Fonseca Mourao, Marcelo Jose Da Jardim Paixao Jose Marcio
| 1. | Process for beneficiating anatase titanium dioxide ore comprising: (a) contacting said anatase titanium dioxide ore with an aqueous solution of a mineral acid having a concentration of about 330 percent by weight, said contacting taking place at a temperature of about 150300"C, until at least 10 percent by weight of one or more impurities selected from the group consisting essential of alkali metals, alkaline earth metals, rare earth metals, iron, aluminum, phosphorus, thorium, uranium, chromium, manganese, vanadium and yttrium, are solubilized and a leachate is formed, and (b) removing the remaining anatase titanium dioxide ore from the leachate. |
| 2. | The process of Claim 1 wherein the temperature is about 160250 degrees C. |
| 3. | The process of Claim 1 wherein the temperature is about 170210 degrees C. |
| 4. | The process of Claim 1 wherein the contacting takes place at a pressure of about 4100 atmospheres absolute. |
| 5. | The process of Claim 1 wherein the contacting takes place at a pressure of about 575 atmospheres. |
| 6. | The process of Claim 1 wherein the mineral acid concentration is about 1025 percent by weight. |
| 7. | The process of Claim l wherein the mineral acid concentration is about 1525 percent by weight. |
| 8. | The process of Claim 1 wherein the mineral acid is hydrochloric. |
| 9. | The process of Claim 1 wherein the mineral acid is hydrochloric, the temperature is about 160250 degrees C, and the contacting takes place at a pressure of about 4100 atmospheres absolute. |
| 10. | The process of Claim 1 wherein the mineral acid is hydrochloric, the temperature is about 170210 degrees C. , and the contacting takes place at a pressure of about 575 atmospheres absolute. |
| 11. | The process of Claim 1 wherein the mineral acid is hydrochloric, the temperature is about 170210 degrees C. , the contacting takes place at a pressure of about 1060 atmospheres absolute, and the acid concentration is about 330 percent. |
| 12. | The process of Claim 1 wherein the mineral acid is hydrochloric, the temperature is about 170210 degrees C. , the contacting takes place at a pressure of about 1060 atmospheres absolute, and the acid concentration is about 525 percent. |
| 13. | The process of any one of the preceding Claims 112 wherein prior to contacting with the aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to mineral dressing. |
| 14. | The process of any one of the preceding Claims 112 wherein prior to contacting with the aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to reductive roast ing at a temperature of up to about 400 degrees C with subsequent magnetic separation. |
| 15. | The process of any one of the preceding Claims 112 wherein prior to contacting with the aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to reductive roast¬ ing at a temperature of about 9001700 degrees C. |
| 16. | The process of any one of the preceding Claims 112 wherein prior to contacting with an aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to a preleach treatment. |
| 17. | The process of any one of the preceding Claims 112 wherein the ore remaining after step (b) is subjected to washing with an aqueous solution of an alkali metal compound selected from the group consist¬ ing essentially of alkali metal carbonates, hydroxides or mixtures thereof. |
| 18. | The process of any one of the preceding Claims 112 wherein: (i) prior to contacting with the aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to mineral dressing; reductive roasting at a temperature of up to about 400 degrees C with subsequent magnetic separation; and a preleach treatment; and (ii) the ore remaining after step (b) is subjected to washing with an aqueous solution of an alkali metal compound selected from the group consisting essentially of alkali metal carbonates, hydroxides or mixtures thereof. |
| 19. | The process of any one of the preceding Claims 112 wherein: (i) prior to contacting with the aqueous solution of a mineral acid, the anatase titanium dioxide ore is subjected to mineral dressing, including stage magnetic separation; and (ii) the ore remaining after step (b) is subjected to washing with an aqueous solution of an alkali metal compound selected from the group consisting essentially of alkali metal carbonates, hydroxides or mixtures thereof. |
| 20. | The process of any one of the preceding Claims 112 wherein the temperature is about 190210'C. |
| 21. | The process of any one of the preceding Claims 112 wherein the temperature is about 190*C. |
| 22. | Tiθ2 pigment produced from the beneficiated Tiθ2 ore from the process of claim 1. |
| 23. | Beneficiated anatase Tiθ2 ore produced by the process of Claim 1. |
| 24. | Beneficiated anatase Tiθ2 ore produced by the process of Claim 1 and having a calcium content not exceeding about 0.25 percent by weight, a combined calcium, barium, and strontium content not exceeding about 0.30 weight percent, and a combined thorium and uranium content not exceeding about 200 parts per million, wherein the foregoing percentages are by weight, based on the weight of the ore and are calculated as the metallic oxide. |
This Application is a Continuation-In-Part of U.S. Patent Application No. 07/490,194 filed March 8, 1990.
