Process for recovering primary metal residue from a metal-containing composition

Abstract

A process for recovering metal value-containing precipitates in consistently high concentrations from a metal-containing composition by combining selective roasting and leaching steps.

Claims

1. A process for recovering a primary metal residue from a metal-containing composition comprising: (a) preparing a feedstock of the metal-containing composition and an alkali salt; (b) reductively roasting the feedstock at a roasting temperature for a roasting period to produce a roast; (c) cooling the roast to produce a roasted mass containing metallic iron or an alloy or compound thereof and soluble metal oxides; (d) adding an aqueous medium to the roasted mass to form a substantially insoluble product and a first solution of soluble metal oxides; (e) acid leaching the substantially insoluble product or a fraction thereof to produce a leach residue and a second solution of soluble metal oxides; (f) roasting the leach residue in the presence of a bisulphate or bicarbonate of an alkali metal or alkaline earth metal to produce a roasted residue; and (g) hydrometallurgically extracting from the roasted residue the primary metal residue and a third solution of soluble metal oxides.

2. The process as claimed in claim 1, wherein the bisulphate or bicarbonate of an alkali metal or alkaline earth metal is a bisulphate or bicarbonate of an alkali metal.

3. The process as claimed in claim 1, wherein the bisulphate or bicarbonate of an alkali metal or alkaline earth metal is NaHSO.sub.4.

4. The process as claimed in claim 1, further comprising: recovering one or more metal value-containing precipitates from the first solution of soluble metal oxides.

5. The process as claimed in claim 1, further comprising: recovering one or more metal value-containing precipitates from the third solution of soluble metal oxides.

6. The process as claimed in claim 1, further comprising: (d1) separating a rare earth oxides-containing colloidal solution from the surface of the first solution of soluble metal oxides.

7. The process as claimed in claim 1, wherein the metal-containing composition is titanium rich.

8. The process as claimed in claim 7, wherein the metal-containing composition is a titanium ore concentrate.

9. The process as claimed in claim 7, wherein the primary metal residue is TiO.sub.2.

10. The process as claimed in claim 7, further comprising: recovering one or more sodium or vanadium values from the first solution of soluble metal oxides.

11. The process as claimed in claim 7, further comprising: recovering one or more sodium values from the third solution of soluble metal oxides.

12. The process as claimed in claim 7, further comprising: recovering one or more titanium values from the third solution of soluble metal oxides.

13. The process as claimed in claim 7, further comprising: recovering one or more iron values from the third solution of soluble metal oxides.

14. The process as claimed in claim 7, further comprising: recovering one or more vanadium values from the third solution of soluble metal oxides.

15. The process as claimed in claim 7, further comprising: recovering one or more calcium values from the third solution of soluble metal oxides.

16. The process as claimed in claim 1, further comprising: (d2) magnetically separating from the substantially insoluble product a magnetic fraction and a substantially non-magnetic fraction, wherein step (e) is: acid leaching the substantially non-magnetic fraction to produce a leach residue and a second solution of soluble metal oxides.

17. The process as claimed in claim 1, further comprising: (d3) smelting the magnetic fraction to produce a steel residue and a non-magnetic slag.

18. The process as claimed in claim 17, further comprising: (d3a) acid leaching the non-magnetic slag to produce a slag leach residue and a fourth solution of soluble metal oxides; (d3b) roasting the slag leach residue in the presence of a bisulphate or bicarbonate of an alkali metal or alkaline earth metal to produce a roasted slag leach residue; and (d3c) hydrometallurgically extracting from the roasted slag leach residue a secondary metal residue and a fifth solution of soluble metal oxides.

19. The process as claimed in claim 1, wherein step (b) is: oxidatively roasting the feedstock at a roasting temperature for a roasting period to produce a roast, wherein step (e) is: acid leaching the substantially insoluble product to produce a leach residue and a second solution of soluble metal oxides.

