Patent Application
20160032419
The present invention relates to a process for the selective recovery of heavy, medium and light rare earth metals from an acidic aqueous sulfate solution additionally comprising phosphates and aluminum and possibly titanium, iron(III) and iron(II).
Ores, such as pyrochlore ores, comprising numerous elements of interest, sometimes in low proportions. The rare earth metals are included among these elements. The rare earth metals can also be produced from monazite, bastnaesite and loparite ores. These rare earth metals have numerous advantageous applications in various fields. For example, lanthanum (La) is a component of catalysts employed in the refining of hydrocarbons, neodymium (Nd) is widely used in NdFeB magnets, europium (Eu) and terbium (Tb) are dopants for plasma screens and LCD screens. Yttrium (Y) is for its part used in YAG (Yttrium Aluminum Garnet) ceramics. It is thus advantageous to be able to extract them and to separate them from the other elements present. Rare earth metals can be divided chemically into three groups:
These elements, normally put into one and the same group, have a chemical behavior which is similar but rather different according to the reactions envisaged. In the context of the present invention, scandium is regarded as not being among the rare earth metals. This is because scandium (Sc), nevertheless often put into the family of the rare earth metals, has a different chemical behavior from the elements of the series of lanthanides (rare earth metals). The demand for medium and heavy rare earth metals is greater than for light rare earth metals whereas, in general, their content in ores is lower and whereas they are more difficult to recover. It is thus important to be able to find a process which makes it possible to recover them with a good yield.
During the leaching of pyrochlore ore, in particular the ore resulting from the Mabounié deposit, located in Gabon, the dissolution of the elements of value (Nb, rare earth metals (TR), Ta and U) is quantitative. The leachate obtained comprises not only light, medium and heavy rare earth metals but also iron, in particular ferric iron (FeIII), aluminum (Al), titanium and phosphates (P). This leaching is described in particular in the patent application WO 2012/093170. In point of fact, the presence of aluminum and to a lesser extent of ferric iron interferes with the recovery of the rare earth metals and in particular of the medium and heavy rare earth metals. As has been shown in the examples below, the conventional and known reactions for the recovery of the rare earth metals do not make it possible to recover them all, in particular to recover the heavy rare earth metals, or the whole of the medium rare earth metals:
The patent application US2009/0272230 describes a process for the recovery of rare earth metals from monazite and apatite ores. These ores contain a great deal of phosphates, aluminum and iron. The process provided comprises:
These ores essentially contain light rare earth metals. Thus, the problem of the recovery of the heavy rare earth metals is not tackled.
In addition, the amount of phosphates present in the residue from leaching the ores obtained is in excess with respect to the iron. It is thus recommended in this patent application to add iron to the residue in order to achieve the required stoichiometry (Fe/P=1).
Furthermore, the problem of the recovery of the rare earth metals in the presence of high contents of aluminum is not posed. This is because the solution containing the rare earth metals to be recovered does not contain high contents of aluminum. The presence of aluminum is thus not troublesome for said recovery.
Finally, due to the presence of the light rare earth metals which it is desired to recover, it is not possible to neutralize the liquor containing these rare earth metals with just any base. In particular, it is not possible to use a base containing calcium, which is nevertheless less expensive and easier to supply, as there would be precipitation of gypsum, which would entrain rare earth metals.
The inventors have noticed, surprisingly, that it is possible to recover, with a good yield, heavy rare earth metals despite the presence of ferric iron and in particular of aluminum in the starting solution. In order to do this, they have discovered that it is necessary to selectively precipitate the aluminum by using the phosphates already present with neutralization at a very precise pH, provided that the aluminum is in excess with respect to the phosphates. This stage makes it possible to purify (or deplete) the solution from (or in) aluminum and phosphates. It is subsequently sufficient to add phosphates to the solution obtained in order this time to precipitate the heavy rare earth metals.