BACKGROUND OF THE INVENTION This invention relates to an improved method for purifying anatase Tiθ 2 ore which contains numerous impurities. The purified ore can be used to make Tiθ2 pigment or titanium metal or be used in any other process where a purified Tiθ2 ore is required. Currently, approximately 75 percent of the titanium minerals produced in the world are utilized by the pigments industry to produce Tiθ2. In the production of Tiθ2 by the chloride process, benefici- ated ore is used which generally contains about 55-96% Tiθ2. However, known beneficiation processes do not appear to be capable of satisfactorily purifying anatase Tiθ2 ore which contains numerous impurities such as alkali metals, alkaline earth metals, rare earth metals, iron, aluminum, phosphorus, thorium, uranium, chromium, manganese, vanadium, and yttrium. These impurities may be present as oxides, salts, or other complex forms and generally cannot be readily removed by conventional mechanical means or even conventional chemical means. Especially detrimental to the chloride process are such ores which contain in considerable quantity the impurities of iron, calcium, aluminum, phosphorus, magnesium, barium and strontium, and radionuclides such as thorium and uranium. For example, phosphorus can cause processing problems in the chloride Tiθ 2 process, and thorium and uranium may concentrate in the Tiθ 2 process and present a
potential health hazard. Also, the impurities of aluminum, rare earths, phosphorus, thorium, and uranium are additionally a problem because they are especially resistant to removal by conventional mechanical or chemical means.
Being able to remove such impurities efficiently would be highly desirable because known sources of iθ2 ore not containing such impurities are becoming increasingly scarce and expensive. Con- versely, there exist large bodies of inexpensive carbonatite anatase ores which are rich in Tiθ 2 but also contain significant quantities of such impuri¬ ties. Moreover, while other processes to purify Tiθ2 ore are known, it appears that they either require additional, more complex or more expensive processing steps or are deficient in one or more benefits as compared to the process of this invention.
For anatase Tiθ2 ore that is desired to be beneficiated for use in the chloride Tiθ2 process, impurities which are especially important to reduce to acceptable levels are calcium, barium, strontium, thorium and uranium. It is important to reduce calcium, barium and strontium to acceptable levels because they can cause sticking and, thus, operability problems in the fluidized bed chlorinator, which is the first step in the chloride Tiθ2 process. Reducing thorium and uranium to acceptable levels is important because they can be potential health hazards. Unfortunately, such impurities are especially resistant to reducing to acceptable levels.
Preferably, in the beneficiated anatase ore, the calcium will not exceed about 0.25 weight percent calculated as CaO; the combined calcium, barium and strontium will not exceed about 0.30 weight percent; and the combined thorium and uranium will not exceed about 200 parts per million. More preferably in the
beneficiated Tiθ 2 ore, the calcium will not exceed about 0.20 weight percent; the combined calcium, barium and strontium will not exceed about 0.25 weight percent; and the combined thorium and uranium will not exceed about 150 parts per million. (The foregoing percentages in this paragraph are percent by weight, based on the weight of the ore and are calculated as the metallic oxide.)