Description

(1) The present invention will now be described in a non-limitative sense with reference to the accompanying Figures in which:

(2) FIG. 1A illustrates a first embodiment of the process of the invention;

(3) FIG. 1B illustrates a second embodiment of the process of the invention;

(4) FIG. 1C illustrates a third embodiment of the process of the invention;

(5) FIG. 2 illustrates the results of a microstructural analysis of columbite concentrates used in the second embodiment of the process of the invention;

(6) FIG. 3 illustrates the results of a microstructural analysis of columbite concentrates used in the second embodiment of the process of the invention showing the presence of rare earth oxides (REO);

(7) FIG. 4 illustrates the results of a microstructural analysis of the roasted mass from step B1 of the second embodiment of the process of the invention;

(8) FIG. 5 illustrates X-ray powder diffraction patterns of the roasted mass from step B2 of the third embodiment of the process of the invention;

(9) FIG. 6 illustrates the results of a microstructural analysis of the roasted mass from step B2 of the third embodiment of the process of the invention showing selective separation of Fe, Mn and Sn;

(10) FIG. 7 shows a colloidal layer containing a mixture of rare earth oxides resulting from step Cl of the second embodiment of the invention;

(11) FIG. 8 illustrates SEM/EDX and XRD patterns of a solid raffinate from step D1 of the second embodiment of the invention;

(12) FIG. 9 illustrates XRD patterns of the washed solid residue from step O of the first embodiment of the invention;

(13) FIG. 10 illustrates Al.sub.2O.sub.3-V.sub.2O.sub.5 precipitates obtained after step E of the first embodiment of the invention;

(14) FIG. 11 illustrates the XRD pattern for the Al.sub.2O.sub.3V.sub.2O.sub.5 precipitates obtained after step E of the first embodiment of the invention;

(15) FIG. 12 illustrates XRD patterns of (a) the roasted mass, (b) magnetic fraction and (c) non-magnetic fraction from the first embodiment of the invention;

(16) FIG. 13 illustrates schematically the cold water stream assisted magnetic separation carried out in step D of the first embodiment of the invention;

(17) FIG. 14 illustrate backscattered SEM images of the non-magnetic fraction (see (a) and (b)) and the magnetic fraction (see (c) and (d)) from step D of the first embodiment of the invention; and

(18) FIG. 15 illustrates the XRD pattern of the leach residue 30 from step J of the first embodiment of the invention.

EXAMPLE 1

(19) A first embodiment of the process of the invention is illustrated in FIG. 1A. Metal oxides were recovered from a mineral waste which was the product of the extraction of vanadium from a South African mineral ore. The composition of the mineral waste is given in Table 1.

(20) TABLE-US-00001 TABLE 1 XRF analysis of the as-received mineral sample Fe.sub.2O.sub.3 TiO.sub.2 SO.sub.3 Na.sub.2O Al.sub.2O.sub.3 SiO.sub.2 MnO CaO MgO V.sub.2O.sub.5 Wt 66.5 11.7 2.1 5.6 5.0 5.8 0.3 1.6 0.4 0.3 %

(21) The process in this first embodiment involved two main stages. Stage 1 involved concentration and stage 2 involved removal of impurities. The reactions involved in the first embodiment are shown below. The material and steps involved in each stage were as follows:

