AGGLOMERATION OF FINES OF TITANIUM BEARING MATERIALS

Abstract

A micro-agglomerate of fines of a material that is predominantly titanium dioxide in which the fines are bound in the micro-agglomerate by a polysaccharide gum or cellulose derivative and in which the micro-agglomerate has been heated in the temperature range 250-600 C. so that the polysaccharide gum or cellulose derivative is an effective primary binder of the fines when the micro-agglomerate is subjected to high temperature gas flow conditions equivalent to those in the Chloride Process. Also disclosed is a method of agglomerating fines of a material that is predominantly titanium dioxide.

Claims

1. A micro-agglomerate of fines of a material that is predominantly titanium dioxide in which the fines are bound in the micro-agglomerate by a polysaccharide gum or cellulose derivative and in which the micro-agglomerate has been heated in the temperature range 250-600 C. so that the polysaccharide gum or cellulose derivative is an effective primary binder of the fines when the micro-agglomerate is subjected to high temperature gas flow conditions equivalent to those in the Chloride Process.

2.-3. (canceled)

4. The micro-agglomerate according to claim 1 in which each fines particle is bound to at least two other fines particles by a web of the polysaccharide gum or cellulose derivative whereby the polysaccharide gum or cellulose derivative forms a network of webbing firmly binding the particles in the micro-agglomerate.

5. The micro-agglomerate according to claim 1 wherein the webs have a respective longitudinally central region of a minimum thickness substantially smaller than the size of the respective bound fines particles, and wherein the longitudinally central region is of a minimum thickness in the range 0.1-10 m.

6.-9. (canceled)

10. The micro-agglomerate according to claim 1 wherein the micro-agglomerate is of a size between 125 and 5,000 m; and/or wherein the fines bound in the micro-agglomerates are of a size in the range 10-250 m; and/or wherein the proportion of polysaccharide gum or cellulose derivative is in the range 2-10% with respect to the combined weight of the fines and polysaccharide gum or cellulose derivative.

11.-13. (canceled)

14. The micro-agglomerate according to claim 1 wherein the fines comprise rutile or synthetic rutile.

15. A method of agglomerating fines of a material that is predominantly titanium dioxide, comprising: forming the fines into micro-agglomerates in which the fines are bound in the micro-agglomerates by a polysaccharide gum or cellulose derivative, and heating the micro-agglomerates in the temperature range 250-600 C. so that the polysaccharide gum or cellulose derivative is an effective primary binder of the fines when the micro-agglomerate is subjected to high temperature gas flow conditions equivalent to those in the Chloride Process.

16. The method according to claim 15 wherein said heating of the micro-agglomerates is in the temperature range 275-350 C. and/or the heating of the micro-agglomerates in the temperature range is for 0.1 to 2 hours.

17. (canceled)

18. The method according to claim 16, wherein, in each formed micro-agglomerate, each fines particle is bound to at least two other fines particles by a web of the polysaccharide gum or cellulose derivative whereby the polysaccharide gum or cellulose derivative forms a network of webbing firmly binding the particles in the micro-agglomerate.

19. The method according to claim 15 wherein the webs have a respective longitudinally central region of a minimum thickness substantially smaller than the size of the respective bound fines particles, wherein the longitudinally central region is of a minimum thickness in the range 0.1-10 m.

20.-22. (canceled)

23. The method according to claim 15 wherein the forming step is effected prior to or simultaneously with said heating in a continuous high shear mixer that combines mixing with agglomeration in a single unit.

24. The method according to claim 15 wherein the micro-agglomerates formed are of a size between 125 and 5,000 m; and/or wherein the fines particles bound in the micro-agglomerates are of a size in the range 10-250 m; and/or wherein the proportion of polysaccharide gum or cellulose derivative is in the range 2-10% with respect to the combined weight of the fines and polysaccharide gum or cellulose derivative.

25.-26. (canceled)

27. A micro-agglomerate of fines of a material that is predominantly titanium dioxide in which the fines are bound in the micro-agglomerate by webs that comprise a polysaccharide gum or a cellulose derivative, the webs having a respective longitudinally central region of a minimum thickness substantially smaller than the size of the respective bound fines particles.

28. (canceled)

29. The micro-agglomerate according to claim 27 in which each fines particle is bound to at least two other fines particles by a web of the polysaccharide gum or cellulose derivative whereby the polysaccharide gum or cellulose derivative forms a network of webbing firmly binding the particles in the micro-agglomerate.