It also appears that most prior art processes require prethermal treatment such as prereduction as an essential step. Prethermal treatment is undesirable because it is expensive (due to substantial energy and investment requirements) and tends to make it more difficult to remove radionuclides such as thorium and uranium. It, therefore, would be desirable to have a beneficiation process which did not require prethermal treatment as an essential step.
The following information is disclosed which may be of interest to this invention:
U. S. Patent 4,176,159 discloses a process for the removal of impurities from anatase ore. The process requires high temperature calcining, cooling, reducing, cooling, magnetic separation, mineral acid leaching, neutralizing, and washing.
U. S. Patent 4,562,048 discloses the bene¬ ficiation of titaniferous ores by leaching with a mineral acid. The temperature used is 120-150 degrees C. , and the pressure used is 10-45 pounds per square inch gauge ("psig") . An essential aspect is the venting of water vapor generated during the leaching process. Prior to leaching, the ore is reduced at about 600-1100*C.
U. S. Patent 4,321,236 discloses a process for beneficiating titaniferous ore. The process requires preheating the ore and a mineral acid prior
to admixing them in a leaching operation. The temper¬ ature is maintained at 110-150 degrees C. , and the pressure is maintained at 20-50 psig. For ores containing iron in the ferric state, reductive roasting at about 800-1100 β C is suggested prior to leaching.
U. S. Patent 4,019,898 discloses the addi¬ tion of a small amount of sulfuric acid to the leach liquor used to beneficiate ilmenite ore. The te pera- ture used is 100-150 degrees C. , and the pressure used is up to 50 psig. For ores containing iron in the ferric state, the ore is reduced prior to leaching at a temperature of about 700-1200"C.
SUMMARY OF THE INVENTION
Process for beneficiating anatase titanium dioxide ore comprising:
(a) contacting said ore with an aqueous solution of a mineral acid having a concentration of about 5-30 percent by weight, said contacting taking place at a temperature of about 150-300 degrees C. until the desired amount of impurities are solubilized and a leachate is formed, and
(b) removing the leachate from the product of step (a) .
There is also provided by this invention iθ2 pigment which is produced by the chloride process from the purified Tiθ2 ore of this invention.
In accordance with this invention, it has been found that most of the aforementioned impurities in anatase iθ2 (and especially iron, calcium, aluminum, rare earths, phosphorus, magnesium, barium, strontium and the radionuclides such as thorium and uranium) ore can readily be reduced to acceptable levels. Moreover, the process is especially useful
for removing impurities which are resistant to conven¬ tional removal means, including aluminum, alkaline earths, rare earths, phosphorus, thorium, and uranium to acceptable levels. The ability of this invention to reduce thorium and uranium to acceptable levels is of particular importance because of environmental and health concerns regarding safe handling and disposal of the waste products arising from the Tiθ2 process. Such purified Tiθ2 ore is especially suitable for making Tiθ2 pigment by the chloride process. Finally, the process of this invention is highly useful and desirable because it can make practical the utiliza¬ tion of low grade, inexpensive and more abundant anatase Tiθ2 ore which contains numerous impurities. The process is also simple and requires few steps. Moreover, the process of this invention can have considerably less energy requirements and investment requirements than many prior art processes because a roasting step prior to leaching generally is optional. In addition, it has been found that the process of this invention can reduce calcium, barium, strontium, thorium and uranium to acceptable levels. Specifically, it has been found that the process of this invention (1) often can reduce the calcium in the beneficiated ore to a level generally not exceeding about 0.25 percent by weight, and often not exceeding about 0.20 percent by weight; (2) often can reduce the combined thorium and uranium to a level less than about 200 parts per million, and often less than about 150 parts per million; and (3) often can reduce the combined calcium, barium and strontium to a level not exceeding about 0.30 percent by weight, and often not exceeding about 0.25 percent by weight. (In this paragraph, the foregoing percentages are percent by weight, based on the weight of the ore and calculated as the metallic oxide) .