(22) Stage 1Concentration A. The as-received mineral waste was ground into particles with a dimension less than 106 m. 250 g of the ground mineral waste was mixed with sodium carbonate (50 g) and activated charcoal or coal (72.5 g) to produce a feedstock. B. The feedstock was transferred into an alumina crucible and heated inside a resistance furnace under an inert (nitrogen or argon) atmosphere at 1050 C. for 90 minutes to produce a roast. Carbon produces three parts of carbon monoxide gas which has a large calorific value as a fuel. C. The roast was cooled to a roasted mass and ground into particles with a dimension less than 106 m. The roasted mass was characterised by XRD, SEM and XRF. The main phases identified by XRD (see FIG. 12) were metallic iron and Na.sub.2TiO.sub.3 formed by reactions 1 and 2. The secondary constituents were NaAlSiO.sub.4 and CaTiO.sub.3. D. The ground roasted mass (233 g) was then fed onto a magnetic trough (100 in FIG. 13) for wet magnetic separation. The ground roasted mass was gently poured with a flow of cold water 102 from a nearby tap to wash-off non-magnetic components and dissolve water-soluble components such as NaAlO.sub.2 and NaVO.sub.3. The ground roasted mass on the magnetic separator was scrubbed with a brush to aid separation and a non-magnetic fraction 2 (48 g) suspended in a first solution 3 was collected in a beaker 101 for detailed chemical, physical and microstructural analyses. A magnetic fraction 1 (145g) was retained in the magnetic trough 100. The non-magnetic fraction 2 was allowed to settle and the first solution 3 was decanted. The XRD patterns for the magnetic fraction 1 and non-magnetic fraction 2 are shown in FIG. 12. The non-magnetic fraction 2 included CaCO.sub.3, Na.sub.2TiO.sub.3, CaTiO.sub.3 and NaAlSiO.sub.4. Fe was mainly recovered in the magnetic fraction 1. Na.sub.2TiO.sub.3 is less crystalline in the non-magnetic fraction 2 due to dissolution of a part of the sodium. XRF analysis for the magnetic fraction 1 and non-magnetic fraction 2 are shown in Table 2 and it is evident that the Fe content in the magnetic fraction 1 was very high (88 wt %). The magnetic fraction 1 contains 2.1 wt % alkali due to the presence of residual sodium titanate. By comparing the TiO.sub.2 content in the non-magnetic fraction 2 (Table 2) and the as-received sample (Table 1), it is evident that the concentration of TiO.sub.2 has increased threefold after steps B, C and D. FIG. 14 illustrates backscattered SEM images of the non-magnetic fraction 2 (see (a) and (b)) and the magnetic fraction 1 (see (c) and (d)). E. A first metal value-containing precipitate 4 (2.4 g) was recovered from the first solution 3 by CO.sub.2 gas bubbling for 30 minutes at 80 C. A digital image, XRD and XRF results for the first metal value-containing precipitate 4 are shown in FIGS. 10 and 11 and Table 7 respectively. F. A fourth solution 5 separated after step E was subjected to evaporation to produce a second metal value-containing precipitate 6 (21 g) which contained 94 wt % Na.sub.2CO.sub.3 and 0.6 wt % V.sub.1O.sub.5 (see Table 8). The second metal value-containing precipitate 6 was recycled into step B. G. The magnetic fraction 1 from step D was thoroughly mixed with 1 wt % carbon and transferred to an alumina crucible where it was smelted for 2 hours under a flow of argon gas (3 litres/min) at 1470 C. This led to the recovery of a steel residue 7 (125g) and a non-magnetic slag 8 (16.2 g). XRF analyses of the steel residue 7 and non-magnetic slag 8 are given in Table 5. H. The non-magnetic slag 8 was treated with 0.5M H.sub.2SO.sub.4 and heated at 40 C. for 3 hours to produce a slag leach residue 31. I. The slag leach residue 31 was heated at 800 C. for 