2008:081
M A S T E R ' S T H E S I S
Pulping Wastes and Abandoned Mine Remediation
Application of green liquor dregs and other pulping by-products to the solidification/stabilisation of copper mine tailings
Lucile Villain
Luleå University of Technology D Master thesis
Chemistry
Department of Civil and Environmental Engineering Division of Architecture and Infrastructure
2008:081 - ISSN: 1402-1552 - ISRN: LTU-DUPP--08/081--SE
Luleå University of Technology
MASTER THESIS
Pulping Wastes and Abandoned Mine Remediation
Application of green liquor dregs and other pulping by-products to the solidification/stabilisation of copper mine tailings
Lucile Villain
June 2008
Department of Civil, Mining and Environmental Engineering Division of Architecture and Infrastructure
ACKNOWLEDGEMENTS
This master thesis was realised in Luleå University of Technology and in Ramböll Sverige AB consultancy in Luleå (Northern Sweden).
I would like to express my gratitude to my supervisor Christian Maurice who made the project possible and who guided me throughout this work while granting me autonomy as well.
I am also grateful to Ramböll team who nicely welcomed me in spite of my poor Swedish, and helped in practical issues.
I would like to thank Nils Hoffner for his useful information, Tomas Forsberg for his valuable help in the laboratory, Ulla-Britt Uvemo for her kind and constant assistance, and Lea Rastas Amofah for her friendly company and wise advice.
I am also thankful towards my family who encouraged me and sent me motivation from France; many thanks to my friends in Luleå who gave me support and joy during these days.
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ABSTRACT
Green liquor dregs are one type of chemical by-products produced by the pulp and paper industry which are usually landfilled, and cause concern to the pulp mills due to the cost of landfilling. Their alkaline and impermeable properties render however their re-utilisation possible in several domains. Solidification/stabilisation of sulphide ore mine tailings is one type of potential application of green liquor dregs which is considered in this work.
The project aimed at assessing the efficiency of green liquor dregs associated with other pulping wastes (fly ash, bark sludge) in decreasing the permeability and release of metal contaminants in copper mine tailings from an abandoned mine site. The possibility to use these pulping wastes as a hydraulic barrier to cover tailings or traditional landfills was also considered. To achieve this objective, 2 types of permeability tests were performed, as well as an adapted Column Leaching test and a modified Batch Leaching in oxidising conditions.
Tailings alone, different combinations of pulping wastes, and tailings treated with these combinations of pulping wastes were tested.
Addition of pulping wastes to tailings proved efficient in immobilising copper, in particular when one type of green liquor dregs was added to tailings in the proportion of 10%. Copper release was reduced at least 4 times by all the admixtures. Permeability of tailings was decreased to various extents with the addition of different proportions of pulping wastes. The best result was obtained with a combination of green liquor dregs, fly ash and bark sludge mixed with tailings. Hydraulic conductivities of pulping wastes were not as low as to guarantee their efficiency as a hydraulic barrier. It was suggested that moistening the materials may improve their impermeability.
Variability of the wastes produced by the mill was judged as the major problem if their re- utilisation became effective, and increased green liquor dregs quality control was suggested.
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TABLE OF CONTENTS
1 INTRODUCTION... 4
1.1 Research questions – Aim of the project ... 4
1.1.1 Background... 4
1.1.2 Objectives of the project... 5
1.2 Scope of the study... 6
2 MATERIALS AND METHODS ... 8
2.1 Materials ... 8
2.2 Methods ... 9
2.2.1 Permeability tests... 10
2.2.2 Leaching tests... 12
2.3 Samples characterisation ... 15
2.3.1 Mine tailings from Nautanen abandoned copper mine... 15
2.3.2 Green liquor dregs from Billerud Karlsborg pulp and paper mill... 16
3 RESULTS... 17
3.1 Permeability tests... 17
3.1.1 Constant Head Permeability Test... 17
3.1.2 Constant Rate of Strain test... 18
3.1.3 Results of hydraulic conductivities... 19
3.1.4 Evolution of HC in CRS test after saturation of samples in CHP test... 21
3.2 Leaching tests ... 22
3.2.1 Adapted Column Leaching test... 22
3.2.2 Batch Leaching test in oxidising conditions... 25
4 DISCUSSION ... 33
4.1 Permeability tests... 33
4.2 Leaching tests ... 34
4.3 Discussion on tailings treatment with pulping wastes... 36
4.3.1 Green liquor dregs and pulping wastes as tailings/landfill hydraulic cover... 36
4.3.2 Green liquor dregs and pulping wastes as tailings chemical stabilising agent... 38
4.3.3 Green liquor dregs and pulping wastes in solidification/stabilisation of tailings... 38
5 Conclusions ... 40
5.1 Future works ... 40
6 REFERENCES... 42
I: Detailed Methodology ... 45
II: Green Liquor Dregs... 50
III: Nautanen Abandoned Copper Mine... 60
IV: Solidification/Stabilisation Method ... 63
V: Results of Metal Analysis ... 73
VI: Results of CRS Test ... 89
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1 INTRODUCTION
The pulp and paper industry in Sweden generates large quantities of waste, around 6.4 million tonnes in 2004 (Swedish Environmental Protection Agency). It consists mostly of wood waste and slurries generated by manufacturing processes. Most of this waste can be recycled or used for energy production by the industry. But some fractions are simply landfilled at the industries own facilities. An important part of the landfilled pulping waste is constituted by chemical residues that mainly comprise green liquor dregs (=grönlutsslam in Swedish) from sulphate pulping process mills. Currently, the European policy encourages the recovery of waste by means of recycling, re-use or reclamation or any other process with a view to extracting secondary raw materials (European Council directive 91/156/EEC on waste). Within this framework and considering the costs of landfilling, there is a growing interest in re-utilising the green liquor dregs. Due to their alkaline and impermeable properties, several applications (acidic wastewater treatment, landfill cover, agricultural and forest land applications…) have been considered.