30. The micro-agglomerate according to claim 27, wherein the longitudinally central region is of a minimum thickness in the range 0.1-10 m.

31.-34. (canceled)

35. The micro-agglomerate according to claim 27 wherein the fines comprise rutile or synthetic rutile.

36. A method of agglomerating fines of a material that is predominantly titanium dioxide, comprising forming the fines into micro-agglomerates in which the fines are bound by webs of a polysaccharide gum or a cellulose derivative, the webs having a respective longitudinally central region of a minimum thickness substantially smaller than the size of the respective bound fines particles.

37. (canceled)

38. The method according to claim 36 wherein, in each formed micro-agglomerate, each fines particle is bound to at least two other fines particles by a web of the polysaccharide gum or cellulose derivative whereby the polysaccharide gum or cellulose derivative forms a network of webbing firmly binding the particles in the micro-agglomerate.

39. The method according to claim 36, wherein the longitudinally central region is of a minimum thickness in the range 0.1-10 m.

40.-41. (canceled)

42. The method according to claim 36 wherein the forming step is effected prior to or simultaneously with said heating in a continuous high shear mixer that combines mixing with agglomeration in a single unit.

43. The method according to claim 36 wherein the fines comprise rutile or synthetic rutile.

44. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIGS. 1 and 2 are representative scanning electron microscope (SEM) images of portions of a synthetic rutile micro-agglomerate formed according to the procedure in Example 1, in which the binder is CMC, viewed prior to any thermal shock test as described herein, involving sudden heating to 1000 C. to simulate the chlorination process where ambient temperature feed is introduced into a chlorinator operating at 900-1000 C.;

[0048] FIGS. 3 and 4 are representative scanning electron microscope (SEM) images of portions of a synthetic rutile micro-agglomerate formed according to the procedure in Example 1 in which the binder is CMC, viewed after a thermal shock test as described herein and immediately above;

[0049] FIG. 5 is a graphical representation of the particle size distribution (PSD) for a number of micro-agglomerate samples formed according to the procedure in Example 2, and for the original synthetic rutile fines from which they were formed;

[0050] FIG. 6 is a graphical representation of the particle size distribution (PSD) for the same samples as for FIG. 5 but after thermal shock testing of the samples;

[0051] FIGS. 7 to 9 are respective pairs of SEM images of portions of the dry and heated micro-agglomerates formed according to the procedure in Example 2 for the binders xanthan gum, high viscosity PAC (PAC-PV) and CMC respectively;

[0052] FIG. 10 is a graphical representation of the particle size distribution (PSD) for a number of micro-agglomerate samples formed according to the procedure in Example 3, and for the original synthetic rutile fines from which they were formed;

[0053] FIG. 11 is a graphical representation of the particle size distribution (PSD) for the same samples as for FIG. 10 but after thermal shock testing of the samples;

[0054] FIGS. 12 to 14 are respective pairs of SEM images of portions of the dry and heated micro-agglomerates formed according to the procedure in Example 3 for the binders xanthan gum, high viscosity PAC (PAC-PV) and CMC respectively;

[0055] FIG. 15 is a set of SEM images corresponding to FIG. 14, i.e. for CMC binder, but with a higher loading of binder; and

[0056] FIG. 16 is an SEM image of a micro-agglomerate after heating at 300 C., one of the samples tested in Example 4.

EXAMPLE 1

[0057] Synthetic rutile fines (125 m) were formed into micro-agglomerates, i.e. pelletised, employing small circular, flat top and bottom, plastic moulds with sloping slides to facilitate removal of the pellets. The resulting pellets had the approximate dimensions 8 mm deep, maximum diameter 17 mm, minimum diameter 15 mm. The mean weight of dried pellets was 2.6 g0.2 g.

[0058] A variety of binders were tested. The method of mixing depended on the type of binder being used. In the case of powder binders, the required amount of powder was first thoroughly mixed with 100 g synthetic rutile (SR) fines in a small plastic mixing bowl. Water (30 g) was then added to this mixture whilst stirring. The final mixture was adjusted, if necessary, by adding water in incremental amounts until the mixture was judged to have the required consistency to form satisfactory pellets. Typically, additional water was in the range of 1-2 g per 100 g SR fines and was only required when forming pellets with 4 to 8% binder.

