Ilmenite Mineral's Recovery from Beach Sand Tailings - Springer Link

Hyperfine Interactions 139/140: 485–494, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.

485

Ilmenite Mineral’s Recovery from Beach Sand Tailings ANTOINE F. MULABA-BAFUBIANDI1, DAVID MUKENDI-NGALULA1 and FRANS B. WAANDERS2, 1 Technikon Witwatersrand, Faculty of Engineering, School of Mining and Metallurgy, Department of Extraction Metallurgy, P.O. Box 17011, Doornfontein 2028, Johannesburg, South-Africa 2 School of Chemical/Minerals Engineering, Potchefstroom University for Christian Higher Education, Potchefstroom, 2520, South Africa; e-mail: [email protected]

Abstract. The mineral ilmenite is the major source of rutile for industrial use and is of interest to paint and fertiliser industries. Enormous unutilised tailing dams lie on the eastern coast of the South Africa. Although covered by a simulation of the original indigenous vegetation, these tailings are still ilmenite bearing and of economic value. Tailings emanating from beach sand mineral slimes dams of the Kwazulu-Natal area (South Africa) have been processed. Screening, flotation, spiral concentration and magnetic separation methods were used either separately or successively. The present work sheds light on alternative routes for the extraction of the ilmenite, from these tailings. It moreover points out the usefulness of the Mössbauer spectroscopy in the mineral processing product monitoring. Tailings from the beach sands were used in the present study after the economic industrial minerals zirconia, ilmenite and rutile had been extracted in previous mining operations. About 61% natural ilmenite recovery was observed in the flotation concentrate of a Humphrey Spiral concentrate while a 62% recovery of hematite was found in the flotation tailings. The combination of screening, spiral concentration and magnetic separation, and flotation yielded a product with the highest ilmenite and hematite concentration being 71% and 19%, respectively. A natural ilmenite mineral, containing 87% ilmenite and 13% hematite, could be produced and extracted from the tailings of the flotation process, collected subsequently to the spiral concentration and the initial screening. Key words: recovery, ilmenite, tailings, minerals processing, Mössbauer spectroscopy.

1. Introduction Important heavy mineral bearing sands have been found and mined in South Africa. They are found in the North coast of Natal, at Hillendale and Fairbreeze, in the Gravelotte area of the Northern Province and in the Eastern Cape. Dredging is used as mining technique where vegetation is initially cleared and topsoil removed. A pond is then excavated and filled with water. Float dredges mine the front of the pond and feed the sand to the float concentrator where the valuable heavy minerals are extracted by gravity concentration. The mining tailings are fed to a stacker  Corresponding author.

