Multielement analysis of a municipal landfill leachatewith total reflection X-ray fluorescence (TXRF). A comparisonwith ICP-OES analytical results

Franco Cataldo

Received: 28 December 2011 / Published online: 17 April 2012

� Akademiai Kiado, Budapest, Hungary 2012

Abstract A complete analysis of a landfill leachate

coming from a landfill site of several years old was per-

formed with a total reflection X-ray fluorescence (TXRF)

spectrometer in comparison with an inductively coupled

plasma optical emission spectroscopy (ICP-OES). The

results of the two analytical techniques are compared and

advantages and drawbacks emphasized. The TXRF ana-

lytical technique appears a reliable, economic, rapid and

simpler technique for the everyday monitoring of the

composition of the landfill leachate before the purification

treatment and after the treatment to check the quality of the

resulting purified water. The TXRF and the ICP-OES

analytical techniques were also employed in the analysis of

three groundwater samples.

Keywords Landfill leachate � Groundwater � TXRF �ICP-OES � Multielement analysis

Introduction

Total reflection X-ray fluorescence (TXRF) is a very fas-

cinating analytical technique for elemental analysis even of

complex matrices. TXRF has been reviewed extensively

[1–8] showing that this analytical technique has reached a

remarkable success in elemental analysis in recent years.

TXRF provides significant advantages compared to other

methods of trace element analysis. For instance: it detects

exceptionally small mass quantities (ng or pg); it is mul-

tielemental, meaning that it can simultaneously (in one

spectrum) analyze almost all the elements above a certain

atomic numbers higher; it has the ability to perform the

direct analysis of solid deposits (like membranes); the time

of analysis is short (typically 100–400 s) and the sample

preparation is minimal.

The TXRF technique was initially adopted in the quality

control of semiconductor fabrication [9] but then was

extended in environmental analysis and especially in water

analysis [8, 10, 11] including rainwater analysis [12],

wastes and leachates [13]. Many efforts were dedicated to

the improvement of the TXRF analytical technique looking

at the calibration and sample preparation [14–17] or other

equipment and design aspects [18–20].

Examples of application of TXRF analytical technique

are not limited to water analysis, there are reports on the

use of this technique in the analysis of metals in coal [21],

trace elements in diesel soot [22], trace metals in sugar

cane spirits [23], sweat extractable metals from textile

fabrics [24]. TXRF is an ideal technique in the materials

analysis [25], glasses [26], materials inhomogeneity as in

the case of boron carbide [27], archaeological samples [28]

and medieval pigments [29]. TXRF can be applied to the

determination of certain metal ions, after their concentra-

tion on a selective membrane [30]. In biological matrices

the TXRF is used for the determination of trace metals in

blood and in hairs [31, 32], in the determination of trace

elements in human cancerous and healthy tissues [33], as

well as in the search of trace elements in the blood of seals

of the North Sea [34] and in lichens [35].

Despite this large applications of the TXRF technique,

coming back to water and wastewater analysis, it can be

affirmed that relatively little work has been made in the

analysis of heavily polluted waters [36, 37] and in partic-

ular the analysis of the polluted water known as landfill

leachate. The present work is dedicated to the analysis of

the water coming from a landfill leachate. The TXRF

F. Cataldo (&)

Bioenergy Srl, Via Casilina 1626/A, 00133 Rome, Italy

e-mail: franco.cataldo@fastwebnet.it

123

J Radioanal Nucl Chem (2012) 293:119–126

DOI 10.1007/s10967-012-1777-z

analytical results will be compared with those produced

with an optical inductively coupled plasma spectrometer

(ICP) on the same landfill leachate sample.

