CA2171185A1

CA2171185A1 - Upgrading titaniferous materials

Info

Publication number: CA2171185A1
Application number: CA002171185A
Authority: CA
Inventors: Ross Alexander Mcclelland; Michael John Hollitt
Original assignee: Individual
Current assignee: Technological Resources Pty Ltd
Priority date: 1993-09-07
Filing date: 1994-09-07
Publication date: 1995-03-16
Also published as: NO960917D0; WO1995007366A1; JPH09504828A; CN1042349C; NO317932B1; EP0717783A4; NO960917L; ZA946864B; EP0717783A1; CN1134730A

Abstract

A process for upgrading a titaniferous material by removal of impurities from the titaniferous material is disclosed. The process comprises alternate leaching of the titaniferous material in a caustic leach and a pressure sulphuric acid leach.

Description

~PGRADING TITANIFEROlJS M~'l'RRT~T.. ~

This invention relates to the removal of impurities from naturally occurring and synthetic titaniferous materials.
The invention is ~articularly ~uited to the en~ncement of titaniferous materials used in the ~roduction of titanium metal and titanium dioxide pigments by means of indu~trial chlorination systems.

15 Embo~;m~ntg of the pre~ent invention have the common features of the use of caustic le~ch;ng and ~re~sure sulphuric acid l~ch;ng for the upgrading of titaniferous materials, e.g.
titaniferous slags, derived from hard rock ilmenite~.
Additional steps may be employed as will be described below.
In industrial chlorination processes titanium dioxide bearing feedstocks are fed with coke to chlorinators of various designs (fluidised bed, shaft, molten salt), operated to a ~o~;~lm temperature in the range 700 - 1200C. The most 25 C~ 'n type of industrial chlorinator is of the fluidi~ed bed de ign. Gaseous chlorine is passed through the titania and carbon bearing charge, converting titanium dioxide to titanium tetrachloride gas, which is then removed in the exit gas stream and con~enced to liquid titanium tetrachloride for further purification and processing.

The chlorination process as conducted in industrial chlorinators is well suited to the conversion of pure titanium dioxide feedstocks to titanium tetrachloride.
~owever, most other inputs (i.e. impurities in feedstocks) cause difficulties which ~reatly complicate either the chlorination process itself or the subsequent stages of S~ lUl~SHEET ~R~e ~) -- 2 1 7 1 1 8 5 PCT/AUg4mOS28 W095/07366 ~

co~n~ation and purification and dis~osal of waste. The attached table ~ro~ides an indication of the types of problems encountered. In addition, each unit of inputs which does not enter ~roducts contributes substantially to the generation of wastes for treatment and disposal. Some inputs (e.g. particular metal~, radioacti~es) result in waste cla sifications which may require s~ecialist disposal in monitored re~ositories.

Preferred inputs to chlorination are therefore hi~h ~rade materials, with the mineral rutile (at 95-96% Tio2) the most ~uitable of ~re~ent feeds. Shortages of rutile ha~e led to the de~elopment of other feed~tocks formed by upgrading naturally occurring ilmenite (at 40-60% Tio2), such as titaniferous slag (a~roximately 86% Tio2) and synthetic rutile (variouQly 92-95% Tio2). The~e upgrading processes ha~e had iron le~oval as a primary focus, but have extended to removal of magnesium, mangane~e and alkali earth im~urities, as well as ~ome aluminium.

