ES2709399T3 - Recovery procedure for titanium dioxide from titanium-containing compositions - Google Patents

Abstract

A method of recovering a titanium dioxide product from a titanium oxide-containing composition comprising: (a) adding to the titanium oxide-containing composition one or more alkali salts and an alumina-containing material to produce a charge; (b) oxidatively toasting the charge at a temperature in the range of 700 to 875 ° C to produce a toasted mass; and (c) recovering the titanium oxide product from the toasted mass.

Description

DESCRIPTION

Recovery procedure for titanium dioxide from compositions containing titanium

The present invention relates to a process for recovering titanium dioxide from a composition containing titanium oxide such as a mineral.

Existing supplies of ilmenite and natural rutile are under pressure due to steady growth in the markets for TiO2 and increased demand for high-grade minerals for direct chlorination or for the production of synthetic rutile. The new sand / beach sand deposits are of variable quality and many are not suitable for improvement and beneficiation using existing commercial procedures (in particular, 'Challenges and Opportunities in the TiO2 Feedstock Industry', AJM Global Mineral Sands Exploration and Investment Conference, Melbourne, 2003).

The majority of TiO2 minerals have high concentrations of zirconium and monazite minerals due to their geological proximity. The impurities of zirconium and monazite in the raw material reduce their market value. Impurities of actmides and lanthanides create operational problems (eg, high consumption of chlorine or sticky beds) and generate hazardous waste with high concentrations of actmides, lanthanides and other heavy metals. Due to strict environmental regulations in many countries, the treatment and disposal of such hazardous wastes from the pigment industries has become a major problem that is increasing the cost of treatment and waste management.

The conventional procedures for the beneficiation of the minerals of TO 2 are

a) Physical procedures such as gravitational, magnetic and electrical separation that are used to separate magnetite, monazite, zirconium and other silky gangs and

b) chemical procedures, namely, acid leaching and formation of TiO2 slag (reduction at high temperature) that are mainly used to remove iron (Becher, Benilite, Austpac).

However, these procedures require high quality ilmenite minerals. If used for the beneficiation of low grade / highly radioactive TiO2 minerals, the level of critical impurities such as C ^ Oa, V2O5, Nb2O5 (which degrade the properties of the pigment) and CaO and SiO2 (which create operational problems such as sticky beds) is very high in the final product. In addition, solute impurities (Fe, Nb, U, Th, Ce) in the TiO2 phases (pseudorutile, ilmenite, anatase) remain in the raw material and end up in the waste stream of the pigment manufacturing process (chlorination or sulfation). ). The process of slag formation (which is the main source of raw material for the manufacture of pigments) separates only iron oxides and most of the other impurities enter the raw material, for example, in the slag of TiO2. The slag formation process also faces uncertainties due to its high energy consumption and emission of greenhouse gases.

In view of the changing sources (deposits) of TiO2 ores and environmental concerns in relation to waste disposal, there is a need for an environmentally more acceptable approach for the benefit of TiO2. Several investigations have been carried out on roasting ilmenite with soda, mainly in a reducing atmosphere with carbon (ed. Fathi Habashi, Handbook of Extractive Metallurgy, Vol. II, Publ .: Wiley-VCH, Berlin, 1997). However, the TiO2 yield in this technique is not very high (<90% by weight). The main drawback of this procedure is that neither iron is separated in metallic form nor is a leachable product produced (Handbook of Extractive Metallurgy, [supra]). A limited number of investigations on oxidative alkaline roasting techniques have been carried out. However, the yield of TiO2 and the separation of actmides and lanthanides is below the levels required for chlorination (US-A-6346223).

The present invention seeks to improve the benefit of a composition containing titanium oxide (such as a low-grade or highly radioactive TiO2 mineral) by the combination of roasting and selective leaching steps. In particular, the present invention relates to a beneficiation process for the separation of impurities from non-lanthanides (e.g., Fe, Ca, Si, V and Cr), pre-lanthanides (e.g., Zr and Nb), lanthanides ( for example, Ce and Nd) and actmides (for example, U and Th) of titanoferrous deposits.

