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TliE COMPARATIVE STUDY OF CONTENTS OF ZINC ANDLEAD IN ORE SAMPLES OF NAMTU - BAWD WIN MINE

BY -WET ANALYSIS, X-RAY FLUORESCENCE; AND 1

X-RAY DIFFRACTION METHODS

KYAW SOE

m 2 a hm b I POOR QUALITYORIGINAL |

May, 1990M. Sc. Thesis

OF ZINC' ANDi'HE „OMt’ARATi VL STUDY OF 'ONTDN'l'ELE.tD IN ORE SAMPLES OF NAMTU-HAWDWTN MINE

BYWET ANALYSIS, X-RAY FLUORESCENCE AND

X-RAY DIFFRACT LON METHODS by

KYAW SUE

DISSERTATIONOSubmitred in partial fulfilment of the requirements

for the degree of

MASTER " OF SCIENCE

in

PHYSICS

of the->:

University of Yangon

Approved

External Examiner ChairmanBoard of Examiner s

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V ^

Superv i soi

"3 QUO

Lee Vur t©CYpLo^Pi

Un u '

ACKNOWLEDGEMENTS

The author wishes to thank former Professor Dr. Tin Aung of the Physics Department for his kind consent of this work.

The author would also like to convey his thanks to former Professor Dr. Ko Ko Gy 1 of the Chemistry Department tot ai...

kind permission to use the data of the original thesis concerning chemical analysis in the comparative study of the various methods.

The author wishes to express his gratitude to Daw May Su, Lecturer, Physics Department, for her valuable guidance and s upervision.

The author is also indebted to Dr. Zin Aung, Head of the Physics Department and Head of the Universities' Research Centre, U Nay Oo, U Hla Win (2) , U Win Tha Htwe, U Myat I'hu and U Mg Mg Bo of the Physics Department for their help, cooperation, encouragement and fruitful discussions .

The author is grateful to U Hla Toe of the Physics Departmental Library for his help in finding the required literature .

Finally, the author wishes to express his deepest gratitude to his motner and sisters for their kind help and encouragement.

ABSTRACT A

Lead-Zinc Ores taken from Karatu-Bawdwin Area had been analysed by wet processes in the Department of Chemistry,

' 1984. ,These ore samples have been analysed by energy

dispersive x-ray fluorescence method in the Department of Physics and x-ray diffraction method is also used to determine elements of lead and zinc compounds in these ore samples in the Universities’ Research Centre.

In brief, we study comparatively the contents of lead and zinc and r.neir compounds using the methods of wet processes, x-ray fluorescence and x-ray diffraction.

Q

INTRODUCTION

Most lead and sine occur as cavity fillings and replacementsformed by low temperature hydrotnermal solutions. Generally•tney are found in limestones or dolomites.1 The world'srgreatest concentration of zinc-lead ores occurs in the Mississippi Valley region, centering around the Tri-State ’ district of Missouri, Oklahoma and Kansas and diminishing; north-ward into Wisconsin.

Myanmar is very rich in mineral deposits of petroleum,lead, silver, and zinc, tin and tungsten ores, rubies,sapphires, and spinels, jade, amber, gold, coal and so on.These occur in different localities. Among them lead-zincores happen to be the major sources of foreign-exchangeincome for the Union of Myanmar. Lead and zinc wnich areproduced from Bawdwin Mine has been regarded as one of the

2world's ranking lead mines.The ore samples studied throughout this work are waste

products of 1=ad-zinc ores from Namtu-Bawdwin Mine, In Northern Shan State, Myanmar.

Wet processes'Survey of literature revealed tnat studies on ore samples of

3Namtu-Bawdwin Mine were also conducted by wet processes.cjaaU tatJi/e . ,tAccording to this work, determination of the ore was carried

out by using semi-micro analysis technique and quantitative determinat'd or oi the samples was carried out by volumetric, gravimetric £..id atomic absorption spectroscopy.

X-ray diffraction method^

The penetrating radiation discovered by Roentgen in 18 95 was x-ray. Diffraction o.t x-ray can be demonstrated by replacing the diffraction grating of visible-light with a diffracting crystal. From these angles we can obtain the values of the interatomic distances of the ore samples. Thus, identification of the compounds present in the ore can be carried out in this manner.

Scope of the present workThe samples analysed are the tailings from Namtu-Bawdwin Mine. These tailings are the waste-products of lead-zinc concentration which were treated by floatation method.

The qualitative determination were performed by using wet process of semi-micro analyses and the quantitative determina­tion of elements, lead, zinc, and nickel were carried out by conventional volumetric and gravimetric methods in the Department of Chemistry, Yancon University. 'Moreover, this work also describes the analyses of lead and

zinc ores from Namtu-Bawdwin Area of Myanmar by Energy Dispersive X-Ray Fluorescence System. Concentrations of the major elements, lead and zinc were determined. For this purpose Energy Dispersive X-Ray Fluorescence System was the method of choice using lithium-drifted silicon Si(Li) detector. '

The results by atomic absorption spectroscopy shows that the* .elements, lead and zinc,are present in fairly larger content than

other elements. Quantitative analyses of the elements were, e" also made by conventional wet processes, such as volumetric and gravimetric methods.

The analytical results provide some valuable information for the feasible mineral exploitation of metals especially zinc and lead from the waste mineral tailings.X-ray fluorescence spectrometry^ vX-ray fluorescence is applied to evaluate lead and zinc concentration of the ore samples from Namtu-Bawdwin Mine.