DETAILED DESCRIPTION OF THE INVENTION The following sets forth a detailed descrip¬ tion of this invention. It should be noted that the process of this invention can be run on a batch or continuous basis.
Ore
It is believed that any anatase titanium dioxide ore in any form can be used for the process of this invention. Preferred is Brazilian anatase, and especially preferred is anatase from a carbonatite source. As used herein, the term "anatase titanium dioxide ore" includes the raw ore and beneficiates and derivatives thereof such as reduced titania, blowover fines from chlorinators or other process streams from a iθ2 manufacturing process.
The following sets forth the mineral composition of a typical anatase ore which is suitable for being processed in accordance with the process of this invention:
Ti Minerals
Major: Anatase Tiθ2
Minor: Ilmenite FeTiθ 3
Schorlomite Ca3(Fe, Ti)2(Si, Ti)3O12 Ti-pyroxenite (e.g. Ti-biotite)
Fe Minerals Major: Magnetite Fe3θ
Maghemite ϊ-Fe2θ3
Minor: Goethite FeOOH Hematite -Fβ2θ3 Ilmenite FeTiθ3 Schorlomite Ca 3 (Fe, Ti)2(Si, i) 3 θi2
Al Minerals
Major: avellite Al 6 (P0 4 )4 (OH) s • 9H2O
Crandallite CaAl 3 (P0 4 ) 2 (OH)5 • H2O
Minor: Phlogopite KMg 3 (Si 3 A10ι 0 ) (OH) 2 Clay Minerals (essentially aluminum silicate hydrates)
Ca Minerals Major: Crandallite
Hydroxyapatite Ca5(PO4) 3 (OH)
Calcite (CaCθ 3 )
Minor: Perovskite CaTiθ 3
Pyroxene (e.g. Diopside)
P and Rare Earth Minerals
Major: Rhabdophane (La, Nd, Y) (PO4) • H2O
Crandallite sub-group minerals such as Florencite CeAl 3 (P0 4 )2(OH)6
Minor: Brockite (RE, Th) (PO4) • H2O Aeschynite (Ce, Ca, Fe, Th) (Ti, Nb) 2 (0, OH) 6
Th and U Minerals
(For example, such as, lattice substitutes, interstitials or solid solutions.)
Major: Crandallite
Gorceixite - BaAl 3 (PO4)2(OH)5Η2O Goyazite - SrAl 3 (PO4)2(OH)5-H 2 0 Florencite
Minor: Zirkelite - (Ca,Fe,Th) 2 (Zr,Ti,Nb)2O 7 Rhabdophane Calzirtite - CaZ 3 iOg
Other Minerals f anσue)
Vermiculite MgnAl5FeSinθ42 • OH2O Quartz Siθ2
Wavellite Al 6 (P0 4 ) 4 (OH)β • H20 Some amorphous phase Pyroxenes Clay minerals
Impurities The impurities which can be removed in accordance with the process of this invention include alkali metals, alkaline earth metals, rare earth metals, iron, aluminum, phosphorus, thorium, uranium, chromium, manganese, vanadium and yttrium. Especially suitable for removal by the process of this invention are the impurities of iron, phosphorus, aluminum, calcium, barium, strontium, chromium, manganese, vanadium, yttrium, lanthanum, cerium, neodymium, thorium, and uranium. The impurities of phosphorus, aluminum, iron, calcium, barium, strontium, and radionuclides such as thorium and uranium are especially detrimental to the chloride process for making Tiθ2 pigment? such impurities can be readily reduced to acceptable levels by the process of this invention. Also, while the impurities of aluminum, rare earths, phosphorus, thorium, and uranium are especially resistant to removal by conventional chemical or mechanical means, they can readily be reduced to acceptable levels by the process of this invention. The high levels of impurities of phosphorous, rare earth elements, thorium and uranium
are quite unique to the Brazilian carbonatite anatase ores. Effective removal of these impurities are critical to the Tiθ2 chloride process and is a unique feature of this invention. By the term "impurities" is meant the foregoing metals in their elemental state, oxides thereof, salts thereof and other complexes thereof.
