Patent Application
20140308197
During the past seventy years titanium metal has been carried out using Kroll reduction of titanium tetra-chloride [TiCl4] using magnesium [Mg] metal at about 900° C. Large quantity production of each batch of about 8 tons of titanium sponge takes a cycle time of about four days. The titanium tetra-chloride production is done from naturally occurring high titanium oxide rutile [˜92-94% TiO2], or high TiO2 containing slag called synthetic rutile[82-88% TiO2] processed from ilmenite [FeTiO3] or other iron-titanium oxide raw material containing between 45 to 60% TiO2. Conversion of iron-titanium oxide has been typically carried out by a carbo-thermic process emitting CO2, and consumes energy which is mostly from fossil fuel source . Prior to carrying out the magnesium reduction, the titanium oxide is chlorinated using coke and chlorine at 800 to 1400° C. depending on the process. Additional steps purify undesirable impurities from TiCl4. This step also emits CO2. Since the step of magnesium reduction of TiCl4 is exothermic—and the management of temperature control is done with water cooling during portions of reaction, the external energy consumption in this step is minimal; however, an average of 900° C. is considered the reduction temperature. The products of reaction are magnesium chloride melt and sponge titanium. The magnesium chloride melt is typically, recycled to produce the metallic magnesium needed for further reduction in most cases when the price of magnesium is high; otherwise solidified magnesium chloride is sold as a separate product (as practiced in China).
During the past 20 years, several processes based on calcium as a reductant utilizing electrolysis as a method have been developed and none has come to a production scale of even 100 kg of titanium per batch. These have been using pure titanium oxide as a starting material in their process. Most of the titanium oxide used is produced using pure TiCl4 produced as per steps indicated in the previous paragraph.
In this invention, a unique production of titanium compounds and metal by sustainable methods using iron-titanium oxide starting material such as ilmenite, leucoxene, or rutile is described. Sustainable method is a process having as low a carbon dioxide emission, as well as having a near zero effluent or waste. Here the iron-titanium oxide compound is prepared by converting the iron portion of the compound to ferrous chloride at low temperatures by using close to stoichiometric amounts of sulfur and chlorine required for all the iron oxides and the other non-titanium oxides. The ferrous chloride thus formed is removed recovering a marketable product of ferrous chloride and the ‘sustainable’ titanium oxide starting material containing 93-99% TiO2, which is equivalent to or better than synthetic rutile available. This can be converted to ‘sustainable’ titanium chloride by process shown herein for further conversions to titanium dioxide pigment by present chloride process or supplied to existing titanium sponge producers, benefitting them in having a ‘sustainable process’.
Alternately, he ‘sustainable process’ titanium oxide starting material is subjected to metallo-thermic reduction using alkaline earth metals, such as magnesium and or calcium, in preparing the titanium powder by additional processing by controlled techniques. The purity of titanium powder is adjusted by needed secondary processing. The magnesium oxide formed is removed from the titanium powder in a series of steps and recycled to make the magnesium or calcium metal by electrolysis after conversion to anhydrous magnesium chloride by unique steps including sulfo-chlorination.
There is no existing prior art describing as a ‘low carbon dioxide foot print’ titanium oxide, although most of the titanium oxide made worldwide, using the sulfate process titanium oxide can be considered a low carbon dioxide foot print. But cannot be considered as a sustainable process as the co-produced ferrous sulfate or ‘copperas’ is allowed to pile up as a waste. Because of that reason, most of the sulfate process in the United States has been closed.
The iron oxide—titanium oxide compounds naturally occur as ilmenite [FeTiO3], or leucoxene with a higher TiO2 content, and these are upgraded to synthetic rutile as mentioned earlier. Du Pont corporation practices a different method where they convert the ilmenite to iron chlorides in an intermediate step and titanium tetra chloride by using carbo-chlorination in a selective manner, where the chlorine used for converting the iron oxide portion of the ore is returned to the process resulting in metallic iron as a co-product, as Glasser H. H. disclosed in patent U.S. Pat. No. 4,017,304. Here the carbo-chlorination is carried out at temperatures of 950 to 1400° C.—supplying the energy needed for iron chloride reduction as well as the endothermic heat for the formation of TiCl4.
Patents describing production of synthetic rutile precursor by utilizing carbonaceous reductants and fuels for making the tetrachloride needed for either the production of the pigment TiO2 or the titanium sponge by Kroll Process, are too numerous to be shown here. Some of these processes are recognized by names as benelite, ishihara, murso, Dupont selective chlorination and Becher process. Muskat. I. E., et al, in 1941, described chlorinating iron-titanium oxide containing ore using carbon and chlorine or carbonaceous chlorine gases such as phosgene at temperatures in the 600 to 1250° C. range in U.S. Pat. No. 2,245,076. McKinney. R. M, in 1951, discussed carbo-chlorination of ilmenite using coke and chlorine in U.S. Pat. No. 2,701,179.
