Patent Application
20230373809
Embodiments of the disclosure are generally related to the production of titanium dioxide, and more specifically to a process for the production of titanium dioxide from anatase ore through digestion with sulphuric acid, leaching, hydrolysis and calcination.
Titanium dioxide, also known as titanium (IV) oxide or titania, is the naturally occurring oxide of titanium having the chemical formula TiO2. Titanium dioxide is used in a wide range of applications, including, but not limited to, paint, pigments, toothpaste, sunscreen, pharmaceuticals, food stuffs, soaps, and food coloring.
Titanium dioxide is sourced from titaniferous ores including ilmenite which is an iron-titanium oxide with a chemical composition of FeTiO3, rutile which is a mineral composed primarily of titanium dioxide, and is the most common natural form of TiO2, and anatase which is a rarer, metastable mineral form of titanium dioxide. Two main processes are used to recover commercial grade titanium dioxide from these ores: a sulphate process and a chloride process. Although the chloride process has some advantages over the sulphate process in both cost and waste management, the sulphate process allows low grade titanium raw materials to be used. The decrease in rutile and ilmenite reserves makes necessary the study of other methods to obtain TiO2. Since 1980, anatase has been studied as a source for obtaining high TiO2 purity. However, technical and economic viability issues still remain.
Anatase is one of the titanium dioxide polymorphs, in addition to rutile and brookite, as described above. It has a tetragonal crystalline system, a specific density from 3.82 to 3.97 g/cm3, and a hardness between 5 and 6. Anatase is a low-temperature polymorph and occurs in weathered and metasomatized rocks (Moraes and Seer, 2015).
Despite being rare compared to reserves of ilmenite and of rutile, anatase ore reserves are found in Minas Gerais (Brazil), more specifically in the Tapira Alkaline-Carbonatitic Complex. It consists of a weathering mantle with anatase and ilmenite. The mass of ore in the mantle in situ is estimated between 1.0 and 1.5 billion tons, with TiO2 grades between 12% and 15%. In the city of Tapira, in addition to being found in the geological layer, anatase is a component of the piles of waste material from the production of apatite ore. The mass of titanium ore in the piles is estimated at 200 million tons, with average TiO2 grades from 12% to 15%.
Examples of processes that produce TiO2 from these ores include International Application Publication No. WO 1992008816 to Chaves, EP 0475104 to Bernard et al. (hereinafter “Bernard”), U.S. Pat. No. 7,625,536 to Smith Jr. and Bernard (hereinafter “Smith Jr.”). Bernard, for example, describes digesting residues of titanium dioxide production from ilmenite in 94 to 98% sulphuric acid at a temperature of 220° C., baking the mixture between 220-300° C. (2 to 18 hours), followed by hydrolyzing and calcining the mix. Bernard also teaches that the precipitate may be treated before calcination by leaching under reducing conditions. Smith Jr. generally teaches a double leaching process, and states that iron removal from anatase that is not “pretreated by a reduction step” can be “surprisingly efficient.” Additional references such as PI 8805053 A to Paixão et al., PI 9005841 and PI 9201125 A to Chaves, PI 9100482 A and PI 9101138 A to Mendonça, describe using sulfuric leaching to remove impurities and raise the product content.
In contrast to the noted references and the Background section described above, the present disclosure seeks to solubilize the titanium and, later, hydrolyze it as titanium dioxide, in part based on the mineralogical complexity of the anatase ore. The process described in the present disclosure may be capable of sufficiently solubilizing titanium in anatase using H2SO4, while overcoming the low reactivity of the ore to this acid. Moreover, the present disclosure may not require a reduction step prior to anatase digestion.
Embodiments of the disclosure are directed to processes for obtaining titanium dioxide (TiO2) from anatase ore that can include the unit operations of sulphuric acid digestion of raw ore, leaching, hydrolysis, and calcinations to produce titanium dioxide. The digestion step utilized rigorous conditions of acid concentration, high temperature, and residence time to solubilize TiO2 as TiOSO4. Furthermore, in embodiments of the disclosure, the anatase ore is ground to a desired particle size and is then subjected to stages of magnetic separation to remove iron oxides from the anatase ore before sulphuric acid digestion. This eliminates the need for a separate reduction step traditionally used to remove iron oxides (i.e. the Becher process) before sulphuric acid digestion. The process may be based on the following sequence of unitary operations: granulometric classification, grinding, magnetic separation at low, medium and high field, regrinding, sulphuric digestion, leaching with water, filtration, hydrolysis, precipitate washing, filtration and calcination.
The above summary is not intended to describe each illustrated embodiment or every implementation of the subject matter hereof. The figures and the detailed description that follow more particularly exemplify various embodiments.
Subject matter hereof may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying figures, in which:
While various embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the claimed inventions to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims.
