r/r-

METHODS OF COAL AND COAL ASH ANALYSIS

CHAPTER-2

METHODS OF COAL AND COAL ASH ANALYSIS

INTRODUCTION:

Analytical methods used in trace and toxic

elements analysis of coal and its ash may be separated in

to two categories. There are certain methods which can

not be easily used for multi-element analysis on an

individual sample. Certain trace elements are volatile.

Atomic absorption spectrscopv, potentiometrv, voltmetrv

and absorption spectrometry, require Sample preparation

for coal and fly ash matrices. Precision depends largely

on the individual analyst's Skill. [1] [2] [3] [4]. Several

organisations have published individual summaries of

procedures used in their laboratories. [5] [6] [7] [8], The

present trend is towards development of multielemental

instrumental procedures to cover quantitatively as many

elements as are possible. Because any particu la r

analytical discipline is better suited for certain elements

than for others for var ious inherent reasons. A

combination of methods is usually necessary to determine

[5(3

all elements of interest.

The below mentioned block diagram describes

the methods used in coal analysis by U.S. Geological

Survey [9],

Table N o .l

Methods used in Coal analysis by U.S. Geological Survey.

Coal as received

IAir dry (298"K)

Then ground to 80 mesh.

1

Ashing at 798V’K

1M ethod-1 - A.A.S. fror Mg, Li,

iNa,^Mn, Cd, Pb, Cu and Zn.

M ethod -2 - X-rav fluorescence

for Al, Si, Ca, S, Fe, Ti, K, Cl, P.

iM ethod -3- Semi quantitative

spectrographic analysis tor B,

Ba, Be, Co, Cr, Ga, Go, Mo, \i

and V.

— IStorage

IRaw coal

IM ethod -1- Spectrographic

method for As, Sb.

M e th o d -2- Specific ion

electrodes for F.

M ethod-3-X-rav fluorescence

tor Se.

M ethod-4- Xeutron actu ation

analysis for As, Sb, Se, Fe, Be.

Co, Cr, Zn and others

M ethod-5- Flameless A A S

for Hg, Sb, As and Se

The preferences for a particular technique are

often expressed in the literature. Such preferences are the

results of analysts experience equipment available and

m any other subjective factors. A tom ic absorption

spectroscetry and colorimetry have been employed in the

present context.

A n a l y t i c a l p r o c e d u re s for a t o m i c a b s o r p t i o n

spectroscopy :

A.A.S. is a m ethod w ith h igh sensitiv ity;

sensitivity of the method declines in increasing non

metallic character of the element.

Analytical Procedures for A.A.S.

Sample preparation:

The prob lem s encountered in the sample

dissolution are discussed in some details by Slates. [10].

The Bernas procedure [11] is often used for dissolution of

slag, flv ash and soils with very low organic content.

Silicates are decomposed in 30 to 40 minutes at T10°C

without volatilization losses. The decomposition medium

of HF, H 3B 03 and aqua regia provides a salt free matrix

that offers negligible interferences during AAS analysis.

Bernas procedures permits volume measurements in

calibrated glass containers. The dissolution procedure

has been satisfactorily applied to AAS. analysis. [12] [13]

[14]. Results of AAS Method as applied bv Dreher and

Schleicher [15] has been described below\

Table No. 2

Concentration of Trace and Toxic elements

Element CoalAnalytical A. (in n.m.)

Cone in ppm.

S.D.

[1] Pb 283.307 2.8 8.0

[2] Cu 327.396 4.5-69 5.4

[3] Cr 425.435 4.4-33 3.4 .

[4] Mo 317.035 <0.3-30 5.0'

[5] Zn 334.50 7>200■

[6] Mn 257.61 5.27-400 19

For Cd, Gluscoter [16] obtained the following results.

Cd - l (n n i ) 228.80 <0.1 - 29

Wet chemistry has been employed by us for the

sample preparation of conventinal AAS. It is possible to

determine Li, Be, Cr, V, Mn, Co, Ni, Cu, Ag, Cd and Pb

after dry ashing and acid dissolutions. The procedure

employed is that used by Simon and Huffman [17].

Methods of Analysis :

Accordingly to their method coal ash 0.5 to 1

gm. is weighed in to a 100 ml Pt. d ish. 10 ml of

demineralised water, 10 ml H N O , and 10 ml HF are

added to the dish. The dish is covered and allowed to

stand overnight. Then 7 ml of HCIO^ added to the dish.