[0059] In the case of liquid binders, the required amount was weighed into the clean mixing bowl, sufficient water added to bring the total amount of water plus binder to 30 g and then the SR fines (100 g) added with continuous mixing. It was found that adding 30 g water plus the liquid binder invariably resulted in mixtures that were too wet to form satisfactory pellets.

[0060] Even if the amount of water in the liquid binders was calculated such that the total amount of water added was 30 g per 100 g fines the mixture was generally too wet. In several instances, especially at higher binder loadings, the amount of water had to be reduced to well below the calculated amount required in order to obtain satisfactory pellets.

[0061] The pellets were formed by scooping up sufficient of the blended material to overfill the mould and then the material was compressed into the mould using a metal spatula. Excess material was scraped off the mould using the edge of the spatula and the pellet discharged from the mould with a sharp tap.

[0062] Ease of discharge from the mould was partly a function of the binder. Some binders made the pellets very easy and clean to discharge, others caused difficulty with the material not discharging easily or breaking in the mould. As a general rule pellets with good green strength were easier to work with than those with little or no green strength.

[0063] Pellets were placed in aluminium foil trays and oven dried at 110 C. for 1 hour. After removing from the oven, the pellets were allowed to cool and left for a minimum of 2 hours before being tested. Dry strength was monitored over a period of 7 to 10 days after the initial testing for any changes to dry strength.

[0064] Green strength and dry strength were assessed using a drop test. Green strength is useful for minimising breakage during agglomeration and subsequent conveying to the drier, while an adequate dry strength ensures resistance to breakage during conveying, storage and shipping. The method consisted of dropping ten pellets from a height of 50 cm onto a steel plate. The number of pellets surviving the drop was recorded and the surviving pellets dropped again. The number of pellets surviving the second drop was recorded and the process repeated for a third time.

[0065] Pellets used in the green strength test were discarded.

[0066] Crush strength, also significant for resistance to breakage during storage and shipping, could not be measured accurately. A qualitative scale was adopted as follows:

[0067] 0 No strengthpellets disintegrate with little or no applied force

[0068] 1 Very poorpellets easily crushed by hand

[0069] 2 Pellets can be crushed by hand with some difficulty

[0070] 3 Pellets cannot be crushed by hand

[0071] The reporting of the crush strength, particularly the distinction between 1 and 2 was somewhat arbitrary. It was intended as a guide to the relative performance of the different binders after drying. The significance of crush strength is mainly in relation to stockpiling of micro-agglomerates.

Results

[0072] Xanthan Gums

[0073] Three grades of xanthan gum were supplied. The three products differed with respect to purity, the higher the purity the more expensive the product. On paper the best product (for oilfield use) is Xanthan CY. This product was tested at 2, 4 and 8%. The other oilfield xanthan gum (Xanthan PY) and the cheapest grade (Xanthan TJ) were only tested at 2% addition.

[0074] The results are set out in Table 1.

[0075] All three products mixed easily with the SR fines (similar to Guar gum). At highest rate of addition (8%) the mixture was difficult to work with.

[0076] There was no observable difference between the three products at 2% addition either qualitatively or in the drop test results.

TABLE-US-00001 TABLE 1 Drop Drop Strength Strength Crush % Binder Green Oven Dried Strength Notes Xanthan Gum CY 2 10 10 10 10 10 10 3 4 10 10 10 10 10 10 3 Extra water required (1%) 8 10 10 10 10 10 10 3 Extra water required (2%) Xanthan Gum PY 2 10 10 10 10 10 10 3 Xanthan Gum TJ 2 10 10 10 10 10 10 3

[0077] Other binders tested in a similar fashion included cellulose gum, technical grade carboxymethyl cellulose (CMC), high and low viscosity polyanionic cellulose (PAC), hydroxymethyl/hydroxypropyl cellulose, sodium carboxymethyl cellulose, water soluble and raw starches, partially hydrolysed polyacrylic acid, acrylic-styrene polymer, styrene-acrylic co-polymer emulsion, vinyl acrylic emulsion, PVA (polyvinyl acetate), ferric chloride, ferrous chloride and sodium silicate.

[0078] The potential binders that were found to give good green strength, good dry strength, and good crush strength comprised only natural products or derivatives of natural products. These were: [0079] The polysaccharide gums guar gum and xanthan gum [0080] The cellulose derivatives cellulose gum (sodium carboxymethyl celluloseCMC), technical grade CMC and polyanionic cellulose [0081] A number of hydroxymethyl/hydroxypropyl cellulose derivatives.

