Patent Grant
9889421
The present invention relates to processes for the recovery of metals and ore processing, and hydrochloric acid that is recovered for recycle within the process. The processes also relate to the simultaneous oxidation and precipitation of ferrous iron as hematite, and to the recovery and recycle of the associated acid within the process. More specifically, the process relates to the oxidation of ferrous chloride and recovery of hydrochloric acid. It further relates to a novel reactor for effecting these reactions.
Various hydrometallurgical techniques have been developed for recovering metals such as zinc, nickel, copper, cobalt, lead, aluminum, titanium, and magnesium from sulfide and oxide ores, concentrates and intermediates. One such technique involves leaching the ore with a lixiviant that promotes dissolution of one or more metals into the leaching solution. Various compounds have been used individually as leaching agents in the lixiviant, for instance, sulfuric acid, hydrochloric acid, nitric acid, ferric chloride, ferric sulfate, cupric chloride and magnesium chloride. Recently there has been much work in the area of chloride-based leaching processes. All of these techniques inevitably involve the dissolution of iron, which then has to be removed from the system in order to facilitate the recovery of the value metals.
Iron is and has always been considered a major problem in hydrometallurgical processes such as those referred to above. In atmospheric processes, the iron is usually precipitated as an oxy-hydroxide, and in higher temperature autoclave processes, as an impure hematite. Often, small amounts of copper are added to act as a catalyst in the oxidation of ferrous to ferric. A more acceptable method of controlling iron is to form FeOOH, either β-FeOOH (akaganéite) or α-FeOOH (goethite) as described by D. Filippou and Y. Choi, “A Contribution to the Study of Iron Removal From Chloride Leach Solutions”, in Chloride Metallurgy 2002 Volume 2, (E. Peek and G. van Weert, Editors), Proceedings of the 32nd Annual CIM Hydrometallurgical Conference, CIM, Montreal (2002), p. 729. This approach is based to some extent on a controlled supersaturation precipitation technique, and is more efficient than, for example, the turboaeration process proposed by Great Central Mines in their chloride copper process, as described by R. Raudsepp and M. J. V. Beattie, “Iron Control in Chloride Systems”, in Iron Control in Hydrometallurgy (J. E. Dutrizac and A. J. Monhemius, Editors), Proceedings of 16th Annual CIM Hydrometallurgical Meeting, Toronto, October 1986, CIM Montreal (1996), p. 163.
Ferrous chloride solution, containing minor amounts of steel alloys such as manganese, vanadium and nickel, is the principal by-product of steel pickling lines (commonly referred to as waste pickle liquor, “WPL”). This solution is generally treated by a process called pyrohydrolysis, where the solution is injected into hot combustion gases at 700-900° C., causing oxidation of the ferrous iron to ferric and subsequent decomposition to recover hydrochloric acid and generate an iron oxide product for disposal or sale. The strength of the hydrochloric acid recovered from this process is limited to 18% because the off-gases have to be quenched in water, and using this method it is impossible to exceed the azeotropic concentration of hydrochloric acid in water, 20.4%.
The background to the present application has been largely covered in World Intellectual Property Organization International Publication Number WO2007/071020, Jun. 28, 2007 of Harris and White, which describes a process for the recovery of iron as hematite from a sulfide ore or concentrate. The process of Harris and White teaches a method for recovering iron as hematite from ferric chloride solutions containing a background chloride, preferably magnesium chloride, comprising heating the solution to 220-250° C. and adding water or steam to cause the precipitation of hematite and recovery of HCl.
U.S. Pat. No. 3,682,592 issued to Kovacs describes a process, the PORI Process, for recovering HCl gas and ferric oxide from waste hydrochloric acid steel mill pickle liquors (WPL). WPL typically contains water, 18 to 25% weight of ferrous chloride (FeCl2), less than 1% weight ferric chloride (FeCl3), small amounts of free hydrochloric acid and small amounts of organic inhibitors. The process of Kovacs includes two steps namely, a first oxidation step and a second thermal decomposition step. During the first oxidation step, the ferrous chloride in the WPL is oxidized using free oxygen to obtain ferric oxide and an aqueous solution containing ferric chloride. No hydrochloric acid is liberated at this stage. The first oxidation step is carried out under pressure (preferably, 100 p.s.i.g.) and at an elevated temperature (preferably, 150° C.), and therefore requires an autoclave.