90 minutes to burn off excess carbon and produce a slag 9 (11.2g). XRF analysis of the slag 9 is shown in Table 6. The slag 9 may be subjected to magnetic separation of any residual iron (in a manner analogous to step D) or fed back into the feedstock in step A for the same purpose. J. The non-magnetic fraction 2 was treated with 0.5M H.sub.2SO.sub.4 and heated under normal atmosphere at 40 C. for 2 hours to produce a leach residue 30 and a second solution. The XRD pattern for the leach residue 30 is given in FIG. 15 and it is evident that CaO is present in the form of acid insoluble CaTiO.sub.3. K. The leach residue 30 was heated at 800 C. for 90 minutes to burn off excess carbon and produce a solid residue 10 (24.5 g). XRF analysis of the solid residue 10 is shown in Table 3 from which it is evident that most of the MnO, MgO, SiO.sub.2 and Al.sub.2O.sub.3 constituents were removed into the second solution whereas CaO was only partially removed. The proportion of TiO.sub.2 has more than doubled due to dissolution of NaAlSiO.sub.4, CaCO.sub.3 and metallic Fe and Na from Na.sub.2TiO.sub.3.
Stage 2Removal of Impurities L. 11 g of NaHSO.sub.4 was added to slag 9 which was then roasted for 60 minutes at 650 C. to produce a roasted slag 40. M. The roasted slag 40 was leached with hot water to produce a secondary metal residue 11 (7.2 g). XRF analysis of the secondary metal residue 11 is shown in Table 6. N. 26 g of NaHSO.sub.4 was added to the solid residue 10 which was then roasted for 60 minutes at 650 C. to produce a roasted residue 41. Reactions 5 to 7 are the major reactions. O. The roasted residue 41 was leached for 45 minutes with hot water at 70 C. to produce a primary metal residue 15 (16.5g) and a third solution 13 which contained water soluble compounds (CaSO.sub.4, Na.sub.2SO.sub.4 and FeSO.sub.4) and about 5 wt % TiO.sub.2. Although CaSO.sub.4 is insoluble in water, it was found that dissolution was caused by the presence of FeSO.sub.4 and Na.sub.2SO.sub.4. The primary metal residue 15 was washed in 0.2M HCl to remove Na.sub.3Fe(SO.sub.3).sub.3 which was found to be slightly soluble in water. XRF analysis of the washed primary metal residue 15 is presented in Table 4 from which it is evident that the metal sulphates had dissolved during leaching and washing. From the XRD pattern shown in FIG. 9, it can be observed that highly crystalline TiO.sub.2 was obtained in the form of anatase and rutile with the major impurity being SiO.sub.2. P. A third metal value-containing precipitate 14 (2.9g) was recovered from the third solution 13 by CO.sub.2 gas bubbling for 20 minutes at 80 C. XRF analysis of the third metal value-containing precipitate 14 is shown in Table 9. Q. A fourth solution 15 separated after step P was heated at 90 C. and after about 60 minutes yielded a fourth metal value-containing precipitate 17 (2.1 g). XRF analysis of the fourth metal value-containing precipitate 17 is shown in Table 9. R. A fifth solution 16 separated after step Q was subjected to evaporation and drying to yield a fifth metal value-containing precipitate 18 (29.8 g). XRF analysis of the fifth metal value-containing precipitate 18 is shown in Table 9. XRD analysis showed a phase of sodium hydrogen carbonate Na.sub.2SO.sub.4NaHSO.sub.4(HNa.sub.3(SO.sub.4).sub.2).
Reactions
FeTiO.sub.3+Na.sub.2CO.sub.3+2C=Na.sub.2TiO.sub.3+Fe+3CO(g)1
Fe.sub.2O.sub.3+3C=2Fe+3CO(g)2
Al.sub.2O.sub.3+Na.sub.2CO.sub.3+C=2NaAlO.sub.2+2CO3
V.sub.2O.sub.5+Na.sub.2CO.sub.3+C=2NaVO.sub.3+2CO4
CaTiO.sub.3+2NaHSO.sub.4=CaSO.sub.4+Na.sub.2SO.sub.4+TiO.sub.2+H.sub.2O5
NaFeTiO.sub.3+2NaHSO.sub.4=CaSO.sub.4+Na.sub.2SO.sub.4+FeSO.sub.4+TiO.sub.2+H.sub.2O6
Fe.sub.2(SO.sub.4).sub.33Na.sub.2SO.sub.4=2Na.sub.3Fe(SO.sub.4).sub.37