486

A. F. MULABA-BAFUBIANDI ET AL.

boom, which deposits it at the opposite end of the pond. As the pond moves forward the topsoil is replaced and indigenous vegetation is replanted. From the commonly encountered ore body, the minerals of economic importance are ilmenite, rutile, zircon and monazite. The gangue minerals are garnet, pyroxenes, amphiboles and quartz. The specific gravities of the valuable minerals range between 4.2 for rutile, 4.9 for monazite, while the specific gravities of the gangue minerals are less than 4.0 with the main constituent being quartz at 2.7. Because of the higher specific gravities of the economically interesting minerals they lend themselves to separation by wet gravity concentration. A recovery of approximately 90% for the heavy minerals is obtained by utilising the Humphreys spirals. The concentrate from the spiral plant is partially dewatered and fed to a wet magnetic separator, which removes approximately 70% of the iron oxide(s). This is generally discarded as a tailing. Ilmenite, rutile, zircon and monazite in the concentrate are separated from each other and from other minerals present in the raw concentrate using the variation in their electric conductivity and their magnetic susceptibility. By feeding a dry concentrate of conductive and non-conductive minerals on to an earthed rotating steel roll in a very thin layer, conductor minerals quickly lose their charge and flow a normal trajectory as they leave the surface of he roll, while non-conductive minerals are firmly attached to the surface. Brushes remove the non-conductors from the roll surfaces. Additionally, minerals vary in their susceptibility to magnetic influence an by passing a dry concentrate of mineral through an induced roll magnetic separator, minerals of similar magnetic susceptibility are separated at specific magnetic intensities and roll speeds. Imperfect electrical and magnetic separation, due to occlusion or masking, leads to discarding of valuable products, which add to the tailings volume. Although it is common practice to loop the process circuit or increase the number of process stages in order to improve the efficiency and the recovery, still more than 45% of the economically interesting ilmenite mineral is lost. An attempt was made to recover ilmenite mineral (FeTiO3 ) from the beach sand mining and processing tailings. The high iron content in the studied tailing materials (30–80%) suggested the use of 57 Fe Mössbauer effect technique. Tailings are being be processed by an unusual combination of screening, flotation, spiral concentration, magnetic separation and products thereof monitored using the γ -ray resonant emission and absorption spectroscopy (Mössbauer spectroscopy, MES). Various workers [4–8] have extensively documented the theoretical background on Mössbauer spectroscopy and its applications in metallurgy, gold ore and product characterisation and the use in reduction processes. Little is known about the applications of Mössbauer spectroscopy in the broad field of minerals processing, nor for the recovery of ilmenite mineral from the mining and the mineral processing tailings. This paper will shed light on some routes for the extraction of ilmenite from the mining and processing tailings and will illustrate the versatility, usefulness and power of the Mössbauer technique in monitoring the yields from different steps in the processing of beach sands tailings.

ILMENITE MINERAL’S RECOVERY FROM BEACH SAND TAILINGS

487

2. Experimental 2.1. TAILINGS PROCESSING AND ILMENITE RECOVERY Residues from the ilmenite, rutile, zircon and iron oxides extraction circuits added to the discards from dredging, were reclaimed from the slime dams in the Kwazulu Natal area in South Africa and used in this study. A 8000 Gauss magnetic field and 17 cm inner Humphrey Spiral separator were used. The as-received tailings with a representative composition of 42% ilmenite, 6% rutile, 6% iron oxides and balance for others, were referred to as the run of mine minerals (ROM1). These samples were homogenised, riffled, coned and quartered. An initial fraction was screened, passing −212 + 106 µm, and was referred to as SF1. The Humphrey spiral concentrate of SF1 was labelled HSC1. The spiral tailings were referred to as HSC2. HSC1 was subjected to the magnetic separation, and the process yielded the magnetic fraction (M-HSC1) and the non-magnetic fraction (NM-HSC1). SF1 was also subjected to the flotation process as described below. The operation produced the float fraction of SF1 (F-SF1) and the sink fraction of SF1 (S-SF1). A separated amount of the spiral concentrate HSC1 was subjected to flotation after spiral concentration. The process yielded the float fraction of the spiral concentrate (F-HSC1) and the sink fraction of the spiral concentrate (S-HSC1). The magnetic product of the spiral concentrate M-HSC1 was subsequently floated. It produced FM-HSC1 (the float fraction) and SM-HSC1 (the sink fraction). 2.2. FLOTATION EXPERIMENTS The flotation experiments were conducted in a modified Hallimond tube where 2 g of beach sand tailing were dispersed in 100 ml distilled water contained in a Hallimond tube. A concentrated solution of sodium metasilicate (depressant) was added to the agitated slurry, bringing the concentration of the pulp to 800 mg/l sodium metasilicate. A pH adjustment at 7 was done and the pulp conditioned for 5 minutes. A collector solution (200 mg/l sodium oleate) was added followed by a second pH adjustment and a further 5 minutes conditioning. The flotation process was carried out for 8 minutes with an airflow rate of 60 ml/min. 2.3. MÖSSBAUER SPECTROSCOPY MEASUREMENTS The as-received beach sand tailings as well as all the products from the screening process, the flotation process, spiral concentrator and magnetic separation were monitored with γ -rays using the Mössbauer effect technique. Room temperature 57 Fe-Mössbauer measurements were performed in the conventional transmission geometry. A K3 Austin Associates linear motor driven by a triangular reference wave form was used to scan the resonance profile. A Xe-CO2 proportional counter detected the transmitted 14.4 keV resonance radiation from a 1–2 mCi 57 Co(Rh) radioactive source. Fe-bearing tailing samples were mounted in a specially designed