The patents describing the use of sulfur as a reductant as prior art are presented here, in understanding the novelty of the present invention. Jenness. L. G. showed, in 1931, the use of sulfur higher chlorides and chlorine over the ore to make the metallic chloride vapors of the metals in the ore, in U.S. Pat. No. 1,834,622. He also teaches use of varying temperatures to make the metallic vapors in sequence as a means of separating the metals—examples cited include removal of titanium from aluminum containing ores, and tantalum separation from columbium or tin.
In 1961, Hill. C. T. described suspending ores such as TiO2—rutile, in molten sulfur [excess sulfur] and chlorinating the ore to make volatile chlorides and sulfur dioxide, in U.S. Pat. No. 2,970,887. The reactions are carried out using ferric chloride, sulfuryl chloride or chlorine and the temperatures being in the range 250 to 350° C. while keeping sulfur in the molten liquid state.
Baetz. H. B. et al. discussed converting both iron and titanium in red-mud from alumina production into iron and titanium chlorides using sulfur chlorides at 350 to 450° C. preventing silicon chloride formation, using a chlorine to sulfur ratio ˜4.5 to 1, in U.S. Pat. No. 3,690,828.
Lumsden J. describes, in U.S. Pat. No. 4,179,489, the chlorination of ilmenite using sulfuryl chloride, chlorine and recycled dimeric ferric chloride vapors in the temperature of 200 to 670° C. range to simultaneously form ferrous chloride solids [below its melting point] and titanium chloride vapors and sulfur dioxide gas. The process produces titanium tetra chloride and iron oxide. The iron oxide solids being formed by reaction with oxygen in a second reactor where dimeric ferric chloride vapors [Fe2Cl6] formed is recycled to the first reactor.
The TiCl4 by any of the different processes is further purified before being used in producing the pigment TiO2 or the metallic titanium either as a powder, or as a spongy agglomerate. The pigment production involves special oxidation to produce submicron nano particles of titanium dioxides. The production of metallic titanium has been typically carried out in Kroll Process using magnesium as a reducing agent, or by the Hunter or other variations such as Armstrong Process using sodium metal as the reducing agent.
The flowchart for Titanium by sustainable Methods is shown in
It is to be noted that even naturally occurring rutile has about 5 to 8% iron oxides, and some other oxide impurity. The ilmenite and leucoxene occur either as weathered beach sands or as hard rock ores containing 45 to 60% TiO2, 35 to 55% iron oxides and other oxides such as vanadium and other metals. The industrial waste product from bauxite conversion to alumina typically contains recoverable titanium oxides mixed with iron oxides which may also be recovered by the present sustainable chlorination techniques. The present invention uses sulfur as a reductant along with chlorine in producing a ‘low carbon dioxide footprint process’ for making ‘sustainable’ titanium compounds and metal. The invention discloses methods of selectively removing the iron as saleable ferrous chloride solution, and producing near pure ‘sustainable’TiO2 produced at a low cost along with cleaned sulfur dioxide for conversion to marketable sulfuric acid. The invention further discloses methods for making low cost, ‘sustainable TiCl4’ in one of the embodiments and a ‘sustainable Ti powder’ in another embodiment.
The present invention teaches to carryout the sulfochlorination of iron bearing titanium oxide minerals in sequential steps. The first step will use chlorine in stoichiometric proportion to convert all the iron component of ilmenite alone without converting the titanium component in a Stage One Reactor. Ilmenite mineral is a compound of iron oxides in the divalent and trivalent states along with titanium dioxide. It usually depicted as FeTiO3 or as FeO.TiO2, containing some Fe2TiO5 or Fe2O3.TiO2. The invention teaches the use of sulfur as an oxygen remover during the chlorination to avoid carbon oxide release.
The reactions taking place in the first step will be
FeTiO3+0.5S+Cl2=FeCl2+0.5 SO2+TiO2 [Reaction 1]
0.5 Fe2TiO5+0.75S+1.5 Cl2=FeCl3+0.5TiO2+0.75SO2 [Reaction 2]
The sulfur dioxide coming in the off-gas will be recovered into sulfuric acid using conventional catalytic reactors. The temperature of the reactions will be controlled to minimize the formation of ferric chloride vapors—and the equipment in the offgas will have conventional stepwise condensers to remove condensable vapors such as fern chloride, etc to send the cleaned sulfur dioxide vapors for recovery as sulfuric acid. The ferrous chloride, FeCl2 and the ferric chloride, FeCl3 are water soluble matter in the process. The solid reaction products of combined Reactions 1 and 2 will be washed with water to filter out essentially clean titanium dioxide filter cake, TiO2, and remove the Ferrous chloride containing some ferric chloride solution as a marketable product. The water washed filter cake titanium dioxide may contain some other insoluble impurities and these are removed in Stage 2 Purification of TiO2; using methods such as flotation, followed by secondary sulfo-chlorination to remove rest of the iron while loosing a minimal quantity of titanium as titanium tetrachloride to vapors which is recoverable from the condensers before releasing pure sulfur dioxide to its recovery process.