The present invention thus relates to a process for the selective recovery of the rare earth metals from an acidic aqueous sulfate solution comprising phosphates, aluminum and heavy rare earth metals, and possibly medium rare earth metals, iron(II) and titanium, characterized in that it comprises the following successive stages:
Within the meaning of the present invention, “rare earth metals (REs)” is understood to mean the rare earth metals chosen from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu+Y and their mixtures. In particular, scandium (Sc) is not included among the rare earth metals according to the present invention. Advantageously, the rare earth metals are classified into three groups:
Stage a) of the process according to the present invention makes it possible to purify (or deplete) the solution from (of) phosphates, aluminum and titanium (if titanium is present) in order to obtain a solution containing the heavy rare earth metals and the possible medium rare earth metals from which at least 90% by weight of aluminum, of the phosphates and the possible titanium have been removed, advantageously at least 95% by weight, with respect to the total weight present at the start in the solution. This is because, without being committed to theory, it appears that the majority of the phosphate, of the aluminum and of the possible titanium (at least 90% by weight, advantageously at least 95% by weight, with respect to the total weight present at the start in the solution) precipitate. In particular, as a result of its affinity for the aluminum, the phosphate appears to precipitate preferentially in the form of aluminum phosphate AlPO4 at a pH of between 3 and 4, advantageously of 3.5, preferentially to the rare earth metals phosphates. Once the phosphates have been removed, the remaining aluminum will quantitatively precipitate in the form of aluminum hydroxide, which will make possible the removal of the remaining aluminum. As the phosphates are deficient with respect to the aluminum, the heavy rare earth metals and the possible medium rare earth metals will not precipitate or will not precipitate very much in the form of phosphates (at most 40-50%). On the other hand, the precipitation of the aluminum in the form of phosphates is quantitative. Thus, the majority of the heavy rare earth metals and of the possible medium rare earth metals will remain in the sulfate solution (at least 50-60% by weight, with respect to the total weight of the initial acidic aqueous sulfate solution).
The base which can be used in stage a) of the process according to the present invention can be any base. It is advantageously chosen from NH4OH, KOH, a basic sodium compound, such as, for example, NaOH or Na2CO3, a basic magnesium compound, such as, for example, MgO or MgCO3, a basic calcium compound, such as, for example, CaCO3, CaO and Ca(OH)2, and their mixtures, more advantageously still chosen from MgCO3, a basic calcium compound and their mixtures.
In a particularly advantageous embodiment of the process according to the present invention, the base of stage a) is a basic calcium compound advantageously chosen from CaCO3, CaO, Ca(OH)2 and their mixtures; advantageously, it is CaCO3. This type of base is particularly advantageous as it is relatively inexpensive. In addition, given that only the recovery of the heavy rare earth metals is being looked for, the use of such a base is possible since the precipitation in the form of gypsum entrains only predominantly the light rare earth metals, moderately the medium rare earth metals, and marginally the heavy rare earth metals.
Advantageously, the temperature of stage a) of the process according to the present invention is between 20 and 90° C.; in particular it is approximately 70° C.
Advantageously, the duration of stage a) is between 30 min and 6 h and it is advantageously 1 h.
Stage d) of the process according to the present invention is used to extract all the rare earth metals present in the solution by precipitation in the form of rare earth metal phosphates. Since the majority of the phosphates of the solution have already been removed during stage a) of the process according to the present invention (advantageously at least 90% by weight, advantageously at least 95% by weight, with respect to the total weight present at the start in the acidic aqueous sulfate solution), it is necessary to add it during stage d). The precipitation is then quantitative since there is virtually no more aluminum in the solution (advantageously, the solution contains less than 10% by weight of aluminum, with respect to the initial aqueous sulfate solution, advantageously less than 5% by weight).
Advantageously, the phosphate used in stage d) is chosen from Na3PO4, K3PO4, (NH4)3PO4 and their mixtures; in particular, it is Na3PO4.
Advantageously, the aqueous sulfate solution in stage d) has a pH of between 3 and 4, advantageously, it is 3.5.
Advantageously, the temperature of stage d) of the process according to the present invention is between 50° C. and the boiling point, which is advantageously 90° C.; in particular it is between 70° C. and the boiling point.
Advantageously, the duration of stage d) is between 30 minutes and 2 hours. Advantageously it is less than or equal to 1 hour.
In a specific embodiment of the present invention, the acidic aqueous sulfate solution comprising phosphates, aluminum and heavy rare earth metals, and possibly medium rare earth metals, iron(II) and titanium, is the leachate obtained by acid attack on a pyrochlore ore in a sulfate medium, for example as described in the patent application WO 2012/093170. In particular, this solution contains:
The acidic aqueous sulfate solution can also contain iron (Fe), advantageously at least 50 g/l, advantageously between 50 and 70 g/l, in particular in the form of Fe(II).
