CA1152752A - Chlorination of titaniferous ore using porous carbon - Google Patents

Abstract

ABSTRACT
Vanadium impurities in chlorinated titaniferous materials are rendered easily removable by reacting said titaniferous materials with a high surface area carbon during the chlorination process. A process for preparing said high surface area carbon is also described.

Description

BACKGROUND OF T}IE IN~NTION
This invention relates to the separation of vanadium values from titanium values in mixtures of titanium and vanadium chlorides.
Titaniferous materials are often subjected to chlorination, as chlori-nation is an efficient and economical way to obtain a high purity titanium source for making titanium alloys, titanium compounds, and especially pigmentary titani-um dioxide.
Several processes have been described in the art for the chlorination of titaniferous materials. Such processes generally react a titanium-containing lQ raw materlal such as rutile or ilmenite ore, with a chlorine-providing material and a carbon-containing reductant according to one or both of the following equ-ations:
TiO2 + 2CL2tg) + C(s) ~ TiCl4~g) + CO2(g) TiO2 + 2C12(g) + 2C(s) -~ TiC14(g) + 2CO~g) Iron is a common impurity in titaniferous raw materials, and most chlorination processes are effective for simultaneously chlorinating the Ti and Fe values of these raw materials as shown in the following reactions:
2FeTiO3 + 6C12(g) ~ 3C(s) ~ 2TiC14(g) + 3CO2(g) + 2FeC12 FeTiO3 + 3C12(g) + 3C(s) ) T~C14(g) + 3CO(g) + FeC12 Chlorination reactions are generally carried out at about 1000~C., but can be carried out at any temperature in the range from about 800C. to about 2000C., using various carbon reductants and chlorine sources, including chlorine gas and chlorine-containing compounds. The titaniferous raw materials to be chlori-nated can be preformed into briquets or the process can be conducted in a fluid bed using granular materials. When a fluid-bed process is used, generally the chlorine-providing material is supplied to the bottom of the bed and product titanium tetrachloride (TiC14) is removed from the top. Fluidization is general-- 1 - ~
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~27S2 ly controlled such that the bed remains fluidized and yet fine, solid particulate materials are not carried out with the product.
Selective chlorination processes also exist and are designed to chlor-inate only the Ti values or the Fe values of the raw material. A carbon reduct-ant and a chlorine source are used and reaction temperatures are similar to non-selective processes. However, selective processes utilize a chlorine source consisting at least partially of iron chlorides, react the titaniferous raw materials in a dilute phase, react the titaniferous raw materials at a specially high temperature, or a combination of the above.
Titanium raw materials such as rutile and elmenite ores also usually contain vanadium compounds as impurities which adversely affect the titanium products produced. For example, pigmentary TiO2 can only tolerate about 10 ppm.
vanadium in the titanium tetrachloride from which the TiO2 is made without discoloration. Removal of such impurities has heretofore been a complicated and burdensome process because of the similarity between the chemical and physi-cal characteristics of titanium compounds and vanadium compounds. For example, TiC14 melts at -25C. and boils at 136.4C. and VC14 melts at -28C. and boils at 148.5C. This parallelism of properties permeates a comparison of the com-pounds of these two elements. Therefore, in the conventional chlorination process the vanadium values in a titaniferous raw material react in substantially the same manner as the titanium values, and their respective chlorinated products have nearly identical chemical and physical properties. Therefore, it is extreme-ly difficult to separate the undesirable chlorinated vanadium values from the desirable titanium values. Fractional distillation, for example, will remove most impurities from TiC14, but is ineffective for removing vanadium impurities.
Processes which are used commercially remove vanadium impurities from TiC14 by refluxing with copper, treating with H2S in the presence of a heavy 1~i2'752 metal soap, or treating with an alkali metal soap or oil to reduce vanadium impurities to a less volatile form. In each of these processes the treated TiC14 is then subjected to a further distillation. However, the organic materials used tend to decompose and deposit sticky, adhering coatings Oll heat exchanger surfac-es, pipes, and vessel walls. This causes shutdowns of the process and requires frequent maintenance of the equipment.
In accord with this invention, a simple, efficient, and economical process has now been discovered for separating the vanadium values from chlorin-ated titaniferous materials. The process of this invention utilizes a high sur-face area carbon for reacting with the titaniferous materials during the chlorin-ation process. The use of this high surface area carbonaceous material causes the vanadium values present in the titaniferous material to be reduced to a less volatile form so that they can he easily removed as a solid from the gaseous or liquid TiC14 product. In particular, titaniferous materials and porous carbon reductant having micropores with a pore di~m~ter of less than about 20A are fluid-ized in a fluid-bed and contacted with a chlorine-providing gas selected from the group consisting of C12, HCl, organochlorides, or mixtures thereof at a tempera-ture in excess of about 800C. Efficient chlorination is achieved and upon cool-ing the product's vanadium impurities are readily separable from the chlorinated titanium.
One advantage of the present process is that it can be performed in existing equipment for the chlorination of titaniferous material. Another ad-vantage is that it employs economical raw materials. Still anotner advantage is that the C0 value of the tail gas produced is sufficiently enhanced such that said tail gases will support combustion and can be burned to effect complete conversion to C02 and thus eliminate the pollution problem they previously createdO These and other advantages will become more apparent in the "Detailed Description of the Invention"O

