WO2008157275A1

WO2008157275A1 - Solvent extraction of titanium using an aromatic diluent

Info

Publication number: WO2008157275A1
Application number: PCT/US2008/066811
Authority: WO
Inventors: Bob Zhengqi Wang; Bruce James Sabacky; Dirk Edmond Verhulst; Jacob R. Ward
Original assignee: Altair Nanotechnologies, Inc.
Priority date: 2007-06-14
Filing date: 2008-06-13
Publication date: 2008-12-24

Abstract

An improved process for solvent extraction of titanium from an aqueous solution into an organic phase containing an aromatic diluent is taught. The process includes pre-reduction,loading, scrubbing of loaded organic, pre-stripping, stripping and scrubbing of stripped organic, and produces pure titanium solutions with good kinetics and improved phase separation and purity.

Description

SOLVENT EXTRACTION OF TITANIUM USING AN AROMATIC DILUENT

FIELD OF THE INVENTION

[0001] The present invention relates to the processing of titaniferous ores or ore concentrates to titanium dioxide or titanium metal. Particularly, the process relates to solvent extraction of titanium from an aqueous solution and the transfer of titanium into a concentrated and purified titanium stream.

BACKGROUND OF THE INVENTION

[0002] US Patent 6,375,923 teaches a process to make TiO₂ pigment from ilmenite ore by digestion and separation by solvent extraction followed by spray hydrolysis and calcination. The present invention presents an improved method for the solvent extraction step.

SUMMARY OF THE INVENTION

[0003] In the solvent extraction step of the process of US patent 6,375,923, the preferred extractant is a tri-alkyl phosphine oxide (commercial name: Cyanex 923).

The preferred diluents are kerosene or Orfom SX-11 (Chevron-Phillips). This system has good extraction and stripping characteristics, but the organic phase is relatively viscous, and requires a temperature of at least 40° C to achieve a sufficiently fast phase separation between the organic and the aqueous phases. Heating to a higher temperature improves phase separation but increases the HCI partial pressure, requiring ventilation of all solutions to a scrubber and causing significant losses of HCI.

At the same time, a higher temperature increases the tendency of the solutions to hydrolyze, forming solid TiO₂ deposits which impede the flow of solution, may cause plugging of the lines and contribute to titanium losses. [0004] It has now been found that a different diluent used with Cyanex 923 over a well defined range of concentrations, achieves good phase separation at room temperature, while keeping acceptable loading and stripping properties. In one aspect, the diluent is xylene, but other low-viscosity aromatic compounds may be used.

[0005] Chemical properties of the solvent extraction system are also modified by the new diluents, leading to other unexpected surprising modifications and improvements in the process. Those improvements are also part of the present invention. Choice of the Nature and the Amount of Diluent

[0006] Replacing kerosene or Orfom SX-11 by xylene has a beneficial effect on the viscosity and the phase separation, as compared to using kerosene or SX-11 with decanol as a modifier. The concentration ranges of 5 to 15% or 35 to 40% Cyanex 923 in xylene are useful. No modifier is needed in this system. Instead of xylene, mesitylene, or mixtures of similar organics can also be used.

Pre-Reduction

[0007] In US 6,375,923, the feed solution to solvent extraction is thoroughly reduced with iron. All iron in solution is present as Fe++, and no reoxidation to Fe+++ occurs. In practice, such conditions are difficult to maintain, and some reoxidation generally occurs. Any ferric iron present in the solvent extraction system will be extracted and will eventually find its way into the eluate. Iron removal from the eluate is possible, but requires an extra processing step. In the process of the present invention, the titanium concentration in the eluate tends to be somewhat lower than in the original process, so the same amount of iron in the eluate causes a relatively higher contamination of the titanium dioxide product and the iron removal problem is more accute. To solve this problem, the feed solution is over-reduced by addition of extra iron to form titanous ion following the reaction:

Fe + 2Ti(IV) → Fe⁺⁺ + 2Ti(III) [0008] The amount of iron is adjusted in such a way that a concentration of about 3 g/l Ti(III) is obtained. Besides preventing the oxidation of ferrous iron, the titanous ion also insures that V and Cr are present in the (III) oxidation state and Mn and Fe are present in the (II) oxidation state. Besides metallic iron, other reactive metals such as aluminum may be used to achieve the same effect. Scrubbing of Loaded Organic

[0009] Even with the new diluent, the loaded organic phase contains significant amounts of impurities, particularly coloring impurities that may be extracted into the organic phase or entrained as a dispersed aqueous phase into the organic. The most important coloring impurities are Cr, Fe, V and Mn. Therefore, a scrubbing step is introduced. In the scrubbing step, the loaded organic is brought into contact with a HCI solution at high concentration (typically 9 M). In these conditions, the impurities are stripped preferentially. The scrubbing step is conducted in a mixer-settler. The mixing and settling actions also promote removal of the aqueous phase entrained in the organic phase.

Pre-Stripping [0010] Although the new diluent (xylene, etc.) provides a satisfactory eluate that can be treated further in the process, the titanium concentration of the eluate is generally lower than what is achieved with the preferred diluents in US patent 6,375,923. Without being bound by any theory, the inventors believe that the less favorable stripping conditions are due to the higher HCI loading observed in the presence of aromatic diluents in general, and particularly in the case of xylene. In the pre-stripping stage, HCI is preferentially stripped. As a consequence, the HCI concentration in the actual stripping stage is lower and higher titanium concentrations, together with lower HCI concentrations, can be obtained in the stripping step. Two methods for performing pre- stripping are presented here, and are both part of the present invention: 1. The loaded organic phase is equilibrated with a small amount of dilute HCI solution. In such conditions, HCI is stripped preferentially and the chloride loading of the organic phase can be decreased without significantly decreasing the titanium content. The equilibrium titanium concentration in the eluate in the main stripping step is favorably influenced by the pre-stripping operation, and a larger concentration of Ti in the eluate can therefore be obtained. ^• -

2. The loaded organic phase is placed in a condition where a substantial vapor pressure of HCI is in equilibrium with this phase and where a substantial amount of HCI can be removed by sweeping the gas phase. This method allows the removal of chloride without entraining any titanium. Scrubbing of the Stripped Organic Phase

[0011] It was also found that in the conditions of the present process, the stripped organic often does not separate completely from the eluate. Therefore, a significant amount of eluate with a relatively high concentration of Ti is recycled to the loading stage, and this decreases the net amount of titanium extracted. A scrubbing stage, where the stripped organic phase is contacted with a small amount of HCI solution of moderate concentration (1.5-3 M) has therefore been introduced. The contacting may occur in a mixer settler where the aqueous phase is recirculated from the settler to the mixer. The mixing action in the mixer promotes disengagement in the settler. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. 1 is a general flow sheet of the solvent extraction of titanium, showing, by way of example, two extraction stages and four stripping stages.

[0013] Fig. 2 is a flow sheet of an embodiment of the process according to the present invention, showing additional steps of pre-reduction, pre-stripping, scrubbing of the loaded organic and scrubbing of the stripped organic. [0014] Fig. 3 is a schematic drawing showing the principle of pre-stripping by vacuum evaporation.

[0015] Fig. 4 shows an embodiment of the pre-stripping unit including vacuum evaporation and condensation, where HCI gas is removed from the loaded organic phase and is redissolved in a dilute HCI solution in a condensation column. [0016] Fig. 5 shows the effect of the HCI concentration in the pre-stripping solution on the titanium concentration in the pre-stripping eluate.

[0017] Fig. 6 shows the molar ratio of the amount of Cl to Ti stripped from the organic phase as a function of the ratio of the organic phase to aqueous phase.

