Document Xz56bQaVY31qXkBLK3JJxR04g

v E. L du Pont de Nemours and Company PATENT DIVISION DU PONT BUILDING . - - WILMINGTON, DEL. . . APPLICATION m">v'"raiTO--R_=_-i*^^! i6i&IMa..-iuagBa__ ______________ ______ mvEtmoN..^^^r^r^. 77Q, , OSEnRsIAiirL uNOn----------c--/32<>3a3r?j >0.f*t/iVLU& rtSt__________ .NOTICE RECTI..... /* /, _____INVENTOR'S ADDRESS. "_z/a RECORDS DESTRUCTION SCHEDULE RECORDS CATEGORY OR TITLE: ftrems aeAftreo COPY "0" (OFFICIAL) Jgf "X" (EXTRA) fc,. TOTAL IRETENTION: _ ______________ fer; .JftNOftPf iH. 1001 GJ?-11050 .J9.. ..19.. ..19.. JU ~W~ REFERENCES IGNMENT ...ASSIGNEE!___ DATE_______MfJjU . /~7; luff/, SENT FOR RECORDING._________$U.^aUrJ13lU~f. BECD ASSIGN2ZutAa^.&r~193iX RECORDED-------------------------j(9iCASvJ9Sl^ REEL..3.9.3?.. SENT FHAMEs=isV ALLOWED. FINAL FEE SENT. ....3aaa...4+..wX^ r e c e ip t b e c d .. NUlfBEB OF^PA- SENT TO lOHAf) -C+P 3ZJ^4IJ0177Z.ISZ7 ATTORNET OF RECORD.. ATE AT /* _ _19 PATENT RECD.. ^ISSUED. N36774 THE STAMP OF THE PATENT OFFICE HEREON ACKNOWLEDGES THE RECEIPT, ON THE DATE INDICATED, OF THE FOLLOWING: Applicant (s) : MICHAEL RAPHJl Title: PREPARATION OF TiOj SLUg Sr0* to Oath Declar, Yes Pages of Claims \|> ^ Fee $65.ff0. How 1181 ATTORNEY THEODORE C. GREGORY DUP050302061 THE STAMP OF THE PATENT OFFICE HEREON ACKNOWLEDGES THE RECEIPT, ON THE DATE INDICATED, OF THE FOLLOWING: Applicant (s': MICHEL RAPHAEL k^LOGA CH 1181 Title- PREPARATION.^ SLURRIES Pages of Spec. Oath Declar. Yes A S'' of Claims "- "isfieets of 1 ./ytyurawings AD'-y^ 1 Fee $65.00 How paid Check ATTORNEY THEODORE C. GREGORY DU PO 50302062 BCC: MRBaloga-C&P, NJ GELynskey-C&P, NJ RAFenoglio-C&P, EM (CH 1181) IN THE UNITED STATES PATENT AND TRADEMARK OFFICE In the Application of MICHAEL RAPHAEL BALOGA SERIAL NO.: 303,044 FILED: SEPTEMBER 17, 1981 FOR: PREPARATION OF Ti02 SLURRIES GROUP NO.: 113 Wilmington, Delaware January 21, 1982 PRIOR ART LETTER Commissioner of Patents and Trademarks Washington, D.C. 20231 Sir: The following references (copies of which are attached) have come to the attention of Applicant and may be of interest to the Examiner: 1. U.S. Patent 4,170,485 discloses Ti02 pigment slurries of high solid content (70-80% TSC) prepared from inprocess material of relatively fine particle size, i.e., thickener underflow. The thickener underflow and regular dry finished product Ti02 with one or more organic disper sants make up the solids of the slurry prepared. The fines in the thickener underflow are required to sit for an extended period. The present invention does not require such an extended period of sitting and does not require the addi tion of solid product or even filtration. 2. U.S. Patent 4,227,935 discloses Ti02 slurries prepared from in-process material, i.e., that which has not been fluid energy milled and dried, if it is coated with low amounts of aluminum oxide. It is disclosed that in paint applications the hiding power is high and the tinting strength better than paint with standard Ti02. N36774.01 DUP050302063 PRIOR ART LETTER & ATTACHMENTS THE STAMP OF THE PATENT OFFICE HEREOOK^.'' ACKNOWLEDGES THE RECEIPT, ON T^D^TE* INDICATED, OF THE FOLLOWING: ' f ' BALOGA CH 1181 /3 V,.0 S.N. 303,044 l ti'-~ Filed: September 17, ,1981 For: Preparation of ^iO, Sldrfj.es ATTORNEY THEOpQfU2 GREGORY DUP050302064 Domestic Rate E. I. DU PONT DE NEMOURS & CO. (INC.) LEGAL DEPARTMENT WILMINGTON, DELAWARE 19898 DUPO 50302 065 There is no disclosure of the use.of Ti02 fines carried over with spent steam from the micronizer or of the concentration of the slurry without filtration or concentration with heat. There is absolutely no disclosure in either of the above references that suggest the use of Ti02 fines from spent steam or of the concentration of a slurry in water of such fines without adding dry Ti02 product, filtration or evaporation. Respectfully submitted. TCG/kac Telephone: (302) 774-6184 Attachments Theodore C. Gregory Attorney for Applicant Registration No. 25,243 DUP050302066 f o r m PTO-1449 RE V. 7.SO u.s PM -PARTMENT OF COMMERCE AND TRADEMARK OFFICE LIST OF PRIOR ART CITED BY APPLICANT (Use several sheets if necessary) ATTY. DOCKET Sheet_1 SERIAL NO. 1181 APPLICANT MICHAEL RAPHAEL FILING DATE 9/17/81 303,044 BALOGA GROUP 113 of 1 U.S. PATENT DOCUMENTS e x a min e r INITIAL DOCUMENT