CA1160849A - Process for recovering non-ferrous metal values from ores, concentrates, oxidic roasting products or slags - Google Patents

Abstract

Abstract of the Disclosure A process for recovering non ferrous metal values from their ores, minerals, concentrates, oxidic roasting products, or slags by sulphating said starting material using a mixture comprising iron(III) sulphate and alkali metal- or ammonium sulphate as a reagent.

Description

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A process for recovering non-ferrous metal values from ores, concentrates, oxidic roasting products or slags The present invention relates to a process for re-covering non-ferrous metal values from ores, concentrates, oxidic roasting products, or slags by converting them into sulphates by using principally mixture of solid matters and molten salts as the sulphating agent. Said sulphating agent consists of alkali metal sulphate and iron (III~ sulphate and one or more preferred non-ferrous metal sulphates.
The process described in this invention thus re-lates to a method that is widely used by the metallurgi-cal industry for converting selectively particular non-ferrous metal values, which will be referred to as Me inthe text, into their sulphates. These sulphates can then be separated from the tailings and in soluble hematite by a simp]e water leaching procedure. The non-lerrous ~alues in the solution can thereafter be recovered by method known per se.
However, the known method, i~e. the sulphating roasting, involves some disadvantages which have often made it unfeasible for more extensive use. The main dis-advantages have been difficulties in controlling reaction conditions, such as the SO3 partial pressure and tempera-ture, so that it is practically impossible to achieve the maximum yield of the wanted water-soluble metal sul-phate and, simultaneously, the maximum conversion of iron to non-soluble hematite in a reasonable reaction time, and further on, to avoid the thermodynamically and, especially in higher temperatures, also kinetically ~avourable conversion reaction between hematite and said metal oxide into the ferrites. Another serious disadvan-tage is the forming of a sulphate layer on the reacting particle which, in certain cases, strongly affects the reaction rate.
~.

In general, it is presently believed that during the course of the roast, the metal value Me is converted first into the oxide form in the following manner:
~I) MeS t 3/2 2 ~ MeO + SO2

2 ~ 1/2 2 ~ SO3

(3) MeO ~ SO3 ~ MeSO4 Thus in the reacting particle, there are simultaneously present the oxide of the wanted metal value ~leO and the iron oxide Fe2O3. Thus, there are prerequisites for the ferrite foxmation, in other words for the reaction ~4) 2 3 ~ MeFe2O4 - In general, it has been shown that all the sul-phation reactions have occurred through the sulphate shell which has grown on the surface of the ~leO particle during the course of the sulphation. It is through this shell that tile reacting ions have to migrate before they can react~further. The solid-state diffusion is, as well~
known, a very slow phenomenon, especially when the mi-grating ionic species is large, such as an oxygen ion (see, for example, W. Jost and K. Hauffe: Diffusion.
2nd ed. Steinkopf Verlag, Darmstadt, 1972). On the other hand, the aforesaid formation reaction of ferrites is also a solid-state reaction when the oxides are diffu-sing into each other by counterdiffusion mechanism. The latter phenomenon is often considerably faster than the - sulphation reaction. ~ commonly believed explanation for this is that in the ferrite formation reaction, only those ionic species with small dimensions (for example, metal ions) are migrating into each other in a relative~y looscpacked oxygen lattice (see, for example, ~.Hauffe: l~eaktionen in und an der festen Stoffen, Springer Verlag, Berlin, 1955, p. 582 and H.Schmal~ried:
Solid State Reactions, Verlag Chemie, Weinheim, 1954, - p. 90).
As the most important argument in favour of the previous review remains the experimental fact that from the competing reactions involving the Me-oxide, that is the reactions (3) and (4), reaction (4) occurs when there are thermodynamically favourable conditions, while the sulphation reaction ~3) is normally very slow because it requires the diffusional migration of the reacting species through the growing sulphate shell.
It is well-known that, ~or example, the sulphation of nickel compounds is very difficult to perform because of the nonporous sulphate shell which does not offer any new reaction paths for the gas phase, for example, in the form of cracks or pores. It has been experimentally observed that the nonsulphated nic~el has been mainly in the form of ferrite. Thus, the prior art of the sulpha-tion can be described shortly:
When performin~ sulphating roasting with gaseous reagents (2' SO2), it is impossible to avoid the forma-tion of ferrites if one wants to operate under react;on conditions where iron and the wanted metal value Me are to be selectively partitioned.
Attempts have been made to eliminate these afore-mentioned disadvantages which characteristically occur in the gas phase sulphation by means of a very accurate control of the gas atmosphere and tcm~erature, for e~amp-le, with the aid of a fluid-bed reactor or, on the other hand, by using so~eadditives.
Thus, the Finnish patent 31124 discloses that the yield of the metal va]ues, such as Cu, Co, Ni and Zn, may be increased by sulphating roastincJ the concentrates with the addition of small amounts of inorganic chloride, e.g., NaCl or CaCl2. Accordingly, in the U.S. Patent No.
3 442 403 gaseous HCl is used for ~he same purpose.