Viewed from a first aspect, the present invention provides a method for recovering a titanium dioxide product of a composition containing titanium oxide comprising:

(a) adding to the composition containing titanium oxide one or more alkali salts and an alumina-containing material to produce a charge;

(b) oxidatively toasting the charge at a temperature in the range of 700 to 875 ° C to produce a toasted mass; Y

(c) recovering the titanium oxide product from the toasted mass.

The process of the invention can successfully improve a wide range of compositions containing titanium oxide and produce a high purity titanium oxide product (preferably synthetic rutile) for direct use in the production of pigments (chlorination and sulfation). When roasting in the presence of a material that contains alumina or a material containing calcium oxide, the process of the invention can achieve a complete, efficient and economical separation of large concentrations of iron oxides and impurities of lanthanides and actmides that would otherwise contribute to the raw material in the production of pigments The addition of a material containing alumina or a material that contains calcium oxide helps eliminate not only the zirconium and monazite minerals, but also the impurities of lanthanides and actmides (solutes) present in the network of the TO 2 phases ( rutile, pseudorutile, brookite, etc.). In certain embodiments, the process also recovers the metal values as value-added by-products and alkali salts, which substantially reduces the amount of waste and the use of raw materials (namely, alkaline salt and alumina) that can be recycled to make the process economically viable

By "composition containing titanium oxide" is meant a mixture of metal oxide species in the form of a compound or forms including titania (TO2). The composition containing titanium oxide can be synthetic or (preferably) natural, such as a powder, ore or mineral or a mixture thereof. A material rich in titanium, such as a ore (eg, ilmenite, anatase, ilmenite beach sands, low grade titanium slag, natural rutile or perovskite) is preferred. Preferred are titanoferrous mixtures which further include at least one species of iron such as a ferrous or ferrous species (preferably an iron oxide such as FeO, Fe2O3 or Fe3O4). The titanoferrous mixture may further comprise alumina or silica. The composition containing titanium oxide can be a residue of a chlorination or sulfation process.

Preferably, the mineral ores are selected from the group consisting of ilmenite, anatase and perovskite. Preferably, the mineral ore is a mixture of ilmenite and perovskite.

Preferably, the one or more alkali salts are one or more alkali or alkaline earth metal salts. Preferably, the one or more alkali salts are one or more carbonates, hydroxides, bicarbonates or sulfates of a metal of group IA or group IIA or a mixture thereof. For example, the one or more alkali salts can be selected from the group consisting of Na2CO3, K2CO3, Na2SO4, K2SO4, NaOH, NaHSO4, KHSO4, KHCO3, NaHCO3 and KOH. Sodium carbonate and / or potassium are preferred. The amount of alkaline salt can be calculated based on the formation of alkaline compounds of TiO2, Fe2O3, A ^ O3, SiO2 and P2O5 present in the composition (eg, mineral).

Preferably, step (a) comprises: adding to the composition containing titanium oxide one or more alkali salts, a material containing alumina and a material containing calcium oxide.

Step (b) can be carried out in air or another source of oxygen. Step (b) can be carried out in a conventional rotary kiln or in a rotary hearth furnace. Step (b) can be carried out for a suitable period of time (for example, 120 minutes).

Step (b) generally forms alkaline titanates and complex oxide salts.

Step (a) typically includes mixing (e.g., homogeneously mixing) the titanium oxide containing composition with one or more alkali salts and with at least one of the alumina-containing materials and the calcium oxide-containing material to produce the load. The alumina-containing material or the calcium oxide-containing material can be subjected to a controlled addition to the composition containing titanium oxide. Preferably, the alumina-containing material (eg, alumina) is present in the filler in an amount in the range of 5 to 30% by weight of the composition containing titanium oxide, preferably 10 to 25% by weight of the composition containing titanium oxide, more preferably 15 to 22% by weight (for example, about 20% by weight) of the composition containing titanium oxide. The precise amount of alumina-containing materials in the filler generally depends on the proportion of the composition containing titanium oxide: alkaline salt, liquid phase formation and the concentration of various impurities (mainly iron oxides, silicates and phosphates). The alumina-containing material can be alumina, aluminum hydroxide, clay containing A ^ O3 or a mixture thereof. An aluminate (for example, NaAlO2) can also be used. During step (b), the alumina and other phases of the gangue in the titanium oxide-containing composition react with the alkaline salt and form complex oxide phases (such as the Na-Al-Si-MO phases) which increase the solubility and stability of ferrites, such as sodium ferrite. This complex salt phase helps separate the iron oxides from the composition containing titanium oxide.

