Recovery of apatite from flotation tailings

Recovery of apatite from flotation tailings

Separation and Purification Technology 79 (2011) 79–84 Contents lists available at ScienceDirect Separation and Purification Technology journal homepa...

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Separation and Purification Technology 79 (2011) 79–84

Contents lists available at ScienceDirect

Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur

Recovery of apatite from flotation tailings Michelly S. Oliveira, Ricardo C. Santana, Carlos H. Ataíde, Marcos A.S. Barrozo ∗ Federal University of Uberlândia, School of Chemical Engineering, Bloco K - Santa Mônica, 38400-902 Uberlândia, MG, Brazil

a r t i c l e

i n f o

Article history: Received 12 November 2010 Received in revised form 3 February 2011 Accepted 9 March 2011 Keywords: Flotation Apatite Waste

a b s t r a c t Apatite is the most common phosphate mineral and a vital nonrenewable resource which is the only economically feasible source of phosphorus for phosphate fertilizers and chemicals. The progressive depletion of ore deposits, allied to the growing demand for food in the world, makes it imperative to use phosphate deposits rationally and to develop recycling processes for accumulated mineral processing wastes. The work reported here involved an evaluation of the possible reuse of phosphate flotation tailings from a Brazilian fertilizer manufacturer. A special flotation apparatus was used in operations in order to examine the effect of the mixture of two different collectors, as well as operating variables (air flow rate, recycle flow rate, and conditioning time) and reagent dosages. The results indicate that the use of a mixture of the synthetic reagent and rice bran oil soap increased the selectivity of the concentrate considerably. A grade of 29.4% P2 O5 and a recovery of 46.2% were obtained under selected operating conditions. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Mineral resources are being depleted at faster rates than ever. These resources are finite; therefore, they must be used sparingly to ensure their availability for future generations. The extraction of valuable minerals from ores results in a wide variety of by-products. Some of these by-products contain residual minerals of commercial value. Many efforts are under way to minimize or reduce the volume of tailings generated and render the process more efficient. Recycling of resources from accumulated wastes has a positive environmental impact, minimizing the hazards of toxic elements and contributing to sustainable development. Therefore, for economic and environmental reasons, the recovery of resources from processing wastes has attracted growing attention in recent years [1]. Phosphate rock minerals are the only significant global sources of phosphorus [2]. Most phosphorus is consumed as a principal component of nitrogen–phosphorus–potassium fertilizers applied on food crops, but it is also used in animal feed supplements, food preservatives, anti-corrosion agents, cosmetics, fungicides, insecticides, detergents, and in pharmaceuticals [3,4]. Phosphate rock is a general term referring to rock with high concentrations of phosphate minerals, most commonly those of the apatite group, containing varying percentages of P2 O5 in a calcium matrix in association with a wide assortment of accessory miner-

∗ Corresponding author. Tel.: +55 34 32394189; fax: +55 34 32394188. E-mail address: [email protected] (M.A.S. Barrozo). 1383-5866/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2011.03.015

als such as fluorides, carbonates, clays, quartz, silicates, and metal oxides. The composition varies from one deposit to another [5,6]. Most phosphate rocks, as mined, are of low grade and require beneficiation. Plants of beneficiation produce large quantities of waste materials with a relatively high P2 O5 content, which are considered as environmentally hazardous and a pollutant source of air, water and soil. In addition, the disposal of these materials represents a loss of valuable natural resources [7]. The most satisfactory way of dealing with wastes is reprocessing to recover additional values. The phosphate industry has long shown great interest in reprocessing the tailings of processing plants [1]. The progressive depletion of ore deposits under exploitation, allied to the growing demand for food in the world, makes it imperative to use phosphate deposits rationally. Based on known reserves, the supply of phosphate rock of the earth may be exhausted in as little as 100 years if the demand continues to increase. The recovery of phosphorus, which is currently discharged into the environment through waste streams, must be seriously addressed to reduce our dependence on phosphate rock-based sources. This is essential to help ensure a supply of phosphorous for future generations. Recovering phosphorus from these tailings could provide additional and substantial amounts of phosphate. The separation of the desired mineral (apatite) from impurities (gangue minerals) and nonphosphate materials in phosphate rock requires grinding and beneficiation units [8] for some operations such as froth flotation [9]. Flotation, a physicochemical separation process that exploits the difference in the surface properties of valuable minerals and unwanted gangue minerals, is currently the most important and versatile mineral processing technique [10]. Hydrophobic particles are selectively attached [11] and remain on