During the second step, the resultant ferric chloride solution is thermally decomposed to obtain ferric oxide and HCl gas, which is recovered as hydrochloric acid. More specifically, the resultant solution is heated up to 175-180° C. at atmospheric pressure, and hydrolysis effected by the water in the fresh ferric chloride being added. The HCl is stripped off at a concentration of 30% with >99% recovery and good quality hematite is produced. While recovery of hydrochloric acid and hematite may be achieved using this process, its application tends to be limited to liquors containing only ferrous/ferric chlorides. When other chlorides are present in the solution, for instance and especially magnesium chloride as in the process of Harris and White, the activity of the chloride ions and protons tends to be too high to permit any reaction to take place simply by heating the solution to the temperature specified by Kovacs. Accordingly, this process tends not to be well adapted for use in leaching processes involving chlorides other than ferric chloride.
Applicant has found that the process of Harris and White will work in the laboratory in batch mode, but not in a continuous mode, because as the background chloride, e.g. magnesium chloride, calcium chloride, sodium chloride, aluminum chloride or base metal chlorides, concentration increases relative to that of iron, then the solution freezes, and is a solid at the temperatures indicated by Harris and White, and in some cases at the temperature indicated by Kovacs. This is true once the concentration of other chlorides reaches approximately 30% of the total in addition to ferric chloride. Accordingly, the processes of Harris and White and of Kovacs are impossible to operate if there are significant concentrations of other metal chlorides present in the solution.
SMS Siemag of Vienna, Austria, published a paper describing a process almost identical to that of Kovacs. The paper, Regeneração Hidrotérmica De Ácido Um Modo Econômico De Regenerar Líquidos De Decapagem E Produzir Óxidos Férricos De Alta Qualidade, published in Portuguese by Vogel, et al., follows the same procedures as Kovacs. More recently, a patent application describing the SMS Siemag process has been published by N. Takahashi et al., entitled Processing Method for Recovering Iron Oxide and Hydrochloric Acid, International Patent Application WO2009153321A1, Dec. 23, 2009. In the flowsheet published in the paper and patent application, the feed solution contains base metals such as manganese, and when this builds up, the liquid phase has to be discarded. This can be seen from
In light of the foregoing, it would be advantageous to be able to both oxidise and hydrolyse ferrous iron in a single process, generating a high-strength stream of hydrochloric acid. Further, this hydrochloric acid may be used for recycle or re-use within the overall flowsheet, as well as a pure hematite product.
In accordance with a broad aspect of the present invention, a process for recovering hydrochloric acid and useful metal oxidic materials from any chloride-based feed solution. Such solution may have been generated by treating any base or light metal-containing material with any lixiviant comprising acid and a chloride, but in particular with hydrochloric acid generated and recycled within the process, or WPL. The chloride solution is then treated to separate and recover therefrom hydrochloric acid and metal oxides as products of high purity.
In accordance with one aspect of the present invention, there is provided a method for recovering hydrochloric acid and metal from a chloride liquor comprising: providing the chloride liquor comprising the metal; and mixing the liquor and a matrix solution to produce a reaction mixture, wherein the matrix solution assists hydrolysis of the metal with HCl production.
In accordance with another aspect of the present invention, there is provided the method described herein, further comprising mixing an oxygen containing gas into the mixture.
In accordance with yet another aspect of the present invention, there is provided the method described herein, wherein the matrix solution comprises ZnCl2.
In accordance with still another aspect of the present invention, there is provided the method described herein, wherein the hydrolyzed metal is removed from the matrix solution by a solid/liquid separator.
In accordance with yet still another aspect of the present invention, there is provided the method described herein, wherein the chloride liquor comprises base and light metals that are dissolved in the reaction mixture, the method further comprising at least one step of base metal removal from solution or hydrolysis solid/liquid separation.
In accordance with a further aspect of the present invention, there is provided a method of recovering hydrochloric acid and metal from a chloride liquor wherein the improvement comprises injecting the liquor into a matrix solution to produce a reaction mixture, wherein the solution assists hydrolysis of the metal in the reaction mixture and produces HCl.
In accordance with yet a further aspect of the present invention, there is provided the method described herein wherein an oxygen containing gas is injected into the reaction mixture.