Experimental

Some aspects of the TXRF spectrometer employed

in the present study

The TXRF spectrometer used in the present work, the S2

Picofox from Bruker, involves the total reflection of the

X-ray beam on a reflective medium like polished quartz

glass or polyacrylate glass disc (Fig. 1). The sample is

deposited as a thin film where the X-ray spot is focused and

the sample fluorescence is collected by a detector as shown

in Fig. 1. The X-ray tube of S2 Picofox is air cooled and

made in metal-ceramic with Mo or W target producing a

spot size of 1.2 9 0.1 mm2 with an energy of 35 W/mm2.

Alternatively, it is possible to adopt a microfocus tube as

the X-ray beam source, so that a spot of 0.05 9 0.05 mm2

is obtained with a specific energy of 4,000 W/mm2 and in

this configuration the detection limits are 5–10 times better

than the standard configuration and become comparable to

the KW TXRF spectrometers. As shown in Fig. 2, with the

Mo target it is possible to detect nearly all elements from

Na–U with the exclusion of Zr, Nb, Mo and Tc. In the

present work we have used the Mo target. However, it is

possible to mount the W target and in this other case the

range of detectable elements is comprised from K–U with

the exclusion of Hf, Ta, W, Re. With the W target it is

possible to detect Zr and Mo and it is possible to achieve

improved detection limits for Cd, Sn, Sb (\50 ppb) in

comparison to the Mo target. The monochromator of the S2

Picofox is a flat Mo/B4C multilayer with 80 % reflectivity.

The detector used in the S2 Picofox is a silicon drift

detector (10 mm2 XFlash�) having an energy resolution

\150 eV. This detector is extremely fast in its response

with no dead time. Furthermore it does not need any

external cooling for instance with liquid nitrogen since it is

Peltier-cooled.

Materials and equipment

Landfill leachate sample was obtained from a landfill

located in the central Italy. The multielemental analysis on

the landfill leachate samples was performed on the TXRF

spectrometer S2 Picofox from Bruker. As reference, the

same sample of landfill leachate was also analyzed

according to standard procedure on an ICP-OES. Use was

made of a Perkin-Elemer Optima 7300 V ICP-OES.

Fig. 1 The TXRF configuration involves the total reflection of the

X-ray beam on a reflective medium like polished quartz glass or

polyacrylate glass disc. The sample is deposited as a thin film where

the X-ray spot is focused

Fig. 2 Elements which can be

detected with the TXRF

spectrometer S2 Picofox with a

Mo target. Nearly all elements

can be detected from Na to U

with the exclusion of Zr, Nb,

Mo and Tc

120 F. Cataldo

123

Experimental TXRF apparatus

The energy dispersive S2 Picofox TXRF spectrometer from

Bruker used in the present work was equipped with a Mo-

tube and a 30 mm2 silicon drift detector. The microfocus

X-ray tube is air-cooled with a power of 50 W. As the

detector was Peltier cooled, no additional cooling unit (e.g.

liquid nitrogen) was needed. The total power consumption

of this benchtop system was only 180 W. No external

calibration is needed for quantitative measurements of

element concentrations ranging from high wt% to the low

ppb range. With S2 Picofox all elements from Al–U can be

detected, but even Na and Mg are detectable although with

some difficulty.

Sample preparation and measurements

Sample preparation for qualitative analysis was done by

transferring 10 ll sample material to a quartz glass sample

carrier with subsequent drying in vacuum. For quantitative

analysis 1 ml of sample was mixed with 10 ll of a Ga-

solution (10 mg/L) and 100 ll of a polyvinyl alcohol

solution. After thorough homogenization 10 ll sample

were transferred to quartz glass sample carriers and dried in

vacuum.

The samples were analyzed with the following TXRF

parameters: tube setting at 50 kV and 600 lAmp. Mea-

surement time employed 1,000 s.

Analysis and quantification

In general all elements from sodium to uranium (with the

exclusion of the elements zirconium, niobium, molybde-

num and technetium) can be analyzed by the S2 Picofox.

The TXRF analysis is based on internal standardization.

Therefore, an element, which is not present in the

sample, must be added for quantification purposes.