(23) TABLE-US-00002 TABLE 2 XRF analysis of the magnetic fraction 1 and the non-magnetic fraction 2 Fe TiO.sub.2 Na.sub.2O CaO Al.sub.2O.sub.3 SiO.sub.2 MgO MnO V.sub.2O.sub.5 1 88.3 5.4 2.1 0.6 1.3 1.2 0.4 0.1 0.05 2 4.5 34.1 27.1 3.3 12.7 13.3 3.3 0.6 0.6

(24) TABLE-US-00003 TABLE 3 XRF analysis of the solid residue 10 from step K TiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O SO.sub.3 MgO SiO.sub.2 Fe.sub.2O.sub.3 CaO MnO Cr.sub.2O.sub.3 V.sub.2O.sub.5 Wt % 77.2 0.7 4.8 2.7 0.5 2.5 6.1 3.6 0.1 0.4 0.9

(25) TABLE-US-00004 TABLE 4 XRF analysis of the washed primary metal residue 15 from step 0 TiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O SO.sub.3 SiO.sub.2 Fe.sub.2O.sub.3 CaO Cr.sub.2O.sub.3 V.sub.2O.sub.5 Wt % 94.0 0.3 0.3 0.7 2.8 0.6 0.2 0.1 0.8

(26) TABLE-US-00005 TABLE 5 XRF analysis of the steel residue 7 and non-magnetic slag 8 from step G Steel Residue 7 Element Fe C V Al Mn Ni Si S Ti K Wt % 98.0 0.8 0.1 0.07 0.07 0.07 0.05 0.03 0.02 0.02 Slag 8 TiO.sub.2 Fe.sub.2O.sub.3 Na.sub.2O CaO SiO.sub.2 Al.sub.2O.sub.3 Cr.sub.2O.sub.3 V.sub.2O.sub.5 MgO SO.sub.3 MnO Wt % 38.3 1.0 18.0 5.6 9.1 24.7 0.1 0.1 2.1 0.4 0.5

(27) TABLE-US-00006 TABLE 6 XRF analysis of the slag 9 from step I and the secondary metal residue 11 from step M TiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O SO.sub.3 MgO SiO.sub.2 Fe.sub.2O.sub.3 CaO MnO Cr.sub.2O.sub.3 Slag 66.7 11.9 6.4 0.4 3.6 0.7 1.2 7.9 0.7 0.1 Secondary metal residue 85.5 4.2 3.1 1.8 1.4 1.2 1.2 0.8 0.3 0.1

(28) TABLE-US-00007 TABLE 7 XRF analysis of the first metal value-containing precipitate 4 from step E Fe TiO.sub.2 Na.sub.2O SO.sub.3 SiO.sub.2 Al.sub.2O.sub.3 CaO V.sub.2O.sub.5 Cr.sub.2O.sub.3 Wt % 0.9 1.2 12.3 2.3 2.6 76.9 0.8 2.4 0.1

(29) TABLE-US-00008 TABLE 8 XRF analysis of the second metal value-containing precipitate 6 from step F TiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O SO.sub.3 MgO SiO.sub.2 Fe.sub.2O.sub.3 Cr.sub.2O.sub.3 V.sub.2O.sub.5 Wt % 0.0 0.2 93.7 4.5 0.1 0.0 0.01 0.6

(30) TABLE-US-00009 TABLE 9 XRF analysis of the third metal value-containing precipitate 14, fourth metal value-containing precipitate 17 and fifth metal value-containing precipitate 18 from steps P, Q and R respectively TiO.sub.2 Al.sub.2O.sub.3 Na.sub.2O SO.sub.3 MgO SiO.sub.2 Fe.sub.2O.sub.3 CaO V.sub.2O.sub.5 14 71.9 0.2 1.1 6.7 0.2 11.1 6.1 2.4 17 2.8 0.3 8.8 44.7 0.2 1.2 41.1 0.1 18 0.2 0.3 52.9 44.7 0.5 0.1 0.5 0.4 0.0

EXAMPLE 2

(31) A second embodiment of the process of the invention is illustrated in FIG. 1B. The mineral concentrates processed in Example 2 belonged to the columbite and tantalite families. The chemical composition is shown in Table 10 and the results of a microstructural analysis of the concentrates are shown in FIGS. 2 and 3.