In accordance with still a further aspect of the present invention, there is provided the method described herein, wherein the matrix solution comprises ZnCl2.
In accordance with yet still a further aspect of the present invention, there is provided a use of a matrix solution for recovering hydrochloric acid and metal oxide from a metal containing chloride liquor, the use comprising: mixing the liquor and a matrix solution to produce a reaction mixture, wherein the matrix solution assists hydrolysis and oxidation of the metal with HCl production.
In accordance with one embodiment of the present invention, there is provided the use described herein, wherein an oxygen containing gas is injected into the mixture.
In accordance with another embodiment of the present invention, there is provided the use described herein, wherein the matrix solution comprises ZnCl2.
In accordance with yet another embodiment of the present invention, there is provided a reactor for recovering hydrochloric acid and for oxidation/hydrolysis of metal from metal chloride solution, the reactor comprising a tank compatible with a mixture comprising the metal chloride solution, a matrix solution, an oxygen containing gas and a solid comprising a metal oxide, the tank comprising a base, the base defining a first diameter and a first cross sectional area, the base comprising a metal oxide slurry outlet, a matrix solution outlet and a gas inlet; a top opposite the base, the top comprising a solution inlet, a hydrochloric acid outlet, a matrix solution inlet, the top defining gas an expansion zone having a second cross sectional area and, a wall attached to the top and the base defining a volume and a height of the tank; wherein a ratio of the second cross sectional area to the first cross sectional area is greater than 1 and whereby the hydrochloric acid leaves the mixture as a hydrochloric acid containing gas in the gas expansion zone at the top of the tank.
In accordance with still another embodiment of the present invention, there is provided the reactor described herein, wherein the reactor is a column reactor.
In accordance with yet still another embodiment of the present invention, there is provided the reactor described herein, comprising a ratio of the height to the first diameter from 5:1 to 20:1.
In accordance with a further embodiment of the present invention, there is provided a process for recovering hydrochloric acid and oxidation/hydrolysis of ferrous iron from a ferrous chloride solution, the process comprising providing a ferrous chloride solution, mixing the solution and a matrix solution together to produce a mixture, wherein the matrix solution comprises a metal chloride, and injecting an oxygen containing gas into the mixture, to oxygenate the matrix.
In accordance with yet a further embodiment of the present invention, there is provided the process described herein, wherein the metal chloride is ZnCl2.
It is an aspect of the invention to provide a single method which permits the recovery of iron, hydrochloric acid and base or light metals. Rather than heating said chloride solution to high temperatures which causes the iron to hydrolyse as described in the processes of the prior art, it has been discovered that this can be achieved by adding/mixing/injecting the solution into a matrix solution to produce a reaction mixture at 130-230° C., preferably 160-180° C., wherein the iron hydrolyses and precipitates as hematite with simultaneous recovery of hydrochloric acid which distils off and is collected in an off-gas system to be recycled to the leaching stage.
It is a further aspect that any base or light metals present in the initial solution are dissolved into the matrix solution. Thus, there is an immediate recovery of iron and hydrochloric acid, and an immediate and effective separation of iron from the other metal chlorides in solution. The matrix solution may be any compound which is inert and liquid at temperatures up to 250° C., and which will also act as a solvent for the base and light metals. In practice, there are very few such materials. Applicant has identified one as being zinc chloride, and accordingly, this is the preferred matrix. However, it is understood that there may be other such matrices. Zinc chloride is preferred since it is a chloride salt, and therefore introduces no additional ions into solution, and may be used together or with other materials in solution or suspension.
The matrix solution remains fluid at such temperatures, and the hematite solids are removed by any suitable separation device, for example hot vacuum or pressure filtration.
The matrix solution is substantially inert, and likely acts as a catalyst to accelerate the numerous possible hydrolysis reactions, therefore is a matrix for the various reactions. The ZnCl2 solution is generally a molten salt hydrate, e.g. ZnCl2.2H2O in a liquid state and in various states of hydration ZnCl2.2H2O to ZnCl2.5H2O depending on the temperature.