The complete process of analysis and quantification is

described by the following steps:

(a) Measurement of the complete spectrum. All detect-

able elements are measured simultaneously.

(b) All identified elements are be marked for further

quantification, which can be done manually or

automatically by the software.

(c) Spectral deconvolution.

(d) On the basis of the chosen elements, the software

performs the deconvolution of the spectra. The net

intensities of the element peaks are calculated with

regard to corrections of line overlaps, background

factors, escape peak correction etc.

(e) Calculation of concentrations.

(f) The element concentration is calculated by the simple

formula:

Cx ¼ Nx=Sx½ � Nis=Sis½ ��1Cis

where N is the net intensity, S the relative sensitivity and C

the concentration—each either of the analyte x or the

internal standard is, as indicated. The S2 Picofox can

measure the elements Al–Y using spectral K-lines. Ele-

ments Ru–U are measured using L-lines. The typical lower

limits of detection (LLDs) of the S2 Picofox for many

elements is close to or below 1 lg/L.

Results and discussion

TXRF as the simplest analytical technique

for the monitoring of the metal ions in a leachate

Landfill leachate varies widely in composition depending

on the age of the landfill and the type of wastes stored in

the landfill. A young leachate is acidic while a late-type,

older leachate is basic and rich in ammonia and ammonium

ions. A landfill leachate is usually dark in color and con-

tains both dissolved and suspended material. The genera-

tion of leachate is caused principally by the rain waters

percolating through waste deposited in a landfill. The

percolating water passing through the decomposing wastes

becomes contaminated and once it flows out of the waste

material it is termed leachate. A further contribution to the

total leachate volume is produced during the decomposi-

tion of carbonaceous material producing a wide range of

other products including methane, carbon dioxide and a

complex mixture of organic acids, humic and fulvic acids,

aldehydes, alcohols and simple sugars. In actively

decomposing waste the temperature rises and the pH falls

rapidly and many metal ions which are relatively insoluble

at neutral pH can become dissolved in the developing

leachate. Leachate is corrosive and reacts with materials

that are not themselves prone to dissolve in tap water such

as fire ash, cement based building materials, iron and steel

wastes, aluminium wastes and gypsum based materials

changing the chemical composition of the leachate [38].

Therefore, one of the main concern regarding the landfill

leachate is the difficulty of treatment and disposal because

of the relatively large content of metals and especially

transition metals. In developed countries the municipal

wastes are no more mixed with industrial wastes in the

landfilling practice and therefore the heavy metals content

in the leachate is reduced in comparison to previous

practices when the mixing of different types of wastes

having different origin was allowed. Notwithstanding these

Multielement analysis 121

123

restrictions, the landfill leachate remains a waste which

poses serious risks of pollution of the environment and in

particular of the groundwater. Furthermore, the transition

metals content is variable in the leachate, depending from

the degree of ‘‘maturation’’ or aging of both the landfill site

and the resulting leachate [38]. Moreover, the concentra-

tion of the transition metals are also varying seasonally and

this is linked to the frequency of the rainfall which can vary

considerably from month to month. In order to be able to

know in advance the current content of transition metals in

a certain leachate, to decide what could be the most

appropriate treatment to which submit the leachate, but

also to monitor the effectiveness of the treatment in the

removal of the transition metals from leachate [39], it is

necessary to have available a simple, fast and effective

analytical technique which does not require any sample

preparation before the analysis without any need of using

reagents and with the possibility to analyze simultaneously

all elements of interest. The best analytical technique

which should fulfill all the mentioned wishes is the TXRF.

In the present work we have analyzed a sample of

landfill leachate coming from a landfill having about

6–7 years old. The purpose of the present study is to show

that the last generation of TXRF afford reliable analytical

results also on extremely complex matrices like a landfill

leachate. The validation of the results of our analysis with

TXRF was made using an ICP-OES classical analysis.

