Process for the recovery of metals and hydrochloric acid

Abstract

A method for recovering hydrochloric acid and metal oxides from a chloride liquor is described. The method uses a chloride liquor including the metal and mixing the liquor and a matrix solution to produce a reaction mixture, wherein the matrix solution assists oxidation/hydrolysis of the metal with HCl production. In a preferred embodiment the matrix solution includes zinc chloride in various stages of hydration and an oxygen containing gas is added to the mix. A method where the improvement is the mixing of a liquor and a matrix solution where the solution assists hydrolysis of the metal with HCl production is also disclosed. The reactor is a column reactor in a preferred embodiment. Further disclosed is the method of using the matrix solution and a reactor for recovering hydrochloric acid and for oxidizing/hydrolysis of a metal.

Claims

1. A method for recovering hydrochloric acid and metal from a chloride liquor, the method comprising the steps of: providing the chloride liquor comprising the metal; mixing the chloride liquor and a matrix solution comprising ZnCl.sub.2 to produce a reaction mixture; and mixing an oxygen containing gas into the reaction mixture; wherein the matrix solution assists hydrolysis of the metal with HCl production.

2. The method according to claim 1, further comprising the step of recovering hydrolyzed metal from the reaction mixture using a solid/liquid separator.

3. The method according to claim 1, wherein the chloride liquor further comprises base and light metals and the method further comprising the step of removing the base metal from the reaction mixture.

4. A method of recovering hydrochloric acid and metal from a chloride liquor, the method comprising the steps of: injecting the chloride liquor into a matrix solution comprising ZnCl.sub.2 to produce a reaction mixture; and injecting an oxygen containing gas into the reaction mixture; wherein the solution assists hydrolysis of the metal in the reaction mixture and produces HCl.

5. A method for recovering hydrochloric acid and metal oxide from a metal containing chloride liquor, the method comprising the steps of: mixing the chloride liquor and a matrix solution comprising ZnCl.sub.2 to produce a reaction mixture; and injecting an oxygen containing gas into the reaction mixture; wherein the matrix solution assists hydrolysis and oxidation of the metal with HCl production.

6. A reactor for recovering hydrochloric acid and metal from a chloride-based feed 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 located adjacent a bottom region of the base; a top opposite the base, the top comprising a metal chloride solution feed inlet, a hydrochloric acid outlet, a matrix solution inlet, the top defining a gas 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 the oxygen containing gas injected at the gas inlet raises through the mixture contained in the tank; wherein a ratio of the second cross sectional area to the first cross sectional area is greater than 1 and whereby hydrochloric acid leaves the mixture as a hydrochloric acid containing gas in the gas expansion zone at the top of the tank.

7. The reactor of claim 6, wherein the reactor is a column reactor.

8. The reactor of claim 6, comprising a ratio of the height to the first diameter from 5:1 to 20:1.

9. A process for recovering hydrochloric acid and metal from a chloride-based feed solution, the process comprising: providing a ferrous chloride solution; mixing the ferrous chloride solution and a matrix solution together to produce a mixture, wherein the matrix solution comprises ZnCl.sub.2 ; injecting an oxygen containing gas into the mixture, to oxygenate the matrix; and recovering oxidized or hydrolyzed ferrous iron and hydrochloric acid.

10. The method according to claim 3, wherein the step of removing the base metal includes hydrolyzing the base metal and removing the hydrolyzed base metal from the reaction mixture in a filtration step.

11. The process according to claim 9, wherein the step of recovering oxidized or hydrolyzed ferrous iron and hydrochloric acid includes producing a mixture containing the oxidized or hydrolyzed ferrous iron and hydrochloric acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will now be made to the accompanying drawings, showing by way of illustration a particular embodiment of the present invention and in which:

(2) FIG. 1 illustrates a block diagram of a process for recovering HCl and base metals from a mixed chloride liquor according to one embodiment of the present invention;

(3) FIG. 2 illustrates a block diagram of a process for recovering HCl and base metals from a mixed chloride liquor according to another embodiment of the present invention, where the liquor includes ferric chloride and the process includes an inert matrix solution and no iron oxidation step;

(4) FIG. 3A illustrates a block diagram of a process for recovering HCl and base metals from a mixed base metals chloride liquor, the method conducted in an inert matrix solution according to yet another embodiment of the present invention;

(5) FIG. 3B illustrates a block diagram of a process for recovering HCl and light metal from an aluminum chloride liquor, the method conducted in an inert matrix solution according to a further embodiment of the present invention; and

(6) FIG. 3C is a block diagram of a method for recovering HCl and light metal from a magnesium chloride liquor, the method conducted in an inert matrix solution according to yet a further embodiment of the present invention.