X-ray fluorescence is a relatively fast, *nondestructive, sensitive and versatile technique widely used for elemental analysis of solids, powders, slurries and liquids In principle, suitable sources of excitation are used toproduce characteristic x-rays of the element of interest in

♦ .

the sample ; appropriate detectors are then used to measure the energy and intensity of these characteristic x-rays enabling a determination of the element and its relative amount in the sample. Energy Dispersive X-Ray Fluorescence

' ,3is advantageous for quick survey work and for repetitive quantitative analysis where an adequate resolution exists.In this investigation, an EDXRF system utilizing lithium drifted silicon Si(Li) detector is used to determine the concentration of lead and zinc in the ore samples.

CHAPTER IWET ANALYSIS3

1.1 Occurrence of Lead

Lead (Pb) is known native but is of exceedingly rare occurence. Lead is the lithophil element in a large number of rock forming minerals and is usually mined from rich veins of massive galena as (PbS). Lead occurs as the sulphide in galena (PbS), sulphate in anglesite (PbS04), carbonate in cerussite (PbCOg).The principal ores of lead are galena, anglesite and

cerussite. The percent of lead in these three minerals are summarized in Table 1.1.

Table 1.1 Percent of lead in lead minerals

Type of ore Chemical formula Percent of lead

galena PbS 86.6cerussite PbC03 77.5anglesite PbSO.4 68.3

1.2 Occurence of Zinc

Zinc occurs as oxides in zincite (ZnO) and franklinite ((Fe,Zn,Mn)(Fe,Mn)20^], sulphide in sphalerite (ZnS), carbonate in smithsonite (ZnCOg), basic carbonate in hydro-

2

zincite [Zn^^O^ (OH) 2 • ^O] , and sulphate in go s la rite(ZnSO^^HgO). The chief sources of zinc are blende or sphalerite and smithsonite. The percent of zinc in six zinc minerals are summarized in Table 1.2.

Table 1.2 Percent of zinc in zinc minerals

Type of ore Chemical formula Percent of zinc

zincblende ZnS 67.0smithsonite ZnC03 52.0hemimorphite Zn4Si04(OH)2.H20 54.2zincite ZnO 80.3willemite Zn2Si04 58.5frankalimite (Fe,Zn,Mn)(Fe,Mn)20^ 15-20

1.3 Origin of the Samples

The samples used throughout this work were taken from the waste- product of the lead-zinc-silver ore concentration by the wet floatation process from the Namtu-Bawdwin Mine. It was procured by the Metallurgical Egineering Department of the Yangon. Institute of Technology.

3

1.4 Results

On visual inspection of the representative sample it was found to have bluish-gray colour.

The powdered form (120 mesh) is insoluble in cold and hot distilled water, but quite soluble in concentrated nitric acid and aquaregia.

The elemental analysis by using atomic absorption spectroscopy shows the very complex nature of composition of the ore sample. The ore sample is chiefly composed of zinc (30-34 %), lead (9-10 %), iron (7-9 %), and sodium (4-5 %). The data are shown in Table (1.3) and the results are shown in Table 1.4 .

From the atomic absorption spectroscopy analysis, it is also found that the sample investigated contains fairly high contents of zinc and lead but it is almost depleted of the rare elements, such as silver and gold.

Since pre-war,the investigation had been performed with the object of finding out whether it would be feasible to extract the rare elements, silver and gold from the vast tailing dumps within the Namtu-Bawdwin surroundings. However, contrary to the expectation it was found that representative sample does not contain silver and gold, in amounts sizable enough to be commercially extracted.

4

Today efforts are made to extract almost all silver, lead, and zinc from ore tailings. Volumetric methods were applied for quantitative determination of lead, zinc and nickel. The results determined by these methods are summarized in Tables 1.5 , 1.6 and 1.9 . Gravimetricmethods were also applied for determination of lead, zinc, and nickel. The results determined by these methods are summarized in Tables 1.7 , 1.8 and 1.10 . ,

According to the research work of Chemistry Department, all the results determined by atomic absorption spectroscopy, volumetric and gravimetric analysis are in good agreement with one another.

1

Table 1.3 Chemical analysis of the ore samples by atomic absorption spectroscopy

No* of ppm (based sample) x 10"■4

expt. Li . Na K Ca Mg Mn Fe Co Cu Zn Pb Ni Ag

1 0.020 4.89 ND 0.031 0.84 0.56 9.8 0.233 0.045 39.33 10.87 0.48 0.021

2 0.015 4.17 ND 0.048 0.81 0.56 7.4 0.179 0.035 30.28 11.49 0.32 0.030

3 0.008 5.31 ND 0.037 0.91 0.70 7.7 0.181 0.034 30.68 11.84 0.34 0.231

4 0.014 4.22 ND 0.040 0.89 0.57 8.1 0.174 0.050 31.19 8.98 0.31 0.047

5 0.005 6.15 ND 0.056 0.92 0.60 7.4 0.108 0.034 31.63 7.59 0.31 0.145

SD0.012

+4.95+

ND 0.042+

0.87+

0.60+

8.1+

0.175±

0.040+

32.62+

10.15±

0.35 0.095±

0.006 '0.32 0.009 0.05 0.06 1.0 0.040 0.007 3.78 1.81 0.07 0.090

SD = Standard deviationND = Not detected

iTable 1.4 Qualitative elemental analysis of ore samples

No. ofexpt.