Particle Size of Ore For the process of this invention, prefer¬ ably, the ore should be in particulate form. The optimum particle size for any Tiθ2 ore desired to be processed can readily be determined by comminuting (such as by grinding, crushing, milling, etc.) the ore into several different particle sizes and evaluating the amount of impurities removed by the process of this invention.
Generally, it can be desirable to liberate the minerals to be separated from the ore, i.e., to comminute the ore into as fine particles as practical so that the presence of discrete minerals or nearly discrete minerals in the particles is improved.
Ordinarily, the ore should have a particle size of less than about one-fourth inch. If ore treated in accordance with this invention is to be used in the chloride process for making Tiθ2 its particle size can be adjusted so that it is compatible with such process. In such case, the particles preferably will fall within the range of about -20 mesh to +400 mesh. Of course, some ores in their natural state have a particle size within this range. If so, additional comminuting is not necessary.
Mineral Dressing If desired, the ore can be subjected to mineral dressing prior to the leaching treatments. By
mineral dressing is meant mechanical processes which can remove some of the undesired impurities, including desliming (removing fine particles by a cyclone, grating or settling process) , crushing, grinding, classification, screening, flotation, electrostatic separation and magnetic separation. The magnetic separation is one of the important steps of this invention and generally involves low, medium and high intensity magnetic field strength and/or gradient; including, preferably, staged magnetic separation sequential through low, medium and high intensity magnetic field strengths. Suitable mineral dressing processes are disclosed in U.S. Patent 4,243,179, which is hereby incorporated by reference. If mineral dressing is used, it can be designed to reduce the ore to the desired particle size in order to satisfy both mineral liberation and Tiθ2 ore chlorination requirements.
Low Temperature Reductive Roasting and Magnetic Separation
Optionally, prior to the leaching process of this invention, the ore can be subjected to low temperature reductive roasting. The purpose of such low temperature reductive roasting is to convert some of the iron bearing minerals to magnetic form, which can be removed by magnetic separation techniques.
If low temperature reductive roasting is used, it generally will be carried out at a tempera- ture in excess of ambient conditions up to about 400 degrees C. , in the presence of a carbonaceous reducing agent. Preferably the temperature will be about 200-400 and most preferably about 250-300 degrees C. Suitable carbonaceous reducing agents include coke, lignite char, charcoal, coal, lignite, petroleum such as residual oil, carbon monoxide, producer gas.
hydrogen, gaseous hydrocarbons, and natural gas. Preferred is carbon monoxide. Note that to use reducing agents other than carbon monoxide, the roasting temperature should exceed about 300 degrees C. The roasting should take place under reductive conditions, i.e., in the substantial absence of air or oxygen or under conditions which favor reduction rather than oxidation.
If low temperature roasting is used, it can be carried out by any suitable means, process or device. For example, a fixed bed, rotary kiln, fluidized bed, a plasma jet, batch or continuous process can be utilized.
The time required for the low temperature roasting step can readily be determined by making several experimental trials and selecting those which produce the desired results with the lowest tempera¬ ture and the least time so that output can be opti¬ mized and energy consumption can be minimized. Suitable times often will be in the range of about five minutes to 8 hours, preferably about five minutes to 2 hours, and most preferably about 15 minutes to one hour.
If the low temperature roasting step is used, it preferably should be followed-up with wet or dry magnetic separation to remove the iron containing materials which have been converted to magnetic form.
It has been found that low temperature reductive roasting may make phosphorus, aluminum, thorium and uranium more resistant to the leaching step of the process of this invention. Therefore, if these impurities are present in appreciable amounts, low temperature reductive roasting may not be suitable. Running a few experimental tests can readily determine whether or not a low temperature reductive roast will be beneficial.
