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REPORT NO. 1912

LABORATORY METHOD NO 7826 THE DETERMINATION. BY X-RAY-FLUORESCENCE SPECTROMETRY. OF NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

Director of Division T W Steele

Investigator C E Austen

Date l'i!i Scptcmhet. iT-

Project 04875

Project Report No. ;>

KJ • >'.

NATIONAL INSTITUTE for METALLURGY 2">0 Hans Strydom Avenue RANDBURG 2194 South Africa ^

NATIONAL INSTITUTE FOR METALLURGY

Report No. 1912

LABORATORY METHOD NO. 78/26 THE DETERMINATION, BY X-RAY-FLUORESCENCE SPECTROMETRY, OF NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

16th September, 1977

Investigator: C.E. Austen

ISBN 0 86999 391 7 SYNOPSIS

An accurate and precise method is described for the determination of noble and base metals in matte-leach residues. Preparation of the samples essentiaUy involves fusion with sodium peroxide in a zirconium and leaching with hydrochloric and nitric acids. Matrix correction and calibration are achieved by use of the single-standard calibration method with reference prepared from pure metals or front compounds of the element to be determined.

SAMEVATTING

'n Akkurate en presiese metodc vir die bepaling van edel- en onedele me'"le in matte-uitloogresidu's word beskryf. Die voorbereiding van die monsters behels in hoofsaak smelting met natriumperoksied in 'n sirkoniumkroesie en uitloging met sout- en salpetersuur. Matrikskorreksie en kalibrering word bewerkstellig deur die gebruik van die eenstandaardkalibreermetode met verwysingsoplossings wat van suiwer metale of van verbindings van die element wat bepaal moet word, berei is. >

CONTENTS

1. OUTLINE 1

2. APPLICATION OF THE METHOD 1

3. APPARATUS 1

4. REAGENTS 2

5. PREPARATION OF SAMPLES 2

6. PREPARATION OF REFERENCE SOLUTIONS 3 6.1. THE NOBLE METALS 3

6.2 THE BASE METALS 3

7. PREPARATION OF BLANK 3

8. INSTRUMENTAL PARAMETERS 3

9. PROCEDURE 3 9.1. BALANCING OF SAMPLE HOLDERS 3 9.2. DETERMINATION OF BACKGROUND FACTORS 4 9.3. ANALYSIS OF SAMPLES 5 10. NOTES 6

11. REFERENCES 6

Table 1. Precision and accuracy of results 1 Table 2. Base-metal reference solutions 4 Table 3. Instrumental parameters 5 1. OUTLINE X-ray-fluorescence spectrometry and the single-standard calibration1 method are used for the determination of the elements in matte-leach residues. The matte-leach residue (0,5 g) is fuued with sodium peroxide in a zirconium crucible, and the melt is leached in dilute hydrochloric acid. After the sample solution has been brought to dryness, 1 ml of concentrated nitric acid, 2 ml of concentrated hydrochloric acid, and 30 ml of distilled are added. Any undissolved material is filtered off, and the silica is removed by fuming with a mixture of hydrofluoric and sulphuric acids. The residue is fused with sodium peroxide in a zirconium crucible and is leached with 60 per cent hydrochloric acid. The filtered sample solution resulting from the first fusion is then combined with the solution from the second fusion, and is brought up to . The following three solutions are used in the single-standard calibration method1: a reference solution, a 1-to-l mixture of the sample and reference solutions, and a sample solution. The net intensity of the analytical line is measured for each solution, and this value, the of the sample per unit volume, and the mass of the element determined per unit volume of the reference solution are substituted in a simple equation that, when solved, yields the concentration of the element as would be measured in a solid sample of matte-leach residue.

2. APPLICATION OF THE METHOD The procedure has been applied to the analysis of matte-leach residues for the following elements present in concentrations above about 0,2 per cent: platinum, , iridium, , palladium, rhodium, ruthenium, , selenium, , nickel, , and . The values and the precision of values obtained for noble and base metals by the X-ray method of analysis at the National Institute for Metallurgy (N1M) are listed in Table 1.