~U~lllUl~ SHEET ~e 21 7 l l 85 PCT/AU9~/00528 Blemental Chlorination Cond~n~ation Purification Input Fe, Mn C o n R u m e sSolid/liquid chlorine, c h l o r i de 8 c o k e ,f o u increasesductwork, gas volumes make sludges Alk:~l; lic Def luidise a l k a l i fluid beds e a r t h d u e t o metals l i ~ u i d chlorides, c o n 8 ume chlorine, coke Al ConsumesC a u 8 e g C a u g e s chlorine, corrosion corrosion, makes coke sludges Si Ac.;l 1 Ates Can May reguire i nencourage distillation chlorinator, d u c t from product r e d u c i n gb 1 o c k a g e .
c a m p a i g nC~n~n~es in life. part with Consumes t i t a n i u m c o k e , tetrachloride chlorine V Must be L. ~ved, by chemical treatment and distillation Th, Ra AC cumul at e s i n chlorinator brickwork, radioac t ive;
c a u g e g d i g p o 8 a 1 dif ficulties In the prior art synthetic rutile has been formed from titaniferous minerals, e.g. ilmenite, via various techniques . According to the most commonl y al?~lied technique, as variously operated in Western Australia, the 5 titaniferous mineral is reduced with coal or char in a rotary kiln, at temperatures in excess of 1100C. In this process the iron content of the mineral i8 gubgtantially ~U~ Ul~ SHEET (Rule 26) W095/~7366 2 ~ 7 1 1 8~ ~CT1~94/0~528 ~

metallised. Sulphur additions are also made to convert manganese impurities partially to sulphiaes. Following reduction the metallised product is cooled, separated from associated char, and then subjected to a~ueous aeration for removal of virtually all cont~; n~ metallic iron as a separable fine iron oxide. The titaniferous product of separation is treated with 2-5% aqueous sulphuric acid for dissolution of manganese and some residual iron. There is no substan~ial chemical c~oval of alkali metals or alkaline earths, aluminium, silicon, vanadium or radionuclides in this process as disclosed or operated.
Further, iron and manganese removal is incomplete.

Recent disclosurec have provided a process which operates reduction at lower temperature~ and provides for hydrochloric acid l~ch; n~ after the aqueous aeration and iron oxide separation step~. According to these disclosures the proce~ is effective in ~o-ving iron, manganese, alkali and alkaline earth impurities, a substantial proportion of aluminium inputs and some ~anadium as well as thorium. The process may be o~erated as a retrofit on existing kiln based installations. However, the process is ineffective in full vanadium removal and has little chemical impact on silicon.
In another prior art invention relatively high de~rees of ~ - ~val of magnesium, man~anese, iron and aluminium have been achieved. In one such proces~ ilmenite is first therm~lly reduced to substantially com~lete reduction of its ferric oxide content (i.e. without substantial metallisation), norm~lly in a rotary kiln. The cooled, reduced product is then leached under 35 psi pressure at 1~0-150C with excess 20% hydrochloric acid for remo~al of iron, ma~nesium, aluminium and manganese. The leach liquors are spray roasted for re~eneration of hydroqen chloride, which is recirculated to the leachin~ ste~.

~U~Slllul~ SHEET ~e26) -2 1 7 1 1 8 5 PCT/AUs~/00~28 In other ~rocesse~ the ilmenite undergoes grain refinement by therm~l oxidation followed by therr~l reduction (either in a fluidised bed or a rotary kiln). The cooled, reduced product is then subjected to atmospheric leAch;n~ with exce~s 20% hydrochloric acid, for ~ e~G~al of the deleterious impuritie~. Acid regeneration is also performed by spray roa~ting in this ~rocess.

In all of the above mentioned hydrochloric acid leaching based proces~es impurity removal i~ ~imilar. Vanadium, aluminium and ~ilicon le a~al i8 not fully effective.

In yet another ~roces~ ilmenite i~ thermally reduced (wil:hout metallisation) with carbon in a rotary kiln, followed by cooling in a non-oxidising atmosphere. The coo:Led, reduced ~roduct is le~che~ under 20 - 30 p~i gauge ~re~ure at 130C with 10 - 60% (typically 18 - 25%) sul~huric acid, in the ~resence of a ~eed material which ass:ists hydrolysis of dissolved titania, and consequently ass:ists l~ch;ng of im~urities. Hydrochloric acid usage in place of ~ulphuric acid ha~ been claimed for this process.
~nder such circumstances similar impurity removal to that achieved with other hydrochloric acid based systems is to be expected. Where ~ulphuric acid i8 used radioactivity removal will not be com~lete.