NUMBER DATE NAME CLASS SUBCLASS FILING DATE |p APPROPRIATE AA 4 1 7 0 4 8 5 10/79 Blake et al. 106 300 AB 4 2 2 7 9 3 5 10/80 AC Blake et al. 106 308B AD AE i AF j i i AG i i i l J AH i | |i A! i 1 t i | i j AJ t AK i i _____ L_ I i | FOREIGN PATENT DOCUMENTS DOCUMENT NUMBER DATE COUNTRY AL i AM CLASS SUBCLASS t r a n s l ATION YES NO AN AO AP OTHER PRIOR ART (including Author, Tide, Dale, Pertinent Pages, Etc.) AR * AS AT XAMINER DATE CONSIDERED -EXAMINER: Initiol if reference considered, whether or not eitotion is in conformance with MPEP 609; Draw line through citation if not in conformance and not considered, include copy of this form with next communication to onolieont DUP05 0302067 N36774.02 Gft H?/ `X United States Patent [19] Baloga in] 4,427,451 [45] Jan. 24, 1984 [54] PREPARATION CONCENTRATED TIO2SLURREES FROM SPENT STEAM [75] Inventor: Michael R. Baloga, Big Sandy, Tenn. [73] Assignee: E. I. De Pont de Nemours and Company, Wilmington, Del. [21] Appl. No.: 303,044 [22] Filed: Sep. 17,1981 [51] Int. Cl.*................................................ C09C 1/36 [52] U.S. CL.................................... 106/300} 106/309; 241/5; 241/21; 423/610 [58] Field of Search.................... 106/300, 308 B, 309; 423/610; 241/5, 21 [56] References Cited U.S. PATENT DOCUMENTS 3,622,084 11/1971 Ross.................................... 241/5 4,083,946 4/1978 Schurr et al....................... 423/610 4,170,485 10/1979 Blake etal. ...................... 106/300 4,227,935 10/1980 Blake etal..................... 106/308 B Primary Examiner--Helen M. McCarthy [57] ABSTRACT A process for preparing concentrated slurries of TIO2 and water with a solids content of 30-70% by weight from Ti02 micronizer tailings that are carried in steam separated from T1O2 and steam from a micronizer by scrubbing the steam and T1O2 micronizer tailings with a slurry of Ti02 and water, separating Ti02 and water from the steam and circulating a portion ofthe T1O2 and water to the absorber until the solids content desired is reached. 6 Claims, 1 Drawing Figure N36774.03 DUPO 50302 068 U.S. Patent Jan. 24, 1984 4,427,451 DUP050302069 4,427,451 12 has been found for preparing a concentrated slurry of PREPARATION CONCENTRATED TIO2SI.URHIES FROM SPENT STEAM titanium dioxide in water from titanium dioxide tailings from a titanium dioxide finishing treatment process which comprises DESCRIPTION 5 (a) passing spent steam from a TiOj micronizer un 1. Technical Field avoidably carrying with it TiC>2 into a scrubber where it This invention relates to a process for preparing con is contacted with an aqueous slurry of TiC>2; centrated slurries of TK>2 and water from T1O2 tailings (b) separating the TiC>2 and water from the steam; in spent steam. More particularly, this invention relates (c) collecting the separated Ti02 and water in a ves to a process for preparing concentrated slurries ofTi02 10 sel; from T1O2 tailings in spent steam by limiting the amount (d) pumping a part of the Ti02 and water from the of water used to separate the TK?2 from the spent steam. vessel as an aqueous slurry to the scrubber with addi 2. Background Art tional water; U.S. Pat. No. 4,227,935 discloses a method for mak (e) continuing the above treatment until the total ing slurry from T1O2 fines recovered from TKJ2 that 15 solids content of the Ti02 and water slurry from the was not micronized or fluid energy nulled. The T102 vessel is 30-70% by weight, preferably 50-70% and fines in slurry form are coated with aluminum oxide and most preferably 50-65%. concentrated either by filtration or rotary evaporator. U.S. Pat. No. 4,170,485 discloses the preparation of The Ti02 pigment that is present in the spent steam which is the starting material in the present process can high solid slurries of TiC>2 with increased gloss relative 20 be obtained by the combustion of titaniferous salts from to conventional slurries. The TiC>2 fines from the fluid the chloride process such as titanium tetrachloride or by energy mill micronizer which is the bottom 10-20% of hydrolyzing, filtering, washing and calcining a soluble the product from the micronizer are trapped in water titanium salt'from the sulfate process. and allowed to stand. This T1O2 in water is concen The crude T1O2 pigment obtained from either