TABLE 1

Precision and accuracy of results

NIM internal standard no. 28/74

X-ray analysis Relative standard Mean concn, Element* Concn, % deviation, % %t

Au 2,48 2,08 2,28 Pt 25,25 0,78 25,40 Ir 0,32 12,4 0,39 Pd 11,13 0,98 11,20 Rh 1,34 2,89 1,31 Ru 2,47 5,92 2,54 Te 0,78 4,65 - Se 0,34 22,5 - Cu 6,34 1,69 - Ni 1,39 0,96 - Fe 13,66 2,22 -

'Osmium and coball were not delected, both being below the limit of determination, i.e.. 0,2 per cent for all elements +Mean of values obtained by three external and NIM

3. APPARATUS

(1) Zirconium (40 ml)

(2) Platinum Crucibles (about 30 ml)

(3) Fisher Blast Burner

l NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

(4) Philips PW 1220 Spectrometer Coupled loaPW 1140 Generator

(5) Sample Holders Prepare three sample holders (Note 1) by mounting a 12 /im Mylar window on each. (6) A-grade Obtain two 7 ml A-grade pipettes, one for the sample solution and the other for the reference solution.

4. REAGENTS (1) Hydrochloric Acid (Relative 1,19) A.R. grade. (2) Nitric Acid (Relative Density 1,40) A.R. grade. (3) Hydroflmoilc Acid (Relative Density 1,16) A.R. grade. (4) Sulphuric Acid (Relative Density 1£9) A.R. grade. (5) Sodium Peroxide Granules A.R. grade. (6) Sodium Hydroxide Pellets A.R. grade. (7) Tellurium, Selenium, Copper, Nickel, and Iron In the form indicated in Table 2.

(8) Cobalt Chloride (CoCI,6H20) A.R. grade. (9) Platinum, Palladium, Gold, Rhodium, and Ruthenium See Mallett el al.1 for the preparation of solutions of these metals.

5. PREPARATION OF SAMPLES a. Transfer 0.5 g (± 0,2 mg) of sample, previously dried at 120 °C overnight or for 12 hours, and 4 g (± 0,1 g) of sodium peroxide to a zirconium crucible, and mix well with a rod. b. Fuse the sample over a Fisher blast burner, starting at low heat and gradually increasing the temperature until the sample has dissolved completely. Continue with the fusion at the maximum temperature (dull-red heat) for about 2 minutes, and then fuse for about 25 seconds at the full heat of the blast burner. c. Allow the zirconium crucible and the melt to cool to room temperature, and then leach the melt (while still in the crucible) with 90 ml of 5:4 solution of hydrochloric acid to water in a 600 ml squat beaker, covering the beaker with a watch-glass. d. Htat the leach liquor to boiling-point, then lift the crucible out of the leach liquor, and, holding it above the beaker, rinse it with water. e. Carefully evaporate the solution to Incipient dryness. f. Transfer the beaker containing the sample to a drying oven and dry at 140°C for 1 hour. g. After cooling the beaker, add 1 ml of concentrated nitric acid and 2 ml of concentrated hydrochloric acid drop by drop to moisten the dried salt. Stir with a to promote the moistening process. h. Add 2 ml of water, stir again, then warm on a hot-plate for a few seconds. i. Add 30 ml (±0,5 ml) of hot water, and heat to just below boiling-point, thereby dissolving the salts formed on dehydration of the sample solut'on. j. Add about 5 ml of cellulose powder, stir, and heat to just below boiling-point for about 3 minutes, k. Without delay, filter the hot sample solution through a no. 40 Whatman (of 12,5 cm diameter) set up for rapid filtration-, and allow the filtrate to flow into a 50 ml . I. Using a fine of water, wash the filter paper twice, ensuring that the volume of the filtrate does not exceed 40 ml. m. Remove the 50 ml volumetric flask,an d place a 50 ml squat beaker under the stem of the filter funnel.