A co~ly adopted method for upgradin~ of ilmenite to higher grade productA is to smelt ilmenite at temperatures in excess of 1500C with coke addition in an electric furnace, producing a molten titaniferous slag (for casting and cru~h; ng) and a pig iron product. Of the problem impuritie~ only iron is removed in this manner, and then only ;nco~letely as a result of compo~itional limitation~
of t:he proces~.
In another proces~ titaniferous ore i~ roa~ted with alkali metal compounds, followed by leaching with a ~trong acid SUB~ Ul~SHEET ~e26) : : ~ 1 7 1 1 8 5 PCT/AU91/~0528 W095/07366 ~

other than sulphuric acid (Au~tralian Patent No. A~-B-70976/87). According to this aisclo~ure substantial removal of various impurities is achieved, with ~ub~Anti~7~ defined to mean greater than 10%. In the context of the present invention such poor l~o~al of impurities, especially of thorium and uranium, would not re~resent an effective process. No ~pecific ~hase structure after roasting is indicated for this process but it is evident from analytical re~ults provided (where product analyses, unlike feed analyses do not sum to 100%
and analyses for the alkali metal added are not given) that there may have been significant retention of the additi~e in the final product. ~nder the condition given it is herein disclosed that it is to be expected that alkali ferric titanate com~ounds which are not Am~n~hle to subsequent acid l~ch;ng will form. The consequent retention of alkali will render the final product unsuitable as a feedstock for the chloride ~igment proces~.

In yet another ~rocess a titaniferous ore is treated by alternate leaching with an agueous solution of alkali metal com~ound and an aqueous solution of a non-sul~huric mineral acid (~S Patent No. 5,085,837). The process is specifically limited to ores and concentrates and does not contemplate prior processing aimed at artificially altering phase structures. Consequently the ~rocess requires the applica~ion of excessive reagent and harsh processing conditions to be even partially effective and i~ unlikely to be economically im~lemented to produce a feedstock for the chloride ~igment ~rocess.

A wide range of ~otential feedstocks is available for upgrading to high titania content materials suited to chlorination. Examples of primary titania ~ources which cannot be satisfactorily upgraded by prior art processes for the ~urposes of ~roduction of a material suited to chlorination include hard rock (non detrital) ilmenites, SUB~lllUl~SHEET ~e26) W095/07366 ~ 2 1 7 1 1 a 5 PCT/AU94/00528 ~iliceous leucoY~n~, many ~rimary (unweathered) ilmenites and large anatase resources. Many such secondary sources (e.g. titania bearing slags) also exist.

5 In particular, for titaniferous materials cont~;n;ng J elevated levels of silica, alumina and ~gn~ia, such as titaniferous slags derivea from hard rock ilmenite sources, none of the previously aisclosed upgrading methods is eff0ctive for the ~roduction of a feedstock for the 10 co_~ercial chloride pigment processing route. The combination of silica which cannot be removed ~conomically by the ~reviously identified techniques and alu_ina and magnesia which together as~ist in the formation during ~h~r~- 1 ~roce~sing of ~seudobrookite - anosovite ty~e 15 ~hages which are not amenable to leachin~ with hydrochloric acid under commercially realistic conditions limits the u e of such materials to sul~hate ~igment process feedstocks.
Since the ~igment ~rocess expected to su~ly all growth in pigment ~ n~ is the chloride ~rocess such a limitation is 20 a severe con~traint.

A lar~e ~ortion of the world~s identified titania reserves i~ in the form of hard rock ilmenites.

25 Clearly there is a considerable incentive to discover methods for u~grading of such titaniferou~ materials which can economically ~roduce high grade products which are suitable as feeastocks to the chloride pi~ment process.

30 The ~resent invention ~rovides a combination of processing teps which may be incor~orated into more general ~rocesses for the upgraaing of titaniferous materials, rendering such proc~esses ap~licable to the treatment of a wider range of feed$ and producin~ higher quality products than would 35 otherwise be achievable.

Accordingly, the ~resent invention ~roviaes a ~rocess for SUB~ Ul~sHEET ~e ~) W095/07366 - 2 1 7 ~ 1 8 5 PCT/AU9~/00528 ~

u~grading a titaniferou~ material by removal of impurities, which proce~s involves alternately le~ch;n~ of the material in a caustic leach and a pressure sul~huric acid leach.