Mining is the industry that generates the greatest volume of waste in Sweden, which mainly consists of waste rocks (rocks to remove to reach the ore) and mine tailings (waste left after the ore has been extracted). The volume of waste rocks generated in Sweden in 2004 was over 32 million tonnes and the volume of tailings over 25 million tonnes (Swedish Environmental Protection Agency). The main environmental problem associated with sulphidic mine waste is known as acid mine drainage (AMD), a metal-rich acidic solution produced when sulphides are in contact with water and oxygen, and spread into the environment.
Remediation of sulphidic mine waste is a potential application for green liquor dregs used as a cover preventing intrusion of water and oxygen in the waste, or as a mixture with mine residues aiming at immobilising the metals. This possibility has received little attention so far and is examined in this work. With green liquor dregs samples provided by Billerud Karlsborg pulp and paper mill (Kalix, Northern Sweden) as well as other pulping wastes on the one hand, and mine tailings sampled in the abandoned copper mining area of Nautanen (region of Gällivare, Northern Sweden) on the other, experiments were carried out to assess the beneficial effects of green liquor dregs (combined with other pulping by-products) on mine waste. Two fields were investigated: the hydraulic properties and the chemical effects.
1.1 Research questions – Aim of the project
1.1.1 Background
Solidification/stabilisation technique is a method used to chemically and/or physically bind the contaminants in a waste to prevent their leaching into the environment. A common stabilising agent is Portland cement which helps to lower the permeability of waste and the mobility of inorganic contaminants. As a consequence, the transport of water through the waste is reduced as well as the release of contaminants.
In the natural environment, the most important factor controlling the distribution of inorganic compounds between stable and mobile phases is pH. This is also true in wastes treated by solidification/stabilisation, because precipitation, adsorption and redox reactions immobilising the metals are strongly influenced by pH. Therefore, the success of solidification/stabilisation
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is really dependent on binder reactions which will impact the pH of the treated waste (Batchelor, 2006). Most of the metals are immobilised in neutral to alkaline conditions.
Green liquor dregs consist in a sludge exhibiting in general low permeability and high alkalinity, which could make them an interesting binding agent in solidification/stabilisation of metal-bearing wastes. They contain sodium carbonate, sodium hydroxide at the origin of high pH value, calcium carbonate, unburned carbon and traces of other elements.
Wastes from metal mines consist mainly of waste rocks, ore rests, slags and tailings (processing wastes from a mill, washery or concentrator). These by-products are usually rich in sulphide minerals containing heavy metals. The main environmental problem associated with these sulphide minerals is the exposition to air and water which leads to oxidation of the sulphides into sulphates and generation of hydrogen ions. The production of hydrogen ions with sulphate anions results in an acidic solution, which is known as Acid Mine Drainage (AMD). The oxidation of sulphide minerals does not only create acid, but it also liberates metals and sulphate into waters and accelerates the leaching of other elements from gangue minerals. As a consequence, AMD is associated with the release of sulphate, heavy metals (Fe, Cu, Pb, Zn, Cd, Co, Cr, Ni, Hg), metalloids (As, Sb), and other elements (Al, Mn, Si, Ca, Na, K, Mg, Ba) (Lottermoser, 2003). The whole ecosystem is at risk in such a situation. To meet environmental quality requirements, mining companies must make sure that the prevention or treatment of AMD will be done.
In mine sites in current exploitation, one way used to avoid this AMD generation is to control the sulphide oxidation with one or more of the following strategies: exclusion of water, exclusion of oxygen, pH control, control of Fe3+ generation, control of bacterial action, removal and/or isolation of sulphides. This can be achieved through covering of wate rocks and tailings with wet/dry covers, encapsulation, in-pit disposal and mixing, co-disposal and blending with benign or alkaline material, addition of organic wastes or bactericides (Lottermoser, 2003). Treatment of AMD may also be required (neutralisation of the acidic water with an alkaline agent or other chemical treatments, anoxic limestone drains, wetlands...).
Generally speaking, in abandoned mines, the outcome of a sulphidic mine waste which is considered as dangerous for the environment is excavation followed by landfilling. This drastic method is becoming more and more costly, and solidification/stabilisation of the mining wastes could be used as a milder alternative. Several studies have already been carried out with cementitious materials and/or recycled alkaline by-products, in order to increase cohesiveness, reduce water transport through the mine waste and increase pH.
1.1.2 Objectives of the project
A potential solution to avoid the landfilling of green liquor dregs and treat sulphidic mine waste as well is to apply solidification/stabilisation with green liquor dregs on tailings. Green liquor dregs are expected to decrease the flow of water and act as a good stabilising agent to counter the generation of acidity and release of metals from mine waste.
The objective of the present work is to evaluate the efficiency of green liquor dregs from Billerud Karlsborg mill in solidifying/stabilising copper mine tailings from Nautanen
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abandoned copper mine. To achieve this, hydraulic and chemical properties of the wastes will be evaluated with two types of experiments:
• Permeability tests
• Leaching tests
According to a previous study (Hargelius, Ramböll, 2008) the properties of green liquor dregs as a hydraulic barrier in landfills were enhanced when two other by-products – fly ash and organic sludge – were added. Fly ash has a high content of lime CaO and can exhibit cementitious properties during the reaction of carbonation (cf. equation 1). The addition of fly ash to GLD is expected to lower its permeability.
