flowsheet shown in Figure 14. Low-pH fatty acid flotation improved both concentrate grade and flotation recovery for feeds with more coarse (+35 mesh) phosphate particles. Table 17 is the feed analysis.

Table 17. Size, P₂0₅ and Insol Distribution (wt.%) of the Coarse Feed

Mesh size wt.% IP₂Q₅ %Insol

+20 2.51 14.10 57.57

20/28 8.55 9.10 73.46

28/35 26.43 9.60 71.95

35/48 33.11 10.70 68.18

48/65 21.86 11.20 67.46

65/100 5.76 21.30 38.04

100/150 1.32 20.90 39.43

-150 0.47 11.49 59.89

Total Feed 100 11.21 67.50

Table 18 shows batch scale flotation test results on the coarse flotation feed. The flotation procedure is the same as described in example 6, except that sulfuric acid is added in the fatty acid flotation stage. Reagent dosages for this test are: a pound of amine, 0.012 pound of polymer, 0.27 pound of soda ash, 0.45 pound of fatty acid/fuel oil, and 0.16 pound of sulfuric acid per ton of feed. In this case the -35 mesh fraction accounts for 48.6% by weight of the prefloat concentrate.

Table 18. Material Balance on the Coarse Feed Using the Improved "Reverse Crago" with Low-pH Fatty Acid Flotation

Stream Weight Wt.% iP₂Ω_ %Insol _%P₂Q. Distribution

Head 1929.9 100 11.79 63.75 100

Pre-float tails 1031.2 53.43 1.40 92.70 6.34

P r e - f l o a t 898. 7 46. 57 23. 71 32. 07 93. 66

Concentrate

-35 M, product #1 436.5 22.62 31.80 6.92 61.00

+16 M, product #2 17.5 0.91 19.20 42.79 1.48

Fatty acid tails 224.2 11.62 0.28 98.88 0.28

F a t t y a c i d 220.5 11.43 31.90 6.84 30.91 concentrate, product #3

Total product 674.5 34.95 31.51 7.82 93.38

(#l+#2+#3)

EXAMPLE 8

A relatively low grade flotation feed from a central Florida mine was also tested. Table 19 shows the feed properties.

Table 19. Size, P₂0₅ and Insol Distribution (wt.%) of the Low Grade

Feed

Mesh size wt.% %P_Ω. %Insol

+20 1.82 17.77 32.56

20/28 3.17 19.19 36.42

28/35 11.50 13.49 56.72

35/48 28.20 9.07 71.20

48/65 33.07 6.28 80.32

65/100 17.85 5.13 83.99

100/150 3.57 4.75 84.43

-150 0.82 4.48 79.04

Total Feed 100 8.24 73.48 Table 20 shows average results of three batch scale flotation tests. The flotation procedure is the same as described in Example 6. Reagent dosages for this test are: a pound of amine, 0.012 pound of polymer, 0.27 pound of soda ash, and 0.45 pound of fatty acid/fuel oil per ton of feed. The -35 mesh fraction accounts for 50.6% by weight of the prefloat concentrate.

Table 20. Material Balance on a Low-grade Feed Using the Improved

Reverse "Crago"

Stream Weight Wt.% %P₂0₅ %Insol %£₂θ5_

Distribution

Head 6097.6 100 8.36 75.21 100

Pre-float tails 4329.9 71.01 0.99 96.74 8.39

P r e - f l o a t 1767.7 28.99 26.41 22.47 91.60 Concentrate

-35 M, product 893.7 14.66 32.00 6.62 56.10

#1

+16 M, product 48.4 0.79 27.70 16.31 2.63 #2

Fatty acid tails 276.1 4.53 1.14 95.04 0.61

Fatty acid 549.5 9.01 29.92 12.37 32.25 concentrate, product #3

Total product 1491.6 24.46 31.10 9.04 91.00 (#l+#2+#3)

EXAMPLE 9

As is pointed out above, the optimal screening size for the prefloat concentrate depends on size and P₂0₅ distribution of flotation feed. Amine dosage in the prefloat stage also has an significant effect on the ideal cut size. Several prefloat tests were conducted on a low-grade feed analyzing 3.9% P₂0₅ and 88.2% Insol to demonstrate the effect of amine dosage. Table 21 summarizes analyses of several size fractions of prefloat concentrates from different amine dosages. Table 21. Effect of Amine Dosages on P₂0₅ and Distribution (%) in Different Size Fractions of the Pre-float Concentrate

Amine dosage, -35 Mesh Fraction -48 Mesh Fraction -65 Mesh

Fraction lb/ton of wt . % Insol wt.% _-_Q₅ Insol wt _% .?_--. Insol feed

0.64 57. 00 26.30 22.09 31.80 31.87 5.48 14 94 33.20 3.37

0.60 58. 65 23.97 29.09 30.80 31.63 7.30 14 45 32.90 3.69

0.54 60. 96 22.09 34.02 30.64 31.29 7.58 15 22 32.50 3.62

While the invention has been described and illustrated with details and references to certain preferred embodiments, those skilled in the art will appreciate that various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the invention.