In a particular embo~;m~nt the ~resent invention ensures that caustic leAch; ng can be conducted economically and effectively des~ite the need for the use of exces~ caustic in the leach by circulation of caustic leach liquor~ after ~olid/liquid se~aration through a caustic regeneration step using lime addition to ~reci~itate complex aluminosilicates and regenerate caustic solution. The complex aluminosilicate~ are then separated ~rom the regenerated caustic solution which is recycled to the leach.

The treatment of titaniferous material~ cont~;n;ng both all ; n~ and silica in such a manner has not previously been disclo~ed, and it is herein revealed that only under s~ecific operating conditions can such a ~roce~s be operated without precipitation of com~lex aluminosilicates in the cau~tic leach.

It has been surprisingly discovered that by limiting the concentrations of ilica, alumina, titania and other impuritie~ in caustic leach liquor, i.e. by leACh; ng at low slurry densities and recirculating leach liquors through caustic re~eneration, the complex aluminosilicates otherwi3e formed in the caustic leach can frequently be avoided.

It ha~ also been surprisingly discovered that complex aluminosilicates formed in the caustic leach csn actually be le~o-ved in the subsequent acid leach along with other impurities. This is a ~articularly surprising outcome as under most circum~tances silica in titaniferous materials cannot be le~oved by acid le~ch;ng.

Consequently, in a further embodiment it is possible to SUB~ u l ~. SBET (Rule 26) . 2 1 7 l 1 ~ 5 PCT/AUs~/00~28 Woss/o7366 operate a simple process invol~ing a two stage treatment in which complex aluminosilicates are formed in a first stage and consumed by acid l~ch;ng in a second stage, wherein silica remo~al is achieved in the acid l~ch;ng stage along with the other benefits of acid l~h;nq in more general upgrading.

In ~articular it is re~ealed that the ease of formation in caustic leaching and ~o-val in acid l~ch;ng of complex aluminosilicates depends on the caustic to silica ratio in the leach liquor (which determines whether the aluminosilicates are of the sodalite type or in another form), with high caustic to silica ratios allowing greater ease of removal. Thus, the circulation of caustic leach liquors through a caustic leach and caustic regeneration by lime (which keeps the caustic to silica ratio high) folLowed by pressure sulphuric acid le~c~; n~ is under many circumstance~ a most effective means of u~rading titaniferous materials, especially titaniferous materials deri~ed from hard rock ilmenite.

It has been discovered that the process of the in~ention can ~-ove iron, magnesium, aluminium, silicon, calcium, magnesium, manganese, phosphorus, chromium and ~anadium, which impurities form an almost comprehenQi~e list of im~urities in hard rock ilmenite sources of titania.

Additional ste~s may be incorporated in the process, as desired. For example:
(1) The titaniferous material may be roasted in any suitable de~ice and to any temperature under reducinq or oxidising conditions prior to le~rh; ng, Such roasting may be conducted in order to ~nh~nce the response of the material to the leachinq steps or to reduce the production of sulphur dioxide in the leach by oxidation of any SUB~ ul~-SBET ~e ~) W095/07366 - PCT/AU9~/00528 tri~alent titania in the titaniferou~ material.

(2) Additi~es may be made to the titaniferous material prior to such a roasting step in order to ~nh~nce the response of the material to the leAch;ng steps, or for any other purpose.

(3) The titaniferous material may be preground prior to roasting or le~ch;ng in order to ~nh~nce reaction rates or in ~reparation for agglomeration steps which are improved by generation of a broad particle ~ize distribution in the material to be agglomerated.

15 (4) An agglomeration step via which additi~es are incorporated into the titaniferous material prior to roasting may be operated.

(5) Physical separation of material (e.g. maqnetic se~aration of final product in order to ~electively e~e and recycle iron rich material) for further upgrading.

(6) ~he final titaniferous ~roduct may be agglomerated by any suitable technique to produce a size consist which is suitable to the market for synthetic rutile. After agglomeration the product may be fired at temperatures sufficient to ~roduce sintered bonds, thereby removing from dusting losses in fluidised bed chlorinators.