the trated by filtering and/or adding dry Ti02 to give the high solids slurry. TiC>2 is generally produced by hydrolyzing an aque ous solution oftitanium sulfate and calcining the hydrolyzate at 750*-1000' C. or oxidizing a titanium tetra chloride at elevated temperatures followed by cooling 25 30 chloride process or the sulfate process is cooled to a temperature ranging from 300-800 " C., e.g., by proce dures disclosed in U.S. Pat. Nos. 2,833,637 and 2,721,626. Separation of the cooled gaseous products from the T1O2 phase can be by recourse to suitable to temperatures below 600* C. The TiC>2 thus prepared gravitational means, such as centrifugal or cyclone sep is dry or wet ground and then dry milled. One method of dry milling is a fluid energy mill which can also be aration or by filtration or by electrostatic, ultrasonic and other means. referred to as a micronizer. A fluid energy mill involves The separated Ti02 pigment fraction from either the introducing dry Ti02 pigment and a fluid, e.g., steam 35 chloride or sulfate process is slurried in water, and hy into the outer portion ofan inwardly spiraling vortex so drous oxides of silica and/or alumina are applied by as to convey the T1O2 at high velocity against the hous procedures disclosed in the art Examples of such prior ing of' the spiral vortex to fracture aggregates. The art describing how the addition of the silica and/or material exiting the fluid energy mill is separated as dry alumina is made, U.S. Pat. Nos. Re 27,818 and Ti02 and steam containing Ti02 tailings. Ti02 tailings 40 4,125,412, are incorporated by reference. However, the are Ti02 that is carried out with the steam when separa tion is achieved. This steam with HO2 tailings is gener TiC>2 source for the present process may be TiOz with out silica and/or alumina. ally scrubbed with water to separate the steam and Soluble salts are removed from the treated slurry T1O2. The TiC>2, after the water scrubbing, generally through a filtration/washing procedure in order to re constitutes a slurry of about 1-10% total solids content. 45 duce the concentration of aqueous teachable salts to This slurry can be treated in a variety of ways to conform to the American Society for Testing Materials recover the TiC>2 content. It can be reground with regu specifications for pigment resistance, ASTMD476. lar production or it may be concentrated to form high The washed filter cake is dewatered on a vacuum solid slurries or added in limited quantities to high solids rotary drum filter in order to reduce its water content aqueous Ti02 slurries. Such Ti02 slurries are usually 50 and thereby minimize energy consumption when the marketed as slurries for the production of coated papers filter cake is dried. Depending upon the hydrous oxide and water based paints. treatment levels, the water content of the filter cake In any facility built for the preparation ofdry Ti02 it before drying will typically range between 30 and 70% would require the use of extremely large quantities of pigment solids content by weight. high solid slurries to dispose of the dilute T1O2 tailings 55 After the drying step, the pigment is subjected to a slurries that are recoverable from fluid energy mills. If final dry milling operation in a fluid energy mill which added to regular dry Ti02 production, the energy re quired to refilter, redry and regrind such tailings would can also be referred to as a micronizer. The fluid energy milling involves the introduction of significantly add to the cost of the product. Additional dry T1O2 pigment into the grinding chamber of the filtration capacity would also be required. If one were 60 micronizer where superheated steam accelerates the to simply concentrate the Ti02 tailing slurries by evapo pigment aggregates to a high velocity in a spiralling ration or other conventional methods, the energy de vortex within the micronizer chamber. The grinding mands required would be substantial. action occurs when the pigment aggregates collide with DISCLOSURE OF THE INVENTION 65 each other and with the walls of the grinding chamber. The mixture of steam and ground pigment that leaves Now a process has been discovered that permits the the fluid energy mill is routed through a cyclone classi concentration of Ti2 tailing slurries