In another specific embodiment of the present invention, the process according to the present invention comprises an additional stage g) of washing the precipitate obtained in stage f), advantageously by repulping with water, advantageously at ambient temperature.
The recovery of the heavy rare earth metals and of the possible medium rare earth metals from the precipitate obtained in stage f) or in stage g) can be carried out by methods well known to a person skilled in the art, such as, for example, purification by conversion into rare earth metal hydroxides.
Advantageously, the recovery yield of the heavy rare earth metals of the process according to the present invention is greater than 50%, advantageously greater than or equal to 60%.
In yet another embodiment of the process according to the present invention, the acidic aqueous sulfate solution comprising phosphates, aluminum, heavy rare earth metals and medium rare earth metals, and possibly iron(II) and titanium, additionally comprises light rare earth metals and an attempt is made to recover all the rare earth metals (medium, heavy and light). In point of fact, the light rare earth metals are partially entrained by the precipitation of gypsum during stage a), if the precipitation is carried out with a basic calcium compound. In addition, there are losses of light rare earth metals and of medium rare earth metals by precipitation in the form of phosphates during stage a), whatever the base used. Thus, if it is desired to recover the light rare earth metals and all of the medium rare earth metals, and thus to avoid the losses, the process according to the present invention comprises, before stage a), a prior stage A) of double salt precipitation of the light rare earth metals (advantageously at least 85% by weight, in particular 90% by weight, with respect to the total weight of the medium rare earth metals present in the initial acidic aqueous sulfate solution), so as to recover an acidic aqueous sulfate solution depleted (or purified) in (or from) light rare earth metals (advantageously, at most, there remains 15% by weight of light rare earth metals, in particular 10% by weight, with respect to the total weight of the light rare earth metals present in the initial acidic aqueous sulfate solution) and comprising phosphates, aluminum, heavy rare earth metals and medium rare earth metals, and possibly iron(II) and titanium. In particular, the stage of double salt precipitation precipitates not only the light rare earth metals but also a portion of the medium rare earth metals (approximately 50% by weight, with respect to the total weight of the medium rare earth metals present in the initial acidic aqueous sulfate solution) and advantageously a minority of heavy rare earth metals (at most 15% by weight, in particular 10% by weight, with respect to the total weight of the heavy rare earth metals present in the initial acidic aqueous sulfate solution). Thus, after this stage, there remains, in the acidic aqueous sulfate solution, at least 50% by weight of the medium rare earth metals, with respect to the total weight of the medium rare earth metals present in the initial acidic aqueous sulfate solution, and advantageously at least 85% by weight of the heavy rare earth metals, in particular 90% by weight, with respect to the total weight of the heavy rare earth metals present in the initial acidic aqueous sulfate solution.
The process for the double salt precipitation of light rare earth metals of stage A) is well known to a person skilled in the art. In particular, it concerns sodium, ammonium or potassium double salt precipitation, advantageously sodium double salt precipitation. In the case of the sodium double salt precipitation, stage A) advantageously takes place by addition of sodium sulfate, which results in the formation of an insoluble rare earth metal compound according the following reaction:
RE2(SO4)3+Na2SO4+2H2O→2NaRE(SO4)2.H2O.
Advantageously, the addition of Na+ is carried out in excess with respect to the rare earth metals, so as to obtain a quantitative recovery of the light rare earth metals.
In order to recover these light rare earth metals, the precipitate is separated from the acidic aqueous sulfate solution depleted in light rare earth metals. It is advantageously washed, for example with water and a 5% Na2SO4 solution.
Advantageously, the temperature of stage A) is between 50° C. and the boiling point, which is in particular 90° C. Advantageously, the duration of stage A) is between 30 minutes and 3 hours. In particular, it is 1 hour.
Advantageously, by virtue of this stage A), the recovery yield of the light rare earth metals is greater than 85%, advantageously greater than or equal to 90%, of the medium rare earth metals is greater than 50% and of the heavy rare earth metals is greater than 10%.