(7) Irrespective of final product agglomeration the final product may be calcined in order to remo~e ~olatile matter (e.g. water, sulphur dioxide and sulphur trioxide).

(8) A caustic solution bleed or caustic solution S~SlllUl~sHEET ~e26) 2 1 7 1 ~ ~ 5 PCT/AU94/00528 _ W095/07366 eva~oration step (for wash water removal) may be operated.

(9) The sulphuric acid leach exit liquor may be neutralised to produce solid sulphates and hydroxides for dis~osal.

(10~ The sul~huric acid leach exit liquor may be treated for regeneration of sul~huric acid from the aqueous sulphate solutions formed in the process.

(11) Other leach steps, filtration steps and w~qhing steps may be incorporated into the process as desired. For example, a hydrochloric acid leach may; be conducted to assist in the ~oval of trace levels of radioactivity. Pressure filtration of the com~lex aluminosilicate precipitated in caustic recovery may be operated to assist solid/liquid se~aration.

(12) Flocculants and other aias may be used to assist solid/li~uid separation.

ExamPles The following examples describe a nnmher of laboratory testa which serve to illustrate the t~hn;~ues described herein.

Example 1 This exam~le i to ~rm~natrate the ineffectiveness of trea~ments found to be effective for upgradin~ other titaniferous materials on materials such as titaniferous ~lag~ produced from hard rock ilmenites.
Comme~cial titaniferous slag having the composition indicated in Table 1 was subjected to oxidation roasting in air at 750C for 30 minutes, followed by reduction roasting SUB~lllUl~sHEET ~e ~) W095/07366 2 ~ 7 1 1 8 5 PCT/AU9~100528 ~

in a 1:3 hydrogen to carbon dioxide (volumetric basis) gas mixture at 680C for one hour. The cooled product of this therm~l treatment cont~;ne~ no ferric iron and no trivalent titania. The phase composition of the material was indicated by X-ray diffraction as pseudobrookite.

The ~h~rm~l ly treated material was leArhe~ in refluxing 10%
caustic soda solution at 10% slurry density. After filtration and wA~hing the solid residue had a composition as indicated in Table 2.

It is clear that caustic leach had no appreciable effect on the silica or alumina contents of the material.

The re idue of the caustic leach was subjected to a leach with refluxing 20% hydrochloric acid at 30% slurry density for 6 hours. After filtration and w~h;ng the solid residue had the com~osition which is also indicated in Table 2.
Clearly a roast/leach process using 10% caustic soda at 10%
slurry density and 20% hydrochloric acid at 30% slurry density as leAch~nts is almost totally ineffective in upgrading the slag.
Exam~le 2 The treatment indicated in ~xample 1 was re~eated with the exception that the caustic leach was con~cted under pressure at 165C.
The compositions of the caustic and acid leached products are indicated in Table 3. It i clear that the caustic leach had no appreciable effect on the silica or alumina contents of the material. The acid leach, however, despite being largely ineffective in producing an upgrade which might be suitable for the chloride pigment proces~ did have a substantial effect on the silica and alumina contents.

~U~S'lll'U'l'~. SHEET (Rule 26) ~ W095/07366 = ~ 2 ~ 7 1 ~ 8 5 PCT/AUs~/00528 There was no such effect on a sample of slag submitted directly to hydrochloric acid leaching.

Clearly the ~ressure caustic leach had altered the state of the silica to allow its subsequent ~o~dl in hydrochloric acid le~chi ng but had not resulted in direct removal.
Investigations revealed the proauction of a complex aluminosilicate precipitate in the caustic leach. The caustic leach had been conducted under conditions in which silica could be leAche~ but was not soluble.

The re~ults of thi~ example combined with the result~ of subsequent examples in which effective caustic l~A~h;n~ is demonstrated illustrate the dep~n~ence of the removal of ~ilica and alumina in caustic l~ch;ng on the leach conditions.

Example 3 A sample of the slag whose composition is indicated in Table 1 was mixed with 2% borax, formed into pellet~ and ~ubjected to reduction roasting in a 19:1 hydrogen to carbon dioxide (volumetric basis) gas mixture at 1000C for 2 hours. The phase composition of the cooled product of this thermal treatment wa3 indicated by X-ray diffraction a~ ~seudobrookite.