If the low temperature reactive roasting is not used, the anatase ore should be subjected to medium and high intensity and gradient magnetic separations to a desired level of Tiθ2 and FeO x before the leaching process of this invention.
High Temperature Reductive Roasting
Optionally, prior to the leaching process of this invention, the ore can be subjected to a high temperature reductive roasting. It has been found that such roasting can further reduce the amounts of phosphorus compounds in the ore and lower the tempera¬ ture needed for the leaching step. If a high tempera¬ ture reductive roasting is used, it generally will be carried out at a temperature of about 900-1700 degrees C, in the presence of a carbonaceous reducing agent. Suitable carbonaceous reducing agents include coke, lignite char, charcoal, coal, lignite, petroleum such as residual oil, carbon monoxide, producer gas, hydrogen, and natural gas. The roasting should take place under reductive conditions, i.e., in the sub¬ stantial absence of air or oxygen or under conditions which favor reduction rather than oxidation. A preferred temperature range is about 1100-1500 * C. It has also been found that a high temperature reductive roasting can enhance the removal of thorium and uranium, but may be detrimental to the removal of aluminum.
If roasting is used, it can be carried out by any suitable means, process or device. For example, a fixed bed, rotary kiln, fluidized bed, a plasma jet, batch or continuous process can be uti¬ lized.
The time required for the high temperature roasting step can readily be determined by making several experimental trials and selecting those which
produce the desired results with the lowest tempera¬ ture and the least time so that output can be opti¬ mized and energy consumption can be minimized. Suitable times often will be in the range of about five minutes to 8 hours, preferably about five minutes to 2 hours, and most preferably about 15 minutes to one hour.
It is emphasized that generally a low or high temperature reductive roast is not needed, because ordinarily, satisfactory results can be obtained without it. Thus, a substantial advantage of this invention is that it generally can produce a high quality beneficiated ore without the use of any reductive roasting, and this can save substantial investment and operating costs.
Preleach
If desired, prior to the leaching step, the ore can be subjected to a preleach operation. The purpose of the preleach step is to remove impurities which can be removed with milder conditions than the leaching step described below. Use of the preleach step could enhance the economics of the process and, in some grades of ore, could improve quality. The acids and concentration of acids described below for the leaching step can be used. Also, if desired, the spent acid from the leach step can be used as the feed for the preleach step. Suitable temperatures are about 50-100"C, preferably about 60-90'C and most preferably 70-80 # C. The pressure ordinarily will be about atmospheric.
Leaching
For this step of the process of this inven- tion, suitable acids include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and mixtures
thereof. Especially preferred are hydrochloric acid, nitric acid, hydrofluoric acid, and mixtures thereof. Most especially preferred is hydrochloric acid.
The acid should be utilized in an effective amount, i.e., an amount and concentration sufficient to solubilize substantially the impurities. Analysis of the leachate, i.e., the acid solution containing the dissolved impurities, and the leached ore can readily determine whether or not the amount and/or concentration of acid is sufficient. The acid concen¬ tration should be at least 3% by weight, based on the total weight of the solution. Ordinarily, the acid will be present in an amount of about 3-30% by weight, based on the total weight of the solution. Prefer ably, the concentration of the acid will be about 5-25 percent, and most preferably about 15-25 percent by weight, based on the total weight of the solution. If sulfuric acid is used, lower concentrations within the foregoing ranges may be preferable because higher concentrations of sulfuric acid may dissolve undesir¬ able amounts of Tiθ2«
The acid leaching treatment will take place at a temperature and pressure, and for a time which is sufficient to solubilize substantially the mineral impurities present. Ordinarily, the time required will be at least about 5 minutes. Typical ranges of time are about 10 minutes to four hours, preferably about 10 minutes to two hours and most preferably about 10 minutes to one hour. The temperature will ordinarily be about 160-300, preferably about 160-250, and most preferably about 170-210 degrees C. The broadest temperature range is about 150-300 * C and preferably is in excess of 150'C up to about 300*C. An especially preferred temperature range is about 190-210'C. An especially preferred temperature is about 190 * C.