The complete chemical analysis results of the landfill

leachate sample

The leachate sample was taken from a landfill in September

2011. The chemical oxygen demand of the sample (COD)

was 5,550 mg/L, a value quite typical of a leachate coming

from a landfill site having several years old. The pH was

basic, 8.7 and the electrical conductivity of the leachate

was found at 10,880 lS/cm, indicating a quite high level of

electrolytes. The basic pH is attributable to a high ammonia

and ammonium ion concentration which can exceed easily

200 mg/L. The ionic chromatographic analysis of the

leachate sample (after filtration) revealed also a concen-

tration of 0.5 mg/L of formiate ion (HCOO-) and 70 mg/L

of acetate ion (CH3COO-). Other ions found with ionic

chromatography are: nitrites (NO2-) 0.9 mg/L, nitrates

(NO3-) 6.7 mg/L, phosphate (PO4

3-) 31.6 mg/L and sul-

phate (SO42-) 109.3 mg/L.

As described in the experimental section, the landfill

leachate sample was directly dried on the support for the

TXRF analysis and spiked with the internal standard (a Ga

solution) without any further treatment and without any

filtration and mineralization. This aspect is a really great

advantage of TXRF over the necessity to filtrate or, better

to mineralize the sample needed to be submitted for

analysis in the ICP-OES which does not accept the injec-

tion of the raw sample. Indeed, the typical procedure for

the ICP-OES sample preparation before injection into the

plasma torch, requires the mineralization. The leachate

sample is heated in a microwave oven in an autoclave in

presence of nitric and hydrochloric acid for 15 min. The

resulting mineralized leachate is then injected in the ICP-

OES torch. Our feeling is that the TXRF offers much less

alteration of the sample, which can be analyzed simply

after drying without the aggressive degradation led by

nitric and hydrochloric acid which in their turn may add

some undesired transition metal ion contamination. The

analytical results of the ICP-OES in comparison with the

TXRF results are shown in Table 1. For the TXRF results

Table 1 Landfill leachate elemental composition ICP-OES versus

TXRF

ICP-OES (mg/L) TXRF (mg/L) TXRF LLD (mg/L)

B 4.94

F 2.9

Na 300 1104 32.8

Mg 45 27.5 7.4

Al 0.348

Si 35

P 21 7.5 0.587

S 70 49.3 0.379

Cl 2519 1862 0.223

K 450 762 0.066

Ca 154 79.9 0.038

Ti 0.861 0.715 0.018

V 0.069 0.049 0.014

Cr 0.351 0.426 0.011

Mn 0.75 0.944 0.0089

Fe 5.9 7.1 0.0073

Co 0.074

Ni 0.179 0.21 0.0038

Cu 0.03 0.028 0.0033

Zn 0.306 0.538 0.0029

As 0.223 0.232 0.0023

Se 0.0009

Br 8.4 10.1 0.0021

Rb 8.6 7.1 0.0026

Sr 4.5 5.7 0.0019

Cd 0.0008

Mo 0.012

Sn 0.271

Sb 0.258

Ba 3.85 2.7 0.029

Hg 0.001 0.0026 \0.003

Pb 0.045 0.008 \0.003

LLD lowest detectable limit by TXRF

122 F. Cataldo

123

in the last column in the right are reported also the LLD

values in mg/L. The data reported on Table 1 were

obtained from the fluorescence spectra shown in Figs. 3, 4.

Figure 3 displays the detail of the TXRF spectrum taken in

the lower energy range while Fig. 4 displays the spectrum

taken in the higher energy range.