(32) TABLE-US-00010 TABLE 10 Chemical composition of columbite and tantalite concentrates Chemical composition (% wt) Ta.sub.2O.sub.5 (4.0-39.0) Nb.sub.2O.sub.5 (14.0-51.0) MnO (2.0-17.0) Fe.sub.2O.sub.3 (16.0-28.0) Al.sub.2O.sub.3 (1.0-7.0) SiO.sub.2 (2.0-12.0) SnO (0.8-2.5) Rare earth oxides (0.0-0.2)

(33) The material and steps involved in this embodiment were as follows: A1. A columbite concentrate was mixed as-received with NaHCO.sub.3 in the weight ratio alkali:concentrate=1:1 to produce a feedstock. B1. The feedstock was roasted isothermally in air at 900 C. for 2 hours to form a roast which was cooled to a roasted mass. During oxidation, alkali complexes of the metallic elements present in the concentrate were formed according to reactions (1) to (7) below. FIG. 4 illustrates the results of a microstructural analysis of the roasted mass showing the formation of transition metal sodium salts. C1. The roasted mass was leached with water at 25-70 C. for 0.5-5.0 hours. The sodium salts of Fe and Mn decomposed to the corresponding hydroxides (reactions (8)-(11)) and sodium titanate was polymerized to sodium octa-titanate (reaction (12)). Tin, aluminium and silica salts were dissolved in a first solution 4 whilst niobium and tantalum salts remained unaltered in a first solid raffinate 1. A colloidal solution 2 with 5 to 30 wt % of mixed rare earth oxides (REO) 10 was recovered from the top surface of the first solution 4 as indicated in FIG. 7. D1. The solid raffinate 1 was leached with a mixture of 10% w/v oxalic acid and 5% w/v ascorbic acid at 25-100 C. in a reductive atmosphere of ArH.sub.2 for 1-10 hours at a pH below 4. The ascorbic acid enhanced the reduction of iron (III) to iron (II) and the oxalic acid complexed Fe and Mn to form soluble Na, Fe, Mn and Sn oxalates in a second solution 11 (see reactions (16) to (19)). Titanium was obtained as synthetic rutile and niobium and tantalum remain unaltered in a second solid raffinate 3. FIG. 8 illustrates SEM/EDX and XRD patterns of the second solid raffinate 3 showing a content of Mn and Fe lower than 1.5 wt % and combined Nb.sub.2O.sub.5 and Ta2O.sub.5 of 65 to 70 wt %. E1. The second solid raffinate 3 and NaHSO.sub.4 (ratio in the range 0.2:1 to 3:1) was then roasted in air at 400-700 C. for 0.1 to 4 hour to produce a roasted residue 20. The remaining Ca, Mg and Na formed sulphates as shown in reactions (20) to (23). The presence of Ca and Mg increased the solubility of Na.sub.2SO.sub.4. F1. The roasted residue 20 was leached in water at 25 to 70 C. for 0.5 to 5 hours to remove soluble Ca, Mg, Na, Mn and Fe sulphates in a third solution 9 which could be subjected to