Silvergroup*

Copper-arsenic group**Nickel-aluminium

group***Barium-magnesium

group****

1 Ag Pb,Bi,Cu, and As Fe,Ni,Mn,Al,and Zn Ba,Ca,and Mg

2 Ag ‘ Pb,Bi,Cu,Cd,and As Fe,Ni,Mn,Al,and Zn Ba,Ca,and Mg

3 Ag Pb,Bi, and Cu Fe,Ni,Mn,Al,and Zn Ba,Ca,and Mg

4 Ag . Pb,Bi and Cu Fe,Ni,Mn,Al,and Zn Ba,Ca,and Mg

5 Ag Pb,Bi and Cu Fe,Ni,Mn,Al,and Zn Ba,Ca,and Mg

Silver group comprisesAg, Hg(I), and Pb.Copper-arsenic group contains Hg(II),Pb,Bi,Cu,Cd,As,Sb, and Sn. Nickel-aluminium group contains Fe,Al,Cr,Co,Ni,Mn,and Zn. Barium-magnesium group contains Ba,Ca,Mg,Na and K.

7t

Table 1.5 Lead percent in ore samples(volumetric method)

No.of Mass taken Lead Meanexpt. (g) content(%) (%)

1 0.5025 9,15

2 0.5023 9.16 9.11 - 0.10

3 0.5009 9.01

Table 1.6 Zinc percent in ore samples(volumetric method)

No.of Mass taken Zinc Meanexpt. (g) content(%) (%)

1 0,5021 27.95

2 0,5003 27.88 27.97 ± 0.11

3 0,5025 28.10

8

Table 1.7 Lead percent in ore samples (gravimetric method)

No. ofexpt.

Mass taken(g)

Lead content(%)

Mean(%)

1 0.5039 9.08

2 0.5028 ' 8.95 t—i

o+1oCT:

3 0.5030 8.96

Table 1.8 Zinc percent in ore samples (gravimetric method)

No. ofexpt.

Mass taken(g)

Zinc content(%)

Mean

1 0.5010 27.94

2 0.5029 28.87 28.38 ± 0.46

3 0.5019 28.31

9

Table 1.9 Nickel percent in ore samples(volumetric method)

No. of Mass taken Nickel Meanexpt. (9) content(S) (%)

1 0.5000 0.32

2 0.5022 0.32 0.32 - 0.01

3 0.5025 0.32

Table 1.10 Nickel percent in ore samples(gravimetric method)

No. of Mass taken Nickel Meanexpt. (g) content(%) (%)

1 0.5005 0.28

2 * 0.5022 0.30 0.29 ± 0.01

3 0.5010 0.28

CHAPTER IIX-RAY FLUORESCENCE SPECTROMETRY

2.1 Principles of X-Ray Fluorescence Method 4

2.1.1 X-Ray Fluorescence Analysis

X-rays may be produced from a target by bombarding it with any particle or radiation which causes electrons to be ejected from their orbits. In the practical application of x-ray energy spectrometry analysis, two different approaches are employed, they are:fluorescence by means of a primary source of electromagnetic radiation and by means of charged particle beams. Of the two, the basic process governing the excitation with electromagnetic radiation is the best understood and also the most widely used.There are three modes through which low energy electro­

magnetic radiation interacts with an atom; photoelectric absorption, elastic scattering (coherent scattering) and inelastic scattering (incoherent scattering).For the purpose of inducing characteristic x-ray of the

atom, the photoelectric absorption is the desired interaction and the photoelectric effect is by far the most important process.

2.1.2 Fluorescent Yield

The true x-ray yield following photoelectric absorption is effected by a process internal to the atom, called the Auger

11

effect which reduces the number of x-ray photons in the emission radiation. The Auger effect is more common in elements of low atomic number because their atomic electrons are more loosely bound and their characteristic x-ray photons more readily absorbed. The Auger effect is also the basic for the fluorescent yield.The fluorescent yield is the probability that the filling

of a vacancy in a specified shell will result in emission of a characteristic x-ray photon regardless of whether the vacancy arose from primary or secondary excitation. It is a major limitation of sensitivity for elements of low atomic number where the yield is down to a few percent or less.

2.1.3 The Escape Peak

The energy transfer in the detector is in part through photo-, electric absorption creating silicon x-rays which are again reabsorbed. However a finite probability exists for the escape of a SiK x-ray (energy 1.74 keV) from the detector in the process of depositing an energy package E. Relative to the full energy peak, the energy deposited in the detector

Iis then (E-1.74) keV. These events are again lost from the full energy peak (parent line) and reappear in the spectrum as a separate peak (the escape peak) of energy (E-1.74keV) in the case of Si(Li) detectors. This requires caution in

63 J8

12

peak identification, as a number of escape peaks fall very near certain full energy peak values for other element lines.

2.1.4 Excitation

X-rays required for radioisotope XRF may be produced from asuitable target by bombarding it with any particle orradiation which causes electrons to be ejected from their

109 241orbits. The main primary sources are Cd and Am.By suitable choice of target it is possible to select the most efficient excitation energy for the element to be measured. In practice the type of source assembly used*is the one which can produce nearly monochromatic x-rays in the energy range from 5 keV to 100 keV. Secondary x-ray sources have considerably enriched the number of low-energy sources available and have greatly widened the already varied range of possible applications of radioisotope x-ray fluorescence analysis.

2.2 Instrumentation2.2.1 The Si (Li) Detector

The detector used in measuring the x-ray spectra for the content of lead and zinc in ore samples was the Si(Li) detector (7383 Cryostat detector Model 7500S) . This detector was coupled to a Canberra Series 40 MCA system.

13

The ore samples were measured by using Mo and Dy target with an 241. .Am primary source. The time taken for the measurement of the spectrum of each sample was 600s. Spectrum of each ore sample was taken with the following settings:

Detector bias voltage = 1 VAmplifier coarse gain = 300Fine gain = 2MCA (ADC) gain = 4096 '

A time constant of 12 /is was used in the present work.The data were read out on Dec Writer Model LA 36-CJ and digital cassette recorder Model 5411. Net area under each peak was obtained from the "MCA. From this net area , the area for the same energy peak from background spectrum was substractied. Electronic set up for this investigation is shown in Figure 2.1. , •

2.2.2 Energy Calibration

Energy calibration of the detector system is done by using5 5 109standard sources of Fe and Cd from I.A.E.A. The energy

calibration process can be done by establishing a direct relationship between photopeak energy and multichannel analyser channel number.