(7) FIG. 4 is a flowsheet of operation of a single column reactor according to one embodiment of the present invention;

(8) FIG. 5 is a flowsheet of operation of two column reactors in series according to a further embodiment of the present invention;

(9) FIG. 6 is a perspective view of a column reactor in accordance with one embodiment of the invention;

(10) FIG. 7 is a perspective view of a base portion of the column reactor according to FIG. 6;

(11) FIG. 8 is a perspective view of a sampling and injection unit portion above gas inlet ports at the base of the column reactor according to FIG. 6;

(12) FIG. 9 is a perspective view of the gas expansion zone at a top portion of the column reactor according to FIG. 6; and

(13) FIG. 10 is a perspective view of the top portion of the column reactor of FIG. 6.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(14) 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.

(15) 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.

(16) 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.

(17) 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. ZnCl.sub.2.2H.sub.2O in a liquid state and in various states of hydration ZnCl.sub.2.2H.sub.2O to ZnCl.sub.2.5H.sub.2O depending on the temperature.

(18) 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.

(19) The definition of a base metal is understood as a non-ferrous metal but excluding the precious metals (Au, Ag, Pt, Pd, etc.)

(20) 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.

(21) Referring to FIG. 1, there is shown a schematic representation of a process 1 in accordance with an embodiment of the invention. Broadly speaking, the process involves the recovery of iron material, base metal materials and hydrochloric acid from a chloride-based feed solution/liquor 2 containing ferrous iron, ferric iron and base metals, such as might be derived from: a steel pickling process; the leaching of a base metals sulfide ore, or refractory gold ore. The method is conducted in an inert matrix solution according to one embodiment of the present invention, the method steps comprising: an iron oxidation 6 from the liquor 2 including base metals (Cu, Ni, Co, Pb etc.), iron hydrolysis 12 with HCl removal 13 and hematite production, solid/liquid separation 16 of the hematite 15, a hydrolysis of base metals 20 with a further HCl recovery 23 and base metal separation 26, and recycle of the inert matrix solution 28.

(22) 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:
12FeCl.sub.2+30.sub.2.fwdarw.2Fe.sub.2O.sub.3+8FeCl.sub.3I
4FeCl.sub.2+O.sub.2+4H.sub.2O.fwdarw.2Fe.sub.2O.sub.3+8HClII
2FeCl.sub.3+3H.sub.2O.fwdarw.Fe.sub.2O.sub.3+6HClIII

(23) 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.

(24) FIG. 1 shows separate iron oxidation 6 and iron hydrolysis/precipitation 12 steps, but these may be combined into a single step at the higher temperature of 170-180 C.

(25) 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.

(26) 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.

(27) 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:
2MeCl.sub.2+3H.sub.2O.fwdarw.Me(OH).sub.2.Me(OH)Cl+3HClIV

(28) 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.

(29) The process 30 in FIG. 2 comprises: iron hydrolysis 33 from the liquor that includes base metals (Cu, Ni, Co, Pb etc.) and lighter metals (Mg, Al, etc) with HCl 31 removal and hematite 37 production, solid/liquid separation 34 of hematite, a hydrolysis 40 of base metals with further HCl recovery 42 and base metal separation 44, a hydrolysis of light metals 50 with yet a further HCl recovery 54 and light metal separation 56, and recycle 58 of the inert matrix solution. In process 30, a separate embodiment is shown with a ferric chloride solution containing base metals, aluminum chloride and magnesium chloride, such as might be derived from the leaching of a nickel laterite ore or an aluminum ore such as bauxite. In this embodiment, the chloride solution is injected into the matrix solution at 170-180 C. to effect the hydrolysis of ferric chloride and precipitation of hematite as in the reaction III with the production of HCl 34. The hematite may be separated from the matrix solution by any appropriate separation device 34.