Detailed Description of the Invention [0018] The present invention is a solvent extraction process for extracting titanium from an aqueous feed solution and transferring it to a product solution or eluate. The solvent extraction process may be part of a processing method to make T1O₂ pigment, TiC"₂ nanoparticles, or another form of Tiθ₂ from a titaniferous ore. In particular, the method of the present invention is an inventive improvement over the solvent extraction step taught in US Patent 6,375,923. [0019] The solvent extraction process may include a number of loading steps and a number of stripping steps. The loading steps and the stripping steps may take place in mixer-settlers. The loading and stripping steps may also take place in columns. Primarily, the object of the present invention is an improved organic mixture that allows better separation of phases while keeping good extraction and stripping characteristics. This central idea becomes more valuable and leads to a better process when it is associated with the other features of the invention. The improvements of the present invention comprise a pre-reduction step, a loaded organic scrubbing step (scrubbing 1), a pre-stripping step, and a stripped organic scrubbing step (scrubbing 2). [0020] Figure 1 shows a general flow sheet of a solvent extraction process. Figure 2 is the same solvent extraction process but with the addition of the extra steps of the present invention.

Feed Solution

[0021] The feed solution to the titanium solvent extraction process of the present invention is an aqueous, acidic solution of titanium. The solution may be obtained by digestion of a titaniferous ore according to the process of US Patent 6,375,923 or by any other suitable process that provides an aqueous, acidic soultion of titanium. In one embodiment of the present invention, the solution contains titanium chlorides or oxychlorides, hydrochloric acid and impurities. The impurities may be Fe, Mn, V, Cr, Mg, Ca and other impurities present in titanium ores. In this embodiment, the impurities are also generally present as chlorides or oxychlorides. Choice of the Organic Mixture

[0022] The organic phase is a mixture of an extractant, a diluent and, optionally, a modifier. The extractant is a chemical compound capable of binding titanium from an aqueous solution. The diluent is added for purposes of viscosity. The modifier is primarily added to prevent the formation of a third phase. It may also influence the behavior of the extractant, in such a way that the loading capacity of the mixture is higher than the loading capacity of the extractant taken alone. When the mixture is too viscous, it is usual to increase the temperature. In the case of the present process, however, an increase in temperature causes hydrolysis. Therefore, the present process is directed to an organic phase mixture that allows the process to be operated at or close to room temperature.

[0023] The extractant is desirably an organic phosphorus compound or a mixture of two or more organic phosphorous compounds. The organophosphorus compound may have the general formula (I)

R₁R₂R3PO where R₁, R₂, and R₃ may be the same or different and are each a hydrogen atom, a substituted or unsubstituted linear or branched chain, a cyclic, saturated, or unsaturated hydrocarbon radical, with the proviso that the sum of the carbon atoms of the radicals Ri, R₂, and R₃ is equal to at least 12 carbon atoms.

[0024] Where a mixture of organophosphorus compounds are used, the other organophosphorus compound(s) will have the formula (II) R₄R₅RePO where R₄, R₅, and R₆ may be the same or different and are each a hydrogen atom, a substituted or unsubstituted linear or branched chain, a cyclic, saturated, or unsaturated hydrocarbon radical, with the proviso that the sum of the carbon atoms of the radicals R₄, R₅, and Re is equal to at least 12 carbon atoms. [0025] Exemplary radicals Ri, R₂, R3, R₄, R₅, and R₆ include but are not limited to methyl, ethyl, n-propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1 -methyl- butyl, isopentyl, tert-pentyl, neo-pentyl, n-hexyl, n-heptyl, n-octyl, n-n-nonyl, n-decyl, n- undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, and n-octadecyl, together with the corresponding branched alkyl radicals and cycloalkyl radicals.