The dish is placed on a steam bath for 1 hr. and then

placed on hot plate to fume off the acids near to drvness.

25 ml of water and 5 ml of HC1 are added to the dish,

digested in an steam bath for 30 minutes. The solution in

transferred to a 100 ml volumetric flask and diluted with

water up to the 100 ml mark. Aliquots of this sample are

then aspirated in to the air-acetvlene flame on an atomic

absorption spectrometer to determine the elements

namely Na, Mg, Cu, Li, Mn, Zn, Pb and Cd.

O ther comprehensi\’e reviewsand b ib l io ­

graphies [18] [19] are available in the literature. Several

organizations have published individual summaries ot

procedures used in their laboratories [20] [21]. Atomic

absorption spectroscopy has certain principles, limitations

and areas of applications. Combined use analytical

disciplines give fruitful results. Sample dissolution has

certain problems; it has been discussed in details bv slates

[22], The Bernas procedure [23] is often used for

dissolution of slag, flvash and soils with very low organic

content. [24] [25j Simon and Huffman [26] determined

coal ash bv AAS. Coal ash in weighed. (0.5 to 1 g.) in to

Pt dish. Demineralised water, 10 ml, H X O , 10 ml and

LIP 10 ml are added to the dish. The dish is covered and

allowed to stand overnight, then 7 ml of HCIO, is added

to the dish. The dish is covered, placed on a steam bath

for 1 hour to fume off the acids to drvness. 25 ml of water

and 5 ml of HC1 are added. The dish is covered and

placed on a steam bath and digested for 30 minutes. The

solution is transferred to a 100 ml volumetric flask and

diluted to volume with water. Aliquot is then aspirated

in to air acetylene flame of an A tom ic Absorption

Spectroscope to determine the concentration of the trace

and toxic elements. The sample aliquot used for the

determination of Mg is made to contain 1 % Lanthanides.

Cd and Ca mav also be determined using a heated

graphite atomizer.

For many elements eg. Cd and Ca, solvent

extraction offers a means for increasing the sensitivity of

the determinations bv isolation and concentration of the

metals of interest. A procedure developed for detection

Cd and Pb bv Cavallaro et.al. [27] using the extraction of

iodide complexes of Pb and Cd in to methvi isobutvl

Ketone. The preparation of coal samples for Cr, Cu, Mn

and Ni was the same as employed for Cd and Pb. Below

mentioned table shows the recommended instrument

parameters for AAS.

Table No. 3.

Recommended instrument parameters for A.A.S.

S.N. Flement Ain run.

SpectraCurrent(M.A.)

Lamp Fuel Support

1. Cu 324.8 0.5 3.5 c =h 4 Air

2. Cr 337.9 0.2 / C :H 4 Air

3. Cd 337.9 0.2 3.5 c :h 4 Air

4. Zn 337.9 1.0 5 Air

5. Pb 405.78 0.7 4 c ;h 4 Air

6. Be 234.9 4-?/ c :h 4 Air

Detection limits for elements in coal ash [28] is as

belovv:-

Table No. 4

Elements Sampleweight

Lower limit of 1

detection in \xg/g.

Na 0.5 100

Mg 0.5 100

Li 0.5 5 j

Mn 0.5 15 i

Zn 0.5 10

Pb 1.0 1Cd 1.0 1.

SPECT RO PH O T O M ET RIC D E T E R M IN A T IO N S

OF SOM E TRACE A N D T OXIC

ELEMENTS IN C O A L .

[1] Z i n c :

For spectrophotometric determination of Zn

following procedure has been employed-[l] Zn

solutions containing 5 to 25 ppm of Zn were

prepared from the stock s o lu t io n .[220 mg

ZnS04. 7H20 /500 ml].

[2] Zn was estimated spectrophotometrically using

dithiozone. [29], Powdered coal sample was

treated 10 ml concentrated H N 0 3 (A.R. Grade).

Solution wras heated in a steam bath. W hen

digestion is complete, the solution was heated

to dryness. Diluted with w'ater to 20 m l with

water.

[3] Dithiozone was dissolved ( lm g /m l) in 0.1 M

NaOH solution.

[4] The pH of the sample was adjusted between 5.5

to 6 by adding 1:15 v /v N H 4OH solution. One

ml. of sample solution was pipetted out, 0.1 ml

of dithiozone solution added. The solution was

suitably diluted to obey lamberts and Beers law.