Equation 1: Carbonation reaction, occuring only in the presence of water (hydrated lime) Ca(OH)2 + CO2 → CaCO3 + H2O
Organic sludge turned out to retard the hardening of the mixture green liquor dregs with fly ash and increase its plasticity during the previous study. That is why fly ash and bark sludge (organic sludge made of bark and wood waste) from Karlsborg mill were used as additives to green liquor dregs in the experiments, and their effect on the properties of green liquor dregs in solidification/stabilisation were assessed.
Thus, permeability tests and leaching tests were conducted on tailings alone, on green liquor dregs alone or combined with fly ash and bark sludge (pulping wastes), and on the mixture of tailings and pulping wastes.
From the results obtained, we tried to answer the following questions:
• How to select a suitable utilisation for green liquor dregs (called GLD in the work) based on the hydraulic and chemical properties of these GLD associated with the other pulping wastes and tailings?
9 If the permeability of the pulping wastes is low enough (~10-9 m/s), they could be used as a hydraulic barrier covering tailings or landfills.
9 If their alkaline properties allow a chemical immobilisation of the metals in the tailings, they would be suitable as tailings stabilising agent.
9 If both permeability and alkalinity give relevant results, they could be used as a binder in solidification/stabilisation of mine tailings. The mixture could be placed back in situ if the whole pile of tailings is treated or used as an impermeable cover on the rest of the tailings if only a part is mixed with pulping wastes.
• Does the addition of fly ash and organic sludge improve the properties of the green liquor dregs in these applications? Which combinations are most efficient in each case?
1.2 Scope of the study
The research work is carried out in the framework of a master thesis consisting in a semester internship in Ramböll Sverige AB consultancy in Luleå and Luleå University of Technology (LTU). The experiments are set in two laboratories of the university: the geotechnical laboratory, and the environmental laboratory. The work may be considered as a preliminary
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study to potential field tests since no such study of application of green liquor dregs to mine tailings was published before as far as we know.
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2 MATERIALS AND METHODS 2.1 Materials
The experiments were carried out using mine tailings from the mining area of Nautanen (province of Lappland, Northern Sweden) on the one hand, and wastes from Billerud Karlsborg pulp and paper mill (Kalix, province of Norrbotten, Northern Sweden) consisting of green liquor dregs, fly ash and bark sludge on the other. Fly ash from Stora Enso Hylte mill (province of Småland, Southern Sweden) and sewage sludge from Uddebo waste water treatment plant (Luleå, province of Norrbotten, Northern Sweden) were also used in some experiments.
Mine tailings from Nautanen abandoned copper mine
The tailings used for the experiments consist in a composite sample formed with 55 subsamples collected at different points of the abandoned copper mine of Nautanen, in the area of Gällivare, in October 2007. The subsamples were dried and 2 mm sieved. They were sorted; those containing more than 2000 mg/kg copper (55 of them) were selected and mixed together. Tailings in the area of Nautanen contain a high amount of copper (table 2), which leaching is currently the main threat for the environment (cf. appendix III).
Figure 1 Copper mine tailings dried and 2 mm sieved. The aspect is sand-like.
Wastes from Billerud Karlsborg pulp and paper mill
The main by-product from the pulp and paper industry used in the experiments consist in green liquor dregs – named GLD in the work–, which are produced in the process of causticization (recovery of pulping chemicals). They form a basic and rather impermeable sludge composed of sodium carbonate, sodium hydroxide, calcium carbonate, unburned carbon, sulfides and traces of heavy metals and other elements. Three samples of GLD (GLS 30, GLS 30 EM, GLS 31) were provided by Billerud Karlsborg mill, collected over 2 days.
They were sampled in the location right before the GLD are spilt in a tank before being landfilled.
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Figure 2 Green liquor dregs GLS 30 (left), GLS 30 EM (middle), GLS 31 (right)
The mill also supplied fly ash (FA and FA1) from the electrostatic filter placed after the fluidized bed boiler, which is formed of residues from the combustion of bark and wood waste. Fly ash is composed of inorganic nutrients, silicon dioxide, calcium oxide and heavy metals. It is used here to cement the material with which it is mixed.
In addition, bark sludge (BS) was provided by the mill, which was sampled from the debarking process and mainly composed of bark compost from pine trees, sand and NaOH added to bark in order to increase pH and avoid corrosion of the machines. It aims at moistening the mixtures and increasing their plasticity.
Figure 3 Fly ash FA which was moistened in the mill (left), dry fly ash FA1 (middle) and bark sludge BS (right) from Billerud Karlsborg pulp and paper mill (Kalix, Norbotten, Sweden)
Fly ash from Hylte mill (FA2a) and sewage sludge from Uddebo waste water treatment plant (SS) were used in some tests to broaden the source of wastes. FA2a was of the same type as FA1, and sewage sludge, though not a pulping waste, was used as an organic sludge with the same role as bark sludge.
The wastes were tested either separately or in combinations which are listed in table 1.
2.2 Methods
The experiments aimed at assessing the properties of GLD and pulping wastes, and their influence on stabilisation of mine tailings in two main domains: the hydraulic aspect and the
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chemical one. To achieve this, two types of experiments were conducted: permeability tests and leaching tests.
Important note: all the proportions given for mixtures were calculated on the basis of the dry matter weight.