A sample of the thermally treated material was l~che~ in refluxing 10% caustic soda solution at 5% slurry density.
After filtration and w~h;n~ the solid residue had a composition as indicated in Table 4. It is clear that the caustic leach was highly effective in the le~o~al of ~ilica, despite the much poorer performance of a leach conducted at 10% slurry den~ity in Example 1, in which complex aluminosilicates were formed.
The residue of the caustic leach was ~ubjected to a pressure leach at 150C with 20% sulphuric acid at 5%

S~SlllUlhSHEET ~e26) W095/07366 - 2 ~ 7 1 I 8 5 PCT/AU9~mOS28 ~

slurry density for 6 hours. After filtration and wA~hing the ~olid residue had the composition which i~ al~o indicated in Table 4.

Clearly the combined effects of a low slurry density caustic leach and a subsequent pressure sulphuric acid leach (which is ca~able of decomposing ~seudobrookite) were to substantially upgrade the slag to a very high grade product which is suitable in composition a~ a chloride pi~ment proce~ feedstock.

The leach liquor from the above caustic leach was ~re~erved and after analysis was treated with microni~ed lime at the weight ratio of 1.3 units of lime per unit of dissolved silica. The resulting complex aluminosilicate ~recipitate and any exce3s lime were removed by filtration and the "re~enerated~l caustic solution was preser~ed for reuse in leaching.

A further sample of the th~ -lly treated material was l~ch~ with the regenerated cau~tic solution under the same conditions as indicated above. There was no difference of any consequence between the re~ults of the leach with fresh caustic and the results of the leach with re~enerated caustic.

Example 4 Thi3 example i~ to demonstrate the ineffecti~eness of acid leaching alone in the e~val o~ silica from titaniferous materials such as titaniferous slags produced from hard rock ilmenite~.

Co cercial titaniferous slag having the composition shown in Table 1 was subiected to roasting for two hours in an atmosphere of 1:19 (volumetric basi~) of hydrogen to carbon dioxide at 1000C. After cooling in the roaating atmos~here the roasted slag wa~ pressure leAch~ at 135C

SU~lllUl~SHEET ~e26) ~ W095/07366 2 1 7 1 1 8~ PCT/AUs~/00528 in 20% sul~huric acid at 25% w/w slurry density for six hours.

- The composition of the leach resiaue is given in Table 5.
Such direct acid leach treatment of a roasted titaniferous material may be antici~ated to result in little im~rovement of ~roduct quality by l~ch;ng~ and no removal of SiO2.

Example 5 A nample of slag to which no addition of additive had been made and which was not ~ubjected to any thermal treatment was treated by the same leaching steps as indicated in Example 3.

The composition of the final ~roduct was as recorded in Table 6. Substantial 1.- ~,-val of impuritie~ have been achieved without thermal treatment.

S~SlllUl~ SHEET ~e26) 2 1 7 1 1 8 5 PCT/AU9~/00528 Table 1: Com~o~ition of Titaniferou~ Sla~