Absorbance was read at 555 nm. By extrapolation

concentration of the unknow n solution was

obtained.

[2] C d :

Cd was estimated by dithiozone method.[30] 25

ml of 1:10 H 2S 0 4 (v / v ) was added to the powdered coal.

The solution was heated to dryness and repeated if

digetsion is not complete.

The solution was neutralized by N H 4O H (1:12

v /v ) . Then 4 ml of l :1 0v /v HC1 was added and the

volume was made to 100. The pH of the solution was

adjusted to 6 by add ing N H 4O H . The so lution was

filtered in a whatman 42 filter paper. 1 ml of the

sample solution was pipetted out. 0.2 1 of dithioxone

solution was added and concentration of Cd estimated

spectrophotometricallv.

Stock solution of Cd was prepared bv dissolving

l).8 (.ig Cd/m l. Standard solution was obtained b\' dilution

method to contain 0.2 to 0.8 ppm. of Cd.

[31 ESTIMATION OF Cr :

Chromium was estimated spectrophotometricallv

using diphenvl carbazide [31], To the powdered coal, 10

ml of IN H,SO, was added. Then 0.5 ml of 0.5 N KMnO - t

solution was added. Heated in steam bath till sample is

digested completely. Excess of KMnO was decolorised

by add ing 5°o sodium azide solution at the rate of 1

drop per second. Flask was shaken after adding each drop

till brownish tint was destroyed. The solution was

filtered in whatman 42 filter paper. To 1 ml of above

sample, 1 ml of 0.25% d iphenvl carbazide solution

(in acetone) was added. [10]. It was diluted with 10 ml

with water. The absorbance was read at 540 nm.

The standard Cr so lution was prepared by

dissolving 50 mg of K-,Cr.,0, in 1000 ml of water. 1 his

solution contains 10 m g /m of Cr.

Standard solution containing 2fig to 20 fig of Cr

was prepared and standard curve was obtained.

Cu was determined by method described in ref. [32]A.

[4] DET ERM IN AT ION OF Mo [33]B

1 gm of oven dry coal sample is powdered, taken

in a Pt crucible. 5 c.c. HF and 5 c.c. of H C I0 4 were added.

Heated at 300°C till liquid is evaporate!. When digestion

is complete 5c.c. of HC1 and a little quantitv of water is

added. Heated in an electrical bunsen till drvness. The

aliquot is transferred to 100 ml volumetric flask and

diluted to 100 ml mark. This solution is empolved for

colorimetric determination of Mo.

Reagents required

(1) 5% w /v aqueous solution of KI.

(2) 5°o w /v aqueous solution, freshly prepared.

(3) 10% w /y aqueous solution of tartaric acid.

(4) 10% w /v aqueous solution of thiourea,

freshh' prepared and filtered.

(5) D ithiol solution : To 0.2 gm of melted

dithiol, 100 ml of 1% w /v NaOH solution

is added, mixture is stirred for 15 minutes.

1.8 c.c. thiglycollic solution is added to it.

An aliquot of test solution containing 1 ug/c.c. of

Mo is taken. Treated with excess KI. Liberated L is cleared

by adding ascorbic acid,dropwise. 1 c.c. of tartaric acid

solution and 2 c.c. of thiourea solution were added. Then

4 c.c. of dithiol solution added. The solution was allowed

to stand for 30 minutes. The Mo-dithiol complex was

extracted in to isoamyl acetate. The organic phase is dried

and optical density measured at 680 nni.

[5] DET ERM IN AT ION OF Se

[1] Discussion :

Sill, C.YV. and Peterson, H.E. [34] found that Se

has tendency to accompany 'S'. Bowen and Covvse [35]

were able to separate Se from As, Br, Mn, Na and Zn

and determine the element rapidly with sensitivity of

0.005 jig. The permangnate method of Schrenk and

Browning [36] has been extented to the determination o;

Se [37], A procedure with excellent results have been

reported. [38], No. Tellurium has been found to interfere,

even if its concentration is 1000 times greater. Mellichamp

[39] deve loped a sem iquan tita t ive spectrograhic

procedure for Se. Photometric method based on 3,3'

diamines benzidine and 2,3 diaminonaphthalene base

gained w ide acceptance, in the analysis of Se. The

sensitivity of the reagent has been increased bv EDTA.