[0082] None of the synthetic polymers tested gave acceptable green strength.

[0083] The micro-agglomerates found satisfactory from the perspective of green strength, dry strength and dry crush strength, i.e. the micro-agglomerates made with the binders listed immediately above, were further tested for their high temperature (thermal) shock resistance, in order to determine their suitability as micro-agglomerates for the pigment chlorination process (i.e. the Chloride Process or Chloride Pigment Process). For this purpose, the micro-agglomerates were subjected to a thermal shock test by being instantaneously heated in a muffle furnace to 1000 C. for 15 minutes, to simulate the chlorination process where ambient temperature feed is introduced into a chlorinator operating at 900-1000 C. To simulate the reducing conditions prevalent in a chlorinator, the pellets were covered with a layer of char fines and fired in a closed crucible.

[0084] The number of pellets that cracked and/or exploded upon thermal treatment was considered a measure of the thermal shock resistance. On cooling, the intact pellets were subjected to a compression test to provide an indication of hot strength.

[0085] The results of the high temperature thermal shock tests are set out in Table 2.

TABLE-US-00002 TABLE 2 Cellulose PAC - Low PAC - High Binders Gum Guar Gum Xanthan Gum CMC Viscosity Viscosity Binder 2 4 2 4 2 4 8 4 8 4 8 4 8 Addition (%) Average 360 1660 <30 200 1110 >2000 >2000 >2000 >2000 350 1725 1055 1860 Crush Strength (g)

[0086] It will be seen that only the xanthan gum (>2%), cellulose gum (4%), CMC (4%) and low and high viscosity PAC (8%) demonstrated adequate high temperature thermal shock resistance, i.e. greater than 1000 g.

[0087] Surface regions of a selected pellet or micro-agglomerate were then viewed in a scanning electron microscope. A cross section was removed by sectioning the pellets with a scalpel. The cross section was placed with the newly-exposed side facing upwards on a double sided carbon tab and held stable with silver DAG. The sample was not carbon coated. The sample was analysed using a Carl Zeiss EV050 scanning electron microscope (SEM) fitted with an Oxford INCA X-Max energy dispersive spectrometer (EDS).

[0088] . Representative SEM images are appended hereto as FIG. 1 to 4. A 50 m or 500 m scale is provided on each image. FIGS. 1 and 2 are for an SR microaggregate in which the binder is CMC, viewed prior to the thermal shock test. FIGS. 3 and 4 are for an SR microaggregate in which the binder is CMC, viewed after the thermal shock test.

[0089] It will be seen that in all four images the particles of synthetic rutile are each bound to two or more other particles by bridges or webs of the CMC binder whereby the CMC binder forms a network of webbing firmly binding the particles in the micro-agglomerate. Each web is less than 5 m in minimum thickness, and at each end fans out to join the respective particle along an extended line of contact, i.e. a curving peripheral surface line. Some of these fanned out web portions join along the particle surfaces to one or more other fanned out portions of other webs.

[0090] It is postulated that the webs visible in the SEMs may form strong bonds with the particles by being firmly locked into the multiple pores of the particles in the interface zone.

EXAMPLE 2

[0091] Synthetic rutile fines (105 m) were formed into dry micro-agglomerates, i.e. pelletised, using a Hosokawa Alpine Gear Pelletiser. The dry pellets produced were spherical in form with a particle size in the broad range 100-1000 m.

[0092] In this instance, adopting the results of Example 1, only three binders were used to produce respective sample sets of agglomerates for further testing. These binders were xanthan gum, sodium carboxymethyl cellulose (sodium CMC) and a high viscosity polyanionic cellulose (PAC-HV). The added proportion of binder was 4%.

[0093] FIG. 5 depicts the particle size distribution (PSD) for each sample, i.e. the cumulative percentage of particles passing each size fraction (for each binder) compared to the original SR fines sample. It will be seen that there has been a dramatic increase in the PSD for all agglomerated samples compared to the SR fines. The CMC-binder agglomerates had the greatest increase in particle size followed by Xanthan gum and PAC-HV. Visually the CMC agglomerates included a significant quantity of soft particles that were >1 mm in size.