more efficiently fier which separates about 95% of the pigment stream than conventional processes. Accordingly, a process from the spent micronizer steam. The spent steam and DUP050302070 4,427,451 34 the remaining unseparated TiOj (about 5%) is then The water addition to the suction side of the pump is treated according to the invention. This remaining preferred. However, water can be added at various T1O2 is referred to herein also as micronizer tailings. other points in the described process including addition The process of the invention can be further described to the scrubber directly and addition to the slurry be by reference to the FIGURE which is a schematic 5 fore it reaches the absorber. drawing that illustrates the present invention. Referring The invention is further illustrated in the examples niow to the FIGURE, the micronizer tailings stream 1 that follow: is scrubbed with a recirculating stream of a slurry of the micronizer tailings that pass through rotameter 3A. The EXAMPLES T1O2 slurry becomes concentrated in TiOj within the 10 Example 1 scrubber unit 2 and the enriched T1O2 slurry is then separated from the mncondensed steam in the wet cy clone 4. The spent steam exits the wet cyclone 4 via 4A. The condensed T1O2 slurry is collected in a catch tank vessel S and recirculated by means of a high capacity pump 6 back to the wet scrubber 2 for additional con centrating. The specific gravity of the tailings stream is regulated by the addition of water 7 to the suction side of the high capacity recirculating pump 6, the rate of water addi tion being regulated by a nuclear density measuring device that operates from radiation source 8 across the flow in line 9 to the radiation gauge 8a. The concentra 15 20 Ti02 prepared by the chloride process was slurried in water and oxides of silicon and aluminum deposited on the TiC>2 in the amount of 8% by weight oxide ofsilicon and 8% by weight oxide of aluminum based on the TiC>2. After removal of soluble salts by filtration and washing, the filter cake was dewatered and dried. The dried 1102 pigment was milled in a fluid energy mill. The TiD2 pigment from a fluid energy mill was sent to a cyclone classifier where spent steam that carries with it unseparated TiOj was separated from Ti02- This unseparated Ti02 was processed in the system described in the drawing in the present specification except that initially water was fed directly to the ab tion of Ti02 solids is directly related to the optical den sity of the nuclear radiation that is transmitted across 25 sorber at a rate of 5.5 gpm without any slurry ofmicro nizer tailings going to the scrubber. The concentration the optical slurry pathway 9 by the equation: of the tailings leaving the wet cyclone was 149 grams Optical Density = per liter. After 1 hour of operation, the water to the scrubber was gradually reduced from 5.5 gpm to 2.0 where I0 is the radiation intensity of the nuclear source, I is the intensity of the radiation after it is attenuated by the slurry stream, k is: an attenuation coefficient that is a unique property of the absorbing medium, C is concen tration of the Ti02 in the slurry stream and 1 is the thick ness of the optical pathway. The notation In refers to 30 35 gpm over a period of 5 hours and a slurry of TiC>2 tail ings from the catch tank were also routed to the scrub ber at 20 gpm. The slurry of T1O2 tailings gradually increased to a concentration of 30% by weight solids. The table below summarizes the water and tailing flows. the natural logarithm and e refers to die natural expo nential base 2.718. A change in the concentration of Fresh Water T1O2 in- the slurry stream will cause a proportional Flow to Tailings Flow Pigment Concentration change in the optical density that is perceived by the Scrubber to Scrubber Expected Measured detector portion of the nuclear density device, and this 40 TimegpmgpmWt %________Wt % signal is converted to pressure in pressuxe/current con 0 verter XI to throttle the control valve 10 that admits fresh water to the suction side of the pump. A set point 60 min 75 min 90 min for automatic control of the system will be dependent 120 min upon the pumping characteristics of the concentrated 45 180 min Ti02 tailings slurry. This set point will correspond to a slurry