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~ lS2752 According to the present invention; there is provided a process for chlorinating vanadium-containing titaniferous materials which comprises:
fluidizing particulate titaniferous material and porous carbon reductant, contacting said fluidized particulate materials with a chlorine-providing gas selected from the group consisting of C12, HCl, organochlorides, and mixtures thereof at a temperature of at least about 800C. until the titanium content of said titaniferous material is substantially chlorinated, said porous carbon reductant being characterized in that said carbon has at least about lOm2/g.
of internal surface area in micropores said micropores having a pore diameter of less than about 20A.
Preferably, the process is for removing vanadium compounds from vanadium-contair.ing titaniferous materials, the process compris-ing: chlorinating said titaniferous material in the presence of carbon under chlorination conditions effective to chlorinate the titanium, vanadium, and iron values of said titaniferous material, reducing said vanadium values to a less volatile form by reacting with an effective amount of a high surface area carbon, said : reducing being during said chlorinating, cooling said chlorinated titaniferous materials containing reduced vanadium values to a temperature of less than about 450C., producing a chlorinated reduced vanadium-values containing phase and a chlorinated titaniferous material-containing phase distinct from said chlorinat-ed, reduced, vanadium-values containing phase, and separating said chlorinated, reduced, vanadium-values containing phase from said . - 3a -f~ ' , ,'~ ' . ~ ,;

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;2752 chlorinated titaniferous material-containing phase.
Furthermore, the invention provides a process for chlor-inating vanadium-containing titaniferous materials and removing vanadium compounds from said vanadium-containing titaniferous materials, which comprises:
chlorinating under fluidized bed conditions said titaniferous material in the presence of carbon reductant and a chlorine-providing gas selected from the group consisting of C12, HCl, organochlorides, and mi~tures thereof at a temperature of at least about 800C. to chlorinate the titanium, vanadium and iron values of said titaniferous material, reducing said vanadium values to a less volatile form by reacting with an effective amount of a high surface area porous carbon reductant which has at least about lOm2/g. of internal surface area in micropores, said micropores having a pore diameter of less than about 20A, said reducing being during said chlorinat-ing, cooling said chlorinated titaniferous materials containing reduced vanadium-values to a temperature of less than about 450C., producing a chlorinated reduced vanadium-values containing phase and a chlorinated titaniferous material-containing phase distinct from said chlorinated, reduced, vanadium-values containing phase, - and separating said chlorinated, reduced, vanadium-values containing phase from said chlorinated titaniferous material-containing phase.
Thus a high surface area carbon is reacted with a vanadium ~.

