BR112020026581B1 - PROCESS FOR RECOVERING TITANIUM DIOXIDE FROM TITANIUM-CONTAINING MATERIALS - Google Patents

Abstract

PROCESS FOR RECOVERING TITANIUM DIOXIDE FROM MATERIALS CONTAINING TITANIUM. A process operating at super atmospheric pressure for leaching a titanium-containing ore with an HCl and producing titanium dioxide with integrated solvent extraction steps for removing iron from the leached ore and solvent extraction of a resulting enriched titanium raffinate for produce particles suitable for pigment grade TiO2 finishing. The process can integrate HCl recovery from the solvent recovery and solvent recovery steps. The process also produces commercial grade ferric chloride.

Description

CROSS REFERENCE FOR RELATED ORDERS

[001] This application claims the benefit of US Patent Application No. 16/022,603, filed on June 28, 2018. The entire contents of this application are incorporated herein by reference.

FIELD OF INVENTION

[002] This invention generally relates to the processing of titanium-containing ores and the production of titanium-based products, such as pigment grade titanium dioxide.

BASICS OF THE INVENTION

[003] There are known methods for converting titanium-containing ores into titanium dioxide, metallic titanium and related pigment grade products for use in coatings applications. Such known methods have focused on manufacturing using sulfuric acid, chlorine or aqueous hydrochloric acid as leachants to extract titanium from a variety of ores. Several known methods refer to conditions, compositions, processing steps and mechanisms for ore processing, but they have a number of disadvantages, including commercial viability, efficiency and environmental issues. Typical conventional methods use batch rather than continuous processes and fail to effectively convert ore components into useful and/or environmentally friendly materials. Limitations in conventional methods often limit the process conditions and ores suitable for processing.

[004] Iron recovery processes can also produce another useful product. Such products include ferric chloride for use as a coagulant in water treatment processes. Currently, residues from iron pickling, such as cold rolling milling, provide a common source for such coagulants. However, such sources leave significant cationic content and may have residual acidity (excess HCl will degrade the pH of the water), both of which undermine the use of such sources as a water treatment coagulant.

[005] Thus, there is a need for new and distinct technologies to advantageously process titanium-containing ores and produce titanium dioxide, as well as other products.

SUMMARY OF THE INVENTION

[006] This invention overcomes or improves the above-described problems of the prior art with a process that efficiently recovers metal values and other products from titanium-containing ore in a unique arrangement of specialized steps. Implementations of processes and systems described herein can facilitate the processing of titanium ore in a commercially viable manner with materials to produce titanium dioxide products that are pigment grade. The process can also provide a superior ferric chloride solution for coagulant use in water treatment.

[007] Some embodiments of this invention use specific flow continuous processes and unit arrangements to increase economic viability and reduce environmental impacts relative to those of existing commercial processes. The unique ore conversion approach employed in the processes and systems of this invention can eliminate or improve the various foregoing restrictions on ore processing and use conditions, while still producing commercially acceptable pigment grade products efficiently and economically. Thus, the general technology and various technological aspects described in this document are distinct from and advantageous with respect to conventional and known technologies.

[008] Implementations of processes and systems described in this document facilitate the processing of titanium ore or materials more efficiently to produce pigment grade titanium dioxide products, as well as obtain other by-products, in a commercially viable manner. Preferred implementations use a continuous process and various features described in this document to increase economic viability and reduce environmental impacts common to existing business processes. Any of the process steps described herein may use the vessel configuration as described or another suitable type of pressure vessel and internal parts. This invention also provides a greater benefit in that it comprises the use of pressurized vessels and these can employ inert gases such as N2 or CO2 for diluent and medium pressure purposes where appropriate.

[009] This invention improves on conventional methods that use batch rather than continuous processes and fail to solve previous problems of converting ore components into useful and/or environmentally friendly materials. Conventional methods also suffer from limitations in process conditions and limitations in ores in known processing methods. Implementations of processes and systems described in this document facilitate the elimination of various constraints on processing conditions and provide a unique approach for converting ores into commercially acceptable pigment grade products with concomitant economic benefit.

[010] In a comprehensive and broad process embodiment, this invention is a process for producing a pigment grade titanium oxide product. The process leaches a feed material comprising titanium-containing ore at high intensity with an acid leaching solution comprising water and HCl to form a leaching slurry optionally having a solids content of at least 20% by weight on a total slurry basis and separates the leach slurry into a solid waste stream and a fertile liquor comprising titanium and iron compounds. Solvent extraction then removes iron compounds from the fertile liquor and provides an iron-enriched stream and an iron-depleted stream. Solvent extraction then extracts titanium compounds from the iron-depleted stream and produces a titanium-enriched stream and a titanium-depleted raffinate stream, and recovers HCl from the iron-enriched stream and the titanium-depleted raffinate stream for reuse. in the leaching stage. Hydrolysis of the titanium-enriched stream under plug flow conditions produces a hydrolyzate stream comprising TiO2.H2O particles. All previous steps of the process operate in super atmospheric conditions. Drying the hydrolyzate stream under mild conditions removes pore water while inhibiting rupture of the TiO2.H2O particles to produce a dry hydrolyzate stream that undergoes calcination of the TiO2.H2O to produce a calcined TiO2 material suitable for conversion to a product of pigment grade titanium oxide.

[011] This embodiment can incorporate a wide range of variations. In a simple variation, the leach slurry optionally has a solids content of 20% by weight to 35% by weight. In another variation, HCl mixed with water has an HCl concentration above 11N. In another variation, the water and HCl in the acidic HCl solution have an HCl concentration above the HCl azeotrope concentration. In yet another variation of the above embodiments, plug flow conditions are provided by a reactor arrangement. Other embodiments of this invention may vary the steps and arrangements as taught herein.