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the surface of gas bubbles rising through a pulp, and are thus concentrated or separated from the pulp in the form of froth [12]. According to Sis and Chander [2], more than half of the production of marketable phosphate of the world is upgraded by flotation. Inefficiencies in flotation translate into an enormous loss of revenue and an unnecessary waste of these reserves [13,14]. Among the various types of flotation devices, the flotation column has achieved a good performance in mineral processing. In recent decades, column flotation has received considerable attention and its use has become widespread because of its significant advantages over the conventional mechanical flotation machine, such as low capital and operating costs, reduction of gangue entrainment in the froth, increase of bubble residence time in the pulp, better adaptability to automated control and improved metallurgical performance [15–21]. The flotation selectivity between apatite and the main gangue minerals can be quantified by the selectivity ratio. The selectivity ratio indicates how much larger the P2 O5 content is than the main undesirable species. The indices considered satisfactory and required by the phosphate industry are of about 4 and 10, respectively, for the P2 O5 /Fe2 O3 and P2 O5 /SiO2 ratios. Considering that the recovery of phosphorus which could be discharged to the environment through wastes streams must be considered seriously to reduce the consume of the phosphate rocks and ensure a supply of phosphorous for the future, the purpose of this work was to investigate the possibility of reusing phosphate flotation tailings from a Brazilian fertilizer manufacturer. Combinations of two different types of collectors, reagent dosages, air flow rate, recycle flow rate and conditioning times are analyzed from experiments carried out in a flotation column to evaluate their effects on the grade and recovery of apatite in the concentrate. The reagent mixing aimed at taking advantage of the higher selectivity of the synthetic collector and the stronger recovery capacity of the fatty acids. 2. Experimental 2.1. Materials The sample of reject used in this study was taken from the phosphate concentration circuit of Bunge Brazil SA, which processes a phosphate deposit that is part of the Barreiro carbonatite complex located in Araxá, state of Minas Gerais in mid-southern Brazil. The host rocks consist mainly of carbonates and glimmerites. The apatite concentration process at Bunge’s fertilizer division produces approximately ten rejects, among them the so-called reground reject. The non-floating fraction from the two coarse particle flotation columns passes on to a grinding and classification circuit, while the de-mudded underflow is subjected to conditioning and subsequent flotation. The reject from the latter flotation column, i.e., the reground reject, is currently deposited in a waste disposal pond. The particle size distribution of the material was determined by the laser diffraction technique using a Malvern Mastersizer particle size analyzer. The experimental data of particle size distribution were fitted to RRB model (Eq. (1)), whose parameters were: dp63.2 = 114.1 ␮m; n = 1.66.

  n  dp

X = 1 − exp −

dp63.2

(1)

The chemical composition, measured by the X-ray fluorescence spectrometry (XRF) technique using a Philips spectrometer, resulted in the following values of the listed compounds: 9.52% of P2 O5 , 26.20% of Fe2 O3 , 1.59% of BaSO4 , 11.50 of CaO, 3.49% of MgO and 22.69% of SiO2.