[0026] Exemplary substituents include hydroxy or nitro groups, halogen atoms, particularly chlorine and fluorine, lower alkoxy radicals having from one to four carbon atoms, cyano groups and the like. [0027] In one aspect, the extractant is a mixture of an organophosphorus extractant of formula (I) and (II), where Ri, R₂, and R₃ are identical linear alkyl radicals and where

R₄, R₅, and R₆ are identical linear alkyl radicals but different from those of the Ri, R₂, and R₃ radicals. The proportion of the two organic phosphorus compounds of formulae (I) and (II) is determined such that a phosphine oxide mixture exists that is liquid at ambient temperature. [0028] In another aspect, the organophosphorus extractant is a mixture of the phosphine oxides tri(n-hexyl)phosphine oxide and tri(n-octyl)phosphine oxide and is commercially available from Cytec under the trade designation CYANEX 923. [0029] As noted above, the diluent is xylene, mesitylene, or other suitable dilutent for the extractant that allows the organic phase to be contacted with and to load the titanium at or close to room temperature. [0030] Modifying agents are generally added to improve the hydrodynamic properties of the system without adversely affecting the extracting properties of the organic phosphorus compounds. An example of such modifying agents includes alcohols having from 4 to 15 carbon atoms, phenols, and the like. While a modifying agent may be optionally incorporated into the organic phase mixture, it is believed that a modifying agent is not necessary when the amounts of the organic phosphorous compounds are incorporated within the range contemplated by the present invention. [0031] Desirably, the organic phase includes from about 5-15% or greater than 35% of an organophosphorous extractant, e.g, Cyanex 923, with the balance being a diluent, e.g., xylene. It has been found that when the organic phase contains from about 20 to

30% organophosphorous extractant, phase separation problems are encountered

Pre-Reduction

[0032] Phosphine oxides such as Cyanex 923 generally load elements better when the elements are in their oxidized state rather than in their reduced state. To avoid loading impurities such as Fe, Cr, V and Mn, it is critical to keep the redox potential of the solution below the level where the oxidized species Fe(III), Cr(VI), V(V) and Mn(IV) are stable. If the oxidation potential is lowered too much, however, Ti(IV) is converted to Ti(III), which is not extracted and decreases the efficiency of the extraction process. [0033] Pre-reduction is achieved by adding a reactive metal phase. In practice, iron powder or aluminum flakes have been found to be the most effective. Good prereduction conditions correspond to a redox potential between about 0.0 and about 0.35 V versus a standard Ag/AgCI electrode and suitably between about 0.2 to about 0.3 V. This redox level corresponds to the formation of about 1 to 4 g/L Ti(III) in the feed solution. [0034] Control of the redox potential is particularly important in the conditions of the present invention. Since the use of an aromatic diluent leads to somewhat lower titanium concentrations in the eluate, the impurity levels also have to be kept lower such that the impurity level in the final titanium dioxide product, proportional to the impurity/Ti ratio, does not increase. Loading

[0035] The pre-reduced solution is brought into contact with the organic extractant phase described previously. The contact may occur by any means that ensures good contact between the phases. Industrial equipment used in solvent extraction, such as a series of mixer settlers or a solvent extraction column may be used. The number of equilibrium stages needed is generally between 2 and 4. The contacting is typically conducted at a temperature less than about 35° C, desirably between about 10° and 30° C, and in one aspect about 25° C.

Scrubbing of Loaded Organic Phase [0036] Typically, a loading concentration of about 10 to 20 g/l Ti is achieved in the organic phase, and in some instances, about 15 g/l Ti. If the feed solution contains significant levels of impurities, some of these impurities will be transferred with the organic phase. The impurities may be present as dissolved species in the organic phase, or they may be present in an entrained aqueous phase. The organic phase is therefore brought into contact with a concentrated solution of HCI. Typically, a concentration of about 6 to 9 M HCI is used. Impurities which have a smaller extraction coefficient than Ti will be stripped while Ti will not be substantially stripped. The process will also liberate entrained aqueous particles from the organic phase and thereby decrease the level of elements which are not chemically extracted in the organic phase.