[012] A more limited process embodiment of this invention leaches a feed material comprising titanium-containing ore having an average particle size below 100 microns at high intensity, by contacting the feed material with an acidic leaching solution comprising water. and HCl at an HCl concentration above 11N to form a leach slurry having a solids content of 20 to 35% by weight on a total slurry basis. This arrangement leaches the slurry into a solid waste stream and a fertile liquor comprising titanium and iron compounds, and then adds chlorine to the fertile liquor to promote the conversion of FeCl2 (ferrous chloride) to FeCl3 (ferric chloride). This forms a fertile treated liquor from which solvent extraction removes FeCl3 and to produce a FeCl3-enriched stream and a FeCl3-depleted stream. Additional solvent extraction removes titanium compounds from the depleted FeCl3 stream to produce a titanium-enriched stream and a titanium-depleted raffinate stream that is returned to high-intensity leaching as recycling. Plug-flow hydrolysis of the titanium-enriched stream at a temperature of 110 to 125°C produces a hydrolyzate stream comprising TiO2.H2O particles. All previous steps and operations take place at super atmospheric pressure. The TiO2.H2O particles are subjected to drying under mild conditions of 100 to 250°C for 2-4 hours to remove pore water while inhibiting the rupture of the TiO2.H2O particles to produce a dry hydrolyzate stream. Calcination converts the dry TiO2.H2O in the hydrolyzate stream to TiO2 and produces a calcined TiO2 material that further finishing can convert to a pigment grade titanium oxide product.

[013] A simplified independent aspect of this invention is a high-intensity leaching method for leaching titanium from a titanium-containing ore. The method contacts a feed material comprising a titanium-containing ore with an acidic leach solution at super atmospheric pressure to form a leach slurry having a solids content above 20% by weight on a total slurry basis. The acid leaching solution comprises water and HCl at an HCl concentration of at least 5% by weight above the water-HCl azeotrope concentration.

[014] Another independent aspect of this invention is a hydrolysis method for hydrolyzing a titanium-rich stream to produce a hydrolyzate stream comprising TiO2.H2O particles. The method includes feeding the titanium-rich stream into a plug flow reactor at super atmospheric pressure and a temperature of 110 to 125°C.

[015] The invention also provides a method for drying a hydrolyzate stream comprising TiO2.H2O particles under mild drying conditions maintained in a range of 100 to 250°C for 2-4 hours. These mild conditions remove pore water from the hydrolyzate stream while inhibiting rupture of the TiO2.H2O particles, to produce a dry hydrolyzate stream with intact TiO2.H2O particles and a moisture content below 5% by weight.

[016] One form of the system of this invention produces a pigment grade titanium oxide product. The system delivers a feed of titanium-containing ore to a leaching unit configured for high-intensity leaching by contact with an acidic leaching solution comprising water and HCl at an HCl concentration above 11N to form a leach slurry having a content of solids between 20-35% by weight on a total paste basis. A separator in the system separates the leach slurry into a solid waste stream and a fertile liquor comprising titanium and iron compounds to which a chlorine addition unit supplies chlorine which contacts the fertile liquor with chlorine to promote the conversion of FeCl2 to FeCl3 to form a fertile treated liquor. The system contacts fertile liquor treated with an organic solvent in a first solvent extraction unit configured to remove FeCl3 and provide an enriched FeCl3 stream and a depleted FeCl3 stream. A second solvent extraction unit with a system configuration for receiving the depleted FeCl3 stream and an organic solvent composition extracts titanium-containing compounds from the depleted FeCl3 stream to produce a titanium-enriched stream and a depleted raffinate stream. titanium. An HCl recovery unit of the system receives the enriched FeCl3 stream and the depleted titanium raffinate stream is configured to recover a high concentration HCl stream for reuse in the high intensity leaching unit. A hydrolysis unit configured to receive the titanium-enriched stream converts it into a hydrolyzate stream to produce a hydrolyzate stream comprising TiO2.H2O particles under plug flow conditions at a temperature of 110-125°C. The system configuration operates all previous steps at super atmospheric pressure. The system incorporates a drying unit to dry the hydrolyzate stream under mild conditions to remove pore water while inhibiting disruption of TiO2.H2O particles, to produce a dry hydrolyzate stream. A calcination unit of the configuration dries the hydrolyzate stream and converts TiO2.H2O to TiO2, thereby producing a calcined TiO2 material that a final conversion unit of the system can convert into a pigment grade titanium oxide product.

[017] Additional independent aspects of this invention include reactors for use therein. In one such aspect, a hydrolysis reactor comprising a boustrophedonic reaction conduit having an inlet that receives the titanium-rich stream, and an outlet that releases the hydrolyzate stream for further processing. The reactor arrangement may include temperature and pressure controls to operate at a temperature of 110 to 125°C and super atmospheric conditions. In another reactor aspect of this invention a hydrolysis reactor is used to hydrolyze a titanium-rich stream and a hydrolyzate stream comprising TiO2.H2O particles is produced by passing through a plug flow reaction conduit having a inlet that receives the titanium-rich stream, and an outlet that releases the hydrolyzate stream. The reactor operation includes temperature and pressure control systems to maintain a temperature of 110 to 125°C and super atmospheric pressure.

[018] Other technological aspects of the invention apply to the processing of titanium-containing chains. For example, an advantageous reactor design hydrolyzes a titanium-rich stream to produce the hydrolyzate stream comprising TiO2.H2O particles that includes feeding the titanium-rich stream into a plug flow reactor and/or a boustrophedonic reaction conduit. operated above atmospheric pressure and at a temperature of 110 to 125°C. The drying method also provides ore processing benefits by drying the hydrolyzate stream of TiO2.H2O particles under mild drying conditions of 100 to 250°C for 2 to 4 hours. Gentle drying removes pore water from the hydrolyzate stream while inhibiting rupture of the TiO2.H2O particles, thereby keeping the dry particles in the hydrolyzate stream intact while reducing the moisture content, optionally to less than 5% by weight. Specific features utilized in the practice of the invention, alone or in combination, include selectively operating certain process steps above atmospheric pressure, providing a high-intensity leaching stage to leach titanium from the feed material, and operating an HCl recovery system that breaks down the HCl-water azeotrope to regenerate a high-concentration (i.e. above azeotrope concentration) HCl material for reuse in the leaching stage.

BRIEF DESCRIPTION OF THE DRAWINGS

[019] The additional description of the invention, together with the drawings, provides additional unique technological features for incorporation into the practice of the invention.

[020] Figs. 1a and 1b show a flow diagram for processing titanium-containing ore.

