US2980508A - Oxidation of trivalent titanium compounds contained in solid titaniferous materials - Google Patents

Description

United States Patent OXIDATION OF TRIVALENT TITANIUM COM- POUNDS CONTAINED IN SOLID TITANIF- EROUS MATERIALS Olav Moklebust and Harald Bjoeraanesset, Hauge I Dalane, Norway, assignors to National Lead Company, New York, N.Y., a corporation of New Jersey dation of trivalent titanium compounds contained in concentrates produced by thermo reduction of titniferous ores such as ilmenite. The instant process is particularly useful in the production of a titaniferous composition which is amenable to digestion by concentrated mineral acids.

' Titaniferous slags, sintered masses, or other types of 'agglornerates or finely divided materials produced by thermo reduction of titaniferous ores or ore concentrates with a carbonaceous reducing agent such as coke, with or -without simultaneous supply of heat by burning liquid or gaseous fuels. Such reduction operations may take place 'in a smelting furnace and in such cases the titanium dioxide rich slag and the metallic iron are normally tapped separately. In another procedure the reduction may be carried out without any smeltering or sintering, for instance, in a rotating furnace. In this case the reduced "concentrate is normally crushed, subsequently washed and separated magnetically or by other mechanical means in order to recover a titanium dioxide rich concentrate and a concentrate of metallic iron.

Such concentrates rich in titanium dioxide can also be produced by mixing a crushed titaniferous ore concentrate and small amounts of fluxes, such as sodium chloride and/or sodium carbonate, agglomerating the mixture so formed and heating the same in the presence of reducing agents so as to achieve formation of finely divided metallic iron which is subsequently separated from the titanium oxide concentrate by mechanical means.

In order to obtain high grade titanium oxide concentrates by any of the processes just mentioned, it is important that a substantial part of the iron content be reduced to the metallic state. Under strongly reducing conditions, a considerable part of the titanium oxides in the concentrate are also reduced to oxidic compounds of trivalent titanium. It has been observed that between 50 and 80 percent of the total amount of titanium present in the titanium oxide concentrate resulting from the reduction, may be present in the trivalent state. When hydrolyzing titanium sulfate solutions, trivalent titanium is not precipitated and will consequently be lost with the socalled mother liquor. The amounts of trivalent titanium which are lost may be considerable and the presence of same is in large quantities obviously not desirable in the ti o n of titaniferous concentrates, it has been proposed to Patented Apr. 18, 1961 blow air through the titanium solution in order to oxidize the trivalent titanium compounds. Another proposal has been to add various chemical oxidizing'agents; however, the use of same is often expensive and may very well impair the quality of the final products. Therefore. until the development of the instant invention, it has been important to use titanium oxide rich concentrates containtaining only moderate amounts of trivalent titanium compounds. Still another proposal was to oxidize the material containing trivalent titanium compounds and air at temperatures of 150 C. or higher. However, it was noted that materials oxidized at such elevated temperatures are not easily digestible-in sulfuric acid.

Accordingly, an object of the instant invention is to provide a process for rendering materials containing solid trivalent titanium containing values to a form amenable to digestion in concentrated mineral acids. Another object is to provide a simple method for converting the trivalent titanium compounds contained in materials of the type described to tetravalent compounds. These and other objects of the instant invention will become apparent in the following more complete description and from the examples.

Broadly, the instant invention relates to a method for rendering materials containing solid trivalent titanium compounds amenable to digestion with concentrated mineral acids which comprises admixing such materials in a finely divided state with sufficient water to form a wet mass, contacting the wet mass with oxidizing gas to oxidize trivalent compounds to tetravalent compounds while maintaining the temperature during the oxidationbelow 100 C. In a more specific embodiment of the instant invention, the oxidation is efiected in the presence of oxi- 'dation catalysts.

According to the instant invention, trivalent titanium compounds contained in solid titaniferous materials may be subjected to oxidation under controlled temperatures in the presence of electrolytes such as dilute solutions of mineral acids or dilute solutions of mineral salts with the result that there is obtained a high recovery of acid soluble titanium compounds.

According to the instant process, the oxidation of the trivalent titanium compounds takes place in the presence of controlled amounts of water or steam and an oxygen containing gas such as air while maintaining the oxidation temperature below about 100 C. Addition of water or steam should be made in such a way to maintain the mass to be oxidized in a thoroughly wet condition; however,

introduction of water in such amounts that a pasty con- 50 :sistency will result is to be avoided since this situation oxygen containing gases.

would counteract the reaction of the material with the If the the oxidation is carried out under too dry a condition, for instance by rapid evaporation of the water, the process may be retarded or even stopped. It is however possible to admix the amount of water required in the oxidation reaction with the material in advance. In this case, the material which is being oxi .dized is normally maintained in the form of a static layer of some suitable thickness. In representative cases, a moisture content of 20-30 percent of the dry weight of the concentrate has been found suitable.

