spcfrrochinica AC&I, Vol. 478, No. 7. pp.947-955, 1992 Pnnted tn Great Britain.

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0584.8547/92 $mo + .m @ 1992 Pergamon Press Ltd

MATERIALS

Inductively coupled plasma deter~ation of nine rare-earth eiements in five ferro-manganese nodule reference samples

IWAN ROELANDTS Department of Geology, Petrology and Geochemistry, Un~ve~i~ of Liege, B-4000 Sart Tilman, Li&ge 1,

Beigium

(Received 2 January 1992; accepted 30 January 1992)

Abstract-Nine rare-earth elements (REE) were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) in five international ferro-manganese nodule reference samples (USGS-Nod-A-l and USGS-Nod-P-l; RIAP OOPE 601, OOPE @2 and OOPE 603) after acid digestion and cation-exchange separation of the REE fraction from matrix elements. Along with these new data, updated compilations are presented for USGS-Nod-A-l and USGS-Nod-P-l. Application of a one-way analysis of variance on these USGS nodules indicated both samples may be considered as homogeneous at the 95% confidence level for their REE contents.

THE LAST two decades have seen a strong interest among oceanographers and marine geochemists in fe~o-mang~ese nodules from the Atlantic, Indian and Pacific Oceans. Enriched in Cu and Ni, these economically important concretions also contain relatively large concentrations of Co, Pb, Zn, rare-earth elements (REE), MO, Tl, Bi, etc. . , Different models have been proposed to explain these enrichments [l, 21.

Several papers on the rare-earth element geochemistry of marine nodules have appeared (e.g. [3-lo]). The major relevant features of these studies are the high concentration of REEs compared to sediments and a generally strong positive Ce anomaly relative to adjacent REEs. It has been suggested that the magnitude of ‘this Ce anomaly (caused by oxidation of Ce 3+ to Ce4+) might be related to the redox conditions of the environment of deposition [4]. Therefore, REE data may be extremely useful to explain processes that control the genesis of these polymetallic nodules. REEs in fe~o-m~ganese deposits are generally thought to be of seawater origin and a number of mechanisms of their incorporation into nodules have been suggested f6, 71.

Geochemical studies of these elements need sensitive, precise, accurate, and relatively rapid analysis of a large number of samples. The increasing use of physico-chemical methods of analysis requires the availability of appropriate reference samples. These are aimed at testing and calibrating analytical instruments, evaluating new analysis methods, checking and controlling analytical quality, and ensuring measurement compatibility between different laboratories.

At present, while many reference silicate rocks are available [II], ferro-manganese nodule reference samples adequately characterized for REEs seem to be lacking.

Following FLANAGAN’S suggestion (121, two proposed reference samples of manganese nodules from the Atlantic (USGS-No-A-l) and Pacific (USGS-Nod-P-l) Oceans were prepared in limited amounts by the U.S. Geological Survey. They were distributed for collaborative study to 22 laboratories throughout the world in 1975. A U.S. Geological Survey preliminary report on these samples was made available in 1980 [13]. It incorporated preparation of samples, analytical data and “best” values for some elements. Unfortunately, no recommended values for REEs in both samples had been assigned because only two la~ratories sub~tted results for these elements. Since then, although further REE data have become available, the producers did not issue any compilation report. In his latest “Special Issue of Geostundardr Newsletter” (“SIGN II”) on 272 international geostandards, GOV~NDARAJU [14] listed no “working values” for REEs in these samples.

947

948 I. ROELANDTS

Table 1. Sampling locations for the ferro-manganese nodule reference samples analysed in the present work

Reference sample Longitude Latitude Depth (meters)

USGS-Nod-A-l 78”22’W 31”02’N 788 USGS-Nod-P-l 124”28’W 14”50’N 4340 OOPE601 (SDO-4) 146”26’W 9”SO’N 5200 OOPE602 (SDO-5) 153”22’W lO”58’N 4800 OOPE603 (SDO-6) 161”54’W 22”41’N 4800

A set of three ferro-manganese nodules SDO-4, SDO-5 and SDO-6 (now designated as OOPE601, OOPE602 and OOPE603, respectively) has been prepared by the Research Institute of Applied Physics (RIAP) jointly with the Institute of Oceanology of the USSR Academy of Sciences and investigated during 1983. They were described in some detail by BERKOVITS et al. [15]. “Certified values” for major, minor and trace elements (including five REEs) have been recently published [16].