Additional heating of the iron-free matrix solution to 180-200° C. and injecting steam or water causes the base metals, but not aluminum and magnesium, to hydrolyse and precipitate as basic chlorides, with a generic formula of Me(OH)2.MeOHCl, where Me represents for example Cu, Ni or Co. Equivalent hydrochloric acid is recovered in manner similar to that recovered from iron hydrolysis. Therefore it is clear that the use of the matrix would allow for the recovery of metal and HCl.
These basic chlorides may be separated from the matrix by any suitable separation device and redissolved in dilute hydrochloric acid, the resulting solution from which can be treated by standard methods known in the industry for the recovery of the metal(s), such as, but not limited to, ion exchange, solvent extraction or electrowinning.
Alternatively, the basic chlorides are amenable to low temperature calcination (200-400° C., depending on the particular metal), to generate the metal oxide, and recover the associated chloride as hydrochloric acid.
It has been found that copper will hydrolyse before nickel and cobalt, and may therefore be separated preferentially.
Further heating of the matrix solution to 200-230° C. and injecting additional water or steam promotes the hydrolysis and precipitation of both aluminum and magnesium as basic chlorides.
In an alternative aspect of the invention, individual metal chloride solutions may be directly added to or injected into the matrix to recover the metal oxide or basic chloride and the associated hydrochloric acid without the addition of any extra water or steam.
In a further embodiment of the process, ferrous iron chloride, such as might be present in a steel pickling liquor or from the leaching of a base metal sulfide ore, may be injected on its own, or simultaneously with ferric iron chloride, along with oxygen or an oxygen containing gas, such as air, into the matrix solution at a temperature of 109-190° C., preferably 130-160° C., and more preferably at 140-150° C. It has been discovered that the ferrous iron will oxidise under these conditions, and that if the temperature is then raised to 170-180° C., hematite will precipitate. Thus, oxidation and hydrolysis may be achieved by the use of a matrix solution in a single vessel, and advantageously without recourse to an autoclave as described in the processes of the prior art.
In accordance with another aspect of the present invention, there is a provided a reactor for recovering hydrochloric acid and for oxidation/hydrolysis of ferrous iron from a ferrous chloride solution, the reactor comprising a tank compatible with a mixture comprising the ferrous chloride solution, a matrix solution, an oxygen containing gas and a solid comprising hematite, the tank comprising a base, the base defining a first cross sectional area, the base comprising a hematite slurry outlet, a matrix solution outlet and a gas inlet; a top opposite the base, the top comprising a solution inlet, a hydrochloric acid outlet, a matrix solution inlet, the top defining gas an expansion zone having a second cross sectional area and, a wall attached to the top and the base defining a volume of the tank; wherein a ratio of the second cross sectional area to the first cross sectional area is greater than 1 and whereby the hydrochloric acid leaves the mixture as a hydrochloric acid containing gas in the gas expansion zone at the top of the tank.
In accordance with yet another aspect of the present invention there is provided a process for recovering hydrochloric acid and oxidation/hydrolysis of ferrous iron from a ferrous chloride solution, the process comprising providing a ferrous chloride solution, mixing the solution and a matrix solution together to produce a mixture, wherein the matrix solution comprises a metal chloride, and injecting an oxygen containing gas into the mixture, to oxygenate the matrix.
Reference will now be made to the accompanying drawings, showing by way of illustration a particular embodiment of the present invention and in which:
The embodiments of the present invention shall be more clearly understood with reference to the following detailed description taken in conjunction with the accompanying drawings.
A matrix solution is used in the present process, and may be any compound which is capable of being oxygenated to form, even transiently, a hypochlorite compound, and which remains liquid at temperatures up to at least 190° C. and preferably to 250° C. It is also preferable that said matrix solution will act as a solvent for any base and light metals which might be present in the feed ferrous iron solution. In practice, there are very few such materials. Zinc chloride is a preferred matrix. Other such compounds are calcium chloride and magnesium chloride, and it is understood that there may be other such matrices alone or in combination. In this application, particularly where the feed is ferrous chloride, zinc chloride is preferred since it is both a chloride salt and remains liquid to a temperature >250° C. In a nitrate medium, suitable matrices may be silver nitrate and zinc nitrate.
The matrix solution remains fluid at such temperatures, and the hematite solids are removed by any suitable separation device, for example hot vacuum or pressure filtration.