Further, U.S. Pat. No. 2 813 016 discloses a process for sulphating roasting which utilizes sodium sulphate Na2SO4 as an addltive. It is proposed tha~ sodium sulphate reacts with yaseous SO3 and forms Na-pyrosulphate Na2S2O7 which is commonly known as a very effective liquid state sul-phating agent:

(5) Na2SO ~ SO3 ~ Na2S2O7 The formation of pyrosulphate according to reac-tion (5~ is also the basis of a process described in U.S. Patent No. 4 110 106 in which the reaction mi~ture consists of potassium and sodium sulphates. Pyrosulphate has long been known from literature as a sulphating agent 15 (see, for example, Ingraham et al. Can Met Quart. = ~1965) no 3 p. 237~244. Can Met Quart = (1968) no 4 p. 201-204 and 205-210~. The promoting effect of Na?SO4 in the sul-phating roasting has been discovered as early ~s 1905 by N.V. Hybinette (German pat. 2Gu~72).
The common factors for the above processes are that the reagent effective in sulphation is sulphur triox;.de present in the ~as phase and that the aim is to obtain selective sulphàtion, that is, reactions are per-formed under such reaction conditions that Fe2(SO4)3 decomposes while yielding hematite Fe2O3. These reaction conditions are, according to the thermodynamics of the Fe-S-O system, dependent upon the partial pressure of the SO3 gas and the temperature of the reacting system so that the temperature with the usually used SO3 pres-sures is above 650-675C (see figure 1). The process according ~o the present invention differs from the above in that the reagent used for sulphatation is principally the iron (III) sulphate which ls added to the reaction mi~ture and in that the operation is carried out in such a-temperature range that this reagent (Fe2(SO4)3) forms a stable phase, either alone or togeth-er with a salt melt.

On the basis of the foregoing~ it can be claimed that there are at least two ways to influence the two competing reactions~ i.e. the ferrite formation reaction (4) and the sulphate formation reaction (3). They can be used together or separately as follows:
a) by operating under conditions where Fe2O3 is not stable and thus the ferrite formation reaction is totally prevented, o~
b) by assuring that the relative rate of the sulphatation reaction is promoted by removing the barring, sulphate shell when it is formed.
Conventional sulphating roasting with gaseous reagents in practice offers no possibility to operate either accord-ing to solution a) or b). The situation is quite different when utilizing the characteristics of the melt phase consist-ing of the ternary system of certain sulphates. A2SO4 -Te2(SO4)3 - MeSO4 is a ternary system where A is an alkali metal ion ~usually sodium or potassium) or the NH4 ion.
According to the invention there is provided a pro-cess for recovering non~ferrous metal values selected from the group consisting of copper, cobalt, nickel, zinc, manganese, beryllium, uranium, thorium, cadmium, magnesium and the rare earth metals9 from starting material selected from the group consisting of ores, concentrates, oxidic 2~ roasting products, ferrites, and slags, by converting said metal values to sulfates with the aid of thermal treatment under oxidi~ing conditions in the temperature range of 400 - 800C, the improvement which comprises (a~ forming a reaction mixture of said starting material containing at least one of said metal values and of iron(III)sulfate and another sulfate selected from the group consisting of alkali metal sulfate, ammonium sulfate, a compound containing said sulfates, and a mixture thereof, in which sulfate mixture the molar ratio of iron(III)sulfate to the alkali metal sulfate is from 0.1 to about 0.5, said alkali metal being selected from the group consisting of sodium, potassium, lithium and a mixture thereof and the total amount of said iron(III)sulfate being at least the stoichiometric amount needed to react with the metal value Me according to the reaction.
3 ~eO(melt~solid) + Fe2(~4)3(melt) 3 MeSO4(melt) ~ Fe2o3(solid) and (b) adjusting the temperature and the partial pressure of SO3 in the gas atmosphere so that the thermal decom-position of said iron~III)sulfate in the melt according to 10 the reaction 2 4)3(melt) Fe2O3(solid) ~ 3 S3( is substantially prevented.
First the fundamentals of the process according to the present invention will be discussed. In the text, reference is made to the drawings and tables as follows:
Figure 1 is a graph showing the stability diagram of the system Fe2(SO4)3 - Fe203 with the temperature and the partial pressure of SO3 in the gas atmosphere as variables.
The diagram shows the equilibrium curves for iron (III) sulphate with activities of 1, 0.1, 0.01 and 0.001, respec-tively (curves 1-4). There is also shown an equilibrium curve for SO3/SO2 (maximum SO3 content at a pressure of 1 bar) when the initial mixture contains pure 2 and SO~ in stoichiometric relation (curve 5) and when the initial mixture consists of technical air and SO2 in stoichiometric relation, i.e. SO2:02 = 2:1 (curve 6).
Figure 2 and the associated table 2 at the end of this specification show the values of the molar Gibbs energy (known earlier as the free energy)with respect to temperature for the reac-tion (6) MeO + S03 --~ MeS04 S
calculated for one reacting S03 mole.
The technically most important known reactions for which reliable thermodynamical values are avail-able are compiled in Fig. 2 and Table 1.