The rate of oxidation is accelerated when the material is stirred or ploughed since this action facilitates access of air and exposes fresh unoxidized material. The manner of-stirring and aerating the material is of importance when choosing the most effective thickness of the layer of material. Experiments have indicated that a suitable thickness of a static bed when no stirring or agitation is employed is between 10 and 25 millimeters.

Theoxidation rate also increases with increased temperatures below 100 C. It has been observed that effective oxidation takes place between 40 and C. and

particularly in the range 60-85 (3. During the oxidation process, heat is developed and generally no additional heat is applied from an externalsource. It is however of importance that the thickness of the layer of material under treatment he so 'controlled'that excessive heat losses do not occur with the result that the temperature would drop to a point which is not suflicient to maintain the oxidation reaction. Further, it is important that sufl'icient quantities of oxidizing gas such as air be available to provide intimate contact with the material to be oxidized.

It has been found quite unexpectedly that the oxidation of trivalent titanium materials of the type disclosed herein may be considerably accelerated by an addition of small amounts of electrolytes such as for example dilute solutions of mineral acids and mineral salts. Among the electrolyte solutions which have been found particularly effective are those containing sulfuric acid, hydrochloric acid, sulfates, chlorites, chlorates, and the like. Dilute sulfuric or hydrochloric acid in quantities of 0.1-2 percent H 50 or HCl (calculated on the weight of the concentrate) seem preferable, but even traces of electrolyte in the water appeared to have a beneficial influence on the rate of the oxidation process.

The water addition to the mass may be done in one step as has been described or may also be extended over the whole period of oxidation, that is from the start to the interruption of the oxidation reaction. In such practice, it becomes important to closely control the moisture content of the material, that is to take steps to see that the material neither becomes too wet or too dry but rather that it maintains a moisture content dependent upon the specific material being handled and the temperature which it is proposed to maintain during oxidation. The material may be moistened by spraying a liquid over the surface in the form of small droplets using a spray nozzle and at the same time pelletizing the moist material. Pellets which are moistened throughout without having a pasty consistency may be prepared in this manner. These pellets should have a size between 1 and 10 millimeters and should preferably be in the 2-5 millimeter range. Such moist pellets of the particle size indicated have proved suitable for quick oxidation and are conveniently placed in layers of suitable thickness.

The particlesize of the concentrate has been found to be significant in actual operation of the oxidation process. Initially finely divided material is preferred although thismay be pelletized as just indicated. The concentrate should have a particle size not in excess of about 50 microns and should preferably be in the range of 2 to 10 microns.

X-ray diffraction patternsindicate that when the oxidation is carried out according to the present invention there is no latice rearrangement. Material both before and 'after the oxidation is identified as (Fe, Mg) -2TiO admixed with substantial quantities of titanium oxides. Anatase, rutile, and free Tigog could not be traced. It is known that compounds of the type indicated by the formula (Fe,.Mg)-2TiQ are easily digested by sulfuric acid treatment as is known to the art.

Still another unexpected advantage of the method of the present invention is the observation that material in the oxidized trivalent state as produced may be subsequently heated at temperatures up to about 250 C. without any apparent formation of free T10 or other physical or chemical changes in the material, which would result in subsequent low recoveries when the material is subjected to sulfuric acid digestion.

In order to illustrate the advantagesof the instant invention the following examples are offered.

Example I -in tne trivalent state (calculated as T i was thoroughly wetted with dilute sulfuric acid (1:20) and the material was then spread out in a layer of 12 millimeters thickness. Upon contact with air the oxidation of the trivalent compounds began and the oxidation was accompanied by an increase in temperature, the temperature of the material reaching a peak of .84" C. in about fifteen minutes. At this time it was determined that after the oxidation the amount of trivalent titanium had fallen from 55.0 percent to 24.7 percent of the total amount of titanium. This corresponded to about 18.5 percent trivalent titanium calculated as TiO in the final product.

The oxidized concentrate was digested'with sulfuric acid according to known laboratory methods using a thermos flask as the digestion chamber. Upon analysis it was determined that about 96.8 percent of the TiO, was acid soluble. This high content of soluble TiO was proof of the easily digestible. compounds which are. in the oxidized material.