14

MCACANBERRA Series 40

VDigital Cassette Recorder

5 411

DecWriter

LA 36-CJ

Fig- 2. 1 Electronics set up of Si(Li)detector

15

Powdered sample

Am ring sourceTungsten alloy shieldDy (or) Mo ring target

4 Lead shield

Si(Li) detector

Fig.2.2 Sample-source-detector arrangement inEDXRF spectrometry

Table 2.1 Qualitative analysis of the tore samples by x-ray fluorescence spectrometry

Sample ElementsNumber .Major Elements Minor Elements

1 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calcium,Lithium and Silver

2 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calcium and Lithium

3 Zinc and Lead Iron,Magnesium,Manganese ,Sodium,Nickel, cr.Cobalt,Copper and Lithium,Manganese

4 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Lithium and Silver

5 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calcium,Lithium and Silver

6 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calcium,Antimony and Silver

7 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calcium and Antimony

8 Zinc and Lead Iron,Magnesium,Manganese,Sodium,Nickel,Cobalt,Copper,Calciurn,Antimony,and Silver

17

2.3 Experimental Procedure2.3.1 Preparation of Standard and Ore Samples

The samples used throughout this work are taken from the waste-product of the lead-zinc-silver ore concentration obtained by the wet floatation process from the Namtu- Bawdwin Mine. It was received from Metallurgical Engineering Department, Yangon Institute of Technology (YIT).

The ore sample, (10 g) was powdered into particles of mesh size (120). Each of the eight similar samples to be analyzed by the Si(Li) detector was weighed out in cylindrical polystyrene sample cups using Jupiter C2-20 micro-balance. The dimensions of the cylinder were depth 27 mm , inside diameter 23 mm, wallthickness 3 mm, and base thickness 0.03 mm(1 mil) Mylar, respectively. If the concentration of lead or zinc or other elements in a sample were found to be outside the range of the standard calibration curve, an appropriate dilution was carried out by mixing with pure sand powder, SiC>2* Concentration of these standard samples were as follows: Pb 1 percent to 10 percent; Zn 1 percent to 5 percent; Fe .1 percent to 5 percent; Ag 0.05 percent to 0.5 percent and Ni 0.05 percent to 0.5 percent. The x-ray spectra of Pb, Zn, Fe and Ag standard samples were then obtained with the Si(Li) detector.

13

2.4 Results

As for the qualitative analysis of the ore sample using Si (Li) detector, the x-ray spectra should reveal not only the contents of the major elements such as lead and zinc but also the contents of other minor elements such as iron, sodium, magnesium, manganese, nickel, cobalt, copper and silver. But in our determination we could not identify all the minor elements completely. However the elemental contents of these minor elements that we obtain in our eight ore samples are found t"o match with the observations of the Chemistry Department by wet analysis method. The results are summarized in Table 2.1.

For the quantitative analysis of each of the ore samples it is necessary to measure the x-ray intensity. This was done by drawing standard calibration curves using the known standard concentrations of lead and zinc as mentioned before, The intensity of the characteristic x-rays from lead and zinc were obtained by taking the ratio of the net areas of the peaks to the integral of scattered peak ZnK^ x-rays excited by -the ^ *Am source with Mo as the target were used

in this measurement. The counting time was 600 s. The Net/ Total value for each standard was calculated from the ratio of the net area of ZnK^ to the total integral value

19

of the back-scatter peak . The results obtained for Zn standard are shown in Table 2.2 and the calibration curve is shown in Figure 2.3 . Using this calibration curve the concentration of Zn in the ore samples were determined and the results obtained were shown in Table 2.3. The average value for the Zn content is found to be 23. 09+ 0.03 %.

Similarly the results obtained for Pb, Fe, Ag and Ni are

shown in Tables 2.4 to 2.11.

20

j1 Table 2.2 Results for standard calibration curve takenI 2411 with Si(Li) detector, (ZnK ), Am-Mo target,.5 **#I counting time 600 s.

ZnStandard<%)

Net AreaZn*oc

IntegralBack

ScatterNet (ZnJ^)Total(B S )

1 15010 51025 0.29417

2 29018 45912 0.632045

3 39985 41015 0.97489

4 60121 40281 1.49254

5 66945 36119 1.85346

►-3IZ 2.10

1.90

1.60

1.30

1.00

0.70

0.30

0. 000.00 0.50 1.50 2.50 3.50 4.50 5.50

wt.%. ZnK

r2 = 0.999800.03109 + 0.25510 X + 0.02239 X20.00138 0.00083 0.0002

Fig. 2.3 Calibration curve for ZnK Standard.241Si (li) detector, Am - Mo target, counting time 500 s .

22

' . 241Si (Li) detector, Am-Mo target, countingtime 600 s.

Table 2.3 Results of zinc determination in ore samples.

SampleNo.

NetArea

ZnK<K

IntegralBack

Scatter

Net(ZnK*)Total(B S )

ZnConcentration

(%)

1 36895 19386 1.90318 24.13 ± 0.022 37761 19410 1.94544 24.59 * 0.013 4 4 612 19210 2.32233 28.59 - 0.034 45061 21018 2.14392 26.73 - 0.025 41010 21105 1.94314 24.56 - 0.016 41206 22317 1.84695 23.49 ± 0.017 13261 10203 1.29972 17.16 - 0.038 14289 12302 1.16152 15.46 ± 0.01

Average percentage of Zn concentration = 23.09 - 0.03 %

23

2 41with Si(Li) detecter, (PbL^), Am-Mo target counting time 600 s.

