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Volume 48, 1915
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Art LIII—The Distribution of Titanium, Phosphorus, and Vanadium in Taranaki Ironsand.

[Read before the Technological Section of the Wellington Philosophical Society, 10th November, 1915.]

The present writer, in the course of an analysis of ironsand from Patea two years ago, found the amount of phosphorus present to be 0.11 per cent. The highest previously recorded percentage of phosphorus in Taranaki ironsand was 0.039 per cent., returned by Dr. J. S. Maclaurin in 1902 from a New Plymouth sand forwarded by Mr E. M. Smith.* It seemed important to ascertain whether the high result was accidental, or abnormal in any way, or whether the ironsand deposits generally contain more phosphorus than has hitherto been supposed. In view, too, of the fact that the commercial utilization of the sands would seem to depend on the

[Footnote] * Thirty-sixth Annual Report, Colonial Laboratory, p. 7.

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successful application of magnetic concentration, it appeared desirable to obtain some data as to the extent to which the percentage iron-content could be increased and objectionable impurities eliminated by such means.

Representative samples were obtained by Mr W Gibson, B E., Assistant Geologist, from Patea, covering an area estimated to contain at least 5,000,000 tons of sand, and also from the neighbourhood of New Plymouth. These were analysed for iron, titanic oxide, phosphorus, and vanadium.

Iron.—This was estimated by reduction of 0.5 gram of the finely ground sample in a current of hydrogen gas at a red heat, followed by solution in semi-dilute sulphuric acid, and titration with deci-normal potassium permanganate.* The titrations were made at a temperature of 70° C., and corrected for vanadium by deducting 0.4 c c. for every 0.001 gram of vanadium present.

Titanium—Titanium was estimated colorimetrically by adding hydrogen peroxide to the solution after the permanganate titration, and comparing with a standard solution (Weller's method).

Phosphorus—The determination of phosphorus in ironsand is rather difficult. In the presence of titanium there is a tendency, when eliminating silica, for a highly insoluble trtano-phosphate to be formed. An excess of iron in solution would appear to retard the precipitation of traces of phosphoric acid. On the other hand, vanadium, when present, is partly carried down with the phosphorus, and contaminates, though only slightly, the final precipitate.

The method finally adopted was to fuse 1 gram of ironsand with 8 grams sodium carbonate, and extract with water. The insoluble residue was refused, and again extracted. A complete separation was thus obtained between the titanium and iron, which remained in the insoluble portion, and phosphorus and vanadium, which were entirely soluble.

The water-extract was acidified with nitric acid, evaporated to dryness, taken up with hot dilute nitric acid, filtered to remove silica, and again evaporated, this time to small bulk. The phosphorus was precipitated by the method of Stunkel, Wetzke, and Wagner (as described in Crooke's “Select Methods in Chemical Analysis,” 3rd ed, p 509), and weighed as magnesium pyrophosphate. Any vanadium in the precipitate was determined colorimetrically, and deducted.

Blank determinations with known amounts of phosphorus, iron, and titanium gave excellent results.

Vanadium—This was estimated colorimetrically with hydrogen peroxide in the presence of nitric acid. One gram of the sample was fused with 6 grams of sodium potassium carbonate, and extracted with water. The extract was acidified very slightly with nitric acid, and 1 c c of hydrogen peroxide (10 per cent by volume) added. The brown tint developed was compared with that of a similar solution containing a known amount of vanadium.

Magnetic Separation.—The samples were also separated by the action of first a weak and then a strong magnet into three portions No 1, strongly magnetic, separated by a very weak magnet; No 2, feebly magnetic, by the use of a triple horse-shoe magnet, after removal of portion 1; No 3, non - magnetic residue. Portions 1 and 2 were then analysed for iron, titanium, phosphorus, and vanadium, and the results compared with the analyses of the original sands, as shown in Table I.

[Footnote] * Trans. N.Z. Inst., vol. 41 (1908), pp. 4951.

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Table I.—Patea Sands.
  • (1).

    From sand-dune area west of Kakaramea and a quarter of a mile from coast-line.

  • (2).

    Breakwater to 70 yards west, above neap-tide mark.

  • (3).

    Same as No. 2, but neap tide to mean tide.

  • (4).

    From 70 yards west to 220 yards west of breakwater, and above neap tide.

  • (5).

    From 220 yards to 400 yards west, width 44 yards, and including sand-dune rising 12 ft.