Table 1:
Equilibriumreactions of different metal sulfates as in.figure 2 1 S02 + 1/2 2 = S3 1~ 2 1t3 Al203 + S03 = 1/3 Al (SO ) 2 3 3 /3 e2(S04)3

4 BeO + S03 = BeS04 CuO . CuS04 + S03 = 2 CuS04 6 ZnO . 2 2nS04 + S03 = 3 ZnS03(~ ) 2~ 7 2 CuO + S03 = CuO . CUSO4 8 NiO + S03 = NiS04 9 1/2 ThO2 ~ S03 = 1/2 Th(S04)2 10 3/2 ZnO + S03 = 1/2 (ZnO . 2 ZnS04) 11 CoO + S03 = CoS04 12 1/2 (CdS04 . 2 CdO) + S03 = 3/2 CdS04 13 1/2 (La203 . S03) + S03 = 1/2 La2(S04)3 14 MnO + S03 = MnS04 15 PbS04 . PbO + S03 2 PbS04 16 MgO + S03 a MgS04 17 3/2 (PbS04 . 4 PbO) + S03 = 5/3 (PbS04 . 2 PbO) 18 2 (PbS04 . 2 PbO) + S03 = 3 (PbS04 . PbO) 19 3/2 (PbS04 . 4 PbO) -~ S03 = 5/2 (PbS04 . 2 PbO) 03 PbS04 . PbO
a S03 CaS04 G~

Unfortunately, for some of the metals which this in-vention concerns, the available data about required thermodynamic values are insufficient to calculate similar curves as presented in Fig. 2. Thus, for examp~
le, it can be supposed that the ~a~ppropriate curve for uranium is located between curves 14 and 16. According-ly, the appropriate curve for cerium is located bet-ween curves 7 and 9. The equilibrium reactions connect-ed with Fig. 2 are described in Table 2. The reactions of Table 2 and the respective ~ G values from Fig. 2 are to be combined, and thus it is easy to calculate the thermodynamic prerequisites for the reactions (8) under different temperatures.
Figure 3 contains a phase diagram of the sys-tem Na2SO4-Fe2(SO4)3 according to the Measurements made by the author and according to P. I. Fedorov and N. I. Illina: ~uss. J. of Inorg. Chem. 8 (1963) p. 1351.
The mechanism of the sulfation according to the present invention is as follows:
When heating in oxidi.zing conditions, e.g. in aix, the mixture that contains some compound ~usual-ly sulfide) of the wanted metal and the Na-rich mix-ture of the binary partial system of the beforesaid ternary system (as an example, the system Na2SO4-Fe2(SO4)3 can be lnto consideration) to 605C, a small amount of the eutectic melt of the system Na2SO4-Fe2(SO4)3 begins to form. In the beginning the melt contains 17 mole per cent Fe2(SO4)3.