[40] [41],A tom ic absorp tion analysis by Rann and

Humbly [36] has been found to be excellent.

Reagents required

[1] S o d i u m selinite solution lml= 2 ug of So.

[2] HC1, (density 1.19 g/c.c.) and diluted to

1:7.

[3] H N O v density 1.5 g/c.c.

[4] N H 1 solution diluted (1:1)

[5] EDTA : 5% and 0.1 M solutions.

[6] H CO O H (1:9) solution.

[7] SnCln solution : 10 gms dissolved in 4ml.

HC1, (density 1.19 g/c.c.). Heated, cooled

& diluted with 16 ml of water. Solution

is to be prepared just before analysis.

[8] Sodium hvpophosphite = 10% solution in

HC1 (1:7)

[9] 5% Carbamide solution.

[10] Citric acid 25% and 10% so lu tion of

Sodium arsenite = 1 ml = 50 mg of As.

[11] Cresol red soln.- 1 % in 20% C H .O H

solution.

[12] 0.5% solution of 3.3’ diaminobenzidine in

C fH^ or Toluene (keep the solution in

Procedure :

The solutions containing 1, 3, 5, 7, 9 (Ag of Se in

50 ml beakers are prepared. 2.5% EDTA solution (1 ml)

and 2ml. of H C O O H acid added in each beaker. pH

adjusted between 2 to 3 with NH^ to get yellow color o

cresol red indicator. Two ml of 0.5 solution of 3,3

diaminobenzidine is added to each beakers. Solution is

allowed to stand. NH^ is added to adjust the pH at 8

(violet color of the indicator is obtained). Transfer the

solutions to 100 ml separating funnel.Add 11 ml of C,H

or C6H-CHr anc extract the coloured complex. Percent

absorbance is measured at 415-420 nm.

Mg is determ ined bv titrimetrv and 'S' bv

Eschka method. [43]

Ox ides ot m inera ls associated w i th b i t u m in o u s

coal ash. [44] are as m en t ioned below:

Table No. 5

Constituent Oxide Percentage

SiO, 20-60

a i a 10-35

SO, 0.1-12

Fe2° , 5-35

CaO 1-20

MgO 0.3-4

Na20 + K 20 1-4

Average concentration ot elements in coal ha\'e

been described below : [4b]

Table No. 6. (Cone, in %)

S.N. Hlement U.S. Average World wide

Bv Spectroscopy By A AS Average

1. s 2 2 15 "I 1

Si 2.b 2.89 2.8

AI 14 1 (i7 1.0 i

4 (/a 0.54 0.72 1.01

5. Mk 0.12 0.25 0.02 !1

6. \'a 0.06 0.091

002 i

K 0.18 0.0(1 0 01

s !:e 1.0 - 10

u Mn 0 01 - 0.005

■ [ 6 ' 1

Concentration of some elements in ppm. [46] has

been mentioned below :

Table No. 7.

(Concentration of trace and toxic elements)

S.N. Element Spectroscopic determ ination W orld w ide average

1. Be 2.0

1 1

1

3 1■

2. Bi 0.7 5.5

3. B 50 75

4. Cd 1.3' ' i

5. Cr 15 10

6. Cu 19 15

7. Pb 16 25

8. Li 0.08 0.07

9. M o 3 r>

10. Se 4.1 3

11. Zn 39 50

M g in coal :

Mg conc. in North Dakota lignite is reported bv

Somer ville and Elder. [47] to be 5039 ppm. Burchett [48]

has reported Mg concentration in eight coal samples

from Nebraska to be in the range of 0.047 to 0.574 raw

coal samples from three Illinois based plants had some

what lower value (0.14 ±0.07%) [49], Cooley and Ellman

[49] studied lignite and subb itum inous coals from

Eastern Montana. They found Mg concentrations in

subbituminous coal samples in western direction. In the

present case Mg concentration was found tobe 4350 ppm.

Mg was estimated titrimetricallv.

Ca Concentration :

Ca concentration in coal occurs around 1% or

smaller. The average concentration of coal in North

Dakoita lignite is reported to be 1.6% [51] Nebraska coal

has 0.25 to 2.4% Ca [52] Raw coals from Illinois basin has

0.12 to 1.77% of Ca [53]. In the present study it was

found between 0.7% and 0.86%. Ca was estimated

titrimetrically.