Table 2.4 Results for standard caliberation curve taken

PbStandard(%)

NetAreaPbL , oC

IntegralBack

ScatteringNet (PbL.)oc

Total (B S )

1 11002 53025 ' 0.20749

2 19943 45892 0.43456

3 30128 41130 ' 0.73251

4 36112 38123 0.94725

5 44139 34901 1.26469

6 49025 32021 1.53103

7 53981 29612 1.82294

8 59967 2 6118 2.29600

9 70123 ' 26105 2.68619

0 72361 25618#

2.82462

►3IZ

Si (li) detector

25

I

Table 2.5 Results of lead determination in ore samples. • 241Si(Li)detector, Am-Mo target counting time

600 s .

Sam­pleNo.

NetAreaPbL<x

IntegralBack

ScatterNet (PbLj

Total(B S.)

PbConcentration

(%)

1 49677 21013 2.36411 9.55 - 0.01

2 60218 21208 2.83940 11.19 - 0.01

3 61168 21318 ' 2.86931 11.08 1 0.01 .

4 68139 21679 3.14309 11.86 - 0.02

5 69128 21428 3.22606 12.10 ± 0.03

6 68692 22116 3.10599 11.75 ±, 0.01

7 69961 21108 3.31443 12.33 t 0.03

8 89861 31320 2.86913 11.08 ± 0.02

Average percentage of Pb concentration = 11.37 ± 0. 03%

26

Table 2.6 Results for standard caliberation curvetaken with Si (Li)target, counting

detector,time 600 s .

(FeK^),241Am-Mo

Fe Net IntegralStandard Aera Back Net (Fel^)

(%) FeKcx Scatter Total(B S )

1 4401 51289 0.08581

2 8021 49611 0.16168

3 11031 45015 0.24505

4 .14812 43018 0.34432

5 17415 40610 0.42884

•-3IZ

t

0.45

0.35

0.25 ‘

0.15

0.05.

0.00

r 2 Y

0. 00

= 0.99991= 0.0148Q + 0.07010 X + 0.003010 X2 = 0.000004 = 0.000006 = 0.001494

] . 50 2.5 0 3.50 4.50 5. 50wt.%

Fig. 2.5 Calibration curve for FeK Standard„Si (lx) detector, 14 1 Ain - Dy target, counting time 600 s.

NJ

28

241Si(Li) detector, Am-Mo target, counting time 600 s.

Table 2.7 Results of iron determination in ore samples.

Sam­pleNo.

NetAreaFeK<K

. IntegralBack

ScatterNet(FeK )ocTotal(B S )

FeConcentration

(%)

1 3166 31698 0.09988 4.14 + 0.02

2 3018 29698 0.10162 4.21 + 0.02

3 4021 32218 0.12481 5.17 ± 0.02

4 6320 33189 0.19042 7.59 + 0.03

5 6420 33290 0.19285 7.68 0.0 3

6 6521 33318 0.19572 7.7 7 + 0.02

7 2010 30281 0.06638 3.49 ± 0.02

8 1912 28162 0.06789 ,2 . 68 + 0.04

Average percentage of Fe concentration = 5.34 dooo

.VfltertSttto Si.i.n,.;.

29

Table 2.8 Results for standard calibration curve takenwith Si(Li) detector, (AgK^ ), Am-Dy target,counting time 600 s.

Ag Net IntegralNet(AgK^)

Standard Area Back Total(B S )(%) AgK, Scatter

0.05 16995 641015 0.02651

0.1 30518 649951 0.04695

0.2 64518 616925 0.10458

0.5 146018 601128 0.24291

25

20

15

10

05

00

0.99875(-0.00023) + 0.50544 X0.003510-01276

LOO

^9- 2.7

o\ 10 0.20 o'. 3 0 6.40 6. 50 0.60vsz t • % Ag ^

Calibration curve for AgK Standard.Si (li) detector, 24lAm _ Qy target, counting time 600 s.

31

241Si(Li) detector, Am-Mo target, counting time 600 s .

Table 2. 9 Results of silver determination in ore samples.

Sample

No.

NetAreaAgK

IntegralBack

ScatterNet (AgKof)Total(B S )

AgConcentration

(%)

1 1250 54296 0.02302 -Hoo 0.02

2 — — —

3— — —

4 1950 51472 0.37880 0.07 - 0.03

5 1985 52102 0.03810 0.07 ± 0.0 3

6 3150 37103 0.08490 0.17 1 0.02

7 — — —

8 1969 80459 0.02447 0.04 - 0.02

Average percentage of Ag concentration = 0.08 - 0.0 3

32

Table 2.10 Results for standard Calibration curve taken with Si (Li) detector, (N i K*,. ) . ^Dy target, counting time 600 s.

NiStandard(%)

NetAreaNiK

IntegralBackScatter

Net (NiK=cTotal (B.5

0.1 42091 649650 0.064790.5 199768 583079 0. 34 26 11.0 376301 536 16 5 0.701842.5 764940 401865 1.903483.5 9511578 348432 2.731035.0 1162501 302514 3.84 28 0

►3IZ

*

4.00,

3. 00

2.00 -

1.00

0.0 00.00 1 . 00 2.00 3. 00 4.00

Fig 2.6 Calibration curve for Ni Standard.241

5.00 6.00wr. * NiKoc

Si (li) detector, Am - Dy target, counting time 600 s.

ww

34

■ uliirtMH—an

Table 2.11 Results of Nickel determination m ore samples.