[0094] The hot testing of the agglomerates used the same procedure previously used for the hand formed pellets, namely weighed amounts (100 g) of agglomerates were placed in small ceramic crucibles which were then covered with powdered carbon to prevent oxidation during heat treatment. Ceramic lids covered the crucibles and the crucibles were then placed into the pre-heated muffle furnace at 1000 C. for 15 minutes (timed from when the temperature of the furnace recovered to 1000 C.). The PSD of the heat treated agglomerates (FIG. 6) indicates that some deterioration of the agglomerates occurred, which resulted in a reduced PSD when compared to the dry as received agglomerates, for each binder.

[0095] XRD traces of the dry (as received) and heat treated agglomerates showed that some oxidation occurred during the hot testing of the agglomerates. The phase structure of the dry agglomerates had been transformed from mostly reduced rutiles (TiO.sub.2-x) to rutile (TiO.sub.2). This was also confirmed from the carbon contents of the dry and heat treated agglomerates, which showed that 50% of the carbon had been lost from the agglomerates, as shown in Table 3.

TABLE-US-00003 TABLE 3 Dry Agglomerate Heat Treated Agglomerate Binder Carbon Content (%) Carbon Content (%) Xanthan Gum (R1) 1.86 0.81 PAC-HV (R2) 1.68 0.72 CMC (R3) 1.62 0.84

[0096] The partial oxidation of the agglomerates may have caused the loss in strength of the agglomerates indicated by the reduced particle size distributions observed for all binders.

[0097] The hot tests were repeated with similar results to the first hot test. The PSD for each binder was almost identical to the first hot test results shown in FIG. 6. The XRD traces indicated the structure had partially oxidised to rutile with some reduced rutile phases still present.

[0098] FIGS. 7, 8 and 9 are respective pairs of SEM images of the dry and heated agglomerates for the binders xanthan gum, PAC-PV and CMC respectively. It will be seen that the PAC and CMC binders of FIGS. 8 and 9 have coked into a more spongy appearance than the xanthan gum of FIG. 7.

[0099] Table 4 indicates the spectrum analysis of the binder phases in the SEMs of FIGS. 7, 8 and 9. The analysis indicates the presence of C, O, Na and CI in the binder phases, ranging from trace (<5% Full Scale SpectrumTr), to minor (5-50% Full Scale SpectrumMin), to major (50-100% Full Scale SpectrumMaj). Most of the oxygen, sodium and chlorine were removed when the agglomerates were heat treated. The removal of oxygen is associated with decomposition of the various binders which removes the OH from the cellulose structures.

TABLE-US-00004 TABLE 4 Agglomerate Carbon Oxygen Sodium Chlorine R1 - Xanthan Gum (dry Maj Maj Maj 0-Tr agglomerate) R1 - Xanthan Gum (heat treated) Maj 0 0 0 R2 - PAC-HV (dry Maj Maj Maj Tr agglomerate) R2 - PAC-HV (heat treated) Maj Tr Tr 0 R3 - CMC (dry agglomerate) Maj Maj Min Min R3 - CMC (dry agglomerate) Maj 0 Tr Tr

[0100] The maintenance of the carbon is consistent with the reducing atmosphere, and no doubt contributes to maintaining the integrity of the web network (now predominantly carbon webs) after heat treatment: a crucial property for the utility of the micro-agglomerates in the Chloride Process.

[0101] The conclusion from Example 2 is that all three binders produced titanium dioxide agglomerates suitable as a feed for the Chloride Process.

[0102] The hot testing of the agglomerates resulted in some deterioration of the agglomerates but still resulted in 85 to 93% of the agglomerates having a particle size >100 m. This is only an indicative test and does not directly relate to conditions in a chlorinator. The deterioration of the agglomerates could be a result of the partial oxidation of the agglomerates during the hot testing or insufficient binder. Oxidation would not occur in a chlorinator.

[0103] A slightly higher binder addition (6%) might be expected to increase the agglomerates hot strength.

EXAMPLE 3

[0104] Synthetic rutile fines (125 m) were formed into dry micro-agglomerates, i.e. pelletised at Hosokawa's Testing Facility located at Doetinchem in the Netherlands. The test used a Hosokawa continuous FX-160 High Shear Mixer and batch fluid bed drier. The dried pellets produced from the equipment were spherical in form with a particle size in the broad range 100-1000 m.