[021] Figs. 2a and 2b show an alternative flow diagram to that shown in Figs. 1a and 1b for processing titanium-containing ore.

[022] Figs. 3a-3g are schematic diagrams of hydrolysis reactor configurations.

[023] Fig. 4 is a schematic of an arrangement for a hydrolysis reactor.

DETAILED DESCRIPTION OF THE INVENTION

[024] The techniques described herein refer to improved processes and systems for processing titanium-containing ore and producing titanium dioxide, particularly pigment grade. The processes and systems described in this document include several innovative features that facilitate increased efficiency and/or product quality, as will be described in more detail below.

Definitions

[025] The term “about” means a variation of plus or minus 5% of any declared value.

[026] The notation “bar-g” means gauge pressure.

[027] The term “super atmospheric pressure” means pressure above atmospheric pressure.

Titanium-containing ores and preparation

[028] In some implementations, the process can be used to process one or more types of titanium-containing ore, such as rutile, which has a high Ti content, and/or ilmenite, which has a notably lower Ti content. Other sources of titanium can also be used as raw materials for the process. For example, sources of titanium may include upgraded slag, mine tailings, and the like. In some implementations, the process includes preparing a titanium-containing feedstock from one or more sources and includes, for example, at least any amount from 20% by weight to 50% by weight of Ti in the feed into the process.

[029] The process can accept mined ores of various compositions having a suitable particle size and for most applications will have an average diameter of less than 100 microns, preferably less than 75 microns, and typically between 50-100 microns, 60 -90 microns, or 70-80 microns. Commercially available ores typically do not meet this specification and will be subjected to milling in an initial pretreatment step of the process. Preferably, the ore feed comprises ilmenite with a relatively low titanium oxide content of 35-55% by weight, 40-50% by weight or 45% by weight, for example.

[030] Multiple different titanium sources can be mixed upstream, such that the ground material fed into the process has certain predetermined or desired properties, for example, Ti content, particle size and/or other compositional properties.

Detailed description of the drawings

[031] Figs. 1a,b and 2a,b show two versions of the many different flow arrangements for practicing the process of this invention. These figures are schematic and do not show all of the related equipment and controls that are well known and commonly used to practice such flow arrangements. Reference numbers refer to the contents of the conduits that touch your main lines.

[032] In the flow arrangements of Fig. 1a and 2a, the titanium-containing material 10 undergoes a size reduction pretreatment carried out by the grinding step 12, which may include sieving to produce ground material 14. The preferred ground material It has a relatively consistent grain size.

Acid leaching

[033] The ground material 14 goes through one or more leaching steps carried out in the respective leaching units. Preferably, leaching occurs continuously, as shown by a continuous leaching step 16, in which the ground material is brought into contact with an acidic leaching solution 18 (also referred to as the leachant). A leaching solution 22, preferably comprising a high concentration of HCl, passes to the continuous leaching step 16.

[034] Preferably, leaching 16 is carried out with a relatively high solids content and high acid concentrations. For example, leaching typically occurs with a solids content at least greater than 10% by weight, more typically at least greater than 15% by weight, and in many cases greater than 20% by weight. Common solids content ranges in leaching range from 20 to 35 wt%, preferably 25 to 35 wt%, and often in a narrow range of 27 to 33 wt%. Acidic conditions can be provided using a normal leach solution having an HCl concentration of about 11 to 13N, 11.5 to 12.5N, or about 12N. The HCl solution may be supplied with an HCl content of at least 30% by weight, or between 30 to 37% by weight, or 35 to 37% by weight, for example. The acidic solution can also be augmented with anhydrous HCl. Conventional technologies for leaching operations tend to use low solids (e.g. below 10% by weight) and low acidity levels (e.g. below 10N). This invention uses a considerably higher than conventional ore solids content in leaching, which is notably higher than conventional levels, since dilution is often the basis for driving this conversion.

[035] Fig. 1a shows the acid leaching solution 18 prepared by combining leaching water 20 and a source of HCl 22 before supplying the acid leaching solution 18 to the leaching unit. In this scenario, water and HCl can be mixed in a mixing unit and then the acidic leaching solution 18 can be fed into the leaching unit through a single inlet.

[036] Alternatively, Fig. 2a shows water 20 and HCl source 22 supplied through separate inlets in leaching step 16 to form the acidic leaching solution in situ within one or more vessels. Introduction via multiple individual streams can improve control reaction parameters.

[037] The leaching step 16 can use a combination of feeding a mixture of HCl and water as in Fig. 1a and also as a separate stream as in Fig. 2a. Thus, the leaching unit 16 can accommodate various ways of feeding leaching solution with corresponding inlets and flow controls. The source of HCl may include HCl recovered from a recycling system, as described in detail below.

[038] Anhydrous HCl can be added to the leaching step 16 at one or more points in the digestion train and can stabilize the proton content of the solution as chloride is absorbed by the reaction to make the ore components soluble as chloride and/or or hydroxy chloride salts. The continuous leaching step 16 can thus be equipped with appropriate inlets for adding compounds of different streams and additives at different locations. The leaching step 16 may inject HCl gas into a leaching vessel through distributors located therein.

[039] High-intensity leaching can provide operational advantages and benefits in the titanium extraction process of this invention. Some benefits include reduced equipment sizes, reduced reaction time (e.g. by 50%) and an extraction of titanium above 90% by weight of the ore feed. Energy consumption is also reduced as exothermic reactions generate a significant level of thermal energy in the leaching reaction system.

[040] Preferably, HCl comprises the substantial acidifying component of the acid solution used in leaching step 16. However, some alternative implementations may employ any process modification necessary to use HCl in combination with other compounds and/or other acids. The process may use overpressure to contain volatile components such as HCl vapors.

[041] The continuous leaching step 16 produces a leaching slurry 24 that passes to a solid-liquid separation step 26 that produces a solid residue 28 together with a fertile liquor 30 depleted in solid material. A separation step 26 may use any type of solid-liquid separator, including those that use one or more separation stages. Possible methods for separation include centrifugation to remove suspended solids. Additionally, the solid waste may be subjected to additional downstream treatments to remove residual liquid or otherwise prepare the solid waste for disposal (e.g., via landfill, as shown in Figs. 1b and 2b). For example, a washing step (e.g., acid washing) can recover compounds such as Ti from the solid residue with the resulting washing liquid recycled back to the leaching unit.

