The Science of the Total Environment 217 Ž1998. 251]256
Speciation of trace elements in discharges from
the pulp industry
L. Skipperuda,U , B. Salbua , E. Hagebø b
a
˚ Norway
Laboratory of Analytical Chemistry, The Agricultural Uni¨ ersity of Norway, N-1432 As,
b
Department of Chemistry, Uni¨ ersity of Oslo, N-0315 Oslo, Norway
Received 2 March 1998; accepted 20 April 1998
Abstract
The concentrations and size distribution pattern of trace elements in wastewater discharged from a pulp industry
located at Oslo Fjord, Norway, have been studied. The annual discharge to the fjord amounts to approx. 34 kg Cd, 18
kg Ce, 15 kg Co, 10 kg Cs, 1500 kg Cu, 8200 kg Fe, 150 kg Ni, 420 kg Pb, 1100 kg Rb, 1.2 kg Sc, 3 kg Sm, 5100 kg Sr
and 3500 kg Zn. Information on the size-distribution pattern of the trace elements in discharged waste water was
obtained using the tangential cross-flow ultrafiltration technique. Instrumental neutron activation analysis, INAA,
was employed to determine the concentration levels of Cd, Ce, Co, Cs, Eu, Fe, La, Rb, Sc, Sm, Sr and Zn. Lead, Cu
and Ni were measured by atomic absorption spectroscopy with graphite furnace, GFAAS, and inductively coupled
plasma atomic emission spectroscopy, ICP-AES. Almost all of the alkali metals Cs and Rb, the alkaline earth metal
Sr and also Ni in discharged waste water were found to be present in the low molecular weight fraction. A major
fraction of Co, Cu and Pb was present in the low molecular weight fraction, while a significant fraction was found as
colloids, particles or both. Cadmium, Fe and Zn in discharge waste water were predominantly present as colloids.
Approx. 50% of Sc was present as particles, 100% of Ce was present as particles, and most of the Sm was found as
colloids. Due to coastal currents and trace element background levels in coastal water, the contribution of mobile
trace elements to Norwegian coastal sea water is probably of minor importance provided that wood from highly
contaminated areas is not utilised in the pulp industry. If the particle fraction accumulates outside the outlet,
however, a local environmental impact over the years should be expected. Q 1998 Elsevier Science B.V. All rights
reserved.
Keywords: Trace elements; Pulp industry; Waste water; Speciation; Particle impact
U
Corresponding author.
0048-9697r98r$19.00 Q 1998 Elsevier Science B.V. All rights reserved.
PII S0048-9697Ž98.00200-9
252
L. Skipperud et al. r The Science of the Total En¨ ironment 217 (1998) 251]256
1. Introduction
Many industries process raw materials which
contain natural and artificially introduced trace
elements. The elements become redistributed via
industrial processes and are released into the
environment. Mobility and bioavailability of the
trace elements found in raw material may increase during industrial processing. Information
on discharges of trace elements from industrial
processes is, however, relatively scarce.
The forest industry is an important raw material processing industry in Norway and the discharge of different elements from a pulp production plant to coastal water was studied. The pulp
industry in Norway processes alone, approx. 6
million m3 annually. The Norske Skog, Tofte Industries is centrally located at the Oslo Fjord and
processes 1.1 million m3 spruce and pine wood
annually, produced in the southern part of Norway, and 0.3 million m3 of eucalyptus imported
from Argentina and Uruguay. Pulp production at
this plant is based on the sulphate process, with
combustion of bark as the main energy source.
Wood, bark and water used in processing have
low concentrations of trace elements. Due to the
volume processed within the pulp industry, however, a considerable amount of elements are
transferred from terrestrial to aquatic ecosystems
on an annual basis. Fig. 1 illustrates the sulphate
process, including the recovery cycles of NaOH,
Na 2 S and CaO ŽKrosshavn et al., 1996a..
The concentration levels, fluxes and annual
budgets of the different elements in raw materials, process materials, products and wastes have
been presented previously ŽSkipperud et al., 1998..
The purpose of this investigation was to study the
speciation of trace elements in discharge waste
water from the pulp plant.
2. Experimental
Multi-element determination was carried out
by instrumental neutron activation analysis, INAA
ŽSalbu and Steinnes, 1992., while lead, copper
and nickel were analysed by atomic absorption
spectroscopy with graphite furnace, GFAAS, and
inductively coupled plasma atomic emission spectroscopy, ICP-AES.