The pressure will generally be autogenous, i.e. that generated in a closed vessel under the leaching conditions. However, additional pressuri- zation can be added, if desired, which may speed removal of impurities from some ores. Ordinarily, the pressure range will be about 4-100 atmospheres abso¬ lute, preferably about 5-75 atmospheres absolute, and most preferably about 10-60 atmospheres absolute.
By the term "solubilize substantially," as used to describe the leaching treatment, is meant the concentration of acid and conditions of temperature, pressure, and time which will solubilize at least about 10% by weight of the total impurities. Prefer¬ ably, at least 50% of the total impurities will be solubilized. Often, a graph of the concentration of the acid and conditions of temperature and time, compared to the amount of impurities removed will help to determine trends and optimizations.
Wash with Alkali Metal Compound
Optionally, following the leaching step, the ore can be subjected to washing with an aqueous solution of an alkali metal compound after the leachate has been removed from the ore. It has been found that such washing can be helpful to reduce further the amount of phosphorus, aluminum, and silicon impurities.
Suitable alkali metal compounds which can be used include sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, lithium hydroxide, and lithium carbonate. Preferred are sodium hydroxide and sodium carbonate. Most preferred is sodium hydroxide.
The alkali metal compound should be used in an effective amount, i.e., an amount and concentration sufficient to solubilize substantially at least some
of the impurities. Analysis of the leachate, i.e., the solution of the alkali metal compound containing the dissolved impurities, and the leached ore can readily determine whether or not the amount and concentration of alkali metal compound are sufficient. Ordinarily, the concentration of alkali metal compound will be about 3-30 percent, preferably about 5-15 percent, and most preferably about 10-15 percent by weight, based on the total weight of the solution. The washing treatment with the aqueous solution of an alkali metal compound will take place at a temperature, pressure, and time which is suffi¬ cient to solubilize at least some of the remaining mineral impurities. Ordinarily, the time required will be at least about one-half minute. Typical ranges of time are about one-half minute to three hours, preferably about one minute to two hours, and most preferably about one minute to one hour. The temperature ordinarily will be about ambient to about the boiling point of the washing solution. It should be noted that elevated temperature often will decrease the amount of wash time required. Generally, atmo¬ spheric pressure will be adequate, although elevated pressures can be used if desired. If only atmospheric pressure is used for this step of the process, after the leachate has been removed from the ore, the washing can be done by spraying alkali solution onto the ore which is on a filter or screen.
Removing the Leachate
Following the leaching step and the washing step, if used, the leachate is removed from the treated Tiθ2 ore. Preferably, this is done by removing the leachate followed by washing with water or by washing with water alone. The leachate can be removed by any suitable means, including filtering.
decanting, centrifuging or use of a hydroclone. Preferably, the water will be hot, i.e., up to its boiling point. The amount of washing required can readily be determined by analyzing the wash water for the presence of impurities, acid and/or alkali.
Use of Treated Ore
After the ore has been treated in accordance with the process of this invention, it can be used to make Tiθ 2 pigment or titanium metal or be used in any process where a purified Tiθ 2 ore is desired. Preferably, the Tiθ2 ore treated by the process of this invention can be used to make Tiθ2 pigment, and most preferably, to make Tiθ2 pigment by the chloride process. Suitable chloride processes and reactors for using the Tiθ2 ore treated in accordance with the process of this invention are disclosed in U.S. Patents 2,488,439, 2,488,440, 2,559,638, 3,203,763, 2,833,626, 3,284,159, and 2,653,078, which are hereby incorporated by reference.