2.2.1 Permeability tests
Constant Head Permeability test
The Constant Head Permeability test (CHP test) was carried out in the geotechnical laboratory of LTU, on four series of two to four samples. For each series, the quantity of water discharging from a constant level tank through the sample in a 5 cm diameter cell in a saturated up-flow mode was measured regularly during approximately two weeks, and the hydraulic conductivity was calculated for each interval. The two weeks duration of the test aimed at reaching the saturation of the samples with water. Thus, after stabilisation of the measured values, saturated hydraulic conductivity (HC) was obtained. For more details about the CHP test, see appendix I.
Figure 4 Picture of the Constant Head Permeability apparatus (left) and scheme of the device (right)
First series of tests: hydraulic conductivity of green liquor dregs
The three samples of GLD provided by Billerud Karlsborg mill – GLS 30, GLS 30 EM and GLS 31 – were tested in the first series.
Based on the results of the first series, GLS 30 EM, the most impermeable GLD, was selected for the permeability tests on mixtures with other pulping by-products.
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Second series of tests: hydraulic conductivity of tailings, tailings+GLD, and GLD+fly ash
In the second series, HC of tailings was evaluated as a reference for the mixtures involving tailings. Tailings mixed with GLS 30 in the proportion 90:10 (90 TAIL+10 GLS 30) were also tested, in order to evaluate the evolution of permeability when adding a small proportion of GLD (with the aim of chemical stabilisation only). The most permeable GLD was chosen in this case since the interest is then focused on chemical properties and not on impermeability.
Two other samples were tested: GLS 30 EM + FA and GLS 31 + FA, which are mixtures of the most impermeable GLD with fly ash (in the proportion 70:30). The addition of fly ash, which exhibits cementitious properties through the reaction of carbonation in humid conditions, was expected to decrease the permeability of the GLD.
Yet it was acknowledged during the experiment that FA had been watered in the mill and carbonation had probably already taken place before mixing with GLD. New fly ashes which were not watered (FA1, FA2a) were ordered and used in the next series of test.
Third series of tests : hydraulic conductivity of GLD+fly ash, GLD+fly ash+bark sludge/
sewage sludge, tailings+GLD+fly ash
FA1 from Billerud Karlsborg - 99.5% dry matter content - and FA2a from Hylte mill - 99.8%
dry matter content – were tested, which dryness ensured that the carbonation didn not already take place before mixing with GLD.
The mixture of GLD with fly ash was tested in the proportion 70:30 with FA1. Based on the comments of K. Hargelius (Ramböll Gothenburg) according to which organic matter like sewage sludge or fiber sludge should be added to the mixture to facilitate the blending, bark sludge (BS) and sewage sludge (SS) were added to GLD and fly ash in two other samples.
The following proportions were chosen:
60% GLS 30 EM + 30% FA1 + 10% BS 60% GLS 30 EM + 30% FA2a + 10% SS
A fourth sample was tested in this series: 70% Tailings + 30% (GLS 30 EM + FA1), which aimed at assessing the evolution of the HC of tailings when mixed with this combination of pulping wastes.
Fourth series of tests : hydraulic conductivity of tailings mixed with 30%/60% GLD+fly ash+bark sludge
The fourth series was tested to evaluate the evolution of the HC of tailings with different proportions of one of the most impermeable admixtures according to results of the previous series (GLS 30 EM + FA1 + BS). The proportions 30% and 60% of admixture were chosen:
70 TAIL + 30 (GLS 30 EM + FA1 + BS) 40 TAIL + 60 (GLS 30 EM + FA1 + BS)
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Constant Rate of Strain test
Several samples (cf. table 1) tested with CHP test were duplicated and sent to Ramböll Sverige AB Region Väst laboratory in Gothenburg. There, Constant Rate of Strain (CRS) test using an oedometer was conducted. The samples were compressed during several hours and drainage was allowed from their top surface. Hydraulic conductivity was calculated from the deformation and the pore pressure at the lower undrained surface (cf. appendix I for more details).
3 samples – GLS 30 EM + FA1 + BS bis, GLS 30 EM + FA2a + SS bis and 70 TAIL + 30 (GLS 30 EM + FA1) bis– were sent to Gothenburg for CRS test after being submitted to the CHP test during 18 days, so as to evaluate the evolution of the HC measured by CRS test between the initial sample and the sample saturated with CHP test.
2.2.2 Leaching tests
Adapted Column Leaching test
Constant Head Permeability test apparatus was used to perform an adapted Column Leaching test as well (cf. appendix I). The first leachates obtained from each sample – for a liquid/solid ratio of ~0,2 L/kg dry weight – were analysed for pH and electrical conductivity (EC). pH was measured with a WTW pH 330/ SET-1 pH meter, EC with a WTW inolab EC meter.
The samples tested were those submitted to CHP test, and the role of this leaching test was to characterise the chemical properties of the different combinations of pulping wastes on the one hand, and the evolution of the tailings chemical properties when mixed with pulping wastes on an other.
Batch Leaching test in oxidising conditions
Batch Leaching test in oxidising conditions was adapted from the standard Batch Leaching test at L/S = 10L/kg (ISO/DIS 21268-2). It aimed at allowing leaching of tailings alone or treated with pulping wastes in oxygenated conditions to artificially favour the oxidation of sulphides and assess the release of metals in this situation.
The Batch test consisted in mixing the material and distilled water in a ratio L/S=10 into plastic bottles and let them interact during two weeks. Oxygen was regularly injected (3 days a week) in order to keep oxidising conditions during the whole test period judged as long enough to let the oxidation reaction of sulphides happen. After each injection the bottles were shaken ten times by hand so as to accelerate the intrusion of oxygen into the water and to increase contacts between the material and the water. After 15 days of experiments, about 80 mL of the supernatant liquid was taken out from each bottle and filtered so as to determine pH and electrical conductivity. Metal concentrations in the leachate were determined by a commercial laboratory with the EPA method (modified) 200.8 (ICP-SFMS). A more detailed protocol of the test is proposed in appendix I.