Most often the first step alone does not remove all the iron from the TiO2 as was described earlier. In order to assure cleanliness of the product, the filter cake is dried and put through an intermediate secondary sulfo-chlorination step. The amount of chlorine used in this step will be that required to remove iron and other chlorinatable impurities with minimal loss of titanium to result in essentially pure TiO2 applicable to pigment production. In this step some TiO2 will be lost by Reaction C to the off-gas as TiCl4 which can be recovered in conventional stepwise condensers which remove ferric chloride and other volatile chlorides coming with sulfur dioxide, before the sulfur dioxide is sent to be recovered as sulfuric acid.
TiO2+S+2Cl2=TiCl4 [vapor]+SO2 [Reaction 3].
This invention is a sustainable process as the oxygen remover sulfur is not wasted and is recovered from the off-gas as marketable sulfuric acid and thus minimizes the cost of production of titanium dioxide.
The current invention which produces high purity TiO2 can not only be sold as pigment grade material, but also be used for direct reduction to titanium metal, using magnesium or calcium reducing agents in a metallothermic process. Several examples are shown below as how the invention is put into practice.
The high purity TiO2 can be converted to TiCl4 for use in existing processes, or marketed. The metallo thermic reduction process of TiO2 is exothermic, and the present invention teaches rgy to recover this as Cogenerated ento improve the sustainability of the process further. The titanium metal produced in this step produces a product containing the metal [magnesium or calcium] oxide along with titanium powder; this mixture is separated sending the metal oxide for recycling into metallic reductant. This recycle product will require energy which will be supplied by alternate energy such as solar or wind energy hybrid with grid energy or cogenerated energy from earlier step.
The ore body is analyzed for its iron, titanium and other elemental oxide content; and the ore particle size is reduced to be in the less than 200 mesh or preferably less than 325 mesh size. The first stage partial chlorination is carried out in the 70 to 250° C., preferably in the 125 to 150° C. range with the following mole proportions of 0.5 moles of sulfur per mole of contained iron, and one mole of chlorine per mole of contained iron.
FeO.TiO2+0.5S+Cl2==FeCl2[s]+TiO2[s]+SO2[g] [A]
The sulfur can be mixed with the ore before being fed to the reactor. The reaction can be carried out in a rotating tubular reactor or in a moving or fluid bed reactor while controlling the reaction temperature, to form solid ferrous chloride mixed with the ore body. The proportions of reagents are made to avoid wasted formation of ferric chloride vapors or titanium chloride vapors in this stage. The vapor formed is mainly sulfur dioxide, along with possible minor quantities of low temperature volatile chlorides and water vapor from any moisture in the ore. The sulfur dioxide vapor is sent to the acid production step for recovery, following necessary intermediate scrubbing.
The solids from stage 1 reactor is then taken to a water washing step where controlled amount of water is added to make 30 to 35% ferrous chloride which is saleable to the water treatment chemical market in treating sewage and the like matter. Then the undissolved solid present is upgraded TiO2 with a 97 to 99% content. It is to be understood that this procedure is applicable to upgrading naturally occurring rutile or even the presently marketed synthetic rutile. The solids are then filtered with the filter cake washing to remove residual ferrous chloride, and taken to a secondary step of drying associated with further upgrading the TiO2 to the 99% or better grade. This step is carried out by adding small quantities of sulfur and twice the [sulfur] molar amount as chlorine and adjusting the reactor temperature to 500 to 900° C., preferably about 700° C. removing the rest of the iron, and other volatile chlorides along with less than about 2 to 5% of the TiCl4—the amount being controlled by keeping the temperature of the process and additives managed to keep a balance between the exothermic heats of iron chlorination, sulfur oxide formation and the endothermic heat for TiCl4 formation. The gases formed in this step include Hydrogen chloride, sulfur dioxide, iron chloride vapors and titanium chloride vapors. These gases are processed to recover the sulfur dioxide to the sulfuric acid plant, and the iron chloride to the marketable ferrous chloride solution, and recovered Titanium tetrachloride liquid for further use.