The following examples illustrate this invention. Unless otherwise indicated, all percent¬ ages are on a weight basis.
EXAMPLE 1
An anatase titanium-bearing ore derived from a carbonatite deposit was upgraded by ore-dressing to about 65 percent Tiθ2 hereinafter referred to as mechanical concentrate or "MC". Twenty grams of this MC were leached hydrothermally with 200 milliliters of 20 percent HCl (220 grams HCl/liter) at 190 C for 60 minutes in a tantalum-clad steel bomb at a pressure which varied during the reaction from about 13.6-34 atmospheres absolute. The bomb was mounted on a rocking mechanism for agitation during the reaction.
After reaction, the reactor mass was cooled to approximately 100" C before discharge. The dis¬ charged sample was then filtered immediately while still hot and washed with hot water 3 times. Analysis of the product compared with that of the mechanical concentrate starting material is shown in Table 1, column (b) vs. column (a) . The HC1 leached and water washed ore was then washed with a hot 20 percent NaOH solution and washed with hot water 3 times. Analysis of this product, showing further removal of P, Si, and Al is shown in Table 1, column (c) .
Ti0 2 (%) FE 2 0 3 (%) A1 2 0 3 (%) CaO (%) BaO (%) SrO (%) Cr 2 0 3 (%) MgO (%) Nb 2 0 5 (%) P 2 0 5 (%)
Si0 2 (%) V2O5 (%) Zr0 2 (%)
Y2O3 (%) La 2 θ 3 (%)
Ce0 2 (%) Nd 2 0 3 (%) Th (ppm) U (ppm)
EXAMPLE 2 A hydrothermal HC1 leach was conducted under similar conditions to those described in Example 1 except that the feed ore had been roasted in argon with carbon, and then magnetically separated prior to leaching. The leaching was carried out on the non-magnetic fraction. The experimental conditions were as follows:
ROASTING:
Anatase (mech. cone.) 30.00 grams Brazilian charcoal (-100 mesh) 5.00 grams Roasting Atmosphere Argon Roasting Temperature HOO ' C Roasting Time 60 minutes
MAGNETIC SEPARATION: Low intensity ca. 500 gauss Magnetic fraction 37.5% (ca. 20% Tiθ2 loss)
LEACHING:
20% HC1 solution 200 ml Non-magnetic mech. con. 20.00 grams Leach Time 60 minutes Leach Pressure Autogenous Leach Temperature 170 β C
NaOH WASH: None
Analysis of the initial and final products is shown in Table 2.
TABLE 2
Hydrothermal HCl Leach after
Reductive Roasting with Charcoal
HCl Leach Starting With Reductive Material Roastin
Ti0 2 (%)
Fe 2 0 3 (%) A1 2 0 3 (%)
CaO (%)
BaO (%)
SrO (%)
Cr 2 0 3 (%) MgO (%)
Mn0 2 (%)
Nb 2 0 5 (%)
P2O5 (%)
Zr0 2 (%) Si0 2 (%)
V 2 0 5 (%)
Ϊ2O3 (%) La 2 0 3 (%)
Ce0 2 (%) Nd 2 0 3 (%) Sc 2 0 3 (%) U (ppm) Th (ppm)
Sixty grams of a Brazilian anatase mechanical concentrate similar to the one used in Examples 1 and 2 (-20+200 mesh) were leached hydrothermally with 200 ml of 20% HCl for 60 minutes in a Ta-Clad steel bomb at 110, 130, 150, 170, 190 and
210 degrees Centigrade. The reaction slurry was under constant agitation by rocking the bomb on a rack.
After reaction, the reactor mass was treated in a similar fashion as described in Example 1, including a wash with 20% NaOH.
The result of X-ray fluorescence of the final solid is shown in Table 3.
TABLE 3 Effect of Hydrothermal HCl Leach Temperature on Impurity Removal from a B ase M a cal Concentrate
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