Iron removal

[042] Iron is then removed from fertile liquor 30. Methods for removing iron include a ferrous chloride conversion step 32. Iron recovery continues with a solvent extraction (SX) step 34 (also known as a solvent exchange process). The conversion step 32 adds chlorine 36 to the fertile liquor 30 to promote the conversion of FeCl2 to FeCl3 and produce an enriched ferric chloride solution 38 (fertile leach solution - PLS) for extracting iron from it in the solvent extraction step of iron 34.

[043] Various organic solvents 40 can be used for the iron solvent extraction step and their selectivity for metal in the fertile liquor will vary. Typical solvents are ketone hydrocarbons and, preferably, branched-chain ketone hydrocarbons. Suitable extractive solvents include ketones of the general iso-Cx ketone structure, with a particular preference for ketones with tertiary carbon atoms. The choice of extractive solvents generally depends on the desired solvent selectivity under the desired operating conditions. Specific ketones suitable for the SX step of the process include methyl isobutyl ketone (MIBK), diisobutyl ketone (DIBK), hexyl ketones alone or in combination and with other solvents.

[044] The most useful temperature conditions in the SX step generally vary with the selected solvent composition, as well as the composition of the fertile liquor. The most suitable solvent compounds have relatively low flash vaporization points and are quite volatile under typical operating temperature conditions in SX. SX stage temperatures generally range from 35 to 65°C. Consequently, the SX system will normally operate under positive pressure to prevent the release of volatile solvent compounds. A vent (not shown) is also provided to remove organics before releasing inert gas (e.g., nitrogen, CO2 are potential options for inert gas) to the atmosphere after flushing.

[045] The Fe solvent extraction step arrangement (which can also be referred to as the solvent exchange process) recovers high concentrations of solid metals from the PLS. The invention uses a typical SX organic circuit to clean the solvent by extracting cells, washing cells and removing cells that extract, purify and separate metals from a given solvent to provide purified Fe and Ti metals. The method of this invention contrasts with other methods that rely on higher dilution to increase solvent effectiveness.

[046] The solvent composition may include a modifier, a viscosity reducer and an extractive solvent. Suitable modifiers include Exxal 13® manufactured by Exxon comprising a distillation cut from a propylene oxide production having a branched chain oxyhydrocarbon and a specific steric composition containing polymerized propylene and oxygen units. Suitable viscosity reducers include kerosene having a boiling range different from that of conventional jet fuel. The viscosity reducer reduces the viscosity of the solvent composition to allow for better interaction in the mixing systems of the SX unit(s).

[047] Some arrangements of this invention use a single recirculation approach for purification of the metal extractors in both the Fe (and Ti circuit, as described later). This approach purifies the Fe extractor in the Fe circuit (also applicable to Ti extraction, as described later) with essentially complete removal of the solvent for Fe recovery. Essentially complete separation typically carries away some undesirable cations. The design of the recycling system retains some Fe in the solvent, such that the solvent conditioning step can eliminate at least some of the undesirable cations. For example, the invention may facilitate the recovery of Fe with an SX, whereby the Fe “eliminates” the Ti in the iron solvent extraction stage such that the Ti remains in the Fe raffinate rather than being extracted with FeCl3.

[048] The solvent extraction step 34 feeds the enriched ferric chloride solution 38 into at least one vessel together with an organic Fe extraction solvent 40 to produce an iron-enriched liquor 42 and a fertile iron-depleted liquor 48. Treatment of iron-enriched liquor 42 can produce one or more final products.

[049] Fig. 1a shows the recovery of iron-enriched liquor 42, often following an evaporation step (not shown) that forms an aqueous concentrate in a manner described below in more detail. Typically, this concentrate has a composition suitable for use as a coagulant in water treatment and purification. The typically very high purity of FeCl3 in iron-enriched liquor 42 facilitates evaporation and the formation of a ferric chloride 43 product.

[050] Fig. 2a shows an implementation where an iron-enriched liquor 42 is subjected to additional treatments to recover HCl from the liquor. This configuration uses crystallization, as described below in more detail.

[051] A second leaching stage (not shown) digests Fe before the crystallization stage. Crystallization of digested Fe to form FeCl2 crystalline material can remove significant amounts of Fe from liquor 42. Some implementations of this invention can recover up to 25% by weight of crystalline FeCl2 (e.g., potential yield of Fe2 crystallites from this second leaching stage.) Proper control of acid concentration, temperature conditions, and solubility of acid salts in the second leaching will promote crystallization of FeCl2. In contrast, these parameters will vary significantly when seeking to avoid crystallization of digested Fe. Removal of iron can provide a yellow pigment precursor. Ferric Chloride 43 finds multiple product uses.

[052] The iron extraction operation can also or alternatively convert iron-enriched liquor 42 into FeOOH through a secondary process (not shown). Conversion to FeOOH may involve neutralization (e.g. with caustic soda) to precipitate FeOOH from the fertile leach solution, which is partially crystallized as FeO in the process. This alternative step neutralizes the FeCl2 with NaOH under controlled temperature to precipitate the hydroxide into crystalline configurations with quality suitable for pigment grade use. Specifically, FeOOH is commercially useful as a yellow pigmentation additive.

Solvent extraction (SX) of Ti

[053] With reference to Figs. 1b and 2b, a depleted fertile liquor of iron 48 produced by solvent extraction of iron 34 passes to a solvent extraction of Ti 50 to extract Ti and produces an enriched liquor of Ti 52 and a raffinate 54. The extraction step 50 uses an organic solvent 56. In a broad sense two solvent extraction steps 34 and 50 operate as a general titanium purification system to separate titanium from other components of the fertile liquor 30.

[054] A variety of solvents will work on the Ti SX. Preferred solvents are those previously described for using Fe SX. Most preferably, Ti SX and Fe SX will use the same solvent. The solvent composition may also include a modifier (of the type described above), a viscosity reducer (of the type described above), together with the extractive solvent.