This leaching test aimed at characterising the evolution of tailings chemical properties and release of metals when they were mixed with different combinations of pulping wastes. To achieve this, the following samples were tested:
9 Distilled water ( blank) 9 GLS 30 EM (reference)
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13 9 TAILINGS
9 90 TAIL+ 10 GLS 30 9 90 TAIL + 10 GLS 30 EM
9 90 TAIL + 10 (GLS30 EM + FA1) 9 90 TAIL + 10 (GLS 30 EM + FA1 + BS) 9 70 TAIL + 30 (GLS 30 EM + FA1 + BS)
Figure 5 Samples of TAILINGS and TAILINGS + GLS 30 in Batch Leaching test in oxidising conditions. On the left, bottles after injection of oxygen and shaking; on the right, bottles after decantation.
The characteristics of the different combinations of wastes and the tests they were submitted to are summarised in table 1.
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Table 1 Different combinations of pulping wastes and tailings used in the experiments. Content with proportions in dry matter weight and tests associated to each combination are indicated.
Content
(% in dry matter weight) Permeability tests Leaching tests Sample name
Tailings
Green liquor dregs
Fly ash
Bark/Sewage sludge
Constant Head Permeability
Constant Rate of
Strain
Column Leaching test
Batch Leaching test
in O2
GLS 30 100 X X
GLS 30 EM 100 X X X X
GLS 31 100 X X
GLS 30 EM + FA 70 30 X X
GLS 31 + FA 70 30 X X
GLS 30 EM + FA1 70 30 X X X
GLS 30 EM + FA1 + BS 60 30 10 X X X
GLS 30 EM + FA1 + SS 60 30 10 X
GLS 30 EM + FA2a 70 30 X
GLS 30 EM + FA2a + BS 60 30 10 X
GLS 30 EM + FA2a + SS 60 30 10 X X X
TAILINGS 100 X X X
90 TAIL + 10 GLS 30 90 10 X X X
90 TAIL + 10 GLS 30 EM 90 10 X
90 TAIL + 10 (GLS30 EM + FA1) 90 7 3 X
90 TAIL + 10 (GLS 30 EM + FA1+ BS) 90 6 3 1 X
70 TAIL + 30 (GLS 30 EM + FA1) 70 21 9 X X X
70 TAIL + 30 (GLS 30 EM + FA1 + BS) 70 18 9 3 X X X X
40 TAIL + 60 (GLS 30 EM + FA1 + BS) 40 36 18 6 X X
2.3 Samples characterisation
2.3.1 Mine tailings from Nautanen abandoned copper mine
A part of the tailings selected for the experiments was sieved and separated into 3 fractions according to grain size: 0-0.125 mm; 0.125-0.5 mm and 0.5-2 mm. Figure 6 illustrates the distribution of the particle size. The 3 fractions were analysed for their metal content by a commercial laboratory. The procedure comprised drying of the samples at 50°C and leaching in nitric acid/hydrogen peroxide in closed teflon vessels in a microwave oven (concentrations were corrected to dry weight 105°C). Analysis was realised according to EPA method (modified) 200.7 (ICP-AES). The results are given in table 2.
0.5-2 mm 0.125-0.5 mm 0-0.125 mm
Figure 6 Distribution of particle size in the tailings.
Table 2 Metal content of the tailings according to the particle size intervals.
ELEMENT (mg/kg TS) 0.5-2 mm 0.125-0.5 mm 0-0.125 mm TOTAL
As 8.97 <3 5.5 5.3
Ba 125 206 246 200
Be 0.311 0.287 0.403 0.333
Cd 0.254 0.356 0.741 0.464
Co 18.3 23.5 22.1 21.7
Cr 2.09 0.368 1.31 1.12
Cu 1250 2700 3910 2760
Fe 30400 33300 44500 36451
Hg <1 <1 1.34 1
Li 4.19 7.47 8.63 7.06
Mn 1620 1010 918 1128
Mo 10.2 11.5 22.8 15.1
Ni 3.49 6.3 7.63 6.1
P 728 1150 1780 1263
Pb 21.3 30.5 59 38
Sr 4.52 5.77 8.83 6.52
V 23.2 28.3 40.4 31.2
Zn 82 116 199 136
TS (%) 99.7 99.8 99.7 99.7
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2.3.2 Green liquor dregs from Billerud Karlsborg pulp and paper mill
Dry matter content of the GLD was evaluated. The GLD were analysed with the Constant Head Permeability test and the adapted Column Leaching test. Hydraulic conductivity was measured as well as pH and electrical conductivity of the leachate, giving the following results:
Table 3 Dry matter content and hydraulic conductivity of the GLD, and pH and EC of their leachates obtained in the adapted Column Leaching test.
Sample Dry content
(%)
Hydraulic conductivity (m/s)
pH of leachate
EC of leachate (mS/cm)
GLS 30 72 1.2 E-06 12.6 2.3
GLS 30 EM 55 2.2 E-08 12.1 31.3
GLS 31 65 2.5 E-07 13.0 177.5
The characterisation indicates that green liquor dregs, sampled within only several hours of interval in the pulp and paper mill, show very different properties. In particular, hydraulic conductivity varies on three orders of magnitude. A correlation is suggested between the dry matter content and the hydraulic conductivity, i.e. the drier the GLD, the more permeable.