concentration that is generally less than 70% 240 min 300 min 360 min solids. The volume of tailings that must be disposed of 5.5 5.5 5.0 4.5 3.5 3.0 2J 20 2.0 0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Base Cond Base Coad 14.2 15.6 19.3 22.0 25.6 30.5 30.5 13.4 11.9 13.9 15.7 19.3 21.8 22.4 29.6 30.7 will define the tower limit of concentration, usually 30%, that is economical to dispose of into the slurry 50 The 30% TiC>2 slurry was added to T1O2 pigment in product stream. place of water to prepare a slurry of TiCh of 64.5% The level in the catch tank is automatically con solids that is a normal commercial production item. The trolled by measuring the hydrostatic pressure of the surfactants normally added to the commercial product slurry in the tank 5 with probe 12 and by electronically were added with the T1O2 tailings slurry. dividing this pressure measurement by the optical den 55 A comparison was made of the slurry properties of sity signal that is a measure of specific gravity at electri normally prepared 64.5% solids Ti02 slurries and cal divider 13. The mathematical equivalent to this ratio 64.5% solids slurry was made with TiC>2 tailings slurries of pressure and density measures is a third variable that to illustrate a use for the micronizer tailings. is proportional to a density corrected level in the tank. The absolute level in the tank is regulated by this signal 60 which is converted to pressure in the pressure/current Conventional 64.5% Tailings 64.5% Solids T1O2 Solids 1102 converter 14 which only controls valve IS in the export line 16 that carries the concentrated Ti02 tailings slurry to the finished product slurry manufacturing process. Finally in the FIGURE, a recirculating stream of 65 T1O2 slurry 17 is continuously routed back to the catch tank through a jet mixer 18 to provide vigorous agita Percent Solids pH Viscoshv fens) Brookfield @ 100 rpm Brookfield 10 rpm Density (Ibs/gal) 64.5 8.2 105 130 15.S 64.8 8.2 115 140 15.9 tion to prevent settling in the tank. DUP0 50302 071 4.427.451 56 The 64.5% solids slurries of TiOjfrom both the con permit a more efficient preparation of Ti02 slurry. The ventional slurry and the tailings slurry were used to process of the invention can be achieved quite rapidly prepare paint. The paint with the micronizer tailings relative to conventional concentration and inherently exhibited a small hiding power and tinting strength thereby provides many advantages in process capacity. advantage over the paint with the conventional slurry. 5 It is to be understood that any of the components and EXAMPLE 2 conditions mentioned as suitable herein can be substi tuted for its counterpart in the foregoing examples and The procedure of Example 1 was followed except that although the invention has been described in con that the starting Ti02 was coated with 1.5% by weight siderable detail in the foregoing, such detail is solely for of an oxide of silicon and 4% by weight of an oxide of 10 the purpose of illustration. Variations can be made in aluminum based on the Ti02. The concentration of tailings from the wet cyclone when only water was being fed to the scrubber at 6 gpm was 101 g/1 or 9.3% the invention by those skilled in the art without depart ing from the spirit and scope of the invention except as set forth in the claims. by weight solids. The slurry of tailings from the catch I claim: tank was then sent to the scrubber at 20 gpm and the 15 1. A process for preparing a concentrated slurry of fresh water rate reduced to 0.75 gpm. In a period of 4 titanium dioxide in water from titanium dioxide tailings hours, the concentration of TiOi tailings in the catch from a titanium dioxide fluid energy steam milling mi tank gradually increased to 844 g/1 or 51.3% by weight cronizer process which comprises solids. The tailings slurry was then used to manufacture a 20 commercial product slurry of 76% solids that is nor mally made from the Ti02 from which the starting material of this example came from by adding to such Ti02 the tailings slurry rather than water. A compari son was made of the slurry prepared conventionally and 25 the slurry from the tailings slurry of the present exam ple. (a) passing spent steam from a TiC>2 micronizer un avoidably carrying with it Ti02 into a scrubber where it is contacted with a recirculating stream of an aqueous slurry of the micronizer tailings of TiOz; (b) separating the TiC>2 and water from the steam; (c) collecting the separated TiChand water in a vessel in which settling is prevented; (d) pumping a part of the TiC>2 and water from the vessel as an aqueous slurry to the scrubber with Percent Solids pH Viscosity (c d s ) Conventional 76% Solids TiOa 76.2 9.7 Tailings 76% Solids TiOj 76.2 9.7 additional water; (e) continuing the above treatment until the total solids content of the Ti02 and water slurry from the vessel is 30-70% by weight. 