In an additional embodiment of the process according to the present invention, the acidic aqueous sulfate solution comprising phosphates, aluminum and heavy rare earth metals, and possibly medium rare earth metals, light rare earth metals, titanium and iron(II), additionally comprises iron(III). In particular, the content of iron(III) is less than or equal to 20 g/l, advantageously between 5 and 20 g/l, very advantageously between 10 and 20 g/l. The presence of the iron(III) promotes the precipitation of phosphates in the form of ferric iron phosphates (FePO4) during neutralization of the solution in stage a) of the process according to the present invention. As the amount of phosphates is deficient with respect to Al and Fe(III) (molar ratio (Al+Fe(III))/P>1 since molar ratio Al/P>1), the ferric iron also precipitates in other forms than that of phosphate, in particular by precipitation of ferric iron hydroxides, during stage a). However, such a precipitation has a tendency to entrain other elements, such as rare earth metals, in the precipitate. In addition, in order to precipitate all the ferric iron, it is necessary to add an additional amount of base in stage a), which results in the formation of additional gypsum when a base such as a basic calcium compound is used. It is thus advantageous, in order to improve the recovery yield of the heavy rare earth metals, of the medium rare earth metals and even of the light rare earth metals, when they are present, to add, to the process according to the present invention, a stage B), before stage a) and after the optional stage A), of reduction of the iron(III) to give iron(II), advantageously by addition of Fe(0) (for example in the form of iron powder), of SO2 or of another reducing agent. Advantageously, this stage makes it possible to obtain a content of ferric iron (Fe(III))<1 g/l in the acidic aqueous sulfate solution obtained comprising phosphates, aluminum and heavy rare earth metals, and possibly medium rare earth metals, light rare earth metals, titanium and iron(II).
Advantageously, by virtue of stages A) and B), the recovery yield of the medium rare earth metals is >80%, advantageously greater than or equal to 85%.
In a final embodiment of the process according to the present invention, before stage a), the molar ratio Al/P of the acidic aqueous sulfate solution comprising phosphates, aluminum and heavy rare earth metals, and possibly medium rare earth metals, light rare earth metals, iron(II), iron(III) and titanium, is <1. This means that the phosphates are in excess with respect to the aluminum. In this case, in order to be able to carry out the process according to the present invention, it is necessary to add a stage C), after the optional stages A) and B) and before stage a), of doping of the solution with aluminum, so as to obtain a molar ratio Al/P>1 which makes it possible to carry out stage a) of the process according to the present invention while minimizing the losses of heavy rare earth metals and of possible medium rare earth metals by precipitation in the form of phosphates.
A better understanding of the present invention will be obtained in the light of the description of the drawings and of the examples which follow.
This reaction is well known in a sulfate medium. Addition of sodium sulfate results in the formation of an insoluble rare earth metal compound according to the following reaction:
RE2(SO4)3+Na2SO4+H2O→2NaRE(SO4)2.H2O.
The optimized parameters of this reaction which give the best yields are as follows:
The solution (obtained by acid leaching in a sulfate medium of pyrochlore ore) on which this stage will be carried out exhibits the following composition:
Under these conditions, the recovery yields (%) of the light, medium and heavy rare earth metals are presented in
Conclusion: the light rare earth metal double salts are insoluble, which makes it possible to recover 90% of them.
Disadvantage: the solubility of the rare earth metal double salts decreases with the increase in the atomic number of the element, resulting in a recovery of 50% of the medium rare earth metals and only 10% of the heavy rare earth metals for the Na contents under consideration.
The pyrochlore ore comprises a source of phosphates (originating in particular from the apatite): consequently, during the attack of sulfuric acid on the pyrochlore ore, all of these phosphates present are attacked and are reencountered in solution. Thus, a typical solution on which the process according to the present invention has to be carried out comprises ˜15 g/l of phosphates (PO43−) for ˜270 g/l of sulfates (SO42−).
One of the main rare earth metal ore sources is monazite, a rare earth metal phosphate (REPO4). This ore is attacked by the sulfate route and the recovery of the rare earth metals takes place in a simple way:
Following this idea, we carried out neutralization tests on the solution obtained by acid leaching in a sulfate medium of pyrochlore ore exhibiting the following composition:
The operating conditions are as follows:
The precipitation yields obtained for Gd from the solution for which the concentration is shown above as a function of the pH are represented in
Given the concentration of salts, the precipitation pH curves are displaced toward the right: thus, the light rare earth metals begin to precipitate in the phosphate form at pH 2.5 and the heavy rare earth metals from pH 3. This process exhibits two disadvantages:
This low precipitation yield is not consistent with the low solubility product of the rare earth metals phosphates: this precipitation yield is understood better if the amount of phosphates present in solution during neutralization at a higher pH is monitored, as presented in
Thus, from pH 3, all the phosphates present in solution are precipitated, in the form of aluminum, thorium and light rare earth metal phosphates. Consequently, phosphates no longer remain available at pH 3 to complete the precipitation of the medium and light rare earth metal phosphates. The precipitation yield of the MRE/HREPO4 compounds thus stagnates at 30% at higher pH.