Table 1 shows that the elemental concentration in the

landfill leachate measured with the TXRF are in reasonable

agreement with the ICP-OES results. Such agreement can

be better appreciated at first glance in the log/log graph

shown in Fig. 5 where a straight line can be obtained by

putting in ordinate the analytical results of the ICP-OES

and in abscissa the analytical results of the TXRF. It is

remarkable that also sodium and magnesium were detected

by the TXRF in reasonable agreement with the ICP-OES

results although, as shown in Fig. 2, these two elements are

rather difficult to detect with TXRF. The agreement

between the ICP-OES results and the TXRF results is

simply impressive for the transition metals like for instance

Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and As but also for Br, Rb,

Sr, Ba. Instead the TXRF seem to give some underesti-

mation of the following light elements P, S, Cl and Ca in

the landfill leachate matrix if we take as reference the

values measured with the ICP-OES.

Analysis of three groundwater samples

Three groundwater samples were taken in three different

weeks in September 2011 and tested also with TXRF

against the ICP-OES. The results are reported in Table 2

and the spectra of these samples are again reported in

Figs. 3, 4. Of course, in the case of groundwater samples

the concentrations of the transition metals are considerably

lower than those found in the leachate. At these concen-

trations the agreement between the TXRF and the ICP-

OES is really impressive for all elements (see Table 2).

Fig. 3 TXRF (low energy range from 0.8 to 4.5 keV). The orange intense

curve is due to the landfill leachate sample while the three curves at the

bottom of the figure with lower intensity are due from three samples

(respectively blue green and red) of groundwater used as reference. Note

the high content of chlorine, potassium and calcium in the leachate sample.

(Abscissa in keV and ordinate in 91000 Counts). (Color figure online)

Multielement analysis 123

123

Fig. 4 TXRF (high energy range from about 5 to 15 keV). The

orange intense curve is due to the landfill leachate sample while the

three curves at the bottom of the figure with lower intensity are due

from three samples (respectively blue green and red) of groundwater

used as reference. (Abscissa in keV and ordinate in 91000 Counts).

(Color figure online)

Fig. 5 Log/log plot of the

elemental concentration

measured in a landfill leachate

sample with ICP-OES and with

TXRF

124 F. Cataldo

123

First of all it must be underlined that even the light ele-

ments show a good agreement between the two methods

while for the heavier elements the TXRF is giving a con-

centration which instead in most cases is not quantified by

the ICP-OES method being beyond the LLD of the latter

analytical methodology. It must be emphasized that in the

analysis of not polluted groundwater also the sample to be

used in the ICP-OES should not be mineralized and

probably it is this similar treatment of the samples for the

two analytical techniques that permit to avoid any alter-

ation of the samples and a better analytical agreement as

shown in Table 2.

Conclusions

A landfill leachate coming from a landfill site of several

years old was fully analyzed for all elements with two

Table 2 Groundwater elemental composition ICP-OES versus TXRF

Sample #1 Sample #1 Sample #1 Sample #2 Sample #2 Sample #2 Sample #3 Sample #3 Sample #3

ICP-OES

(mg/L)

TXRF

(mg/L)

TXRF LLD

(mg/L)

ICP-OES

(mg/L)

TXRF

(mg/L)

TXRF LLD

(mg/L)

ICP-OES

(mg/L)

TXRF

(mg/L)

TXRF LLD

(mg/L)