The matrix solution is substantially inert, but acts as a catalyst for oxygen transfer to accelerate the oxidation and hydrolysis reactions. The matrix solution is generally a molten salt hydrate, e.g. ZnCl2.2H2O in a liquid state and in various states of hydration ZnCl2.2H2O to ZnCl2.5H2O depending on the temperature.
With regard to nomenclature, the term “ferrous chloride solution” applies to any metal chloride solution containing ferrous iron however derived, whether, for example, from an ore or concentrate leaching process, or from, for example, a steel mill pickling process.
The definition of a base metal is understood as a non-ferrous metal but excluding the precious metals (Au, Ag, Pt, Pd, etc.)
The description which follows, and the embodiments described therein are provided by way of illustration of an example, or examples of particular embodiments of principles and aspects of the present invention. These examples are provided for the purposes of explanation and not of limitation, of those principles of the invention. In the description that follows, like parts and/or steps are marked throughout the specification and the drawings with the same respective reference numerals.
Referring to
The mixed chloride liquor feed solution 2 is added and mixed into the matrix solution together with air or oxygen 4 at 130-160° C. to produce a reaction mixture. Any ferrous iron may be oxidized by and subsequently hydrolysed 12 by water 10 at 170-180° C. to form hematite according to the following chemical reactions with HCl 13 produced:
12FeCl2+302→2Fe2O3+8FeCl3 I
4FeCl2+O2+4H2O→2Fe2O3+8HCl II
2FeCl3+3H2O→Fe2O3+6HCl III
Therefore the reaction mixture 8 includes: the liquor solution, the matrix solution, the precipitating metal solids, any dissolved solids, unreacted oxygen and HCl. Whilst air can be used to effect the oxidation, its use is not recommended, unless sub-azeotropic (<20% HCl) hydrochloric acid is acceptable to the overall process. This is because the large quantity of nitrogen present in air requires the addition of water to scrub the hydrochloric acid liberated into the off-gas system.
Following the hydrolysis/precipitation 12 step, the remaining solution 14/reaction mixture (now an iron-depleted matrix chloride liquor) including the hematite product 15 are then subjected to a solid/liquid separation step 16. The hematite product thus recovered may be dried and sold, or simply disposed of.
Sulfates may be present in the chloride feed solution, especially if such solution derives from the leaching of base metal sulfide or refractory gold ores. Normally, the precipitation of jarosites might be expected from the combination of ferric iron, sulfate and high temperatures, as is widely practiced in the zinc processing industry. However, sulfates have been shown to have no impact at all on said iron precipitation process, and remain in the solution phase. If desired, sulfates may be removed by precipitation as calcium sulfate (gypsum, hemihydrate or anhydrite) by the addition of calcium ions at any point in the flowsheet.
Once the iron has been removed (via stream 15), most of the base metal-rich matrix solution 17 is simply recycled 18 in order to build up the concentration of base metals, and a bleed 19 can be hydrolyzed 20 by heating to 180-200° C., more preferably 185-190° C., and water or steam injection 22. This causes the base metals to precipitate as the basic chlorides and HCl 23 to be produced, according to the equations below, where Me represents, for example, copper, nickel or cobalt:
2MeCl2+3H2O→Me(OH)2.Me(OH)Cl+3HCl IV
The basic chlorides 24 may be separated 26 by any suitable separation device. The diagram shows the base metal basic chlorides 27 precipitating and being separated together, but it has been found in practice that copper, nickel and cobalt may be individually recovered, or redissolved, separated and recovered by any method known in the art such ion exchange, solvent or electrowinning. The remaining liquor 28 from solid/liquid separation 26 may be recycled 28, and even combined with other recycles 48, and returned to the top of the process 1.
The process 30 in
Once the iron has been removed, most of the base metal, aluminum and magnesium-rich matrix solution 36 is simply recycled 38 in order to build up the concentration of these metals, and a bleed 39 can be heated to 180-200° C., more preferably 185-190° C., and water or steam 41 injected. This causes the base metals to precipitate as the basic chlorides, according to the reaction IV.
The basic chlorides 43 may be separated by any suitable separation device 44. The diagram shows the base metal basic chlorides 46 precipitating together, but it has been found in practice that copper, nickel and cobalt may be individually recovered, or redissolved, separated and recovered by any method known in the art such ion exchange, solvent or electrowinning.