Exampl I A sample of TiO;; rich concentrate analyzing in total 80.5 percent TiO of which 78.0 percent was present--in the trivalent state (calculated as TiO Was rolled in a pelletizing apparatus to form pellets of the 2-3 millimeter size range. 7 During the pelletizing operation, dilute hydrochloric acid (1:20) was added. The temperature during oxidation rose to about 68 C. The pellets were then placed in a layer of about20 millimeters thickness and oxidation commenced. The temperature reached about 68 C. in short order and continued upward to about 84 C. in nineteen minutes. After oxidation of the pellets it was determined that the amount of trivalent titanium had decreased from 78.0 percent to 25.5 percent of the total amount of titanium. This corresponded to about 19.5 percent trivalent titanium calculated as TiO- Digestion tests of this material were conducted as indicated in Example I and it was determined that about 96.0 percent of the titanium values in the oxidized prod-- not were acid soluble TiO Example '11] A sample of the oxidized concentrate described in Example II was furtherheated to 200 C. and kept at this temperature for half an hour. The heated material was then found to contain 25.2 percent of total titanium in the form of trivalent titanium (calculated as TiO Sulfuric acid digestion of thismaterial indicated that about 95.6 percent of the titanium was present as acid soluble TiO For purposes of comparison, the sample of the same Ti0 rich concentrate as was employed in Example I was initially heated in air to about C. The temperature of the material increased further in a. rapid manner to about 500 C. and this temperature was maintained for an additional thirty minutes. Upon cooling the material was found to have completely oxidized. The oxidized concentrate was digested with sulfuric acid according to the same technique as described in Example I. The content of soluble Ti0 was determined to be as low as 52 percent of the total amount of titanium oxides calculated as Ti0 in the concentrate. This result indicated considerable formation of sparingly soluble TiO during the oxidation period.

It has thus been shown that the instant process provides a simple and effective process for converting trivalent titanium values to tetravalent values whereby the subsequent digestion or solubilization of the titanium modifications and variations may be employed within the scope of the following claims.

We claim:

1. Method for rendering a material consisting essentially of a finely divided titanium concentrate having a particle size not in excess of about 50 microns and containing solid trivalent titanium oxide amenable to digestion with concentrated sulphuric acid which comprises wetting the finely divided concentrate with water and a small amount of oxidation accelerator without dissolving the concentrate and without forming a slurry, contacting the so wetted concentrate, prior to digestion, with oxygen containing gas to oxidize the trivalent compounds to tetravalent while maintaining the temperature during oxidation below 100 C.

2. Method according to claim 1 wherein the temperature is maintained between about 40 C. and about 90 C. Y

3. Method according to claim 1 wherein the particle size is between 2 and 10 microns.

4. Method according to claim 1 wherein the oxida- 6 tion accelerator is sulphuric acid, said acid being present not in excess of 2 percent calculated on the weight of the material under treatment.

5. Method according to claim 1 wherein the oxidation accelerator is hydrochloric acid, said acid being present not in excess of 2 percent calculated on the weight of the material under treatment.

6. Process according to claim 1 wherein the amount of oxidation accelerator is between 0.1 percent and 2.0 percent calculated on the weight of the material ,under treatment. 2

References Cited in the file of this patent UNITED STATES PATENTS 1,656,572 Schultze Jan. 17, 1928 2,125,340 Hager Aug. 2, 1938 2,149,370 Smith Mar. 7, 1939 2,339,808 Ravnestad et al. Jan. 25, 1944 2,589,910 Schnieder Mar. 18, 1952 2,724,636 Mullin et al. Nov. 22, 1955

Claims (1)

1. METHOD FOR RENDERING A MATERIAL CONSISTING ESSENTIALLY OF A FINELY DIVIDED TITANIUM CONCENTRATE HAVING A PARTICLE SIZE NOT IN EXCESS OF ABOUT 50 MICRONS AND CONTAINING SOLID TRIVALENT TITANIUM OXIDE AMENABLE TO DIGESTION WITH CONCENTRATED SULPHURIC ACID WHICH COMPRISES WETTING THE FINELY DIVIDED CONCENTRATE WITH WATER AND A SMALL AMOUNT OF OXIDATION ACCELERATOR WITHOUT DISSOLVING THE CONCENTRATE AND WITHOUT FORMING A SLURRY, CONTACTING THE SO WETTED CONCENTRATE, PRIOR TO DIGESTION, WITH OXYGEN CONTAINING GAS TO OXIDIZE THE TRIVALENT COMPOUNDS TO TETRAVALENT WHILE MAINTAINING THE TEMPERATURE DURING OXIDATION BELOW 100*C.