A Batch Leaching test in oxidising conditions (cf. 2.2.2) was performed on GLS 30 EM in triplicates during one week. The metal concentrations (as well as chloride content) in the leachate are provided in table 4:
Table 4 Metal concentrations in the leachate from the triplicates of GLS 30 EM in the Batch Leaching test in oxidising conditions, and limit values for non-hazardous waste with standard Batch Leaching test L/S = 10 L/kg. Chloride content is indicated as well.
mg/kg TS GLS 30 EM 1 GLS 30 EM 2 GLS 30 EM 3 Limit non- hazardous waste
As <0.011 <0.011 <0.011 2
Cd <0.001 <0.001 <0.001 1
Co <0.001 <0.001 <0.001
Cr 0.272 0.302 0.270 10
Cu <0.011 <0.011 <0.011 50
Mo 0.097 0.099 0.101 10
Ni <0.005 <0.005 0.007 10
Pb <0.002 <0.002 <0.002 10
V 0.012 0.015 0.021
Zn 0.072 0.047 0.050 50
Cl 89.8 248.8 96.3 15000
Data for other green liquor dregs sampled in 1999 and 2005 in the same mill Billerud Karlsborg are provided in appendix II.
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3 RESULTS
3.1 Permeability tests
3.1.1 Constant Head Permeability Test
The three GLD samples provided by Billerud Karlsborg mill – GLS 30, GLS 30 EM and GLS 31 – were tested in the first series. 18 measurements were done during 15 days from which the following hydraulic conductivities were calculated (figure 7):
1,0E‐09 2,0E‐07 4,0E‐07 6,0E‐07 8,0E‐07 1,0E‐06 1,2E‐06 1,4E‐06 1,6E‐06
0 5 10 15 20
Calculation points over 15 days
Hydraulic Conductivity (m/s)
GLS 30 GLS 30 EM GLS 31
Figure 7 Hydraulic conductivity of GLS 30, GLS 30 EM, and GLS 31 with time. Each point represents a calculation of HC from the flow of water measured in an interval of time.
The results of this first series led to the following observations:
• The 3 GLD show different hydraulic conductivities (HC):
o HC of GLS 30 EM varies in the interval 3.7E-09 – 2.6E-08 m/s o HC of GLS 31 varies in the interval 8.4E-08 – 2.7E-07 m/s o HC of GLS 30 varies in the interval 6.4E-07 – 1.4E-06 m/s
• The HC vary on different magnitudes for each GLD during the two weeks. GLS 30 shows the largest variation.
• A total stabilisation of HC after 15 days was not observed, but a tendency appeared.
The saturated hydraulic conductivity was calculated as an average from the last six points (the 15th point was excluded for GLS 30).
The other series of samples tested with CHP test were analysed in the same way, and HC was calculated from the average of the values exhibiting a near stabilisation. The results of this analysis are given in table 5, in which duration of the test, number of HC values selected for the calculation of average saturated HC and days associated to these values are indicated.
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Table 5 Duration of CHP test, number of HC values selected for calculation of average saturated HC and days associated to these values for each sample submitted to CHP test.
Sample name
Duration of the CHP test
(days)
Number of HC values for average HC
Days of
selected values Comment
GLS 30 15 5 4-15
GLS 30 EM 15 6 4-15
GLS 31 15 6 4-15
GLS 30 EM + FA 11 5 6-11
GLS 31 + FA 11 4 3-7 HC rise from d 7
TAILINGS 11 5 6-11
90 TAIL + 10 GLS 30 11 4 3-7 Pbs on d 7-11
GLS 30 EM + FA1 14 10 4-14
GLS 30 EM + FA1 + BS 14 10 4-14
GLS 30 EM + FA2a 14 10 4-14
70 TAIL + 30 (GLS30EM+FA1) 14 9 4-14
70 TAIL + 30 (GLS30EM+FA1+BS) 15 7 9-15 40 TAIL + 60 (GLS30EM+FA1+BS) 15 8 11-15
Average saturated hydraulic conductivities of the samples with CHP test are given in table 6.
3.1.2 Constant Rate of Strain test
Results were obtained in the form of a curve of hydraulic conductivity function of deformation of the sample (figure 8). A trend line was drawn from the curve, which intersection with horizontal axis (0 deformation) gave the saturated hydraulic conductivity.
When the curve presented a significant change in the slope of HC with deformation two extreme trend lines were drawn and HC was given in an interval (figure 8).
Hydraulic Conductivity (m/s)
Deformation (%) Hydraulic Conductivity (m/s)
Deformation (%)
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19
Figure 8 Determination of the hydraulic conductivity from the curve HC function of deformation in CRS test: 3 examples (GLS 30 EM + FA1 + SS and GLS 30 EM + FA2a above, GLS 30 EM + FA2a + BS below). Intersection of trend lines with horizontal axis gives the saturated hydraulic conductivity.
Results of saturated hydraulic conductivities with CRS test are given in table 6.
3.1.3 Results of hydraulic conductivities
Hydraulic Conductivity (m/s)
Deformation (%)
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Table 6 Results of hydraulic conductivities with CHP and CRS tests for the different combinations of pulping wastes and tailings. Content of the combinations is also indicated.