2.1. Sampling and sample treatment
Samples of wood and fresh water were collected during May and October 1993 while waste
water was collected during May, October and
December 1993. Sampling of discharge waste water was also carried out in February 1994 when
the samples were subjected to an ‘in situ’ tangen-
Fig. 1. The sulphate process.
L. Skipperud et al. r The Science of the Total En¨ ironment 217 (1998) 251]256
tial cross-flow ultrafiltration technique ŽSalbu,
1991.. Pore sizes of the membranes were 0.45 m m
and 10 kDa, respectively. In order to reduce sorption, the system was conditioned with a sample
aliquot Ž- 250 ml. prior to sampling the fraction.
In order to pre-concentrate, 20]250 ml freshwater and waste water sample were freeze-dried,
and the residues dissolved in 5 ml 0.1 M ultrapure
HNO3 . This solution was then pipetted into acid
washed ampoules for instrumental activation
analysis, INAA ŽOughton and Day, 1993; Skipperud et al., 1998..
Wood was dried at 1058C for 24 h. In order to
pre-concentrate, the wood was then carefully
ashed at 4008C for 5 h. Unbleached and bleached
pulp samples were also carefully ashed at 4008C
for 5 h. At this temperature, loss of the elements
studied due to volatilisation is avoided. The ash
was then weighed into acid washed ampoules for
INAA.
Blank samples were prepared from empty vials,
or vials into which 0.1 M ultrapure HNO3 Žthe
same number of aliquots. had been evaporated.
Analytical calibration was based on gravimetrically prepared solutions of the elements dissolved
in 0.1 M nitric acid prepared with doubly distilled,
deionized water. Calibration materials for INAA
were prepared from bulked homogenised sample
materials Žsoil, sediment or grass., spiked with
aliquots of calibration materials, and thoroughly
mixed. Calibration materials and solutions were
weighed into ampoules and irradiated alongside
the sample ampoules. Thus a number of multielement calibration standards were produced,
having a wide range of concentrations. Their uniformity were established by replicate NAA. Analytical accuracy was tested by analysis of three
standard reference materials: Ža. GBW 07405
ŽGSS-5., Chinese soil, Chemical Research Centre
for China, China; Žb. SL-1, Lake sediment, International Atomic Energy Agency, Austria; and Žc.
BCR No 186, Lyophilised pig kidney, Community
Bureau of Reference, Belgium.
2.2. Methods of analyses
2.2.1. INAA
All ampoules were heat sealed, placed in stan-
253
dard aluminium cans Ž13 cm = 6 cm diameter.
and then irradiated with thermal neutrons in the
Jeep II reactor at Kjeller. Ampoules with sample
and standard reference materials were packed
into layers within the can. Irradiation time was
approx. 15 h and the thermal neutron flux 5 = 10 12
neutronsrcm 2 s. The activated products were then
measured using gamma spectrometry with Ge-detectors ŽCanberra, 20% efficiency and approx. 2
keV resolution at 1.332 keV. interfaced to a PC
equipped with Spectran AT software ŽCanberra,
CT..
2.2.2. GFAAS and ICP-AES
Water samples were acidified prior to GFAAS
ŽAAS: Perkin Elmer 3030, GF: Perkin Elmer
HGA 400. and ICP-AES ŽPolyscan 61E, model
1268900, Thermo Jørrel ASH., using standard
techniques. Wood samples were ashed and digested in aqua regia ŽHNO3rHCl 2:1. prior to
GFAAS and ICP-AES using standard techniques.
3. Results and discussion
3.1. Annual production
Spruce and pine Ž1.1 million m3 . produced in
the southern part of Norway are processed annually along with 0.3 million m3 eucalyptus from
Argentina and Uruguay by the pulp industry.
Approx. 22 million m3 of fresh water from two
local lakes are utilised per annum. Approx. 0.23
million m3 bark is combusted yearly in order to
generate energy. The production in 1993 was
325 000 tons of bleached pulp.
Solid waste, mostly bark and green liquor
sludge, are deposited at the industrial site. The
bark ash volume is approx. 2600 m3 and the green
liquor sludge volume is nearly 8000 m3. The annual waste water volume is approx. 17 million m3.
