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Title:
PROCESSING ILMENITE ORE TO TiO2 PIGMENT
Document Type and Number:
WIPO Patent Application WO/1996/024555
Kind Code:
A1
Abstract:
A hydrometallurgical process is provided for producing pigment-grade TiO2 from an ilmenite ore concentrate containing by weight a relatively high magnesium content ranging up to about 10 %, an iron content of at least about 15 % and a titanium dioxide content of at least about 25 %. The concentrate is selectively leached with hydrochloric acid at a concentration ranging up to about 30 % of concentrated hydrochloric acid at a temperature ranging from about 25 �C to 80 �C while inhibiting TiO2 formation by hydrolysis and provide solids containing titanium and a liquid phase. The solids are separated from liquid phase at the aforementioned temperature and the titanium-containing solids leached at a temperature of about 25 �C to 80 �C with hydrochloric acid at a concentration of at least about 18 % and thereby form a pregnant solution of titanium chloride containing iron and magnesium and waste solids containing silica. The waste solids are separated from the solution at a temperature of about 25 �C to 80 �C. The solution is cooled to a low temperature not exceeding about 15 �C sufficient to form crystals of FeCl2. The FeCl2 crystals are then separated from the solution at the stated low temperature, and thereby provide a pregnant solution containing titanium. Titanium-containing solution deficient in iron is subjected to hydrolysis at a temperature in excess of about 75 �C to form a precipitate of TiO2 and a waste solution containing Mg and Fe chlorides and hydrochloric acid. The TiO2 precipitate is then separated from the waste solution at a temperature in excess of about 75 �C. The waste solution is then subjected to hydrolysis by spray roasting the solution at a temperature of at least about 600 �C and thereby regenerate HCl and form solids containing MgO and Fe2O3.

Inventors:
DUYVESTEYN WILLEM P C (US)
HULS BERNARDUS J (US)
SHRESTHA PURUSOTAM L (US)
Application Number:
PCT/US1996/000897
Publication Date:
August 15, 1996
Filing Date:
January 22, 1996
Export Citation:
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Assignee:
BHP MINERALS INT INC (US)
DUYVESTEYN WILLEM P C (US)
HULS BERNARDUS J (US)
SHRESTHA PURUSOTAM L (US)
International Classes:
C01F5/10; C01G23/053; C22B34/12; (IPC1-7): C01G23/00; C22B34/00
Foreign References:
US3649243A1972-03-14
US3518054A1970-06-30
US3903239A1975-09-02
US4321236A1982-03-23
CA775046A1968-01-02
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Claims:
WHAT IS CLAIMED IS:
1. A hydro etallurgical process for producing pigmentgrade Ti02 from an ilmenite ore concentrate containing by weight a relatively high magnesium content ranging up to about 10%, an iron content of at least about 15% and a titanium dioxide content of at least about 25% which comprises: selectively leaching said concentrate with hydrochloric acid at a concentration ranging up to about 30% of concentrated hydrochloric acid at a temperature ranging from about 25"C to 80"C while inhibiting Ti02 formation by hydrolysis and provide solids containing said titanium and a liquid phase, separating said solids from said liquid phase at said temperature of about 25'C to 80*C, leaching said titaniumcontaining solids at a temperature of about 25C to 80"C with hydrochloric acid at a concentration of at least about 18% and thereby form a pregnant solution of titanium chloride containing iron and magnesium and waste solids containing silica, separating said waste solids from said solution at said temperature of about 25"C to 80"C, cooling said solution to a low temperature not exceeding about 15"C sufficient to form crystals of FeCl ,_» separating said FeCl2 crystals from said solution at said low temperature, and thereby provide a pregnant solution containing said titanium, subjecting said titaniumcontaining solution deficient in iron to hydrolysis at a temperature in excess of about 75*C to form a precipitate of Ti02 and a waste solution containing Mg and Fe chlorides and hydrochloric acid, separating said Ti02 precipitate from said waste solution at said temperature in excess of about 75'C, subjecting said waste solution to pyrohydrolysis by spray roasting said solution at a temperature of at least about 600*C and thereby regenerate HCl and form solids containing MgO and Fe203.
2. The process of claim 1, wherein said magnesium in the ore ranges from about 2% to 8%.
3. A hydrometallurgical process for producing pigmentgrade Ti02 from an ilmenite ore concentrate containing by weight a relatively high magnesium content ranging up to about 10%, an iron content of at least about 15% and a titanium dioxide content of at least about 25% which comprises: selectively leaching said concentrate with hot hydrochloric acid at a concentration ranging up to about 25% of concentrated hydrochloric acid at a temperature ranging from about 90'C to 110"C and form solids containing said titanium and a liquid phase, separating said solids from said liquid phase at said temperature of about 90*C to 110"C, leaching said titaniumcontaining solids at a temperature of about 90*C to 110"C with hydrochloric acid at a low concentration ranging up to about 25% of concentrated hydrochloric acid and thereby selectively dissolving iron and magnesium and providing solids comprising TiO, separating said Ti02 solids from said solution at said temperature of about 90*0 to 110'C, cooling said solution containing iron and magnesium to a low temperature not exceeding about 15*C sufficient to form crystals of FeCl2, separating said FeCl crystals from said solution at said low temperature, and thereby provide a pregnant solution containing said titanium, subjecting said iron crystals to pyrohydrolysis, thereby regenerating HCl and forming an iron containing waste solids, spray roasting said solution of said hydrochloric acid at a temperature of at least about 600"C and thereby further regenerate HCl and form solids containing MgO and Fe203.
4. The process of claim 3, wherein the magnesium content ranges from about 2% to 8%.
5. A hydrometallurgical process for producing pigmentgrade Ti02 from an ilmenite ore concentrate containing compounds including by weight a relatively high magnesium content ranging up to about 10%, an iron content of at least about 15% and a titanium dioxide content of at least about 25% which comprises: selectively leaching said concentrate with hot hydrochloric acid at a concentration ranging up to about 25% of concentrated hydrochloric acid at a temperature of at least about 85C with the formation of solids comprising TiO and a liquid phase, separating said solids from said liquid phase at said temperature of at least 85*C, warm leaching said titaniumcontaining solids at a temperature of about 25"C to 80*C with a solution of hydrochloric acid of concentration ranging up to about _36% of concentrated HCl and thereby solubilizing substantially all of the compounds except for silica impurities, separating said silica impurities from said solution at said temperature of about 25 ' C to 80*C, cooling said solution containing iron and magnesium to a low temperature not exceeding about 15"C sufficient to produce crystals of FeCl2, separating said FeCl2 crystals from said solution at said low temperature, and thereby provide a pregnant solution containing said titanium, subjecting said FeCl2 to pyrohydrolysis, thereby regenerating HCl and forming a solids product containing iron and a pregnant solution containing titanium, separating said solids product from said solution, subjecting said pregnant solution deficient in iron to hydrolysis at a temperature in excess of about 25'C to form a precipitate of Ti02 and waste solution containing Mg and Fe chloride and hydrochloric acid, separating said Ti02 precipitate from said waste solution at said temperature in excess of about 25'C crystallizing FeCl from said waste solution, separating FeCl crystals from said waste solution, and subjecting said waste solution to pyrohydrolysis by spray roasting said solution at a temperature of at least about 600*C and thereby regenerate HCl and form solids containing MgO and Fe203.
6. The process of claim 5, wherein the magnesium content ranges from about 2% to 8%.
Description:
PROCESSING ILMENITE ORE TO TiO- PIGMENT