[055] The Ti SX step arrangement recovers high concentrations of solid metals. As in the case of iron recovery, the SX 50 step also contrasts with other methods that rely on higher dilution to increase solvent effectiveness and may again employ the unique recirculation approach as previously described for iron 34 solvent extraction. Complete solvent removal for Ti recovery can carry away undesirable cations as described for Fe solvent extraction (as can happen with Fe solvent recovery) and the recycling system and solvent conditioning step retains some Ti in the solvent to eliminate at least a portion of these cations. Ti solvent cleanup will preferably use an organic circuit as previously described. In the case of Ti, the organic circuit processes a supply of mainly Ti.

[056] The present process produces high concentrations of Fe and Ti in the feed for the solvent extraction units. The process can produce concentrations typically 2 to 3 times higher than conventional processes and in the range of 60,000 to 70,000 g/l. This distinctive feature can facilitate smaller equipment, faster settling times in the SX, and easier solvent removal and washing to recover the metal(s) of interest. While the SX hardware (e.g., equipment such as piping and vessels) may be conventional, the mixing and settling operating conditions are much more efficient with respect to solvent consumption and residence time in the SX unit cells.

[057] In many cases, the Ti 52-enriched liquor passes as a feed for hydrolysis. Liquor 52 control can adjust its composition to meet specific standards (e.g., TiOCl2 and chloride concentration) that facilitate hydrolysis to exact size and morphology standards.

Hydrolysis

[058] Figs. 1b and 2b show Ti-enriched liquor 52 passing to the hydrolysis step 58 to produce the hydrolyzate 60. The hydrolysis step 58 can use different process control parameters and any suitable hydrolysis reactor design, such as hydrolysis reactors. 62 shown in Figs. 3 and 4 and described below.

[059] Hydrolysis reactors, such as hydrolysis reactors 62, operate under conditions that form TiO2.H2O particles. Highly suitable hydrolysis reactors are those that have a plug flow design. A plug flow design means substantially laminar flow with no appreciable back mixing. Preferred plug flow design reactors will have a Peclet number of at least 100.

[060] Preferably, the piston reactor will comprise a series of tubes containing mixing elements, such as tubes arranged in series and separated by in-line mixers. A variety of suitable in-line mixers will work, such as static mixers. Preferably, the configuration of the mixers in conjunction with the operating conditions (e.g., flow rate), will provide substantially forward-flow mixing with little or no back mixing. Unacceptably high return mixing can complicate residence time control and adversely affect particle size control.

[061] In some implementations, the hydrolysis reactor 62 is configured as a Buss-type reactor to promote intense mixing (as illustrated and offered by IPP - International Process Plants). A Buss-type reactor constitutes a new approach for TiO2 production.

[062] The residence time and temperature in the hydrolysis reactor are controlled to provide particles having suitable morphology (rounded shape) and approximately the desired size for commercial pigment grade TiO2. Preferably, the particle size ranges from 180 to 400 nm in distribution (e.g., as measured by an optical analyzer which typically generates a bell curve). The hydrolysis reactor operates at a pressure that controls the generation of HCl in the reaction and at a temperature well above the azeotropic boiling point at atmospheric pressure. In most cases, the hydrolysis operates at a pressure of up to 5 bar-g, preferably 0.15 to 4 bar-g, more preferably 0.15 to 2 bar-g and most preferably 0.15 to 0. 25 bar-g; and generally at a temperature of up to 125°C, and preferably 110 to 125°C, and more preferably 115 to 120°C.

[063] Conventional hydrolysis methods operate under atmospheric conditions that limit the temperature to about 104°C which, in turn, slows down the reaction considerably and fails to provide improved morphology for the hydrolyzed product. Pressure control also allows for controlled ventilation that protects the surrounding atmosphere near the reactor and allows for the recovery of substantially all of the HCl produced by the hydrolysis reaction. A preferred implementation of the hydrolysis reactor described herein operates at elevated pressure and temperature to form suitable morphology and particle size of the TiO2 hydrolyzate.

[064] Conventional hydrolysis processes have used batch or stirred tanks operating at the boiling point of the HCl azeotrope under atmospheric conditions. Figs. 3a-3g illustrate some of the preferred configurations for the hydrolysis step 58 and associated reaction zones in the form of a reaction conduit 66 comprising a tube. The reaction conduit tube type 66 may use any configuration that preferably provides an extended tube length. Although Figs. 3a-3g show a single conduit, the hydrolysis step 58 may use multiple reaction conduits operating in series and/or parallel. The configurations of the hydrolysis reactor 62 also include a feed inlet 68 and a product outlet 70 at the ends of the reaction conduit 66.

[065] The reaction conduits 66 may include one or more in-line mixers 71, as depicted in Figs. 3a-3d. Preferred configurations place the mixer in-line at regular intervals and typically on straight portions of the conduits. Thus, the invention will preferably use at least one and more preferably multiple mixers distributed along the length of the reaction conduit.

[066] Figs. 3a-3g show just a sampling of the wide variety of shapes for the tube that the reaction conduit 66 can take. The reaction conduit 66 may comprise one or more linear lines. Figs. 3a and 3d show the respective arrangements of a single line and two linear pipe sections connected by a curved section. Figs. 3b, 3c and 3e show the reaction conduit 66 in a boustrophedonic configuration, i.e., serpentine. Fig. 3f illustrates a spiral configuration for the reaction conduit 66. Additional configurations for the reaction conduit include pulse waves. Fig. 3g represents a square wave array of pulse waves as a reaction conduit 66 configuration.

[067] As shown representatively in Fig. 3b, the hydrolysis step 62 may also include one or more temperature sensors 72 coupled to a controller 74, as well as a residence time sensor 73 and controller 85. The hydrolysis reactor may generally operate adiabatically by controlling the inlet flow of cores and TiOCl2 in such a way that the temperature of the fluid does not decrease substantially from that of the inlet feed. Measuring effluent particle size by optical analysis prior to feeding downstream (e.g., to the dryer) can provide inlet control set points.