2 NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

n. Using a fine jet of water, wash the filter paper four times with 5 ml of 5 per cent (v/v) hydrochloric acid, thus removing the bulk of the zirconium adhering to the filter paper, o. Place the filter paper in a platinum crucible, and dry in an oven at 110 "C. Ash the filter paper in a muffle furnace at 700 X. p. After cooling the platinum crucible and ash to room temperature, add 6 drops of SO per cent sulphuric acid and 2 ml of concentrated hydrofluoric acid, q. Evaporate the solution to fumes of sulphuric acid on a hot-plate or sand-bath, and continue heating to incipient dryness. Cool the platinum crucible to room temperature, r. Using one or two small pieces of no. 541 Whatman filter paper (moistened with about 0,5 ml of water) and a rubber policeman, quantitatively transfer the residue in the platinum crucible to a zirconium crucible, s. Dry the residue and the filter paper in the zirconium crucible on a hot-plate, and then ash them in a muffle furnace, gradually raising the temperature from room temperature to 650 °C. t. After cooling the zirconium crucible and ash, fuse the residue with 0,5 g of sodium peroxide, and leach the cooled melt in 10 ml of 60 per cent hydrochloric acid in a 150 ml squat beaker, u. Heat the beaker and zirconium crucible on a hot-plate. Then lift the crucible out of the leach liquor, and, holding it above the beaker, rinse it with water, v. Boil the leach liquor for 1 minute, w. Combine the solutions in the 50 ml beaker (see step m) and the 150 ml beaker (see step u), and evaporate to moist dryness. Immediately add 5 ml of hot water, and swirl the mixture in the beaker until all the salts are dissolved. Do not boil the solution at this stage since zirconium salts may come out of solution, x. While the mixture is hot, combine the leach liquor from step w with the leach liquor in the 50 ml volumetric flask (see step k), rinsing the beaker with hot 5 per cent hydrochloric acid, y. Dilute the combined leach liquors in the 50 ml volumetric flask to about 48 ml with 5 per cent (v/v) hydrochloric acid, the flask, and thoroughly mix the contents. Make up to 50 ml when the temperature of the leach liquor is 20 °C.

6. PREPARATION OF REFERENCE SOLUTIONS 6.1. The Noble Metals Prepare individual reference solutions of approximately 10 g/l, accurate to four decimal places, for platinum, gold, palladium, iridium, osmium, rhodium, and ruthenium, according to the methods gi' en by Mallett el al.3.

6.2. The Base Metals Prepare base-metal reference solutions as indicated in Table 2.

7. PREPARATION OF BLANK SOLUTION a. Dissolve 50 g (± 0,1 g) of sodium hydroxide in 200ml of water in a 500ml squat beaker. b. While stirring, carefully add 150 ml of concentrated hydrochloric acid to the sodium hydroxide solution. c. Cool the solution, dilute to 500 ml (± 10 ml), and transfer to a clean reagent bottle.

8. INSTRUMENTAL PARAMETERS For analysis of the samples, use a Philips PW1220 spectrometer coupled to a PW1140 generator with the parameters given in Table 3.

9. PROCEDURE 9.1. Balancing of Sample Holder» a. 14 ml (7 ml twice) of a reference solution into each sample holder, and insert the three sample holders in the chamber of the X-ray spectrometer. b. Several times for each sample holder, measure the count-rate at the analytical line of the element being determined (Note 2).

3 NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

TABLE 2 Base-metal reference solutions Final volume of sample solution 1 litre. (Distilled water is added to make up final volume.)

Final mass of element Mass of per 100ml Source of material of solution Element element g Diluent g Te Finely 100 ml HCI divided +

Te metal 5,0000 50 ml HNOs 500 ml HCI 0,5000 + 100 ml water Se Finely 200 ml HCI divided +

Se metal 10,0000 100 ml HNO:, 400 ml HCI 1,0000 + 300 ml water

Cu Cu-metal 100 ml HNO:, foil 10,0000 + - 1,0000 100 ml water

Ni Ni-metal 100 ml HNO:, foil 10,0000 + - 1,0000 100 ml water

Co Dry 100 ml HNO:I (120°C) + - 1,0000 CoCI, 22,0194 100 ml water

Fe Iron 100 ml HCI wire 10,0000 + 20 ml HNO, 1,0000 + 100 ml water

c. Calculate the average count-rate for each sample holder, and compare the count-rates for any two of the three sample holders (Not/? 3). d. If necessary, apply factors to correct the average count-rates of the second and third sample holders to that of the first sample holder.

9.2. Determination of Background Factors a. Pipette 14 ml (7 ml twice) of the blank solution into the first sample holder, and insert the sample holder into the sample chamber. b. From repeated measurements of the blank solution at the 2 0-angle of the analytical line and background of the element being determined, determine the background factor (F) required for calculation of the true background under the peak. c. Calculate F as follows

F =PIB (1)

where P is the intensity at the peak angle, and B is the intensity at the background angle. d. Carry out a check on the value for the background factor F by determining a blank solution as a sample with each batch of samples analysed (Note 4),