The mineralogical analysis by XRD indicated the presence of the following minerals: apatite, quartz, goethite, anatase, goyazite, dolomite, magnetite, rutile, vermiculite, diopside, hematite, ilmenite, micaceous minerals, barite, pyrochlore and monazite. 2.2. Reagents and ore conditioning In Brazilian industries, rice oil soap is used traditionally as a collector in apatite flotation while alternative reagents are tested, among them several commercially available synthetic collectors. In the present work, a specific conditioning procedure was employed to render the surfaces of apatite hydrophobic, using corn starch, crude rice bran oil, KE (synthetic collector) and sodium hydroxide. Some reagents used as collectors (for example, fatty acids from some vegetable oils such as rice bran), also have the action of frother. They decrease the surface tension of the liquid surface making possible the formation of an intense and stable froth phase and increasing the number of bubbles with a more appropriate bubble size (smaller bubble), required to hold and transport the bubble-particle aggregates [22]. Corn starch is the gangue depressant utilized in the flotation of igneous phosphate ores in all Brazilian concentrators. The performance of corn starches is consistently superior to that of others depressants such as guar gum, tanins, ethyl cellulose, and carboxy methyl cellulose [23]. The KE, a synthetic anionic collector, is a sulfosuccinate (ROOC–CH2 –CH–COO− –SO3 − ) produced by Henkel. Starting with the corn starch, a macromolecular depressant was prepared by gelatinization, yielding a solution of 3.0 wt.%. The collector oils were saponified at a temperature of 70 ◦ C under constant stirring. The resulting soaps were then dispersed in water to produce a ready solution with an oil concentration of 2.5 wt.%. The KE collector was diluted to 2.5 wt.%. Process water from the processing plant in Araxá was used in all the flotation tests and for the preparation of the reagents. The ore conditioning procedure was carried out in four stages: (a) suspension of the ore in water, percentage of solids 60% (pH 11.3); (b) addition of the depressant (pH 11.5); (c) addition of the collectors (pH 11.5); and (d) dilution of the pulp with water up to 13.6 wt.% of solids (pH 11.5). These pH values are typical for the flotation of igneous phosphate ore in Brazilian phosphate industry [10,14]. The mechanical agitation conditioning stage was performed in a 2 L beaker by using a mechanical stirrer (IKA Labortechnik RW20.n). 2.3. Apparatus and experimental procedure A special flotation apparatus was used in the experiments. The tests were performed in an acrylic cylindrical flotation column, 1.50 m high and with 40 mm internal diameter, as illustrated in Fig. 1. In batch operation, the pulp was introduced at the top of the column and air was injected and distributed by a sparger (a porous conical device made of sintered bronze) at the bottom of the column. The column operated by recycling the bottom product. The air and wash water flow rates were measured by rotameters. The flow rate of washing water was of 0.20 L/min (0.27 cm/s of superficial washing water velocity) and remained unchanged during the tests. The column operated with a circulating load that suspended the feed particles and ensured their passage through the collection zone. The pulp was preconditioned and then diluted to feed the batch flotation column from the top (13.6% of solids in the feed), after adjusting the airflow rate and connecting the pulp recirculation device. The wash water was turned on and the floating material was collected until the froth layer was depleted. In each flotation test, both floating and non-floating products were drained from

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Fig. 1. Diagram of the test setup with the experimental flotation column.

the device and oven-dried at 110 ◦ C for 24 h, weighed, and their chemical composition determined. The chemical composition of the flotation products was determined by X-ray fluorescence spectrometry using a Philips spectrometer. In these apatite concentrates, the quality of the floating product was evaluated based on the recovery and grade of P2 O5 and the selectivity of the separation. For the recovery of phosphorus from the waste stream under study (reground reject), concentrations of about 28–30% of P2 O5 and recovery of 40% are considered commercially viable for industrial flotation, hence they are the target values for this study. The apatite recovery of each flotation test was calculated by Eq. (2). R(%) =

MF xap,F × 100 MA xap,A

(2)

where R is the apatite recovery, MA is the mass (g) fed into the column, MF is the mass (g) of the floated fraction, xap,A is the P2 O5 content of the feed, and xap,F is the P2 O5 content of the concentrate. The flotation selectivity between apatite and these main gangue minerals was quantified by the selectivity ratio. The selectivity ratio for the main undesirable species (Fe2 O3 and SiO2 ) is defined according to Eqs. (3) and (4). SRFe2 O3 = SRSiO2 =

P2 O5 Grade Fe2 O3 Grade

P2 O5 Grade SiO2 Grade

Table 1 Nondimensionalization of the variables. Variable

Nondimensionalization

Collector dosage (C)

X1 =

(C−70 g/t) 10 g/t

Depressant dosage (D)

X2 =

(D−350 g/t) 150 g/t

Air flow rate (Q)