[068] Figs. 3a-e show auxiliary elements of the hydrolysis reactor 62. Figs. Fig. 3a-3d show each reaction conduit 66 within a housing 74. Fig. 3e shows a reaction conduit 66 in a boustrophonic arrangement without a housing and conduit held in place by a support structure 75 having arms extending vertically to from a base.

[069] Fig. 4 illustrates another example of the hydrolysis reactor 62. A heating jacket 77 surrounds the reaction conduit 66 of the hydrolysis reactor 62 to receive and expel a heating fluid to conductively heat the hydrolysis fluid as it passes through conduit 66. Heating fluid typically enters heating jacket 77 at the downstream end of reaction conduit 66 and exits at the upstream end. Although Fig. 4 shows a single flow of heating fluid through tube 66, heating fluid may enter and/or exit reaction conduit 66 at various points anywhere along its length. The hydrolysis fluid may also pass through one or more plug flow elements 67 that completely or partially obstruct the path through the reaction conduit 66.

[070] Fig. 4 also shows the flow path of hydrolysis fluid from the feed tanks to a storage tank. Preferably, the separate feed tanks will supply cores and TiOCl2 which pass through a mixer 79 and then enter the reaction conduit 66 through an inlet 68 and exit through an outlet 70. A back pressure valve 81 controls the pressure. in the reaction conduit 66. Fig. 4 shows a typical storage tank that communicates with the outlet 70 to receive the hydrolysis effluent.

[071] Cores can be added based on various parameters and methods; produced by various methods; and added to the reaction conduit 66 in a variety of ways other than those represented by Fig. 4. Addition of nuclei often ranges from 0.1 wt% to 2.5 wt% and sometimes at a concentration of less than 1.0% by weight. Cores can be produced using a neutralization step to precipitate TiOCl2 in the hydrolysis feed. The size of the cores typically falls below 35 nm in size and preferably below 25 nm in size. The above description is not a limitation of the properties of cores, production methods and addition methods.

Pre-calcination/drying

[072] Figs. 1b and 2b show the hydrolyzate stream 60 passing from the hydrolysis reactor 58 to a solid-liquid separation section 99. The separation section 99 may use any type of separation and often employs a centrifuge or filter, typically in plate form. , to remove the concentrated acid and wash water from the hydrolyzate contained in the acidic medium of the hydrolysis reactor. A fraction containing solids 76 including TiO2.H2O particles passes to a pre-calcination stage 78 to remove moisture prior to pre-calcination or calcination.

[073] The pre-calcination stage 78 or stage removes or reduces moisture in the solid fraction before undergoing calcination at elevated temperature. Preferably, the pre-calcination stage 78 operates under low intensity conditions, in which time and temperature control during drying prevents the boiling of interstitial moisture in the solid fraction. Avoiding rapid boiling prevents or inhibits pressure from creating internal particle pressure on the particle and resulting in particle rupture or explosion, much like popcorn popping. Conducting the pre-calcination drying step in a manner that slowly removes any moisture, including surface, unbound and bound water contained in the particles, will prevent pressure build-up and prevent or mitigate particle damage. Thus, the pre-calcination stage 78 gently dries the solid fraction 76 to produce a dry solid fraction 80 containing TiO2.H2O. The dry stream from the pre-calcination stage 78 may pass through a solid-liquid separation section 79 which supplies the dry solid fraction 80.

[074] The drying unit typically operates at temperatures of 100 to 250°C with a preferred range of 120-230°C and a residence time typically of no less than 2 hours and no greater than 4 hours. These operating conditions can cause corrosive damage to internal parts by releasing residual HCl in the TiO2.H2O particles which combine with the evolution of water to make a corrosive dilute acidic material. This acidic material can corrode the usual stainless steel material used for such equipment. Constructing the internal parts of the dryer with corrosion-resistant materials protects against such damage.

[075] This dried solid fraction 80 can then pass to a calcination step 82. In some implementations, the output from the dryer is a free-flowing solid with only a lower moisture content of 1 to 3% by weight and, preferably, about 2% by weight or less. Before entering the calcination step 82, the solid fraction may receive additives for agglomeration control purposes, etc.

Calcination

[076] The dry solid fraction 80 passes to a calcination step 82 to produce a TiO2 hydrate. Calcination can use any suitable equipment and operating conditions. Preferably, the calciner comprises a direct firing design and more preferably the calciner will use indirect firing gas circulation. Typically, calcination includes zone control to manage temperature escalation and will include multiple control points. BET surface area measurements can provide a control parameter indicating the desired reduction that occurs during the calcination heat cycle of the calciner. TiO2 hydrate has a typical surface area of 100 m2/g or higher and the surface area of calcination products should ideally be less than 15 m2/g and preferably less than 10 m2/g. The invention can gain a particular advantage when using a calciner temperature in a range of 900 to 1050°C.

[077] The calcined TiO2 particles pass to finishing step 84. Preferred direct firing units can create a color problem in TiO2, caused by incomplete combustion of circulating gases that deposit carbon on the surface of the particles. The final calciner temperature governs the reduction of particle surface area to create a surface on the particles suitable for surface coating of chemicals added in the finishing process. In most cases, calcination operates at a pressure of up to 5 bar-g, preferably 0.15 to 4 bar-g, more preferably 0.15 to 2 bar-g and most preferably 0.15 to 0. 25 bar-g.

Finishing and packaging

[078] The calcined material 83 may undergo additional treatments, such as wet and/or dry grinding to remove agglomerates formed in the calciner and/or finishing by adding surface coatings that may include metal oxides to impart strength, weathering resistance, gloss of the surface and other coating properties. Treatment equipment and methods include parallel agitated tanks that receive inorganic salts of relevant metals (e.g., Zr, Al, Si, etc.) and/or oxygen-functionalized resins such as methoxy hydrocarbons to cause precipitation of the finished material. from the additive containing solution out of solution. The precipitated material may undergo sizing and jet milling to remove residual materials and aggregates from the coating process. The final product can then be spray dried and packaged for shipment to commercial users.

[079] The finishing treatments 84, schematically shown in Figs. 1a and 2b, are generally selectively selected to meet recipes and specifications provided by recipients of finished materials or specifications dictated by customer requirements. Thus, the process produces ground calcined titanium dioxide which, with or without optional coatings and additional components, serves as a component of final or intermediate products. Figs. 1b and 2b also show finishing products 84 passing to packaging 86.