The calcium oxide-containing material may be lime (i.e., CaO or Ca (OH) 2), calcium oxide (eg, calcite) or a mixture thereof. Preferably, the calcium oxide-containing material (eg, CaO) is present in the filler in an amount in the range of 0.1 to 5% by weight of the composition containing titanium oxide, preferably 1 to 4% by weight of the composition containing titanium oxide, more preferably 2 to 3% by weight of the composition containing titanium oxide. The addition of calcium oxide-containing material is based on the formation of perovskite and the pyrochlore-type phases of TiO2 and ZrO2 that can dissolve high concentrations of, among others, rare earth elements -ETR- (eg, U or Th) and Nb (De Hoog et al., Mineralogical Magazine, 61, 721-725, 1997). During step (b), CaO reacts with TiO2 and zirconium minerals and forms several compounds of Ca-Na-Ti-MO such as perovskite (CaTiO3), zirconolite [(Ca, Fe, Y, Th) 2 (Fe, Ti, Nb) 3Zr2O7] and hiarneite [(Ca, Mn, Na) 2 (Zr, Mn) 5 (Sb, Ti, Fe) 2O-i6] which advantageously absorb the most of the impurities of lanthanides and actmides in the minerals of monazite and zirconium. The impurities of the solute in the phases rich in TO 2 diffuse towards the CaTiO3 formed on the surface of the TO 2 grains.

Step (c) may comprise:

(c1) adding to the toasted mass an aqueous medium to produce an aqueous solution and a substantially insoluble residue.

The aqueous medium can be water or an alkaline solution (for example, a dilute alkaline solution). Normally water is used at an elevated temperature. The hot water may be at a temperature in the range of 70 to 90 ° C. Step (c1) can be carried out in hot water for 20 to 200 minutes, preferably 25 to 100 minutes (for example, 40 minutes).

In step (c1), water-soluble alkali compounds such as aluminate, silicate, chromate, vanadate and metal phosphate (eg, sodium) can be dissolved in the aqueous solution. The aqueous medium can be added repeatedly to wash the substantially insoluble residue (usually until the pH of the washings reaches about 7).

Preferably stage (c1) comprises:

(cla) adding water at a high temperature to the toasted mass to produce an aqueous solution and a substantially insoluble residue;

(clb) adding to the aqueous solution a source of alkalinity to improve the selective separation of a fine precipitate.

The fine precipitate generally comprises fine particles of composition containing titanium oxide (eg, mineral) and constituents of complex alkali salts (eg, Na-Al-Si-Fe-MO) which precipitate as oxides or hydroxides of Fe, Nb , Al or ETR (for example, U and Th) due to its limited solubility. The fine precipitate can be separated from the aqueous solution by conventional techniques, such as filtration.

The source of alkalinity is preferably an ammonium salt such as a carbonate, sulfate, bisulfate or bicarbonate. Normally, the ammonium salt is added in an amount of up to 5% by weight to optimize the kinetics of precipitation.

Preferably, the method further comprises:

(d) the recovery of metallic values of the fine precipitate.

In step (d), the metal values can be selected from the group consisting of alumina-containing material (eg, alumina), calcium oxide-containing material (eg, CaO), and metal oxides (eg. iron such as Fe2O3 or niobium oxide such as Nb2Os).

Preferably, the method further comprises:

(e) recovering the metal values of the aqueous solution.