4 NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

TABLE 3

Instrumental parameters

Counting time 20 s Radiation path Air

X-ray tube Peak Background Element Analytical Crystal angle angle measured line Target kV mA Collimator and cut Detector '26 •2» Au Lo Mo 53,25 57 JO Pt La Mo ] j ] 54,91 53,00 60 40 Ir La Mo 1 1 | 56,65 5930 Os Lp Mo > Fine > LiF (220) ) Scintillation 49,"'2 52.30 Pd Ka Au ) I I 1 23,7-. 27,00 Rh Ka Au >50 20 I j I 24,93 27,00 Ru Ka Au ) ' ' ' 26,16 27.00 Te La Cr \ Coarse LiF (100) Flow 109,58 121,00 Se Ka Mo 1 | 45,71 43,50 Cu Ka Au 65.55 69.00 »60 40 Fine LiF (220) 1 Scintillation Ni Ka Au 71,26 75,00 Co Ka Au 1 1 77,89 75,00 Fe Ka Au ) , 1 85,73 82,00

9.3. Analysis of Samples a. With a 7 ml A-grade pipette (Note 5), pipette 14 ml of the appropriate reference solution into the first sample holder. b. With the same pipette, transfer 7 ml of the reference into the second sample holder, and, with a second pipette, add 7 ml of the sample solution. Mix thoroughly. c. Use the second pipette to transfer 14 ml of the sample solution into the third sample holder. d. Using the appropriate instrumental parameters (Table 3), determine the net intensity (/) of the analytical line for each of the solutions (i.e., reference, mixture of reference and sample, and sample solutions) by means of equation (2):

I-P-BxF. (2)

e. During the analysis of the samples, read all the values for P of the three solutions, followed by the values for B for the same three solutions (Notes 6 and 7). f. Using equation (3), calculate the percentage concentration (C) of the element as would be measured in the solid sample of matte-leach residue:

Wr C = v Mi Lú. x — x inn (3) Ws (/„"/,) /,*100' where W, is the concentration (in per 100 ml) of the element measured in the reference solution, W, is the concentration (in grams per 100 ml) of the matte-leach residue in the sample solution,

/r is the net intensity of the analytical line of the reference solution, /„ is the net intensity of the analytical line of the mixed reference and sample solutions, and /, is the net intensity of the analytical line of the sample solution.

g. Determine the concentration of the element measured three times on the same aliquot portion, and report the average result. NOBLE AND BASE METALS IN MATTE-LEACH RESIDUES

10. NOTES (1) Standard Philips plastic or titanium holders (of 32 mm interna! diameter) have been found to be satisfactory. (2) If sample holders are in balance at one wavelength, they should be in balance at all other wavelengths, and correction factors for any three holders should remain the same at all wavelengths. It is therefore necessary only for holders to be balanced at one wavelength or 2 0-angle. (3) The difference between the average count-rates obtained for any two of the three sample holders should be less than 0,5 per cent of the overall average count-rate. If the difference is greater, correction factors must be applied. (4) The background factor should be constant if instrumental parameters have been kept constant. (5) A pipette with a volume of less than 7 ml may be used if infinite thickness is attained with a smaller volume of solution. (6) This sequence of measurement of peaks and backgrounds is necessary since there is a tendency for bubbles to form when solutions are exposed to X-rays, and greater relative errors can be tolerated for values of B than for values of P. Frequent clearing of bubbles is necessary if repeated measurements are being made. (7) The sample chamber is protected against corrosion by acid fumes as follows: all the sample holders have lids, and a flow of air is directed into the crystal chamber, from where the air flows up the collimator into the sample chamber and out through the entrance for sample holders. The flow of air through the spectrometer also increases its stability.

11. REFERENCES 1. AUSTEN, C.E.,TOLM AY, R.T., and STEELE, T.W. A single-standard calibration method for use in analysis by X-ray-fluorescence spectrometry. Johannesburg, National Institute for Metallurgy, Report no. 1784. 6th Feb., 1976. 13 pp. 2. WALL, G., ROYAL, J., DIXON, K., MALLETT, R.C., and STEELE, T.W. The rapid and precise determination of noble metals in matte-leach residues by atomic-absorption . Johannesburg, National Institute for Metallurgy, Report no. 1837. 12th Nov., 1976. 16 pp. 3. MALLETT, R.C., WALL, O.J., JONES, E.A., ROYAL, S.J., and STEELE, T.W. The preparation of primary standard solutions for each of the noble metals. Johannesburg, National Institute for Metallurgy, Report no. 1864. 14th Jan., 1977. 9 pp.

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