X3 =

(Q −90 L/h) 20 L/h

Recycle flow (F)

X4 =

(F−0.51 L/min) 0.12 L/min

Conditioning time ()

X5 =

(−22.5 min) 7.5 min

second stage, the tests were performed with a mixture of 20% KE and 80% ROS collectors and the results were analyzed statistically by multiple regression technique. The variables studied here were nondimensionalized, as indicated in Table 1. 3. Results and discussions 3.1. Effect of mixing collectors Fig. 2 shows the P2 O5 grade in the concentrate as a function of the percentage of rice oil soap (ROS) used in the KE and ROS mixture. A P2 O5 grade of more than 28% was observed in tests performed with 10–40% of KE in the mixture of collectors. The test performed

(3) (4)

2.4. Experimental design The first stage of the experiments consisted of analyzing the effect of the mixture of two different collectors, rice oil soap (ROS) and KE, on the P2 O5 grade and apatite recovery. This involved performing tests with varying percentages of ROS, i.e., 100%, 90%, 80%, 70%, 60% and 50%. Corn starch was used as depressant. A collector dosage of 80 g/t and a depressant dosage of 500 g/t were used. The ore conditioning procedure with the collector lasted 15 min and with the depressant 15 min. These conditioning times were determined from preliminary tests. The second stage involved analyzing the flotation performance in response to the following variables (with the respective range values): collector dosage (60–80 g/t), depressant dosage (200–500 g/t), air flow rate (70–110 L/h, with this values the superficial gas velocity ranged from 1.55 cm/s to 2.43 cm/s), recycle flow rate (0.39–0.63 L/min), and conditioning time (15–30 min). In this

Fig. 2. Effect of the mixture of two types of collectors on the P2 O5 grade. Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; air flow rate = 90 L/h; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min; conditioning time for each reagent = 15 min; collector dosage = 80 g/t; depressant dosage = 500 g/t.

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Fig. 3. Effect of the mixture of two types of collectors on the apatite recovery. Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; air flow rate = 90 L/h; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min; conditioning time for each reagent = 15 min; collector dosage = 80 g/t; depressant dosage = 500 g/t.

with a mixture of 20% KE and 80% ROS generated the highest P2 O5 grade (29.4%). A higher percentage of ROS in the mixture (>90%) caused the P2 O5 grade to decrease. Fig. 3 illustrates the results of apatite recovery as a function of the percentage of rice oil soap used in the KE and ROS mixture. Apatite recovery increased as the percentage of ROS in the mixture increased. The test with pure rice oil soap (100 wt.% ROS) yielded the highest P2 O5 recovery rate, but this condition resulted in a lower P2 O5 grade (Fig. 2). Tests with 70–90 wt.% of ROS in the collector mixture generated phosphorus contents above 28.5% and apatite recovery rates of 43 and 46 wt.%, respectively. The best flotation result corresponded to a P2 O5 grade of 29.4 wt.% and a recovery rate of 46.2 wt.%. This condition corresponded to a collector dosage of 16 g/t of KE and 64 g/t of rice oil soap (80 wt.% ROS). The selectivity ratio is important to determine how selectively the apatite is separated from its impurities. Figs. 4 and 5 present the results of the first stage of the tests, showing the selectivity ratio of apatite separation from silicate and iron minerals as a function of the percentage of rice oil soap (ROS) used in the KE and ROS mixture. These results indicate that an increasing KE percentage and hence a decreasing ROS concentration increases the selectivity of the concentrate, i.e., the P2 O5 grade becomes higher than iron oxide

Fig. 5. Effect of the mixture of the collectors (KE/ROS) on the selectivity ratio of SiO2 in the concentrate. Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; air flow rate = 90 L/h; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min; conditioning time for each reagent = 15 min; collector dosage = 80 g/t; depressant dosage = 500 g/t.

