AU2011364769A1

AU2011364769A1 - Method for producing titanium dioxide concentrate

Info

Publication number: AU2011364769A1
Application number: AU2011364769A
Authority: AU
Inventors: Ryuichi ARAYASHIKI; Shigeki Ikeda
Original assignee: JFE Mineral Co Ltd
Current assignee: JFE Mineral Co Ltd
Priority date: 2011-04-07
Filing date: 2011-05-26
Publication date: 2013-10-10
Anticipated expiration: 2031-05-26
Also published as: WO2012137359A1; CN103459625A; CN103459625B; JP4870845B1; AU2011364769B2; BR112013025554B1; BR112013025554A2; JP2012219313A; ZA201307181B

Abstract

The present invention enables a high-grade concentrate in which titanium dioxide has been highly concentrated to be inexpensively produced from a low-grade titanium dioxide ore. A powdery titanium dioxide ore is subjected to reverse flotation (A) and flotation (B) in this order. In the reverse flotation (A), a concentrate is sedimented in an aqueous solution to which a cationic collector and starch have been added and which has a pH adjusted to 10 or higher. In the flotation (B), a concentrate is floated in an aqueous solution to which an anionic collector, hydrofluoric acid, and a frothing agent have been added and which has a pH adjusted to 2-3. It is preferred that the reverse flotation (A) and the flotation (B) should be preceded by a step in which a powdery titanium dioxide ore obtained through particle size regulation (F) is subjected to gravity concentration (G) and magnetic separation (H) in this order, and that the reverse flotation (A) and the flotation (B) should be succeeded by a step in which the concentrate separated through flotation in the flotation (B) is subjected to gravity concentration (C), drying (D), and magnetic separation (E) in this order.

Description

DESCRIPTION Title of Invention METHOD FOR PRODUCING TITANIUM DIOXIDE CONCENTRATE Technical Field [0001] The present invention relates to a method for producing a titanium dioxide concentrate, the method including benefication of titanium dioxide ore, for obtaining a concentrate with an increased titanium dioxide concentration and preferably a high grade concentrate containing highly concentrated titanium dioxide. Background Art [0002] Metallic titanium and titanium dioxide used in industrial products are produced from concentrates containing highly concentrated titanium dioxide produced by benefication of titanium dioxide ore (natural ore) such as rutile. Examples of the conventional techniques for performing benefication of titanium dioxide ore to obtain a concentrate in which titanium dioxide is concentrated are as follows: (1) Method for separating and removing gangue components (quarts, magnetite, monazite, zircon, etc.) in - 2 the ore through combining gravity concentration, magnetic separation, electrostatic separation, and the like (for example, see Non Patent Literature 1) (2) Chemical method that combines acid leaching for removing mainly iron and high-temperature reduction for forming TiO 2 -slag (for example, see Patent Literature 1) (3) Method that combines magnetic separation, flotation, electrostatic separation, high-temperature reduction, and the like (for example, see Patent Literature 2) Citation List Patent Literature [00031 [PTL 1] Japanese Unexamined Patent Application Publication No. 2009-511755 [PTL 21 Japanese Unexamined Patent Application Publication No. 55-59853 Non Patent Literature [0004) [NPL 1] Kenji TOMITA, National Research Institute for Pollution and Resources, "Benefication of non-metallic minerals", Ceramic Society of Japan, July 10 (1974), pp. 193-197 Summary of Invention Technical Problem [0005] - 3 However, of the conventional techniques described above, the methods (1) and (3) could only increase the titanium dioxide concentration in the concentrate to a limited level and thus there is a problem in that it is difficult to obtain high grade titanium dioxide concentrates. In particular, rutile from the Brazilian state of Minas Gerais occurs with kyanite (SiO 2 -A120 3 ) and it is difficult to obtain high grade concentrates therefrom by conventional techniques. The methods (2) and (3) have limitations in increasing the titanium dioxide concentration in the concentrate at low cost. Accordingly, an object of the present invention is to provide a method for producing a titanium dioxide concentrate, by which a concentrate having an increased titanium dioxide concentration can be obtained from low grade titanium dioxide ore at low cost and, preferably, by which a high grade concentrate containing highly concentrated titanium dioxide can be obtained at low cost. Solution to Problem [0006] The inventors of the present invention have conducted extensive researches on a method for obtaining a high grade concentrate at a low cost by employing only physical benefication to achieve the object described above. As a result, they have found that a high grade concentrate - 4 containing highly concentrated titanium dioxide can be obtained from low grade titanium dioxide ore by sequentially performing reverse flotation and flotation on powdery titanium dioxide ore under particular conditions and more preferably by combining steps such as size control, gravity concentration, and magnetic separation in a particular manner before and after the reverse flotation and flotation steps. In particular, they have found that a high grade concentrate can be obtained from low grade titanium dioxide ore that occurs with kyanite, for example. [0007] The present invention has been made based on these findings and can be summarized as follows. [1] A method for producing a titanium dioxide concentrate containing titanium dioxide at an increased concentration through benefication of titanium dioxide ore, the method comprising performing reverse flotation (A) and flotation (B) sequentially in that order on powdery titanium dioxide ore, wherein the reverse flotation (A) includes adding a cationic collector and starch and separating a concentrate by settling in an aqueous solution having a pH value adjusted to 10 or more, and the flotation (B) includes adding an anionic collector, hydrofluoric acid, and a foaming agent and separating a concentrate by flotation in an aqueous solution having a pH value adjusted to 2 to 3.