The remaining matrix solution 45 will contain aluminum and magnesium chlorides. These may be precipitated together, or aluminum may be preferentially precipitated as a pseudo-boehmite compound, by heating the solution to 200-220° C. Once again, a recycle 48 may be used to increase Al/Mg solution concentration.
Heating the solution 49 to 220-225° C. will effect the precipitation 50 of both aluminum and magnesium, according to the following reactions using water and/or steam 51 and with HCl 54 produced:
AlCl3+2H2O→AlOOH+3HCl V
MgCl2+H2O→Mg(OH)Cl+HCl VI
The aluminum and magnesium compounds 57 may be separated 58 from solution 53 leaving hydrolysis by any appropriate separation 56 device, washed and dried, and the matrix solution is recycled to the head of the circuit.
Turning now to
The principles of the present invention are illustrated by the following examples, which are provided by way of illustration, but should not be taken as limiting the scope of the invention:
A series of boiling point tests was carried out for single and mixed chloride salt solutions with the objective of determining the point at which these solutions would freeze, since the freezing aspect is a severe drawback in the processes of Kovacs and SMS Siemag. The solutions were heated up to 225° C., or to the point where significant freezing took place. The following table shows the results of these tests.
It is apparent from these data that zinc chloride solution is the only material tested which does not exhibit any crystallisation or hydrolysis tendencies in the temperature range up to 225° C. Furthermore, the solution remains liquid and fluid even with 50% base metals present.
The data demonstrate that any significant build-up of base metals in ferric chloride in the processes of Kovacs and SMS Siemag will result in the ferric chloride starting to crystallise and freeze, thereby necessitating to either recycle high levels of solution, or to bleed and treat the solution in another manner.
The data pertaining to magnesium show that the process of Harris and White also suffers from the same drawback, but not to the same extent.
The solution from test #7 in Table 1, comprising 70% zinc chloride, and 30% (copper chloride plus nickel chloride plus cobalt chloride in the ratio of 10:10:1 on a molar basis) was cooled to 180° C., and water injected. Pale blue crystals were obtained, analysing 50.6% Cu, 0.7% Ni and 0.06% Co. Zinc was not detected. This analysis is equivalent to the basic chloride Cu(OH)2.Cu(OH)Cl.3H2O, and also demonstrates that an effective separation of copper from nickel and cobalt can be achieved from the zinc chloride matrix solution.
A solution of 400 g/L aluminum chloride was injected into zinc chloride at 200° C. HCl of concentration 180 g/L was distilled off. At the end of the test, after 500 mL of feed solution had been injected into 1 L of zinc chloride, 96.7% of the Al fed reported to the solid phase, which analysed 41.6% Al and 0.4% Zn. XRD analysis of the precipitate showed it to be predominantly a pseudo-boehmite.
One litre of saturated zinc chloride solution was heated up to 165 C. 680 mL of a solution analysing 232 g/L ferric iron and 65.3 g/L Ni was injected into the zinc chloride at a rate of 8 mL/min. After the injection was finished, the test was stopped, with 137.2 g of HCl recovered 131.2 g of hematite residue. The final solution in the reactor (volume 750 mL) analysed 117 g/L Fe and 47.1 g/L Ni. The solids analysed 54.2% Fe and 14.0% Ni, but after washing with dilute HCl, there was no Ni left in the solids. This example demonstrates that iron and nickel can be successfully separated by this methodology.
Referring to
Broadly speaking, the process involves the oxidation and hydrolysis of ferrous iron of the ferrous chloride solution with recovery of associated hydrochloric acid and an iron material (hematite). The embodiment of reactor 100 in
In one embodiment of the present invention, ferrous iron is oxidized to ferric, hydrolysing the ferric iron and recovering hydrochloric acid and useful metal oxidic materials from any chloride-based feed solution. It is also understood that such processes are not limited to chloride-based solutions, but can be applied to nitrate and fluoride solutions, for example. Such solution may have been generated by treating any base or light metal-containing material with any lixiviant comprising acid and a chloride, but in particular with hydrochloric acid generated and recycled within the process, or WPL (Waste Pickle Liquor).