Pre-Stripping

[0037] After scrubbing, the loaded organic phase, containing extracted titanium and chloride is transferred to the stripping section. It has been found that in the conditions of the present invention, Cl tends to strip before Ti, therefore limiting the concentration of Ti that can be obtained. This is particularly true of the xylene system. To compensate for this effect, a pre-stripping section is introduced. [0038] The purpose of the pre-strip section is to remove a significant fraction of the Cl from the organic phase, without removing a significant amount of Ti. In the subsequent stripping section, a higher concentration of Ti and a lower concentration of Cl will therefore be obtained. The definition of pre-stripping as it is understood in the context of the present invention is that it is a solvent extraction step where Cl is removed preferentially to Ti.

[0039] Pre-stripping can be achieved by any suitable process that provides preferential removal of Cl with respect to Ti. Two means of pre-stripping are described below.

1. Pre-stripping using a small amount of high-HCI solution

[0040] Since HCI strips more easily than Ti, stripping at a high organic to aqueous ratio will strip a limited amount at a high Cl/Ti ratio. A solution concentrated in HCI and dilute in Ti will form. This solution will be recycled to the feed of the reactor. As a consequence, less Cl will be present in the second stripping step, and a larger Ti concentration will be present in the eluate.

2. Pre-stripping by evaporation

[0041] The loaded solution is subjected to conditions where the vapor pressure of HCI gas over the organic solution is greater than the total pressure over the organic phase. This condition can be achieved by applying a vacuum to the loaded organic phase, or by increasing the temperature of this phase, or by a combination of both. Fig. 3 and 4 show two embodiments of a pre-stripping by evaporation process.

Stripping [0042] The pre-stripped organic phase undergoes stripping by an aqueous solution with a low chloride concentration. The concentration of the stripping solution is generally in the range 0.25 to 2 M HCI. If the concentration is too high, stripping is less effective. If the concentration is too low, significant hydrolysis occurs. Stripping produces a solution containing 25 to 60 g/L Ti, which is further concentrated before going to spray hydrolysis. Scrubbing of Stripped Organic Phase

[0043] It has been observed that a significant amount af an aqueous phase with a relatively high titanium concentration is entrained in the stripped organic phase. Therefore, a mixer-settler apparatus may be added at this stage. By adding a small amount of an HCI solution to the mixer and collecting the aqueous phase from the settler, a significant amount of the entrained aqueous phase can be recovered. If the titanium concentration in this product aqueous solution is high enough, it may be added to the eluate stream. The removal of this aqueous phase reduces the return of a significant amount of titanium to the loading stage and significantly increases the efficiency and throughput of the solvent extraction operation.

Examples [0044] The following examples are meant to describe but not limit the present invention.

Example 1 - Effect of the ratio of extractant to diluent

[0045] Equal volumes (100 ml) of a feed solution containing 50 g/L Ti and 400 g/L Cl, and stripped organic phase (containing 15% Cyanex 923 in xylene) were mixed by shaking for 1 min in a decanting flask at room temperature to simulate loading. After shaking, the time needed for separation of the phases was observed. The separated loaded organic phase was put in contact with an equal volume of a 0.5 M HCI solution and shaken in the same fashion as for the loading part. Whereas separation time after loading was always reasonabley fast, and increased with the proportion of extractant, it appeared that the separation time after stripping was higher in an intermediate concentration range, i.e., 20-30%.

[0046] Table Ia shows that the separation time after shaking for loading took between about 1 min and 5.5 min, with the separation time increasing with the extractant concentration. For stripping, however, the separation time is much longer (> 1 h) at the intermediate range of 20-30% Cyanex in the organic phase mixture. Table Ib shows the separation time after stripping. In general, the ranges 5 to 15% and 35-50% Cyanex have been shown to give favorable separation times.