and silica grades. A large amount of ROS collector induces the augmented collection of gangue because of the greater availability of this reagent for adsorption on the surfaces of other mineral particles (quartz and iron minerals), increasing the flotation of these impurities. The use of the synthetic collector KE 883-B enhanced the selectivity of the flotation process. However, a large quantity of this reagent reduced the recovery rate to levels lower than 20%, rendering the reprocessing of this reject unfeasible. This can be explained by the fact that a higher percentage of KE in the mixture, i.e., a lower percentage of ROS, reduced the foam layer, thus impairing the recovery of mineral particles transported within it. The fatty acid soap from rice bran oil used as collector, also acts as frother agent. In the mixture, when the proportion of the synthetic collector (KE) increases and thus, the proportion of the rice bran oil decreases, the surface tension of the liquid surface does not decrease enough and consequently the thickness of the froth layer formed is shorter and less stable. Then the amount of the desired mineral in the froth phase and its recovery decreases. The adsorption mechanism of KE in minerals containing calcium in the crystal structure is similar to a chemisorption [24]. The use of vegetable oil as rice oil soup combined with a sulphosuccinate as KE aims at taking advantage of the higher selectivity of this synthetic collector and the stronger recovery capacity of the fatty acids [23]. It should be pointed out that the commercial viability of the product of reprocessed rejects depends on the achievement of several targets. As said before, in the industrial flotation of phosphate ore, a selectivity ratio of about 4.0 between apatite and iron minerals and of 10 between apatite and silicate minerals are considered satisfactory. Additional requirements are a phosphorus grade of about 28–30% and an apatite recovery rate of more than 40%. According to the aforementioned criteria, the best flotation result corresponded to a P2 O5 concentration of 29.4% and a recovery rate of 46.2%, which was obtained with a dosage of 16 g/t of KE (20%) and 64 g/t of ROS (80%). 3.2. Analysis of the influence of the variables

Fig. 4. Effect of the mixture of the collectors (KE/ROS) on the selectivity ratio of Fe2 O3 in the concentrate. Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; air flow rate = 90 L/h; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min; conditioning time for each reagent = 15 min; collector dosage = 80 g/t; depressant dosage = 500 g/t.

For a global analysis of the influence of the process variables, the tests performed with collectors in the proportion of 20% KE and 80% ROS were grouped and subjected to a statistical analysis, since this conditions proved the most favorable for flotation of the reground reject. The results were statistically analyzed by multiple regressions in order to quantify the effects of each variable independently, as

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well as of their interactions, on the responses under study (grade, recovery and selectivity ratio). Regression Eqs. (5)–(8) were adjusted to represent the variation in grade (G) of P2 O5 (r2 = 0.99), recovery (R) of apatite (r2 = 0.88) and selectivity ratio (SR) in relation to Fe2 O3 (r2 = 0.98) and SiO2 (r2 = 0.91), respectively. Parameters with significance level higher than 0.10 were considered insignificant, i.e., the statistical hypothesis test considered a maximum error probability of 10%. G = 24.1 − 0.21X1 + 1X2 − 0.14X3 − 0.35X5 − 0.79X1 X2 + 0.62X12 + 0.21X22 − 0.12X42

(5)

R = 58.0 − 0.79X2 − 0.29X1 X2 + 0.22X3 X4 + 0.22X32

(6)

SRFe2 O3 = 2.18 + 0.84X2 − 0.2X3 − 0.12X5 − 0.54X1 X2 − 0.13X3 X4 − 0.14X4 X5 +

0.49X12

+ 0.21X22

− 0.19X32 − 0.14X42

(7)

Fig. 7. Response surface of apatite recovery as a function of collector (X1 ) and depressant (X2 ) dosages (with the other variables at the intermediary level). Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; collector mixing = 20% KE and 80% ROS; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min.