Locations for these five reference samples are given in Table 1. In the present paper, inductively coupled plasma (ICP-AES) determinations

performed in this laboratory for nine REEs in these five manganese nodule reference samples, using a procedure that has been reported previously [17, 181 are presented. Thus, we intend to contribute to better characterization of these valuable geostandards and encourage other laboratories engaged in the analysis of nodules to provide more REE results on such materials. In view of the usefulness and impact of U.S. Geological Survey reference samples in the past on analytical geochemistry, we have also tried to collate most of the new REE data on USGS-Nod-A-l and USGS-Nod-P-l samples to present updated compilations and attempted to provide “consensus values” for the REEs considered. Surely, we have not exhausted all possible sources of data; still our efforts to compile literature results should prove useful to the international geochemical community, at least until a more authoritative report is issued by the U.S. Geological Survey.

EXPERIMENTAL

Our analytical procedure consists of three steps: dissolution, separation and ICP-AES measurements [17, 181. In brief, a 0.5 g sample was digested in a mixture of concentrated hydrofluoric-nitric acids on a steam bath. After evaporating the solution, the dry residue was dissolved in concentrated hydrochloric acid and again taken to dryness. It was dissolved in 1.75 M HCl. This attack solution was then passed through an equilibrated resin column (10 mm diam x 180 mm long) containing 17 ml of Dowex 50 WX8 resin (100-200 mesh). The unwanted elements (Fe, Ca, . . .) were eluted using 1.75 M HCl. The REE group was quantitatively desorbed with 8 M I-IN03. The REE eluate was evaporated on a hot plate and diluted with 25 ml of 0.7 M HN03. ICP-AES measurements were carried out on that solution using an ARL Model 3510 sequential ICP spectrometer. Detailed descriptions of the equipment, working conditions, calibrations, and interference corrections can be found elsewhere [17-191.

RESULTS AND DISCUSSION

USGS-Nod-A-l and USGS-Nod-P-l As homogeneity is an important property of reference materials, two bottles of each

nodule sample USGS-Nod-A-l and USGS-Nod-P-l, randomly selected from the stock, were received. Four separate portions of 0.5 g from each of the bottles were analysed in random order for nine REEs (La, Ce, Nd, Sm, Eu, Gd, Dy, Yb and Lu), on an “as received” basis. Our experimental results of the individual samples (average of

News on reference materials 949

Table 2. Determination of nine rare-earth elements in USGS-Nod-A-l (all concentrations in

Ia)

Bottle # 42l8 # 48120 Mean + Std.dev.

Determination Determination Element A B C D A B C D

La Ce Nd Sm Eu Gd

DY Yb Lu

104 107 104 105 105 104 105 108 105 + 1 703 687 703 706 694 710 707 701 701 -t8

92.0 92.8 95.0 93.0 92.6 94.2 92.8 92.0 93 21 21.1 20.7 20.5 21.2 21.0 20.8 21.3 21.1 21.0 f 0.3

5.18 5.19 5.26 5.22 5.28 5.23 5.25 5.31 5.24 ? 0.04 22.3 22.3 22.4 21.9 22.2 22.1 22.5 22.5 22.3 f 0.2 21.6 21.4 21.6 21.7 21.2 21.8 21.8 21.7 21.6 + 0.2 13.9 13.5 13.4 13.1 13.7 13.3 13.5 13.2 13.4 + 0.3

1.97 1.97 2.00 2.10 1.97 2.01 1.99 2.00 2.00 + 0.04

Table 3. Determination of nine rare-earth elements in USGS-Nod-P-l (ah concentrations in

l&g)

Bottle # 40/21 # 5017 Mean + Std.dev.

Determination Determination Element A B C D A B C D

La Ce Nd Sm Eu Gd

DY Yb Lu

104 103 101 105 105 103 103 107 104 22 321 318 314 317 320 315 308 318 316 f 4 128 129 131 129 128 127 129 128 129 + 1

32.6 32.5 31.2 32.4 32.5 32.1 32.2 31.6 32.1 + 0.5 7.90 7.79 7.76 7.92 8.14 7.90 7.92 7.72 7.88 + 0.13

29.3 29.4 28.9 29.0 29.4 29.1 29.5 30.2 29.4 f 0.4 26.1 25.9 25.8 25.9 26.1 25.4 25.9 26.3 25.9 rt 0.3 13.5 13.3 13.0 12.9 13.6 12.9 13.3 13.4 13.2 f 0.3