TABLE Ia. LOADING

TABLE Ib. STRIPPING

Example 2 - Pre-Reduction

[0047] A feed solution to the solvent extraction step of the process of the present invention contained 55 g/L Ti, 400 g/L Cl, 5 g/L Fe and less than 5 g/L each of the impurities Cr, V, Mn and Mg. The redox potential of the solution, measured with a standard Ag/AgCI electrode was 35OmV vs Ag/AgCI (or 570 mV vs a standard H2 electrode). Aluminum chips were added to the solution until the measured potential droped to 225 mV vs Ag/AgCI. Chemical analysis showed that the solution after reduction contained 3 g/L of Ti in the titanous (Ti(III)) form.

Example 3 - Comparitive Example - Loading and Stripping Without Scrubbing. [0048] The feed solution from example 1 was fed to the top of a solvent extraction column with an internal diameter of 40 mm and a height of 8 m. An organic mixture consisting of 15% Cyanex 923 and 85% xylene was fed at the bottom. Titanium was loaded on the organic phase whereas the impurities were not. The loaded organic phase was stripped by passing it through a second column, fed with a dilute (1.5 M) HCI solution. The aqueous product of the stripping column (eluate) contained 28 g/L Ti, 21 mg/L Mn, 0.76 mg/L Cr and 0.69 mg/L V.

Example 4 - Effect of Loaded Organic Scrubbing Stage [0049] Testing conditions were the same as in Example 3, except that a scrubbing stage, consisting of a mixer-settler, was installed on the loaded organic stream. The scrubbing stage was fed with a small stream of 9 M HCI. The eluate in the present example contained 27.1 g/L Ti, 2 mg/L Mn, 0.5 mg/L Cr and 0.4 mg/L V, showing the marked improvement in the impurity levels achieved, particularly for Mn. Example 5 - Pre-Stripping by Vacuum Evaporation

[0050] A volume of 300 ml of the organic phase produced by loading the organic phase as in Example 3 was placed in a spherical, air-tight glass flask and heated to 60 °C. The flask was connected through a cooler to a conical flask containing water to a source of vacuum. A vacuum of about 0.1 atm was maintained in the spherical flask. Samples were taken out of the conical flask at intervals and their chloride concentration was determined. A chlorine mass balance showed that 20% of the amount of chloride in the organic phase was removed in 20 min. No titanium or other metal compounds were recovered in the conical flask.

Example 6 - Pre-Stripping with a Small Amount of Acid.

[0051] A volume of 100 ml of the same loaded solution used in Example 4 was equilibrated with different amounts of HCI solutions of different molarities. The amounts of HCI solution were 100, 20, 10 and 5 ml respectively, i.e. the organic to aqueous (O/A) ratio was 1 , 5, 10 and 20 respectively. This series of tests was repeated with different concentrations of the HCI solution. The HCI concentrations varied between 0.5 and 9 M HCI. Figs. 5 and 6 summarize the results obtained. Fig. 5 shows that as the concentration of HCI in the pre-stripping strip feed solution is increased, the equilibrium concentration of Ti in the resulting strip solution (or eluate of the pre-stripping step) for a given Ti concentration in organic phase decreases very significantly. For a 9 M HCI strip solution, the equilibrium ratio is 0.2, i.e. if the Ti concentration in the organic phase is 15 g/L, the aqueous phase will contain no more than 3 g/l Ti. The relationship shown in Fig. 5 is, in first approximation, independent of the O/A ratio used in the pre-stripping step..

[0052] Fig. 6 is calculated from the Cl and Ti mass balances of the tests. As the O/A ratio is increased, relatively more Cl and less Ti is transferred from the organic to the aqueous phase. At an O/A ratio in the range 1 to 3, the Cl/Ti ratio stripped from the organic phase corresponds approximately to the formula TiCI₄. At higher O/A, the amount of chloride stripped can be up to 3 times as high. Preferential removal of HCI in the pre-stripping step makes it possible to achieve a higher Ti concentration in the subsequent stripping operation.