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~. ' containing titaniferous material during chlorination of said titaniferous material. The reacted, chlorinated~titaniferous material is cooled to a temperature of less th~n about 450C.
forming a vanadium-containing solid phase separate from the chlorinated titanium product-containing phase, and the vanadium containing-phase is separated from the chlorinated titanium product-containing phase.
DETAILED DESCRIPTION OF T~E INVENTION
The present invention is an improved process for rendering vanadium - 4a -,~

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2 7 5 impurities readily removable from chlorinated titaniferous materialsO
According to an embodiment of the present invention, during the chlorination process the titaniferous material is reacted with a high surface area carbon. The amount of carbon, the carbon's surface area, pore size, and pore size distribution and the reaction temperature being effective to cause the vanadium-values to be reduced to a less volatile form.
The reduction of the vanadium-values to a less volatile form can be accomplished by substituting the high surface area carbon for all or part of the carbon-containing reductant in a conventional chlorination processO Also, the high surface area carbon can be added in addition to the carbon-containing reductant. This is done in the chlorinator itself during the chlorination process. The carbon-containing reductant used in the conventional chlorination of titaniferous materials is typically a granular material which will substan-tially pass through an 8-mesh screen (U.SO Standard Sieve). Such materials, however, have a relatively low surface area, typically, less than about lOOm /gO
For example, granular petroleum coke has a surface area of less than OOlm2/g., natural graphite about 0.4m2/gO, and coke breeze about 0~3m /gO However, carbons useful in the present invention have a surface area of at least about lOm2/g.
Such carbons must also have sufficient average pore size and pore size distribu-tion such that substantially all of this surface area can be utilized during the reaction. If, however, the surface area is at least lOOm2/g., then suf-ficient surface will be present for adequate reaction to take place regardless of the average pore size or pore size distribution. Carbons with a surface area of at least lOOm2/gO are preferredO
The surface area of the carbon can be temperature dependent and there-fore change during the chlorination reactionO The change is dependent upon the preparation and origin of the carbonO Carbons with small pores (<20A diameter) ~;2752 tend to exhibit decreased surface area when heated to 1000C. in N2(conditions similar to those encountered during the chlorination process). It is believed the very small pores tend to close up and thus a lesser surface area is exposedO
Also, carbons that have predominantly larger pores (>20A diameter) tend to ex-hibit increased surface area when heated to 1000OCD in N2. In this case, the heat is believed to cause the evolution of more volatiles and thus create more pores and expose more surfaceO
Therefore, if a carbon has a surface area of l~m2/gO to lOOm2/gO, that carbon must also have a sufficient distribution of larger pores such that the surface area will not decrease below lOm /g., and preferably increase, wh0n heated to reaction temperaturesO Further, a carbon with a surface area of at least lOOm /gD will usually have sufficient surface area remaining after heating to reaction temperatures to be effective, regardless of the pore size or pOre size distributionO
It is advantageous for fluid-bed chlorination processes that the carbon comes from a mineral rather than an animal or vegetable source. Animal-and vegetable-derived carbons have higher levels of impurities, especially calcium and alkali metal impurities~ Such impurities form nonvolatile liquid chlorides at about 1000C. during the chlorination processO Such chlorides re-main in the fluidized bed and tend to cause stickiness and decrease the amount of fluidization in the bed.
A preferred high surface area carbon is granular coal treated to in-crease its surface areaO Coal is an inexpensive source of carbon and can be obtained relatively free from calcium and alkali metal impuritiesO Coal is ; readily available in granular form of various sizes and size distributionsO
Granular coal of -8 mesh tcommercially known as #4 Buck~ or finer is typicalO
The granular coal is treated by introducing it into a fluidized bed ~, ~5'~752 at an elevated temperature with air, CO and/or ste~m until the surface area has increased sufficiently~ About 5% or more of the coal by weight will be burned off during treatmentO Generally to get a higher surface area, higher coal burn-off is requiredO Therefore, it is preferred to treat to the minimum effective surface area in order to obtain maximum yield from the raw materialsO
This treatment should be carried out above about 400Co When steam or CO2 is used, the reaction is endothermic, with air the reaction is exothermic and will maintain itself without the introduction of any outside heat sourceO Preferably, such process is carried out on a continuous basis with continuous feeding of coal and removal of treated productO
The control of average pore size and pore size distribution is difficult with this treatment processO Typically the average pore size produced (< about 20A diameter) is such that the surface area will decrease when heated to chlorination temperatures in N2O Therefore, it is preferable to treat coal with this process until a surface area of at least about 100m2/g. is obtained such that average pore size and pore size distribution will not be factors in the effectiveness of the treated coal for use in the present invention, and an effective amount of surface area will always be present.
The coal used is preferably high rank ~anthracite) rather than low rank (bituminous) because the high rank coals attain a higher surface area during the above treatmentO The coal introduced into the treatment process can be either wet or dry. Dry coal is actually preferred; however, wet granular coal is a much more readily available commercial product, water being present only to hold down dusting during transportationO
Other processes for making high surface area carbons are readily availableO Any available process for increasing the surface area of a carbon can be used for making a carbon useful in the present invention, so long as a ~Z752 sufficiently high surface area or surface area, pore size, and pore size distri-bution combination are obtained. Such processes are typically used for producing activated carbonO Commercially available activated carbons have surface areas from about 300 to about 3000m2/g. and are effective in the instant process~
However, such materials are substantially more expensive at the present time then the above-described treated coalsO Also, it has been found that the high surface area carbons useful in the present invention do not require the proper-ties of activated carbon. Specifically, a carbon can be effective in the instant process without possessing any of the absorption or adsorption properties of activated carbons, because the present procPss is not a sorption process.
When the chlorinating and reacting steps of the process of the present invention are followed, the chlorinated vanadium values produced are in a different physical form from the chlorinated titanium values. For example, between about 450C. and 136C~ the chlorinated titanium values (primarily TiC14) are gaseous whereas the chlorinated vanadium values produced (believed to be VC13) are solid, and below about 136Co to about -25C. the chlorinated titanium values are liquid, while the chlorinated vanadium values remain solidO Further-more, the chlorinated vanadium values are insoluble in both the gaseous and the liquid chlorinated titanium valuesO Therefore, below about 450C. a conventional solid-gas separation or solid-liquid separation is effective to remove the vanadium values contained in the chlorinated titaniferous materialO
A preferred solid-gas separation is the use of a cyclone separator at a temperature of about 140C. to about 300C~ and preferably about 175-200CD; such separation is used in conventional chlorination processes to collect particulates in the TiC14 gas stream, but does not remove vanadium values during conventional processingO
Preferred solid-liquid separations are decanting and filtrationO