In accordance with one aspect of the present invention, there is provided a method for recovering hydrochloric acid and hematite from a ferrous chloride liquor comprising: providing the ferrous chloride liquor, which may optionally contain other metals such as copper, nickel, cobalt, zinc, aluminum and magnesium; adding the liquor to an oxygenated matrix solution, such matrix solution being capable of forming a hypochlorite, wherein the solution assists hydrolysis of the metal and HCl production.
In accordance with another aspect of the present invention, there is provided a method of recovering hydrochloric acid and metal from a ferrous chloride liquor wherein the improvement comprises injecting the liquor into an oxygenated matrix solution in a reaction column countercurrent to the gas flow, wherein the solution assists hydrolysis of the metal and HCl production.
It is an aspect of the invention to provide a single method which permits the oxidation and subsequent hydrolysis of ferrous iron to form hematite and hydrochloric acid. It has been discovered that this can be achieved by adding the said ferrous iron solution into an oxygenated matrix solution at 130-180° C., preferably 140-160° C., wherein the ferrous iron is oxidised and then hydrolyses and precipitates as hematite with simultaneous recovery of hydrochloric acid which distils off and is collected in an off-gas system to be recycled to the leaching stage.
In a further embodiment of the process, there is provided a column reactor, in which the oxygen gas is injected at the bottom and the ferrous iron chloride, such as might be present in a steel pickling liquor or from the leaching of a base metal sulfide ore, may be injected on its own, or simultaneously with ferric iron chloride, from the top. The weight of the liquid in column, of height 1-2 meters, and preferably 1.4-1.8 meters, holds up the oxygen gas in the column, thereby providing sufficient time for the reactions to take place. There may be a plurality of such reactors, maintained at a temperature of 109-250° C. In a specific embodiment of the invention, the first reactor is preferably at 130-170° C., and more preferably at 140-160° C.
The temperature of additional reactors in series may be raised to 170-250° C., and more preferably to 170-190° C., in order for the hematite particles to grow. It has been discovered that by maintaining temperature gradients, different particle sizes of hematite in the range 1-100 microns may be formed, thus generating hematite particles with differing color and size. Finer particles will be red in colour, whereas larger, more dense particles vary in color from purple to black.
Referring to
The base 110 may also include a further inlet 114 for recycled gas, where this gas comprises HCl and oxygen recycled generally from the top or top portion 120 of the reactor. The base 110 defines a first diameter and a first cross sectional area 116 (as seen in
The uppermost sampling and injection port 130 typically includes an inlet 127 for the circulation of the matrix solution.
The matrix solution is usually withdrawn from the bottom-most sampling and injection unit 130 via outlet 128. From outlet 128 the matrix solution including a slurry of produced hematite is pumped to a solid removal step, such as filtration.
In a specific embodiment of the invention, the first reactor 100 is preferably at 130-170° C., and more preferably at 140-160° C.
The oxygen sparged into the base 110 of the reactor 100, is preferred over air if concentrated hydrochloric acid (>20% by weight) is desired. The recycled gas through inlet 114 added at the base 110 of the reactor 100 increases the utilisation efficiency of the gas.
The unit 130 that may include a plurality of ports used for various purposes is illustrated in
The present reactor is meant to oxygenate the matrix solution that generates a concentration, however transient, of hypochlorite, according to the following reaction (using zinc as an example):
ZnCl2+O2→Zn(OCl)2 (1)
This reaction is favoured in the temperature range 140-160° C., and if there is relatively little associated free water present. Free water is water which is purely a solvent and is not bound in any way to the ions of the matrix compound. As described earlier, the zinc chloride is present as a molten salt hydrate, thus satisfying these requirements.
The ferrous chloride solution may be added from the top of the reactor, such that it meets the oxygenated matrix solution countercurrently. The hypochlorite solution is a very powerful oxidant and thus highly reactive, and instantaneously reacts with the ferrous iron according to the following reaction:
Zn(OCl)2+4FeCl2+4HCl→4FeCl3+ZnCl2+2H2O (2)
The HCl for reaction (2) is provided by reaction III (previously presented):
2FeCl3+3H2O→Fe2O3+6HCl (III)
The overall effect is thus as shown in reaction II (previously presented):
4FeCl2+O2+4H2O→2Fe2O3+8HCl (II)
Additional water for the reaction is provided by that associated with the incoming feed solution. The concentration of the incoming feed solution may be adjusted to give the desired strength. The Matrix reactor 100 has ports for the addition of fresh ferrous iron feed, a port for the collection of hydrochloric acid vapour, and a third port for unused oxygen gas to proceed to the next reactor.