[5] Cr Concentration :

Cr was determined by Bureau of mines in the

ash of two Pennsylvania bitunimous coals. One ash coal

sample from Washington country contained 0.019% Cr^O,

in the ash. Another sample from Cornbria county,

contained 0.039% 0\ 03 in the ash. [54], Cr concentration

in North Dakota lignite is found to be 65 ppm . [55]

Swanson et.al. [48] 63 have reported Cr concentration in

U.S. coals as mentioned below :

Coal Type Cr. concentration

Anthracite - 20 ppm.

Bituminous coal - 15 ppm.

Sub-bituminous coal - 7 ppm.

Lignite - 20 ppm.

Cu in U.S. coals has on average concentration of

19 ppm. [5b]. 1'he highest concentration of (27 ppm.) is

found in anthracite [57], 'I'he worldwide average is 15

ppm. [58]

Se Concentration :

Se in U.S. coals was discussed in reports bv

Zubovic et.al. [61] and Gluskoter [62]. Se is most stronglv

enriched of all the elements. Se is present in both organic

and inorganic combination in coals. Se in Xorth Dakota

lignite was determined bv Sommerville and Elder [63]

to be 0.85 ppm. (average value for 12 coal samples)

Mo Concentration :

Ternieulen [64] discussed the occurrence of Mo

in coal and some plants. Mo in coal in England, Xew

Castle is 0.033%.

L’nashed coal samples were digested by 11X0,

and analysed for Cd and Zn concentration by atomic

absorption spectroscopy. The results of analysis were.as

mentioned below. [65]

Cd - 0.3 to 28 ppm.

Zn - 18 to 300 ppm.

Schultz el.al. [66] have reported Cd

concentrations in pitts bury seam, coal to be 0.14 ± ppm.

Pb Concentrations :

Sawanson V.E. et.al. [67] have examined samples

of coal and ash deposits from a boiler bv Chemical and

spectroscopic methods, concentration have been reported

to be from 0.0001 to 0.00461 bv Dunn and Bloxam. [68]

Pb contents of coal, coal ash and flyash were

recently discussed bv Block and Dams. [69], simple

gravimetric method and atomic absorption spectroscopv

were emploved in the present work. Pb in U.S. coals came

within the range (in ppm.) 0.37 - 86, 0.78 - 59, 1.4 - 17,

1.5-8 in Appalachian Interior province, N. Great plains

and North Dakota coals. [70] [71],

COAL - UTILIZATION

Combustion converts the organic part of coal to

CO., and water and the non volatile inorganic constituents

to coal ash residues. Loevblad [72] has presented data

for ash, volatile compound and ’S’ content and heat of

combustion of coals of different origin, in the table

below :

Table No. 8

Ash, volatile compounds, 'S1 content and heat of

combustion of various coals.

Name of country Ash °„ Volatile

compound %

S °« Ileat of

l ombustio:'

Norway 7 39 0.78 8.4

England 9 30 1.12 7.4

U.S. - 35 1.02 8.1

West Germany 5 28 0.85 9.7

Poland - - 0.60 7.1

Soviet Union 15-17 34-35 0.70 7.8-8.0

Davison et.al. demonstration that Pb, Ga, Sb, Cd,

Se, As, Zn, Ni, Cr and S were markedly increased with

decreasing particle size of ashes. [73], The concentrations

of Ga, Ge, Hg, Pb showed approximately 3 fold increase

between the coarse ( 50 mm) and fine (2 mm) flv ash of

Australian coal sources. [74] [75],

Schwitzgebel, K., et al [78] [79] reported the effect

of particle size of flvash on the concentration of 17 tract'

elements as .shown in the table below:

Table No. 9.

D istribution of trace and toxic elements in bottom

ash, fly ash and flue gas.