Referring to
Starting with step 102, raw anatase ore is classified by grain size in a wet stage. The portion classified as −105 μm is discarded. At step 104, the classified grains +105 μm are ground to smaller size using a tubular mill. The ore is ground to a desired particle size, and in one embodiment, the desired particle size is such that about 60% of the particles are smaller than 210 μm
The ground ore is then subjected to stages of wet magnetic separation in step 106, in which the naturally occurring iron oxides in the ore are removed, thereby eliminating the need of a reduction step. In one particular non-limiting embodiment, the ground ore is depicted to three different magnetic separation steps 106a, 106b, and 106c, with increasing of magnetic field strength in each step. For example, in the first step (106a), the intensity of magnetic field is low and can be around from about 1,000 to about 2,000 Gauss, and more specifically about 1,500 Gauss. In step 106b, the non-magnetic material from step 106a is processed in a magnetic field increased to from about 6,000 to about 8,000 Gauss, and more specifically about 7,000 Gauss. Finally, in step 106c, the non-magnetic material from step 106b is put in an inducted magnetic field increased to from about 11,000 to about 15,000 Gauss, and more specifically about 13,000 Gauss. One of ordinary skill in the art would recognize more or less magnetic separation steps can be included, until the iron oxides are sufficiently removed to eliminate the need for a reduction step.
The resulting separated ore is then subjected to a second grinding step at 108, in which the separated ore is finely ground such that about 99% or more is less than about 62 μm, thereby increasing the surface area for efficient and more complete acid digestion.
In step 110, the ground ore is subjected to rigorous conditions of sulphuric acid in a concentration 98%, ore:acid ratio 1:2, temperature between 180° C. and 240° C., and residence time between about 3 hours to about 6 hours. During digestion step 110, the TiO2 in the ore is solubilized in the form of titanium oxide sulphate (TiOSO4), or oxotitanium sulfate, using the reaction:
TiO2+H2SO4→TiOSO4+H2O
Once solubilized, at step 110, the titanium oxide sulphate is leached, at step 112, from the digested ore cake using water at a solid:liquid ratio of about 1:4, temperature in the reactor between 50° C. and 70° C., with mechanical agitation, residence time between about 2 and 4 hours.
The leached titanium oxide sulphate is then filtered at 114 to remove residual impurities. The filtrate, which comprises a solution of titanium oxide sulphate is then subjected to hydrolysis at step 116 to form TiO2·nH2O, such as heat hydrolysis. The titanium sulfate solution and the water are heated, separately, up to the temperature range between 50° C. and 75° C., and they are mixed in a liquor:water ratio 1:5, and the temperature is increase between 80° C. and 105° C. The system is kept in mild agitation and heating between about 2 and 5 hours. During hydrolysis, the hydrated TiO2 precipitates from the solution, based on the reaction:
TiOSO4+2H2O→TiO(OH)2+H2SO4
The precipitate, which is the hydrolyzed monomeric form TiO(OH)2 is then washed at step 118 to removed free sulphuric acid, and filtered at step 120. Finally, at step 122, the hydrolyzed TiO(OH)2 is calcined between 900° C. and 1,100° C. for about 1 to 4 hours, to thermally decompose the TiO(OH)2 to TiO2, the end product.
EXAMPLE 1: After steps 102 to 108, a physical concentrate was obtained with the composition shown in Table 01, characterized by the technique of Wavelength Dispersive X-Ray Fluorescence Spectroscopy (WDXRF).
A mass of 20.00 grams of anatase concentrate ore was weighed, with the composition shown in Table 01, which was then subjected to the stages 110 and 112, according to the conditions in Table 02:
The leached TiO2 percentage was calculated based on the final residue's chemical composition, after leaching with water. The residue mass obtained was 5.53 g, and this composition is in Table 03, characterized by Energy-dispersive X-Ray spectroscopy (EDX):
Therefore, a solubilization of approximately 81.6% of titanium was obtained. To make the hydrolysis, step 116, the liquor used was characterized by Energy-dispersive X-Ray spectroscopy (EDX) and the composition is shown in Table 04:
The liquor and water were heated separately to 60° C., using a liquor:water ratio 1:5, after this they were mixed and the temperature was raised to 95° C. After the start of hydrolysis, which can be seen visually, 10% of additional water was added. Heating and stirring were maintained for 3 hours. During the step 120, filtration, the hydrolysate was washed with water. Table 05 shows the hydrolyzated composition, before and after calcination, carried out at 950° C., for 2 hours. The concentrate obtained has 88.5% of TiO2.
In some embodiments, the technical features of the present disclosure may be described by one or more of the following clauses:
Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed inventions.
Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above.
The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted.
Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended.
Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein.
For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.
The present application claims the benefit of U.S. Provisional Application No. 63/088,289 filed Oct. 6, 2020, which is hereby incorporated herein in its entirety by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/053779 | 10/6/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63088289 | Oct 2020 | US |