[0105] In this instance, adopting the results of Examples 1 and 2, only three binders were used to prove the agglomeration process using the high shear mixer and to provide sufficient micro-agglomerate samples for further test work, namely the micro-agglomerate performance in laboratory scale chlorination equipment. These binders were xanthan gum, sodium carboxymethyl cellulose (sodium CMC) and high viscosity polyanionic cellulose (PAC-HV). The added proportion of binder was increased from the laboratory scale tests (Example 2) of 4% to 6%. Two higher CMC binder additive tests were also completed, namely 6.6 and 8.8%. In total 9 separate tests were completed which varied the binder type, moisture content of the mixer discharge, binder addition rate (CMC only), dry and moist SR fines. The agglomeration results are indicated in the Table 5.

TABLE-US-00005 TABLE 5 Max. Max. Air Moisture Product SR Binder Water Product Inlet ex- Moisture - Bulk Fines <125 Run Fines Binder Amount Addition Temp. Temp. Flexomix Product Density m d.sub.50 No. (kg/h) Type (kg/h) (kg/h) C. C. (%) (%) (kg/m.sup.3) (%) (m) 1 500 CMC 32 30 80 100 6.3 0.5 987.4 32.2 158 2 500 CMC 32 70 65 150 12.5 0.5 8.8 321 3 500 CMC 32 75 65 150 13.2 0.6 1020 14.7 279 4 500 Xanthan Gum 32 25 65 150 4.9 0.8 1031.9 34.8 161 5 500 PAC-HV 32 25 65 180 4.9 0.4 801.1 30.6 204 6 500 PAC-HV 32 35 70 150 6.0 0.6 730.1 14.7 308 7 500 CMC 32 100 65 165 14.9 0.3 915.0 3.9 386 8 .sup.500.sup.(1) CMC 32 40 65 165 15.5 0.6 955.0 7.4 329 9 .sup.500.sup.(1) CMC 43.5 40 60 168 16.0 0.8 895.0 4.4 374 .sup.(1)Fines contained 10% moisture

[0106] For each test, metered rates of SR fines, binder and water was added to the high shear mixer, which operated at 3000 rpm mixer speed with +2 mixer knife setting. The residence time in the mixer is approximately 1 second. The wet agglomerated mix was discharged into the fluid bed drier where the micro-agglomerates were batched dried until the agglomerate bed temperature reached 60 C. The micro-agglomerates were then discharged from the drier, sampled and sieve analysis and bulk density were measured.

[0107] FIG. 10 depicts the particle size distribution (PSD) for each sample, i.e. the cumulative percentage of particles passing each size fraction (for each binder) compared to the original <125 m SR fines feed. It will be seen that there been a dramatic increase in the PSD for all agglomerated samples compared to the SR fines. The CMC and PAC-HV binder agglomerates had the greatest increase in particle size while Xanthan gum performed the worst under the test conditions. The moisture content during agglomeration had a significant impact on the Flexomix performance based on the quantity of micro-agglomerates that had <125 m in particle size. The best results from the Flexomix trial test conditions achieved fines values of <10% of the agglomerate weight with a particle sizes <125 m. Increasing the CMC binder addition rate from 6 to 8.8% for the wet SR fines slightly improved the dry agglomerate results but not when compared to the lower addition rate made to the dry SR fines.

[0108] The hot testing of the agglomerates used the same procedure previously used in the preceding examples, namely weighed amounts (100 g) of agglomerates were placed in small ceramic crucibles which were then covered with powdered carbon to prevent oxidation during heat treatment. Ceramic lids covered the crucibles and the crucibles were then placed into the pre-heated muffle furnace at 1000 C. for 15 minutes (timed from when the temperature of the furnace recovered to 1000 C.). The hot testing of the agglomerates resulted in some deterioration of the agglomerates (FIG. 11 and Table 6) but still resulted in 86 to 90% of the agglomerates having a particle size >100 m for the best results under these test conditions (CMC). This is only an indicative test and does not directly relate to conditions in a chlorinator. The deterioration of the agglomerates could be a result of the partial oxidation of the agglomerates during the hot testing or insufficient binder. Similar to Example 2, the XRD traces indicated that some oxidation of the agglomerates occurred during the heat treatment testing, which may have had an impact on the PSD deterioration of the heat treated agglomerates.