In step (e), the metal values can be selected from the group consisting of alkaline salt, alumina-containing material (eg, alumina), material containing calcium oxide (eg, CaO), V2O5, Fe2O3 and Cr2O3. The oxides of Nb, Ta, Zr and ETR can also be recovered (for example, NbO, ZrO2, U3O8, UO2, UO3, ThOx).

Preferably, step (e) comprises:

(e1) acidifying the aqueous solution.

The step (e1) can be carried out by the addition of a weak acid. Normally, the acid is an inorganic acid (for example, an inorganic acid selected from the group consisting of fluortudic acid, clortudric acid, metric acid, sulfuric acid, an acidic oxide and mixtures thereof). The step (e1) can be better controlled by the use of a weak organic acid such as formic acid, oxalic or acetic acid and / or CO2. Preferably, the acid is an acidic oxide, in particular preferably carbon dioxide. For example, step (e1) may include: bubbling CO2 gas through (or passing oxalic acid) to the aqueous solution. The addition of weak acid and / or CO2 provides precise control of the pH for the selective precipitation of oxides. The use of an acid with CO2 also helps the kinetics of the thickening of the precipitation and, therefore, reduces the entrapment of small particles of impurity oxides with coarser TiO2-rich particles in the coarse residue.

When recovering the metallic values as by-products of added value and alkaline salts in stages (d) and (e), the amount of waste and the use of raw material (in particular, alkaline carbonate and alumina) is reduced so that the procedure is economically viable

Step (c) of the method preferably further comprises:

(c2) acid leaching the substantially insoluble residue to produce an acidic leachate and a solid residue consisting essentially of titanium oxide.

Step (c2) can be carried out in an acid solution, preferably an inorganic acid solution (such as a 2-10% mineral acid (for example, HCl, HNO3 or H2SO4 solution) An example of a suitable acid is 5% HCl Preferably, the acid is at an elevated temperature (eg, 70-90 ° C.) Step (c2) can be carried out for 5 to 200 minutes, preferably 5 to 100 minutes (e.g. 10 minutes) The acid concentration and the solid / liquid ratio are generally based on the amount of insoluble salts of Fe2O3, SO2 and the CaO compounds in the substantially insoluble residue of step (c1) .The solid residue can be separated from the leached acid by conventional techniques, such as filtration.

In step (c2), the acid soluble salts of, among others, Nb, Zr and ETR (e.g., U and Th) can be dissolved in the acidic leach. The alkaline titanates are decomposed in TO 2. Dilute acid (and optionally water) can be added repeatedly to wash the solid residue.

Preferably stage (c2) comprises:

(c2a) recover the metal values of the leached acid.

In step (c2a), the metal values can be selected from the group consisting of acid compounds, alkali compounds and oxides. Specific examples are ZrO2, Nb2O5 and Th / UO2.

Normally, the solid residue after step (c2) is rich in TO 2 and can comprise 87% by weight or more of TiO2 (depending on the fineness of the oxides produced in step (c1)), preferably 87- 95% by weight. Further purification of the solid residue can be carried out (for example, by means of electrolytic purification or calcination techniques). The calcination can be carried out using bisulfates and alkaline bicarbonates to further reduce the levels of iron, aluminum, silica, phosphate, lanthanide and actido to produce whiter grades of synthetic rutile.

The purification and agglomeration of the solid residue can form synthetic rutile with a desired level of particle size distribution and purity. Preferably, step (c) of the method further comprises:

(c3) to toast at least a proportion of the solid residue with one or more sulfates of hydrogen and / or alkali carbonates to produce a toast.

Preferably, step (c3) is performed at a low temperature, such as 200-400 ° C (for example, at about 300 ° C) in air or another source of oxygen for 1 to 4 hours. Preferred alkaline hydrogen sulphates are NaHSO4 and / or KHSO4. Normally, the ratio of NaHSO4 or KHSO4 to solid residue is about 1: 1. Normally stage (c3) is carried out for 1 hour.

Step (c) of the method preferably further comprises:

(c4) Leaching with roasting water to produce the titanium oxide product.