This invention relates to the production of pigment grade Ti0 2 .

STATE OF THE ART Titanium dioxide is considered the principal white pigment of commerce. It has exceptionally high refractive index, negligible color and is quite inert.

There are two main processes for making raw pigmentary titanium dioxide, the sulfate process and the chloride process. The sulfate process was the first used commercially, starting about 1930 in Europe and in the United States. It is a batch process and nearly 60% of all TiO- produced presently is made by the sulfate process.

Two forms of titanium ores are available. One is the mineral rutile which is comprised of 95% Ti0 2 . The other is ilmenite. Ilmenite (FeOTiO-) is plentiful and is the usual source for TiO- pigment. The ore, following grinding, is concentrated by known methods. Concentrated ilmenite ore generally has a TiO- content of at least about 40%, and generally in the range of about 45% to 65% Ti0 2 . There are two types of ilmenite; a primary or rock ilmenite and secondary or alluvial ilmenite. The latter has often been upgraded in Ti0 2 content by mother nature, as the FeO is leached out. Not all ilmenites are created equal. This is an important finding of the present invention. Some rock ilmenites have part of the FeO replaced by MgO as the ionic radius Fe * * is very similar to Mg ** . In instances where this replacement has occurred, the behavior of ilmenite in an hydrochloric leaching process is different from the ore in which some of the iron has not been replaced by magnesium. Pigment producers have developed several methods for the treatment of ilmenites that do not leach well. One method is to

employ a prereduction step prior to leaching. Another method is to convert the ilmenite into a titania slag which can then be leached.

Present day chloride pigment processing methods which utilize a chlorination pretreatment step have their limitations in that they cannot tolerate magnesium levels greater than 1% by weight.

Primary ilmenites are not generally amenable economically to produce pigment grade Ti0 2 using conventional technologies. As a consequence, ilmenite deposits containing high magnesium (at least 2%) are difficult to process.

The present invention provides a process that can directly convert magnesium-containing ilmenites into pigment, especially those that contain a relatively high amount of magnesium as MgO.

Thus, an improved hydrochloric acid leaching process is provided which enables the production of pigment-grade Ti0 2 directly from primary grade ilmenite containing relatively high amounts of magnesium.

The process depends on the application of a novel combination of operational steps on an intermediate concentrate of ilmenite ore. In producing the concentrate, known benefication steps are employed which involve comminution, classification, gravity separation, magnetic separation, electrostatic separation and drying.

OBJECTS OF THE INVENTION It is an object of the invention to provide a process for producing pigment-grade Ti0 2 from primary ilmenite. Another object of the invention is to provide an improved hydrochloric acid leaching process for treating ilmenite ores having a relatively high amount of magnesium.