- 5 {2] The method for producing a titanium dioxide concentrate according to [1] above, wherein the concentrate separated by flotation in the flotation (B) is subjected to gravity concentration (C), drying (D), and magnetic separation (E) sequentially in that order. [0008] [3] The method for producing a titanium dioxide concentrate according to [2] above, wherein the magnetic separation (E) includes performing dry high magnetic separation at 8000 gauss or higher. [4] The method for producing a titanium dioxide concentrate according to any one of [1] to [3] above, wherein powdery titanium dioxide ore obtained through size control (F) is subjected to gravity concentration (G) and magnetic separation (H) sequentially in that order and then to the reverse flotation (A) and the flotation (B). [5] The method for producing a titanium dioxide concentrate according to [4], wherein the size control (F) includes performing crushing and classification on titanium dioxide ore so as to obtain the powdery titanium dioxide ore. [0009] [6] The method for producing a titanium dioxide concentrate according to [4] or [5] above, wherein the concentrate that underwent the gravity concentration (G) is subjected to size control (I) and then to magnetic separation (H).

- 6 [7] The method for producing a titanium dioxide concentrate according to any one of [2] to [6] above, wherein, in the gravity concentration (C) and the gravity concentration (G), at least one selected from concentration by using a table concentrator, concentration by using a spiral concentrator, and concentration by using a jig concentrator is performed. [8] The method for producing a titanium dioxide concentrate according to any one of [1] to [7] above, wherein the titanium dioxide ore is rutile. [9] The method for producing a titanium dioxide concentrate according to any one of [1] to [8] above, wherein the produced titanium dioxide concentrate has a titanium dioxide content of 90 mass% or more. Advantageous Effects of Invention [0010] According to the present invention, a high grade concentrate containing highly concentrated titanium dioxide can be obtained from low grade titanium dioxide ore at low cost without using chemical or thermal concentration techniques. Thus, a high grade concentrate containing highly concentrated titanium dioxide can be obtained at low cost from rutile that occurs with kyanite (SiO 2 -A120 3 ) mined from the Brazilian state Minas Gerais. Brief Description of Drawings [0011] -7 Fig. 1 is a diagram showing a process flow according to an embodiment of the present invention. Fig. 2 is a diagram showing a part of a process flow of a more specific embodiment of the present invention. Fig. 3 is a diagram showing another part of a process flow of the more specific embodiment of the present invention (continuation from the process flow in Fig. 2). Fig. 4 is a diagram showing another part of a process flow of the more specific embodiment of the present invention (continuation from the process flow in Fig. 3). Description of Embodiments [0012] A method for producing a titanium dioxide concentrate according to the present invention is a method for obtaining a concentrate containing concentrated titanium dioxide through benefication of titanium dioxide ore. Basically, the method involves sequentially performing reverse flotation (A) and flotation (B) on powdery titanium dioxide ore in that order under particular conditions. Preferably, (1) before the steps of reverse flotation (A) and flotation (B), powdery titanium dioxide ore obtained through size control (F) is subjected to gravity concentration (G) and magnetic separation (H) in that order (followed by the reverse flotation (A) and then the flotation (B)); or (2) after the steps of reverse flotation (A) and flotation (B), - 8 the concentrate separated through the flotation (B) is subjected to gravity concentration (C), drying (D), and magnetic separation (E) in that order. For the purposes of the present invention, a Concentrate" refers to a "mineral that contains titanium dioxide" processed or separated in each of the steps for obtaining a concentrate (product) containing concentrated titanium dioxide. [0013] A representative example of the titanium dioxide ore to be subject to beneficiation of the present invention is rutile. Other examples include anatase and brookite. These can be used alone or in combination. In particular, although it is considered difficult to obtain high grade titanium dioxide concentrates from rutile mined in the Brazilian state of Minas Gerais because of kyanite (SiO 2 -A120 3 ) that occurs therewith, such rutile can be subjected to the benefication. In a region that produces such rutile, metamorphic rocks such as gneiss and schist are mainly distributed and the rutile deposits occur with pegmatite lodes penetrating the metamorphic rocks. Such deposits are of a residual type that arose as a result of weathering of pegmatite and concentration of rutile. The grain size distribution of the rutile is about 80 mass% for 0.5 to 0.045 mm and isolated rutile becomes notable from -9 about a grain size of 0.15 mm. [0014] In general, the TiO 2 content of titanium dioxide ore (natural mineral) such as rutile is about 2 mass% or less. The present invention aims to obtain a concentrate containing highly concentrated TiO 2 (a concentrate with a TiC 2 content of preferably 90 mass% or more and more preferably 95 mass% or more) from titanium dioxide ore having such a TiO 2 content. Note that from the viewpoints of production cost and process efficiency, the titanium dioxide ore (natural mineral) used as a raw material in the present invention preferably has a TiC 2 content of 0.5 mass% or more. Examples of the gangue components of the ore to be separated and removed through a series of steps of the present invention include quartz (SiC 2 ), kyanite (SiO 2 -Al 2