As shown above, the reverse Crago process or amine-fatty acid process described supra is much more efficient and economical than the conventional Crago process, and it also offers significant environmental benefits over the conventional process (e.g., reducing the amount of sulfuric acid, soda ash and organic reagents significantly) . Moreover, particular aspects of the present invention allow problems associated with the clay (slime) effect in siliceous phosphate-containing feeds to be controlled.

Claims

What is claimed is:

1. A method of beneficiating siliceous phosphates comprising the steps of:

(a) subjecting a siliceous phosphate-containing material to amine flotation so as to form a prefloat concentrate; and

(b) subjecting the prefloat concentrate to fatty acid flotation so as to beneficiate the siliceous phosphates.

2. The method of claim 1, wherein the siliceous phosphate- containing material is a siliceous phosphate ore material, and wherein between steps (a) and (b) , the prefloat concentrate is screened to separate the prefloat concentrate into a fine predominantly phosphate fraction without substantial amounts of silica, and a coarse fraction comprising a fatty acid floatation feed portion of the prefloat concentrate containing phosphate and substantial silica; and wherein during step (b) it is the fatty acid floatation feed portion of the prefloat concentration which is subjected to said fatty acid floatation so as to produce a fatty acid floatation concentrate.

3. The method of claim 2, wherein the siliceous phosphate ore material is a deslimed silicious phosphate ore material.

4. The method of claim 3, wherein the siliceous phosphate ore material is further deslimed with a slime binding polymer.

5. The method of claim 4 , wherein said amine flotation takes place in the present of said slime binding polymer.

6. The method of claim 2, wherein prior to subjecting the fatty acid flotation feed to fatty acid flotation, the fatty acid flotation feed is subjected to fatty acid conditioning.

7. The method of claim 2 wherein said screening is carried out at about 35 mesh or finer to produce said fine fraction and said coarse fraction.

8. The method of claim 7, wherein prior to screening at said about 35 mesh said prefloat concentrate is screened at about 16 mesh to obtain an about +16 mesh fraction.

9. The method of claim 1, wherein amine is added as one dose during amine floatation.

10. The method of claim 1, wherein amine is added stagewise during amine flotation.

11. The method of claim 1, wherein amine is added continuously during amine floatation.

12. The method of claim 1, wherein amine flotation is conducted at a pH of from about 5 to about 8.

13. The method of claim 2, wherein an acid is added during fatty acid flotation.

14. The method of claim 13, wherein the acid is selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, fluosilicic, phosphoric acid, organic acids and mixtures thereof.

15. The method of claim 6, wherein fatty acid conditioning is conducted at a pH of from about 9 to about 11, and fatty acid flotation is conducted at a pH of from about 5 to about 11.

16. The method of claim 2, wherein amine flotation is conducted at a pulp density of from about 20% to about 40% solids, and fatty acid flotation is conducted at a pulp density from about 20% to about 35% solids .

17. The method of claim 2, wherein the prefloat concentrate is sized by screening to at least two fractions at sizes ranging from about

14 to about 100 mesh.

18. The method of claim 4 wherein the polymer is an anionic polymer.

19. The method of claim 4 wherein the polymer is a non-ionic polymer selected from the group consisting of a polyethelene oxide and a polyacrylamide .

20. The method of claim 4 wherein the polymer is a polyacrylic acid or a salt thereof.

21. The method of claim 3 wherein the deslimed phosphate ore material is subjected to comminution prior to amine flotation.

22. The method of claim 1, wherein fatty acid flotation occurs in a mixture comprising at least one fatty acid and at least one fuel oil.

23. The method of claim 22, wherein the at least one fatty acid is a sulfonated fatty acid.

24. The method of claim 22, wherein the mixture further comprises a surfactant.

25. The method of claim 22, wherein the at least one fatty acid is selected from the group consisting of oleic acid, tall oil fatty acids, crude tall oil, tallow fatty acids, vegetable fatty acids, tall oil pitch soap and mixtures thereof.

26. The method of claim 24, wherein the surfactant is selected from the group consisting of sulfonated fatty acids, petroleum sulfonates, petroleum oxidates, alkyl alcohol ether sulfates, alkyl alcohol sulfates and mixtures thereof.