Conclusion: Possibility of precipitating all of the light rare earth metals.
Disadvantages: the purity of the precipitate is mediocre as all the aluminum precipitates in the same pH range as the light rare earth metals. There are not enough phosphates available in solution to precipitate all the medium and heavy rare earth metals.
The precipitation conditions of comparative example 2 are repeated, with furthermore the addition (approximately 3 g/l more) of phosphates (in the form of Na3PO4) in order to study the influence on the precipitation yield of the medium and heavy rare earth metals.
This addition of phosphates has no impact: the amount of P present is in such deficiency that, as the aluminum phosphate precipitates before the medium and heavy rare earth metals, the phosphate added is expelled in the form of aluminum phosphate.
Specifically, the molar ratios: [n(Al)/n(P)]solution comparative example 2˜2 and in this instance [n(Al)/n(P)]solution comparative example 3˜1.2.
Thus, even by virtually doubling the amount of phosphates, the latter serve above all to precipitate the aluminum in the phosphate form and there is no effect on the precipitation yield of the heavy rare earth metals.
Conclusion: the doping with phosphate has no effect on the precipitation yield of the rare earth metals.
Disadvantage: AlPO4 precipitates before the medium and heavy rare earth metal phosphates and the aluminum is in marked excess with respect to the phosphates; thus, the least addition of phosphate promotes the precipitation of the aluminum phosphate.
We have seen that the amount of phosphates present in solution is too low (in particular with respect to the aluminum) to be able to recover MRE/HRE phosphates, even by doping the solution beforehand with phosphate. Thus, by operating the other way round, we can try to expel the phosphates and the aluminum in a first step in order to obtain a solution containing the medium and heavy rare earth metals which is purified from or depleted in Al and P.
Operating Conditions
The starting solutions used for the precipitation of the aluminum phosphate have approximately the composition shown in the following table 1:
The conditions used are as follows:
Results
The precipitation yields of the moderate and heavy rare earth metals and of the aluminum in the form of phosphates are represented in
This will make it possible to test several routes for the recovery of the medium and heavy rare earth metals which have failed to date due to the presence of aluminum.
This reaction is selective because the following conditions are combined:
Under these conditions, the precipitation of rare earth metals phosphates is limited. From an economic viewpoint, the addition of a base of lime (Ca(OH)2) or limestone (CaCO3) type makes it possible to obtain a satisfactorily profitable process
The objective is to selectively and quantitatively precipitate the rare earth metals present in low concentration in an aqueous sulfate solution containing virtually no more aluminum or phosphates.
As the rare earth metal phosphates are very sparingly soluble, the addition of phosphates is carried out in order to promote their precipitation.
The composition of the solution for the precipitation tests on the rare earth metals is shown in table 2 below.
The precipitation of rare earth metal phosphates was carried out by addition of phosphates in the form of Na3PO4.
The conditions used for the precipitation are as follows:
Results
The precipitation yield of the rare earth metals are given in
The precipitation of the light, medium and heavy rare earth metals is quantitative (approximately 90%, with the exception of praseodymium at 70%). The stoichiometry does not exert a significant effect on the precipitation yield, which allows it to be supposed that the amount of reactants to be added may be reduced in the future (such that the molar ratio P/REs=PO4/REs is less than 40).
Operating Conditions
The initial solution for recovering the rare earth metals is shown in table 3 below.
The conditions used for the precipitation of the aluminum phosphate (stage a) of the process) are as follows:
The conditions used for the precipitation of the rare earth metals phosphates (stage d) of the process) are as follows:
The diagram of the process used is represented in
Results
Subsequent to this sequence of stages, the recovery yield of the rare earth metals for the scheme of the process provided is represented in
The process makes it possible to recover the rare earth metals in the phosphate form with very good yields from a solution initially containing large amounts of iron, aluminum and phosphorus.