When it is heated to higher temperatures, the amount of the liquid phase in the mixture increases and it is able to dissolve the Me-oxide which is formed by the reaction with atmospheric o~y~en ~and it also dissolves the minor amount of Me-sulphate which is probably formed~. If the starting material consists of the incon~ruently melting compound NaFe(SO4)2, which is also included in said binary system, it forms a melt phase at the temperature 680C which contains about 40 percent Fe2(SO4)3 and, at the same time, the pure Fe2(SO4)3 precipitates. It has now an activity value of 1 and it shows a strong tendency to decompose in conditions according to Fig. 1, curve 1, if that tendency is not abscured by a sufficient SO3-pressure of the surrounding atmosphere. On the other hand, the amount of Fe2(SO4)3, which is already present in the liquid phase, remains essentially unaffected because of the favourable activity conditions.
At the same time as the amount of the third sul-phate (MeSO4) in the ternary MeSO4-E`e2(SO4)3-Na2SO4 ~0 mixture increases, the total amount o~ the liq~id phase increases and thus also its ability to moisten the reac-tion mixture and to dissolve the formed reaction product ~eO or MeSO4 increases. If the reaction temperature is constant, the dissolving process is an autocatalytic one.
It increases until the limiting factor is either the total amount of the dissolvable materi~l or, in principle, the mixture becomes saturated with the dissolved salt MeSO4 in which case the salt be~ins to precipitate.
It has been experimentally noticed that the forma-tion of the liquid phase in the ternary MeSO4-Fe2(SO4)3-Na2SO4 system can also proceed as a reaction b~tween solid materials below 605C.
- Although the text has been concerned only with ternary mixtures to illustrate the objects of the present invention, this should not in any way be constxued as a limiting factor. Thus it is also an object of the present invention to extract metal values from complex concen-trates containing several metals. It is also an object of the invention to use Na-K-Fe-sulphate as a starting material.
It should be particularly noted that the reactions of this type which are taking place in the melts of the ionic saltsare extremely fast, because they are charge transfer reactions which are thus taking place between ionic constituents ~s follows:
Me2 + 3 o2 ~ 2 Fe3 ~ 3 SO4 3 Me + 3SO4 + Fe2O3 w As a consequence of the reaction, the produced hematite ~Fe2O3) precipitates out of the melt because of its low solubilit~, whereas the wanted metal value Me remains in the melt as an ionic species and is recoverable with difEerent methods.
When performing sulphation ~ith the process of this invention, particular care must be taken that the ! amount of the ironIIII)sulphate in the reaction mixture is suficient to obtain a full conversion with respect to the wanted metal oxide or oxides according to reaction 7.
Thus, the iron~III)sulphate present in the reac-tion mixture should not be allowed to decompose undulY, at least before all the metal value Me is in the sul-phated form. Its amount should be optimi2ed by selecting the temperature and SO3 pressure of the surrounding gas atmosphere in the known and controlled manner so that there is always enough iron(III)sulphate available for use according to reaction 7.
It should be particularly noted that the SO3 content of the gas atmosphere has in principle no other role in the reactions than to keep the iron(III)sulphate stable in higher temperatures as is advantageous.
. ~s a natu.ral starting material fox the applica-- tion of the present invention, various sulphidic ores and concentra-tes can be used which nearly always contain also iron. Minerals present in such ores are typically pyrite, pyrrhotite, galena, sphalerite, pentlandite, chalcopyrlte, cubanite, bornite, covellite and millerite.
Thus, by performing the oxidation needed for the preli-minary treatment in the controlled conditions and at low temperature, it is possib].e to get as a reaction product, a part or the existing iron and the wanted metal al-. ready in the sulphate form because they have reacted withthe SO2 and SO3 released in the oxidation, while the rest of the wanted metal oxidizes is oxidi~ed into the corresponding oxide. It should be particularly noted thatJ when oxidizing sulphidic material, the reaction is highly exotermic and the heat evolved easily causes local overheating. Table 1 shows the ignition points of various sulphide minerals.
Table 1: The ignition points of some pure sulphide minerals (F.Habashi:Chal.copyrite, its Chemistry and Metallurgy, McGraw-Hill Inc, Chatmam, 1978,-p. 45) Ignition temperature C
particle size Pyritè Pyrrhotit~ Chalco- Sphalerit~ ~alena mm pyrite ~- . (53~4~S) (36.4%oS) (34~5%S) (32~9%S) (29~4~S) 0.10-0 ~ 15 422 460 364 637 720 0.15-'J ~ 20 423 465 375 644 730 30 0~20-0.30 424 471 3~0 646 730 0.30~0.50 426 475 385 646 735 0~50-1.00 426 480 395 646 740 1.00-2.00 428 482 410_ 646 750 f 35 With the aid of thermal analysis it has been noted that the oxidation and conversion to sulphates progress at .