C

3 ), zircon (ZrSiO 4 ), monazite ((Ce-Th)PO4), garnet (3FeO-Al 2

O

3 .3SiO 2 ), and bauxite (A1 2 0 3 .3H 2 0). Separation and removal of these gangue components give a concentrate containing highly concentrated TiO 2 . [0015] Fig. 1 shows a process flow according to an embodiment of the present invention. In this embodiment, the process is performed on ore (raw ore) in the order of size control (F), gravity concentration (G), size control (I), magnetic separation (H), reverse flotation (A), flotation (B), - 10 gravity concentration (C), drying (D), and magnetic separation (E) and a high grade titanium dioxide concentrate is obtained as a result. In the first step of size control (F), raw ore (raw material ore) is subjected to classification, crushing, and pulverizing to adjust the size of the ore to a level suitable for benefication. The ore may be washed (water washed) to also perform classification. Usually the classification in the size control (F) is conducted in two or more stages and the classification of the last stage is preferably conducted by using a cyclone separator which is a wet-type classifier. In size control (F), the size of the ore is preferably adjusted to 1 mm or less (preferably 0.020 mm or more and 1 mm or less). [0016] The gravity concentration (G) is performed on the powdery titanium dioxide ore obtained through the size control (F) and aims to separate and remove low-specific gravity minerals. A table concentrator, a jig concentrator, a spiral concentrator, or the like can be used as the gravity concentrator but a spiral concentrator that utilizes centrifugal gravity is particularly preferable. The size control (I) is performed as needed so that the concentrate that had been concentrated in the gravity concentration (G) can be further subjected to classification - 11 and pulverization so as to decrease the grain size and adjust the grain size to a level more suitable for benefication (reverse flotation (A) and flotation (B)). In the size control (I), the size of the ore is preferably controlled to 0.25 mm or less (preferably 0.020 mm or more and 0.25 mm or less) . A cyclone separator which is a wet type classifier is preferably used in the classification of this step also. The magnetic separation (H) is performed on the concentrate that underwent the gravity concentration (G) or the size control (I) and iron oxides (magnetic materials) are mainly removed as a result. Magnetic separation is preferably performed by using a wet-type magnetic separator. [0017] The reverse flotation (A) and flotation (B) are sequentially performed on a concentrate that underwent the magnetic separation (H). The reverse flotation (A) is mainly performed to substantially completely remove the remaining quartz and the subsequent flotation (B) is performed to separate and remove gangue components which are mainly kyanite and zircon. In the reverse flotation (A), a cationic collector and starch are added and the concentrate is settled and separated in an aqueous solution having a pH value adjusted to 10 or higher. In the reverse flotation, the gangue - 12 components are separated as froth and the concentrate is recovered as sinks. Thus, a cationic collector that hydrophobizes the surfaces of the gangue components to be separated and removed as froth and generates air bubbles and starch that hydrophilizes the concentrate and promotes settling are added. Minerals with high heavy element contents easily bond with starch and become hydrophilic and easier to settle because the bubbles do not easily attach thereto. The pH of the aqueous solution is adjusted to 10 or higher in order to disperse the mineral particles and suppress aggregation and settling of the gangue components. [0018] The cationic collector is particularly preferably an amino-based collector such as a monoamino-based collector or a diamino-based collector. A monoamino-based collector (for example, trade name "EDA 3" produced by Clariant S.A.) is most preferable. The amount added is preferably about 200 to 300 g/t (g/t: amount added per ton of solid matter in the material to be processed, the same applies hereinafter). If the amount added is low, the effect of addition is small and if the amount added is excessively high, the concentrate may float. The amount of starch added is preferably about 300 to 600 g/t. If the amount added is low, the effect of addition is small and if the amount added is excessively high, the - 13 gangue components may settle. When the pH of the aqueous solution in which the reverse flotation (A) is performed is less than 10, the gangue components are not smoothly dispersed. Although a pH exceeding 11 does not affect dispersing of the gangue components, the amount of the pH adjustor used is increased. Accordingly, in order to suppress the amount of the pH adjustor used, the upper limit of the pH is preferably about 11. An alkali such as caustic soda is usually used as the pH adjustor. [00191 In the flotation (B), an anionic collector, hydrofluoric acid, and a foaming agent are added and the concentrate is separated by flotation in an aqueous solution having a pH adjusted to 2 to 3. In this flotation, the concentrate is recovered as froth and the gangue components are separated as sinks. Accordingly, an anionic collector is added to selectively separate the concentrate from other heavy minerals (gangue components) and hydrofluoric acid (depressant) that adheres to and hydrophilizes surfaces of the gangue components to be separated and removed is added. Moreover, a foaming agent is added to generate air bubbles. In order to ensure floatability of the concentrate by accelerating adsorption of the anionic collector, the pH of the aqueous solution is adjusted to 2 to 3.