(30) 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.

(31) 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.

(32) 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.

(33) 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:
AlCl.sub.3+2H.sub.2O.fwdarw.AlOOH+3HClV
MgCl.sub.2+H.sub.2O.fwdarw.Mg(OH)Cl+HClVI

(34) 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.

(35) Turning now to FIGS. 3A, 3B and 3C, there are shown three separate circuits 70, 80 and 90, wherein a pure base metals chloride 72, or a pure aluminum chloride 82 or a pure magnesium chloride 92 represent the feed solutions. Each of these solutions may be added/injected directly into a matrix solution at the appropriate temperature range defined earlier in this application. The chemical reactions are those present as IV, V and VI. The precipitates may be separated from the matrix solution by any suitable separation device 76, 86, 96, such as a vacuum belt filter or pressure filter. The process steps in FIG. 3A include: base metal hydrolysis 74 from the liquor 75 containing base metals (Cu, Ni, Co, Pb etc.) with HCl removal 73, followed by a base metals recovery 77, and recycle 78 of the inert matrix solution. The method steps in FIG. 3B comprising: aluminum hydrolysis 84 from the liquor 82 containing Al with HCl removal 83, followed by aluminum recovery 87 from solution 85, and a recycle 88 of the inert matrix solution. The method steps in FIG. 3C comprising: magnesium hydrolysis from the liquor 92 containing Mg with HCl 93 removal, followed by magnesium 97 recovery from solution 95, and a recycle 98 of the inert matrix solution

(36) 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:

EXAMPLE 1

(37) 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.

(38) TABLE-US-00001 TABLE 1 Boiling Tests on Various Chloride Salts Test Regime Comments 1 ZnCl.sub.2 alone Liquid at 225 C. 2 MgCl.sub.2 alone Hydrolyzes beyond 192 C. Solid at 220 C. 3 FeCl.sub.3 alone Significant solids at 188 C.; black residue. Solid at 200 C. 4 FeCl.sub.3/MgCl.sub.2/ Slope change around 140 C. A little ZnCl.sub.2 hydrolysis. Final solution had dark brown/black/purple residue. Remained liquid. 5 FeCl.sub.3/FeCl.sub.2 At 201 C., significant hydrolysis, 11N (34%) HCl, remained liquid. 6 CaCl.sub.2 alone Bath froze at 175 C. 7 30-70% base No significant HCl produced in condensate metals in until 223 C. Remained liquid ZnCl.sub.2 8 50-50% base Remained liquid. metals in ZnCl.sub.2 9 50% base Bath started freezing at 150 C. (crust metals in formation). FeCl.sub.3 10 70% base Bath started freezing at 138 C. metals in FeCl.sub.3 11 FeCl.sub.2 alone Froze at 145 C. 12 AlCl.sub.3 alone Froze at 150 C.

(39) 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.

(40) 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.

(41) 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.

EXAMPLE 2

(42) 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).sub.2.Cu(OH)Cl.3H.sub.2O, and also demonstrates that an effective separation of copper from nickel and cobalt can be achieved from the zinc chloride matrix solution.

EXAMPLE 3

(43) 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.

EXAMPLE 4

(44) 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.

(45) Referring to FIG. 6, there is shown a perspective representation of the process reactor 1 in accordance with an embodiment of the invention. The reactor in a preferred embodiment is a column reactor, defined as tank with a height that is greater than its diameter by at least 5 times. A column reactor is distinguished from a stirred tank reactor, in that it does not have mechanical agitation. In a particularly preferred embodiment of the column reactor the liquid flow through the column reactor is downward and countercurrent to the oxygen containing gas flow upward through the column reactor. Advantages of such a column reactor include a preliminary separation of hematite solid in the direction liquid flow downward towards a solids separation apparatus. In a stirred tank reactor the solids would remain equally suspended. However, the process could be performed at lower efficiency in a stirred tank reactor as will be seen in the Examples.