temperatures that are a little higher (50 - 150C) than the ignition temperatures. Under these conditions,a considerable part of the iron ancl the wanted metal value is in the sulphate form, which is preferable both from the point Gf view of a much easier formation of the ternary melt and a smaller consumption of the iron(III) sulphate. ' ' ' When oxidizing for example chalcopyrite in air atmosphere, it has been noted (F.Habashi:Calcopyrite, its Chemistry and Metallyrgy, ~lcGraw-Hill Inc., Chatmam 1978, p. 51) that the amount of water-soluble copper has been 40-60% and iron 10 - 15 ~ of the amount needed : when operating at 500C.
The described application of the process of this ~5 invention is not by any means considered to be limited only to sulphidic mine-als or concentrates that contain iron. However, the application that is described does offer a convenient solution of the processina of iron-containing substances because the starting materials consist of reaction components such as the elements Fe, Me, S, and 0, which are in a convenient form for the application of the process. Further, the appre~iable heat of reaction when the sulphidic material oxi~izes is a significant advantage for the heat economy of the process, and said heat can be used in other steps of,the process.
When making a thermodynamic examination of the reaction (7) in component form (Fig~ 2):
-30 (8) 3~e,0 + ~e2(SO~)3 t 3 MeSO4 Fe2 3 it is observed that reaction (8) is thermodynamically favoura~le for most of the important metals. The most important exception is aluminium. Thus, referring to 35 well-known thermodynamics and, on the other hand, to r the remarkahle higher speed of the ionic reactions in salt melts compared to the speed of solid state reactions, it can be supposed with good reason that the process is, with the exception of aluminium, applicable to the produc-t-ion of most of the metals of industrial signi~icance when convertin~ them from their oxide form to their sulfate form.
To what extent it is possible to use its sulfate form to extract a metal value Me by a simple water leach-ing procedure, depends in various cases on both the solu-bility of the metal sulfate in question, and also on theexisting methods to remove the harmful substances, in this caseespecially iron, from the solution.
Recently, the method for the precipitation of iron(III) compounds as a jarosite compound from the mild-- ly acidic solutions first described by Steinveit (Norwe-gian Patent No. 103 047) has gained very wide use, especially in the zinc process industry. Another known method to precipitate iron is the so-called goethite process (Belgian Patent No. 724 214, Australian Patent No.424 095).
There are several known jarosite compounds (Na, K and NH4 jarosites) which are being used in industrial zinc processes. The jarosites form a series of compounds ln which the alkali metal can be isomorphically substi-tuted by another. Their chemical formuia can be written in the general form:
AX(H30)1-xFe3(so4)2(o )6 Thus, a part of the alkali-ions are isomorphical-ly substituted by the H30 ion. This is the situation especially with sodium jarosite; usually at least 20 % of the sodium has been substituted by the hydronium ion. On the contrary1 in the case of potassium~jarosite, the amount of substitution is considerably less. The decomposition of the mixed jarosites proceeds as is schematically described in Table 3.

f~

o~ o X N

OC) + 0 _ N
ON ~ ~
X ~ ~ >~
X ~ ~
N / _ ~ $

N N O O n n ~
ô" ôl ~70~\oR R
æ

*
o~ +
--~ Ou x Ou ~

z ~

a æ~
x x .