488

A. F. MULABA-BAFUBIANDI ET AL.

powder-clamp holder (∅ = 1.5 cm). Typically 55–65 mg/cm2 of samples were distributed in the sample holder to form a disk of uniform thickness for transmission Mössbauer measurements. The velocity calibration was done by means of a 25-µm thick 57 Fe foil measured before and after the series of measurements. Data analysis was effected by using the non-linear least squares Mössbauer analysing programme “NORMOS”, using a minimum number of spectral components, each having a Lorentzian lineshape. Final parameters of the fitted components were compared with the accepted literature hyperfine interaction parameter values for various iron oxides and iron–titanium-oxides to make a phase identification. All the δ values are expressed with respect to α-Fe.

3. Results and discussion 3.1. TAILINGS PROCESSING AND MÖSSBAUER ANALYSIS The as-received run of mine tailing material (ROM1) was an amalgam of ironbearing minerals. Its room temperature Mössbauer spectrum is displayed in Figure 1. Noticeable is a 10% hematite and 40% ilmenite contribution which is distributed between 13% Fe3+ - and 27% Fe2+ -components, and three other Fe2+ compounds of following respective abundance: 23%, 13% and 14%. The undersize −212+106 µm fraction (SF1) displays a room temperature Mössbauer effect spectrum very similar to that of the as-received tailing material. Although the relative abundance’s of the iron-bearing compounds in the screened −212 + 106 µm products remain similar to those of the as-received material (see Table I), it is worth noticing that the screening operation decreases the bulk amount of different ironbearing phases collected in the screened fraction. This is expressed by the decrease in the γ -ray resonant absorption effect from 6% for the ROM1 to 2% for SF1 in the same amount of the measured sample (65 mg/cm2 ). Size fractionation by screening alone may not necessarily yield concentration in ilmenite-bearing minerals. A similar phenomenon was observed in the −700 + 500 µm, −500 + 300 µm and −300 + 150 µm screened fractions of the ferric pseudobrookite mineral [Fe2 TiO5 ]. The smaller the mesh size of the screen was, more hematite small grains were collected (6%), resulting in a smaller abundance of the final pseudobrookite (94%) [9]. The use of the Humphrey spiral concentrator on the screened fraction of the as-received tailings resulted in the concentration of the ilmenite related minerals in HSC1 (73%) and in the concentration of the “gangue” or non-ilmenite related minerals in the spiral’s tailings (72%). The Mössbauer spectrum of the spiral concentrate presents a higher resonant absorption effect (4%) than that of the tailings (2%) where mostly garnets and other Fe2+ -compounds were accumulated (see Figure 1). This indicates an increase in the amount of 14.4 keV γ -ray absorbing atoms which in this case are iron bearing phases. One notices that the abundance of the ilmenite mineral in the HSC1 concentrate (the concentrate from the Humphrey spiral) has increased to 63% while that of the accompanying hematite remains

ILMENITE MINERAL’S RECOVERY FROM BEACH SAND TAILINGS

489

Figure 1. Room temperature Mössbauer effect spectra of S-SF1 the sink products of the −21 + 106 µm fraction, of F-SF1 the float products of the −21 + 106 µm fraction, of FM-HSC1 the float products after magnetic separation subsequent to the spiral concentration.