2. The process of claim 1 wherein the total solids Brookfield @ 100 rpm 168 189 content of the Ti02 and water is 50-70% by weight. Brookfield @ 10 rpm Density (lbs/gal) 550 19.16 700 19.23 3. The process of claim 1 wherein the total solids content of the Ti02 and water is 50-65%. 4. The process of claim 1 wherein the additional It may be necessary to add surfactants to the catch water is added directly to the scrubber. tank to reduce the viscosity of the Ti02 slurry especially 5. The process of claim 1 wherein the additional at solids levels near 70%. water is added to the slurry after leaving the vessel and INDUSTRIAL APPLICABILITY before the scrubber. 6. The process of claim 1 wherein the additional The process of the present invention is industrially applicable to any Ti02 producing facility. It would water is introduced b*et*we*en *the*vessel and the pump. 60 65 DUP0 50302 072 CH 1181 11 CLAIMS 1. A process for preparing a concentrated slurry of titanium dioxide in water from titanium /" dioxide tailings from a titanium dioxide tr-eatiitent process which comprises (a) passing spent steam from a Ti02 micronizer unavoidably carrying with it TiO~ into a scrubber where .. * alAion* t it is contacted yith an aqueous drfy DlU: itHt-hlt ^ 10 slurry.iooff^Ti02 ; (b) separating the Ti02 and water . from the steam; (c) collecting the separated(Ti02 and\^ IT water in a vessel?^ V* . 5 1 /Y 15 (d) pumping a part of theTiC^ and water '\ (S' from the vessel as an aqueous slurry >* v to the scrubber with additional water; <e) continuing the above treatment until the total solids content of the lio2 20 and water slurry from the vessel is 30-70% by weight. 2. The process of Claim 1 wherein the total solids content of the Ti02 and water is 50-70% by weight. 25 3. The process of Claim 1 wherein the total solids content of the TiC>2 and water is 50-65%. 4. The process of Claim 1 wherein the addi tional water is added directly to the scrubber. tional 5. water The process of is added to the Csllauirmry1awftehre^rtehiSn ^tvheessaedl,d*bi eC 30 fore the scrubber. 6. The process of Claim 1 wherein the addi tional water is introduced between the vessel and the pump. 11 N36774.04 DUP050302073 CH 1181 1 TITLE Preparation of Ti02 Slurries DESCRIPTION Technical Field 5 This invention relates to a process for pre paring concentrated slurries of Ti02 and water from Ti02 tailings in spent steam. More particularly, this invention relates to a process for preparing concen trated slurries of Ti02 from Tio2 tailings in spent 10 steam by limiting the amount of water used to separate the Ti02 from the spent steam. Background Art U.S. Patent 4,227,935 discloses a method for making slurry from Ti02 fines recovered from TiO-, 15 that was not micronized or fluid energy milled. The Ti02 fines in slurry form are coated with aluminum oxide and concentrated either by filtration or rotary evaporator. U.S. Patent 4,170,485 discloses the prepara20 tion of high solid slurries of Ti02 with increased gloss relative to conventional slurries. The Ti02 fines from the fluid energy mill micronizer which is the bottom 10-20% of the product from the micronizer cire trapped in water and allowed to stand. This Tio2 25 in water is concentrated by filtering and/or adding dry Ti02 to give the high solids slurry. Ti02 is generally produced by hydrolyzing an aqueous solution of titanium sulfate and calcining the hydrolyzate at 750-1000C or oxidizing a titanium 30 tetrachloride at elevated temperatures followed by cooling to temperatures below 600C. The Ti02 thus prepared is dry or wet ground and then dry milled. One method of dry milling is a fluid energy mill which can also be referred to as a micronizer. A fluid energy 35 mill involves introducing dry Ti02 pigment and a fluid. 