TABLE-US-00006 TABLE 6 comparison of the fines content and d.sub.50 (m) between the dried and heat treated agglomerates Heat Treated Dry Agglomerates Agglomerates Fines Fines Binder <125 m <125 m Run No. Type (%) d.sub.50 (m) (%) d.sub.50 (m) 1 CMC 32.2 158 55.5 119 2 CMC 8.8 321 20.0 268 3 CMC 14.7 279 24.5 227 4 Xanthan 34.8 161 50.1 125 Gum 5 PAC-HV 30.6 204 50.8 124 6 PAC-HV 14.7 308 36.3 177 7 CMC 3.9 386 16.3 320 8 CMC 7.4 329 19.1 276 9 CMC 4.4 374 16.8 294

[0109] Table 7 indicates the SEM spectrum analysis of the binder phases for each of the nine test runs. The analysis indicates the presence of C, O, Na and Cl in the binder phases as defined in Example 2. Most of the oxygen, sodium and chlorine were removed when the agglomerates were heat treated leaving carbon rich filaments which bind the particles. The removal of oxygen is associated with decomposition of the various binders which removes the OH from the cellulose structures. These results are consistent with those observed in Example 2.

[0110] Increasing the CMC binder addition rate from 6.6 to 8.8% for the wet SR fines slightly improved the heat treatment results, but not when compared to the lower addition rate made to the dry SR fines.

TABLE-US-00007 TABLE 7 SEM spectral analysis of the binder phases for the dry and heat treated agglomerates Run Binder Dry Agglomerates Heat Treated Agglomerates No. Type Carbon Oxygen Sodium Chlorine Carbon Oxygen Sodium Chlorine 1 CMC Maj Maj Min Min Maj Tr 0 0 2 CMC Maj Maj Min Min Maj 0-Tr 0 0 3 CMC Maj Maj Min Min Maj 0-Tr 0 0 4 Xanthan Gum Maj Maj Min Tr Maj 0 0 0 5 PAC-HV Maj Maj Min Tr Maj 0 0 0 6 PAC-HV Maj Maj Min Tr Maj 0-Tr 0 0 7 CMC Maj Maj Min Min Maj Tr 0 Tr 8 CMC Maj Maj Min Min Maj 0 0 Tr 9 CMC Maj Maj Min Min Maj Tr 0 0

[0111] The maintenance of the carbon is consistent with the reducing atmosphere, and no doubt contributes to maintaining the integrity of the web network (now predominantly carbon webs) after heat treatment: a crucial property for the utility of the micro-agglomerates in the Chloride Process.

[0112] FIGS. 12, 13 and 14 are respective pairs of SEM images (for selected tests) of the dry and heated agglomerates for the binders; xanthan gum, PAC-HV and CMC respectively. It will be seen that the PAC-HV and CMC binders of FIGS. 13 and 14 have coked into a more spongy appearance than the xanthan gum of FIG. 12, which indicates a more dispersed structure.

[0113] The other interesting observation is that the CMC binder has behaved differently to the previous laboratory test in that the binder in the dry agglomerates was rarely seen as the filament or web type structure previously observed (FIGS. 1 to 4) and more like small particles coalesced together between the SR fines particles (FIG. 15). Mixtures of filaments or webs and particles were also observed, which when heat treated remained as individual filaments/webs or particles respectively. The moisture content of the agglomerate post mixer also appeared to have an impact on the binder structure, at low moisture contents (<13.2%) only individual binder particles were observed while >13.2% a mixture of individual and filaments were observed. This feature was not observed in the laboratory mixer tests (Example 2) which produce agglomerates with 14.8% moisture content. Even at higher moisture contents of 16% (FIG. 15) for the Flexomix trials the individual binder particles persisted and may be a result of continuous mixing (1 second residence time) compared to the batch laboratory mixer, which was considerably longer.

[0114] The conclusions from Example 3, for the test conditions studied, are that CMC and to a lesser extent PAC-HV binders would be suitable to produce titanium dioxide (SR) agglomerates suitable as a feed for the Chloride Process. CMC is the only binder that can be used to agglomerate wet SR fines.

EXAMPLE 4

[0115] Synthetic rutile CMC-bound micro-agglomerates produced in accordance with Example 3 were tested for elutriation in an experimental environment of high temperature gas flow conditions, intended to mimic, i.e. be equivalent to, those in a titanium pigment chlorinator of the Chloride Process. Samples that were respectively (1) not heat treated, (2) and (3) heat treated at 300 C. and 600 C. for 30 minutes at the respective target temperature, and (4) fired at 1000 C. (as in the earlier described hot testing procedure) were subjected to elutriation tests that also employed a structural synthetic rutile sample and synthetic rutile fines used to produce the micro-agglomerates as references.