- 14 [0020] The anionic collector is particularly preferably a phosphonic acid-based collector (for example, trade name "Flotinor 1683" produced by Clariant S.A.) The amount added is preferably about 150 to 200 g/t. If the amount added is small, the effect of addition is small and if the amount is excessively large, heavy minerals (gangue components) other than the concentrate may float. Hydrofluoric acid is preferably hydrogen fluoride or a salt thereof, for example. These may be used alone or in combination. The amount added is preferably about 600 to 1000 g/t. If the amount added is small, the effect of addition is small and if the amount is excessively large, floating of the concentrate may be suppressed. [00211 The foaming agent is preferably a petroleum-based foaming agent (trade name "MIBC" produced by Shell Oil Company), a synthetic alcohol-based foaming agent (trade name "AEROFROTH 65" produced by Cytec Industries Inc.), or the like. These may be used alone or in combination. The amount added is preferably about 1 to 2 g/t. If the amount added is small, the effect of addition is small and if the amount is excessively large, the minerals (gangue components) other than the concentrate may float. When the pH of the aqueous solution in which the - 15 flotation (B) is conducted is less than 2, adsorption of the collector is likely to decrease. In contrast, at a pH exceeding 3, the minerals (gangue components) other than the concentrate may float. An acid (a hydrochloric acid solution or the like) is usually added as a pH adjustor. Since a small amount of TiO 2 is contained in the sinks in the flotation (B), the sinks may be recovered and returned to the flotation (B) system. A flotation machine used in reverse flotation (A) and flotation (B) may be any of an Agitair flotation machine, a Denver A flotation machine, and the like. In a typical flotation machine, stirring is conducted with stirring means such as an impeller while air is injected to a process tank containing an aqueous solution (slurry) containing minerals so as to mix the minerals with air (air bubbles) to allow air bubbles to adhere to some of the minerals. Then the minerals are separated and removed as froth and the remaining minerals are settled as sinks. [0022] The gravity concentration (C) is performed on the concentrate (froth) obtained by the flotation (B) and aims to separate and remove the gangue components which are mainly kyanite and zircon that were left unseparated and unremoved by the flotation (B). In general, a vibrating table (for example, a James table and a Wilfley table) is - 16 used as a gravity concentrator. When small-size minerals are concerned as in the gravity concentration (C), a James table is particularly preferable among vibrating tables. In drying (D), the concentrate recovered in the gravity concentration (C) is dried. The drying (D) is performed to facilitate the subsequent step of magnetic separation. In general, a high magnetic separator is of a dry type. In the drying, the concentrate is dried until the moisture content is about 1 to 2 mass%. The dryer can be a rotary dryer or the like. [0023] The magnetic separation (E) is performed on the concentrate dried in the drying (D). The magnetic separation (E) aims to separate and remove mainly monazite and it is preferable to perform dry high magnetic separation involving a magnetic force of 8000 gauss or higher. In general, it is difficult to remove monazite at a magnetic force less than 8000 gauss. Note that the upper limit of the magnetic force of typical magnetic separators is about 10000 gauss. As a result of the magnetic separation (E), a titanium dioxide concentrate having a TiO 2 content of 90 mass% or more (preferably 95 mass% or more) can be obtained as non magnetics. [0024] - 17 In general, among various types of titanium dioxide ores, rutile that occurs with kyanite (SiO 2 'Al 2 0 3 ) is considered particularly difficult to separate titanium dioxide from kyanite. However, according to the present invention, combining reverse flotation (A) and flotation (B) under particular conditions and more preferably combining steps such as size control, gravity concentration, and magnetic separation to be performed before and after the reverse flotation (A) and the flotation (B) in a particular manner enable efficient separation and removal of gangue components including kyanite and thus a high grade titanium dioxide concentrate can be obtained. [0025] Figs. 2 to 4 show a process flow according to a specific embodiment of the present invention. The steps will now be described in the order in which they are performed in this specific embodiment. - Size control (F) As shown in Fig. 2, ore (raw ore) of a particular size (for example, 100 mm or less) is fed into a drum washer 20 having a particular sieve mesh (for example, a sieve mesh of 20 mm) through a vibrating feeder 25, and washed with water while being classified in the drum washer 20. The undersize ore (e.g., -20 mm fraction) is sent to a sieve 22 of the next step. Meanwhile, the oversize ore (e.g., +20 mm - 18 fraction) is crushed with a crusher 21 such as a cone crusher and again charged into the drum washer 20. The drum washer 20 also has a function of loosening the ore with water. [0026] The undersize ore (for example, -20 mm fraction) of the drum washer 20 is sifted with the sieve 22 having a smaller sieve mesh (for example, a sieve mesh of 1 mm) and the undersize ore (for example, -1 mm fraction) is sent to a cyclone separator 24 of the next step. The oversize ore (for example, +1 mm fraction) is again crushed with a wet type crusher 23 and again sifted with the sieve 22. A ball mill, a rod mill, a vibration mill, or the like can be used as the wet-type crusher 