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(0. = Original sand; S.M = Strongly magnetic portion; F.M. = feebly magnetic portion.)
(1.) (2.) (3.) (4.) (5.)
0. S.M. FM. 0. SM. F.M. 0. S.M. F.M. 0. S.M. F.M. 0. S.M. F.M.
Iron (as metal) 21.03 54.26 9.97 57.12 60.42 39.62 35.42 50.93 13.50 37.47 56.55 6.00 33.60 52.29 4.90
Titanium dioxide 3.80 10.00 1.60 10.60 11.00 6.80 6.90 10.10 1.92 5.20 9.60 0.50 4.10 8.70 0.46
Phosphorus 0.16 0.27 0.21 0.16 0.18 0.25 0.31 0.19 0.19 0.22 0.18 0.20 0.26 0.18
Vanadium (as metal) 0.08 0.18 0.03 0.16 0.17 0.14 0.14 0.14 0.05 0.16 0.12 0.03 0.13 0.24 0.03
Phosphorus (as percentage of iron) 0.76 0.50 2.10 0.28 0.30 0.70 0.61 1.41 0.50 0.39 3.00 0.60 0.49 3.68
Titanium dioxide (as percentage of iron) 18.1 18.4 16.1 18.5 18.2 17.2 19.5 19.8 14.2 13.9 16.9 8.3 12.2 16.6 9.8
Sulphur: From nil to 0.03 per cent.

Degree of concentration for strongly magnetic portion: No. 1, 30 per cent, of original sand; No. 2, 95 per cent. of original sand; No. 3, 65 per cent. of original sand; No. 4, 52 per cent. of original sand; No. 5, 61 per cent. of original sand.

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New Plymouth Sands

Six representative samples were received from New Plymouth, and these, on analysis, gave the following results.—

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No Iron (as Metal) Titanium Dioxide Phosphorus. Vanadium
1 49.56 9.2 0.28 0.34
2 45.00 10.0 0.26 0.29
3 59.92 10.6 0.29 0.26
4 59.36 10.6 0.26 0.15
5 36.62 6.2 0.27 0.16
6 56.89 9.8 0.29 0.33

Of these six sands, No. 1, representing a fair average sample, and No 5, the poorest in iron, were separated magnetically, as previously described, into three portions, and the analyses of the strongly magnetic portions, together with those of the original sands, are given in Table II.

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Table II.
(1) (5)
Iron (as metal) 49.22 56.22 47.0 36.46 49.30 41.0
Titanium dioxide 9.20 10.30 6.6 6.20 7.60 5.7
Phosphorus 0.28 0.32 0.28 0.32
Vanadium (as metal) 0.29 0.27 0.16 0.23
Phosphorus (as percentage of iron) 0.56 0.57 0.76 0.64
Titanium dioxide (as percentage of iron 18.7 18.3 14.0 17.0 15.4 13.9

Degree of concentration for strongly magnetic portion: No 1, 80 per cent. of original sand; No 5, 37 per cent. of original sand.

More complete analyses were made of two of the strongly magnetic concentrates: A, Patea sample No 2, being highest in iron-content, Patea; B, New Plymouth No. 1, being the richer of the New Plymouth samples treated.

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Analyses. A. B.
Silica (S1O2) 1.10 6.20
Alumina (Al2O3) 2.60 2.00
Lime (CaO) Nil 0.62
Magnesia (MgO) 1.90 2.80
Titanium dioxide (T1O2) 11.00 10.30
*Phosphoric anhydride (P2O3) . 0.39 0.74
Vanadium pentoxide (V2O5) 0.31 0.39
†Ferrous oxide (FeO) 32.49 30.28
(Ferric oxide (Fe2O3) 50.21 46.67
100.00 100.00
*Equivalent to phosphorus 0.18 0.32
†Equivalent to metallic iron 60.42 56.22

These may be taken as typical analyses of magnetically separated concentrate, and afford data for determining the nature and quantity of flux necessary for smelting.

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The results of the investigation may be summarized as follows :—

  • (1)

    The percentage of iron in the magnetically separated concentrates lies between 50 and 60 per cent., and under good working-conditions would approach the latter figure.

  • (2)

    Vanadium varies with the iron-content—from 0.08 per cent, in the poorer samples to 0–25 and 0–34 in the richer ores. The greater portion of it remains with the iron when the sand is magnetically separated. Its presence in such small quantities confers no advantage, as, on smelting, it would pass into the slag, and not into the iron. But if means could be devised to completely recover all the vanadium, and convert it into ferroalloy, 1 ton of sand containing 0.2 per cent of vanadium would at the present prices produce alloy worth approximately £2.

  • (3)

    The titanic oxide varies in the original sands from 6–2 to 10–6 per cent., and remains with the strongly magnetic portion, being slightly increased relatively to the iron. This confirms the results obtained by W. Skey (33rd Annual Report of the Colonial Laboratory, N.Z., p. 17)

  • (4)

    The phosphorus in the untreated sands varies from 0–16 to 0–28 per cent. It is not appreciably decreased, relatively to the iron, by magnetic separation. Fine grinding prior to separation did not give any better result. The phosphorus still remained in such quantities in the concentrated ironsand as would necessitate the use of the basic process for the manufacture of steel from the ore.

The results from a commercial standpoint are disappointing. They indicate that the phosphorus and titanium are intimately associated with the iron in the sand, and cannot be readily eliminated, if at all, by magnetic means. It is possible, however, that a method will be found which will achieve this end.

In conclusion, I would acknowledge the ready assistance of Messrs. N. L. Wright and R. P. Wilson in much of the analytical work involved. I would also thank Dr. J. S. Maclaurin, Dominion Analyst, for permission to publish these results.