[0116] In the elutriation test, around 600 g of agglomerates were placed in a fluidizing column with ID 80 mm. The setup was heated to 1000 C. and fluidized with N.sub.2 or Ar at a superficial gas velocity of 0.22 m/s (at 1000 C.). No Cl.sub.2 or CO or particulate carbon was used in this test. Fine ore particles elutriating from the bed were captured in the off-gas vent and labelled as blowover. After 30 min at 1000 C., the test was terminated and the sample allowed to cool. The initial and final bed masses, and captured blowover, were recorded. As stated, these high temperature gasflow conditions are equivalent to those in the Chloride Process.

[0117] Two sets of numbers were used to calculate elutriation losses: the captured blowovers, and the difference between the initial and final bed masses. Theoretically these two numbers should give the same result. The difference in bed masses is however usually a bigger number. After ruling out the probability of mass loss due to reactions at the experimental conditions, the actual elutriation losses were assumed to be within the range set by the blowover and bed difference.

[0118] In the case of micro-agglomerates that contain binder, which (partially) burns off during the test, calculating the actual elutriation losses is a bit more complicated. It is unknown how much of the binder burned off during the pre-heat treatment (where this was done), and/or during the elutriation test. This is dealt with by giving two numbers for both the bed losses and the blowovers (Table 8): the first number assumes all losses to be actual particles lost (i.e. no binder was burned off), while the second number is calculated assuming that all of the binder was burned off. For this case the binder mass was subtracted from the losses to calculate the particle losses. Where the second number is negative (as in the case of S8 pre-fired samples), the implication is that some or all of the binder was already burned off during pre-firing. The actual bed losses are likely between these two numbers.

[0119] Initial elutriation tests run in nitrogen atmospheres showed excessive elutriation losses. Disintegration of the binder in the nitrogen atmosphere was suspected, and the fluidizing gas was changed to argon. Though the elutriation losses did improve somewhat, the improvement was not dramatic. A substantial improvement was achieved though when the pellets were pre-fired at 1000 C., or pre-heated at 500 C. and 300 C. before subjecting them to the elutriation test.

[0120] The results are shown in Table 8.

TABLE-US-00008 TABLE 8 Elutriation losses under different conditions for fine and typical SR, and CMC bound micro-agglomerates S8. In the last two columns, the first number is calculated by assuming all losses to be particle losses; the second number provides for binder losses by assuming that all of the binder was burned. Atmosphere, Initial Final Bed Blowover Pre-heat bed mass bed mass Blowover losses losses treatment T [g] [g] [g] [%] [%] Fine SR N.sub.2 600 464.7 98.9 22.6 16.5 Typical SR N.sub.2 600 592.8 1.6 1.20 0.27 S8 N.sub.2 600 471.6 83.4 .sup.21.4/14.3 13.9/15.0 Ar 580 446.8 114.4 .sup.23.0/15.9 19.7/21.2 Ar, 1000 C. 574.3 536.7 28.0 6.55/<0 4.88/5.25 Ar, 500 C. 600 577.9 5.8 3.68/<0 0.97/1.04 Ar, 500 C. 600 587.8 3.5 2.03/<0 0.58/0.63 Ar, 300 C. 600 580 7.7 3.33/<0 1.28/1.38

[0121] It will be seen that the best outcome, in terms of reduced elutriation or blowover, was with micro-agglomerates heat treated at 300 C. or 500 C. No heat treatment gave a poor outcome. Firing at 1000 C., while better than heat treatment, was still clearly inferior to lesser heat treatment. Firing at 1000 C. may degrade the quality of the binding webs, The results in Table 8 also suggest the benefit of heat treatment at 500 C. rather than 300 C. may be marginal and that the lower temperature is sufficient for practical and cost purposes.

[0122] FIG. 16 is an SEM image of the last S8 sample in the above elutriation test, after heat treatment at 300 C. and before admission to the test fluidizing column.

[0123] The image shows evidence of a phase that remains linking SR particles or grains together, which phase is assumed to be the residual CMC binder following the heat treatment. Most of the SR fines particles are still agglomerated with other SR particles. The spongy masses are thought to be a sodium phase derived from the sodium CMC employed as the binder. The conclusion is that the binder is still functioning well, and this is supported by the elutriation test. Indeed, the test confirms that the heat treatment has enhanced the micro-agglomerates.