B 0.01 0.01 \0.01

F 0.36 0.36 0.19

Na 11.3 18.4 8.6 11.3 25.5 9.36 12.5 22.1 13.7

Mg 13.6 10.9 1.8 13.5 10.7 2.01 24.8 8.67 3.05

Al \0.001 \0.001 \0.001

P 0.166 0.152 0.125 0.183 0.319 0.144 0.036 1.00 0.22

S 1.85 1.67 0.074 2.60 1.503 0.082 1.35 2.88 0.133

Cl 8.69 13.4 0.043 9.9 10.7 0.05 8.04 12.36 0.0790

K 7.65 12.1 0.0016 7.95 9.41 0.025 10.0 10.45 0.0040

Ca 27.2 29.4 0.0092 50.9 62.14 0.01 187 168.56 0.0140

Ti 0.01 0.0044 \LLD 0.0046 \LLD 0.0062

V 0.003 \LLD 0.0037 0.005 0.0063 0.0038 \0.001 0.0086 0.0051

Cr \0.001 \LLD 0.0029 \0.001 \LLD 0.003 \0.001 \LLD 0.0039

Mn 0.003 0.0081 0.0022 0.045 0.059 0.0023 0.077 0.015 0.0030

Fe 0.01 0.024 0.0017 0.014 0.0044 0.0018 0.015 0.016 0.0024

Co \0.001 \0.001 \0.001

Ni \0.001 0.0023 0.0012 \0.001 0.0017 0.0013 \0.001 0.0069 0.0016

Cu \0.001 0.04 0.0011 \0.001 0.0033 0.0011 \0.001 0.0058 0.0014

Zn \0.001 0.209 0.0009 \0.011 0.534 0.00098 0.019 0.346 0.0012

As \0.001 0.83 0.0006 \0.001 0.0012 0.00065 \0.001 0.0013 0.0009

Se \0.001 \0.001 \0.001

Br 0.04 0.04 0.0006 0.035 0.00058 0.112 0.0008

Rb 0.112 0.0007 0.102 0.00071 0.112 0.0009

Sr 0.44 0.677 0.0005 0.48 0.684 0.00053 0.69 1.013 0.0007

Mo \0.001 \0.001 \0.001

Cd \0.001 \0.001 \0.001

Sn \0.001 \0.001 \0.001

Sb \0.001 \0.001 \0.001

Ba 0.12 0.129 0.00066 0.12 0.133 0.0007 0.12 0.14 0.0094

Hg \0.001 \LLD 0.00073 \0.001 \LLD 0.00076 \0.001 \LLD 0.0010

Pb \0.001 0.003 0.00076 \0.001 0.0026 0.00079 \0.001 \LLD 0.0010

NO2 0.37a 0.19a 0.14a

NO3 15.2a 14.8a 12.7a

PO4 0.51a 0.47b 0.56a 0.94b 0.11a 3.06b

SO4 5.55a 4.98b 7.8a 4.5b 4.06a 8.64b

a Measured with ionic chromatographyb Calculated from the concentration of P or S

Multielement analysis 125

123

analytical techniques based respectively in TXRF and on

ICP-OES. A reasonable agreement between the analytical

results obtained with the two techniques was found for

light elements and a good agreement for the higher atomic

weight elements. The great advantage of TXRF is in the

sample preparation. Practically there is no sample prepa-

ration, only drying on a support the raw landfill leachate

after the addition of an internal standard. On the other hand

the ICP-OES techniques requires the acid digestion and

thermal mineralization of the landfill leachate before the

injection in the plasma torch. This operation is certainly

time consuming and if not properly conducted may lead to

alterations and contaminations of the original sample. Such

an event is rather improbable with the TXRF technique

where the sample is used raw. Additional advantages of the

TXRF technique is the compactness of the bechtop spec-

trometer which in principle is even portable and the very

low energy consumption. Instead, the ICP-OES analytical

technique requires a rather large equipment with large

consumption of energy and also an important consumption

of Ar gas which instead is not required at all for the TXRF

spectrometer.

The goal of this work was to show that the quick and

everyday monitoring of a landfill leachate can be achieved

simply, economically and with reliability in the analytical

data with a TXRF spectrometer. Such a monitoring is

needed either to check the analytes in the leachate which

are changing continuously due to the type of wastes put in

the landfill and mainly due to the changes in the atmo-

spheric conditions from rainy seasons to dry seasons.

Furthermore, after the leachate treatment [39], it is needed

to check again the analytical composition of the purified

water and again the TXRF provides a very quick and

reliable response to this requirement.

Acknowledgments The author is indebted with Dr. Hagen Stosnach

from Bruker for the chemical analysis made at the S2 Picofox TXRF

spectrometer and also with Mr. Cristian Vailati also from Bruker for

the helpful discussion of the results.

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