Normally, water is used in step (c4) at an elevated temperature. The hot water may be at a temperature in the range of 70 to 90 ° C. Step (c4) can be carried out in hot water for 20 to 200 minutes, preferably 25 to 100 minutes (for example, 30 minutes). The titanium oxide product can be separated from the leached water by conventional techniques, such as filtration. The water and the optionally diluted acid solution can be added repeatedly to wash the toasting (usually until the pH of the washings reaches about 7).

The titanium oxide product is preferably in the rutile synthetic form. The process of the invention is capable of achieving TO 2 (synthetic rutile) with a purity of 95% by weight or more.

The titanium oxide product may contain Fe2O3 of 7.5% by weight or less, preferably 6.5% by weight or less, more preferably 2% by weight or less.

The titanium oxide product may contain A ^ O3 of 2.0% by weight or less, preferably of 1.5% by weight or less, more preferably 0.9% by weight or less.

The titanium oxide product may contain SiO2 of 1.5% by weight or less, preferably 1% by weight or less, more preferably 0.75% by weight or less, especially preferably 0.1% by weight or less. The titanium oxide product may contain U of 250 ppm or less, preferably 200 ppm or less, more preferably 155 ppm or less, especially preferably 50 ppm or less.

The titanium oxide product may contain Th of 750 ppm or less, preferably of 600 ppm or less, more preferably 580 ppm or less.

The titanium oxide product may contain Zr of 5500 ppm or less, preferably of 2500 ppm or less, more preferably of 1000 ppm or less.

The present invention will now be described in a non-limiting sense with reference to the examples and accompanying figures in which:

Figure 1 illustrates a flow diagram for the beneficiation of a TiO2 mineral according to an embodiment of the method of the invention;

Figure 2 is a photomicrograph of anatase ore after having been subjected to an embodiment of the method of the invention; Y

Figure 3 is the microstructure of the rutile grain in the ilmenite ore after having been subjected to an embodiment of the process of the invention.

The following examples do not agree with the invention.

Example I: Australia ilmenite ore

In an embodiment of the invention illustrated in Figure 1, the following stages are involved in the beneficiation of ilmenite ore.

A. The ore 1 of ilmenite (analysis given in Table 1) was mixed homogeneously with alkaline carbonate (sodium or potassium) 2, alumina (20% by weight of the mineral) and CaO (3% by weight of the mineral) 3 to produce a load 4.

B. Load 4 was put in air at 950 ° C for 120 minutes to produce a toasted mass.

C. The toasted mass was leached with hot water at 80 ° C for 40 minutes. The solution was filtered and a solid coarse residue 7 was leached and washed repeatedly until the pH of leachate 8 dropped to seven.

D. A fine precipitate 6 of mineral particles and hydroxides of, among others, Fe, Al, Nb, U, Th and ETR was formed during the washing and leaching and separated by filtration. The pH of the solution can be controlled by adding ammonium salts A for the separation and thickening of the fine precipitate. The fine precipitate 6 was used for the recovery R1 of metal values such as the recovered additives 3a and the byproducts 20 (for example, Fe2O3, Nb2Os).

E. Alkaline salt, alumina, iron oxides / hydroxides and other metallic values recovered R2 from the leachate 8 of stage C by bubbling CO2 gas and / or organic acids B.

F. The solid coarse residue 7 from step C was treated with acid solution 9 of 5% HCl at 70 ° C for 10 minutes. Solution 9 was filtered and a solid residue 11 was washed thoroughly with dilute acid solution and then with water to remove all impurities.

G. The leachate 10 from step F (containing acid soluble salts of, inter alia, Nb, U, Zr and ETR) was treated to recover R3 from acid and byproducts 21 such as ZrO2, Nb2O5 and Th / UO2.

H. The solid residue 11 of step F is dried in an oven. The analysis of the product (synthetic rutile) is shown in Table 1. It can be used for the chlorination and the residues 22 of the chlorination plant can be subjected to the recovery stage R3.