recovery of alkali for recycling (by CO.sub.2 bubbling for example). A primary metal residue 7 having a concentration of Nb.sub.2O.sub.5 and Ta.sub.2O.sub.5 of 79 to 90 wt % was obtained. G1. Carbon dioxide was bubbled through the first solution 4 at 60 to 90 C. to allow the recovery of tin, aluminium silicate and excess alkali (reactions (13) to (15)) in an alumina-rich precipitate 5 (75 to 80 wt %). H1. The solution 8 separated after step G1 was evaporated to crystallise sodium carbonate 6 which can be recycled. The purity of the sodium carbonate was 85-90 wt %.
Reactions
Fe(TaO.sub.3).sub.2(s)+3NaHCO.sub.3(s)+O.sub.2(g).fwdarw.2NaTaO.sub.3(s)+NaFeO.sub.2(s)+3CO.sub.2(g)+3/2H.sub.2O(g)(1)
Fe(NbO.sub.3).sub.2(s)+3NaHCO.sub.3(s)+O.sub.2(g).fwdarw.2NaNbO.sub.3(s)+NaFeO.sub.2(s)+3CO.sub.2(g)+3/2H.sub.2O(g)(2)
Mn(TaO.sub.3).sub.2(s)+4NaHCO.sub.3(s)+O.sub.2(g).fwdarw.2NaTaO.sub.3(s)+Na.sub.2MnO.sub.4(s)+4CO.sub.2(g)+2H.sub.2O(g)(3)
Mn(NbO.sub.3).sub.2(s)+4NaHCO.sub.3(s)+O.sub.2(g).fwdarw.2NaNbO.sub.3(s)+Na.sub.2MnO.sub.4(s)+4CO.sub.2(g)+2H.sub.2O(g)(4)
SnO.sub.2(s)+2NaHCO.sub.3(s).fwdarw.Na.sub.2SnO.sub.3(s)+2CO.sub.2(g)+H.sub.2O(g)(5)
TiO.sub.2(s)+2NaHCO.sub.3(s).fwdarw.Na.sub.2TiO.sub.3(s)+2CO.sub.2(g)+H.sub.2O(g)(6)
Al.sub.2Si.sub.2O.sub.5(s)+4NaHCO.sub.3(s).fwdarw.Na.sub.2SiO.sub.3(s)+2NaAlO.sub.2(s)+4CO.sub.2(g)+2H.sub.2O(g)(7)
NaFeO.sub.2(s)+H.sub.2O(I).fwdarw.Fe.sub.2O.sub.3(s)+2NaOH(a)(8)
Fe.sub.2O.sub.3(s)+3H.sub.2O(I).fwdarw.2Fe(OH).sub.3(s)(9)
Na.sub.2MnO.sub.4(s)+H.sub.2O(I).fwdarw.Mn.sub.2O.sub.3(s)+2NaOH(a)(10)
Mn.sub.2O.sub.3(s)+3H.sub.2O(I).fwdarw.Mn(OH).sub.2(s)+2OH.sup.(11)
5Na.sub.2TiO.sub.3(s)+H.sub.2O(I).fwdarw.Na.sub.8Ti.sub.5O.sub.14(s)+2NaOH(a)(12)
2NaAlO.sub.2(a)+Na.sub.2SiO.sub.3+2CO.sub.2(g).fwdarw.Al.sub.2SiO.sub.5(s)+2Na.sub.2CO.sub.3(a)(13)
Na.sub.2SnO.sub.3(a)+2CO.sub.2(g).fwdarw.SnO.sub.2(s)+Na.sub.2CO.sub.3(a)(14)
2NaOH(a)+CO.sub.2(g).fwdarw.Na.sub.2CO.sub.3(a)+H.sub.2O(I)(15)
Fe(OH).sub.3(s)+C.sub.6H.sub.8O.sub.6(a).fwdarw.Fe(OH).sub.2(s)+C.sub.6H.sub.6O.sub.6(a)+H.sub.2O(I)(16)
Fe(OH).sub.2(s)+H.sub.2C.sub.2O.sub.4(a).fwdarw.FeC.sub.2O.sub.4(a)+2H.sub.2O(I)(17)
Mn(OH).sub.2(s)+H.sub.2C.sub.2O.sub.4(a).fwdarw.MnC.sub.2O.sub.4(a)+2H.sub.2O(I)(18)
Na.sub.8Ti.sub.5O.sub.14(s)+4H.sub.2C.sub.2O.sub.4(a).fwdarw.5 TiO.sub.2(s)+4 Na.sub.2C.sub.2O.sub.4(a)+4H.sub.2O(I)(19)
CaO(s)+2NaHSO.sub.4(s).fwdarw.Na.sub.2Ca(SO.sub.4).sub.2(s)+H.sub.2O(g)(20)
MgO(s)+2NaHSO.sub.4(s).fwdarw.Na.sub.2Mg(SO.sub.4).sub.2(s)+H.sub.2O(g)(21)
2NaNbO.sub.3(s)+2NaHSO.sub.4(s).fwdarw.Nb.sub.2O.sub.5(s)+2Na.sub.2SO.sub.4(s)+H.sub.2O(g)(22)
2NaTaO.sub.3(s)+2NaHSO.sub.4(s).fwdarw.Ta.sub.2O.sub.5(s)+2Na.sub.2SO.sub.4(s)+H.sub.2O(g)(23).