The loss of rare earth metals during the neutralization can be reduced by optimization of the conditions for precipitation of AlPO4. The recovery yields of the light rare earth metals vary between 50 and 60% and the medium and heavy rare earth metals are recovered with a yield of 65 to 75%.
The precipitation of the rare earth metals in the form of phosphates is thus:
It is not possible to recover the light rare earth metals in the phosphate form as AlPO4 precipitates at the same time during stage a). A precipitation of light rare earth metal double salts (according to comparative example 1) is thus carried out as first stage. Subsequently, we can expel the phosphates and the aluminum in a first step in order to obtain a solution containing the medium and heavy rare earth metals, purified from or depleted in Al and P. Doping at that moment with phosphates should make it possible to precipitate the medium and heavy rare earth metal phosphates.
We thus carry out the stages as shown in the scheme of the process of
The operating conditions are the same as in example 3.
The stage by stage balance shows that:
Conclusion: it is possible to recover the MREs/HREs after removal of the P and Al initially present, by doping the solution in phosphates.
Disadvantage: the RE losses during the stage of precipitation of Al and P are still high and the stoichiometric amount of PO4 with respect to the rare earth metals is high, which impacts the purity of the product.
The presence of ferric iron (Fe(III)) originating from the upstream solution (acidic aqueous sulfate solution comprising the rare earth metals) results in two phenomena:
The idea is thus to neutralize the solution under the same conditions in order to precipitate the phosphorus and the aluminum but while studying the impact of the reduction of the solution: by addition of a reducing agent (Fe(0) or SO2, for example), the Fe(III) is reduced to different concentrations before the neutralization reaction in order to study its effect. Use will thus be made of the scheme of the process illustrated in
The precipitation yield (=loss yield) of the rare earth metals (yttrium Y in %) and the residual concentration of aluminum in the solution after precipitation during this neutralization stage as a function of the initial concentration of Fe(III) in the solution (0, 5 and 10 g/l) and of the amount of base added in g/l are combined in the graph illustrated in
Conclusion: The lower the initial concentration of Fe(III), the lower the loss of MREs/HREs. It is thus highly probable that the presence of Fe(III) involves two disadvantages:
It is therefore necessary to reduce virtually all of the ferric iron, in particular so that [Fe(III)]<1 g/l, in order to minimize this loss of rare earth metals and thus to increase the yield of the process according to the present invention.
The composition of the typical solution obtained after purification from Al and P is shown in table 4 below. The RE concentrations are capable of varying to +/−20%.
The only element which from now on may present a problem is Fe(II): ferrous iron phosphate is more soluble than MRE/HRE phosphate and has to precipitate at a higher pH. However, the ratio between the two elements does not act in favor of the rare earth metals: n(Fe)=n(Fe(II)) and n(Fe)/n(REs)˜500.
By varying the following parameters: temperature, residence time, PO4/REs stoichiometric amount (SA), the operating conditions can be optimized in order to decrease the amount of reactions to be added. The first precipitation test have been carried out at an SA of 100, which is totally unacceptable from an economic viewpoint.
The precipitation yield (%) of the rare earth metals (Ce, Gd and Y) and of iron in the aqueous solution as a function of the PO4/REs SA is monitored, as illustrated in
The selectivity of the reaction is excellent: a low SA makes it possible to precipitate all of the rare earth metals with little ferrous iron. This is made possible by virtue of a high temperature (100° C.) and a deliberately short residence time (<1 h) which makes it possible to limit the reoxidation of Fe(II) to give Fe(III) over time and thus to limit the use of the PO4 groups which are present to precipitate an Fe(III) phosphate.
Thus, with an SA of less than 20, it is possible to precipitate all of the rare earth metals in the phosphate form, with only a 5% of yield for the iron. The tests have proved that an SA of 5 was the optimum.
Conclusion: under economically profitable conditions, it is possible to precipitate all of the rare earth metals remaining after the removal of the aluminum and phosphorus, with a relatively good purity (content of rare earth metal phosphate of ˜10% for an SA of 5). The presence of a large amount of ferrous iron is not thus a constraint.
Overall conclusion: with the sequence of stages as illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1352349 | Mar 2013 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2014/050578 | 3/13/2014 | WO | 00 |