FeO+0.5S+1.5Cl2+TiO2==xFeCl3[v]+((1−x)2)Fe2Cl6[v]+SO2[g]+TiO2[pure]— [B]
The second stage pure titanium dioxide material can then be processed in one of several ways.
In one embodiment of the present invention, it is converted to pure titanium tetrachloride in a third stage sulfo-chlorination reactor using one mole of sulfur per mole of titanium dioxide, and two moles of chlorine per mole of upgraded titanium dioxide. The titanium tetrachloride from the third reactor would have its own off-gas system to recover condensed TiCl4 and send the sulfur dioxide to sulfuric acid recovery plant. This makes a low carbon dioxide foot print and ‘a sustainable’ TiCl4
TiO2+S+2Cl2==TiCl4[v]+SO2 [g] [C]
TiCl4[v][condensing scrubber→]TiCl4[1] [D]
SO2[g]→Sulfuric acid [E]
Reaction of chlorination TiO2 is endothermic, added heat if necessary is supplied by co-burning sulfur with oxygen which produces sulfur dioxide which is another product handled by the process.
In another embodiment of the present invention, the second stage pure titanium dioxide is converted to titanium metal by reaction with magnesium metal in a specially designed reactor where the temperature is controlled—in producing initially a mixture of titanium powder and magnesium oxide. The temperature is controlled in the 400 to 900° C. range and preferably around 500 to 600° C.
The mixture of titanium powder and magnesium oxide is first processed by slurrying in water, followed by flotation of magnesium hydroxide to a froth stream in flotation equipment such as a flotation column, while leaving the titanium powder to the heavier tail stream. The heavier tail stream titanium powder is analyzed for its purity from inclusions, and unremoved magnesium and titanium oxides. Following such analysis sufficient amount of a suitable acid is added avoiding dissolution of titanium powder. Then the powder is filtered, filter cake dried with heated gas inert to the powder—thus making the precursor for near net shape parts by powder metallurgy or converted into an ingot for further processing the metal in a ‘sustainable’ manner and at a lower energy and cost.
The process shown in example 3 is carried out using calcium instead of magnesium providing similar products.
The magnesium hydroxide froth from flotation step is filtered to recover the magnesium values as a filter cake. The filter cake is converted to magnesium sulfate monohydrate by reaction with concentrated sulfuric acid. The magnesium sulfate monohydrate undergoes dehydration around 250° C. in a fluid bed drier, preferably operated with a solar thermal heat exchange mechanism. The anhydrous magnesium sulfate is then transferred to a second fluid bed reactor where it is reacted with sulfur and chlorine in the 200 to 600° C., preferably around 350° C. making anhydrous magnesium chloride solids as a feed to magnesium chloride electrolysis unit. The sulfur dioxide formed is recycled to the sulfuric acid recovery process. The molten magnesium recovered from the electrolysis is processed to make the magnesium powder recycled to the titanium powder plant, while the chlorine is recycled to making the anhydrous magnesium chloride in this sustainable production technique.
MgO+H2O==Mg(OH)2 [F]
Mg(OH)2+H2SO4==MgSO4.H2O+H2O [G]
MgSO4.H2O==MgSO4+H2O [H]
MgSO4+S+Cl2==MgCl2+2SO2 [I]
MgCl2==Mg+Cl2[electrolysis]
Exact similar steps as in example 5 is carried out when calcium used as a reductant in the titanium powder process recovering the calcium hydroxide filter cake from the froth from flotation step in converting it back to calcium metal for the reduction of pure TiO2
The magnesium hydroxide froth from flotation step is filtered to recover the magnesium values as a filter cake. The filter cake is converted to magnesium sulfite by reaction with sulfite. The magnesium sulfite is then dried in a rotary or fluid bed drier, preferably operated with a solar thermal heat exchange mechanism. The anhydrous magnesium sulfite is then transferred to a second rotary or fluid bed reactor where it is reacted with sulfur and chlorine in the 200 to 600° C., preferably around 350° C. making anhydrous magnesium chloride solids as a feed to magnesium chloride electrolysis unit. The sulfur dioxide formed is recycled to the sulfuric acid recovery process. The molten magnesium recovered from the electrolysis is processed to make the magnesium powder recycled to the titanium powder plant, while the chlorine is recycled to making the anhydrous magnesium chloride in this sustainable production technique.
Mg(OH)2+SO2==MgSO3+H2O [J]
MgSO3+0.5S+Cl2==MgCl2+1.5SO2 [K]
Exact similar steps as in example 7 is carried out when calcium used as a reductant in the titanium powder process recovering the calcium hydroxide filter cake from the froth from flotation step in converting it back to calcium metal for the reduction of pure TiO2.