Whilst air can be used to effect the oxidation, its use is not recommended, unless sub-azeotropic (<20% HCl) hydrochloric acid is acceptable to the overall process. This is because the large quantity of nitrogen present in air requires the addition of water to scrub the hydrochloric acid liberated into the off-gas system.
Turning to
The hematite solids are separated from the matrix solution by any suitable solid-liquid separation device that may be kept hot, such as a vacuum or pressure filter. It is necessary to keep the liquid phase hot so that it does not freeze.
The use of column reactors in this manner eliminates the need for mechanical agitation, and therefore eliminates any problems associated with the choice of exotic materials of construction needed in this corrosive environment.
As both non-consumed gas and generated hydrogen chloride (gaseous hydrochloric acid) vapor exit 125 the matrix solution, they expand, and the expansion zone 122 allows for the gases to expand without increasing the internal pressure of the reactor; and
The principles of the present invention are illustrated by the following further examples, which are provided by way of illustration, but should not be taken as limiting the scope of the invention:
A solution containing 1.56 kg of zinc chloride dissolved in 1.5 L of water was initially heated to 160° C., and placed equally in two columns connected in series. A mixture of air (0.2 L/min) and oxygen (0.4 L/min) was sparged into the bottom of the first column. A solution containing 144 g/L ferrous chloride was fed at a rate of 1 mL/min from the top of the first column. The two column set-up was originally intended to effect oxidation in the first and hydrolysis in the second, but it was found that both reactions took place immediately in the first column, with the overflow caused by the froth going into the second column.
Column 1 was then set to 140° C. and column 2 to 160° C. Solution was fed for 4 hours continuously into column 1, and at the end of the test, 14.7 g of black hematite was recovered from the second column, and 0.8 g of red hematite from the first column. The iron concentration at the end was 13.4 g/L in column 1 and 2.8 g/L in column 2.
This example demonstrates the simultaneous oxidation and hydrolysis of ferrous iron, and the growth of the hematite particles. No attempt to collect the HCl generated in this test was made.
Example 6 is provided by way of comparison with a more conventional approach using a stirred tank reactor. A similar volume of ferrous chloride solution to that used in Example 5 was saturated with zinc chloride and heated up to 190° C. in a stirred tank reactor. Oxygen gas was sparged into the reactor at the of 0.6 mL/min. After 13 hours of gas sparging, 94% of the ferrous iron had been oxidised to ferric. No HCl was recovered.
This demonstrates that in a conventional stirred tank reactor, the rate of oxidation of ferrous iron was very much slower than in a column.
A semi-continuous (i.e. continuous feeding of solution into reactor, but that the accumulated solids are not removed until the end of the test) acid regeneration tests to determine the behaviour of especially the alkali metals, potassium and sodium. Feed filtrate from a continuous miniplant run treating a complex gold ore was injected into a matrix of zinc chloride, maintained at 190° C., at a rate of mL/minute. A steady production of acid was achieved, demonstrating that the hydrolysis reaction occurred more or less instantaneously consistent with the feed rate. The concentration of the produced HCl was consistent at around 230-240 g/L (7M HCl), which was equivalent to the iron, aluminium and free acid concentration of the feed liquor.
Table 2 shows the analyses of the final matrix (zinc chloride) solution, the composition of the solids produced, and the distribution of the elements between solids and solution. It is clear that the solids were comprised of primarily of iron and aluminium, with virtually all of the iron reporting to the solids. Potassium (and by inference sodium) and calcium all reported entirely to the matrix solution, as was anticipated. At 190° C., virtually no magnesium was found in the solids. Arsenic in the feed solution reported one third to the final solids, with the balance being distilled as a chloride and collected in the recovered acid.
This application is the U.S. national phase of PCT Appln. No. PCT/CA2011/000141 filed on Feb. 4, 2011, which claims the benefit of U.S. Patent Provisional Application No. 61/305,718 filed on Feb. 18, 2010 and U.S. Patent Provisional Application No. 61/420,500 filed on Dec. 7, 2010, the disclosures of which are incorporated in their entirety by reference herein.
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