EXAMPLE 3

(34) A third embodiment of the process of the invention is illustrated in FIG. 1C. The mineral concentrates processed in Example 3 are the same as those used in Example 2 (see Table 10 and FIGS. 2 and 3). The material and steps involved in each stage were as follows: A2. A columbite concentrate was mixed as-received with NaHCO.sub.3 and charcoal in the weight ratio concentrate:NaHCO.sub.3:carbon=1:0.75:0.05 to produce a feedstock. B2. The feedstock was reductively roasted in argon (1-10 L/min) at 1050 C. for 1.5 hours to form a roast. During reduction, sodium salts of niobium, tantalum, titanium, aluminium and silicon were formed. Iron reacted with manganese and tin to form a double oxide and a metallic alloy respectively. The reactions are indicated below. The roast was cooled to form a roasted mass (referred to as DG) which was ground for XRD analysis (FIG. 5) and for microstructural analysis (FIG. 6). This showed phase segregation into a magnetic phase rich in Fe, Mn and Sn and a non-magnetic phase which hosted the sodium salts of niobium and tantalum and sodium aluminium silicates. C2. The ground roasted mass was made up into a slurry and subjected to wet magnetic separation in the arrangement described above with reference to FIG. 13. This separated out a magnetic fraction 12 (30-60wt % Fe, 1-4wt % Sn and 2-3wt % Mn) and a non-magnetic fraction 1. A colloidal solution 2 with 5 to 30wt % of mixed rare earth oxides (REO) 10 was recovered from the top surface of a first solution 4. The magnetic fraction 12 may be smelted to obtain steel.

(35) Steps D2-H2 are analogous to steps D1-H1 specified in Example 2 and materials 3 to 9 and 20 are analogous to those produced in Example 2.
Fe(TaO.sub.3).sub.2(s)+2NaHCO.sub.3(s).fwdarw.2NaTaO.sub.3(s)+FeO(s)+2CO.sub.2(g)+H.sub.2O(g)
Fe(NbO.sub.3).sub.2(s)+2NaHCO.sub.3(s).fwdarw.2NaNbO.sub.3(s)+FeO(s)+2CO.sub.2(g)+H.sub.2O(g)
Mn(TaO.sub.3).sub.2(s)+2NaHCO.sub.3(s).fwdarw.2NaTaO.sub.3(s)+MnO(s)+2CO.sub.2(g)+H.sub.2O(g)
Mn(NbO.sub.3).sub.2(s)+2NaHCO.sub.3(s).fwdarw.2NaNbO.sub.3(s)+MnO(s)+2CO.sub.2(g)+H.sub.2O(g)
FeO(s)+MnO(s).fwdarw.FeMnO(s)+1/2O.sub.2(g)
32FeO(s)+SnO.sub.2(s)+17C(s).fwdarw.Fe.sub.32Sn(s)+17CO.sub.2(g)
TiO.sub.2(s)+2NaHCO.sub.3(s).fwdarw.Na.sub.2TiO.sub.3(s)+2CO.sub.2(g)+H.sub.2O(g)
Al.sub.2Si.sub.2O.sub.5(s)+4NaHCO.sub.3(s).fwdarw.Na.sub.2SiO.sub.3(s)+2NaAlO.sub.2(s)+4CO.sub.2(g)+2H.sub.2O(g).