The average concentrations of trace elements
in wood, fresh water and discharge waste water
are given in Table 1. The annual fluxes of trace
elements in wood, freshwater and discharge waste
water are given in Table 2. Due to the high
volume processed, the major contributors of trace
elements are the Norwegian spruce and pine. The
concentration levels of the trace elements were
approx. 2]300 times higher in waste water than in
L. Skipperud et al. r The Science of the Total En¨ ironment 217 (1998) 251]256
254
Table 1
Concentrations of Cd, Ce, Co, Cs, Cu, Eu, Fe, La, Ni, Pb, Rb Sc, Sm, Sr and Zn in the chips and fresh water processed and the
discharged waste water from an industrial pulp process in 1993
Sample
Wood
Sprucerpine
Ždry wt..
Eucalyptus
Ždry wt..
Water
Fresh water
Waste water U
Wood
Sprucerpine
Ždry wt..
Eucalyptus
Ždry wt..
Water
Fresh water
Waste water U
Cd
Ž m grl.
Ce
Ž m grl.
130 " 3
Co
Ž mrl.
Cs
Ž m grl.
Cu
Ž m grl.
Eu
Ž m grl.
21 " 1.3
750 " 160
- 0.25
6.9" 0.6
31 " 2
453 Ž n s 1.
0.52" 0.05
12 " 2
- 0.4
0.61" 0.07
0.2" 0.01
67 " 20
- 0.05
- 0.05
Sc
Ž m grl.
Sm
Ž m grl.
Sr
Žmgrl.
0.83" 0.09
0.35" 0.04
9.8" 0.6
0.5" 0.1
1.8" 0.2
2.6" 0.3
12 " 1
0.39" 0.03
- 0.003
0.067" 0.007
0.01" 0.005
0.07" 0.01
0.11" 0.001
0.2" 0.02
- 0.018
0.3" 0.04
0.014" 0.005
0.21" 0.02
7"1
50 " 3
19 " 4
13.9" 0.8
0.2 Ž n s 1.
1.88" 0.06
0.54" 0.03
10.6" 0.06
0.11" 0.05
0.9" 0.1
Ni
Ž m grl.
Pb
Ž m grl.
24.5" 4.5
58 " 34
Rb
Žmgrl.
84 " 3
288 Ž n s 1.
124 Ž n s 1.
- 0.02
9"1
- 0.05
1.7" 0.1
2.4" 2
Fe
Žmgrl.
0.21" 0.09
0.5" 0.1
La
Ž m grl.
300 " 0.4
23 " 2
0.84" 0.04
- 0.9
Zn
Žmgrl.
17 " 1
Average of samples taken in May and October ŽU and December..
the processed fresh water except for La, being
depleted in the waste water. Detailed information
on the concentrations of the trace elements in
raw materials, process materials, products and
waste products as well as annual fluxes are presented elsewhere ŽSkipperud et al., 1998..
Table 2
Annual transfer of Cd, Ce, Co, Cs, Cu, Eu, Fe, La, Ni, Pb, Rb, Sc, Sm, Sr and Zn in chips, fresh and waste water from the industrial
pulp process in 1993
Sample
Wood
Sprucerpine
Eucalyptus
Water
Fresh water
Waste water
Tons p.a.
Cd
Žkgryear.
579 700
134 400
75
3.3
22 100 000
16 900 000
4.4
34
Ni
Žkgryear.
Wood
Sprucerpine
Eucalyptus
Water
Fresh water
Waste water
579 700
134 400
22 100 000
16 900 000
Ce
Žkgryear.
3.7
2.6
12
18
Pb
Žkgryear.
Co
Žkgryear.
29
1.9
2
15
Rb
Žkgryear.
Cs
Žkgryear.
12
4.1
Cu
Žkgryear.
Eu
Žkgryear.
Fe
Žkgryear.
La
Žkgryear.
430
60
- 0.1
0.07
4000
1700
1.7
3.1
-8
10
4.4
1500
- 1.0
- 0.8
5000
8200
18.5
- 15
Sc
Žkgryear.
Sm
Žkgryear.
30
31
48
16
1400
60
0.5
0.3
0.3
0.4
- 0.4
150
- 1.1
420
- 70
1100
0.2
1.2
2
3
Sr
Žkgryear.
Zn
Žkgryear.