These and other objects will more clearly appear when taken in conjunction with the following description and the appended drawings.

IN THE DRAWINGS

Figs 1 to 3 are flow sheets illustrating the various embodiments of the present invention.

DETAILS OF THE INVENTION The feedstock employed in carrying out the invention is a high magnesium primary ilmenite. A typical concentrate is that produced by conventional benefication processes, the concentrate being finely divided and having an average particle size of less than about 100 microns. A typical concentrate of primary ilmenite is given as follows:

TABLE ι

Component

Ti0 2 Fe 2 0 3 cr 2 0 3

V 2 0 5

MnO

Nb 2 0 5 A1 2 0 3

Si0 2 p 2 o 5 Zrθ 2 MgO Caθ

S FeO

As will be noted, the concentrate contains 3.1% of MgO which corresponds to about 1.87% Mg.

Generally speaking, the invention is directed to the treatment of primary ilmenite concentrates containing a relatively high amount of magnesium ranging up to about 10% by weight, e.g. 1 to 10% or 2 to 8%, iron in an amount

of at least about 15% and titanium in an amount of at least about 25%.

Referring to Fig. 1, one embodiment of the invention comprises selectively leaching ilmenite concentrate at stage 1 with hydrochloric acid at a concentration ranging up to about 30% of concentrated hydrochloric acid at a temperature ranging from about 25'C to βO'C while inhibiting Ti0 2 formation by hydrolysis and provide solids containing said titanium and a liquid phase. The solids are separated from the liquid phase at said temperature of about 25"C to 80'C. The titanium-containing solids are then leached at a temperature (stage 2) of about 25"C to 80"C with hydrochloric acid of at least about 18% of concentrated HCl and thereby form a pregnant solution of titanium chloride containing iron and magnesium and form waste solids containing silica.

The waste solids are separated (separation step 2) from said solution at said temperature of about 25'C to 80*C. The solution is then cooled to a low temperature not exceeded about 15"C sufficient to form crystals of FeCl 2 following which the FeCl 2 crystals are separated (separation step 3) from said solution at the aforementioned low temperature, the FeCl- thereafter pryohydrolyzed at 600"C to 1000 * C to provide a pregnant solution containing titanium.

The titanium-containing solution deficient in iron is subjected to hydrolysis at a temperature in excess of about 75*C to form a precipitate of Ti0 2 and a waste solution containing Mg and Fe chlorides and hydrochloric acid. The Ti0 2 precipitate is separated (separation step 4) from the waste solution at a temperature in excess of about 75"C.

The waste solution is then subjected to pyrohydrolysis by spray roasting said solution at a temperature of at least about 600"C and thereby regenerate

HCl and form solids containing MgO and Fe 2 0 3 , the acid being thereafter separated from said solids.

The foregoing is illustrated in Table 2 as follows:

TABLE 2

With respect to the unit operations shown in Fig. 2, a summary of the process illustrated is itemized in Table 3 below:

TABLE 3

As will be noted, a high temperature leach is employed. The Ti0 2 product is produced early in the process at separation step 2.

The example illustrated in Fig. 3 of the drawings is summarized in Table 4 as follows:

TABLE 4

In Table 3, it will be noted that a high temperature leach of 90' to 110"C is employed followed by warm leaching at 25'C to 80 * C.

The titanium hydrolysis is carried out at 90*C to 110"C and continued to solid separation step 5.

As will be clearly apparent, the process of the invention is particularly advantageous in the treatment of ilmenite ores containing relatively high amounts of magnesium.

The novel features described hereinabove permit the following:

1. High magnesium primary ilmenite ores, capable of being processed directly to produce Ti0 2 pigment. The processes are also suitable for processing low magnesium primary ilmenite ores. 2. Primary rock ilmenites capable of being leached with up to 99.5% of the titanium rendered soluble, without the need for preoxidation nor prereduction roasting.

3. Treatment of titaniferous slags, containing both high and low levels of magnesium and silica wherein TiO- pigment is produced in a similar manner as the treatment for primary ilmenite.

4. High and variable levels of silicate forming impurities to be tolerated. This is because all iron, magnesium and titanium ionic species are rendered soluble and thus easily separable from insoluble silica. The separation is effected using conventional solid/liquid separation equipment. 5. Ti0 2 pigment produced from either primary ilmenite or titaniferous slags without constraints on the lower limit of particle size.

6. Very high purity Ti0 2 pigment produced by means of (optional) repulping with hot/cold acid and hot/cold water. This operation results in an elimination of contamination by magnesium and iron. This can be achieved by the addition of metallic aluminum which selectively reduces Fe 3 * to Fe 2 * while not adversely affecting the titanium ion oxidation state.

7. Crystals of FeCl 2 nH 2 0 which are formed on cooling, thus facilitating good separation from the soluble magnesium compounds and the regeneration of 36% HCl to be recycled to the second stage leach.

8. Hydrochloric acid is regenerated and magnesium and iron oxides are recovered by a spray roasting operation on the efflux mixture from the hydrolysis operation. Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.