24 1Si (1 i ) detector, Am - Mo target count.) ng

time 600 s.

Sample Net Integral Net (NiK^ } NiNo. Area Back ■ concentration

NiK Scattering Total(B S ) (%)

1 95184 329292 0.28906 0.42+0.032 95190 331012 0.28757 0.42+0.033 96012 350238 0.28757 0.40+0.024 89713 299914 0.27413 0.78+0.04+5 91039 301822 0.29912 0.78+0.0j6 88991 298987 0.30163 0.4 3 ±0.0 37 96672 332581 0.29764 0.78+0.04b » 9 b 2 5 301257 0 . 2 9 B l / 0.78+0.04

Average percentage of Ni concentration = 0.60 ± 0.04%

CHAPTER III. X-RAY POWDER DIFFRACTOMETRY

3.1 Principles of X-Ray Diffraction Method ^

3.1.1 Diffraction of X-Rays

An electron which is situated in an alternating electromagnetic field will oscillate with the same frequency as the field.Since an x-ray beam can be considered as an electromagnetic wave travelling through space it too will cause all electrons in its path to oscillate. Each electron can then be considered as a separate oscillator emitting electromagnetic radiation at the same frequency as the primary radiation, these separate waves combining to give the resultant wave of the atom. The amplitude of this wave depends on the number of electron waves and their respective phase difference. These phase differences depend on the differences in path lengths.When a beam of monochromatic x-rays falls onto a crystal

lattice, a regular periodic arrangements of atoms, a diffracted beam will only result in certain direction. It is necessary that the waves emitted by the individual atom be in phase with each other in the direction of observation.

The condition for diffraction can be found in two steps.First, the waves emitted by all atoms lying in a single plane must be in phase, and second, the scattering of waves by successive planes must also ne in phase. The first condition is fulfilled if the incident ray, the diffracted ray and the

36

normal to the reflecting surface all lie in one plane, and if the angle of incidence equals the angle of "reflection".In this case it can be proved that all of the waves scattered by the atoms in this plane are in phase. The second condition is illustrated in Figure 3. i .Two parallel rays strike a set of crystal planes at an angle

0 and are scattered as previously described. Reinforcement will occur when the difference in the path lengths of the two rays is equal to a whole number of wavelengths. This path length difference is equal to CB+BD and since CB = BD —- x, n must equal 2x for reinforcement, where n is an integer. However, it will be seen that x = d. sin 0 , where d is the interplanar spacing; hence the ultimate reinforcement condition is that :

n X = 2d.sin © where ^ wavelength

this being a statement of the Braggs law. Bragg's law takes no account of the refraction of x-rays but since this effect is very analKthe index of refraction is of the order of 0.99999) it can be ignored.Where the path length diffrence CBD is equal to a whole

wavelength, n takes a value of 1 (i.e. first order). It is common practice in x-ray powder diffractometry to maintain a value of unity for n and to allow for the higher orders in the Miller indices or in the d-values. For example, the second

B

Condition for diffraction of x-rays.Figure 3.1

38

order reflection for the (100) set of planes of LiF can be­thought of as having a d-value of 4.028/2 = 2.014 and can thus be called a (200) reflection. Similarly a (400) instead of fourth order of the (100) reflection.

3.2 Instrumentation

The instrumentation required for x-ray powder diffractometry consists of three basic parts.

a. A source of radiation,' consisting of x-ray tube and high voltage generator.

b. The diffractometer.c. The detector and counting equipment.

Figure 3.2 shows a diagram of a typical instrumental set-up and indicates the more important units of the output devices.

3.2.1 The Alignment of the Diffractometer

The alignment of the diffractometer is a complex procedure since the specimen, detector, x-ray tube anode and slits, have to be correctly set with respect to each other in all three dimensions.

3.2.2 The Detector and Counting Equipment

The function of detector is to convert the individual x-ray photons into voltage pulses. The voltage pulses are then counted and/or integrated by the counting equipment: giving

x-ray tube & detectortube tower

diffractrometer

scaler

timer

step scan contro

high voltage generatorFigure 3.2 Block diagram o

printer control

rate meter

high voltage supply

linear amplifier

pulse height selector

recorder

40

.. -iSLae^wmoBK*,

various forms of visual indication of x-ray intensity.Detec torsDetectors used in conventional x-ray powder diffractometers are generally one of three types, Geiger or Proportional which are both gas counters or Scintillation counters. Each of the three detectors has its own operating characteristics but all three depend upon the ability of x-rays to ionize matter.

3.2.3 The Automatic Sample Changer

In cases where multiple routine powder analysis are required it may be useful to fit an automatic sample changer to the diffractometer. The device allows the loading -of up to 35 samples and an associated hardware control unit allows scanning over a preset range. Typical applications include the routine production of diffraction patterns or integrated intensity measurements on a selected diffraction peak, in this case the results being displayed in a digital form.Such a system allows unattended operation and car) be further automated by the addition of a stepping motor and control unit.I

3.3 Sample Preparation

The ideal specimen for x-ray powder diffraction analysis is completely homogeneous over the range of less than 1 pm , has constant particle size of between 1 and 50 rim and shows no preferred orientation or strain. Such a specimen may be

4 1

difficult to obtain in practice.In this research we sent some of the similar ore samples

which are the tailings of the Namtu-Bawdwin Mine and observed the structure analysis using x-ray powder diffractometry for the identification of zinc and lead compounds by their diffraction patterns. These samples were pulverized to obtain a fine powder of 300 mesh size.

3.4 Results

The x-ray powder diffraction method can be used not only for routine qualitative phase analysis but also for routine quantitative phase analysis. Powder diffrac tometryis mainly used for the identification of compounds by their patterns.