1.84 1.83 1.76 1.90 1.83 1.84 1.82 1.85 1.83 2 0.04

Table 4. One-way analysis of variance for USGS-Nod- A-l

Mean squares for bottles

between within Element df* = 1 df = 6 F-ratio Conclusion

La 0.5000 2.5080 0.2000 NW Ce 21.1250 62.1250 0.3400 NS Nd 0.1808 1.2467 0.1444 NS Sm 0.0613 0.0763 0.8033 NS Eu 0.0061 0.0013 4.8079 NS Gd 0.0200 0.0458 0.4364 NS DY 0.0050 0.0492 0.1017 NS Yb 1.8721 1.9360 0.9670 NS Lu 0.00061 0.00205 0.2994 NS

* df: Degrees of freedom; t NS: not significant.

three measurements on the solution) are presented in Tables 2 and 3, together with the mean of the eight independent analyses and their standard deviations. Based on these analyses, the precision of our procedure appears to be better than 2% for all elements.

The one-way analysis of variance was applied with our ICP-AES data to determine

950 I. ROELANDTS

Table 5. Compilation of REE determinations in USGS Nodule Nod-A-l (in pg/g)

Concentration Analytical

method Reference

93 104 105 112 115 115 130 132.5 152

620 656 668 676 682 701 760 895 930

81 85.3 93 93 94 94

101 102 105

18 20.4 20.9 21 21.0 22.0 24.7

4.1 4.3 4.48 4.8 4.8 5.0 5.24 5.81 6.10

22 22.3 23.6 24.9 26.0 26.5 29 34.3

k ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES ICP-MS SSMS INAA OES

!& ICP-AES ICP-MS INAA ICP-AES ICP-AES ICP-AES ICP-AES ICP-AES OES

M ICP-AES INAA ICP-AES ICP-AES SSMS ICP-MS OES ICP-AES ICP-AES

s@ ICP-AES ICP-MS INAA SSMS ICP-AES ICP-AES ICP-AES

k! OES ICP-AES INAA SSMS ICP-AES ICP-AES ICP-AES ICP-MS ICP-AES

u SSMS ICP-AES ICP-AES ICP-AES ICP-AES INAA ICP-AES ICP-MS

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News on reference materials

Table 5. Continued

Concentration Analytical

method Reference

951

20 21.6

22 22.1

22.4 25.8

26.0

11.8 12.0

12.2 13.2 13.4

13.5 15.40

16 16.3

1.92 2.0 2.00

2.16 2.21

2.56 2.8

I& ICP-AES ICP-AES

SSMS ICP-AES

ICP-AES ICP-MS

ICP-AES xb

ICP-AES ICP-AES

ICP-AES ICP-AES ICP-AES

SSMS ICP-MS

OES INAA &

ICP-AES ICP-AES ICP-AES

INAA ICP-MS

ICP-AES ICP-AES

whether the bottles were homogeneous with respect to REE content. Table 4 summarizes the calculations and the conclusions from the analysis of variance for USGS-Nod-A-l. The confidence level was 95%. The F-ratios calculated for REEs in USGS samples do not exceed the critical value F 0.95 (1,6) = 5.9874 as shown in F tables. Similar results were obtained for USGS-Nod-P-l. Therefore, the statistical analysis demonstrated that USGS-Nod-A-l and USGS-Nod-P-l may be considered homogeneous for the elements specified, at the 95% confidence level. Because of the random selection of the bottles for the experiment, this conclusion may be extrapolated to the entire lot of bottles.

The compiled data for REEs in USGS-Nod-A-l and USGS-Nod-P-l, are assembled in Tables 5 and 6, respectively. In the first column, individual data are arranged in ascending order of their concentration for a given REE. An asterisk signifies that this result was rejected as anomalous and not included for computing our “consensus values” as listed in Table 7. The analytical method used is shown in the second column. The following abbreviations have been applied: ICP-AES (inductively coupled plasma atomic-emission spectrometry); ICP-MS (inductively coupled plasma mass spectrometry); INAA (instrumental neutron-activation analysis); OES (optical-emission spectroscopy); SA-ICP-AES (spark ablation-inductively coupled plasma spectrometry); and SSMS (spark source mass spectrometry). Column three indicates the individual references to the literature.