(46) 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 FIG. 6 is shown with electrical heating coils 105 which are used to heat the reactor 100 to maintain the desired temperature of operation. The heating coils 105 can alternatively be replaced with a jacketed reactor with a thermal fluid such as steam as the heating medium.

(47) 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).

(48) 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.

(49) 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.

(50) 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.

(51) 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.

(52) 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.

(53) Referring to FIG. 6, at the base or base portion 110 of the reactor 100, an oxygen containing gas such as air and/or preferably oxygen is injected through an inlet 112 into the reactor 100. In FIG. 6, the material of construction is a glass pipe 106, held together with external iron fittings 108. Clearly, any other compatible material of construction, such as PTFE (polytetrafluoroethylene) and/or PFA (polyfluorolokxy resin) and both known under the name Teflon) lined steel, glass lined steel, graphite, titanium alloys as well as fiberglass reinforced resin (FRP) alone or as a support for PFTE or PFA may be used and are known to the skilled person. As can be seen by FIG. 6, the reactor 100 has an aspect ratio of reactor height to diameter (in the base portion 110) of from 5:1 to 20:1.

(54) FIG. 6 further illustrates a top or top portion 120 comprising a further sampling or injection unit 130, as well as a gas expansion zone 122. The top portion 120 further includes a ferrous chloride solution feed inlet 124, a hydrochloric acid collection outlet 125 and an optional gas outlet 126, if a second reactor is connected in series.

(55) 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 FIG. 8). The base 10 also includes an adjacent sampling and injection assembly unit 130.

(56) The uppermost sampling and injection port 130 typically includes an inlet 127 for the circulation of the matrix solution.

(57) 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.

(58) In a specific embodiment of the invention, the first reactor 100 is preferably at 130-170 C., and more preferably at 140-160 C.

(59) 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. FIG. 7 illustrates a detailed perspective view of a base 110 attached to an adjacent sampling and injection unit 130.

(60) FIG. 8 shows a single sampling and injection unit 130 above the gas inlet ports 112 and 114 at the base 110 of the column reactor 100. The base portion comprises a first cross-sectional area 116 that remains substantially constant through the sampling of injection unit 130, and

(61) The unit 130 that may include a plurality of ports used for various purposes is illustrated in FIG. 8. The ports of the unit 130 include but are not limited to: injection port 131, that includes one or more injection valves 132, generally used for recycling (inlet matrix solution with or without solids): sampling ports 132 and 133 that may be in any orientation including a horizontal 133 or downwardly descending 133 orientation, each sampling port 133, and 134 respectively including valves 135 and 136 respectively. The unit 130 may also include ports for a thermocouple 137 and/or a pH/ORP (oxidation reduction potential) probe 138. The unit 130 is optionally found at a plurality of positions along the length of the reactor 100. The units 130 may be flanged together by various means.

(62) 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):
ZnCl.sub.2+O.sub.2.fwdarw.Zn(OCl).sub.2(1)

(63) 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.

(64) 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).sub.2+4FeCl.sub.2+4HCl.fwdarw.4FeCl.sub.3+ZnCl.sub.2+2H.sub.2O(2)

(65) The HCl for reaction (2) is provided by reaction III (previously presented):
2FeCl.sub.3+3H.sub.2O.fwdarw.Fe.sub.2O.sub.3+6HCl(III)

(66) The overall effect is thus as shown in reaction II (previously presented):
4FeCl.sub.2+O.sub.2+4H.sub.2O.fwdarw.2Fe.sub.2O.sub.3+8HCl(II)

(67) 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.

(68) 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.

(69) FIG. 6 shows a single reactor. However, a plurality of reactors may be used in order to give increased residence time and for a higher temperature of 170-250 C. to allow the hematite particles to grow. It can be seen in FIG. 6 that a number of sampling units 130 are provided and typically equidistantly spaced apart. These units 130 allow for the removal of hematite solids at various stages of growth if desired. It has been found that with longer residence times, larger particles are produced. Thus, it is possible to grow hematite particles of any desired size.