Example 7 - Scrubbing of Stripped Organic Phase (Scrubbing 2) [0053] A series of lab-scale mixers and settlers were connected to form four loading stages and four stripping stages. The organic phase from the fourth stripping stage was fed to an additional mixer and settler to form a scrubbing stage 2 . The aqueous feed solution to the solvent extraction system contained 71 g/L Ti and 397 g/L Cl and was maintained at a feed rate of 10 ml/min. A stream of 0.91 ml/min of dilute HCI solution (1.5 M) was fed to scrubbing stage 2. The aqueous product of scrubbing stage 2 contained 56.8 g/L Ti. The mass balance showed that the aqueous stream from scrubbing stage 2 contained between 10 and 40% of the amount of Ti extracted. In other words, the addition of a scrubbing step to the stripped organic phase in this configuration, made it possible to recover a much higher stream of concentrated Ti solution and to avoid sending it back to the feed, where it would significantly decrease the efficiency of the extraction process. [0054] The action of scrubbing of stripped organic combined chemical extraction and physical separation to remove extra Ti from the organic phase. Surprisingly, the additional mixing step in the mixer with the addition of a clean (containing only HCI) strip solution made it possible to obtain a better separation. [0055] Although the invention has been presented on the basis of the behavior of titanium, it is well known in the art that compounds of Zr, Nb, Ta and other metals generally known as transition metal elements have very similar properties. It is intended to claim such known similar elements as included in the scope of the present invention. [0056] While there have been described what are presently believed to be the preferred embodiments of the invention, those skilled in the art will realize that changes and modifications may be made thereto without departing from the spirit of the invention.

Claims

CLAIMS:

1. A solvent extraction process for separating titanium from an impure aqueous solution, wherein the process comprises the steps of: a) preparing an organic phase comprising a phosphine oxide extractant and an aromatic diluent in such proportions that the organic phase exhibits low viscosity and good disengagement characteristics; b) contacting the organic phase with an aqueous feed solution, wherein the aqueous feed solution comprises titanium chloride, hydrochloric acid and impurites, and wherein the aqueous phase has been reduced to an oxygen potential lower than the potential of formation of Ti(III), thereby transferring titanium to the organic phase and forming a loaded organic phase; c) contacting the loaded organic phase with a scrubbing solution to form a scrubbed loaded organic phase; f) pre-stripping the scrubbed loaded organic phase by contacting it with a small amount of HCI solution or by injecting it with inert gas to form a pre-stripped organic phase; g) bringing the pre-stripped organic phase in contact with an aqueous strip solution to form an eluate, to which the titanium is transferred, and a stripped organic solution. h) mixing the stripped organic solution in a scrubbing step 2 with a small amount of an HCI solution to promote disengagement of the phases, thereby forming a disengaged, stripped organic solution; and, i) recycling the stripped organic solution by bringing it in contact with the aqueous feed solution.

2. Titanium dioxide, wherein the titanium dioxide is made by a method comprising a solvent extraction process for separating titanium from an impure aqueous solution, wherein the process comprises the steps of: a) preparing an organic phase comprising a phosphine oxide extractant and an aromatic diluent in such proportions that the organic phase exhibits low viscosity and good disengagement characteristics; b) contacting the organic phase with an aqueous feed solution, wherein the aqueous feed solution comprises titanium chloride, hydrochloric acid and impurites, and wherein the aqueous phase has been reduced to an oxygen potential lower than the potential of formation of Ti(III), thereby transferring titanium to the organic phase and forming a loaded organic phase; c) contacting the loaded organic phase with a scrubbing solution to form a scrubbed loaded organic phase; f) pre-stripping the scrubbed loaded organic phase by contacting it with a small amount of HCI solution or by injecting it with inert gas to form a pre-stripped organic phase; g) bringing the pre-stripped organic phase in contact with an aqueous strip solution to form an eluate, to which the titanium is transferred, and a stripped organic solution. h) mixing the stripped organic solution in a scrubbing step 2 with a small amount of an HCI solution to promote disengagement of the phases, thereby forming a disengaged, stripped organic solution; and, i) recycling the stripped organic solution by bringing it in contact with the aqueous feed solution.