23. The undersize ore (for example, -1 mm fraction) of the sieve 22 is classified with a wet classifier, cyclone separator 24, and fines (for example, 0.020 mm fraction) are separated by setting a particular size (for example, 0.020 mm) as a cut point. Fines are separated and removed to remove the clay component in the ore. The first-stage classification that uses the cyclone separator 24 is controlled by the pressure at the inlet (for example, 1 kg/cm 2 ) and the dirt component having high alumina (A1 2 0 3 ) and silica (SiO 2 ) contents is discharged outside the system as overflow water and treated as tailings. [0027] - 19 Gravity concentration (G) The ore of a particular size (for example, 0.020 to 1 mm) that underwent classification by the cyclone separator 24 is separated into a concentrate C, a middling M, and tailings T by two stages of gravity concentrators 30 and 31 as shown in Fig. 3. While table-type and jig-type gravity concentrators are available, a spiral concentrator that utilizes centrifugal gravity is particularly preferable. In this embodiment, the first-stage gravity concentrator is a rougher spiral concentrator and the second-stage gravity concentrator consists of a low-grade spiral concentrator and a middle grade spiral concentrator. As shown in the drawings, a concentrate to be sent to a next step is obtained in accordance with the flow shown by the concentrate C, the middling M, and the tailings T in the drawing. The tailings discarded are mainly clay and quartz. [0028] - Size control (I) The concentrate (ore) obtained in the gravity concentration (G) is classified with a wet-type classifier, cyclone separator 40 (the cyclone separator of the second stage) and a coarse component (for example, +0.25 mm fraction) is separated at a cut point of a particular size (for example, 0.25 mm). The classification by the cyclone separator 40 of the second stage is controlled by the - 20 pressure (1 kg/cm2) at the inlet and a small (for example 0.25 mm) concentrate is sent to the next step, which is magnetic separation (H). A coarse (for example, +0.25 mm) concentrate is crushed with a wet-type crusher 41 and classified with a wet-type cyclone separator 42 at the third stage and the fines (for example, -0.020 mm fraction) are separated at a cut point of a particular size (for example 0.020 mm). Meanwhile, the coarse (for example, +0.020 mm) ore is recirculated to the cyclone separator 40 of the second stage. [0029] Magnetic separation (H) The concentrate having a particular size (for example, 0.020 to 0.25 mm) that underwent classification with the cyclone separator 40 in the size control (I) is magnetically separated with a wet-type magnetic separator 50. In this step, for example, a wet-type magnetic separator equipped with a drum-type permanent magnet having a magnetic force of about 1000 gauss is used to magnetically separate magnetics from non-magnetics. The magnetics to be discarded are mainly iron oxides having ferromagnetism and the non magnetics are recovered as a concentrate. [0030] Reverse flotation (A) - flotation (B) The concentrate (non-magnetics) separated in the - 21 magnetic separation (H) is stored in conditioner tanks 11a and 11b as shown in Fig. 4 where the composition is adjusted (for example, adding water and additives) to prepare for reverse flotation. As discussed earlier, the reverse flotation is performed to separate the gangue components as froth and recover the concentrate as sinks. Accordingly, a cationic collector that adheres to surfaces of gangue components to be separated and removed as froth and improves hydrophobicity and frothability is added and, at the same time, starch that hydrophilizes the concentrate and promotes settling of the concentrate is added. The pH of the aqueous solution is adjusted to 10 or more (preferably 11 or less) in order to accelerate dispersion of mineral particle groups. The concentrate (slurry) having a composition adjusted in the conditioner tanks lla and 11b is then sent to a flotation machine 10 and reverse flotation is performed to separate and remove (discard) the gangue components mainly constituted by quarts as froth and recover the concentrate as sinks. [0031] The concentrate (sinks) recovered by the reverse flotation (A) is stored in conditioner tanks 13a and 13b where the composition is adjusted (for example, adding water and additives) to prepare for flotation. As discussed earlier, the flotation is performed to recover the - 22 concentrate as froth and separate the gangue components as sinks. Accordingly, an anionic collector that allows selective separation of the concentrate from other heavy minerals (gangue components) is added, hydrofluoric acid (depressant) that adsorbs to the surfaces of the gangue components to be separated and removed and hydrophilizes the surfaces is added, and a foaming agent that generates air bubbles is added. The pH of the aqueous solution is adjusted to 2 to 3 in order to ensure the floatability of the concentrate. [0032] The concentrate (slurry) having a composition adjusted in the conditioner tanks 13a and 13b is then sent to a flotation machine 12 and flotation is performed to separate and remove (discard) the gangue components mainly constituted by kyanite and zircon as sinks and recover the concentrate as froth. An Agitair flotation machine, a Denver A flotation machine, and the like are available as the flotation machine. In the reverse flotation (A) and flotation (B), any of these flotation machine may be used. The sinks are settled with a thickener and dewatered with dewatering means (dewatering screen or the like) . The overflow water treated with a thickener is recirculated as process water. In Fig. 4, reference numeral 14 denotes a dewatering screen.