I. A part of the solid residue 11 from step H was treated with NaHSO 4 (ratio 1: 1) at 300 ° C for 1 hour in air. The proportion of residue 11: NaHSO4 can be increased when carrying out its analysis for the remaining impurities. J. The toasted mass from stage I was leached with hot water at 80 ° C for 30 minutes. The solution was filtered and another solid residue 12 was leached and washed repeatedly until the pH of the leaching solution was low to 7. K. The remainder of the solid residue 12 from step J was dried in an oven. The concentration of Fe2O3, A ^ O3 and SO2 in the final product had been reduced considerably to <2% by weight, <0.5% by weight and <0.1% by weight, respectively. The purity of the synthetic rutile after stage J was, therefore, better than 95%.

In summary, the purity of TO 2 increases from 87% in step H not optimized to 95% or more after step J.

Table 1: Chemical composition of the ilmenite mineral and the final product (synthetic rutile) after step H of the toasting and leaching process of Example I

Figure 3 is the microstructure of the rutile grain in the ilmenite ore after toasting with alkali and leaching in water. The addition of 5% (with respect to the mineral) of CaO in the toasting charge accelerates the separation of the rutile grain (gray color) from the impurities of the solute as the perovskite phase (bright phase).

Example II: Anatase ore

The anatase ore was subjected to steps identical to those described in Example I. In this case, no extra CaO was added in the roasting charge, since 2% by weight of CaO was present in the ore. The chemical analysis of the anatase ore and the final product after the roasting and leaching steps are listed in Table 2. Table 2: Chemical composition of the anatase ore and the final product (synthetic rutile) after the roasting process and leaching of Example II

Figure 2 is a photomicrograph of anatase ore after an alkaline roasting at 850 ° C for 4 hours. The elementary X-ray map of grain A shows the formation of a complex phase of Na-Al-Fe-Si-O

Claims (15)

A method for recovering a titanium dioxide product of a composition containing titanium oxide comprising: (a) adding to the composition containing titanium oxide one or more alkali salts and an alumina-containing material to produce a charge; (b) oxidatively toasting the charge at a temperature in the range of 700 to 875 ° C to produce a toasted mass; Y (c) recovering the titanium oxide product from the toasted mass. 2. A method according to claim 1, wherein the titanium oxide-containing composition is a mineral. 3. A process according to claim 1 or 2, wherein the composition containing titanium oxide is a titanoferrous mixture. 4. A process according to claim 2, wherein the mineral is selected from the group consisting of ilmenite, anatase and perovskite. A process according to any one of the preceding claims, wherein one or more alkali salts are one or more carbonates, hydroxides, bicarbonates or sulfates of a metal of the group or group IIa or a mixture thereof. 6. A process according to claim 5 wherein the one or more alkali salts are selected from the group consisting of Na2COa, K2CO3, Na2SO4, K2SO4, NaOH, NaHSO4, KHSO4, KHCO3, NaHCOa and KOH. 7. A process according to claim 5 or 6, wherein the one or more alkali salts are selected from the group consisting of sodium and potassium carbonate. A method according to any one of the preceding claims wherein step (a) comprises: adding to the composition containing titanium oxide one or more alkali salts, an alumina-containing material and a calcium oxide-containing material. 9. A process according to any of the preceding claims, wherein the alumina-containing material is selected from the group consisting of alumina, aluminum hydroxide, clay containing A ^ O3, NaAlO2 and mixtures thereof. 10. A process according to claim 8, wherein the calcium oxide-containing material is selected from the group consisting of lime, calcium oxide and mixtures thereof. 11. A method according to any of the preceding claims, wherein step (c) comprises: (c1) adding to the toasted mass an aqueous medium to produce an aqueous solution and a substantially insoluble residue. 12. A process according to claim 11, wherein the aqueous medium is water or an alkaline solution. 13. A process according to claim 11 or 12, wherein the aqueous medium is hot water. 14. A method according to claim 11, 12 or 13, wherein step (c1) comprises: (c) a) adding water at a high temperature to the toasted mass to produce an aqueous solution and a substantially insoluble residue; (cl b) adding to the aqueous solution a source of alkalinity to improve the selective separation of a fine precipitate. 15. A process according to claim 14, wherein the source of alkalinity is an ammonium salt.