The qualitative identification of Pb, Zn and other metals by using XRD method as carried out at the Universities Research Centre on the eight similar ore samples are shownin Table 3.1.

42Table 3.1 Qualitative identification u: r>., neralp

and other metals by XRD method

Sample mark Identification

1 Quartz , SiC>2Wurtzite, (Zn,Fe)S

2 Quartz, SiC>2Galena, PbSWurtzite, (Zn,Fe)S

3 Quartz, Si02Galena, PbSAnglesite , PbSO^Sphalerite, (Zn,Fe)S

4 Quartz, Si02Sphalerite, (Zn,Fe)SPyrite, FeS2

5 Quartz, Si02Sphalerite, (Zn,Fe)SPyrite, FeS2

6 Quartz, Si02Galena, PbSSphalerite, (Zn,Fe)S

7 Quartz, Si02Galena, PbS

8 Quartz, Si02Galena, PbS

CHAPTER IV

-i jasmin

RESULTS AND DISCUSSIONS

We are now in a position to study comparatively the contents of zinc and lead and their compounds in ore samples of tailings from Namtu-Bawdwin Mine by wet analysis, x-ray fluorescence and x-ray diffraction methods. Although we can analyse the contents of major elemental compositions of lead and zinc and minor elements qualitatively and quantitatively by wet analysis method and x-ray fluorescence method, we cannot do the same with x-ray diffraction analysis.With this method we can only get the identification of their compounds by their diffraction patterns. Although most of the diffractometers are used for routine qualitative and quantitative phase analysis, a whole series of attachments are available which allow most data to be obtained in more specialised fields such as texture, stress, strain, high and low temperature phase transformation and particle size studies.

The results obtained by the wet analysis method which includes the method of atomic absorption spectroscopy, conventional volumetric and gravimetric methods are shown in Table 4.1 together with the results obtained by the present work using x-ray fluorescence spectroscopy. The results obtained by x-ray powder diffraction method is shown in Table 3.1.

Since the ore sample used throughout this work is a waste-

Table 4.1 Comparison of the contents of major elements zinc and lead inthe ore samples by wet analysis methods and XRF method

Methods Contents( %

of zinc)

Contents of lead( % )

1. Atomic absorption 32.62 + 3.78 10 15 ± 1.81spectroscopy

2. Volumetric method 27.97 t SD 0.11 9.11 i SD 0.10

3. Gravimetric method 28.38 + SD 0.46 9.00 ± SD 0.10

4. X-ray fluorescence 24.42 + SD 0.03 11.37 1 sc ■>.:>?spectrometry

product from ore processing at the Namtu-Bawdwin Mine, the complete rapid analysis of the representative sample on a preliminary basis can only be achieved by using atomic absorption spectroscopy method among those three wet analyst method!., The elemental analysis by using atomic absorption spectroscopy.method show the very complex nature of the composition of the ore sample. The ore sample is chiefly composed of zinc (30 % -34 %), lead (9 % - 10 %), and iron (7 % - 9 %). From this analysis it is also found that the sample investigated contains a fairly high content of zinc and lead but it is almost depleted of the rare elements such as silver and gold.

From Table 2.3 it can be seen that the values of the percentage of zinc concentrations for the first six ore samples seem to agree within the limit of the experimental technique . The last two data seem to disagree with the others. This could be due to the inhomogeneity of the samples. X-ray fluorescence method is very sensitive to and could vary quite a lot with the homogeneity of the sample. It was found that although we used the same sample, the results that we obtained depended on which portion of the sample we take. The results could vary with the location of the sample in the material if the sample is

46

not homogeneous. The same sort of discrepancy is also found for lead samples.

Table 4.1 show the comparative values of the average for the percentage of zinc and lead concentrations as obtained by the different methods. It will be seen that our results although comparable to, do not quite agree with those obtained by the previous work of the Chemistry Department. This is due mainly to the fact that the sample that we analysed is not exactly identical to but quite different from that of the previous work. Also our method as compared with the others could give only a rough estimate and could not give an accurate result. However, our method is relatively fast, simple,non-destructive, sensitive and versatile technique.

Todgy the government is striving to extract almost all zinc, lead, iron and silver from the ore tailihgs. Hence we mainly describe the contents of the major elements lead and zinc and minor elements iron and silver by our x-ray fluorescence spectroscopy method to be compared with the results of these elemental contents obtained by the wet analysis method.

/

The wet analysis method also gives the percentage of zinc in zincblende (ZnS) to be 67.0 and the percentage oflead in galena (PbS) and anglesite (PbSO^) to be 86.6 and68.3 respectively. Galena is lead sulphide and the principal ore of lead. It is one of the commonest mineral and occurs most frequently together with sphalerite. It i also the important ore of silver, which is present as a valuable impurity. When silver is present in sufficient quantity to justify its being worked for the precious metal galena is regarded as a silver ore and is called "argenti­ferous galena".

Galena often contains recoverable mounts of copper, zinc cadmium, antimony, bismuth, and gold. In addition to various sulphides, commonly associated minerals include barites, fluorite, quartz, calcite, pyrite, and hemimorphite.

Sphalerite is the most important ore of zinc,' a useful metal in industry and the arts. It is found associated with galena in deposits of various types.

The research of the Chemistry Department also gives the content of silica in the ore sample of the tailings from Namtu-Bawdwin Mine. They said that silica (SiO_) was determined by fusion with potassium hydrogen sulphate method.The percentage of silica in ore sample is 25.3 .

X-ray fluorescene method is not used for the identification of compounds. Therefore some of the similar ore samples were sent to the Universities 1 Research Centre to determine the qualitative identification for them by using x-ray diffractometr} using powder method. Powder diffractometry is mainly used for the identification of compounds by their diffraction patterns.