1 DUP050302074 2 e.g., stgam into the outer portion of an inwardly . spiraling vortex so as to convey the TiC^ at high velocity against the housing of the spiral vortex to fracture aggregates. The material exiting the fluid 5 energy mill is separated as dry Ti02 and steam con taining TiC>2 tailings. Ti02 tailings are Ti02 that is .carried out with the steam when separation is achieved. This steam with Ti02 tailings is generally scrubbed with water to separate the steam and Ti02. The Ti02, 10 after the water scrubbing, generally constitutes a slurry of about 1-10% total solids content. , This slurry can be treated in a variety of "" ways to recover the Ti0o content. It can be reground j0 1 11 with regular production or it may be concentrated to 15 form high solid slurries or added in limited quantities to high solids aqueous Ti02 slurries. Such Ti02 slurries are usually marketed as slurries for the pro- f. ductjjifon of coated papers and water based paints. In any facility built for the preparation of 20/ dry Ti02 it would require the use of extremely large quantities of high solid slurries to dispose of the dilute TiC>2 tailings slurries that are recoverable from fluid energy mills. If added to regular dry Ti02 pro duction, the energy required to refilter, redry and re grind such tailings would significantly add to the cost of the product. Additional filtration capacity would also be required. If one were to simply concen trate the Ti02 tailing slurries by evaporation or other conventional methods, the energy demands required would be substantial. E'isclosure of the Invention Now a process has been discovered that per mits the concentration of TiC>2 tailing slurries more efficiently than conventional processes. Accordingly, a. process has been found for preparing a concentrated 2 DUP0503 02075 3 slurry of titanium dioxide in water from titanium dioxide tailings from a titanium dioxide finishing treatment process which comprises (a) passing spent steam from a Ti02 5 micronizer unavoidably carrying with it TiC>2 into a scrubber where it is contacted with an aqueous slurry of Ti02; (b) separating the Ti02 and water 10 from the steam; (c) collecting the separated Ti02 and water in a vessel; (d) pumping a part of the Ti02 and water from the vessel as an aqueous slurry 15 to the scrubber with additional water; (e) continuing the above treatment until the total solids content of the Ti02 and water slurry from the vessel is 20 30-70% by weight, preferably 50-70% and most preferably 50-65%. The Ti02 pigment that is present in the spent steam which is the starting material in the present process can be obtained by the combustion of titanif25 erous salts from the chloride process such as titanium tetrachloride or by hydrolyzing, filtering, washing and calcining a soluble titanium salt from the sulfate process. The crude Ti02 pigment obtained from either 30 the chloride process or the sulfate process is cooled to a temperature ranging from 300-800C, e.g., by pro cedures disclosed in U.S. Patents 2,833,637 and 2,721,626. Separation of the cooled gaseous products from the Ti02 phase can be by recourse to suitable 35 gravitational means, such as centrifugal or cyclone 3 DUP050302076 4 separation or by filtration or by electrostatic, ultra sonic and other means. The separated Ti02 pigment fraction from either the chloride or sulfate process is slurried in 5 water, and hydrous oxides of silica and/or alumina are applied by procedures disclosed in the art. Examples of such prior art describing how the addition of the silica and/or alumina is made, U.S. Patents Re 27,818 and 4,125,412, are incorporated by reference. However, 10 the TiC>2 source for the present process may be TiC>2 without silica and/or alumina. Soluble salts are removed from the treated slurry through a filtration/washing procedure in order to reduce the concentration of aqueous leachable salts 15 to conform to the American Society for Testing Materials specifications for pigment resistance, ASTMD476. The washed filter cake is dewatered on a vacuum rotary drum filter in order to reduce its water content .and thereby minimize energy consumption when 20 the filter cake is dried. Depending upon