SRSiO2 = 5.97 − 0.37X1 + 0.4X2 − 0.16X3 + 1.05X4 − 0.19X5 − 0.97X4 X5 + 0.22X22

(8)

An analysis of the above equations revealed that the equations obtained for the grade (Eq. (5)) and selectivity ratio of Fe2 O3 and SiO2 (Eqs. (7) and (8)) presented a similar tendency when compared to the parameters of each variable. As mentioned earlier, the conditions that promoted the highest recovery rates were the same ones that resulted in a low apatite grade and selectivity ratios. This can be explained by the fact that the conditions that lead to higher apatite recovery rates also favor the non selective collection of larger amounts of the other species that make up the reject, diluting the concentrate and decreased selectivity ratios in the floated mass. The value of the parameters in the regression equations indicated that the dosage of the depressant (X2 ) was the variable that most effective on P2 O5 grade, the apatite recovery rate, and the selectivity ratio of Fe2 O3 . The selectivity ratio of SiO2 was most strongly affected by the recycle flow (X4 ). The surface responses shown in Figs. 6–9 were drawn up from the respective equations to better visualize the effects of the variables on the grade, apatite recovery and selectivity ratios.

Fig. 6. Response surface of P2 O5 grade as a function of collector (X1 ) and depressant (X2 ) dosages (with the other variables at the intermediary level). Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; collector mixing = 20% KE and 80% ROS; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min.

Fig. 8. Response surface of the selectivity ratio P2 O5 /Fe2 O3 as a function of air flow rate (X3 ) and depressant dosage (X2 ) (with the other variables at the intermediary level). Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; collector mixing = 20% KE and 80% ROS; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min.

Fig. 9. Response surface of the selectivity ratio P2 O5 /SiO2 as a function of air flow rate (X3 ) and depressant dosage (X2 ) (with the other variables at the intermediary level). Conditions: concentration of solids in conditioning stage = 60%; concentration of solids in flotation feed = 13.6%; collector mixing = 20% KE and 80% ROS; recycling of the bottom product = 0.63 L/min; wash water flowrate = 0.20 L/min.

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In Fig. 6, note that the P2 O5 grade reaches its highest value when a low collector dosage (level 1 = 60 g/t) and a high depressant dosage (level 1 = 500 g/t) are used. As mentioned earlier, higher depressant dosages augment the hydrophilicity of the oxides, preventing them from being collected, thus increasing the P2 O5 content and hence, the selectivity of the concentrate. A depressant dosage of 200 g/t (level 1) causes the apatite content to decrease as the collector dosage decreases. The reason for this is the greater collection of undesirable oxides at low depressant dosages. To collect a larger quantity of hydrophobic apatite particles it requires increasing the collector dosage. Unlike the grade, the apatite recovery rate increased in response to increase in the collector dosage and the reduction of the depressant dosage, as illustrated in Fig. 7. Therefore, the optimal operating condition to increase the recovery of P2 O5 is a dosage of 80 g/t of collector and 200 g/t of depressant. In Fig. 8, note that a reduction of the air flow allied to an increase in the depressant dosage increases the selectivity ratio of Fe2 O3 , improving the quality of the concentrate. The depressant acts on the surface of gangue minerals, preventing them from being collected. This fact, allied to a condition of low concentration of bubbles, prevents the indiscriminate recovery of particles, enabling the bubbles to preferentially carry hydrophobic particles. The selectivity ratio of SiO2 increased in response to the elevation of the recycle flow rate and the depressant dosage and the decrease in collector dosage and air flow rate, as indicated in Fig. 9. This behavior was also observed from the content of P2 O5 and the selectivity ratio of Fe2 O3 , indicating that these conditions favor the selectivity of the process. 4. Conclusions The use of a mixture of the synthetic reagent KE and rice oil soap, a conventional collector, considerably increased the selectivity of the concentrate, i.e., it increased the P2 O5 grade in the flotation product while keeping the recovery rate at expected levels. A concentration of 29.4 wt.% of P2 O5 and a recovery rate of 46.2 wt.% were obtained by working with a depressant dosage of 500 g/t and a collector dosage of 80 g/t, the collector consisting of a mixture of 80 wt.% of ROS and 20 wt.% of KE. It was possible to quantify the influence of the operating variables on the flotation responses: grade, recovery and selectivity ratios. The operating conditions that benefited from the phosphorus content were the same as those that increased the selectivity ratio of Fe2 O3 and SiO2 and reduced the apatite recovery rate. The results presented in this work demonstrate that the reject from the phosphate concentration process of Bunge Brazil SA, which shows a concentration of 9.52 wt.% P2 O5 , is potentially reusable through the flotation process.

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