Content
(% in dry matter weight) Constant Head Permeability test Constant Rate of Strain test Sample name
Tailings Green liquor dregs
Fly ash
Bark/Sewage sludge
Density (g/cm3)
Dry content
(%)
Hydraulic conductivity
(m/s)
Density (g/cm3)
Dry content
(%)
Hydraulic conductivity
(m/s)
GLS 30 100 1.29 72 1.2 E-06
GLS 30 EM 100 1.38 55 2.2 E-08 1.53 58 1-1.5 E-08
GLS 31 100 1.83 65 2.5 E-07
GLS 30 EM + FA 70 30 1.35 60 2.0 E-07
GLS 31 + FA 70 30 1.52 69 2.5 E-07
GLS 30 EM + FA1 70 30 1.09 66 1.6 E-06 1.35 66 4.0 E-08
GLS 30 EM + FA1 + BS 60 30 10 1.40 57 1.4 E-08 1.47 58 2.0 E-09
GLS 30 EM + FA1 + SS 60 30 10 1.46 60 5.0 E-09
GLS 30 EM + FA2a 70 30 1.40 66 2.0 E-09
GLS 30 EM + FA2a + BS 60 30 10 1.45 59 1-2 E-08
GLS 30 EM + FA2a + SS 60 30 10 1.13 ~58 1.4 E-07 1.47 58 1-4 E-08
TAILINGS 100 1.84 100 5.8 E-07
90 TAIL + 10 GLS 30 90 10 1.97 97 2.8 E-07
70 TAIL + 30 (GLS30EM+FA1) 70 21 9 1.91 ~87 6.4 E-08 2.11 87 1.5-4 E-08 70 TAIL + 30 (GLS30EM+FA1+BS) 70 18 9 3 1.99 82 7.7 E-10
40 TAIL + 60 (GLS30EM+FA1+BS) 40 36 18 6 1.51 68 9.7 E-09
Two samples gave consistent results between the CHP test and the CRS test: GLS 30 EM and 70 TAIL + 30 (GLS 30 EM + FA1). All the other duplicates gave significantly different hydraulic conductivity results between CHP and CRS tests. In this case, HC is always lower with CRS test, on 1 order of magnitude for GLS 30 EM + FA1 + BS and GLS 30 EM + FA2a + SS, 2 orders of magnitude for GLS 30 EM + FA1.
The HC of the three GLD vary on 3 orders of magnitude (E-06, E-07, E-08).
The HC of the GLD is either increased or left unchanged when 30% fly ash is mixed with them (except with FA2a in CRS test). The largest increase is observed with FA1 in CHP test (HC of GLS 30 EM raised 70 times). The addition of BS or SS to the mixture GLD and fly ash tends to reduce the raise of HC of GLD due to fly ash or even decrease the HC (GLS 30 EM + FA1 + BS/SS in CRS test).
The addition of 10% GLS 30 to tailings reduces its HC by 50% in CHP test.
The HC of tailings is reduced ~9 times when mixed with GLS 30 EM + FA1 in the proportion of 70:30 (tailings:GLS30EM+FA1) in CHP test.
The HC of the tailings is reduced ~60 times with 60% GLS 30 EM + FA1 + BS and ~800 times with 30% GLS 30 EM + FA1 + BS in CHP test.
3.1.4 Evolution of HC in CRS test after saturation of samples in CHP test
Three samples were submitted to the CHP test during 18 days and then sent to Gothenburg for CRS test. The results are given as follows: samples called bis refer to the ones that were sent for CRS test after 18 days in CHP test, then results for the same samples in initial conditions are reminded (in italic) both with CRS and CHP tests.
Table 7 Hydraulic conductivities with CRS test of three samples (bis) after 18 days in CHP test.
Hydraulic conductivities for the same samples in initial conditions with CRS and CHP tests are also reminded.
Sample Density
(g/cm3)
Dry content (%)
Hydraulic conductivity (m/s) GLS 30EM + FA1 + BS bis 1.49 55 2.5 E-09 –1.5 E-08
GLS 30EM + FA1 + BS (CRS) 1.47 58 2.0 E-09
GLS 30 EM + FA1 + BS (CHP) 1.40 57 1.4 E-08
GLS 30EM + FA2a + SS bis 1.49 56 2.5 E-08
GLS 30EM + FA2a + SS (CRS) 1.47 58 1–4 E-08 GLS 30 EM + FA2a + SS (CHP) 1.13 ~58 1.4 E-07
70 TAIL + 30 (GLS 30EM + FA1) bis 2.03 80 3.5 E-08
70 TAIL + 30 (GLS 30EM + FA1) (CRS) 2.11 87 1.5–4 E-08 70 TAIL + 30 (GLS 30 EM + FA1) (CHP) 1.91 ~87 6.4 E-08
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Comparing the HC of samples bis with the HC obtained on initial samples with CRS test, it is noticed that:
• There is no significant evolution of HC measured with CRS test for GLS30EM+FA2a+SS and 70 TAIL+30 (GLS30EM+FA1) between sample in initial conditions and sample saturated with CHP test.
• For GLS30EM+FA1+BS, the HC measured in CRS test after saturation in CHP test is more uncertain, but remains in the same order of magnitude as in initial conditions.
3.2 Leaching tests
3.2.1 Adapted Column Leaching test
Pulping wastes combinations
8 9 10 11 12 13 14
GLS 30 GLS 30 EM GLS 31 GLS 31 + FA GLS 30 EM + FA
GLS 30 EM + FA 1
GLS 30 EM + FA 1 + BS
GLS 30 EM + FA 2a + SS
Samples
pH of leachate (L/S~0.2)
Figure 9 pH of leachates from pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)
pH of the GLD and GLD mixed with FA ( fly ash watered in the mill) are between 12 and 13.
pH of GLD mixed with FA1 (dry fly ash) and FA1 + BS are slightly above 13. pH of GLD with FA2a and sewage sludge is ~11. Thus the highest pH are obtained with the mixtures GLS 30 EM + FA1 (+ bark sludge).