~sed In Example 1 - 4 wt~
Tioa 78.9 FeO 8.94 ~gO 4.73 MnO 0.25 Cr2O3 0.16 V2Os 0.56 Al2O3 3.14 SiO2 2.71 Zr2 0.05 CaO 0.42 Table 2: Composition of Products in Exam~le 1 wt% Caustic T~eAch Acid T~e~ch Tio2 78.6 80.8 FeO 9.22 7.4 MgO 4.71 4.69 MhO 0.24 0.23 Cr2O3 0.16 0.16 V2O5 0.59 0 59 Al2O3 3 09 3.06 SiO2 2.94 2.86 ZrO2 0.05 0.04 CaO 0.37 0.16 SUB~lllul~. SHEET (l~ule Z6) W095l07366 2 1 7 1 ~ 8 5 PCT/AU9~/00528 Tab:Le 3: Com~osition of Proaucts in Example 2 wt% Cau~tic Leach Acia T-e~Ch Tio2 78.4 82.7 FeO 9.13 7.66 MgO 4.76 4.81 MnO 0.25 0.23 Cr2O3 0.16 0.16 V25 0.58 0.60 A12O3 3.08 2.73 sio2 3.13 0.96 ZrO2 0.05 0.04 CaO 0.40 0.13 Table 4: Compo~ition of Proaucts in Example 3 wt% caustic T-~ch Acia T-~Ch Tio2 81.3 97.9 FeO 9.56 0.89 ~gO 4.96 0.44 MnO 0.27 0.02 Cr2O3 0.20 0.12 V2Os 0.57 0.12 A12O3 1.75 0.23 SiO2 0.73 0.09 zrO2 0.05 0.06 CaO 0.45 0.003 SUBST~I~ESHEET ~e ~) W095/07366 ~ 2 1 7 1 1 8 5 PCT/AU9l/00528 ~

Table 5: Composition of Product in Exam~le 4 wt% Acid Leach Tio2 84.93 FeO 6.09 MgO 2.92 MnO 0.16 Cr2O3 0.16 V2O5 0.60 Al2O3 1.33 / sio2 3.15 Zr2 0.06 CaO 0.03 Table 6: Composition of Product in Example 5.

wt% Acid T-e~ch Tio2 92.1 FeO 2.98 ~ 1.21 MnO 0.08 Cr2O3 0.16 V2O5 0.18 Al23 0.60 sio2 0.71 Zr2 0.06 Cao o-003 S~ l u l ~. S~ET (Rule 26)

Claims

CLAIMS:

1. A process for upgrading a titaniferous material by removal of impurities from the titaniferous material, which process comprises: alternately leaching of the material in a caustic leach and a pressure sulphuric acid leach, and controlling the conditions of the caustic leach to precipitate complex aluminosilicates in a controlled and desired manner.

2. A process for upgrading a titaniferous material by removal of impurities from the titaniferous material, which process comprises: alternately leaching of the material in a caustic leach and a pressure sulphuric acid leach, carrying out the caustic leach under condition of low slurry density to avoid precipitation of complex aluminosilicates, and separating the leach residue from the caustic leach liquor and regenerating the caustic leach liquor by precipitating complex aluminosilicates.

3. The process defined in claim 1 or claim 2, wherein the caustic leach is carried out before the acid leach.

4. The process defined in claim 1 or claim 2, wherein the acid leach is carried out before the caustic leach.

5. The process defined in any one of the preceding claims, wherein the acid leach is carried out at a temperature of at least 100°C.

6. The process defined in claim 5, wherein the acid leach is carried out at a temperature of at least 135°C.

7. The process defined in claim 2, wherein the slurry density is less than 10%.

8. The process defined in claim 2 or claim 7, which further comprises separating the regenerated caustic leach liquor from the precipitated complex aluminosilicates and recycling the regenerated leach liquor to the caustic leach.

9. The process defined in any one of the preceding claims, wherein the titaniferous material comprises a titaniferous slag derived from hard rock ilmenites.

10. A process for upgrading a titaniferous material derived from hard rock ilmenites by removal of impurities from the material, which process comprises:

(a) leaching the material in a caustic leach under conditions selected to precipitate complex aluminosilicates;

(b) separating the caustic leach residue from the caustic leach liquor; and (c) leaching the caustic leach residue from step (b) in a pressure sulphuric acid leach to remove the complex aluminosilicates and other impurities to form the upgraded material.

11. A process for upgrading a titaniferous material derived from hard rock ilmenites by removal of impurities from the material, which process comprises:

(a) leaching the material in a caustic leach;

(b) separating the caustic leach residue from the caustic leach liquor;

(c) leaching the caustic leach residue from step (b) in a pressure sulphuric acid leach to remove the complex aluminosilicates and other impurities to form the upgraded material;

(d) regenerating the caustic leach liquor from step (b) by precipitating complex aluminosilicates to form a regenerated caustic leach liquor suited to the effectiveness of steps (a) and (c); and (e) recycling the regenerated caustic leach liquor to step (a).