From examination of these tables it can be seen that ICP-AES is currently the main source of data for REEs in both these oceanic nodule samples. This predominance may perhaps be explained because INAA, which is otherwise in wide use in geostandard characterization, is difficult to apply to this type of material owing to the relatively high Co contents. Low integrated neutron flux has been applied by GLASBY et al. [9] to avoid a high gamma-ray background.

Since the sets of data compiled for these samples were limited and the analytical

952 I. ROELANDS

Table 6. Compilation of REE determinations in USGS Nodule Nod-P-l (in &g)

Concentration Analytical

method Reference

* 82 100 103 104 105 107 107

* 120

271 278 280 288 289 296 310 316 318

* 4200

82.6 110 112.8 114 124 129 135 143

20 27.2 28 30.4 32.1 33.8 35.3

* 3.3 6.57 6.8 7.0 7.44 7.75 7.88 9.04

21 24 27.0 29.4 29.4 32.5 33.8

25 25.9 25.99 27.0 28 29.2

k SSMS ICP-AES ICP-AES ICP-AES ICP-MS ICP-AES OES INAA

B ICP-AES OES SSMS ICP-AES INAA ICP-AES ICP-AES ICP-AES ICP-MS

SA-ICP-AES

&! OES SSMS INAA ICP-MS ICP-AES ICP-AES ICP-AES ICP-AES

ti ICP-AES ICP-MS SSMS INAA ICP-AES ICP-AES ICP-AES

Eu OES INAA SSMS ICP-AES ICP-MS ICP-AES ICP-AES ICP-AES

QL! ICP-AES SSMS ICP-AES INAA ICP-AES ICP-AES ICP-MS

& SSMS ICP-AES ICP-MS ICP-AES ICP-AES ICP-AES

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News on reference materials

Table 6. Continued

Concentration Analytical

method Reference

* 8.6 11.5 11.8 12.3 13 13.2 13.26 13.8

1.66 1.7 1.75 1.83 1.85 1.89

yb OES ICP-AES ICP-AES ICP-AES SSMS ICP-AES ICP-MS INAA

Lu ICP-AES ICP-AES ICP-MS ICP-AES INAA ICP-AES

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* Result rejected as anomalous and not included in “consensus values” calculations.

Table 7. Consensus values for USGS Nod-A-l and Nod-P-l (in pg/g)

Nod-A-l Nod-P-l

La 118 f 18 (9) 104 2 3 (6) Ce 732 2 109 (9) 294 +- 17 (9) Nd 94 ” 8 (9) 119 f 19 (8) Sm 21.1 2 2.0 (7) 29.5 2 5.1 (7) EU 4.% t 0.67 (9) 7.50 -r- 0.84 (7) Gd 26.1 f 4.0 (8) 28.2 + 4.5 (7) DY 22.8 k 2.2 (7) 26.8 2 1.5 (6) Yb 13.8 2 1.7 (9) 12.7 ” 0.8 (7) LU 2.24 + 0.33 (7) 1.78 k 0.09 (6)

Table 8. Nine rare-earth elements in three RIAP ferro- manganese nodule reference samples, determined by the

present method* (all concentrations in ug/g)

Element OOPE601 (SDO-4)

OOPE602 (SDO-5)

OOPE603 (SDO-6)

La 184 *l 110 21 182 kl Ce 735 * 2 300 22 1210 -r- 6 Nd 209 *1 133 f 1 168 -r-l Sm 49.9 a 0.2 32.7 + 0.2 37.6 2 0.3 Eu 12.04 2 0.04 8.10 f 0.03 8.99 2 0.04 Gd 47.3 f 0.2 31.4 2 0.2 37.9 + 0.2 DY 42.0 + 0.2 28.6 k 0.3 36.0 2 0.2 Yb 21.4 + 0.1 15.0 f 0.1 20.8 2 0.1 Lu 3.14 f 0.03 2.15 f 0.02 3.09 k 0.02

953

* Mean of three measurements.

dispersion of the results was great in some cases, “consensus values” were calculated using the methodology of GLADNEY et al. [29, 301. For each REE considered here, arithmetic mean and standard deviation (SD) were determined for all the data reported. Then, all data lying outside two SDS from that initial mean were discarded, and a second mean (“consensus value”) and SD recalculated. “Consensus values” and

954 I. ROELANDTS

USGS.

Nod A-l Nod P-l

R.I.A.P.