constant (10–12%). The spiral concentrate of the −212 + 106 µm fraction has been subsequently subjected the magnetic separation. The Mössbauer spectrum of the magnetic products showed an absorption effect of 7% in addition to a higher contribution of ilmenite (71%). This indicates that the magnetic separation process, subsequent to a spiral concentration and a screening process enhances the ilmenite concentration. In the collected magnetic fraction, only a small amount (2–3%) of the previously observed other accompanying Fe2+ compounds was found with the following respective hyperfine interactions parameters [δFe = 0.84(2) mm/s, = 2.54(3) mm/s and δFe = 1.08(3) mm/s, = 3.9(5) mm/s]. These doublets indicate that the Fe2+ -compounds are non-magnetic compounds and possibly of the rutile and zircon related groups. Monazite minerals will then concentrate in the non-magnetic fraction of the beach sand mineral specimen. The room temperature Mössbauer spectrum of the non-magnetic fraction (NMHSC1) gives only a 1% resonant effect. This indicates that most of the iron-bearing compounds were magnetically attracted and collected in the MHSC1 fraction. Moreover the NMHSC1 sample contains 92% relative abundance of the non-ilmenite related or non-magnetic compounds in opposition to

490

A. F. MULABA-BAFUBIANDI ET AL.

Table I. Hyperfine interaction parameters of all the components found in the present experiment from the beach sand minerals processing. (Errors are quoted in parenthesis/brackets, δ is the isomeric shift,

the quadrupole splitting and Bhf the internal magnetic field) Sample

Hyperfine interaction parameters δ/Fe

Bhf (mm/s) (mm/s) (T)

% abundance

Attribution

ROM1 As-received tailings from beach sand minerals

1.11(2) 0.27(2) 0.40(3) 1.20(3) 1.11(4) 0.50(3)

0.68(3) 0.39(4) –0.18(3) 3.71(5) 2.22(5) 1.69(3)

– – 51.2(5) – – –

27(5) 13(2) 10(3) 13(5) 23(4) 14(5)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

SF1 −212 + 106 µm Screened fraction

1.00(2) 0.27(2) 0.34(2) 1.12(3) 1.11(3) 0.62(5)

0.59(5) 0.33(3) –0.30(3) 3.51(3) 2.14(4) 1.67(3)

– – 50.6(4) – – –

32(5) 12(5) 12(4) 10(4) 20(5) 14(4)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

HSC2 Spiral separation tailings

0.97(3) 0.27(3) 0.39(3) 1.13(2) 1.06(3) 0.49(2)

0.70(3) 0.36(3) –0.29(3) 3.68(2) 2.2(2) 1.78(3)

– – 50.3(5) – – –

8(4) 15(4) 5(3) 15(3) 37(3) 20(3)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

HSC1 Spiral Concentrate screened beach sand mineral tailing

1.03(3) 0.27(3) 0.29(3) 1.26(5) 1.23(3) 0.75(2)

0.63(4) 0.31(3) –0.08(4) 3.66(5) 1.65(3) 1.6(4)

– – 51.4(5) – – –

52(5) 11(3) 10(3) 10(3) 4(3) 13(3)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

MHSC1 Magnetic concentrate after spiral separation and screening

1.02(2) 0.27(2) 0.32(3) 1.08(3) 0.84(4) 0.75(4)

0.62(3) 0.24(3) –0.18(3) 3.90(4) 2.54(5) 1.51(3)

– – 51.20(5) – – –

59(5) 12(3) 11(4) 2(2) 3(2) 13(3)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

ILMENITE MINERAL’S RECOVERY FROM BEACH SAND TAILINGS

491

Table I. (Continued) Sample

Hyperfine interaction parameters δ/Fe

Bhf (mm/s) (mm/s) (T)

% abundance

Attribution

NM-HSC1 Non-magnetic fraction after spiral separation and screening

1.05(2) 0.27(3) 0.33(2) 1.18(4) 1.14(3) 0.50(4)

0.65(3) 0.49(3) –0.21(3) 3.67(4) 1.97(3) 1.60(4)

– – 50.8(4) – – –

12(5) 13(2) 23(3) 12(4) 17(4) 23(5)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

F-SF1 Float component after screening (−212 + 106 µm)

1.12(3) 0.27(3) 0.35(3) 1.16(3) 0.88(2) 0.63(2)