Element Bottom ash

22.2 %

Flv ash

77.1 %

Flue Gas

A I 22.5 78.8 0.7

Be 16.9 81.0 2.0

Cd 15.7 80.5 3.8

Cr 13.9 73.7 12.4

Cu 12.7 86.5 0.8 :

Element Bottom ash Flv ash Flue Gas

22.2 °o 77.1 °o

Fe 17 71.3 0.8

Pb 10.3 82.2 7.5

Mn 17.3 81.5 1.2

Mg 17.2 82.0 0 bo

Mo 12.8 77.8

■

9.4

Zn 29.4 68.0 2.6

V 15.3 82.3 2.4

Mukherjee and C houdhary [78] have

investigated ash of Indian coals. The major const i tuents

of the ash are SiOn, A l ,O v and Fe. The SiCX/ALO, ratio

in the samples vary between 1.8 and 2.2. Block et al [79]

have studied the concentrations of elements in coal as the

function of ash content of the coal. V and Si increase with

the increasing content of ash. This is not so for Sb and

Cu. Constituents (Wt% of total) of individual ash [Ref.

80] have been described in the table below :

Table No.10

S.N'o. Gravity Fraction SiO, A 1,0, Fe,0, TiO: P A SO-. CaO____ j

1. Overall G.F. 40 18.9 28.8 0.60 0.08 1.63 02 M 1

2. 1.3 G.F. 33.6 18.3 13.6 0.32 0.19 6.19 2.0 4.4

3. 1.3 -1.50 G.F. 45.5 20.2 27.6 0.40 0.23 0.27 - 0.9

4. 1.50-1.80 G.F. 48.6 21.5 22.6 0.62 0.08 0.40 - 0.7

5. 1.80 (Sink) G.F. 53.2 25.8 13.2 0.67 0.07 0.46 - 1.0

(G.F. = Gravity Fraction)

Average trace element content in ash

(Concentration in ppm .) of coals from different U.S.

regions [81] are shown in the table below :

Table No. 11

Elements Alabama E.kentuckv Medlm Ohio Pasvlvania Tencsst ird'.ana ;

Be 88 20 - 9 8 h 2̂ \'

Cr 207 260 140 235 244 200

i

182

Cu 150 156 75 80 125 U p ̂I I

Pb 40 59 10 43 52 “> i i r> S

Li 812 1 Or 4 140 ?u4 r42 - -t

Mo 117 “1 17 -t ~ s. S . 4”

Zn 243 203 200 284 242

Concentrations of trace and toxic elements

(in ppm.) in coal, and ashes are as mentioned in the

table below :

Table No. 12

Concentration of trace and toxic elements.

(Concentration in ppm.)

Element Coal Bottom Flvash from

precipitator

Be 1.5 5 6

Cd <1 <0.7 <1.6

Cr 4 20 60

Cu 14 53 80

Pb 6.3 26 62

Se 2.7 1.5 6.6

Zn 6 <10 100

Li 50 200 200

Ash has acid insoluble fraction and acid soluble

fractions [82] as described below :

Table No. 13.

Acid Insoluble

fraction

Acid soluble

fraction

S iO , 38.38 to 53.48 0.82 to 0.88

A1,0, 10.13 to 21.80 2.61 to 6.32

Fe.O, 0.88 to 1.09 2.74 to 5.03

T i0 2 0.96 to 1.43 0.40 to 0.42

CaO 1.16 to 1.38 9.42 to 21.65

M gO 0.36 to 0.42 2.57 to 2.97

k 2o 0.31 to 0.61 0.02 to 0.04

Total °o 52.81 to 81 S O , 1.11 to 2.30

M g 0.45 to 6.8

Total 47 to 41.58

Chem ical concentration of trace and toxic

elements in flyash [83] is mentioned below :

Table No. 14.

Element % Range

.... . . . . t

Average

A1 0.1 - 17.3 1 1.7

Si 19.1 - 28.6 26.6

Ca 0.11 - 12.6 4.4

Mg 0.04 - 6.02 0.9

Na 0.01 - 0.66 0.6

K 0.19 -3.0 0.8

Fe 1 - 26 4.1

S 0.1 - 0.5 ' 0.2

Element (ppm.)

Be 3 - 7 5.5

Cd 0.7 - 130 1.0

Cr 10 - 690 54

Cu 14 - 1000 63

Pb 7 - 279 48

Li 50 - 1064 70

Mo 7 - 117 10

Se 0.2 - 134 / .6

Zn 36 - 1333 72

. [ SO 1

Results ol soil, water, coal and ash analysis, for

trace elements of Bhadra, Bartarai and Amadand projects

haye been described in Chapter-3. Spectrophotometry

and atomic absorption spectroscopy haye been employed

according to their feasibility and suitability for different

trace and toxic elements.

★ ★ ★ ★ ★

r " _ ”

REFERENCES s________ _ _____ ____>

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