From Table 3, it is noted that, above the temperature 370C, the aforementioned double sulfate with the gene-ral chemical formula AFe(SO4)2 is formed in the mixture.
This kind of partly decomposed jarosite contains, in addition to said double.sulfate, also different amounts of hematite Fe2O3 and ferric sulfate Fe2(SO4)3, depend-ing on the degree of the isomorphic substitution, and offers thus a particularly convenient starting material for the application of the process of the present inven-tion by forming, as described, the impure double sulf-ate AFe(SO432 where symbol A represents one of the following ions or a combination of them: Na, K or NH4.
By using jarosite compounds as a starting material it is possible to reach situation where the alkali- and 15 iron sulfates present in the process can, to a large extent, be recirculated and, by this means, the environ-mental problems that are typical of the jarosite process can be decreased and the cost of reagents can be reduced.
The amount of hematite that is formed in the reaction mixture can be filtered by simple mechanical filtration before the jarosi.te precipitation and it can thus form a valuable by-product or an object of further processing.
It is often an advisable procedure to thermally decompose the iron(III)sulfate before dissolving it, either in another part of the reactor or in a separate reactor.
The formation of ferrites can thus be avoided beacuse the metal values already exist in the sulfate form and it is much easier to control the temperature because the reac-tions, in this case, are not exotermic.
The recovery of metals by first converting them into sulfates has been applied or suggested for appli-cation to the following metals: copper, cobolt, nickel, ZillC, manganese, beryllium, uranium, thorium, cadmium, magnesium and to rare earth metals such as lanthanium, cerium etc. On the basis the thermodynamic examination, it can be stated that all of the aforementioned metals come into consideration when appl~ing the process of the present invention. All of them also form a sulphate which dissolves sufficiently in water.
Thus, a natural starting material for the applica-tion of the process in question consists of the sulphidesor oxides of the aforementioned metals or of materials which are easily converted into the sulphidic or oxidic form. Also the ferrites of different metals can succes-fully be handled according to the present invention.
Further, it is directly applicable to some silicates, carbonates and phosphates, either as such or combined with oxidizing or sulphatizing treatment.
The invention will be further understood from the following examples which should not in any way be con-~5 strued as limiting. -Examplè 1 .
To solve the usable operating conditions with different starting materials, a series of experimentswere carried out with copper concentrate which contained copper as chalcopyrite. The analysis of the concentrate was 28.0 per cent Cu and 3.8 per cent Zn. The e~periments were carried`~out with Na-1130-ja~osite which contained 0.8 mol of Na, or with Na-K-jarosite which contained O . 43 mol o~ Na and 0.37 mol of ~ (per mole of the jaro-site compound~, or with a syntheticaliy prepared compound ~ NaFe(S04)2 as the sulphate do~ating agent. The experi-ments were performed in a conventional la~oratory furnace in open crucibles and in air atmosphere. The results were as follows:

.

14 ~ 8~9 Temperature Tlme Compound Mixture ratio Yield/%
C mln concentrate/ water-soluble sulphate mg/mg Cu Zn 700 5 NaFe(SO4)2 200/400 67 660 16 - " - 200/600 73 620 37 - " - 100/600 100 95 -620 37 Na--jarosite 100/800 100 580 30 Na-jarosite 200/300 92 560 60 Na-K-jarosite 200/35099 97 10 560 37 NaFe(SO4)2 200/30094 .
600/5608/52 _ 1l _ 200/150 96 600/5608/52 Na-jarosite 200/300 96 600/5608/52 - " - 500/5Q0 98 97 520 60 Na-K-jarosite 200/30092 Example 2 The same concentrate was used as in example 1 except that the SO2-content was increased and the 2-content decreased by covering the crucibles with lids.
The following results were noted:

.. ", .. . .
r~emperature Time Compound Mixture/ratio Yield/~
C min water-- soluble Cu 650 30NaFe~SO~)2 200/300 63 650 30 - " - 200/300 57 An experiment was also pexformed where 200 mg of the concentrate together with 300 mg of NaFe(SO4)2 were closed in an autoclave. It turned out that, after a reac-tion period of 25 minutes, the material still was present - mainly as a suiphide. Thus, it can be concluded that a sufficient availab.ility of oxygen is one of the main re-quirements when performing sulphatation accordin~ to the present method.

Example 3 A similar treatment as described in Examples 1 and 2 was carried out with several Co-concentrates con-taining between 18 and 20 mole per cent Co. The follo-wing results were obtained: .
Temperature Time Compound ~lixture ratio Yi~ld/%
. C min water-. soluble Co 10 600/560 60 Na-jarosite 200/300 94 580 30 Na-jarosite 200/300 91 Example 4 .
15 A similar treatment as described in Examples 1 and 2 was performed with Cu2O and CoO in normal air atmosphere and by using the compound Na3Fe(SO4)2 which i~ included in the Na2SO4-Fe2(SO4)3-system. The following results were obtained:
20 Temperature Time Compounds Mixture ratio Yield/%
C min water-so-~ - lubles Cu 630/S60 20/40 Na3FetSO4)2 100/1000 100 25. Co 630/560 20/40 Na3Fe(SO4)2 100/1000 93 In other words, sulphation can be performed in the melt without any atmospheric sulphuric trioxide, as has been stated.