0.64(4) 0.41(3) –0.33 3.71(3) 2.61(2) 1.27(3)

– — 51.2(4) – – –

4(3) 12(3) 8(4) 12(4) 41(4) 23(5)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

S-SF1 Sink component after screening (−212 + 106 µm)

1.11(2) 0.27(3) 0.42(2) 1.24(3) 1.17(4) 0.56(3)

0.69(2) 0.39(3) –0.18(4) 3.75(2) 2.25(3) 1.58(3)

– – 51.4(5) – – –

33(5) 12(3) 12(5) 13(3) 16(5) 14(3)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound Fe2+ compound Fe2+ compound

F-HSC1 Float fraction – after spiral conc. and screening

1.07(2) 0.19(2) 0.38(2) 1.29(3)

0.72(3) 0.28(3) –0.23(3) 3.58(3)

– – 51.3(3) –

55(3) 12(3) 21(3) 12(2)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound

S-HSC1 Sink fraction after spiral conc. and screening

1.06(3) 0.17(3) 0.41(3)

0.71(3) 0.28(3) –0.16(3)

– – 51.4(2)

75(3) 12(3) 13(3)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like)

FM-HSC1 Float magnetic fraction after spiral conc. and screening

1.07(3) 0.27(2) 0.40(2) 1.30(2)

0.70(3) 0.35(4) –0.22(3) 3.53(3)

– – 51.4(4) –

60(5) 11(2) 19(3) 10(2)

Fe2+ compound (ilmenite) Fe3+ compound (ilmenite) Fe3+ compound (hematite-like) Fe2+ compound

492

A. F. MULABA-BAFUBIANDI ET AL.

Figure 2. The yields (%) of collected minerals are represented in function of the minerals processing route followed. A pure natural ilmenite mineral (87% ilmenite and 13% hematite) has been extracted when combining the spiral separation with the flotation process. The monazite minerals will be more concentrated in HSC2 the spiral’s tailing products. Minerals processing methods are represented by points on the X axis as the following: (1) float products of flotation subsequent to spiral separation, (2) sink products of flotation subsequent to spiral separation, (3) float products of flotation after magnetic separation, (4) magnetic separation products subsequent to spiral separation, (5) non-magnetic products subsequent to spiral separation, (6) float products after screening, (7) sink products after screening, (80 run of mine ore, (9) −212 + 106 µm screening products, (10) tailings of spiral separation, (11) concentrate of spiral separation.

only 22% in the magnetic fraction of HSC1 (see Table I). A comparison between the spiral concentrate and the tailings’ spectra (see Figure 1) indicates that most of the ilmenite group minerals are collected in the concentrate (73% vs. 28%). In Figure 2 the abundance of the ilmenite-bearing products is depicted and that of the non-ilmenite bearing materials after each step of the tailings processing. The screened −212 + 106 µm fraction has been subsequently subjected to the flotation process. It was observed that most of the iron-bearing minerals concentrated in the sink fraction, giving a resonant absorption effect of 6% compared to 2% from the float fraction. When the screened and spiral concentrated material was subjected to the flotation process, a higher resonant absorption effect was observed in the sink fraction (10%). Moreover, the product was purely a natural ilmenite with 75% Fe2+ and 12% Fe3+ in the ilmenite structure and 13% of the accompanying hematite. All the “gangue” components were concentrated in the float products. It has been observed that hematite is mostly concentrated (21%) in the float products of the screened and spiral separated tailings. A 61% ilmenite and 62% hematite recoveries have been respectively achieved in the float and sink products of the spiral separated material. Ilmenite’s recovery or enrichment improved when different concentration methods were combined. It was observed that only 63% ilmenite and 10% hematite were present in the spiral concentrate whereas a subsequent flotation process collected 67% ilmenite and 21% hematite in the float products. A magnetic separation of the concentrate subsequent to the spiral separation resulted in

ILMENITE MINERAL’S RECOVERY FROM BEACH SAND TAILINGS

493

the production of 71% ilmenite and 11% hematite. A further flotation operation subsequent to the magnetic separation of the spiral-separated material yielded also 71% ilmenite but with higher hematite abundance (19%) (see Table I).