HCl recovery and recycling arrangements

[080] The arrangement of the process in Figs. 1a,b differs from Figs. 2a,b in their recovery of HCl and processing of rafinate 54. Both arrangements show recovery steps coupled to solvent extraction steps 34 and 50, followed by recycling of HCl to leaching step 16.

[081] Both arrangements for recycling HCl can use sulfuric acid to dehydrate the dilute HCl streams produced by this invention for reuse of a concentrated HCl solution. Thus, the chemistry of HCl recovery steps and flows can be adapted to suit different processing arrangements and product needs. Bringing dilute HCl streams, which can be recovered from any number of points in the process, into contact with sulfuric acid dehydrates the HCl and creates metal sulfate salts contained in the recycled acid. Subsequent removal of water from the dilute acid (e.g., through evaporation) provides a concentrated HCl for recycling to leaching step 16. The HCl recovery system may also receive chloride sources from internal sources and/or to balance the recycled HCl. Chloride balance in the process can be maintained to facilitate high process stability. Such balance includes dealing with chloride excesses and chloride deficiencies as they occur, to maintain the desired properties of the recycled acid and the overall stability of the continuous leaching step.

[082] The different HCl recovery steps of Fig. 1 and Fig. 2 show how the process of this invention can advantageously control the use of chloride based on the desired titanium dioxide production and its composition. The embodiments of the invention shown and described reduce energy consumption in the recycling cycle and can close the process loop to fully recycle HCl from the process. Conventional methods tend to use roasting to produce byproducts from a TiO2 process (pyrometallurgical approach), such as Fe2O3 for iron removal or MgO for magnesium removal, but these conventional methods are capital and energy intensive and do not economically compensate for recycled chloride for the TiO2 process.

[083] Many configurations of the HCl recovery system can recover an HCl stream with an HCl content above the HCl-water azeotrope of 20.24% by weight of HCl. Various azeotrope breaking techniques recover high concentration HCl from the dilute HCl streams produced by the process. Azeotrope cracking techniques may include the addition of one or more cracking additives. The HCl content is preferably above the azeotrope concentration with water (i.e. above 20.24% by weight HCl), preferably at least 5% by weight, 10% by weight or 15% by weight above it. Accordingly, the multiple arrangement of the invention, including those of Figs. 1 and 2, can easily overcome the presence of an azeotrope.

[084] As highlighted above, this invention provides great flexibility in multiple ways of recovering and recycling HCl having the desired composition and concentrations, as well as adjusting the chemistry of the HCl recovery steps and flows associated with them to meet different processing needs. and product. Figs. 1 and 2 illustrate some of the alternative process steps for doing this. Figs. 1a and b detail a recovery and recycling arrangement that recovers iron liquor 42 as ferric chloride 43 without recovery of HCl from iron liquor 42. Fig. 2 shows an expanded array of HCl recycling and recovery integrated with additional processing.

[085] Fig.1 shows two HCl recovery paths. Both paths ultimately pass the recovered HCl 22 from an evaporation step 90 to continuous leaching 16.

[086] The simplest route passes raffinate 54 directly to evaporation step 90. All raffinate 54 can pass to evaporation 90 through this route. However, to gain more benefits from this invention, only a portion of the raffinate 54 goes to evaporation 90 and then leaching 16 through this route.

[087] Fig. 1b shows a more complex path of steps that treats at least a portion of the raffinate 54 by adding crystals of MgCl2.6H2O 87 and sulfuric acid 88 to all or a portion 55 of the raffinate 54. The resulting mixture 91 enters in an HCl recovery step 89 which produces a recovered magnesium sulfate 93 and a recovered HCl 95 which passes to the evaporation step 90. Again, all but preferably only a portion of the raffinate 54 follows this more complex path.

[088] Figs. 2a,b show three HCl recovery paths with different steps along with steps for supplying an HCl burner 90 with supplemental liquid 61. Each of the three independent paths can be used alone or in combination with one or more of the other independent paths. Figs. 2a,b also show the optional use of a supplemental liquid 61 that can function in conjunction with at least one or more of these three recovery paths. All recovery paths and the use of supplemental liquid feed the recovered material for continuous leaching 16 through an HCl burner 90 which electrolyzes the solution to produce HCl.

[089] The simplest route in Figure 2a passes at least a portion of the raffinate 54 directly to the HCl burner 90. All of the raffinate 54 can pass to the burner 90. However, more benefits are gained from this invention by passing only a portion of the raffinate 54 directly to the burner 90 and passing at least a portion of the raffinate through one or more optional series of treatment steps, such as those shown in Fig. 2a,b.

[090] A more complex step path shown in Fig. 2a, b (also substantially shown in Fig. 1) treats raffinate 54 by adding crystals of MgCl2 87 and sulfuric acid (not shown) to at least a portion of raffinate 54. The resulting mixture 91 passes to a spray roaster reactor 97 [[further description of the spray roaster pyrohydrolysis reactor may be helpful]] which produces magnesium sulfate 93 and recovered HCl 95 which passes to the HCl burner 90.

[091] As mentioned previously, Fig. 2a shows an arrangement that crystallizes at least a portion of iron-enriched liquor 42 in crystallization step 44. This step produces ferric chloride solution 45 containing crystals to provide ferric chloride 43. The solution of ferric chloride may have a composition suitable for commercial use and sale with characteristics as previously described in the context of Fig. 1a. The crystallization step 44 also produces enriched HCl 46 which can be passed alone or in mixture with the raffinate 54 to the HCl burner 90.

[092] Supplemental liquid recovery collects one or both of liquid 63 and/or liquid 65 from solid-liquid separation steps 99 and 79, respectively, via a liquid stream 61. Stream 61 passes one or a mixing of single source liquids 63 and 65 to an HCl burner 90 as a supplementary liquid (the letter F connects chain 61 in Fig. 2b to Fig. 2a).