- 23 [0033] Gravity concentration (C) The concentrate (froth) recovered by the flotation (B) is sent to a vibrating table 60 serving as a gravity concentrator and separated into a concentrate and tailings. A James table is usually used as the vibrating table 60. - Drying (D) The concentrate recovered by the gravity concentration (C) is dried in a dryer 70 such as a rotary dryer. - Magnetic separation (E) The concentrate dried in the drying (D) is magnetically separated with a dry-type high magnetic separator 80 to obtain a concentrate as non-magnetics. The dry-type high magnetic separator 80 is preferably a rare earth roll separator. A titanium dioxide concentrate having a TiO 2 content of 90 mass% or more (preferably 95 mass% or more) can be obtained through these steps. [0034] In the present invention, the steps other than the reverse flotation (A) and the flotation (B) are optional. For example, various steps shown in Figs. 1 and 2 to 4 can be appropriately combined as needed and performed. In the embodiment shown in Figs. 1 and 2 to 4, the gravity concentration (G), the size control (I), and the magnetic - 24 separation (H) may be omitted and the ore that underwent the size control (F) may be sequentially subjected to the reverse flotation (A) and the flotation (B) . Alternatively, in the embodiment shown in Figs. 1 and 2 to 4, the gravity concentration (C), the drying (D), and the magnetic separation (E) may be omitted and the reverse flotation (A) and the flotation (B) may be repeated two or more times instead. In other words, the following embodiments (1) to (3) are possible. Note that in the embodiments (1) and (3) below, the size control (F) is preferably performed to decrease the size of the ore to a sufficiently smaller size (for example, 0.025 mm or less) than the ore obtained in the size control (F) of the embodiment shown in Figs. 1 and 2 to 4. (1) size control (F) -> reverse flotation (A) -+ flotation (B) -> gravity concentration (C) -+ drying (D) -+ magnetic separation (E) (2) size control (F) -+ gravity concentration (G) -4 size control (I) -> magnetic separation (H) -> two or more times of [reverse flotation (A) -> flotation (B)] (3) size control (F) -+ two or more times of [reverse flotation (A) -> flotation (B)] [Examples] [0035] Rutile mined from the Brazilian state Minas Gerais was - 25 concentrated under the following conditions according to the process flow shown in Figs. 2 to 4. The grade of the raw ore and the grade of the concentrate (product) are shown in Table 1. Table I (mass%) TiO 2 Fe 2 0 3 Si0 2 A1 2 0 3