the hydrous oxide treatment levels, the water content of the filter cake before drying will typically range between 30 and 70% pigment solids content by weight. After the drying step, the pigment is sub25 jected to a final dry milling operation in a fluid energy mill which can also be referred to as a micronizer. The fluid energy milling involves the introduc tion of dry Ti02 pigment into the grinding chamber of the 30 micronizer where superheated steam accelerates the pigment aggregates to a high velocity in a spiralling vortex within the micronizer chamber. The grinding action occurs when the pigment aggregates collide with each other and with the walls of the grinding chamber. 35 The mixture of steam and ground pigment that leaves 4 DUP050302077 5 the fluid energy mill is routed through a cyclone class ifier which separates about 95% of the pigment stream from the spent micronizer steam. The spent steam and the remaining unseparated Ti02 (about 5%) is then treated 5 according to the invention. This remaining TiOz is re ferred to herein also as micronizer tailings. The process of the invention can be further described by reference to the Figure which is a schematic drawing that illustrates the present invention. Refer10 ring now to the Figure, the micronizer tailings stream 1 is scrubbed with a recirculating stream of a slurry of the micronizer tailings that pass through rotameter 3A. The Ti02 slurry becomes concentrated in Ti02 within the scrubber unit 2 and the enriched Ti02 slurry is then 15 separated from the uncondensed steam in the wet cyclone 4. The spent sjateam exits the wet cyclone 4 via 4A. The condensed Tio2 slurry is collected in a catch tank vessel 5 and recirculated by means of a high capacity pump 6 back to the wet scrubber 2 for additional con20 centrating. The specific gravity of the tailings stream is regulated by the addition of water 7 to the suction side of the high capacity recirculating pump 6, the rate of water addition being regulated by a nuclear density 25 measuring device that operates from radiation source 8 across the flow in line 9 to the radiation gauge 8a. The concentration of Ti02 solids is directly related to the optical density of the nuclear radiation that is trans mitted across the optical slurry pathway 9 by the 30 equation: -kCl Optical Density = In I = e 5 DUPO50302078 6 where IQ is the radiation intensity of the nuclear source, I is the intensity of the radiation after it is attenuated by the slurry stream, k is an attenuation coefficient that is a unique property of the absorbing 5 medium, C is concentration of the Ti02 in the slurry stream and 1 is the thickness of the optical pathway. The notation In refers to the natural logarithm and e refers to the natural exponential base 2.718. A change in the concentration of Ti02 in the slurry stream will 10 cause a proportional change in the optical density that is perceived by the detector portion of the nuclear density device, and this signal is converted to pressure in pressure/current converter 11 to throttle the control valve 10 that admits fresh water to the suction side of 15 the pump. A set point for automatic control of the system will be dependent upon the pumping characteristics of the concentrated Ti02 tailings slurry. This set point will correspond to a slurry concentration that is gen erally less than 70% solids. The volume of tailings 20 that must be disposed of will define the lower limit of concentration, usually 30%, that is economical to dispose of into the slurry product stream. The level in the catch tank is automatically controlled by measuring the hydrostatic pressure of the 25 slurry in the tank 5 with probe 12 and by electronically dividing this pressure measurement by the optical density signal that is a measure of specific gravity at electri cal divider 13. The mathematical equivalent to this ratio of pressure and density measures is a third 30 variable that is proportional to a density corrected level in the tank. The absolute level in the tank is regulated by this signal which is converted to pressure in the pressure/current converter 14 which only controls valve 15 in the export line 16 that carries the concen35 trated Ti02 tailings slurry to the finished product slurry manufacturing process. 6 DUP050302079