(70) Turning to FIG. 8, the injection and sampling ports provided allow for reacted solution to proceed to the next reactor. Solids may be removed from these ports or from the Teflon sampling units. Alternatively, froth may overflow from the airlift at the top of the reactor. above the gas inlet ports. This assembly allows for the recycle of matrix solution, the ability to sample the reactor, and for process control instrumentation such as ORP (oxidation-reduction potential) and pH probes.

(71) 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.

(72) 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.

(73) 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 FIG. 9 discloses the gas expansion zone 122 where the cross-sectional are 116 defined through the base portion upward expands to a second cross-sectional area 118 assigned to permit the depressurization of hydrochloric acid gas produced within the reactor. At this level of the reactor 100, there is a mixture of ferric chloride solution hydrochloric acid gas in combination with residual oxygen and possibly air, as well as matrix solution entering via inlet 127. The second surface area 118 of the expansion zone is greater than that of the first surface area of the base portion of the reactor. The ratio of second surface area to first surface area is greater than 1 and preferably in the order of 1.2:1.5 and more preferably 1.8:2.

(74) FIG. 10 illustrates a perspective view of the top 120 of the reactor 100. In this embodiment two outlets are shown: particularly, one for the hydrochloric acid (that will be condensed) along with residue oxygen; and a second HCl/O.sub.2 gas stream that could be fed into a second reactor. The top portion 120 also includes an inlet for the ferrous chloride solution and another inlet for the matrix solution (less the solids).

(75) FIG. 4 illustrates a flow sheet 150 where a single column reactor 100 is used. In this embodiment, fresh oxygen 152 is sparged as bubbles into the bottom of the column reactor. The oxygen rises through the mixed solution in the reactor from the base and countercurrent to the fresh ferrous chloride 154 feed entering from the top. Furthermore, recycled matrix solution 156 enters at the top of the reactor also flowing countercurrent to the flow of the gases moving upward. At the bottom of the column, a recycled matrix solution 158 including suspended hematite solids is withdrawn. A filter 160 or other solid liquid separator is used to remove hematite and the now substantially solid free matrix solution 156 is returned to the top of the reactor. Although not shown, solids hematite may be seeded into the reactor to improve the precipitation reaction. A mixed stream of hydrochloric acid vapour and residual oxygen 162 enter a condenser 164 where hydrochloric acid liquid 166 is produced and possibly recycled to the process. Unreacted oxygen gas 168 is compressed in compressor 170 and recycled to the base of the column.

(76) FIG. 5 illustrates a dual column operation 180 with two column reactors in series. FIG. 5 illustrates only one of a variety of process options that are possible. Once again, fresh oxygen 182 is sparged into the base of the downstream column reactor 176. Fresh ferrous feed 184 is fed to the top of the downstream column reactor 176. A matrix solution 186 containing hematite from column reactor 176 is seeded into upstream rector 174. Hematite in a slurry of matrix solution 188 is removed from a column 174. Hematite 190 is removed in filter 189 and solids free matrix solution 191 is typically transferred 192 partially to column 176, and partially combined 193 with hematite slurry stream 186 to produce a seeding suspension 194 for seeding of column 174. Hydrochloric acid and unused oxygen 196 are fed to a condenser 198 where once again hydrochloric acid 195 is condensed and unused oxygen 197 compressed and recycled to the base of both the upstream and downstream column reactor 174, 176.

(77) 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:

EXAMPLE 5

(78) 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.

(79) 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.

(80) 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

(81) 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.

(82) This demonstrates that in a conventional stirred tank reactor, the rate of oxidation of ferrous iron was very much slower than in a column.

EXAMPLE 7

(83) 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.

(84) 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.

(85) TABLE-US-00002 TABLE 2 Matrix and Solids Analyses from Acid Regeneration Test at 190 C. Final Feed, Matrix Solids g/L g/L Analysis Distribution, % Element (mg/L) (mg/L) % Matrix Solids Al 19.0 5.41 17.0 10.2 89.8 As (401) (2.4) 0.16 0.1 34.9 Ca 6.05 13.7 0.10 98.3 1.7 Fe 34.2 (45).sup. 34.1 99.5 0.5 K 10.2 32.6 ND 100 0 Mg 13.7 35.4 0.08 99.3 0.7 Mn (456) 1.34 ND 100 0