Exampl.e 5 A melt was produced ~rom K-Na- and Cu-sulphates with the molar ratios 1:1:1. 200 mg of Fe2O3 was added at 600C to thls melt, and the mixture was treated for .
one hour. The amourlt of water-soluble iron which had reacted to form the sulphate was 0.6 mg. Thus, Fe2O3 is only very slightly soluble in the melt conditions in question.
Example 6 A similar treatment as described in E~amples 1, 2 and 5 was performed on the dumped slag of the slag con-centration plant of a copper sMelter. The analysis of theslag was 0.45 per cent Cu, 3.5 per cent Zn, 1.3 per cent Mg and 0.82 per cent Ca. The compounds were present most-ly as silicates. The treatment was performed at 630C in air atmosphere, and the reaction time was one hour. The silicate-sulphate ratio in the mixture was 1:1. The following results were obtained:

Temperature Time Compound Yield (water-solubles Qo) C min - Cu Zn Mg Ca - 20 630 60 NaFe(SO4)2 89 58 55 46 630 60 Na3Fe(SO4)3 78 71 52 ~1 It can be stated that the present method is appli-cable also to the siliceous slag whicll is a difficult material to treat economically with other methods, and that the present method is applicable also to low metal concentrations of the starting material.

Example 7 A similar treatment as described in 2xamp]es 1, 2

5 and 6 was performe~ on a Na2SO~-FeSO~-mixture (molar ratio 1:1) and the copper concentra~e of Example 1. The temperature was 600C, ancl the reaction time was one hour.
The ratio of Cu-concentrate to sulphate was 200 mg/400 mg.
The yield of the water-soluble copper was ~3 per cent.

Table 2: (cf also figure 2) Equilibrium reactions of different metal sulphates as in figure 2 S02 + 1/2 2 = S3 2 1/3 Al O + SO - ~ /3 Al (SO ) 3 1/3 Fe O + SO ~ 1/3 Fe (SO ) 4 Beo ~ S03 = BeS04 CuO CuS04 + S03 = 2 Cu504

6 ZnO . 2 ZnS04 + S03 = 3 ZnS03 (~ )

7 2 CuO -~ S03 = CuO CUSO4

8 NiO + S03 = NiSo4

9 1/2 ThO2 + S03- = 1/2 Th (S04) 2 3/2 ZnO + S03 = 1/2 (ZnO ~ 2 ZnS04) 11 CoO + S03 CoS04 12 1/2 (CdS04 ~ 2 CdO) + S03 = 3/2 CdS04 13 1/2 (La203 ~ S03) + S03 = 1j2 La2(S04)3 PbS04 PbO + S03 - 2 PbS04 16 g 3 g 4 17 3/2 (PbS04 ~ 4 PbO) + S03 = 5/3 (PbS04 ' 2 PbO) 18 2 (PbS04 ~ 2 PbO) + S03 = 3 (PbS04 ~ PbO) 19 3/2 (PbS04 ~ 4 PbO) + S03 - 5/2 (PbS04 ' 2 PbO) 5 PbO + S03 = PbS04 . 4 PbO
21 CaO + S03 = CaS04 o ~n ~ X
CO r ~_~
O ~
~ O
X O O O +
N U~ N

O O
N N
a) x O a~ a~
Lr~ h ~r / X X
R N / I I tn + / -- _ ~
,1 ~1 ~ U~
O O
U~ ~1 N r--O O
X ~ ~ N O
O N
X ~ ~1 ~ , I _ O O
U~ O ~ r-~ X U~
U~ X ~
~ ~ -- O
O
a) ~ ~ _o ~- + o I
~ ~ o ~ o + ~ rl rl ~ rl O N O _ U~
_ e~ + C~ ,_ N ~ ~D O
O ~ o ~ ~ O
, a)~ u o I ~Y O + ~3 -- ~ ~~ o a~ U~ O O O O
1~ X ~ ~U~ ~ ~ `~ ~ U~el~ ~ C) m "to :c ~ o u~ -- ~D o a~
O O / t~ o ~ N N N ~
(~ X X.i x X X X h Z ~ I I I I '` I O
Z
~, o m~
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Claims (8)

WHAT I CLAIM IS:

1. In process for recovering non-ferrous me-tal values selected from the group consisting of cop-per, cobalt, nickel, zinc, manganese, beryllium, ura-nium, thorium, cadmium, magnesium and the rare earth metals, from starting material selected from the group consisting of ores, concentrates, oxidic roast-ing products, ferrites, and slays, by converting said metal values to sulfates with the aid of thermal treatment under oxidizing conditions in the tempera ture range of 400 - 800°C, the improvement which com-prises (a) forming a reaction mixture of said starting material containing at least one of said metal values and of iron(III)sulfate and another sulfate selected from the group consisting of alkali metal sulfate, ammonium sulfate, a compound contain-ing said sulfates, and a mixture thereof, in which sulfate mixture the molar ratio of iron(III)sulfate to the alkali metal sulfate is from 0.1 to about 0.5, said alkali metal being selected from the group con-sisting of sodium, potassium, lithium and a mixture thereof and the total amount of said iron(III)sulf-ate being at least the stoichiometric amount needed to react with the metal value Me according to the reaction:
3 MeO(melt+solid)+Fe2(SO4)3(melt) ? 3 MeSO4(melt)+Fe2O3(solid) and (b) adjusting the temperature and the partial pressure of SO3 in the gas atmosphere so that the thermal decomposition of said iron(III)sulfate in the melt according to the reaction Fe2(SO4)3(melt) ? Fe2O3(solid) + 3 SO3(gas) is substantially prevented.

2. In process for recovering non-ferrous me-tal values selected from the group consisting of cop-per, cobalt, nickel, zinc, manganese, beryllium, ura-nium, thorium, cadmium, magnesium and the rare earth metals, from starting material selected from the group consisting of ores, concentrates, oxidic roasting products, ferrites and slags, by converting said me-tal values to sulfates with the aid of thermal treat-ment under oxidizing conditions in the temperature range of 600 - 700°C, the improvement which comprises (a) forming a reaction mixture of the said starting material containing at least one of the said metal values and of iron(III)sulfate and another sulfate selected from the group consisting of alkali metal sulfate, ammonium sulfate, a compound containing said sulfates, and a mixture thereof, in which sulfate mix-ture the molar ratio of iron(III)sulfate to the alkali metal sulfate is about 0.5, said alkali metal being selected from the group consisting of sodium, potas-sium, lithium and a mixture thereof and the total amount of said iron(III)sulfate being at least the stoichiometric amount needed to react with the metal value Me according to the reaction:
3 MeO(melt+solid)+Fe2(SO4)3 ? 3 MeSO4(melt)+Fe2O3(solid) and (b) adjusting the temperature and the partial pressure of SO3 in the gas atmosphere so that the thermal decomposition of said iron(III)sulfate in the melt according to the reaction Fe2(SO4)3(melt) ? Fe2O3(solid) + 3SO3(gas) is substantially prevented.

3. The process of claim 1 or 2 wherein said reaction mixture comprises ores, concentrates, roast-ed oxidic products, ferrites or slags of said metal values and a jarosite-type compound of the formula A [Fe3 (OH)6 (SO4)2]

where A is selected from the group consisting of so-dium, potassium, ammonium and a mixture thereof.

4. The process of claim 1 or 2 wherein said reaction mixture comprises ore, concentrate, roasted oxidic product, ferrite or slag and double sulfate having the formula AFe(SO4)2 where A is selected from the group consisting of sodium, potassium, ammonium and a mixture thereof, which double sulfate is formed by thermal treatment of said jarosite compound.

5. The process of claim 1 or 2 wherein said reaction mixture is treated in the temperature range of 600 - 800°C in the SO3-gas atmosphere of 0.03 -0.3 bar.

6. The process of claim 1 or 2 wherein the iron(III)sulfate of said reaction mixture is formed at least partially from the iron compounds of the starting material by simultaneous or preceding therm-al treatment in sulfating reaction conditions.

7. The process of claim 1 or 2 wherein after the sulfation reaction the iron(III)sulfate remaining in the reaction mixture is converted into hematite by means of controlling the SO3 content of the gas atmosphere as well as the temperature in another part of the reactor or in another reactor, after the iron-(III)sulfate has first been used in the sulfation reaction as set forth.

8. The process of claim 1 or 2 wherein the iron(III)sulfate remaining in the reaction mixture after the sulfation reaction is precipitated as a jarosite- or goethite-type compound.