According to XRD results, it is found that among the eight similar ore samples of tailings from Namtu-Bawdwin Mine, galena, and sphalerite are mostly contained in the ore samples. More different compounds were also identified by XRD methods but these compounds are also zinc, lead and iron compounds such as Wurtzite (ZnS, FeS) , Pyrite (Fe? ) .Quartz (SiC^) is also identified by XRD method as with wet analysis method. Therefore, it is satisfactory that the compounds which are found by x-ray powder diffractometry are almost similar with the descriptionsgiven by the Chemistry Department

49

of Yangon University.This comparative research work, also reveals

the fact that the content of iron by wet analysis method and the content of iron by XRF method to be nearly equal and it is also found that the iron compounds such as wurtzite and pyrite are detected by XRD method. it. is also recognized that the contents of lead and zinc percent are found to be rich in the ore samples which contain galena and sphalerite.The next recognizable thing is the contents of silver metal

in similar ore samples of tailings of Namtu-Bawdwin Mine. Qualitative determination of the ore performed by using wet processes involving semimicro qualitative analysis showed that the content of silver is 0.095 %.

In accordance with this research work of x-ray fluorescence spectrometry the content of silver in the ore sample is found out to be 0.08 % . The XRF method does not detect; any content of gold as was done with the wet analysis method. The XRD method does not give any content of silver compound and also any content of gold compound. But XRD method can describe the content of galena, the important, ore of silver. Galena is regarded as. a silver ore and is called "argentiferous galena" and often contains recoverable amounts of silver and gold.The XRF method detects the contents of silver in some of the

50

similar ore sample in which especially galena is contained. This fact is in good agreement with the finding of the XRF

'method and the XRD method. The wet analysis method also give the contents of silver in ore samples of tailings as mentioned above.

4

► ■.iM.i'MflOWrt*—■—Im «Wl »rfittlliMff6n,ii ini „ i

CHAPTER V .CONCLUSION

In this research work, we studied comparatively the contents of zinc, lead and their compounds by wet analysis methods, x-ray fluorescence spectrometry and x-ray diffraction method.

In wet analysis methods, atomic absorption spectroscopy is very sensitive and specific method available for quantitative elemental analysis thoroughly .However , this method has many limitations for routine elemental analysis of mineral ores. The instrument is fairly sophisticated and rather expensive: also, it has considerable running cost. It is also a destructive method.

The volumetric and gravimetric methods are inexpensive and in the hands of skilled workers these methods yield fairly accurate and reproducible results. The results obtained by these methods on both the quantitative analysis of the contents of major elements such as zinc and lead and the quantitative analysis of the content of minor elements such as nickel are found to be in good agreement to that obtained by atoir.io absorption spectroscopy method. However, the wet analysis methods involve lengthy procedures and demand a great skill and patience on the worker. It is also a destructive method and recovery of the original sample is not possible.

In this comparative study, the practical research work describes the qualitative and quantitative analyses of lead and zinc ores from Namtu—Bawdwin Mine by energy dispersive x-ray fluorescence spectrometry. Concentrations of major

52

elements, zinc and lead, as well as those of the minor elements such as iron, silver, nickel etc., were determined.The results obtained by this method are found to iqree to a certain degree with the results obtai.ted by wet analysis methods. X-ray fluorescence analysis of elements is simple, quick, non­destructive, time saving, and a great number of samples can be continuously analyzed, and the results can be obtained almost immediately. Hence this XRF method is the most reliable method to show not only the qualitative analysis but also the quantitative analysis for both major and minor elements.

Finally the similar ore samples of tailings from Namtu- Bawdwin Mine were sent to Universities' Research Centre to obtain the identification of lead and zinc compounds by their diffraction patterns using x-ray powder diffractometer. It is found that the qualitative identifications for lead, zinc and other metals by XRD method are found to be mostly in agreement with the descriptions given by . Khin Lay Kyi , Chemistry Department described that galena islead sulphide (PbS) and the principal ore of lead. It occurs most frequently together with sphalerite which is the most important ore of zinc. It is also recognized that the galena and sphalerite are mostly found in the similar ore samples by XRD method.

53

In brief, it can be said definitely that plenty of zinc and lead can be produced in Myanmar.Although the ore samples used through-out this comparative research work are waste- product ores from Namtu-'-Bawdwin Mine the contents of zinc and lead and their compounds are found in fairly large amounts as Chemistry Department has observed. Hence the above comparative study may be helpful in exploration of the zinc and lead and their compounds in Myanmar.

REFERENCES

1. A.M. Bateman, Economics Mineral Deposits, John Wiley and Sons, Inc., New Yotk, 1956•

2. H.L. Chibber, Mineral Resources of Burma, Macmillan and Co., Ltd., London, 1931.

3- Khin Lay Kyi, Analysis of Metallic Elf ;-•••:■ in Low Grade Ore from Namtu-Bawdwin Mine, M.3c. Thesis (Chemistry), University oJ' Rangoon, 198 b.

4. Win Tha Htwe, Determination of Tungsten and fin Content in Ore Samples by X-Ray Fluorescence Spectrometry, M.Sc Thesis (Physics), University of Rangoon, July, 1982.

5 . R. Jenkins and J.L. de Vries , An Intro 1c ' : o o v X~Pav Powder Dilf'ractometr_, , N.V . Phillip, Ho , la::c , : ’V-,

6. L.V . Azaroil and K.J. Buerger, The Powder Me i !, McGraw-Hill, London, ±958.

7. R. Jenkins and J.L. de Vries, An Inirodrc:ion to X-Ray Powder Diflractometr.,, N.V. Phillip, Horland* 19"9.