P

2 0 5 ZrO 2 Other Grade of 0.77 18.03 56.60 22.68 0.20 0.17 1.71 raw ore Grade of 94 - 0.8 1 N.D 2.3 * concentrate Grade of NbO ThO 2 Ta 2 0 5 concentrate 0.6 N.D N.D (*) ____ ____ _ [0036] Ore (grain size: 100 mm or less) from a mine was fed to a drum washer 20 having a sieve mesh (aperture) of 20 mm through a vibrating feeder 25 at a rate of 500 t/h (t/h: the number of tons per hour, the same applies hereinafter) and classified while conducting washing with water. The +20 mm ore was crushed with a crusher (cone crusher) 21 to -20 mm and re-charged into the drum washer 20. The -20 mm ore was - 26 sieved with a sieve 22 having a 1 mm sieve mesh. The +1 mm ore was crushed with a wet-type crusher 23 (ball mill) and again sieved with the sieve 22. The crushing step was a closed circuit where all of the ore was crushed to -1 mm ore and 500 t/h of the ore was fed to a cyclone separator 24 used in the next step. [0037] The -1 mm ore was classified with the cyclone separator 24 and the fines (-0.020 mm fraction) were separated at a cut point of 0.020 mm. In the cyclone separator 24, the inflow pressure was set to 1 kg/cm 2 so as to set the cut point to 0.020 mm. The amount of fines (-0.020 mm) separated by the cyclone separator 24 was 35 t/h and the fines were discarded as tailings. The amount of the concentrate (0.020 to 1 mm) sent to the next step was 465 t/h. The concentrate was fed to a first-stage spiral gravity concentrator 30 and separated into a concentrate C, a middling M, and tailings T which were each fed to a second stage spiral gravity concentrator 31 for further concentration. The amounts of these fed to the second-stage gravity concentrator 31 were as follows: concentrate C: 35 t/h (8 mass%), middling M: 115 t/h (25 mass%), tailings T: 315 t/h (67 mass%). [0038] - 27 The amount of the concentrate (second concentrate) obtained by the second-stage gravity concentrator 31 was 25 t/h and the amount of the discarded tailings was 440 t/h. The percentage of the obtained concentrate relative to the concentrate fed from the cyclone separator 24 of the previous step was 5.4 mass%. The concentrate obtained by the gravity concentration was classified with a second-stage cyclone separator 40 and the +0.25 mm fraction was separated at a cut point of 0.25 mm. In the cyclone separator 40, the inflow pressure was set to 1 kg/cm 2 so as to set the cut point to 0.25 mm. The amount of the +0.25 mm concentrate generated was 15 t/h. The concentrate was crushed with a wet-type crusher 41 and classified with a third-stage cyclone separator 42. The cut point of a third-stage cyclone separator 42 was 0.020 mm. The -0.020 mm fraction was discarded outside the system as tailings and the +0.020 mm fraction was returned to the second-stage cyclone separator 40. The amount of the concentrate (third concentrate) sent to the next step after classification with the second-stage cyclone separator 40 was 23 t/h. [0039] Next, the concentrate was separated into magnetics and non-magnetics by magnetic separation using a wet-type magnetic separator 50 equipped with a drum-type 1000 gauss permanent magnet. The percentages of the magnetics and the - 28 non-magnetics were 98.7 mass% and 1.3 mass%, respectively. The concentrate (magnetics) separated by magnetic separation was sequentially stored in conditioner tanks lla and 11b and the composition thereof was adjusted to prepare for reverse flotation. In the conditioner tank 11a, a caustic soda (NaOH) solution was added to adjust the pH value to be in the range of 10 to 11 and 600 g/t of starch was added as a depressant. Then in the conditioner tank l1b, 300 g/t of a cationic collector "EDA3" was added. The conditioning time (the time taken for blending after addition of the additive) was 5 minutes. [0040] Reverse flotation was performed in two stages (roughing-cleaning) by using an Agitair flotation machine as the flotation machine 10. The air pressure supplied to the process tank was 2 kg/cm 2 and the rotation rate of the impeller was 1000 rpm. The amount of the sinks obtained by the reverse flotation was 15.7 t/h and the amount of froth obtained was 7 t/h. The percentages thereof were 69.1 mass% and 30.9 mass%, respectively. The sinks were sequentially stored in conditioner tanks 13a and 13b and the composition thereof was adjusted to prepare for flotation. In the conditioner tank 13a, a 50% hydrochloric acid solution was added to adjust the pH value to 3, and 1000 g/t of hydrofluoric acid - 29 serving as a depressant and 1 g/t of a foaming agent "AEROFROTH 65" (synthetic alcohol-based foaming agent) were added. In the conditioner tank 13b, 200 g/t of an anionic collector "Flotinor 1683" was added. The conditioning time (the time taken for blending after addition of the additive) was 5 minutes. Flotation was performed in three stages (roughing cleaning-recleaning) by using an Agitair flotation machine as the flotation machine 12. The air pressure supplied to the process tank was 2 kg/cm 2 and the rotation rate of the impeller was 1000 rpm. [0041] TiO 2 , Fe 2 0 3 , SiC 2 , A1 2 0 3 , P 2 0 5 , and Zr 2 0 balances of the froth separated by reverse flotation (froth 1 separated in the first stage "roughing" and froth 2 separated in the second stage "cleaning"), the sinks separated by flotation (sinks 1 separated by the first-stage "roughing", sinks 2 separated by the second-stage "cleaning", and sinks 3 separated by the third-stage "recleaning"), and the concentrate obtained after reverse flotation and flotation are shown in Table 2. [0042] As shown in Tables 2A and 2B, in reverse flotation, Fe 2 0 3 : 15.9 mass%, SiC 2 : 79.34 mass%, A120 3 : 34.22 mass%,

P

2 0 5 : 35.87 mass%, and Zr 2 0: 58.0 mass% were removed as the - 30 froth 1; and Fe 2 0 3 : 2.4 mass%, SiO 2 : 9.71 mass%, A1 2 0 3 : 5.96 mass%, P 2 0 5 : 4.28 mass%, and Zr 2 0: 11.8 mass% were removed as the froth 2. In the subsequent flotation, Fe 2 0 3 : 62.9 mass%, SiO 2 : 10.59 mass%, Al2O 3 : 52.92 mass%, P 2 0 5 : 48.6 mass%, and Zr 2 0: 18.2 mass% were removed as the sinks 1; Fe 2 0 3 : 14.8 mass%, SiO 2 : 0.32 mass%, Al2O 3 : 6.04 mass%, P205: 8.83 mass%, and Zr 2 0: 8.1 mass% were removed as the sinks 2; and Fe 2