3.2. LIMITATIONS OF THE MES TECHNIQUE The Mössbauer spectroscopy detects only the probe-bearing phases within the sample. The 57 Fe Mössbauer technique for instance will not detect non-ferrous compounds like TiO2 , ZrO2 , Cr2 O3 , CaO, MgO, MnO, Al2 O3 , SiO2 , V2 O, P2 O5 , monazite, sphene [CaOTiO2 –SiO2 ], kyanite [Al2 O3 SiO2 ], nor zircon [ZrO2 HfO2 ]) contained in the processed beach sand tailings. Rutile TiO2 and anatase (tetragonal TiO2 ) produced after a complete reduction of ilmenite minerals could not be detected nor differentiated but ilmenite (FeTiO3 )-hematite (α-Fe2 O3 ) solid-solution, Garnet [Fe3 Al2 (SiO4 )3 ], Leucoxene, Pyroxene (complex silicate of Fe, Mg, Ca and Al) would be qualitatively as well as quantitatively detected. In the field of minerals processing, the Mössbauer effect technique may be suggested as a useful complement to the commonly used XRD, XRF and SEM techniques.

4. Conclusions Screening of the beach sand tailings followed by their concentration, using a spiral column and magnetic separation, complemented by the flotation process, seemed to be the best route to produce the ilmenite–hematite solid-solution from the beach sand mining and processing residues, after ilmenite, zircon and rutile had been extracted in previous operations. A yield of 71% ilmenite and 19% hematite was obtained. Natural ilmenite with the highest ilmenite abundance (87% ilmenite, 13% hematite) was concentrated in the sink fraction of a spiral concentrate subjected directly to the flotation process. A further magnetic separation increased the hematite’s contribution. For the same amount of sample (65 mg/cm2 ) a resonant absorption effect of 10% was observed in comparison with only 7% in the case of the screening, spiral concentration and magnetic separation route. The float products of the magnetic fraction of the spiral separated products contained more hematite (19%), and only 71% ilmenite compared to 13% hematite and 87% ilmenite in the sink products of the spiral separation.

Acknowledgement The logistic support from the University of the Witwatersrand (South Africa) is acknowledged.

494

A. F. MULABA-BAFUBIANDI ET AL.

References 1. 2. 3. 4.

5. 6. 7. 8. 9.

Greenwood, N. N. and Gibb, T. C., In: Mössbauer Spectroscopy, Chapman and Hall Ltd., London, 1971, p. 659. Dunlap, B. D. and Kalvius, G. M., In: G. K. Shenoy and F. E. Wagner (eds), Mössbauer Isomer Shifts, North-Holland, Amsterdam, New York, Oxford, 1978, p. 17. Marion, P., Holliger, P., Boiron, M. C., Cathelineau, M. and Wagner, F. E., In: E. A. Ladeira (ed.), Proc. Conf. Brazil Gold’91, Brazil, 1991, Balkema, Rotterdam, 1991, p. 389. Campbell, S. J. and Gleiter, H., In: G. J. Long and F. Grandjean (eds), Mössbauer Spectroscopy Applied to Magnetism and Materials Science, Plenum Press, New York and London, 1987, p. 243. Tacks, L., Hyp. Interact. 111 (1998), 245. Marion, P., Wagner, F. E. and Regnard, J. R., Industrie minerale, mines et carrieres, les techniques, Aout-Septembre (1989), 112. Afewu, K. I., Mwalula, J. B. and Kaoma, J., Hyp. Interact. 111 (1998), 255. Klingelhöfer, G., Campbell, S. J., Wang, G. M., Held, P., Stahl, B. and Kankeleit, E., Hyp. Interact. 111 (1998), 335. Mulaba, A. and Hearne, G., Mössbauer Laboratory’s report for Iscor (S.A), Report-3, 1999, p. 5.