A further benefit derived from the reaction of the lligh surface area carbon with a titaniferous material during chlorination is an enhancement of the C0 content of the tail gas producedO Tail gases are those gases that accom-pany the product as it leaves the chlorinator and must be disposed of as an effluent of the processO Specifically, the C02:C0 ratio in the tail gases of a conventional chlorination process is about 1 or 2:1. Such tail gas must be treated before being expelled into the environment because of the high C0 level (about 33-50%). This gas cannot support combustion; therefore, treatment by mere burning is precluded and other effective treatments are costlyO However, when a high surface area carbon is reacted with titaniferous material during the chlorination process according to the present invention, the C02:C0 ratio is reduced to about OoOl or 0.02:1 (about 98 or 99 percent C0). Even though this tail gas contains substantially more C0 than does the tail gas from the conven-tional process, this tail gas can be burned directly before expelling inio the atmosphere as a means of treatment and thus is substantially easier and less expensive to treat than the tail gas of the conventional process. Alternatively, the C0-rich tail gas can be used for its fuel value by burning it in a boiler, kiln, or other.

The following examples will show ways in which this invention has been practiced. These examples are not intended to be limiting of the invention.

In the examples, all temperatures are in degrees Centigrade and all percentages in parts by weight, unless otherwise specifiedO

Wet, granular (-18 mesh), anthracite coal was placed in a fluid-bed reactor and fluidized by introduction of hot steam at a superficial velocity of 0.8 feet per second at a temperature of 890C. The surface areaof the granular coal was measured by the BET (~ranauer, Emmett, and Teller) method for surface area determination. Surface area as expressed here and throughout this speci-fication is "effective surface area" as determined from the N2 adsorption isotherm at -195C. and application of the standard BET procedure. Assurance of accuracy is difficult due to the difficulty of measuring surface area in microporous materials. A plot of surface area versus carbon burn-off is shown in Figure 1. Coal treated according to this example with about 5% or greater carbon burn-off is effective in the present process.