Pressurized operation

[093] Conventional Ti recovery operations typically employed employ atmospheric conditions that make it relatively difficult to operate a viable commercial process. This invention can, with well-known standard piping, valve and venting equipment, readily process liquid and slurry streams under positive pressure, that is, an operating pressure above atmospheric pressure, also defined as super-atmospheric conditions. Pressurized operation greatly improves the efficiency and effectiveness of the process over standard prior art systems. Any and preferably all leaching, solvent extraction, hydrolysis and related recovery steps can use pressurized conditions. Solvent extraction (Ti and Fe) and hydrolysis preferably use pressurized conditions. The leaching and solvent extraction steps preferably operate at a pressure of up to 0.25 bar-g and preferably in a range of 0.15 to 0.2 bar-g. The hydrolysis step typically operates at a pressure of up to 3.5 bar-g and preferably in a range of 0.15 to 0.25 bar-g. Appropriate equipment for pressurizing and depressurizing streams can be used within appropriate piping, seals, inert gas systems, and the like.

Advantages of titanium processing techniques

[094] Thus, the implementations of processes and systems described in this document can facilitate the production of pigment grade titanium dioxide and/or the processing of various streams and materials in the context of extracting valuable materials from ore. Additional aspects of the process can be adapted to produce various other grades of titanium dioxide if desired, although pigment grade titanium dioxide is preferably produced. Various processes and systems described herein can also produce other product streams, such as yellow pigment materials and magnesium sulfate. Further processing may extract other compounds or materials from certain process streams, for example, if the original ore or feed material contains certain valuable fractions.

[095] The description of processes and systems in the context of Figs. 1 and 2 do not limit the scope of this invention to the specific arrangement of processing steps; input and output currents; and equipment shown on it. The process of this invention may use intermediate treatment units or operations not illustrated or described here that subject certain streams to processing between two units. For example, the fertile liquor 30 produced by the separator 26 could be subjected to an additional treatment step prior to the addition of chlorine 32. The solid waste stream 28 could undergo additional processing prior to disposal in a landfill, and/or the enriched stream of titanium 52 could receive processing before feeding the hydrolysis reactor 58. Thus, a given output stream from a unit can feed directly into the appropriate auxiliary processing. Accordingly, other units and unit operations may supplement the explicit description without departing from the invention as set forth herein.

Claims (14)

1. Process for producing a titanium dioxide product from a titanium-containing ore capable of processing the titanium-containing ore using a leach slurry with a solids content greater than 20% by weight, the process characterized by comprising: a) continuously leaching the titanium-containing ore in an acid leaching solution at high intensity and super atmospheric pressure to form a leaching slurry having a solids content of 20% by weight to 35% by weight on a total slurry basis, the said titanium-containing ore having an average particle size below 100 microns and said acid leaching solution comprising water and HCl at an HCl concentration above 11N and above the azeotrope concentration of HCl; b) separating the leach slurry into a solid waste stream and a fertile liquor comprising titanium and iron compounds including FeCl2; c) add chlorine to the fertile liquor to promote the conversion of FeCl2 to FeCl3; d) remove FeCl3 by solvent extraction under super atmospheric conditions to provide an enriched FeCl3 stream and a depleted FeCl3 stream; e) recovering titanium compounds from the depleted FeCl3 stream by solvent extraction under super-atmospheric conditions to produce a titanium-enriched stream and a titanium-depleted rafinate stream; f) recover HCl from the enriched FeCl3 stream and the depleted titanium raffinate stream for reuse in the leaching of step a; g) hydrolyzing the titanium enriched stream under plug flow conditions and super atmospheric pressure to produce a hydrolyzate stream comprising TiO2.H2O particles; h) dry the hydrolyzate stream for 2 to 4 hours while maintaining the temperature in a range of 100°C to 250°C to remove pore water, to inhibit disruption of the TiO2.H2O particles and to produce a hydrolyzate stream dry; i) calcining the dry hydrolyzate stream to convert TiO2.H2O into TiO2 and producing a calcined TiO2 material; and j) converting the calcined TiO2 material into a pigment grade titanium oxide product. 2. Process according to claim 1, characterized in that the HCl concentration of the acid leaching solution is 11N to 13N and the solids content of the leaching slurry is 27% by weight to 33% by weight. 3. Process according to claim 1, characterized in that the pressure conditions for the leaching of step a), and the solvent extraction of step e) do not exceed about 0.2 bar-g. 4. Process according to claim 1, characterized in that the hydrolysis of step g) is carried out in a hydrolysis reactor comprising a reaction conduit having at least one in-line mixer in its flow path, providing mixing with substantially no mixing return. 5. Process according to claim 1, characterized in that the dry hydrolyzate stream is a free-flowing solid material with a moisture content of 1% by weight to 3% by weight. 6. Process according to claim 1, characterized in that the solvent extraction of step d) and step e) uses a solvent composition including a modifier, a viscosity reducer and an extractive solvent and the modifier comprises a distillation cut from the production of propylene oxide, the viscosity reducer comprises kerosene and the extractive solvent comprises a ketone. 7. Process according to claim 1, characterized in that the acid leaching solution comprises water and HCl in an HCl concentration of 11.5 N to 12.5 N. 8. Process according to claim 1, characterized in that the extraction of FeCl3 by solvent and the recovery of titanium compounds from the depleted FeCl3 stream use the same solvent composition. 9. Process according to claim 1, characterized in that the plug flow conditions include substantially laminar flow, no appreciable backmixing and a Peclet number of at least 100. 10. Process according to claim 1, characterized in that the leaching in step a) receives recycled HCl recovered with sulfuric acid. 11. Process according to claim 1, characterized in that at least a portion of the titanium-depleted raffinate stream is treated by adding crystals of MgCl2.6H2O and sulfuric acid to all or a portion of the rafinate and magnesium sulfate being recovered from the resulting mixture. 12. Process according to claim 1, characterized in that the process operates with an HCl recovery system that breaks the HCl-water azeotrope formed in the leaching solution to regenerate a high concentration HCl material for reuse in the leaching step The). 13. Process according to claim 1, characterized in that the pressure conditions of the leaching step a) and the solvent extraction of steps d) and e) do not exceed a pressure of 0.25 bar-g. 14. Process according to claim 1, characterized in that the hydrolysis temperature is maintained above the azeotropic boiling point.