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0 50 100 150 200 250
GLS 30 GLS 30 EM GLS 31 GLS 31 + FA GLS 30 EM + FA
GLS 30 EM + FA 1
GLS 30 EM + FA 1 + BS
GLS 30 EM + FA 2a + SS
Samples
EC of leachate (L/S~0.2)
EC (mS/cm)
Figure 10 Electrical conductivity of leachates from pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)
EC of the pulping wastes initial leachates vary between 2.3 mS/cm (GLS 30) and 216.7 mS/cm (GLS 31 + FA).
• EC of leachates from GLD vary in an interval of about 2 orders of magnitude (2.3 mS/cm to 177.5 mS/cm).
• Addition of fly ash increases the EC of leachates, especially with FA1.
• Not only addition of fly ash can induce high EC. Leachate of GLS 31 alone exhibits a higher EC than leachates of 4 of the mixtures containing fly ash.
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Tailings untreated and treated by pulping wastes
0 2 4 6 8 10 12 14
TA ILINGS 90 TAIL + 10 GLS 30 70 TAIL + 30 (GLS30EM +FA1)
70 TA IL + 30 (GLS30EM +FA1+B S)
40 TA IL + 60 (GLS30EM +FA1+B S)
Sample
pH of leachate (L/S~0.2)
Figure 11 pH of leachates from tailings untreated and mixed with pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)
Initial leachate of tailings alone exhibits a low pH (4.7). The addition of all the pulping wastes tends to increase this pH. The addition of 10% GLD is enough to raise the pH up to 8.2. The largest increase (13.2) is when GLS 30 EM + FA1 + BS is added in the proportion of 60% to tailings, though it remains close to the pH obtained with addition of GLS 30 EM + FA1 (+BS) in the proportion of 30% (pH 12.8-12.9).
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0 10 20 30 40 50 60 70 80 90 100
TAILINGS 90 TAIL + 10 GLS 30 70 TAIL + 30 (GLS30EM +FA1)
70 TAIL + 30 (GLS30EM +FA1+BS)
40 TAIL + 60 (GLS30EM +FA1+BS)
Samples
EC of the leachate (L/S~0.2)
EC (mS/cm)
Figure 12 Electrical conductivity of leachates from tailings untreated and mixed with pulping wastes in the adapted Column Leaching test (L/S ~0.2 L/kg)
The EC of the leachate from tailings (2.2 mS/cm) is increased with the addition of all pulping wastes. The highest rise is observed for the admixture GLS 30 EM + FA1 + BS in the proportion of 60%. Contrary to the values of pH, the difference of EC between 30% and 60%
(GLS 30 EM + FA1 + BS) admixtures with tailings is sizeable (EC 1.7 times higher with 60%
admixture).
3.2.2 Batch Leaching test in oxidising conditions
The samples were analysed each in triplicates, except for distilled water (blank) for which only one sample was tested. Average values were calculated from the triplicates, and the results fluctuations are indicated by vertical errors calculated with standard deviations.
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pH and Electrical Conductivity
0 2 4 6 8 10 12 14
Water TAILINGS 90 TAIL+ 10 GLS 30
90 TA IL + 10 GLS 30 EM
90 TAIL+ 10 (GLS30 EM +FA 1)
90 TAIL+10 (GLS 30 EM +FA 1+BS)
70 TAIL + 30 (GLS 30 EM +FA 1+BS)
GLS 30 EM
Samples
pH of leachates (L/S~10)
Figure 13 pH of leachates from samples tested in Batch Leaching test in oxidising conditions (L/S=10 L/kg).
0 500 1000 1500 2000 2500 3000 3500
Water TAILINGS 90 TAIL+ 10 GLS 30
90 TAIL + 10 GLS 30 EM
90 TAIL+ 10 (GLS30 EM +FA1)
90 TAIL+10 (GLS 30 EM +FA 1+BS)
70 TAIL + 30 (GLS 30 EM +FA1+BS)
GLS 30 EM
Samples
EC of leachates (L/S~10)
EC (μS/cm)
Figure 14 Electrical conductivity of leachates from samples tested in Batch Leaching test in oxidising conditions (L/S=10 L/kg).
26
27
Note: 2 measurements of pH and EC were done for distilled water, one directly from the bottle, and one after filtration with the same filter used for the other samples. Average values and standard deviations were calculated from these 2 measurements.
Tailings leachate exhibits a low pH (4.7) and a low EC (128 µS/cm). The addition of GLD in the proportion of 10% increases the pH to 8, value superior to that of distilled water (6.5), and EC is increased to ~600-650 µS/cm. The two types of GLD (GLS 30 and GLS 30 EM) give close results.
The addition of 10% fly ash FA1 along with GLD to tailings raises the pH of 2 units (10.4) and the EC up to 995 µS/cm. If bark sludge is added as well, the raises are more limited. In particular, pH remains at 8.6.
The addition of GLS 30 EM +FA1 +BS in the proportion of 30% (mixture interesting for its low permeability, cf. section 3.1.3) highly raises the pH (11.9) and the EC (2733 µS/cm). The main contribution to such high pH is fly ash, since GLS 30 EM alone generates a leachate with lower pH -10.9- (and bark sludge is present only in a small proportion).
Metal release in the leachates
The metal concentrations directly reflect the release of the contaminants from each material since the same amount of material (30 g dry weight) was tested and the same amount of water (300 mL) was added. They are shown on the graphs in figure 15. Table 8 illustrates the metal release in mg/kg TS.