In the procedure of Example 1, C02, at 950C. was used in place of steam. A plot of surface area versus percent of carbon burn-off is shown in Figure 1. Coat treated according to this example with about 7% or greater carbon burn-off is effective in the present process.

In the procedure of Example 1, air at 450C. was used in place of steam. A plot of surface area versus percent of carbon burn-off is also shown in Figure 1. Coal treated according to this example with about 10% or greater carbon burn-off is effective in the present process.
Figure 1, a graph, is attached.

Rutile ore containing about 96.1% TiO2, 1.2% Fe203, and 0.4% V205 was chlorinated in a fluid-bed chlorinator at 1000C. Chlorine gas and a coal treated in accordance with Example 1 having a 5% carbon burn-off were used. A
fluid-bed depth of 14-15 inches was maintained by continuously feeding fresh ore and treated coal. The chlorination was run for a period of 3 hours, and the C02:CO ratio in the chlorinator tail gas was measured about every 10 minutes via gas chromatography. The gaseous product stream was allowed to cool partial-ly and was passed through a solid-gas cyclone-type separator. The temperature , - 1 0 -,'752 of the gas stream passing through the separator was controlled at about 175C., however, the actual temperature varied between 150 and 200Co The solids collected in this separator include fluid-bed blow-over, FeC12 and most of the vanadium values (believed to be VC13)o TiC14 was then condensed from the pro-duct gas stream and solids were allowed to settle. These solids are present mainly due to the inefficiency of the cyclone separator, and contain essentially the same components as the cyclone solids. The clear sample of supernatant TiC14 was poured off and analyzed for vanadiumO The surface area of the carbon source, the average C02:C0 ratio, and the vanadium impurity level in the TiC14 product are shown in Table Io In the procedure of Example 4, coal treated in accordance with Example 1 having a 40% carbon burn-off was usedO Data from this chlorination are also shown in Table I.

In the procedure of Example 4, coal treated in accordance with Example 3 having a carbon burn-off of 5% was usedO Data from this chlorination are shown in Table Io In the procedure of Example 4, carbon prepared according to Example

3 having a 15% carbon burn-off was used. Data from this chlorination are also shown in Table Io In the procedure of Example 4, granular (-18 mesh) anthracite coal was used without pretreatment. Data from this chlorination are also shown in Table Io ~27S2 In the procedure of Example 4, granular petroleum coke (-8 mesh) was used Data from this chlorination are also shown in Table I.

Carbon Vanadium Surface Impurity Example % Carbon Area CO2:CO Level Number Treatment Burn-Off (m2/g.)(average)(ppm) .

4 Steam @ 890C 5 104 0008 101 Steam @ 890C. 40 540 0.006 <5 6 Air @ 450C. 5 55-63 0.1 225 7 Air @ 450C. 15 163 0006 <5 8 None (Coal 0 0.1 0O4 225 9 None (Petroleum Coke) 0 <O.l 2.2 7~0 In order to further characterize the carbons useful in the present invention, three high surface area carbons were selected. Using the BET techni-que, surface area in <20A diameter pores were measured and then surface area in >20A diameter pores were measured. The total surface area is the sum of these two measurementsO
These carbons were then heated to 1000C. in a N2 atmosphere (to simulate heating to chlorination temperatures) and the respective surface area were again measured. Data are shown in Table 2.
The data show that heating air-treated coals to chlorination tem-perature results in a loss of surface area in both <20A and >20A diameter poresO
Steam-treated coals lose surface area due to a decrease in <20A diameter pores onlyO Charcoal,in contrast to the treated coals, gains surface area after heating ., 7S~:

to a chlorination temperature, due mainly to the Eormation of small poresO
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SUPPLEMFNTARY DISC~OSURE
Further, it has now been found that the porous carbon reductants useful in the present invention must contain micropores having a pore diameter of less than about 20A. Typically, useful carbons will have at least about lOm2/g. of surface area in such micropores, advantageously at least about lOOm2/g.
of surface area in such micropores and preferably about 500m2/g. of such internal surface. Non-porous carbons and carbons having only large pores, e.g. charcoal, are not within the scope of the present invention.
The carbon particles can be any useful size. For a fluidized bed process the particles must be small enough to be fluidized by the fluidizing gasand yet be large enough such that they are not carried out of the fluid bed by the off-gas stream. Granular materials of about -8 mesh are typical. However, the average particle size can range from about 4 mesh to about 200 mesh and be useful. Preferably, the carbon particles wili have an average particle size greater than about 100 mesh and will be substantially retained on a 40 mesh screen.
The granular titaniferous material useful in the present invention can be any titanium-containing compound or raw material such as rutile ore, ilmenite ore, or other. Naturally occurring sand-sized rutile ore is a convenient source, typically being -40 mesh and +140 mesh. However, granular titaniferous materials having an average particle size from about 4 mesh to about 200 mesh can be used. The titaniferous material can be substantially pure or contain a wide variety of impurities. For practical operation the titaniferous material should contain at least about 90% TiO2; however, the process will operate with lesser amounts presentO

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Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for chlorinating vanadium-containing titaniferous mater-ials which comprises:
fluidizing particulate titaniferous material and porous carbon reductant, contacting said fluidized particulate materials with a chlorine-providing gas selected from the group consisting of C12, HCl, organochlorides, and mixtures thereof at a temperature of at least about 800°C. until the titanium content of said titaniferous material is substantially chlorinated, said porous carbon reductant being characterized in that said carbon has at least about 10m2/g. of internal surface area in micropores said micropores having a pore diameter of less than about 20.ANG..

2. The process of claim 1 wherein said porous carbon reductant is of mineral origin.

3. The process of claim 2 wherein said porous carbon reductant is derived from coal.

4. The process of claim 3 wherein said coal is anthracite.

5. The process of claim 3 wherein the pores in said porous carbon reductant is produced by treatment with air, CO2, and/or steam at a temperature in excess of about 400°C.

6. The process of claim 1 wherein said chlorine-providing gas is C12.

7. The process of claim 1 wherein said carbon has at least about 100m2/g. of internal surface area in said micropores.

8. A process for chlorinating vanadium-containing titaniferous materials and removing vanadium compounds from said vanadium-containing titaniferous mater-ials, which comprises:
chlorinating under fluidized bed conditions said titaniferous mater-ial in the presence of carbon reductant and a chlorine-providing gas selected from the group consisting of C12, HCl, organochlorides, and mixtures thereof at a temperature of at least about 800°C. to chlorinate the titanium, vanadium and iron values of said titaniferous material, reducing said vanadium values to a less volatile form by reacting with an effective amount of a high surface area porous carbon reductant which has at least about 10m2/g. of internal surface area in micropores, said micropores having a pore diameter of less than about 20.ANG., said reducing being during said chlorinating, cooling said chlorinated titaniferous materials containing reduced vanadium-values to a temperature of less than about 450°C., producing a chlorina-ted reduced vanadium-values containing phase and a chlorinated titaniferous material-containing phase distinct from said chlorinated, reduced, vanadium-values containing phase, and separating said chlorinated, reduced, vanadium-values containing phase from said chlorinated titaniferous material-containing phase.

9. The process of claim 8 wherein said high surface area carbon has a surface area of at least about 100m2/g.

10. The process of claim 8 wherein said high surface area carbon is of mineral origin.

11. The process of claim 10 wherein said high surface area carbon is derived from coal.

12. The process of claim 11 wherein the pores in said porous carbon reductant is produced by treatment with air, CO2, and/or steam at a temperature in excess of about 400°C.

13. The process of claim 12 wherein said coal is treated until it obtains a surface area of at least about 100m2/g.

14. The process of claim 8 wherein said chlorinating and reducing produces byproduct CO2 and CO in a ratio sufficiently enriched in CO to be combustible in air.

15. The process of claim 8 further comprising oxidizing said chlorinated and separated titaniferous material-containing phase under oxidizing conditions to produce titanium dioxide.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

16. The process of claim 1 wherein said carbon has at least about 500m2/g.
of internal surface area in said micropores.

17. The process of claim 1 wherein said titaniferous materials contain at least about 90% by weight TiO2.