La ce Nd SmEuGd Dy Yb Lu

Fig. 1. Chondrite-normalized REE patterns for the five ferro-manganese nodules investigated in this work.

associated SDS are reported in Table 7. The figure in parentheses indicates the number of literature results considered for the calculation of these parameters.

It is obvious that many more data for the REE group are clearly required before “best values” may be derived. However, judging by comparison with these “consensus values”, it appears that accuracy of our ICP-AES results reported in this work is quite satisfactory considering the marked spread of values obtained by others with these samples. The absence of any serious systematic bias in our REE determinations is evident.

RIAP OOPE601, OOPE602 and OOPE603 samples For this set of ferro-manganese nodules, “certified values” (La, Ce, Nd, Sm and

Yb) and “informative values” (Eu, Gd, Dy and Lu) have been published from 6 to 12 results obtained mainly by Soviet laboratories, which employed different physical, physico-chemical and chemical methods [16]. Our experimental values (mean of three measurements) are shown in Table 8. The relative standard deviations are better than 1% for all REEs. The agreement between our ICP-AES results and compilation data [16] is generally good. Our values fall well within the same ranges as those obtained by other analysts, except for Nd in OOPE601 and OOPE602 where the “certified values” (based on seven results) are somewhat lower than those from the present work. Since complete separation of all REEs was confirmed by previous recovery studies and REE data on numerous geochemical reference samples [31], we have no reasonable explanation for these differences. IvIore data by other workers using independent analysis methods would be desirable.

News on reference materials 95.5

A visual appraisal of the quality of REE data is the usual procedure of normalizing REE abundances to chondritic meteorites and plotting these ratios against atomic number. Owing to the coherent geochemical behaviour of the REE group, such comparison diagrams are likely to exhibit smooth curves, except for Ce and Eu. These chondrite-normalized patterns for the five nodules investigated here are plotted in Fig. 1, the chondritic values used for normalization being taken from LAUL et al. [32, 331.

The REE data obtained in the present work produce fairly smooth REE patterns in all cases, with an expected Ce enrichment.

Acknowledgements-We would like to thank F. FLANAGAN and J. S. KANE (USGS), and L. A. BERKOV~T~ (RIAP), who provided the reference samples investigated in this work. The assistance of V. MI~CQUE and G. DELHAZE is much appreciated.

The ICP-AES equipment used for this study was purchased with funds from the Belgian “Fonds de la Recherche Fondamentale Collective”, under contract no. 9.456983.

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15, 85 (1991). [17] I. Roelandts and G. Michel, Geostand. Newsleff. 10, 135 (1986). [18] I. Roelandts, Chem. Geol. 67, 171 (1988). [19] I. Roelandts, Spectrochim. Acru 46B, 79 (1991). [20] K. Govindaraju (1986); Quoted in Ref. [22]. [21] T. Fries, P. J. Lamothe and J. J. Pesek, Anal. Chim. Acfu 159, 329 (1984). [22] E. H. De Carlo, Sep. Sci. Tech. 25, 781 (1990). [23] B. N. Nath, Personal Communication (1990). [24] P. C.Rankin and G. P. Glasby, in: Marine Geology and Oceanography of the Pac$c Manganese Nodule

Province, Eds J. L. Bischoff and D. Z. Piper, pp. 684-685. Plenum Press, New York (1979). [25] P. A. Baekecker, U.S. Geol. Surv. Prof. Pup. 1155, 14 (1980). [26] N. Rait, U.S. Geol. Surv. Prof. Pup. 1155, 3 (1980). [27] S. T. Neil, Geostand. Newslert. 4, 205 (1980). [28] D. W. Golightly, A. Montaser, B. L. Smith and A. F. Dorrzapf Jr, Tulanta 36, 299 (1989). [29] E. S. Gladney, C. E. Bums and I. Roelandts, Geostand. Newslen. 7, 3 (1983). [30] I. Roelandts, Spectrochim. Acra 44B, 1639 (1991). [31] I.Roelandts, Geostand. Newslerr. 14, 137 (1990). [32] J. C. Laul and L. A. Rancitelli, /. Radioanal. Chem. 38, 461 (1977). [33] J. C. Laul and D. C. Gossehn, Radioanalytical methods for rare-earth elements in geological and

biological materials, in: Lanthanide Probes in Life, Chemical and Earth Sciences. Theory and Practice, Eds J. C. G. Btinzli and G. R. Choppin, chap. 10, p. 381. Elsevier, Amsterdam (1989).