6000
1600
10 100
52
- 400
5100
300
3500
L. Skipperud et al. r The Science of the Total En¨ ironment 217 (1998) 251]256
3.2. Speciation of trace elements
The physico-chemical forms of trace elements
in discharge waste water were investigated using a
tangential cross-flow ultrafiltration technique with
filter pore size of 0.45 m m and 10 kDa yielding
the following fractions:
Particle fraction ) 0.45 m m;
Colloidal fraction 10 kDa } 0.45 m m; and
Low molecular weight fraction - 10 kDa.
The size distribution of trace element species
in discharge waste water is presented in Fig. 2. As
expected for the alkali metals, Cs and Rb, and the
alkaline earth metal, Sr, a major fraction, 84%,
92% and 61%, respectively, was found to be in
the low molecular weight fraction. Approx. 10%
of the remaining Cs is present as colloids while
only 5% is present as particles; 4% Rb is found
both as colloids and as particles. The rest of the
Sr in the waste water is present in the colloidal
and particle fractions as 18% and 21%, respectively. Stable Cs and Sr show similar patterns in
the waste water as 137 Cs and 90 Sr studied earlier
by Krosshavn et al. Ž1996b..
The transition elements, Fe, Co and Ni, are
present in all three fractions. For Fe and Co the
major fraction is colloids, 59% and 55%, respec-
255
tively, while for Ni the major fraction, 82%, is low
molecular weight forms. This indicates that Ni is
more mobile than the other two iron metals. All
the remaining Co is present as low molecular
weight fraction while the remaining fraction of Fe
was equally distributed between the colloidal
fraction, 20%, and particle fraction, 21%.
The lanthanides, Ce and Sm, are present only
in the particulate and colloidal fractions. One
hundred percent of the Ce is present as particles
while 86% of Sm is present in the colloidal fraction and the remainder is present as particles.
Cd and Zn are present mostly in the colloidal
fraction, 83% and 62%, respectively. Six percent
Cd and 12% Zn are present as particles while 4%
Cd and 26% Zn is present as low molecular
weight forms. Pb and Cu are present as 45% and
26% as colloids, 38% and 41% in the low molecular weight fraction while the remaining, 17% and
33%, is present as particles, respectively.
The low molecular weight fraction is more
mobile and bioavailable than colloids and particles. Thus the major fraction of the alkali metals,
Cs and Rb, the alkaline earth metal, Sr, and also
some of the transition elements, especially Ni,
should be considered mobile and potentially
bioavailable when it is released into the fjord.
The colloidal fractions will be transported in the
coastal water downstream from the outlet, while
Fig. 2. Speciation of some trace elements in the discharge waste water from the pulp plant.
256
L. Skipperud et al. r The Science of the Total En¨ ironment 217 (1998) 251]256
the particle fraction might be deposited outside
the waste outlet of the industry. Based on the
present particle fraction, the annual amount that
might be deposited in the fjord right outside the
release point is almost 1700 kgryear Fe, 1100
kgryear Sr, 500 kgryear Cu, 400 kgryear Zn and
100 kgryear Pb. In this case, an environmental
impact assessment close to the site should be
expected.
4. Conclusions
The concentration levels of the elements were
considerably higher in discharge waste water than
in the fresh water processed in the pulp plant.
Most of Cs, Cu, Ni, Rb and Sr in discharge waste
water were present as the low molecular weight
species with just a minor fraction as colloids and
particles. For Cd, Ce, Co, Fe, Pb, Sc, Sm and Zn
in waste water a significant fraction was associated with particles andror colloids with a minor
fraction in the low molecular weight fraction. If
the particle fraction is deposited outside the pulp
plant, sedimentation of approx. 1700 kgryear Fe,
1100 kgryear Sr, 500 kgryear Cu, 400 kgryear
Zn and 100 kgryear Pb could be expected.
Due to transporting currents and dilution, the
contributions of mobile trace elements Že.g. low
molecular weight forms or colloids. from this pulp
plant to the trace element levels in Norwegian
coastal sea water is low, providing that wood from
highly contaminated areas is not utilised. Thus a
local environmental impact over the year should
be expected.
Acknowledgements
Norske Skog, Tofte Industries are acknowledged for their co-operation. We appreciate
particularly the valuable assistance of B. Pettersen and technical assistance from M. BorgeSkaar and G. Brekka. Technical assistance from
G. Østby is gratefully acknowledged.
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