O

3 : 1.3 mass%, A1 2 0 3 : 0.45 mass%, P 2 0 5 : 0.76 mass%, and Zr 2 0: 0.6 mass% were removed as the sinks 3. As a result, a concentrate containing 30.4 mass% of TiC 2 was obtained. (00431 - 31 Table 2A (mass%) Product *1 TiO 2 balance Fe 2 0 3 balance SiC 2 balance Grade Distribution Grade Distribution Grade Distribution Froth 1 57.10 0.00 0.00 5.00 15.90 78.70 79.34 Froth 2 7.40 1.70 16.80 5.70 2.40 73.90 9.71 Sinks 1 29.80 0.70 27.20 38.10 62.90 20.10 10.59 Sinks 2 4.40 3.40 19.60 60.30 14.80 4.00 0.32 Sinks 3 0.40 3.50 1.60 63.70 1.30 2.90 0.02 Concentrate 0.90 30.40 34.80 55.60 2.70 1.60 0.02 Total 100.00 100.00 100.00 100.00 Table 2B Product *1 A1 2 0 3 balance P 2 06 balance ZrO 2 balance Grade Distribution Grade Distribution Grade Distribution Froth 1 57.10 13.60 34.22 0.10 35.87 0.20 58.00 Froth 2 7.40 18.20 5.96 0.10 4.28 0.30 11.80 Sinks 1 29.80 40.30 52.92 0.30 48.60 0.10 18.20 Sinks 2 4.40 30.90 6.04 0.40 8.83 0.30 8.10 Sinks 3 0.40 28.50 0.45 0.40 0.76 0.30 0.60 Concentrate 0.90 10.60 0.41 0.40 1.66 0.70 3.30 Total 100.00 100.00 100.00 100.00 *1 Froth 1 and 2: Froth obtained in reverse flotation (A) Sinks 1 to 3: Froth obtained in flotation (B) Concentrate: Concentrate obtained after reverse flotation (A) and flotation (B) - 32 [0044] The amount of the froth obtained by flotation was 12.7 t/h. Since the froth contained small grains and fines, the froth was subjected to gravity concentration by using a vibrating table 60 (James table) serving as a gravity concentrator. The amount of the concentrate obtained thereby (fourth concentrate) was 9.7 t/h. Next, the concentrate was dried in a dryer 70 and magnetically separated in a dry-type high magnetic separator 80 (rare earth roll separator) under application of 9000 gauss magnetic force. A titanium dioxide concentrate product was obtained as non-magnetics. The amount of the concentrate obtained was 7.5 t/h and, as shown in Table 1, the TiO 2 content was 94 mass%. Reference Signs List [0045] 10 flotation machine lla, 11b conditioner tank 12 flotation machine 13a, 13b conditioner tank 14 dewatering screen 20 drum washer 21 crusher 22 sieve 23 wet-type crusher - 33 24 cyclone separator 25 vibrating feeder 30, 31 gravity concentrator 40 cyclone separator 41 wet-type crusher 42 cyclone separator 50 wet-type magnetic separator 60 vibrating table 70 dryer 80 dry-type high magnetic separator

Claims

1. A method for producing a titanium dioxide concentrate containing titanium dioxide at an increased concentration through benefication of titanium dioxide ore, the method comprising: performing reverse flotation (A) and flotation (B) sequentially in that order on powdery titanium dioxide ore, wherein the reverse flotation (A) includes adding a cationic collector and starch and separating a concentrate by settling in an aqueous solution having a pH value adjusted to 10 or more, and the flotation (B) includes adding an anionic collector, hydrofluoric acid, and a foaming agent and separating a concentrate by flotation in an aqueous solution having a pH value adjusted to 2 to 3.

2. The method for producing a titanium dioxide concentrate according to Claim 1, wherein the concentrate separated by flotation in the flotation (B) is subjected to gravity concentration (C), drying (D), and magnetic separation (E) sequentially in that order. - 35

3. The method for producing a titanium dioxide concentrate according to Claim 2, wherein the magnetic separation (E) includes performing dry high magnetic separation at 8000 gauss or higher.

4. The method for producing a titanium dioxide concentrate according to any one of Claims 1 to 3, wherein powdery titanium dioxide ore obtained through size control (F) is subjected to gravity concentration (G) and magnetic separation (H) sequentially in that order and then to the reverse flotation (A) and the flotation (B).

5. The method for producing a titanium dioxide concentrate according to Claim 4, wherein the size control (F) includes performing crushing and classification on titanium dioxide ore so as to obtain the powdery titanium dioxide ore.

6. The method for producing a titanium dioxide concentrate according to Claim 4 or 5, wherein the concentrate that underwent the gravity concentration (G) is subjected to size control (I) and then to magnetic separation (H).

7. The method for producing a titanium dioxide concentrate according to any one of Claims 2 to 6, wherein, in the gravity concentration (C) and the gravity concentration (G), - 36 at least one selected from concentration by using a table concentrator, concentration by using a spiral concentrator, and concentration by using a jig concentrator is performed.

8. The method for producing a titanium dioxide concentrate according to any one of Claims 1 to 7, wherein the titanium dioxide ore is rutile.

9. The method for producing a titanium dioxide concentrate according to any one of Claims 1 to 8, wherein the produced titanium dioxide concentrate has a titanium dioxide content of 90 mass% or more.